One of the main reasons for global warming is the burning of fossil fuels, natural gas, coal, etc which produces large amounts of greenhouse gases. These gases get trapped in the earth’s atmosphere and increase the global temperature.
A primary cause for this is the electricity production from these non-renewable resources, and hence we must reduce our dependence on them. Passive design strategies help us maintain thermal comfort inside a building without the use of electricity as heating and cooling require the most.
Passive design strategies are decided based on the climate of the place. Temperature and humidity mainly determine the type. Scotland winters require passive heating strategies, whereas Dubai summers require passive cooling strategies. In countries like India, some parts need both heating and cooling strategies.
Passive cooling strategies
In general, for a cooling effect, the orientation of the building should be such that it is not along the north-south axis as the longer sides are exposed to the sun. The house should be well ventilated, both horizontally and vertically, so that heat is lost by air movement and convection.
Trees placed adjacent to buildings reduce the heat gains of walls and admit diffused light into the house. Having courtyards is advantageous as a part of it is heated by the inclined direct sunlight, and the rest remains cool due to shade from the adjacent wall, raising the hot air due to the stack effect.
Windows placed at the right positions along the wind direction pushes the cool air into the house. Windows that open 100% like the casement windows with proper vertical or horizontal sunshades are used in such regions. Apart from these, there are also climate-specific strategies, as listed below.
In hot and humid regions, where air movement is the most preferred method of cooling, wind catchers are built. These are nothing but tower-like structures with openings at the end facing the wind. They direct the wind down into the building, creating air movement and a comfortable environment. The partition wall allows the hot air to exit the building.
Solar chimneys are used in a similar climate but to improve the stack ventilation. These structures have openings at their ends made up of some heat-absorbing material to increase the temperature and speed of the stack effect. It helps in maintaining fresh air circulation within the building.
This method of cooling is adopted in places where the air is very dry and hot. Here the major problem is dryness, and so to increase the relative humidity level, water ponds are placed. The space around a pond is cooled by the removal of latent heat by the evaporating molecules, thus creating a comfortable space.
In places where the nights are cold and days are hot, walls, floors or roofs with high thermal capacity are used so that the heat absorbed during the day gets released at night. This way, the interior is maintained at comfortable temperatures day and night.
Thermal wall with night ventilation
In the case of hot summers, where both day and night require cooling, thermal walls with night ventilation punctures are adopted. The open system at night allows natural ventilation to take place.
Roof ponds are similar to thermal walls. The roof pond is covered with a movable insulated reflective surface, which during the day bounces off the sun rays and maintains a cool temperature inside the house as the pond is filled with cold water. At night, the pond is left uncovered and is naturally cooled.
Passive heating strategies
In cold regions, to utilize the sun’s heat to the fullest, buildings are placed such that the longer side faces the sun. No windows are placed along the wind direction to prevent the cold breeze from entering inside.
While designing sunshades, both summer and winter sun altitudes are to be considered as the summer sun might heat the place too much. The material used should be able to retain this heat inside however low the outside temperature is.
Direct solar gain
Wall apertures allow sunlight to directly enter the building and heat the interior living space. Equator-facing windows are specially used for this purpose. In the northern hemisphere, these are placed at 90deg, facing the south direction to admit as maximum light as possible.
The glazing should be well insulated to prevent the leakage of heat into the exterior. It is also essential to prevent glare and too much heat during summers.
Indirect solar gain
Indirect solar gain is used to heat spaces which or not the living spaces, but a passage or space adjacent to them. The direct sunlight hits the outer wall and heats the passage which acts as a thermal mass and heats the interior wall with less intensity. This design is not preferred much as it blocks views and daylight.
Glass Trombe walls are typically used to heat a particular section and pass it on to the interiors through a thermal wall that retains the heat. Window screens also act as an indirect solar gain wall.
As already mentioned, the wall should be well insulated to retain within the interior and absorb more heat. In places where there are large diurnal temperature variations, high thermal mass walls are preferred. The color of the wall also plays a major role in absorbing heat.
Vernacular passive design strategies
Before the invention of electricity, passive designing was the only choice to achieve thermal comfort. Every vernacular architecture style had a reason behind it.
In cold regions, the houses were small facing the sun, with less surface area, thick stone walls, tightly sealed doors, and windows, a central hearth, and turf-roofed to achieve a comfortable interior.
Whereas in warmer regions, the open-plan, clerestory openings, cooling ponds, mud walls, lattice windows made from dry leaves, courtyard houses, shade from trees, etc., have been used.
In windy regions, a dome-shaped roof is preferred to prevent overturning. There are so many such vernacular design examples around the world that help us design better. Very few architects like Ken Yeang have tried to incorporate them into modern buildings.