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raferguson

Jan 14, 2007, 8:21 PM

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Technical notes about heat pumps.

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I will make a few technical notes here, since I did study many related topics in school.

The combination heat pump and air conditioner is rightly popular in areas where it never gets really cold, but it does get really hot, so you need air conditioning anyway. Think Florida. So the heat pump saves you buying a furnace.

Heat pumps are more efficient than electric resistance heating. The thermal efficiency of a heat pump is a function of the temperature difference between inside and outside. The larger the temperature difference, the less efficient heat pumps become. This is why some people have installed heat pumps that use the ground as a heat sink. The temperature underground is constant, so the heat pump will continue to work well even if the outside air temperature is very cold.

I had thought that heat pumps tend not to work all that well below 40 degrees outside temperature. This was apparently true of early heat pumps. The newer heat pumps will work well below 40F.

It turns out that humidity is a factor when using a heat pump. If the outside temperature is 40 degrees or below, and the humidity is high, the outside coils will ice up. If the humidity was low, the coils would be less likely to ice up. A good heat pump will have a defrost cycle, just like a refrigerator.

http://www.toad.net/~jsmeenen/question.html

Given the high price of electricity in Mexico, I would guess that Propane heat would be more economical than a heat pump. The calculations are not hard to perform, if you know the price of electricity and the price of propane, and the outside temperature. Of course, if you only needed heat once in a while, why buy a furnace? A heat pump or portable electric heaters will keep the house warm when the outside temperature drops.

But if you live where it is cold for a good part of the winter, look into propane heat. Some of the gas fireplaces are pretty efficient (70%), and look good also. We like our gas fireplace, and it will still work if the electricity is off.

Richard

http://www.fergusonsculpture.com