Technology Strategy Board Design for Future Climate (D4FC) - Phase 2
PassivOffices 4 Devon at Devonshire Gate Project Exeter
Final Report April 2013 TSB File Ref:
400237
Application Number:
13317-86173
D4FC – phase 2
PassivOffices 4 Devon at Devonshire Gate Project
April 2013
PassivOffices 4 Devon at Devonshire Gate Project
Prepared by:
Lawrence Millyard, Maria Gale, Tomas Gartner, Jason Fitzsimmons
Checked by:
David Gale
Project:
PassivOffices 4 Devon at Devonshire Gate Project
Version:
Draft
Date:
April 2013
Job No:
B1113
Reference:
Projects\Current\B1113\Reports\Final Report
Rev No
Comments
Date
This document has been produced by Gale & Snowden for the PassivOffices4 Devon at Devonshire Gate D4FC scheme and is solely for the purpose of detailing to the TSB the Climate Change Adaptation Strategies investigated and developed for the scheme.
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Executive Summary 1. What is the building profile? The building project is the design and build of a new state of the art office development to Passivhaus standards in Devon. It is located at Junction 27 on the M5, next to the A38 at the existing access to Swallow Court and next to a major train station. The office project is funded by a private client whose existing business owns the site and rents office space to various businesses from the existing buildings on site. This 2 project forms the first phase of the development which is a new two storey office building of 1200m . The project was at the technical design stage at the start of this research project and the construction is now being determined. Planning approval for the project has been achieved. Construction was planned for autumn 2012, however due to funding constraints this has now been postponed and therefore is not yet on site. Shading strategies, various ventilation strategies, low energy cooling strategies such as ground cooling (earth tubes, piped heat exchangers, and phase change materials have been investigated) together with various integrated landscape design opportunities that help moderate the micro climate, and withstand increased weather severity on the building fabric in terms of wind and rain.
2. What is the risk exposure for the building to the projected future climate? A climate risk assessment was used to analyse the risks related to climate change for an office building with regards to thermal comfort, water management and construction. Comfort Thermal comfort is important in an office building to ensure that the health and welfare of the occupants are maintained. In addition maintaining a comfortable thermal condition affects the productivity of workers in the office. Based on BS 7730 the CIBSE’s recommendation for offices the upper temperature limits throughout the office space are not to exceed 25°C for more than 5% of the occupied period and /or not to exceed 28°C for more than 1% for the occupied period. These upper limits have been used to analyse the risk and frequency of overheating under various climate scenarios and to develop mitigation strategies to minimise overheating. Water The water demand in the office is not significant. Therefore the risk of future climate change scenarios is not significant to this project. That said, considering the uncertainty surrounding the projected precipitation in the South of the UK in future summers and the potential vulnerability to drought it was considered prudent to identify how consumption can be reduced through the detailed design and specification of the water appliances and fittings and in particular the landscape via drought resilient planting. The greater risk to the project in terms of water management will be due to the predicted increased rainfall in winter which will increase the risk of flooding, and penetration from driving rain. Construction The office building will typically use wide spanning constructions and increased precipitation under future weather scenarios during winter months in the form of snow may affect the structural stability. An increase in storm intensity might increase wind loading acting on the facades and again affect the structural stability. Increase rainfall and weather severity (driving rain) could cause premature failure of the building fabric and increase maintenance costs. Increased UV radiation might cause certain types of materials to fail prematurely. Reduced rainfall in the summer and increased evaporation will cause drought and lower the water table potentially affecting ground stability.
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3 What is the adaptation strategy for the building over its lifetime to improve resistance and resilience to climate change and thus extend the commercial viability? The following strategies were approved by the client following the modelling of strategies using IES dynamic modelling and the PHPP (Passivhaus Planning Package) and cost analysis:
Increase thermal performance to Passivhaus Standard Cross and stack flow ventilation Night cooling Intelligent ventilation control Daylight design and daylight dimming Low energy equipment – lighting, computers copiers etc Reduction of internal gains Solar shading, glazing blinds Landscape and planting effects Mechanical Ventilation with Heat Recover (MVHR) constant volume Mechanical Ventilation with Heat Recover (MVHR) variable volume Mechanical Ventilation with Heat Recovery (MVHR) heat exchangers Ground brine to pip heat exchangers Low water use time flow controlled showers and appliances Inclusion of oversized gutters and drainage to allow for increased annual rainfall under future weather scenarios Green roof
Many of the adaptation measures did not add extra capital costs and in some cases made the scheme simpler. It was found that an extra £53,000 was required for thermal comfort adaptation strategies over and above an office building built to 2010 Building Regulations. This equates to an increase in built cost of approximately 3.1%. However an office building designed to just comply with Building Regulations 2010 will not be as thermally comfortable as the adapted design. A building designed to just comply with Building Regulations 2010 will require a full air conditioning system in 2030; this air conditioning will also incur associated on-going running costs for the remaining duration of the building which the adapted building will not need. To be absolutely clear the adapted design does not need air conditioning now or in the predicted scenarios in the future. Cost benefit analysis shows that over the lifetime of the building the net present value of the cumulative energy costs are approximately £1M compared to £4.1M for an office building built to 2010 Building Regulation Standards. This illustrates that it is also cost effective to design to mitigate climate change from the outset.
4 What is the best way to conduct adaptation work? The chance to develop the climate change adaptation strategy alongside the design of the building would be the most effective way to conduct the adaptation work. In this research project the climate change adaptations strategies were considered after the building had received planning application approval. If the strategies had been considered alongside the initial design process the landscape design would have incorporated more future climate adaptation landscape strategies. The team built on their experience from their previous D4FC project that received funding in the first round of D4FC projects. Again an invaluable resource proved to be the ‘study tour’ at the beginning of the project to visit exemplary buildings in more extreme climates that could be representative of a future UK climate. Strategies that were found successful for the Extra Care 4 Exeter Project were transferred and validated for the passiv office project. Methodologies like the risk assessment process were fine tuned and further developed and aspects like, for example, the lack of guidance on overheating criteria were investigated in
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more depth. A better understanding of the strengths and limitations of the different assessment and modelling (IES and PHPP) tools used to simulate summertime performance gained from the Extra Care 4 Exeter Project allowed for a more efficient use of these tools and analysis of the results. 5. How can this work be used to extend adaptation of other buildings? Comfort The research carried out Exeter University on the impacts of Climate Change on the Productivity of Office Workers could be applied to other office projects. Passivhaus principles applied to an office have a positive effect on future overheating and can be applied to most other projects. The principles of optimising daylight to reduce heat load from artificial lighting, whilst optimising glazing size/orientation to minimise solar gain, could be applied to many office projects. This would be limited as aesthetic impacts may not be appropriate for some projects. The principles of cross ventilation and night cooling to minimise overheating in buildings would be appropriate to most buildings. The limitations of using these principles would be the location of the building, acoustic issues and security. The inclusion of thermal mass in a building to reduce the internal temperature fluctuations would be appropriate for all building projects. Thermal modelling has found ground cooling to be a viable strategy at reducing overheating in future climates for this scheme. However for buildings that require fire compartmentation such as a large apartment building or hospital, costs associated with this approach could be significant. Water Management / Construction Designing for high weather severity including simple details and over sizing surface water drainage systems would be applicable to other projects. Incorporating rain screen / cladding would be appropriate for other projects. Minimising water use by including low water appliances (low flush WCs, low flow taps / showers etc is just good practice and is appropriate for all projects. Using turf roofs to slow down surface water run-off and protect the roof from UV to extend the longevity of the roof covering would be appropriate for many projects. Green Spaces / Healthy Buildings / Heat Stress Awareness The green spaces and landscaping strategy and healthy building design strategy can be applied to any type of building design within the UK. It has been found that buildings and landscapes that are pleasant places to be in whether in the leisure or work environment or at home can have a positive impact on the health and well being of an individual. In the work environment raising awareness of the issues and effects of heat stress will also help individuals cope. Relaxed attitudes during heat waves to dress codes, working patterns providing external green spaces to cool down in and cold water drinking stations are all strategies applicable to any building type.
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Contents Executive Summary............................................................................................................................... 3 1.0
Building Profile ........................................................................................................................ 10
1.1
The Project....................................................................................................................................... 10
1.2
The Building ..................................................................................................................................... 10
1.3
The Context - Offices in the UK ....................................................................................................... 10
1.4
Project Drivers ................................................................................................................................. 11
1.4.1
Client ............................................................................................................................................ 11
1.4.2
Energy Use and Economics ........................................................................................................ 12
1.4.3
Day lighting and Cooling .............................................................................................................. 12
1.4.4
Thermal Comfort Standards and Productivity .............................................................................. 12
1.5
Low Energy Office Examples........................................................................................................... 12
1.5.1
Passive Office Study Tour to the Solar XXI Building in Lisbon, Portugal .................................... 13
1.5.2
Phase Change Material Applications Study Tour, Germany ....................................................... 13
1.6
Design .............................................................................................................................................. 14
1.6.1
The Site ........................................................................................................................................ 14
1.6.2
Building Form and Massing ......................................................................................................... 14
1.6.3
Elevations and Daylight Design ................................................................................................... 14
1.6.4
Low Energy Design ...................................................................................................................... 16
2.0
Climate Change Risks ............................................................................................................. 18
2.1
Future Climate and the PassivOffices 4 Devon Project .................................................................. 18
2.2
Comfort ............................................................................................................................................ 19
2.2.1
BS EN 7730: Ergonomics of the Thermal Environment .............................................................. 19
2.2.2
ASHRAE Standard 55 ................................................................................................................. 19
2.2.3
BS EN 15251:2007 ...................................................................................................................... 20
2.2.4
CIBSE Guides .............................................................................................................................. 20
2.2.5
Thermal Comfort and Productivity ............................................................................................... 20
2.2.6
Heat Stress .................................................................................................................................. 21
2.3
Water Management ......................................................................................................................... 21
2.4
Construction ..................................................................................................................................... 21
2.5
Climate Change Risk Identification and Assessment ...................................................................... 22
2.6
Building Type Assessment .............................................................................................................. 23
2.7
Climate Scenarios and Future Climate Data ................................................................................... 24
2.8
Summary.......................................................................................................................................... 25
3.0 3.1
Adaptation Options ................................................................................................................. 26 D4FC Adaptation Strategies - Comfort ............................................................................................ 26
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3.2
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Building Physics – IES Thermal Modelling Assessment ................................................................. 27
3.2.1
Introduction .................................................................................................................................. 27
3.2.2
Base Case Design ....................................................................................................................... 27
3.2.3
Weather Files ............................................................................................................................... 28
3.2.4
Adaptation Measures Simulated .................................................................................................. 28
3.2.5
Simulation Results ....................................................................................................................... 29
3.2.6
Conclusions to Thermal Modelling............................................................................................... 34
3.3
Building Physics – PHPP pre assessment ...................................................................................... 35
3.3.1
PHPP the Base Case Design ...................................................................................................... 35
3.3.2
Weather Files ............................................................................................................................... 35
3.3.3
PHPP and Modelling Scenarios................................................................................................... 36
3.3.4
PHPP Results and Conclusions .................................................................................................. 36
3.4
Phase Change Materials (PCM) ...................................................................................................... 37
3.5
D4FC Adaptation Water Management Strategies ........................................................................... 38
3.6
D4FC Adaptation Construction Strategies ....................................................................................... 38
3.6.1
Strategies to Address an Increase in Wind Driven Rain ............................................................. 39
3.6.2
Increase in UV Levels .................................................................................................................. 39
3.7
Adaptation Construction Details ...................................................................................................... 40
3.7.1 Typical Wall and Ground Floor Slab Junction Detail ....................................................................... 40 3.7.2 External Wall Corner Detail ............................................................................................................. 41 3.7.3 Window Jamb Detail ........................................................................................................................ 41 3.7.4 Window Head Detail ........................................................................................................................ 42 3.7.5
Roof Verge ................................................................................................................................... 42
3.7.6
Roof Eaves .................................................................................................................................. 43
3.8
Landscape Adaptation Strategies .................................................................................................... 43
3.8.1 Microclimate Planting ...................................................................................................................... 43 3.8.2 Relocation of Hard Parking Areas ................................................................................................... 44 3.8.3 External Shading ............................................................................................................................. 44 3.8.4 Shaded External Working Areas ..................................................................................................... 44 3.8.5 Increase Pond Size ......................................................................................................................... 44 3.9
Adaptation Option Appraisal and Cost Analysis .............................................................................. 45
3.9.1
Introduction .................................................................................................................................. 45
3.9.2
Adaptation Strategies Adopted by Client and Associated Costs ................................................. 46
3.9.2
Adaptation Strategies not Adopted by the Client ......................................................................... 51
3.9.3
Costs Associated with a Standard Office Building....................................................................... 51
3.9.4
Cost Benefit Analysis ................................................................................................................... 51
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3.9.5 4.0
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Timescales and Triggers for Implementation .............................................................................. 53
Learning from Work on This Contract ................................................................................... 54
4.1
Summary of the Teams Approach to the Adaptation Design Work ................................................. 54
4.2
The Project and D4FC Adaptation Team ........................................................................................ 54
4.3
The Initial Project Plan ..................................................................................................................... 55
4.4
Review of resources and tools ........................................................................................................ 56
4.4.1
IES Thermal Modelling Software ................................................................................................. 56
4.4.2
Passivhaus Planning Package PHPP ......................................................................................... 57
4.4.3
Architects Tools / Other Software ................................................................................................ 58
4.4.4
Prometheus Weather Files .......................................................................................................... 58
4.5
What Worked Well? ......................................................................................................................... 59
4.6
What Did Not Work Well? ................................................................................................................ 59
4.7
The Most Effective Ways of Influencing the Client .......................................................................... 60
4.8
Recommended Resources .............................................................................................................. 61
5.0
Extending Adaptation to other Buildings .............................................................................. 62
5.1
How can this Strategy be applied to Other Projects and what are the Limitations?........................ 62
5.1.1
Comfort ........................................................................................................................................ 62
5.1.2
Water Management / Construction .............................................................................................. 62
5.1.3
Green Spaces / Healthy Buildings / Heat Stress Awareness ...................................................... 62
5.1.4
MVHR and Ground Cooling ......................................................................................................... 62
5.2
Resources Tools and Materials Developed ..................................................................................... 63
5.3
Further Needs .................................................................................................................................. 63
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List of Appendices Appendix 1 Passive Office Study Tour, Portugal, April 2012 PCM Applications Study Tour, Germany, April 2012 A Study of the Impacts of Climate Change on the Productivity of Office Workers, Scientist Report 138. Tristan Kershaw, University of Exeter, February 2012 The Impact of Climate Change Adaptations on the Productivity of Office Workers, Scientist Report 143; Tristan Kershaw, University of Exeter, July 2012 Planning Application Drawings •
Location Plan
•
Site Plan
•
Ground Floor Plan
•
First Floor Plan
•
Roof Plan
•
Elevations
Appendix 2 Climate Change Risk Assessment
Appendix 3 Thermal Modelling Assessment Report PHPP Pre-Assessment Report Thermal Comfort Passive Adaptation Options Thermal Comfort Active Adaptation Options Phase Change Materials Research Study Water Management Adaptation Options Construction Details: •
Cross Section
•
Timber Cladding Details
•
Timber Cladding External Corner
•
Window Jamb
•
Window Head
•
Roof Verge
•
Roof Eaves
Landscape Drawings •
Base Case Design
•
Proposed Landscape Adaptations
Wind and Rainfall Desktop Study
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1.0
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Building Profile
The following chapter provides an overview of the adaptation project, the building, key aspects of the design, its context, project drivers and special features or aspects which will affect the resistance and resilience to climate change. Further information, drawings and reports from a study tour to the Solar XXI office building in Lisbon Portugal and the Phase Change Material Applications Study Tour in Germany are included in Appendix 1.
