THE AIR CONDITIONING
Warmer summers, a consequence of climate change, have also affected our energy resources due to the increased consumption of electricity for the operation of air conditioning units. In Britain, sales of air conditioners have increased by about a third since the mid-1990s. In the United States, home air conditioning during the summer accounts for a significant percentage of energy consumption. It is now important to look for alternatives to conventional air conditioning. At least try to set your air conditioner at a higher temperature; there is no point in over-cooling your home.
Mechanical cooling, provided by fans and air conditioners, is anything but ecological. Even if you generate your own electricity using an alternative system, it would be an unforgivable waste to spend it on such energy-consuming devices. Note that the operation of the fans, which circulate the air without cooling it, actually produces heat. Some air conditioners can be efficient, eliminating more heat than the energy required for their operation, but from an ecological point of view, they are far from the ideal solution. While heat pumps can provide some air cooling, their performance may not be sufficient in very hot weather to make an interior comfortable. The solution lies rather in the adoption of a traditional passive air conditioning system such as the exploitation of thermal mass, or natural ventilation and shading.
Materials that have a high thermal mass, such as stone, masonry or concrete, slowly absorb heat during the day and release it during the night. They thus help to reduce the amount of energy needed for heating. Good insulation of the house and keeping the windows closed in cold weather will trap this heat inside. In summer, windows should be closed to prevent warm outside air from entering and shaded to prevent excessive solar gain. At night, the windows should be opened to release the heat that has accumulated in the structure of the house. To get the most out of thermal mass, you need very efficient insulation and airtightness. Orientation is also essential. In the northern hemisphere, facades exposed to the south with large bay windows will favor the penetration of heat inside during the winter. In summer, this glazing should be perfectly shaded to reduce solar gain. Planning your interior with this in mind – placing living spaces to the south and bedrooms and utility-rooms to the north – will also help to make the most of these passive strategies. Conversely, in hot climates all year round, the glass surface must be minimal on the side exposed to the sun, and the presence of cloisters, verandas, and porches or other similar elements will protect the structures from the onslaught of the sun.
Air flows naturally based on pressure and temperature differences, and circulating air lowers the humidity level and cools the atmosphere. Passive ventilation strategies can help create a comfortable indoor temperature during the summer months. One of these strategies is transverse ventilation, which exploits the differences in atmospheric pressure. Opening doors and windows on opposite sides of a house creates a draft that cools the interior. If these openings are arranged according to the prevailing winds, the ventilation rate will be much higher. Single-sided ventilation works well for small rooms if the window is large enough. Cross ventilation can be blocked by the lightest of curtains – Venetian blinds have the advantage of providing good privacy and having much lower air resistance.
Hot air tends to rise and cold air tends to descend. This “chimney effect” can also be used to cool the interior, by letting the air rise freely up to the open roof windows at the top of the house.
The central atriums, vents or open stairwells draw hot air upwards, in return causing the suction of fresh air downwards. Traditional sash windows, the upper or lower part of which can be opened, can generate a good chimney effect inside a warm room. In theory, the chimney effect will work even on a windless night, while cross ventilation requires an outside air movement for a pressure difference to be created across the house. In hot climates, the architectural concept of the interior courtyard (or patio) is very widespread. The patio promotes both cooling and cross ventilation. Watering an interior courtyard or patio also promotes drafts. Another traditional cooling technique is the ventilation tower. Mounted on the roof, its openings literally suck the air down to the bottom of the building through a masonry column, where it cools.
Window shading is a way to reduce the solar gain inside and is absolutely essential for the openings of the facade exposed to the south. Here are different types of shading:
– Slat blinds or Venetian blinds. These protections are adjustable and effective against dazzling lights, but they do not stop the heat.
– The window blinds. These blinds are mounted between double or triple glazing. These products are expensive but the blinds do not need to be cleaned and do not prevent the complete opening of the windows.
-Outer blinds and awnings. Effectively protect windows facing south.
– Shutters. Louvered shutters are a way to ventilate homes in hot countries. The interior shutters are suitable for English windows (opening outwards). For sash windows and French windows (opening inwards), external shutters are essential. The shutters provide additional insulation in winter.
– Fixed awnings. They provide very effective protection in summer against the sun on south-facing facades.
– Covered porches and verandas. In hot countries, this is the traditional way to shade exterior walls and windows at the ground floor level.
– The plantations. In temperate regions, deciduous trees shade walls and windows in summer, but let the rays of the winter sun pass.