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Passive Solar Cooling

Passive solar cooling is more complex than is passive solar warming, namely because the sun produces heat does not remove it. The concepts of passive solar cooling generally revolve around the concept of convection, using the movement of air to replace warm with cool.

Windows and Ventilation

Like passive heating, passive cooling begins with windows. In this case, the location, type, size, and number of windows are all relevant. Of course, the most important feature is that they be operable. Windows that do not open cannot be used for ventilation.

Windows that will be used for cooling should face in the direction of the prevailing winds. So, if an area gets most of its wind from the south, then operable windows should face south. The word operable is important in this context. Windows that open are less energy efficient that windows that do not. Thus, if only some of the windows in a home need to be operable, then it is best to locate them on the side of the prevailing wind.

The type of window is also important. Casement windows offer the best ventilation followed by awning windows. Awning windows should always be fully opened to ensure that air is not directed toward the ceiling. Double hung windows are the least effective for ventilation.

If a room only has one possible location for windows, better ventilation is achieved with two separate windows instead of one large window. A larger space between windows also increases ventilation, so they should be separated as much as possible.

Wing Walls

Wing walls are nothing more than vertical structures built next to windows that project perpendicularly from the wall into the environment. Wing walls help to steer and redirect the flow of air by preventing the buildup of pressure differentials between the interior and exterior of a room.

Thermal Chimneys

It is a well-known fact that hot air rises. This simple principle of convection can be used to promote the flow the air in a structure by drawing hot air out through the top. The warm air will be replaced with cooler ground level air.

South-facing sunrooms actually perform the job of a thermal chimney quite well. If vents in the roof of the sunroom are opened and vents at the bottom of the wall between the house and the sunroom are also opened, then the movement of hot air up and out will draw air from the house into the sunroom and create a cooling breeze.

Stairwells with windows at the top also make effective thermal chimneys. The warm air drawn out of the top of the stairwell will be replaced by cool air from the lowest parts of the house.

Thermal Mass

Thermal mass refers to the resistance of a structure to changes in temperature. High thermal mass structures heat up and cool down very slowly, maintaining a relatively constant temperature over long periods of time.

Homes that are built with high thermal mass are best left open at night and closed during the day. The cool air during evening hours will help to cool the thermal mass, which will then resist changes in temperature during the day when the house is closed. Interestingly, fabric furnishings can have huge impact on thermal mass homes. The fewer the furnishings, the more effective the thermal mass will be. More furnishings mean that the thermal mass will be less effective. Fabric is essentially a poor thermal mass, heating and cooling very quickly and thus causing wide temperature swings.
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