Friday, July 31, 2009

Saving the Cool

OK, let's do something different today. The area where I live is (I hope) near the end of a heat wave. I suspect I'm not the only person who tries to keep cool in such times so I'll share what I've learned over the years. This knowledge is the accumulation of my experience plus what I've learned getting two degrees in physics. I've found by experiment that it works. Whether you have no air conditioning and want to keep cool anyway or you just want to save money on electric bills, there are some things you can do.

First, pay attention to how you dress. Light-colored, loose-fitting clothing will allow your body's natural cooling system to work at its best. In fact, loose-fitting clothing can actually be cooler than no clothes at all. That is because of the “chimney effect,” air tends to move upward between clothing and skin enhancing the cooling from evaporation of sweat. The loose, white robes of the Arabs are very practical for their climate. On the other hand, the wool suit with a necktie is an invitation to overheating, cf the humorous blog I wrote on that subject at

Second, stay hydrated. You need to replace the water you lose to sweat so you can sweat more to stay cool. Also, avoid sunburn. Skin damaged by sunburn is not as efficient at cooling you as is undamaged skin. And of course the benefits of being in the shade are obvious.

Third, avoid alcohol and caffeine. Both are diuretics that make it difficult to stay properly hydrated and alcohol likewise can interfere with recognition of problems.

Now on to your home. In most areas it is reasonable to work with nature to keep your home relatively cool, even during a heat wave. The first step is to avoid the misconception many people have that opening the windows cools the house. Open windows may cool the house or they may actually heat it up, depending on if it is warmer outside or inside. What open windows do is allow outside air into the house and thus cause the inside temperature to approach that of the outside air. If the outside air is cooler than that in the house, it will cool the house. However if it is warmer outside, opening the windows will make the house warmer.

The trick is to save up the cool from night and early morning hours. Usually the temperature drops at night, then rises again during daylight. Open the windows when outside temperature drops below that inside, or perhaps a little before*. Then close them next morning once outside temperature gets higher than that inside, or a little after. It helps if you have inside and outside thermometers so you can measure those respective temperatures.

A good fan or two can enhance the cooling effect when you open the windows. Use the fan to either draw the cool air into the house or to blow the hot air outside. However there are some tricks that make this more effective. Depending on your home construction and the power of the fan, this may actually work better if you only open two windows, one at each end of the house. Then have the fan either draw air in at one window or blow it out the other. That will allow the outside air to enter at one end, displace the warm air in the house, and exit the other end. If you open other windows, the moving air will take the path of least resistance and leave dead spots with no air circulating. You will probably have to experiment to find out what configuration of open windows and fan placement works best for your home.

It also helps to work with any breeze available. Arrange the fan so it blows the same direction as the breeze, thus aiding natural convection.

If you have a two-story house, this works even better. Warm air naturally rises so opening selected windows on both floors will allow cool air enter through the first floor windows and push the warm air up the stairs and out the windows on the top floor. Having a fan blow air up the stairs helps this process. You may want to keep the windows upstairs open a bit longer than those downstairs since the second floor will be warmer than the first floor.

*There are two reasons for opening the windows a bit early and closing them a bit late. First, air is not the only warm thing in your house. All the furniture and other stuff also store up heat and it can be warmer than the air. Bringing in outside air helps cool it. Second and more important, humidity makes you uncomfortable and works against your body's natural cooling mechanism. People living and breathing in a closed house raise the humidity so it is usually higher than that outside. Bringing in drier air, even if it is a few degrees above the inside temperature, can be helpful.


Bobkatt said...

Once again great comments. A couple of other suggestions I might add are keeping your head cool by soaking a bandanna in cold water and wrapping it around your head. If your extremities are cool the rest of your body will follow. Also one trick I found that helps is to cover windows that I don't need for light such as bedroom and bathroom with insulated foil that is available at any home improvement stores for very little money. This keeps the heat from even reaching the interior of the home.

Bobkatt said...

P.S. I have also added an attic fan that helps to extract the super heated air that otherwise builds up in the attic and if I open the attic access door I can even suck the hot air from the house directly out the top.

Hal Lillywhite said...

Good ideas. You should also pay attention to your garage. If you park there the car will still be hot and that heat goes to the garage and some of it to your house if the garage is attached. You might even consider parking outside in hot weather if the situation allows. You can also open the garage doors in the morning if you will be where you can keep an eye on it.