Home Sweet Home

Too many homes in hot or humid climates rely on air-conditioning systems as the chief means of cooling during the summer months. But there are alternatives, many of which have been used successfully in different countries for centuries. Of course, in the hottest and most humid climates it may be necessary to use some form of air conditioning when temperatures are at their most extreme, but by using traditional alternatives as well, the need will be much reduced.

To make the home comfortable in this type of climate there are a number of things you need to do. The first and most obvious of these is to lower the air temperature; then you should concentrate on speeding up the movement of the air, making surfaces cooler, and finally reducing the humidity.

Shading

Reducing the amount of the sun’s energy falling on the home and entering through the windows is the initial step. The techniques are basically the same as those used for reducing light levels— wider roof eaves, awnings, shutters, screens,verandahs, blinds, and low-emissivity glass — but here you should place more emphasis on shading the whole structure with trees, shrubs, creepers, and earth-cover. Where shading is difficult, the next-best alternative is to reflect as much light as possible by painting the roof and outside walls white or, as has proved successful in California, covering the roof area with shiny, reflective aluminium sheeting.

The form and layout of the home has a dramatic effect on the level of shading you can achieve, and courtyard houses have proved their worth since ancient times. The thick outer walls and roof protect the inner living spaces, and the sun reaches the floor of the courtyard for only a short period around midday.

The courtyard house is cooled naturally by convection currents. As the cool air from the inner rooms warms, it rises and is drawn into the courtyard. As the sun sets, the outside air temperature drops quickly, the flow reverses, and cool air is drawn into the rooms to cool them. The warm courtyard floor and flat roofs radiate their stored heat at night and are often used as sleeping areas. In winter, shutters retain the heat in the house interior. Trees, planting, pools, and fountains in the inner courtyard all serve to add humidity to dry air.

Ventilation

Increasing the air movement helps evaporation from the skin and makes you feel fresher and more active. Fortunately, in many hot areas there are prevailing winds that can cool the home by natural ventilation. Cross-ventilation, from one side of the home to the other, is the traditional method. Cool air enters, preferably at low level, and expels warm air through windows or vents at high level. If you live in a dry climate you can moisten the air blowing into the home by allowing it to pass over water in a pool, in earthenware containers and wide, shallow bowls, or through vegetation.

As an alternative, wind-scoop devices commonly used in the Middle East, such as the malqaf or badgir can be built to catch cool breezes at roof level and channel them down a shaft to lower-level living areas. High pressure on the windward side and low pressure on the leeward side of the building ensure that cool air is sucked downward. Window lattices and screens, such as the Egyptian ornamental wooden-peg mashrabiya, allow air to filter freely into the rooms while, additionally, reducing the strong glare of direct sunlight.

Where you do not have the benefit of prevailing winds, you can use the thermal-stack effect to induce ventilation. It works on the same principle as convection, and you can use it with passive solar heating systems — sunspaces and solar windows and walls— working in reverse. When used for heating, passive solar heaters deliver the warm and rising air into the interior. But if you vent the warm air at high level to the outside instead, you can use them for cooling by drawing in cool air at low level. The thermal mass of the materials helps to keep the cycle going at night. In order to exploit this method fully, passive thermal chimneys used solely for ventilation, and performing in the same way as a reverse wind scoop, are now being incorporated into many homes in countries such as the US and Australia.

Radiant cooling

There is another way you can use passive thermal storage systems in reverse: by cooling the thermal store at night, the heat of the next day can be absorbed. To do this, open the vents and blinds at night to the outside and close them off from the inside of the home. The next morning the store will be sufficiently cool to absorb that day’s heat. Then the cycle simply repeats and this heat radiates the following night to the outside. To cool the thermal store during summer days in hot climates, shading or movable insulation is essential for solar windows and walls and sunspaces.

Since solar collectors produce heat, you can use them to drive a refrigeration process. Because air-conditioning costs are high it could quickly become an economical proposition to install solar air conditioning, and your home can then be heated and cooled primarily by the sun all year round.

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