If passive heat control can work in Burkina Fasso it can surely be applied in Europe. Brian Ford offers seven design principles to help avoid carbon intensive air conditioning
As global warming pushes up the mercury and temperate zones become hotter, demand for carbon-intensive air conditioning is expected to grow. Rising populations and a wealthier middle class in the developing world only serve to compound the problem.
Reliance on AC can be reduced if architects observe passive environmental design methods and learn some key lessons from best practice. Seven basic design principles can help deliver non-air-conditioned buildings in hot climates.
1 Study the precedents
Many existing buildings demonstrate that cooling without AC is achievable. Examples include the Federal Office building in San Francisco by Morphosis, schools in Burkino Fasso by Francis Kere, and apartment blocks in Brasilia built in the 1960s by Lucio Costa. Torrent Pharmaceutical Laboratories in Ahmadebad, by Abhikram Architects, features six lab buildings that require a very high level of environmental control, but four of them can run without AC owing to various forms of passive cooling, including direct evaporative cooling used during the hot dry season.
2 Factor in the sun’s path and building orientation
It is critical to avoid solar heat gain and the path of the sun changes based on latitude. It’s sad that many architects have no idea where the sun is in relation to their buildings, partly due to historic reliance on mechanical and electrical equipment to solve internal environmental control. If the building is located nearer the equator the roof becomes more vulnerable, in which case a ‘parasol’ roof may be more appropriate. East or west-facing elevations are always vulnerable to solar gain, so architects should consider vented facades.
3 Consider planning and zoning / form and fabric
Different activities require different levels of thermal control; circulation and transition spaces can provide critical thermal buffering. Use building form and fabric to stabilise internal temperatures; for instance, expose the internal surface of structural slabs and intermediate floors and walls.
4 Environmental strategy must be part of the overall design strategy
Efforts to eradicate the need for AC should form part of environmental considerations early in the design process. Early indicators of whether a particular approach is going to be feasible or not will ensure you don’t mislead yourself or your client. Determine the level of cooling load in plan and section, the building form and fabric and the need for and location of openings and the relationship between them.
5 Exploit ambient heat sinks
The night sky can provide radiant cooling or convective cooling (when night time temperatures are below 20oC) to precool the building ready for the following day. If you have access to a sustainable water supply, evaporative cooling can radically lower internal temperatures. ground source heat pumps can be used either for preheating or pre cooling, depending on the season.
6 Design air flow paths
The flow path can promote either stack or cross-ventilation and convective cooling, by exploiting naturally-occurring pressure differences. Warm air rises, cool air falls – we don’t need mechanical fans to drive air around buildings. The lifespan of a fan is maybe five or 10 years, which means high lifestyle costs on top of running and maintenance costs. Why should we get our clients to pay for these things when we can do without them?
7 Develop and test strategies
Use simple modelling tools to test and develop strategies for environmental control. I helped develop the early stage design tool, Optivent2, for convective cooling strategies.
Conventional aircon is major contributor to global warming and a drain on energy resources – the power outages in New York City over the summer were directly linked to peak demand for AC. Architects and engineers need to design out these outdated and wasteful technologies.
Brian Ford is emeritus professor of architecture at the University of Nottingham and author of The Architecture of Natural Cooling