Reviewed and Revised on 11/19/2013
Passive solar cooling of homes involves combination of several different techniques to help lower cooling costs of the home in an environmentally friendly manner. The techniques used should depend upon the climate of the region. They could range from natural ventilation through breezes and thermal mass to carefully designed and built roof, windows, window overhangs etc. Such homes are easily able to stay cool and comfortable, during the summertime, without much use of an air conditioner. This article primarily discusses ventilation as a passive cooling strategy.
Cross-ventilation increases the amount of air flow through a room, carrying heat away. As air moves around a building, high pressure areas occur on the windward side, and low pressure areas occur on the leeward side. Good cross-ventilation strategies place air inlets on the windward side and air outlets on the leeward side of the home.
Windows, vents, and doors are primary ways to create inlets for windward air, and should be located towards the prevailing wind. If this is not possible, landscaping and “wing” walls can redirect incoming air flow toward the inlets.
The best way to incorporate natural cooling is to place operable (openable) windows or vents on two sides of a room to pull air throughout and allow warm air to exit. While open windows directly opposite one another allow for the most air flow, opening windows on any two walls will help air move through the room. Open doors to all rooms to allow air to move throughout the house. Areas allowing inward air flow should be approximately one-half to equal in size to areas where warm air exits the home.
- Stack Ventilation
Stack ventilation takes advantage of the natural tendency of hot air to rise above cold air in a room or a house. A common home example of stack ventilation is a chimney, where cold air is drawn into the fireplace, and warm air rises through the flue and exits the home at the roof.
Properly designed stack ventilation pulls air from the exterior through a strategically placed opening (typically a window or vent), on the low side of a wall. Cool air is pulled throughout the home while warmer air rises above the cool air to exit through an opening near the top of the structure. The warm air exits the house through a high window, skylight, dormer, or vent placed high on a wall.
- Installing overhangs or plantings that shade and protect windows and doors can cool the air being pulled in from the outdoors. This results in even more comfort when using stack ventilation strategies. Areas allowing inward air flow should be approximately one-half to equal in size to areas where warm air exits the home.
- Ceiling fans can assist with both cross and stack ventilation. Consult the manufacturer about reverse switches that allow the fan to push heated air down during the winter months and pull cool air up during the cooling season.
Passive cooling strategies can sometimes add humidity to the indoor air, which may not be desirable. In such instances passive ventilation should be used with caution.
A few additional resources on passive solar cooling of homes are:
An Informational guide on Passive Solar Design for Homes developed by U.S. Department of Energy is a good resource for those interested in passive solar designing of homes.