Heat pumps move heat from one place to another – from outside to inside a home, for example. That’s why they’re called “heat pumps.” Here’s a simplified version of how a heat pump works:
- All heat pumps have an outdoor unit (called a condenser) and an indoor unit (an evaporator coil).
- A substance called a refrigerant carries the heat from one area to another. When compressed, it is a high temperature, high-pressure liquid. If it is allowed to expand, it turns into a low temperature, low pressure gas. The gas then absorbs heat.
- In the winter the normal heat pump system extracts heat from outdoor air and transfers it inside where it is circulated through your home’s ductwork by a fan.
- Even cold air contains a great deal of heat; the temperature at which air no longer carries any heat is well below -200 degrees Fahrenheit. But the coldest temperature ever recorded in the lower 48 states was -70 degrees, recorded at Roger Pass, Montana on January 20, 1954. Obviously in such weather, a heat pump would have to work pretty hard to produce 68-degree temperatures inside your home.
That’s why geothermal heat pumps are so efficient.
Geothermal heat pumps are similar to ordinary heat pumps, but instead of using heat found in outside air, they rely on the stable, even heat of the earth to provide heating, air conditioning and, in most cases, hot water.
From Montana’s minus 70 degree temperature, to the highest temperature ever recorded in the U.S. – 134 degrees in Death Valley, California, in 1913 – many parts of the country experience seasonal temperature extremes. A few feet below the earth’s surface, however, the ground remains at a relatively constant temperature. Although the temperatures vary according to latitude, at six feet underground, temperatures range from 45 degrees to 75 degrees Fahrenheit.
