Energy Efficient Design

Passive Cooling - What's old is New

Until recently passive cooling has been a forgotten practice. With mass production of air-conditioners it has allowed houses to be kept unnaturally cool as long as you were willing to pay the electricity bills. However with the ever increasing cost of energy and growing environmental awareness many home owners are once again including passive cooling into the design of their buildings.

The general definition for passive cooling is the use of technologies or design features to cool buildings in a natural way. Whether you apply passive cooling techniques to your existing home, or incorporate more efficient design principles into a new home these strategies will assist you reduce energy use and promote a comfortable, cool environment. Some of the key strategies used in this approach include:

• Increasing ventilation through the use of fans*, roof ventilators and the appropriate placement of windows at high points in the house to encourage natural heat escape. The use of cross ventilation and passive-stack ventilation also promotes effective ventilation. Cross ventilation requires openings on two sides of a room whereas passive-stack ventilation uses a vertical space, like a tower, to create a vacuum as it rises by natural convection. An inlet for cool air at the bottom of this space encourages an upward-moving air current;

• Reducing solar gain in hot weather through the use of shading from trees and vines. West-facing rooms are especially prone to overheating because the low afternoon sun penetrates deeper into rooms during the hottest part of the day. Insulating your home also reduces heat gain in summer and conserves available warmth in winter. Using pale colours when painting or rendering the exterior of your home reflects light;

• Decreasing internal heat gain by minimizing the use of heat generating light globe and appliances such as the oven; and

• Increasing internal cooling and taking advantage of the mass in the house by capturing cool air at night and when necessary topping up this up in the evening with mechanical* cooling.

* It should be noted that fans and mechanical cooling devices are not true components of passive cooling; however they are often a much more efficient use of energy than air-conditioners.