Removing the legislative barriers to natural ventilation
Natural ventilation in action — 12 Monodraught Windcatchers at Sir William Ramsay School in Buckinghamshire provide natural ventilation for the 600-seat main hall and adjacent dance and performance areas of the performing arts block.
Professor Terry Payne argues that the potential of natural ventilation as a sustainable alternative to energy-hungry air conditioning is in danger of being stifled by Part L2A of the Building Regulations.With climate change now acknowledged as one of the biggest threats to our environment and energy bills soaring at an alarming rate, it is vital that efforts to reduce emissions are focused on low carbon, energy-saving equipment. This will not only help the UK achieve its 20% Kyoto target but will also help us all save energy, save money and reduce our carbon footprint. Even so, businesses, Government, architects, M&E consultants and others have no option but to continue to specify energy-hungry mechanical air conditioning to cool buildings due to the need to comply with the current requirements of Part L2A of the Building Regulations, and therefore having to ignore the perfectly rational reasons for choosing the sustainable alternative — natural ventilation. This innovative solution, which besides being energy free is also maintenance free, is widely recognised as the most reliable and effective means of harnessing the wind’s potential as a renewable energy source, making it ‘comfortably’ the best way to ventilate buildings. In spite of the obvious benefits of natural ventilation and the fact that we are all being encouraged to reduce our carbon footprint to meet the Energy Performance of Buildings Directive, the efforts of many are being constrained by the current requirements in Part L2A of the Building Regulations, where SBEM calculations favour air conditioning over naturally ventilated buildings. Significantly this is at odds with the recommendations of the Carbon Trust, which has emphasised through a series of documents the need to increase the use of natural ventilation and passive cooling to avoid the high carbon-dioxide emissions associated with air conditioning. Crucially, in its Technology Guide the Carbon Trust states that a typical air-conditioned building has double the energy cost and associated carbon-dioxide emissions of a naturally ventilated building, and is likely to have higher capital and maintenance costs. The guide goes on to say: ‘In the UK there are relatively few days per year where the temperature is very high (over 28ºC). Using comfort cooling for this short time can cost as much as a whole year’s heating.’ Surveys have shown that building occupiers prefer an open window or naturally ventilated environment, and, even where air-conditioned spaces are provided, people often open windows and doors when they can. Once installed, air conditioning also tends to be operated well beyond the summer season, often to compensate for poor control of excessive heat gains. Despite the Carbon Trust’s advice on avoiding air conditioning, evidence shows that the implementation of Part L2A 2006 of the UK Building Regulations appears to be biased towards air conditioning rather than natural ventilation and passive cooling. And this applies even when it can be demonstrated that an equivalent naturally ventilated building has a lower carbon footprint than an air-conditioned building! The main reason is that air-conditioned buildings must demonstrate a reduction of about 28% reduction in CO2 emissions and naturally ventilated buildings a 23% reduction compared to equivalent ‘notional’ buildings quoted in Part L2A being a 2002 building. Although this requirement appears at face value to support natural ventilation, that 23% reduction is difficult to achieve because the energy consumption of a 2002 naturally ventilated building was already substantially less than an equivalent air-conditioned building. Indeed, the 28% reduction applied to an air conditioned building will still result in carbon-dioxide emissions greater than that of a naturally ventilated building of a current design. Significantly, while an air-conditioned building can be shown to be compliant with the current regulations, a compliant naturally ventilated building with lower carbon-dioxide emissions is virtually impossible to achieve. Put simply, it is far easier to meet the carbon-dioxide reduction target set for air-conditioned buildings than it is for naturally ventilated buildings.
Even though the best-practice ‘notional’ naturally ventilated building of 2002 has lower carbon-dioxide emissions than an air-conditioned, the requirement to achieve a further 23% reduction is so challenging that a compliant air-conditioned building may be built.
This ‘notional’ approach is also inconsistent with the European Energy Performance of Buildings Directive (EPBD), which requires carbon-dioxide reductions to be compared against a single reference value. Indeed, specifiers report that because Part L does not permit the use of passive methods, they cannot achieve the high targets set by the EPBD! None of this bodes well for the UK’s 2020 target for zero carbon-dioxide emissions in commercial buildings, which is hardly likely to be achieved by increasing the nation’s air conditioning load! To resolve the ambiguities of Part L the CIBSE Natural Ventilation Group, of which Monodraught is a member, is putting forward to Government its representations, prepared by Dr Martin Liddament. For all of our sakes we are determined to succeed to resolve this matter because the benefits of wind-driven and, indeed, solar-driven natural-ventilation systems are too important to ignore. In summary, the Carbon Trust states: ‘Reducing energy use makes perfect business sense; it saves money, enhances corporate reputations and helps everyone in the fight against climate change.’ We consider that as an immediate measure it should be agreed that at no time should a naturally ventilated, passive building be rejected when it can be shown to emit less carbon dioxide and be more energy efficient than an equivalent sized mechanically ventilated and air-conditioned building that has been deemed to satisfy the current Part L Building Regulations. This compliance test fulfils the single reference building concept and associated requirements of the European Energy Performance in Buildings Directive. What does not make sense is the ambiguous message implicit in Part L2A, which suggests that energy-hungry air conditioning can save the planet. Professor Terry Payne is managing director of Monodraught.
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