Case Study: The National Trust Central Office - RIBA Product Selector

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Last year, temperature targets for the building were met which was great news. Guy Nevill Max Fordham LLP ‘‘ 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. 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. 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. 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 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. 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. 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). Fig.1 % Fig. 2 400 350 300 250 200 150 100 50 0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 % Working hours / Temp o C The Last Year 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. secontrols.com Delivering tangible benefits 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. Temperature levels in the office during the last year, including the unusually BRE Energy Efficient Office of Future guide DETR Best Practice Programme ENERGY CONSUMPTION FOR TYPICAL BUILDINGS VRS HEELIS Typical A. C. Deg C NOTE: ‘Other’ is the Server room power & cooling and the kitchen GROUND FLOOR % FIRST FLOOR % EXTERNAL TEMPS % 24 25 26 27 28 29 30 31 32 33 34 Good A. C. OTHER LIGHTING POWER HWS HEATING Typical Nat Vent Good Nat Vent National Trust HQ Building 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 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. 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 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: “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”. “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.” Heelis has also achieved success by scooping the British Council for Offices Innovation Award 2006. Judges said of the scheme: “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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Case Study: The National Trust Central Office - RIBA Product Selector

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