Applying Solutions to Mitigate Overheating in Homes Whitepaper
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Overheating is a growing concern, and according to the English Housing Survey (2020 - 2021), high rise apartments and new build properties are at the most Nrisk.otonly are hot and humid homes uncomfortable for occupants, they also pose a risk to their health. Exposure to excessive heat in homes over prolonged periods can have severe and sometimes fatal consequences.
What is contributing to overheating issues? Urbanisation, density planning restrictions, insulation levels and the development of more challenging sites has seen the rise of overheating issues in homes.
We are building more flats which tend to experience more problems as temperatures rise. This is due to significantly reduced airflow throughout each property and often, single aspect design. Building Standards are also improving with a focus on insulation levels that keeps the heat in!
OVERHEATING IN HOMES
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Overheating definition: ‘to make or become too hot’, to (cause to) become hotter than necessary or wanted
Climate change projections suggest that heat-related deaths will double by 2080 if no action is taken.
During the period 1961-1990, the mean daily temperature during the summer in London was 21.3°C. Climate forecasts suggest that by the middle of the 21st century, this could be as high as 28.1°C!
Why is the topic important?
However, Industry regulations recognise the need to tackle this issue and have released Approved Document O which covers the mitigation of overheating risk in new dwellings in England, providing guidance to help satisfy Building Regulations.
1.It’s getting hot hot hot
2.Building type
3.Energy efficiency is still king Regulations drive energy performance and the need for us to seal up properties, but are we creating a future problem by doing this? Will the 1960’s house be more attractive than the ultra modern energy efficient ones that overheats?
4.Poor installation Good design is only part of the solution. Installed performance is crucial to the delivery of comfort. As the issue of heat rises up the agenda, should we be looking to regulate and control ventilation as part of building services strategy?
OVERHEATING IN HOMES
Overheating is an unintended consequence of our drive toward energy efficiency in homes and other buildings. Add to this the rising global temperature and an increase in the number of people working and living in cities and the issue is now at the top of the agenda for new developments. deaths are caused Governmentyearoverheatingbyeachaccordingtoresearch
We are building new homes, offices and schools, all in close proximity to each other and even more so in cities. As this is combined with the hundreds of existing buildings in these built-up areas, it’s now crucial to manage the issue of heat at the design stage.
And the problem isn’t going away
3 2,000
Urban Heat Island effect – up to 8 degrees warmer in city centres Aspect Design heating schemes or poor ventilation
• Communal
5.Solar Gains
4 Where does the heat come from?
Internal heat gains
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Internal Gains OVERHEATING IN HOMES
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The issue of overheating has been growing in importance due to a number of different factors:
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Climate change – increasing external temperatures Lack of thermal mass Solar gain through increased glazing ratio/orientation of dwellings
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Even opening windows has no effect on overheating if there is no breeze on a hot day to provide any cooling benefits.
The number of occupants in a home, their activity, mechanical services and electrical appliances all contribute to heat gain in a dwelling.
• Limited
Increased levels of insulation, airtightness and large areas of glazing are some of the design factors which result in retained heat.
1.Dwelling Restrictions
Occupants may be prevented from opening windows due to planning restrictions for external noise, pollution, odour and security.
3.Internal Gains
4.Building Design
• Single
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Above we show some examples of heat generation, taking both internal and external factors into consideration:
2.External Temperature
Homes with unshaded, double-glazed windows will feel the heat on warm days, especially through any west facing glazed areas.
There are three major factors causing concern that the issue of overheating will be exacerbated in future years [4].
The Urban Heat Island (UHI) effect and unique microclimate that is generated within cities may Solar Gains
An urban heat island, or UHI, is a metropolitan area that’s a lot warmer than the rural areas surrounding it. Heat is created by energy from all the people, cars, buses, and trains in big cities - places that have lots of activity and lots of people. There are many reasons for UHIs. When houses, shops, and industrial buildings are constructed close together, it can create a UHI. Building materials are usually very good at insulating, or holding in heat. This insulation makes the areas around buildings warmer.
Thepopulationlast50 years has seen a 30% increase in the split between people living in urban areas compared to those in rural areas [5].
1. The Zero Carbon/energy efficiency agendas affecting both new build and refurbishment projects 2.Climate change leading to further increases in temperatures across the UK, according to predictions 3.Increased urbanisation and an ageing
The effectHeatUrbanIsland
What happens at night? At night temperatures continue to rise due to a number of factors. In addition, any thermal mass that has absorbed the heat during the day will start to re-radiate this at night. Unless this is removed via effective ventilation, occupants could be in for an uncomfortable night’s sleep!
