The Miser's Guide to a Better Planet

By Darryl McMahon

Keeping Your Cool and Your Cash

As the hot part of the year is approaching, are you considering buying an air conditioner? Perhaps you can avoid that purchase. Do you already have an air conditioner? Is it running constantly to try to keep your house cool? How much electricity (money) is it consuming? Consider a conventional window unit that consumes 10 amps at 110 volts when the compressor is running (25% of the time on 60 days of the year) and 2 amps to drive the fan alone when the compressor is not running (another 25% of the time on 60 days of the year.) That's 468 kWh of electricity used. At $0.10 / kWh, that's $46.80 on your electrical bill. A central air conditioning unit will probably consume more power than that, it has a bigger compressor, a bigger fan, a bigger power supply and cools the whole house. How can you reduce that expense?

When it is cooler outside than inside (at night), open the windows. Let the breeze move cooler air in and warmer air out. The cool breeze is free. If the air is too still, use fans to draw air in from one window and to push it out another. Simple electric fans cost a lot less than an air conditioner, and use a lot less power. (Don't do this with ground floor windows while you are sleeping, unless you have security bars or other protective measures in place. Saving some electricity is not worth risking your personal safety.) Close and lock the windows again before the heat of the day arrives, locking the coolness in. You can increase the amount of "coolth" in your home with additional thermal mass. Think water, and lots of it. Fill containers (e.g. emptied 2-litre plastic soft drink bottles) with cold water and place them on some kind of waterproof "trays" wherever it is convenient (just in case you have a leak at some point). Put them where they will get some air flow, for example, a single layer of bottles laying down under a double bed -about120 bottles or 240 litres of water. The bottles are pretty much free, and the water will cost you about $0.33 from the tap. Suppose that water in the bottles (and the rest of your house) is cooled to 15 degrees C overnight. As the house warms during the day, it will require heat energy to warm that water. It takes a calorie of energy to raise a gram of water by one degree C. A gram of water is approximately a millilitre of water. So it takes 1,200,000 calories of energy to warm that 240,000 grams of water by 5 degrees C, which is drawn from the warmer air in the house, thus cooling that air. Air conditioners in North America are normally rated by the number of British Thermal Units (BTUs) of (heat) energy they can absorb per hour. A BTU is the energy required to raise the temperature of one pound of water by one degree Fahrenheit, and is equivalent to about 250 calories. To get your air conditioner to supply the same amount of cooling would take 4,800 BTUs, which would require running a conventional window air conditioner (rated at 5,000 BTUs) for an hour at full, using about $0.13 of electricity. If you think it isn't worth the effort for that tiny saving, then you aren't thinking like a miser. Consider that this thermal mass will repeat this saving each day. Over 60 days of the hot season, that mounts up to a savings of $7.80. If the amount of thermal mass is increased by a factor of four (putting the same amount of water in 2 other bedrooms, and in the basement), the savings increase to $31.20 per year. Not bad for a one-time cost of $1.32 worth of tap water, and a bunch of used soft drink bottles. What to use for trays to hold the bottles? How about used tin-foil food serving trays that have been washed out after use? Means a whole bunch of plastic and foil is being re-used instead of recycled (or horrors, being thrown in the garbage). Using cold water to fill the bottles initially not only meant we didn't pay to heat the water going into the bottles, we got a one-time "coolth" bonus, because the water coming out of the tap was probably less than 5 degrees C (after it had run a bit), meaning it had more heat absorbing capacity than warmer water would.