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Case Study
The National Trust Central Office Name: Heelis, The National Trust Central Office
Location: Swindon
Title: Providing a highly sustainable ventilation strategy, one that maintains a comfortable internal temperature for the National Trust’s 430 staff, cuts CO2 emissions and keeps running costs to a minimum.
Challenge: To design, manufacture and commission a natural ventilation system for what is probably the most sustainable, low energy office development in the UK.
Products: ● ● ●
OSO control system 307 actuators installed on 213 windows 156 actuators installed on 78 roof vents
Benefits: Running costs to be reduced by £550,000 a year, with further savings of over £650,000 expected thanks to improved internal working practices and London weighting payments. The building itself is expected to generate only 21kg of CO2 per square metre annually, compared to 169kg for a typical air conditioned office. It has also won a number of industry accolades as a result, including a prestigious RIBA Sustainability Award.
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SE Controls was chosen because of the transparency of their design and the system’s ability to work and communicate easily with the BMS.
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Guy Nevill Max Fordham LLP
The National Trust, as a charity, works to preserve and protect the coastline, countryside and buildings of England, Wales and Northern Ireland. It currently opens to the public over 300 historic houses and gardens, and 49 industrial monuments and mills – as well as preserving a vast number of forests, woods, fens, beaches, farmland, downs, moorland, islands,
archaeological remains, castles, nature reserves and villages. The Trust invests over £160 million a year into the nation’s environmental infrastructure and works with over 40,000 companies, including 2,000 specialist conservation businesses. For an organisation so dedicated to the ecological challenges of our time, it was imperative that The Trust’s new
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conducive to interactive team working between departments.
The benchmark of green building The resulting building, headquarters named Heelis, was created by developers Kier Ventures and architects Feilden Clegg Bradley in collaboration with The National Trust, natural ventilation specialists SE Controls / NVS and Max Fordham LLP . Cutting edge in its design, Heelis beautifully complements the surviving buildings of the Swindon Railway Works with their distinctive facades by Brunel and Gooch. Internally, the striking structure has a generous front-of-house atrium with a shop and café that is open to the public. It also comprises a two-storey deep open plan office. Two courtyards were included in the scheme, introduced by Max Fordham LLP and the architect, to enable cross ventilation. In such a deep space, the courtyards both required vents leading into them – without which the cross ventilation strategy would not be able to function effectively.
Inherent sustainability With staff spread across four different sites, some teams having three or four locations, The National Trust needed a new central office – one that could house everyone under one roof and provide its members with a better, more integrated service. As well as streamlining working practices and cross-team communication, The Trust also wanted to reduce costs and pollution with a smaller carbon footprint. Rather than choosing a typical country house, The National Trust sought better value for money in the former railway town of Swindon. It chose to occupy a large brownfield site in the Great
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The success of our sustainable initiatives is down to managing expectations. Every member of staff has had training on the natural ventilation system.
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headquarters building would possess all the same sustainable and responsible credentials as its work ethos.
Liz Adams National Trust Property Manager Western Railway Works, an area of significant architectural heritage undergoing major regeneration. Sustainability was a key issue for The Trust and its move to Swindon. As such, the new build had to meet stringent and high quality benchmarks for sustainable design – as well as providing an open plan space
A number of ‘green’ products and systems were also specified for the project, including a bank of 1,554 photovoltaic solar panels on the roof. Electricity generated from these panels is used in the building. A lighting control system adjusts the level of artificial light in response to external conditions and movement sensors ensure lights are turned off in unoccupied areas. All of the timber used in construction has been harvested from sustainable woodland, much of it originating from National Trust properties. Even the carpet was specially developed using wool from Herdwick sheep grazed on National Trust farmland. Blue Staffordshire engineering bricks were used as the principal external material, blending in as a contemporary interpretation of the surrounding structures. They are laid in lime mortar to reduce cement use and facilitate recycling. Cast aluminium cladding (visible on parts of the elevation) also provides a subtle tribute to the railway works that once occupied the site.
Ensuring optimum internal temperatures Internally, the building required a ventilation strategy that would provide fresh air and generate a healthy environment for its users. It also needed an alternative method of cooling other than air conditioning – one of the largest producers of co2 emissions and incredibly expensive to run. In line with the building’s myriad sustainability credentials, air conditioning and mechanical ventilation methods were completely unacceptable.