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restaurant
OVERHEATING IN HOMES
A new study to implement the Passivhaus standard on Tall Residential Buildings established that cooling requirements can be reduced by up to 40%, due to the building enclosure performance being significantly improved.
• Buildings in London are more likely to overheat.
Domestic dwellings subject to Part O will have to demonstrate compliance via one of two proposed methods outlined in
The aim of the document is to protect the health and welfare of occupants of the building by reducing the occurrence of high indoor temperatures, through designing and constructing the building to achieve both of the following: limiting unwanted solar gains in summer, through fixed shading devices and considered glazing design and to provide an adequate means to remove excess heat from the indoor environment.
• Uses the following to calculate overheating risk: Location • Materials’ properties Orientation Air change rates Occupancy scenario more flexible method
2. minimise internal heat generation through energy efficient design 3. manage the heat within the building through exposed internal thermal mass and high ceilings 4. provide passive ventilation 5. provide mechanical ventilation 6. provide active cooling systems.
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Approved Document O covers the mitigation of overheating risk in new dwellings in England, providing guidance to help satisfy Building Regulations.
6 RegulationOverheating:and guidance
The Simplified Method This assessment considers the size and orientation of glazing and compares the glazing area to the floor area. Window opening areas are also considered, to deliver suitable purge ventilation.
• A
OVERHEATING IN HOMES
The London Plan recognises the need to tackle overheating, with the introduction of the following cooling hierarchy: London Plan Chapter 9: Sustainable Infrastructure Policy SI 4 Managing heat risk
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It starts at planning
Approved Document O. These methods are summarised below:
• Includes shading and ventilation Dynamic Thermal Analysis (CIBSE TM59) This can be used to ensure dwellings comply with the document by modelling the building to predict the risk of overheating and offers a range of strategies for reducing this risk.
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• Single aspects flats are more likely to overheat
All major developments in the city need to demonstrate how the design, materials, construction and operation of the development would minimise overheating and also meet its cooling needs. New developments especially should be designed to avoid the need for energy intensive air conditioning systems as much as possible. To this effect, thermal dynamic modelling will be required
B Major development proposals should demonstrate through an energy strategy how they will reduce the potential for internal overheating and reliance on air conditioning systems in accordance with the following cooling hierarchy:
Overheating is an issue identified as a major concern around the UK, and mainly in urban areas where density planning restrictions result in high numbers of buildings in close proximity as well as excessive heat generation and gain.
• Dependent on a combination of cross-ventilation and geographical location:
• Uses TM59
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1. reduce the amount of heat entering a building through orientation, shading, high albedo materials, fenestration, insulation and the provision of green infrastructure
For homes with restricted window openings, the CIBSE fixed temperature test must be followed, i.e. all occupied rooms should not exceed an operative temperature of 26°C for more than 3% of the annual hours (CIBSE Guide A (2015a)).
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Compliance is based on passing both of the following two criteria:
Overheating, Noise Penetration and Air Quality are inextricably linked to design. When it comes to overheating, it is important to note that if windows need to be opened as part of the overheating mitigation strategy, but the air quality is poor or it’s a noisy neighbourhood, this could affect how the building is ventilated and how overheating can be tackled.
From TM59: 4.2 Criteria for homes predominantly naturally ventilated
4.3 Criteria for homes which are mechanicallypredominantlyventilated
CIBSE TM59: Design methodology for the assessment of overheating risk in homes
2. number of hours exceeding 26°C in bedrooms at night – the temperature above which research shows sleep patterns are disturbed
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CIBSE's TM59 which is a design methodology to tackle overheating issues at the design stage of new dwellings was published in 2017 and is now the dynamic modeling within Approved Document O. The TM59 methodology is a collaboration of TM52 and CIBSE Guide A and is driven by the following criteria; ‘the percentage of hours that cannot exceed the target temperature, based on the running mean – this is applied to all occupied spaces’
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OVERHEATING IN HOMES 7
Criteria 2 and 3 of CIBSE TM52 may fail to be met, but both (a) and (b)above must be passed for all relevant rooms.
