By Maggie Romuld

Humans have tapped into the enormous heat resources of the earth's crust for thousands of years. From the early native use of geothermally-heated hot spring water for cooking and medicines, and Roman use of geothermal water to heat buildings and treat eye and skin conditions, humans have exploited the heat stored within the planet. However, while we used to be content to use the heat passively delivered to the surface in the form of hot water, today we actively explore to find underground areas that contain geothermal water, so we'll know where to drill geothermal production wells to generate electricity for geothermal power plants. We have also learned to exploit the heat of the earth in other ways.

In recent decades there has been rapid growth in the use of Geothermal Heat Pumps to heat and cool buildings, and to heat water. The temperature of the first few feet of soil varies with the seasons, but below that depth the earth's temperature stays constant. In the winter, that heat can be transferred through buried pipes, into a circulating liquid, and then transferred into a building. During the summer, the fluid in the pipes 'picks up' heat from the building, thus cooling it, and transfers it into the earth.

There are several types of systems used to gather the heat from the ground; the most common are either Closed or Open Loop systems. In a Closed Loop system, a loop of pipe, usually high-grade plastic, is buried in the ground, filled with fluid (water, an anti-freeze solution, or a refrigerant,) and connected to a heat pump. The horizontal loops of pipe are installed in trenches typically dug 1 or 2 metres (4 to 6 feet) deep wherever space and soil conditions are suitable. The vertical loop goes down as far as needed, to depths of up to 250 feet. In an Open Loop system, water is pumped from a well or a body of water such as a pond, passing through a heat exchanger in the heat pump system.

The biggest advantage of geothermal heating is the fact that it's environmentally friendly. Because the source of heat is natural there are no concerns about hazardous effects to the surrounding area - unlike methods that burn fossil fuels. And there is a constant and limitless supply. The method is also efficient and cost-effective. Less energy is used within the system itself and it is cheaper to run the system than heating or cooling a home with electricity, oil, or natural gas. A typical geothermal heating system is small, about the same size as a small fridge, and there is only need for the one unit because it heats, and cools. A geothermal heat system is also low maintenance.

Among the few disadvantages are the use of refrigerants within the system, and the use of some electricity to power the heat pump. Space is also needed to lay the pipe system in trenches, which means it is not ideal for densely populated areas, and the pipes are difficult to repair once buried. Also, for areas that need vertical installation of pipes, a drilling rig may be needed if drilling is difficult. One of the biggest disadvantages to an Open Loop system is that it requires a plentiful supply of well or ground water and a good place for water disposal after the heat has been transferred.

Although air temperatures can change dramatically across the globe, the earth's temperature a few feet below the ground surface is relatively constant and geothermal heat pumps are being used to help heat and cool a variety of building types - single family homes, apartments and condominiums, schools, colleges and universities, office buildings, and factories - around the world. So, while only a few countries, like geothermically active Iceland or New Zealand, are fortunate enough to have heated water delivered naturally from deep underground to the earth's surface to directly heat buildings or provide energy, it is possible to take advantage of the earth's heat in other ways and use geothermal heat pumps almost everywhere.

To learn more about heat pumps, visit How it works Video, Intro to heat pumps and Geothermal energy.