The natural solution Consuming very little energy and with very little carbon emissions, natural ventilation systems demonstrate how buildings can be architecturally exciting while still being efficient, sustainable and, importantly, providing best value. New low energy heating and mechanical ventilation systems can offer impressive energy ratings in a
Image courtesy of Max Fordham LLP
similar league as natural ventilation strategies, but cost implications including capital equipment and maintenance can make them significantly more expensive. SE Controls / NVS displayed its firstrate partnering and project management approach by working with M&E engineers Max Fordham LLP, Schüco (Glazing Systems Supplier) and Parry Bowen (Glazing Fabricator) to design, install and commission a natural ventilation system that would fit perfectly with the building’s design principles. Working with the building’s sense of airiness and open plan space, the winning strategy has enabled the scheme to achieve an ‘excellent’ BRE Environmental Assessment Method rating. This is alongside providing occupants with the flexible, open plan and healthy working environment they desired from the outset.
An innovative ventilation strategy Based around the company’s OSO controller and a series of different actuators, the system was fitted to the façade windows and banks of roof vents. In total, 307 actuators were installed on 213 windows and 156 actuators on 78 roof vents. The innovative OSO Controller acts as an intelligent interface between the actuators and BMS (Building Management System), with which it communicates using the LonWorks interface. As required, the BMS communicates with the OSO Control Systems and appropriately opens or closes windows and rooflights around the building, depending on the
temperature signals received from the sensors placed around the offices. Though SE Controls / NVS were able to offer a full stand alone battery backed control system, there were clear technical and financial advantages in allowing the BMS to be in overall control – a flexible approach encouraged by SE Controls / NVS to give clients a best value solution.
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The fact that occupants could control the vents with override switches was also a very important element.
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A natural ventilation system from SE Controls / NVS provided the answer. Combined with large areas of exposed thermal mass that reduce the need for cooling during warm periods (concrete panels to the first floor and roof soffit that give off ‘coolth’ to the office space during a working day), the solution works by expelling stale air and introducing fresh air through the use of climatic changes.
Guy Nevill Max Fordham LLP As the temperature inside increases above a set parameter, the warm stale air rises. The rooflights are opened to allow this warm air to escape, rather than filling the ceiling space - and eventually the whole room - from the top down. The façade windows are opened to allow cool fresh air to be drawn in, replacing the stale air. This is a typical application of the stack ventilation principal, utilising the buoyancy effect of warm air to create low pressure areas at the bottom of the stack. This in turn draws replacement air from wherever possible – ideally, in this case, an open window. As the temperature levels return to normal, the windows and rooflights close incrementally. During the summer, a night time cooling strategy is triggered - in part due to a comparison of internal and external temperatures during the day.
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Last year, temperature targets for the building were met which was great news.
employees. To provide them with such control, each of the banks of windows and rooflights has an override switch connected directly to the SE Controls OSO controllers.
Guy Nevill Max Fordham LLP
This allows them to be opened or closed as required, while relaying information to the BMS so that it knows the exact position of every actuator around the building.
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If applicable, the strategy results in signals from the BMS to the relevant OSO controllers to open the vents, allowing cool night air to enter the building and purge the interior warm air. The thermal mass of the building simultaneously plays its part in the cooling strategy by cooling down over night. As a result, in the morning there is a degree of stored ‘coolth’ in the exposed concrete structures.
It has been shown that for occupants of a building to truly buy into an adaptive natural ventilation system, people need to feel they have a degree of personal control over it. This is no different with The National Trust’s
Temperature levels in the office during the last year, including the unusually
Fig.1
% Working hours / Temp oC The Last Year
GROUND FLOOR % FIRST FLOOR %
6.0
EXTERNAL TEMPS %
5.0
4.0
BRE Energy Efficient Office of Future guide DETR Best Practice Programme %
3.0
2.0
1.0
0.0 24
When ventilation is required, it is important to minimise draughts and to maximise heat retention. This ensures that much of the heat energy carried in the air is transferred from the escaping warm stale air to the incoming cold fresh air. A reduction in the chilling effect of the incoming air is achieved by tempering it, which in turn reduces cold draughts. This is further encouraged by Max Fordham’s introduction of heat exchangers mounted in a number of the roof turrets (affectionately called ‘snouts’). In the winter, the heat energy in the escaping warm air is absorbed by the heat exchangers and passed via pipework to the heating trenches, where it contributes to the active heating of the building.
The innovative and integrated approach taken in the design of the building and its systems has resulted in the Heelis building being one of the most energy efficient, naturally ventilated offices in the UK. Staff are finding that working in an office with adaptive natural ventilation and an intelligent environmental system means fewer complaints, and no reported ill health or discomfort from air conditioned stuffiness.
When a switch is pressed, the OSO controller locks out the BMS control signal it is receiving, ignoring it for a preset amount of time (typically 60 minutes).
Then during the day, warm air is cooled by these surfaces, which in turn warm up ready for the next night cooling cycle. Such a cooling strategy can typically reduce internal temperatures by a further 1°C during the day. During the winter, heat produced by people and electrical equipment in the office is retained as much as possible by high performance building insulation - and by minimising the opening of windows and vents, reducing the need for mechanical heating.
