Tuesday, June 27, 2006

Hot Weather Tip #1

I grew up in Sacramento, where summertime temperatures can often go over 100º. While air conditioning is common there, my mother came from a frugal depression-era background and so she wouldn’t use electricity for that unless absolutely necessary.

Now I live in the SF Bay Area, where few homes have air conditioning because of the naturally temperate climate. Consequently her tricks on how to keep a house cool have proven very useful for those spells where the temperature climbs uncomfortably high.

The basic idea is this: get up early in the morning and open all the doors and windows to let as much heat escape as possible. It’s best to do this while it is still dark outside. When possible, allow the house to ventilate through the night, without creating security risks like leaving the door to the street unsecured.

Buildings are good at trapping heat. Not only does the structure get warm, but also the insulation tends to keep internal temperatures steady. It takes some energy to move the mass of hot air out during the cooler hours of the night.

My house is two stories; since heat rises, this means leaving upper windows open. I’ll also crack the garage door (not enough for someone to crawl under) to draw cool air from near the ground, and I’ll also open the trapdoor to the attic. This creates a chimney effect so more heat flows out through the attic vents while cooler air is sucked in from the bottom of the house. Opening the chimney vent is another avenue for heat to escape.

I’ll also run fans to push air out open windows, and the ceiling fan to circulate air in the largest room of the house. Sometimes I’ll reverse that fan to disperse the hot air nearest the ceiling, as opposed to blowing down where only cooler air is moving. If there is a fan for central heating, I’ll run that all night to assist distributing cooler air from downstairs through the house, allowing hotter air to escape. This will also store more cool air in the vents for later in the day. If it’s really warm, I’ll use a plant spray bottle in front of the fans to cool the air with mist; this is not unlike the value of courtyard fountains in hot dry climates.

While I’m up in the dawn hours, I’ll open all doors and windows, including screens if possible, to ensure the greatest flow of air (to keep the dog from getting out on the street, I use a portable child gate to block the front door). The dog gets a special view while providing security at that entrance.

As soon as the sun hits the house, close everything up – doors, windows, and drapes! Even if the air hasn’t really warmed much yet, that direct sunlight will quickly have an effect. Turn off the central fan, or set the temperature high (like 85º) so it won’t come on until sometime in the afternoon when that cooler night air will really be appreciated. By closing curtains, the house will stay dark, the interior shaded. This helps, and the heavier the curtains the better (we use pull-down blackout shades – light weight, reflect lots of heat).

With the house dark and shaded, I make an effort to not disturb the cool air I’ve trapped. If I take the car out during the day, I’ll open and close the garage door as quickly as possible, and once the car is hot, I’ll leave it outside rather than put it back in the garage. Parking a hot car back inside can raise the whole house temperature noticeably.

I keep a lawn sprinkler on the roof of the house, one of those ones with a bar with holes that goes back and forth putting a wide spray into the air. A few times during day as it starts to warm up inside, I’ll run the water for 5-10 minutes, usually until I hear water running through the rain spouts. This is like a swamp cooler, using evaporation to draw heat from the roof and cool the attic air space.

Once temperatures start to fall in the late afternoon or early evening there is usually a breeze, at which point I’ll start to selectively open windows to get some ventilation. That’s also a good time to hose off the roof and exterior walls of the house, and especially the yard and driveway, reducing the air temperature around the building itself.

Using these methods, I can keep my house at or below the mid-80’s even if the temperature is much hotter outside. It’ll get warm, but not unbearably hot. If I forget to do these things, or miss the first day of a heat wave, I can certainly tell the difference!