The following post about cooling for houses is a contribution from Rob Dumont Ph.D, adviser to the book, “How to Future Proof Your Home: A Guide to Building with Energy Intelligence in Cold Climates“. This article was originally published in Energy Answers.
I have used a window mounted fan to blow cool outside air into our bedroom in the late evening and through the night. We have used the fan for about 20 years now. A picture of the fan, which is mounted in a piece of quarter inch thick plywood in a casement window, is shown in Figure 1. When at a lumber yard recently, I saw a similar fan for sale for about $40.
Figure 1. Honeywell Dual Fan mounted in a piece of plywood in a casement window as seen from inside the house.
A photo of the fan as seen from outside the house is shown in Figure 2.
Figure 2. Outside view of the fan system for cooling the bedroom.
During rainstorms the casement window is closed to prevent rain from entering. When the fan is running and drawing air into the house, other windows on the second floor of the house are opened so as to get air flow into these other rooms.
In Figure 3, a view of the north side of our house is shown. The fan does not stick out like a window mounted air conditioner.
Figure 3. Outside view of the north side of the house. The window fan is mounted in the upper left window.
I modified the fan by adding an air filter on the outside to limit the amount of dust, pollen and air borne particles that enter. Although the window fan is mounted on the north side of our house, the window fan can be mounted in a window facing any direction.
We live on a relatively busy boulevard, and the fan helps to mask the noise from the street.
The reason that the fan is cooling the house is that the air temperature outside will drop after the sun goes down. Although daytime temperatures outside will go higher than 30 C (86 F) on occasion during the summer in Saskatoon, at night the outdoor air temperature will almost always drop below 20 C (68 F). This cool outdoor air makes for inexpensive cooling. On low speed the fan uses only 48 watts of electricity.
In the morning we turn the fan off and close the windows in the house to limit the daytime heating.
To further reduce the problem of overheating in our house, we have roof overhangs on our south windows to provide summer shading, and we have very few east or west facing windows. Large west facing windows can be a strong source of overheating if there are no external shading devices on the windows. An unshaded 5 foot by 6 foot patio door facing west will dump about 6,000 Btu/hour into a house when the sun is shining. We also use compact fluorescent and light emitting diode lamps, and Energy Star appliances to reduce internal heat gains from electricity use.
Cooling for houses: When the night ventilation technique doesn’t work. Does this apply in your climate?
Here are a few things to keep in mind when considering this technique.
- If the night-time outdoor temperature does not fall below about 20C, the strategy will not work very well.
- Another difficulty with the technique is that it will not lower the humidity in the house. As Saskatoon has a dry climate, this is not a problem for us.
This cooling approach of using a fan to provide night-time cooling uses considerably less energy than a window mounted air conditioner. The fan is also much quieter, less complicated and less expensive than a conventional air conditioner.
In parts of the U.S., whole house fans are sometimes used. The large fans, usually mounted in the ceiling of the upper floor, exhaust air from the house into the attic and draw air in through open windows. My aunt and uncle who lived near Detroit had such a fan in their house, which was built in the 1950s. Whole house fans are so powerful that they can backdraft chimneys, and thus should not be used in houses with atmospheric vented chimneys. For more information on whole house fans, use your search engine to find “Whole House Fans, NREL.”
To learn more about other ways to save energy while building new or renovating, increase your energy intelligence by downloading the free report.