1.1
The Project
The aim of the PassivOffices 4 Devon project is to evaluate various building envelope designs and construction methods in relation to climate change risks. Advantages and disadvantages with regards to thermal comfort, water management and impacts on construction under future climate scenarios have been analysed as part of this study. The project is at the technical design stage and the construction is now being determined. Planning approval for the project has been achieved. Construction was planned for autumn 2012, however due to funding constraints this has now been postponed. The building has to be occupied by January 2014 to meet the planning conditions. Shading strategies, various ventilation strategies, innovative low energy cooling strategies such as ground cooling (earth tubes, piped heat exchangers), and phase change materials have been investigated together with various integrated landscape design opportunities that help moderate the micro climate, and withstand increased weather severity on the building fabric in terms of wind and rain.
1.2
The Building
The building project is the design and build of a new state of the art pioneering office development to Passivhaus standards in Devon. It is located at Junction 27 on the M5, next to the A38 at the existing access to Swallow Court and next to a major train station. The office project is funded by a private client whose existing business owns the site and rents office space to various businesses from the existing 2 buildings on site. The proposed master plan for the 3.5 hectare site includes 3 x office blocks each 1000m 2 2 and 5 x office blocks each of 625m , making the overall development 6,125m internal floor area in total. 2
This project forms the first phase of the development, which is a new two storey office building of 1200m . This new building will set itself apart from other Office buildings in the UK with its energy-saving Passivhaus design. The overriding aim is to design and construct an office building that is bathed in natural daylight but does not require air conditioning to keep the building cool, either now or in 50 years in the future. This will be achieved by a compact design, a high standard building envelope and the highly efficient building services equipment – it is intended that the building will be one of the first Passivhaus certified Office buildings in the UK. It is the intention to provide a low environmental impact building that employs best practice in low energy and healthy building design meeting the client design requirements.
1.3
The Context - Offices in the UK
Office buildings in the UK currently spend £millions on energy every year, resulting in annual CO2 emissions of approximately 2.2 million tonnes of carbon dioxide (CO2). Energy consumption in offices has increased in the UK between 1970 and 2010. It has been calculated that the Passivoffice will produce approximately 26,000kg/yr in its provision of heating, lighting, cooling and hot water. In comparison a typical office building designed to the current Building regulation standards would produce approximately 97,500kg. The cost of running the building has been calculated at £6,500/yr which will equate to 25% of that required by similar sized office buildings.
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Typically space heating is the largest share of energy consumed in offices, followed by lighting, cooling and ventilation and computing (Source: DECC, ECUK 2011 Chart 4). ECON 19 (reference) states that at the 2 high end of office development typical energy consumption can be as high as 480 kWh/m with over 70% of this being building services and 20% being server room. Office buildings have high internal gains from lights, occupants, and IT, and often, due to a lack of shading from high solar gains. These high waste heat inputs often result in the building being unable to limit indoor temperatures and resulting in cooling systems being required to maintain comfort levels. Consequently office buildings rely heavily on the use of air conditioning for comfort control. The adoption of very low energy design principles can ensure that the building can be designed to require minimal space heating input. Therefore the challenge when designing for future climates will be to design office buildings that will not require high energy demand for cooling and ventilation and lighting. The climate adaptation intent is to: 1. Assess the current design to determine how robust it is to changing climates at keeping overheating to a minimum and maintaining internal comfort levels 2. Carry out a thermal investigation into the role of internal gains and reducing these in the future including: relocation of plant outside the envelope of the building, off-site internet based cloud computing taking serves outside offices, relocating servers and IT equipment in underground rooms outside the thermal envelope; extracting heat from server rooms and directing it into MVHR systems for pre-heating in winter; taking people and IT to work in dedicated shaded powered areas outside the office envelope during certain conditions. 3. Consider living planting and landscaping to aid in passive cooling strategies 4. Assess people centre adaptive measures and maximising adaptive comfort levels, e.g. taking people outside to work, relaxing dress codes, working from home during hot periods, risk assessment of adaptive measures. 5. Assess the different construction techniques to determine how appropriate certain constructions are in changing climates, by assessing the current design being a medium weight construction against a heavy weight construction. 6. Consider materials selection and detailing to withstand extreme weather. It is proposed to develop wherever possible some new severe weather details which will look at exposure ratings within the ‘very severe’ category. 7. Consider robust drainage to withstand flash floods 8. Consider reduction in water use achieved through low water appliances, recycling and landscape design 9. Address flooding issues through developing a SUDS innovative landscape design combined with Permaculture principles to keep rainwater on site and to create habitat rich environments using water such as ponds, swales as alternative landscape strategies.
1.4
Project Drivers
1.4.1
Client
The client and design team have been a key driver for this project. The brief from the client was to passively design a building that would not require air conditioning in both the current and future climate change scenarios whilst being primarily day lit. The client was also keen to have the building designed to a recognised environmental and energy standard. Although the building and landscape are being designed to exemplar environmental standards, the BREEAM environmental assessment procedure penalises buildings located in rural areas per se, so the project would not be able to achieve an ‘excellent’ rating as it would not
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be able to gain the required credits for ‘transport’ however well it performed in the other sections. Therefore other environmental standards were considered including the AECB silver standard and the Passivhaus standard. The planning approval has been based on the AECB silver standard, however the client is keen to go beyond that and achieve Passivhaus accreditation. The Passivhaus standard will require the building to 2 achieve a maximum of 15kwh/m for space heating and cooling the building and a specific primary energy 2 demand of 120 kwh/m . Therefore by default air conditioning is not an option to maintain thermal comfort. Another aim is for the building to have a noticeable positive impact on productivity and health. Office buildings are increasingly becoming unhealthy places to use, suffering from Sick Building Syndrome (SBS) and can be contaminated with high levels of VOCs, ozone, pollutants, chemicals, bacteria and poor fresh air quality particularly in offices which are air conditioned. The client has been keen to have a healthy office for its occupants and for the wider environment.
1.4.2
Energy Use and Economics
Energy costs in an office are a relatively low proportion of the total running costs of that business. Typically if 2 2 a business has running costs of £3000/m , energy costs will be in the order of £17/m . Therefore generally speaking there is little incentive for businesses to reduce their energy costs on purely economic grounds particularly if it will incur significantly larger capital outlays to do so. However in this project the client will be 2 renting out the office space. The office can be rented out at about £8/m unserviced. If let fully serviced, 2 which includes space heating, cooling, lighting etc costs this can be increased to £15/m . Therefore if the client can dramatically reduce his energy costs for a relatively small increase in initial capital costs he can increase the profitability of his business, and there will be an economic case for reducing the energy costs of the new building.
1.4.3
Day lighting and Cooling
Most offices today are prone to overheating and are becoming increasingly dependent on air conditioning to maintain summer comfort levels. Passively designed buildings do not use air conditioning. This design also wishes to maximise daylight levels through carefully proportioned glazing (because it is much more pleasant to work in naturally daylight spaces) whilst also minimising the use of artificial lighting, which can in turn lead to overheating with increased reliance on air conditioning. Therefore a detailed exercise has been carried out to determine optimum glazing areas and location of the glazing which is discussed further in the section on Design in 1.6 below. For the purposes of this study as planning has been achieved the glazing levels are already determined. However the main emphasis of the study is to determine strategies to ensure that the building will not overheat given the predetermined and optimal glazing levels included in the design.
1.4.4
Thermal Comfort Standards and Productivity
There is little doubt that environmental conditions can interfere with human activities, affect task performance and reduce productivity. The productivity of office workers is related to the level of thermal comfort or discomfort experienced by an individual. There have been several studies of how variables such as temperature affect the productivity of office workers [Fisk, Seppanen, Roelofsen, de Wilde, Lan, Wyon]. 2 Ratcliffe (2003) estimates that a typical office may have an energy bill of ~£15/m per year whereas its staff 2 costs are ~ £3000/m per year hence maintaining optimal performance of workers is paramount. Exeter University has carried out research to investigate the effects of the thermal environment on worker productivity, and to estimate the potential savings that could be incurred by adapting the design of the Swallow Court development to produce a more comfortable environment. The full reports are included in Appendix 1.
1.5
Low Energy Office Examples
As part of the D4FC work the team undertook two study tours t Lisbon, Portugal and to Berlin, Germany. Gale & Snowden Architects
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1.5.1
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Passive Office Study Tour to the Solar XXI Building in Lisbon, Portugal
The team visited the naturally ventilated office building Solar XXI, The Helder Conçalves, National Energy Laboratory, in Lisbon, Portugal. This building has been designed and built in 2006 in a climate that is warmer than the UK with higher levels of solar gain and could be said to represent a future UK climate change scenario. The office has been in use since 2006 and monitoring of internal temperatures (see paper Solar XXI Toward Zero Energy) revealed that for 95% of the time internal temperatures did not exceed 0 27 C. The office did not have air conditioning and was designed and orientated to optimise solar gain in winter with large glazing areas in a southerly direction. Overheating was controlled through various strategies all working in conjunction with each other - manually controlled ventilation openings, the use of thermal mass and night cooling, solar control via external shading. Ground earth ducts were enabled during hotter periods in a mixed mode approach. The building has been designed with the following key features: •
Natural ventilation – with cross flow, stack and single sided ventilation with high and low level openings – all manually controlled. Glazed louvres above doors enabled air to move from the office space into the stack corridor.
•
Central full height corridor throughout the building with high level stack openings
•
Stairwells at either end of the building on east and west side both of which have high level stack openings
•
Thermal mass in solid floor and internal walls. Walls consisted of external wall insulation system. Innovative use of mass in the floor with a channel for floor services.
•
South facing orientation – maximising solar gain in winter with large south facing double glazed units
•
Integrated vertical PV system on the south facing facade with innovative heat recovery from behind the PV panels to the office space via high and low level openings. Additional pitched PV system in the adjacent car park area.
•
Solar hot Water panels on the roof for pre-heating a thermal store for heating only. The building has no hot water supplies.
•
The design featured 32 x 300mm diameter concrete earth tube system ranging from 5-15 metres in length at a depth of 4-5 m in the ground. During elevated internal temperatures the fans were switched on to pull air through the ground to help cool the space.
The approach to controlling overheating in the Solar XXI Building was conclusive with research carried out by Gale & Snowden under the D4FC phase 1 programme, and the approach used in the adaptation strategies used in this project. The full study tour report can be found in Appendix 1.
1.5.2
Phase Change Material Applications Study Tour, Germany
The team visited the Great Pavilion at the Botanical Garden in Germany’s capital Berlin which is one of the 2 largest greenhouses in the world. It was built in 1907, covers an area of about 1,750 m and has a capacity 3 of 40,000m . The average temperature inside is maintained at 30°C and air humidity is kept high. Over a period of three years the building underwent a complete restoration (completed in 2009) in order to maintain the historical basic structure and to reduce energy requirements by 50%. Refurbishment work included a new facade and glazing system, new heating and ventilation and installation of ‘PCM (Phase Change Material) Towers’. The ‘PCM Towers’ at the Great Pavilion represent an innovative solution to moderate high daily temperature swings within buildings. This method could be applied to office buildings where high ‘non-useful’ internal heat gains during working hours could be stored providing a cooling effect. Instead of simply removing the
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heat, the stored energy could be used during the heating season to maintain background heating when the building is not in use and thus contribute to reducing the energy demand of a system. If combined with a MVHR system that already forms part of most low energy office buildings, the effectiveness of the PCM could be optimised whilst at the same time providing a more cost effective solution. Further investigations are required to establish how this methodology could be implemented into the design and services strategy of a modern office building and also how a retrofit solution might work. The full study tour report can be found in Appendix 1.
1.6
Design
1.6.1
The Site
The site is currently used as pasture land, slightly sloping (gradient approximately 0.6%) to the south west and part of it is sheltered from winds by the proximity of semi-mature trees. The design’s intention is to ‘frame’ Jersey Farm / Swallow Court, mirroring the northern (existing) development by siting a new complex 2 to the south which has a footprint of 650m and 39 car parking spaces not included in the footprint. The existing business complex ‘Swallow Court’ consists of barn-like one and two storey buildings with pitched roofs, arranged around a central courtyard. The proposed expansion of the existing business complex has been designed with a focus on preserving the rural character of the area by scale, design, and siting of the new development. The proposed new building has a similar footprint and height as Jersey Farm and the most recent development. Together they form a single landscaped area preserving the setting of the old farm house and gardens and allow for a contemporary office building design with an economic scale. The existing office complex and the new development then form one architectural ensemble with the new development integrating into the landscape through the earth banks and a green roof as an artificial hill.
Figure 1: Site Section Showing the Height of Adjacent Buildings and the Green Roof Merging into Landscape
1.6.2
Building Form and Massing
The L-shaped building consists of two wings. The eastern wing has a length of approximately 35m the western of approximately 27m. To accommodate high levels of natural daylight the width of the building has 2 2 been limited to 12m. This will result in a gross internal area of 1175m and a gross external area of 1290m over two floors. The scheme has been designed as an artificial hill that integrates with the landscape through earth banks and a green roof. The ridge height is approximately 8.3m and drops down in a smooth curve with the eaves being at a height of 4.5m. The ridge and eaves level of the new building are similar to the existing office complex’s levels. The form and massing of the building is a result of the client’s requirements, for passive design principles resulting in a design requirement to minimise the footprint of the building.
1.6.3
Elevations and Daylight Design
One of the key aims of the design was to achieve best practice daylight levels with a minimum of glazing. Large amount of glazing contributes to internal heat gains and can cause overheating especially in summer. Gale & Snowden Architects
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As the building follows Passivhaus design principles no air conditioning systems will be applied and thereafter the right balance between appropriate daylight levels and minimising solar gains needed to be found. To do this several different fenestration designs were computer modelled.
