OPINION DESIGNING REALITY


Evidence is showing that passive build solutions are at risk from unpredictable user behaviour and technical fallibility, says Chris Butters


Should all future building follow the Passivhaus model – in which


balanced ventilation with heat recovery is an essential component? Both research and fi eld surveys suggest that dogmas surrounding heat recovery are starting to look shaky. We should be testing many ideas for


the future rather than legislating all our eggs into the passive basket. There are two issues with Passivhaus


type buildings. One is technical, the other – much less debated – is human. In theory, heat recovery makes sense – but many factors can reduce the theoretical benefi ts, such as uncontrolled air leakage, bad workmanship and the failure of mechanical ventilation systems. Subtract the negatives from the


positives and the picture for Passivhaus may look very different with regard to payback, energy savings and reduced climate emissions. In some cases heat recovery will be excellent but, in others – particularly small buildings and retrofi ts – it may be pointless.


Forgiving buildings In a new publication looking ‘beyond passive’1


, we explore a more realistic


construction approach that accepts fallibility in people and technology, and considers more resilient or ‘forgiving’ buildings. Researchers are constantly frustrated


at people’s ability to misuse buildings. Actual energy use can be three times what was calculated. Buildings should be able to tolerate change, different uses and an element of neglect or forgetfulness. Ultimately, no amount of theoretically effi cient technology can replace user behaviour. Most people can follow user manuals. However, reality tells us that many don’t – and it’s not just elderly people, problem families or the careless. Failure to operate passive buildings correctly puts both buildings and people’s health at risk. We need robust solutions that can tolerate minor


18 CIBSE Journal April 2013 www.cibsejournal.com


In some cases heat recovery will be excellent but in others – particularly small


buildings and retrofi ts – it may be pointless


mistakes, forgetfulness and misuse. Such people-based solutions also account for failing technology and bad workmanship. Some experts have said it is ‘impossible’ to achieve passive energy levels without mechanical ventilation and heat recovery. Yet Acharacle school in Scotland, designed by our colleagues in the GAIA network, achieves2


just


that. (See page 9 for an obituary on Howard Liddell, principle of Gaia Architects in Scotland). In schools with natural ventilation, including Acharacle and several designed by GAIA in Norway, the users themselves are the ventilation ‘system’. Ventilation is mainly achieved by opening windows for short periods between lessons, and easy-to-read sensors for temperature, humidity, light and carbon dioxide teach pupils to understand and control their environment. There are automatic vents, just in case everyone forgets. This is a very different design philosophy from Passivhaus – nature’s own forces, plus the users are the primary solution; the technology is only a supplement. Sometimes we have to use mechanical ventilation where there


are high ventilation needs – such as high humidity, polluted outdoor air or the presence of synthetic materials – but, with the right materials, the requirement for extra ventilation is minimal3,4


. In buildings with


hygroscopic, low emission materials, the need for more ventilation is low in winter; in summer, natural ventilation is normally enough, given moderate windows, shading, cross ventilation and other truly ‘passive’ solutions. Today’s Passivhaus trend is narrowing our thinking and constricting future building options. These buildings are excellent in some circumstances, but if health, resilience and forgivingness are important, then other design approaches can be preferable and more genuinely ‘green’. We need a far more holistic science5,6


,


as well as more common sense, if we are to achieve what has been our motto in Gaia Architects for 30 years: buildings that are healthy both for people and for the planet. On the technical side, the overall


energy and climate effect of heat recovery needs debate. But it is important that ventilation solutions be simple, resilient and chosen in the light of everyday human reality.


Acharacle school: passive but not Passivhaus


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