TM59 requires designers to run simulations based on 24-hour occupancy. ‘Lifestyles change – it is now reasonable to assume that people might be at home during the day, so the design needs to be fit for purpose and acceptable at all times,’ Important considerations: ventilation, noise and air quality
TM59 also includes other parameters for assessing overheating, including; prescribed occupancy profiles • internal gains • window-opening profiles • communal heating gains future weather data
With over 600 Air Quality Management Areas in the UK, this is a reasonable consideration in new urban developments.
26°C26°C3%
(a)For living rooms, kitchens bedrooms:andthe number of hours during which ∆T is greater than or equal to one degree (K) during the period May to September inclusive shall not be more than 3% of occupied hours. (CIBSE TM52 Criterion 1: Hours of exceedance). (b)For bedrooms only: to guarantee comfort during the sleeping hours the temperatureoperativeinthe bedroom from 10pm to 7am shall not exceed 26°C for more than 1% of annual hours. (Note: 1% of the annual hours between 22:00 and 07:00 for bedrooms is 32 hours, so 33 or more hours above 26°C will be recorded as a fail).
Indoor environmental quality (IEQ) is dependent on air quality (and hence ventilation), thermal comfort and acoustic comfort. These factors are clearly interdependent but, due to lack of guidance, have hitherto typically only been addressed independently.
Acoustics Ventilation and Overheating Residential Design Guide
The new overheating tool is a technical addition to the PHPP software, providing a robust overheating check. As a technical addition to the PHPP software, the Tool aims to reduce overheating risks based upon identified key indicators and stress tests.
Good Homes Alliance Overheating in New Homes
The AVO Guide provides an integrated approach to sustainable design for both thermal and acoustic comfort in our work and living spaces, considering key industry guidance and regulations including Approved Document F, Part L1A Building Regulations and CIBSE TM59.
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Passivhaus OverheatingTrustTool
Developed to provide a good counterbalance between existing high level guidance, often aimed at policy makers, and detailed calculation and modelling tools, often aimed at architects and engineers the simple guide, requiring numerical input, helps establish whether a project has a low, medium or high risk of experiencing overheating issues, which should then determine the further assessment that is required to mitigate the risk.
The PassivHaus Trust has been developing new ways to analyse the risks of overheating and ensuring summer comfort in Passivhaus buildings within the UK’s warming climate.
The Acoustics, Ventilation and Overheating (AVO) Residential Design Guide provides an approach as to how the competing aspects of thermal and acoustic comfort can be managed. For those involved in the design of buildings, including planning, development, design and commissioning the guide aims to prevent noise ingress to reasonable internal levels, issues related to overheating of properties and the adverse impacts that may occur have become more prevalent in recent years. This is an area which has been difficult to reconcile with the competing requirements to ensure that properties do not overheat and a requirement to maintain the acoustic integrity of the proposed buildings.
Building Services Engineering Research and Technology Predictions of summertime overheating: Comparison of dynamic thermal models and measurements in synthetically occupied test houses.
Good Homes Alliance are also launching the beta version of a new tool which provides guidance to identify and mitigate overheating risks for existing homes and retrofit schemes. The new tool will be available from 20th September 2022
Essential tools and guidance to mitigate the risk of overheating
The tool and accompanying guidance aims to help planners and design teams identify and mitigate overheating risks in new homes at an early stage.
Overheating in UK homes is a serious and growing risk to health and well-being. Dynamic thermal models are used to predict overheating risk in existing and proposed dwellings. Comparisons between predicted temperatures and temperatures measured in two test houses shed light on the accuracy of predictions for existing homes. CIBSE Technical Memorandum TM59 provides a strategy for predicting overheating risk in proposed dwellings. There are, however, differences between models’ predictions. The concept of Simulation Resolution is introduced to quantify this inter-model variability. It provides modellers with a firm basis on which to determine whether TM59 overheating predictions are robust.
5 Integrate balanced whole house mechanical ventilation systems such as heat recovery with true summer by-pass
Excessive exposure to heat in homes is not only a result of environmental factors, but also design, which is where thermal modelling is key.
1 Minimise internal heat generation through energy efficient design
3 Manage the heat within the building through exposed internal thermal mass and high ceilings
6 Use active, low carbon cooling systems as opposed to air conditioning, that defeats the object of energy efficient design
9 ConsiderationsoutDesigningtheheat:
In addition to core design features, certain solutions inside the dwelling can create a winwin solution e.g. Low energy lighting reduces energy usage and also contributes to lowering internal heat gains.