Figure 2: Daylight Analysis 1 - First Floor Offices 3 and 4 (vertical glazing)
The above figures show the analysis of daylight factors of an initial concept where vertical glazing is applied to the façade. The different colours indicate different levels of daylight provision (see key to the left). Black indicates areas with poor/substandard daylight provision; red indicates adequate provision of daylight in accordance with best practice (i.e. 2-5%). As can be seen the average daylight factor is below 2% across the space for this glazing approach. The colour rendering also details the lack of uniformity of daylight, as can be seen there are poor daylight factors of 0 – 1% to the rear of each space.
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Figure 3: Daylight Analysis 2 - First Floor Offices 3 and 4 (horizontal glazing)
There is a marked improvement in daylight factor and the average recorded across each space was above the 2% criterion when glazing is applied horizontally in the façade. The colour rending still shows a lack of uniformity to the rear of each space.
Figure 4: Daylight Analysis 3 - First Floor Offices 3 and 4 (horizontal glazing & rear skylight)
Applying skylights to the rear of each office space has significantly improved the uniformity of the day light. The overall average is now well within the 2 – 5% guideline. The skylights will also be a useful strategy for natural ventilation encouraging a cross flow of air through the space assisting wind driven natural ventilation. Each space was analysed in this manner until an optimum glazing system was realized and that average day light factors were above the 2% criterion.
1.6.4
Low Energy Design
The brief from the client was to passively design a building that would not require air conditioning in both the current and future climate change scenarios whilst being primarily day lit. The planning approval has been based on the AECB silver standard. However the client is keen to go beyond that and achieve Passivhaus accreditation. The Passivhaus methodology was developed in Germany in the early 1990s and has since become ‘the world leading standard in energy efficient design and construction’ (BRE London). Worldwide more than 35,000 buildings, including dwellings, schools, offices and sport halls, have been built to the Passivhaus standard but less than 15 currently exist in the UK. In a Passivhaus a comfortable interior climate can be maintained without active heating and cooling systems (Adamson 1987 and Feist 1988). The building heats and cools itself, hence "passive". Increased insulation, exceptional levels of air tightness and a compact building skin are elemental components for this relatively new standard. Heat losses can be reduced to a minimum resulting in a requirement for space heating as low as 15kWh/sqm/year. Heating requirements for a standard building (built to current Building Regulation requirements) are usually around 100-130 kWh/sqm/year. Scientific monitoring on completed projects has proven that using the Passivhaus methodology will reduce the energy demand of a building by up to 90% of that of a standard UK building.
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Figure 5: 3D Artistic Impression of Building
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Climate Change Risks
This chapter starts with a brief over view of future climates in the UK and their associated risks to the project. It then discusses the requirements of the project in terms of comfort, water and construction and how future changing climates may impact these requirements. An analysis is made of the climate change risk assessment for an office building have been summarised in Figure 8. Finally the chapter defines the climate data and climate scenarios used for the design of this building.
2.1
Future Climate and the PassivOffices 4 Devon Project
2.1.1 Increased Average Summer Temperatures Weather recordings in the UK confirm that there has been warming over the UK since 1960 with greater warming in the summer than in winter. At the same time there has been a decreasing trend in cool nights and days and an increasing trend in warm nights and days. In general summer average temperatures over the whole of the UK have increased, making warm summer temperatures more frequent (Met Office). Future trends for a high CO2 emission scenario indicate that the South West of the UK is projected to experience an average summer temperature increase of 4-6°C by 2100 and an increase in UV radiation due to reduced cloud cover. The various models show a moderate agreement. 2.1.2 Changes in Rainfall With regards to precipitation the UK shows a contrast between the North and the South. Whilst for the North an increase of 10% in precipitation is projected the South may experience decreases of up to 5%. Generally there is good consensus between the UK models for the North but only moderate for the South. This indicates some uncertainty about the transition zone between increasing and decreasing precipitation across Europe. According to the latest reports from the Met Office, vulnerability to drought related to climate change is mainly focused on the South and especially the South East of the UK and these regions are projected to experience an increase in the frequency of droughts. Generally rainfall extremes are projected to increase especially during winter and changes during summer are more uncertain. 2.1.3 Increase in Storm Severity Some sources suggest an increase in storm intensity for the UK. Whilst the UK is susceptible for storms from the Atlantic, whether these are extra tropical cyclones or intense low pressure systems in winter, there is currently no systematic observational analysis for storms because wind data are not yet adequate for a robust analysis (Met Office). 2.1.4 Probability Assessment The IPCC’s fourth assessment report concludes that increases in the frequency and magnitude of warm daily temperature extremes are ‘virtually certain’. Extremes in the 21st century will likely increase by about 1°C to 3°C by the mid-21st and by about 2°C to 5°C by the late 21st century. Furthermore it is ‘likely’ that the frequency of heavy precipitation or the proportion of total rainfall from heavy falls will increase. For the climate risk assessment for this project ‘risk’ is understood as the ‘combination of the probability of an event and its impact’, as defined in the risk management standard ISO/IEC Guide 73 (2002). The probability rating was based on the above listed observations from the fourth IPCC report and latest publications from the Met Office.
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The predominant climate related risks to this project are therefore overheating followed by flooding and storm damage and water availability and demand.
2.2
Comfort
Thermal comfort is important in an office building to ensure that the health and welfare of the occupants are maintained. In addition maintaining a comfortable thermal condition affects the productivity of the workers in the office. See ‘A Study of the Impacts of Climate Change on the Productivity of Office Worker’, Tristan Kershaw, University of Exeter, February 2012 in Appendix 1. Future climate scenarios will have increased ambient temperatures and increased average radiation which will affect internal comfort. A range of British Standards and guidance documents has been developed to assist in establishing the thermal comfort range and acceptable upper temperature limits for different types of buildings and uses. Whilst all these standards follow similar principles and thermal comfort is always based on the same factors i.e. temperature, humidity, velocity, clothing and activity, they arrive at different conclusions with regards to acceptable upper temperature limits. The following standards have been considered when analysing the impact of overheating under future climate scenarios:
2.2.1
BS EN 7730: Ergonomics of the Thermal Environment
Analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria BS EN 7730 is based on Fanger’s thermal comfort model. Optimal thermal comfort is established when the heat released by the human body is in equilibrium with its heat production. Based on air temperature, surface temperature, humidity, velocity, clothing and activity the PMV (Predicted Mean Vote) and PPD (Predicted Percentage of Dissatisfied) is calculated. The PMV predicts the mean value of votes of a large group of persons on the following on a 7 point thermal sensation scale ranging from -3 (too cold) to +3 (too hot) with 0 being neutral. From this the PPD is calculated expressing the percentage of people dissatisfied with a given comfort condition. Even for a neutral condition a minimum of 5% of people will express dissatisfaction. Under this standard a 90% satisfaction rate is aimed for and this then defines acceptable upper temperature if the other factors are given. The model described in BS EN 7730 is based on the heat balance model of the human body, which predicts that thermal sensation is exclusively influenced by environmental factors (temperature, thermal radiation, humidity and air speed), and personal factors (activity and clothing).
2.2.2
ASHRAE Standard 55
The purpose of ASHRAE Standard 55, Thermal Environmental Conditions for Human Occupancy, is “to specify the combinations of indoor space environment and personal factors that will produce thermal environmental conditions acceptable to 80% or more of the occupants within a space” (ASHRAE 1992).It is based on ISO 7730 and the standard establishes a comfort zone expressed in comfort charts. For a given clothing level and metabolic rate it provides the comfort zone in relation to humidity, operative temperature and dew point temperature. Changes introduced in 2004 included a new adaptive comfort standard (ACS) that allows warmer indoor temperatures for naturally ventilated buildings during summer. The ACS is based on the analysis of 21,000 sets of raw data compiled from field studies in 160 buildings, both air conditioned and naturally ventilated, located on four continents in varied climatic zones (ASHRAE RP-884: Developing an Adaptive Model of Thermal Comfort and Preference).
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BS EN 15251:2007
This is based on indoor environmental input parameters for design and assessment of energy performance of buildings addressing indoor air quality, thermal environment, lighting and acoustics. The standard recommends parameters to be used when calculating design indoor temperatures, ventilation rates, illumination levels and acoustical criteria for the design of buildings, heating, cooling, ventilation and lighting systems. It describes a method to establish thermal indoor criteria (design indoor temperature in winter, design indoor temperature in summer) on the basis of given comfort conditions.
Figure 6: Temperature for Categories I-III in Relation to Mean Outdoor Temperature
Based on the level of user expectation a building is categorised on a scale of 1-4 with one being the highest (typically a space occupied by fragile and very sensitive persons) and 4 being the lowest (buildings of limited use). Based on the category and the mean outdoor temperature an upper temperature limit is calculated (see Figure 11). EN 15251 is applicable mainly in non-industrial buildings where the criteria for indoor environment concern human occupancy and where the production or process does not have a major impact on the indoor environment. The standard is thus applicable to the following building types: single family houses, apartment buildings, offices, educational buildings, hospitals, hotels and restaurants, sports facilities, wholesale and retail trade service buildings. EN 15251 can be categorized as an adaptive model. An adaptive model states that there is an optimal temperature for a given indoor environment depending on the outdoor air temperature. It takes into account that humans can adapt and tolerate different temperatures during different times of the year.
2.2.4
CIBSE Guides
Based on BS EN 7730 the CIBSE’s recommendation for offices (CIBSE Applications Manual AM10: 1997 – Natural Ventilation in Non-Domestic Buildings and CIBSE TM36 Climate Change and the Indoor Environment) the upper temperature limits throughout the office space are not to exceed 25°C for more than 5% of the occupied period and/or not to exceed 28°C for more than 1% for the occupied period.
2.2.5
Thermal Comfort and Productivity
The research carried out by Exeter University (see Appendix 1) on the impact of climate change on the productivity of office workers indicate that there is a reduction in mental performance at moderate levels of heat stress (26-27°C).
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Heat Stress
Heat stress is caused by an inability of the human body to maintain its core temperature of 37C, which can prove fatal. Heat stress is affected by temperature and high relative humidity which limits the ability of the body to lose heat through perspiration. There are currently no upper limits on acceptable building temperatures in building regulations or health and safety guidance. However it is generally recognised that 35C is the heat stress ‘danger line’ for healthy adults when relative humidity is 50%. This danger line temperature decreases by several degrees for higher humidity levels and for more vulnerable groups such as the elderly. (Source: Fundamentals. 2001 ASHRAE Handbook. American Society of Heating, Refrigeration and Air-conditioning Engineers (ASHRAE).) Given that the design and overheating assessment criteria are set to 23°C – 26°C as per section 2.2.4 there is no danger of heat stress occurring.
2.3
Water Management 3
The average water consumption for offices is approximately 50 litres (0.05m ) per person per day depending on catering and janitorial uses, and the use of water is typically broken down as follows.
Figure 7: Typical water use in office buildings
Source: EPA, US(2009) Water Efficiency in the Commercial and Institutional Sector: Considerations for a Water Sense Program. In this office project the water use will be limited to the 6 WCs, 2 showers a kitchen area and the external landscaping. Since the water demand is not significant the risk of future climate change scenarios is not significant to this project. That said, considering the uncertainty surrounding the projected precipitation in the South of the UK and the vulnerability to drought it would be prudent to consider how consumption can be reduced through the detailed design and specification of the water appliances and fittings and in particular the landscape via drought resilient planting. The greater risk to the project in terms of water management will be due to the predicted increased rainfall in winter which will increase the risk of flooding, and penetration from driving rain. This is discussed further in the following section.
2.4
Construction
The office building will typically use wide spanning constructions and increased precipitation under future weather scenarios during winter months in the form of snow may affect the structural stability. An increase in storm intensity might increase wind loading acting on the facades and again affect the structural stability. Increased rainfall and weather severity (driving rain) could cause premature failure of the Gale & Snowden Architects
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building fabric and increase maintenance costs. materials to fail prematurely.
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Increased UV radiation might cause certain types of
Reduced rainfall in summer and increased evaporation will cause drought and lower the water table potentially affecting ground stability.
2.5
Climate Change Risk Identification and Assessment
To identify and assess potential climate change risks for this building project a site independent, generic, qualitative risk assessment has been carried out (see Appendix 8). The assessment represents a working document that identifies and quantifies climate change risks for a generic building type. The risks are based on the ‘Design for Future Climate’ report (B.Gething, 2010), Gale & Snowden’s experience from their work on a previous D4FC project (Extra Care 4 Exeter) and the original bid for the Passivhaus 4 Devon project. The intention is to provide a holistic overview of the most likely climate change risks, however, not all of these will be further investigated as part of this project but only those identified in Gale & Snowden’s bid to the TSB. The risks are structured in three main sections i.e. comfort, construction and water management. Each risk is rated on a scale of 1 to 5 for its probability and impact and as a result of the multiplication of these two factors is given a risk magnitude. Details are included in the appraisal matrix included in Appendix 2. A graphical analysis of all individual risk magnitudes (see figure 8) shows the overall vulnerability of this building type to specific aspects of climate change. The colours represent the three main section i.e. comfort-red, construction-green and water management-blue. This assessment has been used to also inform the decision on the selection of appropriate weather files from the Prometheus project. The initial impact risk assessment for an office type building shown in Figure 8 indicates the following: -
The user group is expected to be mainly healthy and predominately non-fragile and will be able to cope with increased internal temperatures. However part of the user group should be considered to be vulnerable as the group may include a proportion of elderly, disabled, people with conditions such as asthma etc.
-
The visitors group is expected to be mainly healthy and predominately non-fragile and will be able to cope with increased internal temperatures. However part of the user group should be considered to be vulnerable as the visitor group may include a proportion of elderly, disabled, people with conditions such as asthma etc.
-
Generally British office dress codes should not be considered to be flexible in adapting to temperature fluctuations
-
If a heat wave were to render the office building unusable this would incur financial implications and affect the viability of the scheme. There are currently no legal requirements limiting a buildings use due to high temperatures. However H&S guidelines suggest that a office building's temperature should not be >25°C for more than 5% of occupation and >28°C for more than 1% of occupation
-
Thermal mass can generally be included in office buildings
-
Ventilation strategy can be designed as mechanical, natural or mixed. However, if an open plan approach is not adopted, compartmentation will potentially limit a cross ventilation strategy. Offices are typically deep plan which limits cross ventilation
-
Roof areas could be designed as reflective or green roofs to reduce the risk of overheating
-
There are limited opportunities for shading via trees etc because offices usually have a high car parking requirement and the inclusion of trees close to the building would detrimentally impact of the natural day lighting
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Future financial viability of high water use building types
Potential mitigation measures in landscape design
Water sensitive landscape requirements
Sensitivity to flooding
Sensitivity to seasonal water shortage
Future financial viability of energy intensive building type
Material sensitivity to UV exposure
Increased storm intensity
Increased seasonal rainfall
Sensitivity to UV exposure
Weather exposure/wind loads
Required daylight provision and glazing ratio
Mitigation measures in landscape design
Potential for mitigation through building fabric design
Potential for mitigation through increased ventilation rate
Potential for mitigation through inclusion of thermal Mass
Requirement for maximum internal temperature
Use of building during extreme heat waves
User group adaptable capacity
2.6
User group exposure to health hazards
-
User group vulnerability - staff/visitors/spectators
User group vulnerability - customers/clients
Risk Magnitude (Probability Rating x Impact rating)
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Office buildings generally require high day lighting provision which require large areas of glazing, increasing the risk of overheating
Building Type Assessment
Risk Magnitude
45
40
35
30
25
20
15
10
5
0
Figure 8: Graphical analysis of the climate change risk assessment for a generic office type building
The analysis of the initial risk magnitudes indicates that the building could be classified as medium to low risk under the construction and water management section and a higher risk under the comfort section.
