When we visited Iceland in 1997, we rented a car and did some exploring of the area around its capital, Reykjavik. The picture shows the kind of thermal activity we encountered and it made me aware once more that underneath the Earth’s crust is a layer of molten rock that is about 9000 Celsius. Usually that crust is from 30 km (20 mi) to 50 km (30 mi) thick but under western Iceland it is much thinner and responsible for the thermal pools and steaming cracks. The people of Iceland take full advantage of the available heat by extracting the geothermal energy for warming greenhouses, producing electricity and heating their homes.
Even with the thick crust we have under us, there is plenty of geothermal energy available because the deeper you go in the ground, the warmer the temperature gets. Where we live, if you only go down 6 feet the ground temperature is a constant 70 C [44.60 F] summer or winter.
In the summertime when the air is 320 C [900 F] or warmer, the relatively cool ground water can be circulated in coils and air blown over them to cool a house. Fans use little electricity and this system is much more efficient than any air conditioner.
If you live in the country and get water from a well, you can just circulate well water through a refrigeration unit to extract heat but on a serviced city lot, coils of plastic pipe must be laid in trenches as shown on the right. The initial expense of laying the pipe is amply paid back in energy saved. Compared to other alternate forms of ‘green energy’, a geothermal (ground source) heat pump is the most popular because it is so predictable and cost effective.
There is enough energy stored under your house to more than supply its heating and cooling needs. When compared to an electrically heated or cooled home, geothermal heat pumps use less than 1/3 the amount of electrical energy needed to heat your home and savings are much greater than that to cool it. Well worth considering especially if you're building a new house. Rie