7 key design considerations for overheating
2 Reduce the amount of heat entering a building in summer through orientation, shading, fenestration, insulation and green roofs and walls
7 Use competent, certified and trained installers. Installation quality and design is crucial in order to combat overheating.
OVERHEATING IN HOMES
4 Use natural ventilation including openable windows and cross ventilation where applicable
1 Purge ventilation 2 Oversized MVHR and radial ducting 3 True summer by-pass and passive cooling 4 DuctworkPre-Insulated 5 Ground to air subsoil exchanger 6 Compressor chiller and enthalpy 7 Chilled water coil Zehnder’s seven steps to humidityincludingleveltowhichsolutions,completesomesevenhierarchyThecoolingventilationbetterandventilationcoolingconsistsofstages/options,ofwhicharestandaloneandothersarecombineddelivertherequiredofcoolingcapacity,ventilationandcontrol. OVERHEATING IN HOMES 10 Overheating in homes: Using ventilationtomitigateoverheating Combining ventilation with active cooling can offer a low carbon solution to overheating issues in residential properties and can be designed in conjunction with dynamic thermal modelling. In most instances, a mechanical ventilation system such as MEV (Central Extract System) or more likely MVHR (Heat Recovery) forms the base of the strategy for overheating. This can then be adapted accordingly to ensure compliance with best practice guidance (CIBSE TM59).
Radial ducting ensures a balanced system and reduces noise and leakage to maintain lower running speeds
New
Innovative ComfoTube Therm ducting solutions ensure continuously insulated air distribution, so the living space is cooled and heated in an energy efficient manner. Durable, whilst maintaining its flexible
Quiet in operation and ideal for night time operation! Can be used in conjunction with MEV and MVHR mechanical systems
OVERHEATING IN HOMES 11
Workingproperties.in conjunction with the MVHR system, sealed ground loops and a water to air heat exchanger provide pre-heating in the winter and precooling in the summer on the supply/intake air
largerquietresistanceinnerTheenergy-efficiently.iscomfortablesoofdesignedhave(EPP),expandedaircontinuouslyasandventilationpre-insulatedtubesin90mmFlat51dimensionstheidealsolutionforinsulateddistribution.Madeofpolypropylenethesesolutionsbeenspecificallyforthetransportwarmandcoldair,thatthedesiredclimatecreatedquicklyandsound-optimisedskinensureslowairandextremelyairflow,evenwithairvolumes.
Enthalpy MVHR cell passively reduces humidity of incoming fresh air under favourable internal/external conditions
Acoustically treated inline extractor fans located in habitable rooms provide additional ventilation up to 4 ACH in lieu of openable windows.
Increased extract and supply rates (typically to around 2.5ACH) to provide purge requirements without the need for additional solutions.
Passive cooling can be activated based on external conditions that can help maximise comfort in warmer months by automatically boosting supply air rates
Works in conjunction with a centralised chiller system or reversible heat pump to provide 1.88-5.64KW of cooling capacity via the supply air of a constant volume MVHR system with Enthalpy cell.
ventilation to mitigate overheating
ductworkPre-insulated Introducing the new Zehnder ComfoTube Therm
Modulating bypass within MVHR system constantly aims to improve the internal comfort temperature/humidity by allowing full/partial/no heat recovery depending on conditions. Constant volume motors ensure ventilation rates are met and help overcome increased pressure drops.
Working in conjunction with the MVHR system, this provides 1.5KW active air temperation and dehumidification via refrigerant cycle.
Overheating in homes: Ventilation as a strategy and solution ventilation support the mitigation of overheating based on the 7 stage cooling
A range of
hierachy (see previous page).