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Climate Scenarios and Future Climate Data
To thermally assess the exposure of the proposed design to climate change weather data provided by Exeter University’s Prometheus project was used. The IPCC's fourth assessment report includes different socioeconomic projections of CO2 emissions. Based on these emission scenarios the latest climate projections for the UK have been developed, i.e. UKCP09. These incorporate climate models from the Met Office and others. The projections are probabilistic in nature instead of deterministic so as to allow users to assess the level of risk. Using this probabilistic data Exeter University has created a set of probabilistic future weather files for various locations around the UK including Exeter. Each of the weather files are equally likely and the different percentiles represents a different position within the range of the uncertainty of the climate models and again representing different amounts of climate change. Using a high percentile will cover a higher probability of climate change and therefore more extreme scenarios, ensuring a very robust adaptation strategy and reducing the overall risk. However, because each of the weather files are equally likely, choosing a higher percentile can at the same time lead to over engineered and more costly solutions. It is therefore essential to calculate the risk to identify the most appropriate weather file for a given project. For the Passivhaus Offices 4 Devon project the building type risk assessment has resulted in a medium to high vulnerability to change in temperature conditions and a medium vulnerability for construction and water management. Together the design team and the client decided to use the high emission scenario, 50 percentile files for 2030, 2050, and 2080 for the thermal modelling of the building and to allow for an increased risk scenario for water management and construction.
30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 May
Figure 10 Dry-bulb Temperatures Exeter 2030 DSY 50%
28 26 24 Temperature (°C)
Temperature (°C)
Figure 9 Dry-bulb Temperature Exeter 1961-1991 DSY
22 20 18 16 14 12 10 8 6 4
Jun
Jul
Aug
Sep
Oct
2 May
Date: Sat 01/May to Sat 30/Oct Dry-bulb temperature: (Exeter1961_1991_DSY.epw)
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Sep
Oct
Date: Sat 01/May to Sat 30/Oct Dry-bulb temperature: (WG_2030_2950095_a1fi_50_percentile_DSY.epw)
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Figure 11 Dry-bulb Temperatures Exeter 2050 DSY 50%
Figure 12 Dry-bulb Temperatures Exeter 2080 DSY50%
35
Temperature (°C)
Temperature (°C)
30 25 20 15 10 5 0 May
Jun
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Aug
Sep
Oct
April 2013
36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 May
Jun
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Aug
Sep
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Date: Sat 01/May to Sat 30/Oct
Date: Sat 01/May to Sat 30/Oct
Dry-bulb temperature: (WG_2080_2950095_a1fi_50_percentile_DSY.epw) Dry-bulb temperature: (WG_2050_2950095_a1fi_50_percentile_DSY.epw)
The building has been classed as a medium to high risk, and the 50 percentile a higher probability climate change scenario has deliberately been identified as more appropriate. This is to take into account the current development of actual CO2 emissions worldwide. Current trends already exceed the highest emission scenarios developed by the IPCC in 2006 which again formed the basis for the currently available probabilistic weather data UKCP09. It could be argued that the lower emission scenarios and lower percentiles are already outdated and therefore there is an increased likelihood of more extreme climate scenarios.
2.8
Summary
In summary the key climate change adaptation issues are: •
Increase internal temperatures
•
Increased external temperatures
•
High internal gains
•
Changing rainfall patterns
•
Localised air pollution
•
Daylight requirements
•
Increased weather severity
The predominant climate related risks to this project are therefore overheating followed by flooding and storm damage. Following detailed analysis of the building’s exposure to climate change related risks, the 2030, 2050 and 2080 @ 50 percentile with high CO2 emission scenario was chosen.
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Adaptation Options
This chapter illustrates the design for future climates adaptation strategies, the building physics behind these strategies and how they can be implemented. A costs benefit analysis was carried out for each of the proposed strategies to assess their commercial viability. The adaptation strategies are mapped out for each of the sections of Comfort, Water Management, Construction and Landscape. Landscape adaptations options are looked at separately although they cross over both the comfort and water management topics. Many of the comfort adaptations strategies were analysed using building physics techniques including IES dynamic modelling and PHPP (Passivhaus Planning Package) to look at energy and thermal comfort optimisation. Various strategies to reduce the risk of overheating and also potential adaptation measures were analysed and compared for their effectiveness, life cycle costs and practicality to implement. A cost benefit analysis completes the chapter.
3.1
D4FC Adaptation Strategies - Comfort
The following passive adaptation strategies were considered for the Passivoffice scheme that could be implemented to help alleviate high internal temperatures during elevated external air temperatures. In addition as the project was already developed into RIBA Workstage D, the following strategies only consider those technologies that could be implemented into the scheme simply without involving major re-design. The passive strategy of maximising orientation in future climate change scenarios has not been investigated due to the design stage the building was at. a. Increase thermal performance to Passivhaus standard b. Cross and stack flow ventilation c.
Night cooling
d. Intelligent ventilation control e. Daylight design and daylight dimming f.
Low energy equipment – lighting, computers copiers etc
g. Reduction of internal gains h. Heavyweight construction vs mediumweight construction i.
Solar shading, glazing blinds
j.
Landscaping and planting effects
k.
Phase change materials
The following provides potential active operations for the Passivoffice scheme that could be implemented to help alleviate high internal temperatures during elevated external air temperatures. The criteria being to consider suitable low energy / hybrid active systems that do not involve the use of full air conditioning could be implemented into the scheme simply without involving major re-design. l.
Mechanical Ventilation with Heat Recovery (MVHR) constant volume
m. Mechanical Ventilation with Heat Recovery (MVHR) variable volume n. Mechanical Ventilation Heat Recovery (MVHR) thermal wheels o. Desiccant Wheel as an additional element to the MVHR system
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p. Underground cooling strategies – cooling using brine to air systems or underground air ducts as per the Solar XXI building in Lisbon case study example Super insulated envelope
Air tight construction
External shading
MVHR ground cooling
Inclusion of thermal mass
Thermal bridge free
Reduce internal gains
High performance windows
Intelligent window control
Figure 13: Section through the Building Illustrating the D4FC Strategies Considered
3.2
Building Physics – IES Thermal Modelling Assessment
3.2.1
Introduction
A thermal modelling exercise was carried out in IES to assess the proposed building’s internal comfort levels with current and future weather files, using the base case design and the adaptation strategies. Research was carried out into the suitability of incorporating phase change materials (PCM) into the building design as a means of limiting overheating at the outset of the project. This initial research found that PCM would be costly and technically impractical to use for this project. Also there is a lack of a clear methodology within thermal modelling tools to assess PCM materials. The combination of these factors resulted in PCM not being modelled and considered further. Please refer to the Phase Change Material Study Report in Appendix 3.
3.2.2
Base Case Design
The base case design, prior to any thermal simulations into future climates, consisted of the following key parameters: •
Timber frame, medium weight Passivhaus construction
•
Shading strategies:
•
o
A roof overhang at first floor level
o
An overhang for each window created by all windows being recessed into the external walls
An infiltration rate of 0.6 ac/h at 50 Pa
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•
MVHR for winter fresh air
•
Manually opening windows natural ventilation in summer time overheating control (cross and stack effect)
•
Day and night cooling windows opening 15% free area
•
Normal internal gains office loads (11 W/m lighting, 15 W/m equipment)
•
Upper temperature limits throughout the office space to not exceed 25°C for more than 5% of the occupied period and/or not to exceed 28°C for more than 1% for the occupied period, in accordance with the CIBSE Applications Manual AM10: 1997 – Natural Ventilation in Non-Domestic Buildings
2
3.2.3
2
Weather Files
Weather files used were those that have been generated for the Exeter region by the Prometheus Project at Exeter University. All weather files used were based on the high carbon emissions scenarios (A1F1). Weather file scenarios are as follows: Scenario 1: Exeter 1961-1991 DSY Scenario 2: Exeter 2030 DSY, 50% percentile (A1F1) Scenario 3: Exeter 2050 DSY, 50% percentile (A1F1) Scenario 4: Exeter 2080 DSY, 50% percentile (A1F1)
3.2.4
Adaptation Measures Simulated
The following strategies were investigated as possible adaptation measures: a) Heavy weight construction Changing the construction materials to that of a heavy weight build which essentially would have resulted in the external walls being replaced with block and hard plaster skim directly to the block. b) Shading Replacing the glazing in the future to glazing with improved coefficient – G factor 0.4. In practice this might mean partial closure of an external blind system (with slats open) or full closure of an internal blind system). c) Daylight dimming A daylight dimming control can help to ensure that lights remain switched off and reduced the internal heating loads from unnecessary lighting. d) Reducing other internal gains This may include some of the following scenarios: •
The use of advances in low energy LED lighting systems
•
‘Cloud’ based server systems, where servers are remote from the office building in other dedicated server buildings
•
PC equipment becomes more efficient and using less power
•
Providing shaded external spaces where people and equipment can move outside during hot periods
•
Arranging for flexible working patterns to stagger office staff during the day or allowing staff to work from home during hot periods.
e) The use of MVHR system As the MVHR system would already be installed as part of the Passivhaus base case design an opportunity is present to use the MVHR system to assist natural ventilation at limiting overheating.
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f) Ground cooling As ground temperatures are typically at 10-12°C at 1-2 metres below the ground surface there is an opportunity to harness this energy for pre-heating and pre-cooling incoming air supplies of MVHR systems. Manufacturer’s technical data sheets for the piped system state that external air temperatures could be reduced by up to 15°C during summer periods. For the purpose of this analysis it was decided to simulate with a more cautious 8°C reduction.
3.2.5
Simulation Results
3.2.5.1
Base Case Simulation Results
This initial assessment investigated the base case fabric design against a range of future climate files for 3 office types which were found to be prone to the highest levels of overheating. st
•
Office 4: 1 floor office with South facing corner and South East and South West facades
•
Office 1: Ground floor office with South facing corner and South East and South West facades
•
Office 5: 1 Floor cellular office / meeting room and South West facade
st
Initial simulations switched night cooling off so that its impact could be assessed. It became obvious from these initial simulations that offices 4 and 1 were prone to the higher levels of overheating. Although within acceptable limits in the current DSY, in both 2050 and 2080 temperatures limits are exceeded by quite a margin. Office 4 for example exceeds 25°C by 9% in 2050 and by 16% in 2080.
Figure 14: Base Case Design without Night Cooling % of (occupied) Hours > 25° and 28°C
3.2.5.2
Figure 15: Base Case Design with Night Cooling % of (occupied) Hours > 25° and 28°C
Natural Ventilation Simulation Results
For reason of analysis simplicity office 4 was chosen for further simulations.
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The next set of thermal simulations therefore began to investigate in greater detail the range of adaptation strategies. Firstly, concentrating on the passive natural ventilation adaptation measures and secondly the mechanical measures: •
Base case day natural ventilation only
•
Base case with night cooling
•
Heavy weight and day natural ventilation only
•
Heavy weight with night cooling
•
Daylight dimming
•
Low internal gains
•
Combinations of adaptation measures
3.2.5.3
Natural Ventilation Simulation Analysis
The following conclusions have been drawn from the analysis and results in Figures 15 and 16. Night Cooling Night cooling is the most effective adaptation strategy simulated, even for the base case medium weight building. It reduces the number of hours of overheating above 25°C in 2080 from 29% to 16% when enabled. Throughout the other future weather scenarios there is a reduction in the number of hours of overheating of at least 10% with this approach.
Figure 16: Natural Ventilation Simulations - % of > 25°C (bar chart and line chart below)
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Figure 17: Natural Ventilation Simulations - % of > 28°C (bar chart and line chart below)
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Heavy Weight Comparing the heavy weight scenario with the base case medium weight scenario, the heavy weight overheats slightly more when day ventilation only is enabled but is more effective when night cooling enabled. The heavy weight scenario with night cooling compared to the base case with night cooling has a 2% overheating reduction in the current design summer year and is at a 3% reduction in 2080. Further simulations not detailed here found that for the heavy weight building to be significantly more effective higher air change rates at night are required. The heavy weight day scenario also highlights that a poorly controlled heavyweight building could lead to greater overheating than the base case, as it is reliant upon a good understanding by building users of window openings and controls both day and night to make effective use of the higher mass. An automated window ventilation system would help with the heavy weight approach but would also introduce significant cost.
Reducing Internal Gains and Shading Simulations 5 and 6 show the effect of reducing the internal gains either via daylight dimming or more efficient equipment in the future or occupants working in dedicated areas outside. On average a 4% 2 overheating drop is observed when reducing the internal gains from equipment and lighting to 10 W/m . Comparing this with shading strategy and reducing solar gains where an average 5% overheating drop was observed. It was initially thought that reducing internal gains would have been more effective than solar shading as the shading parameter was only marginally set (G Factor 0.4). Figure 18 compares internal gains and solar gain into a 2080 weather scenario. The light blue curve represents no solar shading; the pink curve with solar shading, the green line - peak internal gains, the red line - reduced internal gains. It can be seen that on a sunny day the internal gains are comparable to the solar gains in the space. On cloudy days the solar gains will be less than the internal gains hence it would appear from this observation that reducing internal gains would be more effective than reducing solar gain.
th
Figure 18 Internal Gains and Solar Gains in Office 3 – 2080 50 Percentile
Key • • • •
Light blue curve = solar gain with no solar shading Magenta curve = solar gain with solar shading Green curve = peak internal gains Red curve = reduced internal gains
Shading The modest change to the G factor from 0.55 to 0.4 does show that solar shading will play an important role at reducing overheating in future climates. An average 5% drop in overheating was observed (see Figures 16 and 17). The optimal shading device is one that is placed externally to block solar gain prior to entering the building and is also moveable either automatically or via occupant control. A fixed external shading device will reduce daylight levels all year round in particular on overcast days resulting in increased lighting use. The next level would be to consider a mid pane controllable blind system which would not be as effective as the external device but would more effective than an internal blind system. The internal blind system would be considered the least effective at reducing internal solar gain as the heat would have entered the space prior to reaching the blind. Some heat would be reflected back out through the window (a
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light coloured reflective blind would assist with this) and as the blind warms up from solar radiation would convect this heat into the space. One option as detailed in CIBSE Journal May 2012 article ‘Angelic Design’ regarding the Angel Office Building refurbishment is to use the MVHR extract system to extract the heat from the blinds at the source. This refurbishment project utilised an innovative approach, a linear return air slot is detailed into the box housing of the blind. As the heat rises from the blind it is removed via the extract slot. In the future external shading could be added to the building when the windows are replaced in for example 25 or 50 years time. A decision could be made based on how the building has been performing against the actual changes in climate change. In 25 years time it might be found that the use of internal blinds and other passive strategies has been robust enough or the opposite might be the case. It might also be found that the climate is changing faster than predicted. External blinds or mid pane blinds could be added when windows are replaced. The latter being the simpler to introduce as no external frame or housing would be required.