Delivering tangible benefits
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Deg C
Fig. 2 ENERGY CONSUMPTION FOR TYPICAL BUILDINGS VRS HEELIS NOTE: ‘Other’ is the Server room power & cooling and the kitchen 400
OTHER LIGHTING
350
POWER
300
HWS
250
HEATING
200 150 100 50 0 Typical A. C.
Good A. C.
Typical Nat Vent
Good Nat Vent
National Trust HQ
Building Heelis performance data and graphic Courtesy of Max Fordham LLP
At the end of this manual override time period, the OSO controller switches back to automatic, responding directly to signals from the BMS system again. However, if there is an emergency during a lockout period, the BMS can always prematurely regain control of the OSO by sending a separate reset signal.
long and hot summer, proved to be well within recommended guidelines set by the DETR Best Practice Programme. This states that temperatures should climb to 25°C or above for no more than 5% of the working year, and to 28°C or above for no more than 1% of the working year. The graph above from Max Fordham LLP clearly shows both ground floor
secontrols.com “Sustainable design that is quite simple, but well delivered. A well handled natural ventilation system with a degree of user control, super insulation, PVs, lots of daylight and sensor controlled lighting”.
and first floor temperatures to easily meet these criteria. Heelis Facilities Management team has taken a very proactive approach to ensure staff understand all the sustainable features of the building. All existing and new staff are trained on why and how the various systems operate.
“The strategy delivers an exceptionally pleasant working environment. It somehow feels healthy without being worthy. There is something very direct about the strategy that makes it understandable to the occupants and general public, which means important lessons can be passed on.”
It is explained that, like all buildings, there will be days when some staff will feel the environment is either too cold or too hot. As such they are encouraged to fine tune their own comfort by wearing layers. A quick look around the office after hours proves this, as almost every chair has a jacket or cardigan hanging on its backrest. Liz Adams, Property Manager for Heelis, and her colleagues have even nicknamed the building “a cardigan building”. Liz is convinced that staff education, which is ongoing and includes weekly news update bulletins, is key to the wholehearted acceptance The Trust staff have given towards their new working environment. Along with photovoltaic solar panels and other energy saving initiatives, the natural ventilation strategy has meant that Heelis is expected to have one of the lowest carbon dioxide emissions ratings of any building in the country. The overall target for the building was ambitiously set by Max Fordham LLP at just 15kg CO2 per square metre per year, compared with 169kg for a an inefficient air conditioned office (with a typically under-maintained air conditioning system). This target is very close to being met; Max Fordam LLP has shown that Heelis has achieved 21Kg CO2 per m2 per year (excluding catering and communications plant). This equates to almost a third of that achievable by a building equipped with a highly efficient air conditioning system, and only 13% of the CO2 footprint of an inefficient air conditioned building. The bar chart (Fig.2 previous page) shows the energy consumption figures
Heelis has also achieved success by scooping the British Council for Offices Innovation Award 2006. Judges said of the scheme: for Heelis compared to other typical buildings. If the ‘Other’ category is ignored - with Heelis this includes the public café with its various ovens and refrigeration units, as well as significant IT server loads - one can see that Heelis performs significantly better than a ‘good’ nat vent building. Initial calculations show that The National Trust’s sustainable design approach to Heelis has also generated massive initial cost savings of £550,000 a year – thanks in part to choosing natural ventilation over air conditioning. The Trust also expects to save around £400,000 annually in future London weighting payments and more than £250,000 in administrative costs, thanks to the improved working practices allowed by the new building that pull together The Trust’s different multi-site teams to one site at Swindon.
Award-winning praise The multi award winning Heelis building has been recognised by RIBA for its eco-friendly attributes; RIBA presented the scheme with its prestigious Sustainability Award. Judges described the project as having:
“It is blessed with a most ingenious and successful strategy for naturally ventilating and cooling the building. Visited by the National Panel on what was one of the hottest days of the year, it was clear the strategy was a proven success.” “Along with natural ventilation, together with the solid south slope of the roofs covered with photovoltaic panels, helped achieve an excellent BREEAM rating. The scheme shows how older forms can be efficient and green without sacrificing value. Heelis was built to a tight budget, yet has emerged as attractive as any of the National Trust’s charges.” The project has also been presented with the Brick Development Association Awards 2005 for Best Commercial Building and The International FX Interior Design Awards 2005 for Best Medium/Large Office Building.
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SE Controls was very responsive to work with. The natural ventilation system works well, as does the speed and responsiveness of the actuators.
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Liz Adams National Trust Property Manager
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