Open the windows - let the air come in. This line is routinely heard, meaning windows let in air. But do we really get that elusive air every time? If it were, there would not have been ceiling fans and air conditioners.
Does that mean windows do not let in air? No, it means the way we are designing the windows may not be effective. There could be something wrong in the way buildings are located or even the town planning could be flawed. If for thousands of years, human settlements lived well without ceiling fans and air conditioners, there must have been some way of living with air.
Designing for natural air is among the very basics of an eco-friendly building, so the more we capture it, the greater the efficiency. Primarily, it means ensuring cross ventilation, displacement ventilation and body-level breeze.
Cross ventilation is a very common term, suggesting air blowing through the inside of a room. Traditionally, it was achieved by windows positioned in the centre of two opposite walls, with the room itself being narrow enough for wind movement. Nowadays, two opposite walls being external is rare, hence need to shift openings to the wall corners. If diagonally placed, even larger rooms will get more indoor air than otherwise. The corner windows create an eddy, a kind of air movement, pulling in possible stale air from all over the room. Even if we get only two side walls as external walls, there can be up to four corner windows. Typically, the openings stop at lintel level, with no way for the air above 7 feet level to go out. As such, even the fan would keep throwing this warmer air down for a while! As a solution, most homes were having a small void on top of the wall to let out this stale air, now rare to see.
The void atop the wall provided displacement ventilation, an essential approach in passive cooling, now out of practice due to maintenance issues. Imagine, the top void becoming a part of the extended window which could be tall, up to the roof bottom. It could facilitate cross ventilation at lower levels and displacement ventilation at the topmost part.
The space between the lower and upper part can be fixed glass to let in light even if the curtain is pulled, with added benefits like saving on time and money by avoiding the lintel beam. Corner tall windows going up to the roof bottom allow eddy currents by bouncing air to side walls and top ceiling; light up the corners which leads to a perception of a larger room while the verticality creates an impression of spacious room.
Will the window design and location alone solve all our needs for air? No, designing for air needs many more deliberations. It’s time to explore.