1 Purge LPID100ventilationLowProfile Induct Fan • Designed to fit within a ceiling void, cupboard or loft space • 100% variable speed control via optional SDC1 controller • High speed only using switching by others without the need for SDC1 controller • Can be installed in any orientation, horizontal, vertical, on floor, wall or ceiling • 4 air changes an hour for rooms up to 15m2 per fan, large rooms can use multiple fans wired in parallel 2 Oversized MVHR ComfoAir Q • Range of airflow performances with excellent pressure handling to reduce installed noise levels • Constant volume motors to ensure the delivery of guaranteed installed performance • Zero leakage, low pressure ducting solution for reduced noise levels and continued airflow performance 3 True summer by-pass and passive cooling ComfoAir Q • Filtered fresh supply air in bypass mode to prevent dust, debris and pollutants entering the house • Summer by-pass works to deliver comfort – open, close, or partially opened or closed depending on internal vs. external conditions and comfort factor • Passive cooling via automatic increase in flow rate during favourable external conditions to rapidly bring in cooler external air • In favourable conditions where internal air is cooler than external air, the unit will disable the summer by-pass and instead look to offer cold recovery of up to 87%. The ComfoAir Q350 is the first unit to be certified by the PHI for its cold recovery efficiency. OVERHEATING IN HOMES 12
strategies can
in homes. Here are examples
4 Pre-Insulated Ductwork ComfoTube • Ideal solution for continuously insulated air distribution. • Optimal thermal insulation properties; tempered air is conducted into the living space with very low temperature loss • The sound-optimised inner skin ensures low air resistance and extremely quiet air flow even with larger air volumes. • Corrosion-resistant and heat-resistant materials ensure longevity of solution. 5 Ground to air subsoil exchanger ComfoFond • Ground closed loop system that works in conjunction with MVHR Unit • Provides pre-heating during the winter and air temperation during the summer • Hygienic closed loop system to prevent water, dust ingress and avoid the need for maintenance of a collector of open air to air systems • Maintain a balanced ventilation rate down to -22°C external conditions 6 Compressor chiller and enthalpy ComfoClime + Enthalpy • 1.5kW cooling capacity integrated with MVHR Unit (CAQ450 and CAQ600) and ducting network • Easy and space-saving installation • Filtered fresh supply air, not recycled stale air. • Controlled via the CAQ450 and CAQ600s including ComfoSense C, KNX or ComfoControl app for IOS or Android 7 Chilled water coil ComfoPost • Cooling and dehumidification of filtered supply air via MVHR, during peak conditions (water at 7°C) • Complete control and setting of temperature and humidity to improve the indoor climate • Good thermal and acoustic solution, no draughts or nuisance noise OVERHEATING IN HOMES 13 Is overheating impacting your design strategy? We can help by discussing with you the best options available for comfort cooling solutions integrated with ventilation. Call our Technical Services on 01276 408 402 or email technical@zehnder.co.uk
control is not enough and that humidity has such a huge impact on our ability to feel 10.5g‘comfortable’.ofmoisture per every 1kg of dry air. Without controlling humidity you will never deliver comfort.
30 30°C 25°C 25°CWettempbulb 15°C 5°C 10°C 2025 KJ/kgEnthalpydry air Dry bulb temperature °C (humiditySpecific ∞ airdrykilogram/moisturegrams) Specific psychometric chart at 1 atm total pressure 1015 20 30 40 50 60 70 80 90 100 50 510152025303540455060%60%40%40%20%20%30%30%40%40%60%60%0.790.790.810.810.830.830.850.850.870.870.900.90Specificvolumem3/kgSpecificvolumem11080%80%10%10%RelativehumidityRelativehumidityComfortzone OVERHEATING IN HOMES Overheating and poor ventilation has direct impact on comfort in homes. Did you know that the intangible aspects of comfort are based on scientific results from psychometric investigations? In homes, we use a number of different controls in our homes for heating and ventilation and we typically gauge our comfort feeling based on temperature – the number we see on the Withindisplay.thehome environment there is an expectation that controls are integrated, working in sync to deliver comfort as effectively as possible! Psychometric chart (separate wet bulb temperature and enthalpy lines) Izzi Urieli - March 2008 14 What is ‘comfort’ anyway?
Scientific studies into the just simple temperature
Comfort
‘comfort factor’ (for example, the Mollier Psychrometric chart above) show that
= 10.5g/kg (10.5 grams of moisture for every 1kg or dry air)
15 OVERHEATING IN HOMES Visit us and experience the comfort. Flat 51 @ The Customer Experience Centre, Camberley – 01276 605800 Zehnder Specification Centre at the Business Design Centre, Islington –020 7328 2225 We can talk about comfort, but you have to experience it. We have created our own 1-bed apartment at our Customer Experience Centre in Camberley where we are using the magic 10.5 to create year round comfort. At our Islington Specification Centre you can see all of our ventilation and cooling components – some of which are keeping the centre and its occupants comfortable (of course!)
For more information contact: Zehnder Group UK Ltd Concept www.zehnder.co.uktechnical@zehnder.co.uk01276GU15SurreyCamberleyWatchmoorHousePoint3AD605800 ZGUK-OiHMaster_0621