Detailed reduced internal gain analysis It was initially thought that the effect of reducing the internal gains was not so noticeable because of the nature of dynamic simulation, which enables natural ventilation control in accordance with the load, i.e. the higher the internal gain the higher the ventilation rate is enabled to compensate. In order to test this and to see what the effect would be with lower ventilation rates against changes in internal loads further simulations were run. With these simulations the dynamic window opening strategy and air change rate was switched off and fixed air change rates were applied against the base case load and a reduced internal gain load.
Figure 19: Fixed Natural Ventilation Simulations % of > 25C
Figure 20: Simulated Scenarios for Ventilation Rates against Internal Loads
Scenario
Natural ventilation rate (air change per hr)
Base case internal loads (Y/N)
Fixed
Reduced internal loads (Y/N)
Base Case Internal Loads Natvent 1
1.0
Y
N
Natvent 2
2.0
Y
N
Reduced Internal Loads Natvent 3
1.0
N
Y
Natvent 4
2.0
N
Y
Figure 19 shows in a 2080 a scenario that reducing internal gains (comparing natvent 2 and natvent 4 both at 2.0 air changes per hour reduces overheating from 33% to 25%, an 8% reduction in overheating. This suggests that at lower natural ventilation rates reducing internal gains or other heat gains such as solar gains will be more effective than is suggested in the dynamic simulations. The perfect control simulated in dynamic modelling software of windows opening and closing when temperature conditions dictate is difficult to realise in practise unless automated or occupants have a very good understanding of how to use and operate the building to avoid overheating. Occupants might not open windows enough, or too early or too late. In addition night cooling might not be enabled due to lack of understanding of when to open and close windows or other issues such as noise and security. For natural ventilation to work manually occupants
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need to have a good understanding of how a naturally ventilated building works. A visual temperature display warning system could be used to assist with manual control. Therefore a 15% opening area was allowed for in the simulation rather than fully open. This is not to say that natural ventilation does not work in buildings as a form of effective overheating control as there are many cases around the world where it does. However the human factor limitations in manual opening control are difficult to include for in thermal simulations and it is therefore important that this is recognised. It can be seen from Figure 16 (simulation 9 combined adaptation strategies) that in 2050 and 2080 that ° overheating was beyond the set parameter of no higher than 5% above 25 C. In 2050 overheating was at 7% and in 2080 at 12%. These figures do not however represent the full potential of the building to passively adapt to in changing climates. There should be no reasons why in the future internal gains cannot be 2 reduced to lower than 5 W / m and that shading is better controlled to a Gfactor that is much lower than 0.4. In addition thermal modelling results also show that if windows are opened more than 15% free area during the day and a larger free area is achieved at night, overheating will be reduced further. It therefore is possible to design a passive naturally ventilated office building that is comfortable even into a 2080 scenario. 3.2.5.4
MVHR and Ground Cooling Simulations
The adaptation strategy of using the MVHR system with or without ground cooling was also simulated as it could be seen from Figure 16 (simulation 9 combined adaptation strategies) that in 2050 and 2080 ° overheating was beyond the set parameter of no higher than 5% above 25 C. In 2050 overheating was at 7% and in 2080 at 12%. Measures such as reducing internal gains further or increasing the solar shading factor could have been implemented which would reduce this and provide a total natural ventilation solution well into a 2080 scenario. It was however, decided not to carry out any further natural ventilation simulations and leave the results as is and to concentrate further on analysing the effect of the MVHR system and ground cooling on limiting overheating. The following table details the MVHR simulations investigated as either a mixed mode approach with natural ventilation and with or without ground cooling. All at various air change rates throughout the day and night.
Figure21: Simulated Scenarios for MVHR and Ground Cooling Scenario
Nat Vent Yes / No
MVHR Yes / No
MVHR air change per hour
Ground Yes / No
MVHR 1 MVHR 2
Day only
Night only
0.5
No
Day only
Night only
1.0
No
MVHR 3
No
Yes
0.5
Yes
MVHR 4
No
Yes
1.0
Yes
MVHR 5
No
Yes
1.5
Yes
cooling
Base Case
With reduced internal gains MVHR 6
No
Yes
0.5
Yes
MVHR 7
No
Yes
1.0
Yes
With reduced internal gains & shading MVHR 8
No
Yes
0.5
Yes
MVHR 9
No
Yes
1.0
Yes
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Figure 22: MVHR Simulations - % of > 25°C
3.2.5.5
April 2013
Figure 23: MVHR Simulations - % of > 28°C
MVHR and Ground Cooling Simulations
Both Figures 22 and 23 show that for ground cooling to be more effective than natural ventilation even with a ° minus 8 C temperature offset, the MVHR needs to achieve 1.5 air changes per hour (MVHR 5 simulation). The MVHR 3 simulation at 0.5 air change per hour shows a dramatic increase in overheating even with ground cooling when compared to natural ventilation. Overheating is between 30-45% throughout the weather scenarios. It is obvious the air change rate is far too low even with an offset temperature to be sufficiently effective at removing the heat gains from the office space whether they be solar or equipment. Simulations MVHR 6-9 show that for the MVHR system with ground cooling to be effective at lower air change rates (0.5 to 1.0 air changes per hour), additional passive measures such as shading and reduced internal gains will be required. Careful consideration of internal gains can keep thermal comfort levels within acceptable limits even into a 2080 scenario. The use of the MVHR system can also be used in a mixed mode approach with the natural ventilation strategy. The following details some possible scenarios. •
Natural ventilation during the day, MVHR at night (simulations MVHR1 and 2).
•
Natural ventilation to an upper temperature limit during the day then MVHR enabled
•
During peak external temperatures MVHR in boost mode
MVHR operating in night cooling mode can also help provide a secure means for night cooling areas with security concerns such as the ground floor.
3.2.6
Conclusions to Thermal Modelling
This report and thermal modelling exercise has assessed various adaptation strategies for future climate change scenarios. There is one clear adaptation strategy that will help ensure the success of the design in the current climate and future climates and this is the implementation of night cooling. Without this it would be difficult to ensure the building can cope using passive adaptation strategies into the future. Not only does night cooling ventilation provide comfortable conditions now, it also provides a fairly stable building moving into future climates. This is regardless of the mass of the building. Once this has been incorporated as part
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of the design a combination of simple measures working together such as the use of passivhaus insulation levels (to reduce fabric solar gain), shading, the use of MVHR systems, ground cooling, display temperature warning systems, and reducing internal gains will ensure the success of the building design in changing climates. Provided the base design allows for sufficient ventilation openings (windows and roof lights at high level), includes low energy lighting and suitable control, good daylight design to ensure lights are switched off during daylight hours, means for occupant control of windows and night cooling; the design will be robust enough to limit overheating into a 2030 scenario even into a 2050 scenario provided equipment internal gains are limited and managed well. If the building is clearly understood and controlled by the end users a combination of simple adaptation measures such as the addition of shading, temperature warning systems, effective night cooling strategies, reduced internal gains, and good lighting control will ensure that the building can cope and remain naturally ventilated into a 2080 scenario. It is likely that internal gains can be reduced further with future advances in equipment and lighting and if people use outside spaces. In addition the shading G factor of 0.4 could be improved upon to provide even further shading control during extremes. It was found that there was not one fixed adaptation solution but several which would be dependent on the type of occupant, how they use and control the building and the equipment and associated loads they bring to the space moving into the future. For example a manual approach might not be suitable for some occupants and a more automated approach would be required which controls windows when temperature conditions dictate. Another approach would be to make use of the MVHR system with pre-ground cooling by earth pipes and operating in mixed mode approach. When assessing this approach it was found to be equally effective at ensuring the occupants of the building are comfortable into a 2080 scenario.
3.3
Building Physics – PHPP pre assessment
The building design was also modelled using the Passivhaus Planning Package (PHPP) which is a design tool allowing specialist planners to assess and calculate the energy demand for low energy buildings. It was decided to assess the design using both of the thermal analysis tools to provide more meaningful results and the opportunity for comparison between the two.
3.3.1
PHPP the Base Case Design
The base case design assumed a passive design strategy including super insulation, high levels of air tightness (0.6 ac/h) and high performance triple glazed windows and doors. Summer time ventilation has assumed cross ventilation throughout the day and night; all high level windows are tilted all night and all window are tilted for 6 hrs/day. Domestic hot water is heated by solar panels and direct electric. Space heating is via direct electric heating. Lighting levels have been assumed to be 15W/sqm in the offices, 9W/sqm in the kitchen and 7W/sqm in the circulation / WC areas. Average internal heat gains of 5.2 W/sqm have been calculated based on the client’s brief.
3.3.2
Weather Files
Weather files used were those that have been generated for the Exeter region by the Prometheus Project at Exeter University. All weather files used were based on the high carbon emissions scenarios (A1F1). Weather file scenarios are as follows: Scenario 1: Exeter 1961-1991 DSY Scenario 2: Exeter 2030 DSY, 50% percentile (A1F1) Scenario 3: Exeter 2050 DSY, 50% percentile (A1F1) Scenario 4: Exeter 2080 DSY, 50% percentile (A1F1)
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3.3.3
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PHPP and Modelling Scenarios
Three different shading scenarios, two different construction methods and two ventilation options have been modelled. In addition ground cooling via an earth tube system has been assessed. Shading: The building has been modelled with shading provided only by roof overhangs and window reveals, with additional shading provided by flexible external blinds to the SW/SE facing elevation and flexible external shading to all windows. Thermal mass: An intermediate weight construction has been modelled as the base case. A heavy weight approach has been assessed as an alternative to assess its potential of reducing overheating. Ventilation: For the base case mechanical ventilation with heat recovery (85%) efficiency has been allowed for in the winter months and natural ventilation via manually opening windows for summer ventilation. As an alternative an oversized MVHR system that is capable of providing 1 ach was allowed which would operate in summer bypass mode to assist the natural ventilation. As a third alternative a subsoil heat exchanger has been allowed for, connected to the fresh air intake of the MVHR to pre-cool fresh air in the summer, and preheat in winter before it enters the MVHR.
3.3.4
PHPP Results and Conclusions
Full results are summarised in the form of an analysis matrix included in the PHPP Pre-Assessment Report in Appendix 3 and full discussion can also be found there. Passivhaus Verification Both construction methods will result in Passivhaus compliant designs for space heating demand, primary energy demand and overheating when modelled with the current weather file.
Figure 24: Overheating, space heating demand and specific primary energy demand for the Swallow Court project when modelled using the Exeter current weather data.
Space Heating Demand: For the PassivOffice project the total energy demand for heating has been 2 calculated as 5 kWh/m /yr. Overheating: Dependant on the construction method the frequency of overheating has been calculated as 0-1% when using current weather data. However, this does not mean the building will not overheat under extreme weather conditions. Depending on user behaviour (e.g. if the windows are opened as assumed here) temperatures within the building may still exceed 25°C.
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Specific Primary Energy Demand: Whilst the calculated specific primary energy demand still fulfils the Passivhaus verification requirements it does not allow for any tolerance and any design change or change of the mechanical design strategy might cause the project to fail the Passivhaus target. The main factor detrimentally affecting the primary energy target for the Swallow Court project is the direct electric heating and hot water system. When applying the Passivhaus methodology to calculate the primary energy demand any electric energy used within a building is multiplied with the factor 2.58 to allow for transmission losses etc. To reduce the primary energy demand the heating strategy could be changed to a biomass based system. The conversion factor for wood is 0.2 and would reduce the primary energy level by approximately 2 10-15 kWh/m /yr. Conclusions 1. Both construction methods will result in Passivhaus compliant designs for overheating when modelled with the current weather file and without a requirement for additional shading. 2. The heavy weight construction without additional shading performs only marginally better in terms of overheating but will result in a slightly lower daily temperature swing from solar gain than the medium weight approach. If the achievable average ventilation rate during summer can be increased by e.g. installing an oversized MVHR, then a heavy weight approach will outperform the intermediate weight solution. 3. Applying some form of shading and therefore controlling solar gains in summer has a far greater impact on reducing overheating in summer than thermal mass. 4. When applying future weather files the frequency of overheating increases for all construction methods. In 2050 the building will require some form of solar control (e.g. shutters) or change in ventilation strategy, in 2080 the building will fail the Passivhaus target of 10% independent from the construction method if no additional measures like for example ground cooling via a subsoil heat exchanger (SHX) is implemented
3.4
Phase Change Materials (PCM)
Phase change materials were considered for this project. Essentially there are two methods of passively cooling a building without the use of mechanical coolers or air conditioning; thermal mass with ventilation or PCM materials with ventilation. Both methods essentially rely on the ventilation to dissipate stored heat. The thermal mass option absorbs heat as the temperature rises and releases the heat later as the internal temperature falls. Without night time cooling the internal temperature would remain constant or continue to rise. The heat gains and losses of materials with high thermal mass are directly proportional and linear to each other. PCM materials also absorb heat but this is done through the material changing its state and absorbing and releasing heat through the latent heat principle. Prior to its change of state and post change of state the PCM material will not absorb or emit any significant amounts of energy and heat but during its state change large amounts of energy and heat are absorbed or emitted. PCM like mass still relies on night cooling to allow the PCM to reabsorb heat the following day. There are advantages to both approaches and both in essence work as a heat sponge albeit in a slightly different manner. The thermal mass approach is simple and understood and the products, whether they are dense concrete blockwork or multiple layers or dense plasterboard, are all readily available. The PCM approach is less well understood but results in a lighter construction which can be made to work at varying temperatures. Finally and probably most importantly, PCM products are more expensive compared to the thermal mass approach and currently PCM products are not widely available in the South West and the majority seem to be imported to the UK.
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Due to the cost and availability PCM was not considered as a viable climate change adaptation strategy for this project. Please also refer to the Phase Change Materials Research Study found in Appendix 3.
