What is Geothermal Energy
Heat contained within the Earth is geothermal energy. This heat could come directly from the ground, from well water or any other body of water. Very warm locations such as hot springs, geysers, or areas of volcanic activity offer a readily available source of geothermal energy. since the second law of thermodynamics states that heat naturally flows from a warmer substance to a colder one, the heat is removed from these places very easily. However, in cases where the ground or water source is colder than the space to be heated, it is still possible to extract the Earth's energy, but we must use a heat pump.
Heat Pumps are Everywhere
Whether we are aware of it or not, we use heat pumps everyday: our refrigerators and freezers pump the heat out of the appliances; our air conditioners pump the heat out of our houses; and HVAC systems, which are true heat pumps, can pump the heat either way depending on the season.
Temerature vs. Heat
To understand heat pumps, one must first differentiate between temperature and heat. Looking out your window on a cold winter day, for example, you may not appreciate that arctic breeze for the heat that it contains. It is counter-intuitive, since you know that if you open that window you will surely get a chill. This is the second law of thermodynamics in its empirical form; you can plainly see that the heat is going straight out the window from your warm room to the frigid outdoors. A heat pump however, allows us to extract the heat from that icy air or the cold ground and pump it into our home.
The Physics of the Heat Pump
Since we can not break the laws of thermodynamics, in order to pump the heat out of the cold ground or cold well water, we must use something that is even colder to absorb the heat. This is accomplished with the use of refrigerants such as R-134a. Here we must introduce another law of physics: Boyle's law. This law, which governs the behavior of gases, states that at a constant temperature the pressure and volume of a gas are inversely proportional. Since the liquid refrigerant has a boiling point that is well below zero at normal atmospheric pressure, as itenters the evaporator, heat is taken from the ground converting the liquid to a gas. This refrigerant, now in a gaseous state, is compressed into the condenser by use of a pump where the pressure is higher than the vapor pressure of the refrigerant and thus becomes a liquid once more. The heat given off by the condenser is used to heat the house and the refrigerant heads back to the evaporator to start the cycle all over again.
The Future of Geothermal Energy
Although geothermal energy is a vastly untapped renewable source of power, the use of the invaluable heat pump allows people living in colder climates to benefit from the energy contained within the Earth. The current situation that the world is confronted with vis-a-vis energy supply and demand is bringing about a change in the way we think about alternative energy sources. Consequently, an energy revolution is under way and geothermal is becoming a major player thanks to the heat pump.
