Noted Egyptian architect Hassan Fathy suggested that “before investing or proposing new mechanical solutions, traditional vernacular architecture should be evaluated and developed to make them compatible with modern requirements.”
For lessons in how to keep energy consumption low in a warming climate, therefore, it may be helpful to look backwards to vernacular buildings to help us move forward, as these buildings have developed over time to offer generic designs that are efficient and a function of their environment.
The city of Yazd, which lies in the Iranian Plateau and the architecture of which has been oriented to avoid significant solar heat gains, exploit the prevailing wind, and use the cooling effects of a local micro-climate provided by vegetation and pools of standing water, serves as a shining example. The buildings are made of heavyweight materials such as brick and stone that have an ability to store latent thermal energy, which reduces internal diurnal temperature differences.
It is well documented that the thermal comfort of occupants is related to the external temperature, but it is perhaps less well known that it is also related to the effect of radiation from surfaces in a room and the air speed in a room. Consequently, the thermal mass of a building and the ventilation rate are very important for thermal comfort.
Yazd’s buildings are often naturally ventilated using the Wind Tower principle, a roof mounted device that channels fresh air into a room under the action of the wind pressure while simultaneously drawing air out of the room by virtue of a low pressure region created downstream from the element. It does this regardless of the direction of the wind and without mechanical assistance. Initially, one might expect the hot external air supplied by the wind tower to create more discomfort, but the physiological cooling and the psychological effect of sitting in a stream of moving air provides thermal comfort to occupants.
So, how can these ancient principles be reapplied to a zero carbon building to keep us cool in hot weather?
For starters, the building’s internal heat gains should be reviewed and a natural ventilation strategy should be created based on the local weather and the type and use of the building. Careful design is important as the two natural driving forces can act in coordination and opposition, increasing or reducing flow rates respectively. The design process becomes more complicated with an increase in the size of the building and the number of openings, so the choice of flow paths is of particular importance in avoiding overheating and thermal discomfort.
The thermal comfort of occupants is maintained by a steady ventilation rate encouraged by an obstruction-free flow path between the natural ventilation inlets and outlets. Perspiration efficiency increases with the speed of the internal air flow, which on very hot days can be augmented by solar powered boost fans. In addition, people want control over their environment that allows them to adapt. At night, natural ventilation can reduce the air temperature at the beginning of the working day and assist available thermal mass to dissipate heat stored during the day.
Night-time ventilation is an important feature of natural ventilation. The Wind Tower can be programmed to open fully during nocturnal hours to bring cool air into a space while simultaneously extracting hot stale air. The influx of cold night air leaves the interior of the building feeling fresh and clean, creating a healthy environment for occupants the next morning.
Today’s natural ventilation systems are making a vital contribution to replacing energy-hungry air conditioning and reducing the carbon emissions produced by burning fossil fuels.
As the climate warms, staying comfortable in a building while minimising energy consumption is a challenge. Already, refrigeration and air conditioning is estimated to account for 15 per cent of electricity consumption globally, leading to surges in electricity consumption in summer months.
Unlike mechanical air conditioning, natural ventilation consumes no electrical energy, relying instead on two forces to drive air flow: the action of the wind and the buoyancy of hot air. At night, cool external air can be drawn into a building, which helps to dissipate heat absorbed during the day, reduces peak temperatures and minimises the day/night temperature swing. During power cuts, the ventilation rate remains unchanged because the strategy does not require mechanical input to function, thus allowing the building to remain operational during extreme events.
Furthermore, tests show that expected CO2 emissions could be half those of an equivalent mechanically ventilated building. The life expectancy of the building also depends upon its internal heat gains, so if heat gains are kept to a minimum, the building is less likely to overheat and will have greater longevity.
Computer based modeling is now widely accepted in the building services sector with the software being used to show compliance with building regulations, generate energy performance predictions, support planning applications, estimate the operating costs of plant, perform life cycle assessment, determine carbon footprints, investigate the feasibility of integrating low carbon technologies into a building, and model the behavior of occupants.
Dynamic (or transient) simulation modeling (DSM) can be used to investigate natural ventilation and daylight strategies, particularly in large and complex buildings such as hospitals, schools, colleges and sports centres. This enables the performance to be quantified over a wide range of environmental conditions, and to confirm that a building meets government and client requirements.
For some, heating, ventilation and air conditioning are everyday commodities to be taken for granted, and essential for the well-being of the population. While this is certainly true for heating and ventilation, air conditioning faces the toughest challenges to its credibility.
Air conditioning systems are sometimes associated with prosperity and status, and are used to convey these attributes rather than because they are necessary for the comfort and well-being of a building’s occupants or because they are the most energy efficient approach.
Though there are proponents of an air conditioned indoor environment who cite their contribution to increased productivity in some regions of the world, air conditioning does not always ensure an indoor environment that is satisfactory for occupants. In fact, occupants often perceive the indoor environment to be better in a naturally ventilated building and report fewer symptoms of sick building syndrome (SBS).
The road to zero carbon buildings will involve the development of new modern materials, but ventilation and cooling strategies can also make use of proven practices within vernacular architecture, which need little or no daily energy input. Together, these technologies can help us to build for a better future.
In Australia, the new carbon tax law is placing a levy on electricity consumption, which is pushing the industry to look more closely at Fathy’s suggestion. Instead of mechanical ventilation, we need to look at natural ventilation first and use mechanical ventilation in cases where natural means no longer meet requirements. The cost of energy is due to rise 30 per cent in 2012 alone. In addition to this new cost, Australian overall power consumption has risen over 25 per cent in the last 10 years. This poses issues with power generation if the trend continues as it is forecast to do.
Without a doubt, the profitability of companies is going to suffer in the coming years if actions are not taken now. Already, the government in Hong Kong has set points to as high as 27 Celsius in their mechanically cooled buildings in order to reduce power consumption. This level can be bettered for 80 per cent of the year in most Australian locations.
There are several installations in Australia using these principles already. So far they are in classrooms, public buildings and offices and all feedback indicates they work well in the Australian climate. Other than these applications, in Europe there has been particular success with major food retail outlets, so really there are many opportunities to use technology like this to lower power consumption.