3.5
D4FC Adaptation Water Management Strategies
The following strategies have been developed to address the predicted future hotter drier summers and wetter warmer winters that are predicted. The strategies considered set out to reduce the water demand from the outset, and then provide potential rain water re-use and attenuation options that could be implemented to help reduce run-off, flash flooding and store and reuse water. •
Oversized 125mm rainwater gutters and downpipes to allow for increased annual rainfall under future weather scenarios
•
Extended eaves with robust construction to protect the windows from driving rain
•
Inclusion of underground oversized drainage system for rain water attenuation on site
•
Landscaping scheme to include drought resistant planting scheme
•
Rainwater harvesting to reduce internal potable water use (this was considered but not progressed as it was not economically viable considering the low water demand for the office, and also considered not aesthetically acceptable for an office to have discoloured water from the rainwater harvesting)
•
Low flow water appliances to reduce internal potable water use
•
Time – flow showers and taps, where appropriate
•
Simple rain water harvesting used for landscape irrigation such as water butts
•
Specification of permeable paving
•
Extension of pond to take flood water as part of SUDS system
•
Other strategies linked to water management have been included in the Landscape Strategies section in 3.8
3.6
D4FC Adaptation Construction Strategies
The following construction adaptation strategies were developed to address future climates: •
•
•
•
Designing for driving rain o
robust timber rain screen cladding
o
enhanced window and door specification and detailing
Designing for Increased wind severity o
eaves and verge robust details
o
robust materials and secure fixings
Designing for increased UV o
turf roof
o
timber cladding
Designing for future adaptability o
future addition for shading devices
o
future external working areas
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•
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Designing for flooding events o
oversized rainwater goods and drains
o
attenuation ponds
These are discussed more fully below and some key details have been included. See also Severe Rain and Wind Study in Appendix 3.
3.6.1
Strategies to Address an Increase in Wind Driven Rain
Probabilistic future climate data for 2050 and 2080 appears to indicate there will be a similar average rainfall in the south west. However it is predicted that winters will be wetter and summers dryer and a greater incidence of flash flooding, this coupled together with an increase in wind velocity may result in the failure of weather tight junctions in building materials. Building Control Approved Documents have been reviewed and Devon is currently located within a severe weather zone for the country. As little documentation is currently available on wind driven rain indexes and the predicted increase in wind velocities it has therefore been agreed that when detailing the building, the prevailing weather conditions are to be increased from severe to very severe. The wind driven rain map puts 2 Exeter in the ‘severe’ exposure zone of 56.5 to less than 100 litres/m per spell. In the absence of future diving rain data it was agreed to design the building and its details to the ‘very severe’ exposure zone 100 or 2 more litres/m per spell. Building guidance from countries that have a greater rainfall and wind velocity than that of the project have been reviewed and it is generally perceived that when utilizing a timber frame construction it is best practice to incorporate a rain screen form of protection to the building. This, as the term suggests, is a screen to the rain which prevents the passage of the majority of the rain from getting past it, to the water tight layer beyond. The rain screen also protects the watertight element from physical damage and UV degradation. To incorporate this, the building’s timber frame, including all weather tight membranes and mastics, are set back from the building’s face and protected with vertical timber cladding. The gap is ventilated to allow any moisture that does penetrate beyond the rain screen layer to evaporate and dry naturally. Vertical high performance DPCs have been added to all corner junctions of the building to ensure that there is a robust water tight junction at all these vulnerable locations. This also includes the perimeter of all window and door openings Timber reveals have been returned to the window jambs to allow the junction between window and the timber frame to be protected from driving rain in this vulnerable location. This also allows insulation to be located behind it which also reduces the thermal bridge in these locations.
3.6.2
Increase in UV Levels
Probabilistic future climate data for 2050 and 2080 appears to indicate there will be longer dryer summers which will result in increased UV levels which have a detrimental effect on numerous building products, in particular paint finishes and mastics are easily degraded. The building has been designed to be clad in horizontal Cedar timber boarding rain screen, the timber boarding has been increased from the usual timber weather boarding thickness of 12mm to 25mm. This timber is widely used for weather boarding because of the natural oil content in the timber which is naturally resistant to weather degradation. The increased timber dimensions have enabled the cladding to remain unfinished with a paint produce which are susceptible to degradation to UV. The weather tight membranes mastics and sealant tapes are all protected from UV by the rain screen system. In the event of any of these failing the rain screen can be removed as it is all to be secured in position with marine grade stainless steel screws and the membranes or mastics repaired or replaced.
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It will be important to incorporate the correct and appropriate specifications for mastics to ensure they are UV stable.
3.7
Adaptation Construction Details
The following selected details include the design strategies for the predicted severe weather.
Figure 25: Cross-section through the building.
3.7.1 Typical Wall and Ground Floor Slab Junction Detail
Figure 26: This shows the continuous insulation underneath the slab and how it connects to the insulated wall construction avoiding thermal bridging.
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3.7.2 External Wall Corner Detail
Figure 27: This shows the robust timber cladding acting as a rain screen to protect the timber frame. Additional DPC has been added to the corner to further protect the corner. Additional insulation has also been added to the 50mm surface void to increase the thermal performance of the wall without increasing its structural size.
3.7.3 Window Jamb Detail
Figure 28: This shows again the robust cladding detail being returned to the window, again with additional DPC to protect the corner and additional insulation under the reveal to reduce thermal bridging.
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3.7.4 Window Head Detail
Figure 29: The window head and sill are both protected with marine grade stainless steel flashing / sills to protect these vulnerable areas from damage and subsequent weather ingress. The timber cladding rain screen has been detailed to prevent any water remaining trapped behind it. Again DPCs have been incorporated at all vulnerable locations.
3.7.5
Roof Verge
Figure 30: This shows large overhangs to shade the upper windows from UV light and provide protection to the building from wind and driving rain. The green roof protects the roof from UV damage which may elongate the life expectancy of the roof membrane. The green roof also aids water attenuation.
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3.7.6
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Roof Eaves
Figure 31: Oversized roof outlets have been incorporated to cater for predicted future heavy rainfall patterns. Eaves provide protection to the building from wind, driving rain and increased UV light.
3.8
Landscape Adaptation Strategies
The following future climate adaptation landscape design strategies were considered:
•
microclimate planting
o green roof attenuation and evaporative cooling (was part of original design but has also become a future climate strategy)
o plant transpiration cooling and shading from planting including trees/orchard around building an earth banking around building
•
relocation of hard surfaces
•
external shading
•
shaded external working areas
•
increased pond size to moderate floor / drought cycle
3.8.1 Microclimate Planting The turf roof of the building will provide rainwater attenuation and potentially evaporative cooling to the building. The use of planting around the building was considered to reduce external and indoor temperatures e.g. tree / orchard. It is recognised that the natural effect of transpiration of plants which is a process similar to evaporation, which is due to the loss of water from plants, introduces localised a moderating effect to the temperature. For further information on the effect of microclimate planting please refer to the D4FC Report October 2011.
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3.8.2 Relocation of Hard Parking Areas The hard surfaces planned around the building may contribute to heat build up during prolonged period of high temperatures – the heat island effect. A landscape adaptation strategy proposed was to relocate the hard car parking areas away from the building in order to reduce localised microclimate and increase soft plant and green space adjacent to the building. Planting has the effect of introducing a cooling effect through plant transpiration, whereas tarmac surfaces near a building absorb heat and therefore locally increase the temperatures immediately adjacent to the building especially. This would be particularly effective as the operation of windows has been identified as a ventilation strategy.
3.8.3 External Shading External shading has been considered as part of the landscape design including tree and trellising around the building to support climbing deciduous plants. This strategy will help to reduce solar gains in the summer into the building and create green walls around part of the building.
3.8.4 Shaded External Working Areas Landscaping strategies have been developed to enable people to work outside in cool shaded areas if temperatures remain too hot indoors. External sheltered workstations with small power and network capability have been suggested to be incorporated into the landscape design. This is to enable an alternative working arrangement for the workforce by removing people from potential high internal gains during hot periods.
3.8.5 Increase Pond Size Part of the landscape adaptation strategy was to adapt the attenuation pond (incorporating wetlands). This is to provide additional attenuation storage and enable cooling via evaporation to the localised area which allows the prevailing wind to take cooled air passing over the pond into the building via the natural ventilation strategy, using water features in a similar fashion to some indigenous/traditional buildings in the Middle East.
Figure 32: Base case landscape design
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Figure 33: Strategic Landscaping Proposals
3.9
Adaptation Option Appraisal and Cost Analysis
3.9.1
Introduction
This cost analysis has been carried out to: •
Establish the costs associated with the various climate adaptation strategies recommended by the design team.
•
Establish the cumulative costs for an office, built to 2010 Building Regulation requirements, for heating, cooling and additional future investments required to maintain adequate comfort conditions under future weather scenarios over the lifetime of the building.
•
Establish the cumulative costs for an office building, including the adaptation strategies detailed in this report, for heating, cooling and additional future investments required to maintain adequate comfort conditions under future weather scenarios over the lifetime of the building.
•
Compare the two sets of cumulative costs to demonstrate to the client the long term benefits of the climate change mitigation and adaptation strategies
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3.9.2
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Adaptation Strategies Adopted by Client and Associated Costs
The following strategies have been approved by the client following the modelling of strategies and cost analysis. Low Energy Active Strategies
Costs General description
Climate Change Adaptation Potential
Super Insulation / Thermal Bridge Free Construction
This involves insulating fabric elements such as walls, roof, and ground floors beyond that of Part L of the building regulations. Uvalues between 0.1 – 0.14 W/m2/k. The use of triple glazing with Uvalues in the region of 0.7 – 0.1 W/m2/k
In warming climates a number of passive strategies working together will be required in order to reduce the effects of overheating. Studies carried out on the ExeterCare4Exeter D4FC change project found compared to standard building envelope that this approach reduced overheating in future climates. This is backed up by in field studies of buildings in warmer climates.
£47,806.00
Cross and Stack Flow Ventilation
Ensuring buildings are designed with adequate ventilation strategies beyond simply single sided ventilation. Windows which can open either side of a space can take advantage of the natural affects of wind pressure in buildings which provides a natural driving force via positive and negative pressures on the opposite facades.
The building has been designed with cross flow ventilation on ground floors with window openings either side. On the first floor openings have been provided at high level via roof light openings. These provide stack and cross flow ventilation.
included cost neutral
Openings at high levels for example via ventilation chimney stacks or roof lights can enhance the cross flow affect via using additional driving forces such as buoyancy and temperature differential between the high and low level openings.
In warming climates robust and adequate ventilation strategies will be an essential requirement to ensure buildings do not overheat when using passive measures.
Studies carried out on the ExeterCare4Exeter D4FC change project found that designing with cross flow ventilation was the most significant strategy at reducing overheating when compared to single sided ventilation design.
Night Cooling
This involves purging the heat that has built up during the day via opening windows at night.
Research carried out on case study passively ventilated buildings around the world in hotter climates than the UK have found night cooling to be an essential element at reducing the effects of overheating. Research carried out from the previous ExeterCare4Exeter D4FC project also concluded this.
Night cooling is particular effective if mass is incorporated into the building envelope.
Would need to be part of the building design at the outset. The building is currently designed for night cooling to take place via restricted night ventilators and high level openings. This can also be backed up via the MVHR system.
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cost neutral
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Unlike the domestic situation heat gains are predominantly during day from solar gain and in-use 8-20 activities. During unoccupied hours this heat can be purged.
Intelligent Ventilation Control
Passive ventilation strategies rely on external air to help cool the building. If external air temperatures are hotter than inside than this can increase the levels of internal overheating. Rather than cool the building down.
In future climate change scenarios there will be increased incidents of hotter external air temperatures than inside.
cost neutral
Intelligent ventilation control involves ensuring that openings are closed to minimum fresh air levels under this scenario.
This could be done manually via a simple temperature warning system or automatically via temperature sensors, BMS system and actuated opening control.
A MVHR system has already been included in the scheme and this provides an ideal strategy to enable this system when windows close. Coupled with ground cooling or other such cooling elements such as exhaust air heat pump or dessicant wheel will enhance this strategy further.
A mixed mode approach could be adopted whereby the MVHR system is enabled for minimum fresh air volumes and if coupled to ground cooling system would further reduce the effects of overheating.
Daylight Design and Daylight Dimming
Ensuring good daylight design in internal spaces helps reduces lighting loads associated energy consumption and internal gains which increases overheating. The optimum has to be designed when sizing, selecting glazing types and the shape of windows to ensure good daylights levels internally, reducing heat loss in winter, and minimising solar gain during the summer. It can also be beneficial in the whole building energy analysis to optimise solar gain in winter.
Reducing internal gains in office buildings will be a key strategy in ensuring buildings can be passively designed to adapt to future climate change scenarios. Reductions in internal gains can help reduce the reliance on energy intensive air conditioning equipment. And adopt more passive measures.
Reducing internal loads such as from lighting can have a significant impact on overheating levels.
A simple strategy using current technology is to ensure lighting systems are designed to switch off when not required provided adequate daylight levels are being met.
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cost neutral
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Lighting systems linked into daylight dimming will ensure that lights are switched off when not required.
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The scheme has been thermally modelled for optimum window design and daylight levels to ensure this strategy can be realised. Daylight dimming from thermal modelling has also been highlighted as key strategy.
Future innovations in low energy lighting technologies such as LED lighting systems will reduce lighting loads further in future climate change scenarios.
Reduction of Internal Gains
As well as utilising advances in low energy equipment other methods at reducing internal gains can be employed. This could include removing some equipment and people entirely form the building to reduce overheating.
Internal layout allows for effective zoning and high performance compartment walls can be included. Site restrictions will make it unlikely that external sports areas will be available.
cost neutral
Equipment: ‘Cloud’ based computing systems ensures that offices do not require server equipment in the building. This moves the server to a dedicated building which can be designed in a different manner to cope with this gain. Solar Shading, Glazing Blinds
Solar gain can be controlled via various means – external shading devices, overhangs and reveals, internal blinds, solar shading glazing, the use of strategically located trees, solar control glazing
The control of solar gain through passive measures such as insulation and shading in the windows or external devices is to be considered a key adaptation strategy for future climate change scenarios.
Overhangs and window recesses have been allowed for at initial design stage to provide a degree of shading. No additional costs for this item are anticipated.
Overhangs are fixed to the building facade above windows to reduce high level south facing solar gain. Recessing windows in the facade can introduce a level of overhang too the glazing. Strategically located trees – these can be located on eastern or western facades to mitigate solar gain in the morning or afternoon. During winter periods with minimum foliage the winter sun can contribute beneficial solar gain.
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Landscape and planting effects
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The local topography shading from other buildings, shading from plants, site exposure, local cooling effects from green and blue landscapes, reduction of hard landscape areas adjacent the building can all contribute to reducing the effects of overheating on the buildings.
In order to reduce heat island effects of buildings green and blue landscapes will play an increasing role in changing climates
In addition externally landscaped spaces can provide cooler pleasant spaces for workers to relax and keep cool in.
A permaculture landscape design proposed as part of the climate change adaptation strategy includes edible plants, shrubs and trees.
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cost neutral
Research carried out from the previous ExeterCare4Exeter D4FC project concluded that external green spaces can reduce local external air temperatures by 30C and have a positive impact in the adjacent building lowering internal temperatures by 1.5oC. This research also found that a green roof can also have a cooling effect to its local vicinity. Low Energy Active Strategies
Mechanical Ventilation with Heat Recovery (MVHR) Constant Volume
Costs General description
Climate Change Adaptation Potential
Ducted fresh air supply and extract system incorporating high efficiency plate heat exchanger or thermal wheel. Thus reducing heating loads associated with fresh air in winter. Constant volume system means that fresh air loads are constant throughout the building when in use throughout the day. In some instances rooms such as meeting rooms may be unoccupied.
As a MVHR system is to be implemented at the outset the MVHR system can be controlled in changing climates to supplement the natural ventilation system to operate in a mixed mode approach.
Cost when implemented during initial construction incl in PH costs
It can help provide secure night cooling and provide minimum fresh air volumes when external air temperatures are hotter than inside.
MVHR systems can be adapted in future climate change scenarios to include additional technology such as ground pipe / earth tube systems and desiccant cooling wheels.
Additional temperature sensors and controls can be added to enable more sophisticated mixed mode cooling control.
Mechanical Ventilation with Heat Recovery (MVHR) Variable Volume
As above - ducted fresh air supply and extract system incorporating high efficiency plate heat exchanger or thermal wheel. Variable air volume systems ramp fan speeds up and down to suit the number of occupants in the building. Control is via PIR / CO2 sensors linked to dampers for each space. Fan speeds ramp up and down
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on differential pressure control. MVHR Plate Heat Exchangers
Typically an air to air metal heat exchanger. Types: Cross flow heat exchanger – up to 60% efficient
For summer control heat exchanger is bypassed so that outgoing heat is not transferred to the incoming air stream unless linked into a desiccant cooling wheel system as described below.
Inc. in PH costs
Ground piped heat exchangers can be retrofitted in the future easier than earth tubes as they are smaller and easier to install. Provided external ground space is considered at the outset ground pipes can be installed without too much ground disruption using for example a vermeer pipe trenching machine.
£5,000
Counter current heat exchanger – up to 95% efficient (small units)
Ground Brine to Pipe Heat Exchangers
Consists of a ground pipe system 40-50 mm in diameter laid in the ground which is connected to heater/cooling wet battery in the incoming supply air duct. As with earth tube can pre-heat in winter and pre-cool in summer. The brine solution is pumped around the pipe in the ground and the through the heat exchanger in the duct. Simple temperature control parameter in winter and summer switched the pump on. Thus is it only uses energy when required.
To be considered a viable adaptation strategy.
Water Management
Costs General description
Climate Change Adaptation Potential
Cost when implemented during initial construction cost neutral
Low water use time-flowcontrolled showers and appliances
Low water use showers and WCs are effective means to reduce water consumptions. If showers are fitted with a push button operated time flow control water use could be further reduced
Effective measure to reduce water consumption and to address seasonal water shortages under future weather scenarios
Inclusion of oversized gutters and drainage to allow for increased annual rainfall under future weather scenarios Green roof
Oversizing drainage provisions will allow for increased rainfall under future weather scenarios
effective in addressing increased rainfall under future weather scenarios
assumed cost neutral
A green roof helps to reduce peak surface water runoffs
effective in addressing increased rainfall under future weather scenarios
Included in original design
Many of the adaptation measures did not add extra capital costs and in some cases made the scheme simpler. The following points provide further explanation of the associated additional capital costs. •
Incorporating the Passivhaus requirements of extra insulation, thermal bridge free design and air tightness and the MVHR system was approximately 3% cost increase when compared to 2010 building regulations envelope base case. It was also found that the Passivhaus design saved £4,400 a year in heating energy alone.
•
Ground to brine pipe cooling system was included
The total additional capital costs for the thermal comfort adaptation measures to be adopted at the outset of the project are £53,000. This equates to an increase in built cost of approximately 3.1%.
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3.9.2
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Adaptation Strategies not Adopted by the Client
Landscape The landscape adaptation strategies were not on the whole approved by the client due to the affect the strategies would have on any future potential development of the site. The following D4FC adaptation strategies were approved by the client:
•
turf roof to office building (already party of scheme)
•
additional planting and earth mound (earth mound already part of scheme)
The following D4FC landscape strategies were not approved by the client:
•
relocation of hard surfaces including the car parking - because the relocated car parking spaces would mean that there would be less space for future potential developments
•
extended attenuation pond – due to the same reason as above
•
shaded external spaces – due to the same reason as above
•
shading around building (e.g. trellises near building) – not included due to the car parking not being relocated
Heavyweight Construction The heavyweight design was found to be 2-5% cheaper to build. On a £2.1M build cost when compared to a medium weight construction method used for the base case design this equates to £50K to £100K. Whilst the medium weight was slightly quicker to build its material costs were higher. In addition, for a medium weight construction, more elements and costs were associated with the thermal, acoustic and moisture protection requirements. For the life cycle costing exercise, both the Building Regulations 2010 compliant design and the adapted building were considered of medium weight construction. The D4FC project commenced after the Planning Application for the original design had been received. Although it would be economically advantageous for the client to change the construction method, this would require the building to be resubmitted for Planning Application. Given that the project is in the ‘open’ countryside, and obtaining the Planning Application Approval was quite challenging it was in the best interests of the client not to resubmit for planning.
3.9.3
Costs Associated with a Standard Office Building
It was found that an extra £53,000 was required for thermal comfort adaptation strategies over and above an office building built to 2010 Building Regulations. However an office building designed to just comply with Building Regulations 2010 will not be as thermally comfortable as the adapted design. A building designed to just comply with Building Regulations 2010 will require a full air conditioning system in 2030; this air conditioning will also incur associated on-going running costs for the remaining duration of the building which the adapted building will not need. To be absolutely clear the adapted design does not need air conditioning now or in the predicted scenarios in the future.
3.9.4
Cost Benefit Analysis
The graph in Figure 23 shows the cumulative costs for an office building, built to 2010 Building Regulation requirements, for heating, cooling and additional future investments required to maintain adequate comfort conditions under future weather scenarios over the lifetime of the building. All costs have been discounted at 5% to represent present value. A conservative annual increase in fuel costs of 4% has been allowed for and a reduction of heating demand of 30% from 2050 to 2080 has been included. In 2030 an air conditioning
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system will need to be installed to maintain acceptable internal temperatures that again will need to be upgraded in 2050.
Figure 34
Figure 35 The graph in Figure 35 shows the cumulative costs for an office building, including the adaptation strategies detailed in this report, for heating, cooling and additional future investments required to maintain adequate comfort conditions under future weather scenarios over the lifetime of the building. All costs have been discounted at 5% to represent present value. A conservative annual increase in fuel costs of 4% has been allowed for and a reduction of heating demand of 30% from 2050 to 2080 has been included. The building is to be constructed to Passivhaus standard, intermediate to high mass construction, optimised cross-flow ventilation strategy and integrated landscape design.
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This graph shows that over the lifetime of the building the net present value of the cumulative energy costs are approximately ÂŁ1M compared to ÂŁ4.1M for an office building built to 2010 Building Regulation Standards. This illustrates that it is also cost effective to design to mitigate climate change from the outset.
Figure 36
Figure 36 is an overlay of Figure 34 and Figure 35. The comparison of the cumulative discounted cash flows for both options shows that after 14 years the additional energy costs of the standard built will exceed the additional investments related to the adaptation strategies detailed in this report.
3.9.5
Timescales and Triggers for Implementation
When developing an adaptation strategy for the PassivOffice Project, as the project is already developed into RIBA Workstage D the design team focussed on strategies that could be implemented into the scheme simply without involving major re-design. The timescale for implementing the adaptation strategies agreed to be adopted by the client at RIBA Workstage E is to implement them all during construction, enabling the building to perform to recognised comfort levels (see section 3.2.2) based on the weather files used (See section 3.2.3) in the research. No further adaptation strategies will be required to 2080. Further adaptation strategies may be required beyond this date, which is outside the scope of this D4FC project, but could include external envelope shading devices for building.
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4.0
Learning from Work on This Contract
4.1
Summary of the Teams Approach to the Adaptation Design Work
April 2013
Our team’s approach has been to look at passive options first and in particular use the physics of the building to make the building thermally comfort in future climate scenarios without having to rely on air conditioning now or into the future. Strategies that were found successful for the extra care project were transferred and validated for this project. The following strategies were found particularly important to achieving our passive approach to designing for future climates: •
Cross ventilation
•
Thermal mass
•
Thermally efficient envelope design
•
User interaction
•
Use of plants and landscaping
An invaluable resource proved to be the ‘study tour’ at the beginning of the project to visit exemplary buildings in more extreme climates that could be representative to a future UK climate. Methodologies like the risk assessment process developed in our Extra Care Project were fine tuned and further developed in this contract and aspects like for example the lack of guidance on overheating criteria were investigated in more depth. A better understanding of the strengths and limitations of the different assessment and modelling (IES and PHPP) tools used to simulate summertime performance gained from the Extra Care project allowed for a more efficient use of these tools and analysis of the results. The requirement to mitigate climate change related risks became part of the client’s brief and a key performance indicator of the design.
4.2
The Project and D4FC Adaptation Team
The project and the D4FC Adaptation Team were one and the same, apart for Exeter University who were part of the D4FC Adaptation Team and not the Project Team. The project team consisted of the following: •
David Disney – Client and site owner
•
Gale & Snowden Architects and Engineers – D4FC Project and Design Team leaders, architects, mechanical engineers, Passivhaus Consultants and building physicists
•
Exeter University – weather data and productivity analysis
Gale & Snowden Architects have an in-house integrated design team which includes the following disciplines: Permaculture Designers, Architects, Landscape Designers, Passivhaus Designers, Building Physicists, Species Specialist, Mechanical & Energy Engineers. This team was already fully experienced in designing passive low energy buildings having been following this design approach for 20 years. The client, David Disney, brought to the D4FC project: •
An enthusiasm and engagement in the D4FC project work and design development
•
Participation in the workshops and design input
•
Commitment to implement the findings wherever financially possible
•
Commitment to delivering low energy and low carbon buildings
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•
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They also brought an appropriate level of staff to all D4FC meetings to make decisions for the design team to implement D4FC measures as the design was ongoing
The architectural designers and passivhaus designers brought to the design the following: •
Experience of designing and building both passivhaus and naturally ventilated passive and low energy buildings
•
Healthy building design principles
•
Ensuring any low energy and passive overheating strategies were developed in an aesthetic manner to create a low energy and comfortable building that will be a pleasure to be in
•
An integrated landscape and permaculture design approach which links the building and external spaces together as part of the design process
•
In depth knowledge of plants, species and landscape design to assess how climate change may impact on the landscape and planting strategy
•
Experience of monitoring low energy buildings after they have been built and handed over to the end users
The building physicists, passivhaus designers and mechanical engineers brought to the project: •
Experience of thermal modelling and the PHPP and designing for summertime overheating in a wide range of both commercial and domestic buildings
•
Linking outputs from thermal simulations into the design process to help inform key D4FC design decisions at early stages
•
Using both IES and PHPP in conjunction to provide a robust analysis methodology into assessing overheating in building designs
•
Investigating active strategies such as the MVHR system that could link in with passive strategies and the early temperature warning system
•
Experience of designing low energy mechanical systems in buildings
•
Experience of designing passivhaus mechanical systems such as the MVHR
•
Experience of designing and implementing ground cooling systems
In addition to this the following disciplines also contributed to the project: Academic Institution (Exeter University), Civils Engineer & Structural Engineer, Quantity Surveyor and Project Manager. Exeter University provided the following: •
In depth knowledge with regard to the future weather files and UKCP09 data
•
Assessment of the Impacts of Climate Change and the Climate Change Adaptations on the Productivity of Office Workers
The quantity surveyor participated in the D4FC process by providing capital costs and life cycle costs against D4FC measures. It was also possible to highlight potential savings that D4FC strategies would eventually lead to. Bringing the D4FC element in after the planning application had been accepted restricted some strategy development, particularly the landscape.
4.3
The Initial Project Plan
The initial project plan was based on the team’s experience from the first round of D4FC projects and in hindsight set out a successful route for the delivery of this project. In practice this meant setting regular clearly defined D4FC workshops with agendas and minutes to enable the adaptation project team to meet and to focus on climate change design measures and approaches. These workshops were separate from
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the usual design team meetings and therefore D4FC matters were not seen as a small part of a larger design team meeting. Each workshop also involved the client whereby climate change risks were presented along with suitable adaptation measures that could be implemented. The client was then able to make clear decisions as to which D4FC measures to adopt in the building design. Some minor impacts due to team members not being available caused some slippage. However all of these minor delays were recovered in the early parts of the next quarter. To address this issue, regular additional status meetings were introduced early on in the project to catch up on progress and to ensure important milestones are met in accordance with programme. Funding for the PassivOffices 4 Devon project became problematic due to the change in the economic climate and the project is not yet on site.
4.4
Review of resources and tools
4.4.1
IES Thermal Modelling Software
The IES software is a useful design tool at assessing the thermal performance and comfort conditions of building design for a wide range of thermal and passive strategies: Details as follows: 1. Calculation engine: Apache 2. Calculation engine (version): v6.0 3. Interface to calculation engine: IES Virtual Environment The thermal modelling software tools utilised to assess the buildings’ thermal performance include: 1.
Calculation engine (version):
v6.0
2.
Interface to calculation engine:
IES Virtual Environment
3.
Model tool:
ModelIT Building Modeller
4.
Thermal tool:
Apache Thermal Calculation and Simulation
5.
Solar analysis tool: Suncast Solar Shading Analysis
6.
Wind & air movement tool: Macroflo: Multi-zone Air Movement
7.
CFD tool Microflo: Computation Fluid Dynamics
Outputs: •
Advanced dynamic thermal simulation at sub-hourly time steps for better computation of building components
•
Assess solar gain on surfaces, surface temperatures and radiant exchanges
•
Extensive range of results variables for buildings and systems
•
Building and room-level annual, monthly, hourly, and sub-hourly analysis
•
Assess passive performance, thermal mass, and temperature distribution
•
Link results from ApacheHVAC, MacroFlo, Suncast&RadianceIES and use as integral thermal simulation inputs
•
Export results to MicroFlo as boundary conditions for detailed CFD analysis
Strengths:
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•
It is a powerful design tool at assessing the thermal performance and comfort conditions of building designs for a wide range of thermal and passive strategies.
•
Can assess mechanical active strategies as well as passive
•
Can assess energy performance as well as overheating
•
Can be used as a concept design tool as well as compliance checking
•
Can be used as a whole building approach analysis and can also be zoned to investigate individual spaces in more detail
•
Is industry recognised software which has been developed in conjunction with industry guidelines such as those produced by CIBSE.
Weaknesses: •
Wide range of user experience inputs required so relies heavily on user competence when assessing future climate change overheating.
•
There is currently no clear industry guidance and methodology on using dynamic simulation software when assessing future climate change impact on building design.
•
Can be sometimes cumbersome to use as a concept design tool for inexperienced users
•
It is difficult to assess the impact some simple adaptation changes have when simulating dynamically for example when including solar shading with windows also opening automatically when temperature conditions dictate. Adding solar shading also changes the way windows open automatically when dynamically simulating as the internal temperature conditions will change with the lower solar gain. This can prove difficult to compare the full impact of some measures.
•
The IES software is unable to analyse the impact of latent heat and therefore it is difficult to fully analyse the benefit of green roofs. Further research is required to develop methodologies to assess the role plants can play at producing cooling effects inside and around buildings
4.4.2
Passivhaus Planning Package PHPP
Details: • Simulation is based on calculations of monthly energy balances. Overheating and cooling load calculations are based on daily intervals. •
It is a one zone model and each temperature zone has to be analysed as a separate assessment
•
It takes into account internal casual gains and solar gains
•
It allows to assess achievable ventilation rates, taking into account building design, window design, user behaviour, weather conditions and controls
•
It takes into account building orientation and properties of the materials used including mass
•
It utilises local weather data
Outputs: • calculates energy balances (including U-value calculation) •
specifying and designing building envelope components
•
designing the comfort ventilation system
•
determining the heating load
•
determining the cooling load
•
determining primary energy demand
•
determining the frequency of exceeding a set temperature
•
design the heating and hot water supply
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Strengths: • simulation tool developed through empirical research and monitoring results of completed Passive Houses (commercial and residential) over the last 20 years •
simplified model which pairs reliable results with justifiable effort for data acquisition
•
has proven track record of reliably predicting the average energy demand and summer performance of a low energy building for both commercial and domestic projects including dwellings, offices, schools and sport facilities.
•
The PHPP includes a reliable tool to help designers assess achievable ventilation rates
Limitations: • only suitable/reliable for low energy buildings with an annual heat demand of less than <40kWh/sqm year and an airtighness<1ac/hr •
summer comfort calculation allows to determine the general performance of a given building design. It is not suitable for zoning or to assess individual ‘critical’ rooms within a building.
•
According to research from the PHI (PHI PB 41, 2012) the calculation method used in the PHPP is limited to where the expected peak heat load is below 50 W/sqm. High temporary peaks beyond this level cannot be reflected by the calculation method.
•
For high ventilation rates i.e. above 3 ac/h the PHPP tends to overestimate the frequency of overheating
•
currently no future climate data files are available for the PHPP but it is understood that a research project at Cardiff University has been set up with the aim to generate this data. For this project PHI uniquely created weather files for the Exeter region based on the Prometheus Weather file
•
the majority of papers/research are only available in German
4.4.3
Architects Tools / Other Software
In addition to thermal modelling and building physics software other tools used include: • Vectorworks •
Sketchup – 3d visualisation tool
•
Therm (thermal bridging analysis)
•
Powerpoint for presentations and dissemination
4.4.4
Prometheus Weather Files
The Prometheus weather files generated by Exeter University have proven to be a useful tool as part of the thermal modelling process. Strengths: • Very easy to access from the Prometheus website and download for the location concerned •
In easily accessible format to incorporate into the IES software
•
They are free which would encourage designs teams to use them in modelling software
•
Are backed up with support by Exeter University
Limitations: • Although future years and high and medium emissions scenarios have been narrowed down from 3000 weather years, it is felt there are still too many for design teams to choose from. Choices for particular scenarios become subjective for design teams and building types. It would be helpful to either narrow down the weather files or provide guidance from industry as to which weather files are appropriate for particular building types.
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•
4.5
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The Prometheus weather files include both wind speed and wind direction which is consistent with the rest of the weather signal. However, the climate change signal of these variables is much more uncertain with very little change currently expected in the winter and a very small negative change in the summer. Also there is little evidence to suggest that the future weather patterns will be fundamentally different to those which are currently experienced so the wind field provided within the weather file is likely to be fit for purpose. The natural variability is more likely to dominate over any climate change signal so the analysis of wind used within the models is robust given current knowledge of future climates. Better knowledge of future weather patterns would be of benefit. Limitations in predicting future wind speeds in changing UK climates and rain patterns to be made clear to design teams at the outset especially if designing natural ventilation strategies in buildings in warmer climates. Future wind patterns are part based on past UK historical records; considering there have not been many days above 0 30 C in the past in the UK, caution is to be exercised when assuming a business as usual approach. This is more a limitation of availability of robust wind data rather than the Prometheus files.
What Worked Well?
•
Having funding to carry out the D4FC research in the first place. The team have learnt an enormous amount with regard to passive design and climate change adaptation which will help inform designs for many years to come
•
It allowed the design team to explore a whole range of new design ideas which have not all been incorporated as part of this work but would help inform future designs for years to come. This would not have been possible without the D4FC contract
•
The combination of using both PHPP and IES flagged up strengths and weaknesses in both approaches and initiated an invaluable discussion on key elements like for example achievable ventilation rates and thus effectiveness of thermal mass and the inherent risk of overestimating or ignoring their potential to control internal temperatures
•
Research into case study buildings and technologies and strategies that have been found to work in warmer climates other than the UK
•
Visiting Passivhaus offices in Lisbon and Germany in warmer climates helped inform key design decisions during the design process
•
Full client engagement in D4FC workshops throughout the design
•
Having access to the Prometheus weather files which were used for summertime overheating modelling and Exeter University providing support in this area
•
Separate D4FC workshops to design team meetings which helped focus the design team and client
•
Having a D4FC project that did not start at the early concept and design stages was interesting and challenging compared to the other 2 projects that the Design Team were involved in which allowed the D4FC to fundamentally shape the projects from the outset. This provided the team an opportunity to work out what you can actually achieve to address future climates without radically changing the building.
•
The client felt that the project added value to his project and has provded him with kudos / creditability in negotiations
•
Interesting to assess how a Passivhaus Office performs in a future climate change scenario
•
The research provided by Exeter University should be useful for other proejects
4.6 •
What Did Not Work Well? Some of the available weather data into changing climates such as wind speed and driving rain and rainfall patterns was limited and not in a useful format for designers to work. More research is required in this area as to how wind speeds and rain patterns will change in the future.
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•
Lack of clear industry guidance into overheating criteria or a generally accepted approach to evaluating the impact on thermal comfort. Today there is clear guidance on assessing the energy demand of buildings and despite some differences in some of the assessments methods buildings within the same category are directly comparable. Research has been carried out to confirm actual energy demand and to review the existing models with the result that some assessment methods like the PHPP already today consistently achieve remarkable compliance with the design aspirations. To assess the summertime performance there is still no generally accepted methodology that leads to reliable results and only very limited research on built projects has been carried out.
•
Coming into the project after planning application had been approved affected some of the climate change adaptation options that could have been employed. In particular the landscape design would have been different if D4FC had been incorporated at the initial design stages.
On the whole the D4FC work was found to be a positive experience for the design team and client and it had a genuine and positive impact on the design and there is little that did not work well.
4.7
The Most Effective Ways of Influencing the Client
Gale & Snowden were fortunate to be employed by a Client who has a clear vision for developing his land and who is open minded enough to embrace new ideas and technologies. The Client is the owner of the site and of the surrounding land, having had the land in his family for generations as a family run farm. In the 1990s the farm was diversified, which involved various barns and outhouses being converted to office use. A new office development was built in the 2000s and this current office development, the subject of this D4FC project, is part of a logical ongoing extension of the commercial office use on the farm. Gale & Snowden’s approach to managing projects includes the client at the heart of the team. Client participation in the design process has been developed from the practice’s early days when working on community projects in the 1990s and when the practices acted as a Community Technical Aid Centre as a founder member of ACTAC (Association of Community Technical Aid Centres). The TSB D4FC team has been successful in persuading the Client to adopt the majority of the climate change adaptation measures as detailed in this report. This success can be attributed to a number of factors: •
Close working relationship with the client - a close relationship with the client has been fostered over a number of years before the TSB D4FC project commenced. As the TSB D4FC team was largely the same team as the project team this enabled a high degree of trust and mutual respect to have been established which in turn enabled the client to have faith in the D4FC work and adaptation strategies proposed.
•
Ownership of the project – since the offices are owned and to be run by the client and likely to be passed to his children the client has a great deal of interest in the operation and performance of the buildings. The Client’s motivations are thus established on a long term view of the development e.g. running costs and performance over time.
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Keeping the client informed - the D4FC team ensured that the client was fully informed of the D4FC project progress and implications on the issues involved and their implication on the design of the building. This was achieved by including the client in a number of D4FC workshops that were kept separate to the main project team meetings. The D4FC team used a number of tools to enable the client to understand the work being undertaken including visualisation tools such as the climate risk radar, sketch up 3D and powerpoint presentations.
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Cost implication of climate adaptation strategies – the client was presented with both capital cost and life cycle cost implications regarding the climate change adaptation strategies.
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The adaptation strategies that were developed were based on Gale & Snowden’s inherent design principle for over 20 years which is to design low energy ecological buildings with a fabric first approach
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at the outset of all projects. This mitigates the need for expensive technical add-on solutions. This has resulted in most of the adaptation strategies being presented to the client having very low cost implications. The items that were not adopted were largely related to the landscape design implications and the desire of the client not to use too much of his land so that future development would not be hindered.
4.8
Recommended Resources
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Fully integrated design team approach with all design team members including engineers involved at early concept stages
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All design team members having the required level of competency, experience and proven track record
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Thermal modelling tools such as IES, PHPP
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3d visualization tools to present climate change adaptation concepts
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Looking abroad – Analysing design strategies in countries that experience a similar climate to what can be expected to affect the UK in the future helps to show new paths.
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Including climate change considerations at feasibility study stage of a project helps to minimise potential adaptation costs and maximises the potential to increase the life expectancy of a building
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The methodology used on this project (i.e. climate risk assessment - site assessment - impact assessment) is applicable to any larger residential or commercial development.
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Extending Adaptation to other Buildings
5.1 How can this Strategy be applied to Other Projects and what are the Limitations? 5.1.1
Comfort
Thermal Comfort and Productivity: The research carried out by Exeter University on the impacts of Climate Change on the Productivity of Office Workers could be applied to other office projects. Passivhaus Principles: Passivhaus principles applied to an office have a positive effect on future overheating and can be applied to most other projects Internal Gains and Solar Gains: The principles of optimising daylight to reduce heat load from artificial lighting, whilst optimising glazing size/orientation to minimise solar gain could be applied to many office projects. This would be limited as aesthetic impacts may not be appropriate for some projects. Cross Ventilation and Night Cooling: The principles of cross ventilation and night cooling to minimise overheating in buildings would be appropriate to most buildings. This approach has been found to effective in all three D4FC projects that the design team have been part of. The limitations of using these principles would be the location of the building, acoustic issues and security. Medium Weight Construction: The inclusion of thermal mass in a building to reduce the internal temperature fluctuations would be appropriate for all building projects.
5.1.2
Water Management / Construction
Designing for high weather severity including simple details and over sizing surface water drainage systems would be applicable to other projects. Incorporating rain screen / cladding would be appropriate for other projects. Minimising water use by including low water appliances (low flush WCs, low flow taps / showers etc) is just good practice and is appropriate for all projects. Using turf roofs to slow down surface water run-off and protect the roof from UV to extend the longevity of the roof covering would be appropriate for many projects.
5.1.3
Green Spaces / Healthy Buildings / Heat Stress Awareness
The green spaces and landscaping strategy and healthy building design strategy can be applied to any type of building design within the UK. It has been found that buildings and landscapes that are pleasant places to be in whether in the leisure or work environment or at home can have a positive impact on the health and well being of an individual. In the work environment raising awareness of the issues and effects of heat stress will also help individuals cope. Relaxed attitudes during heat waves to dress codes, working patterns providing external green spaces to cool down in and cold water drinking stations are all strategies applicable to any building type.
5.1.4
MVHR and Ground Cooling
Thermal modelling has found ground cooling to be a viable strategy at reducing overheating in future climates for this scheme. However, for buildings that require fire compartmentation such as a large apartment building or hospital, costs associated with this approach could be significant. In addition limited
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space externally and competition with other ground services, a ground pipe array might not be a viable option for other schemes. For buildings that do not have extensive zoning and fire compartmentation for example large open space office buildings, schools etc ground cooling linked into MVHR systems could be considered a viable solution for dealing with overheating in changing climates. This is provided it can be simplified and that there is sufficient ground area. Of the 2 systems available, ground air ducts and ground pipe systems, the conclusions drawn from this analysis were that the pipe system would be the better option for the following reasons: •
It requires less ground space
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There would be no issues of air contamination from bacteria developing in the underground ducts as the piped system is hydraulically separated from the supply air.
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The pump distributing ‘coolth’ or heat from the ground only enables when external conditions are not 0 0 favourable. For example below 5 C and above 22 C. A ground duct system pulls air through the duct 365 days of the year even when not required to do so. This results in an oversized fan to overcome the added pressure drop and increased energy costs.
5.2
Resources Tools and Materials Developed
The main resources and tools that were developed: •
A thermal modelling methodology for assessing climate change impact on building designs at concept design stages
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A PHPP methodology for assessing climate change impact on building design at concept and design stages
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A methodology to run PHPP and IES tools in parallel so that they complement each other at concept and design stages as a design tool. This method also provides a means for comparing the results of one against the other.
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A methodology for thermally simulating the impact of evaporation from water surfaces on humidity and energy demand
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A risk assessment methodology that visualises potential risks from climate change using a climate risk radar. It was found this tool was very helpful in communicating climate change related risks to clients and others involved in the project
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A full understanding of climate change and its impact on building designs and appropriate passive climate change adaptation strategies that can be used to limit its effects
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A better understanding of the role green spaces and plants can play to mitigate impacts from climate change
5.3
Further Needs
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Further research into actual summertime performance and user behaviour in the UK. Monitoring studies from the Passivhaus Institute egis suggesting that windows are not opened as widely or as often as generally expected in thermal simulations in the UK. No comparable studies on a representative scale are currently available in the UK.
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Clear guidance on overheating criteria, assessment methodology and input parameters for different building types and users
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Research into how people are likely to adapt to climate change in the UK. Will they become more tolerant to hotter climates?
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Further development of future rain files and accuracy
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Further development of future wind speeds especially if designing for natural ventilation design
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Development of probabilistic weather files for the PHPP
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