The following article has been adapted for the web from Natural Home Heating: The Complete Guide to Renewable Energy Options by Greg Pahl.
I’m going to talk about magic. It’s miraculous to create a viable and renewable home heating and cooling strategy out of thin air, water, or dirt—and that’s what geothermal systems do.This type of geothermal energy relates to the sun rather than hot springs or geysers. (It’s interesting that the sun plays a key role in yet another renewable home heating strategy, but you should be used to that recurring theme by now.)
The concept behind geothermal heating is simple: the Earth is a huge heat-storage device. For millions of years, the Earth has been absorbing and storing solar energy in the air, water, and ground.This stored energy offers enormous potential to meet a major portion of our energy needs.The trick up to now, however, has been to figure out practical ways to harvest and use that energy. One of the most successful ways to accomplish that goal is to use a heat pump. Unlike most other home-heating devices, heat pumps are not based on combustion. Instead, heat pumps move heat from one location to another.
Heat pumps have been around since the early 1900s—refrigerators and air conditioners are types of heat pumps. Heat pumps for residential heating were not successfully developed until the 1970s. Although they have been available for over thirty-five years, heat pumps are still not understood or appreciated by many homeowners, especially those who live in colder climate zones.
Save Oil—Use a Heat Pump
The 1 million GeoExchange systems presently installed in this country equals 21.5 million barrels of crude oil saved per year, according to the Geothermal Heat Pump Consortium, Inc. (GHPC).The GHPC is a nonprofit organization (based in Washington, D.C.) that promotes ground-source geothermal technology.
How Heat Pumps Work
Heat naturally flows from a warmer area (or substance) to a cooler area (or substance). Heat pumps, however, can force heat to flow in the opposite direction, with the aid of a small amount of electricity and a compressor. It’s a little like pumping water uphill.A heat pump transfers or “pumps” heat from a natural source such as the air, ground, or well water to the interior of your home during the winter.While we don’t think of these sources as being especially “hot,” they do, nevertheless, contain useful heat that is continuously replenished by the sun.
Heat pumps can also provide domestic hot water, humidity control, air filtration, and, best of all, cooling during the summer. When the heat-pump process is reversed in the summer, it moves warm air out of your house and into the air or ground (in this case, think of the air or ground as enormous heat sinks).The ability of a heat pump to double as a cooling device is a real advantage, especially in warmer climates, and eliminates the need for a separate air-conditioning system.
One of the most important things to remember about a heat pump is that it operates at such high efficiency (up to 400 percent) because it is primarily moving heat from one place to another rather than creating heat through some form of combustion. This unique design is what sets all heat pumps apart from most of the other home heating strategies we’ve looked at previously.
For those who are less inclined to believe in magic, here is the technical explanation of how air-source and ground-source heat pumps operate. Simply stated, the heat-pump cycle begins as cold liquid refrigerant passes through a heat exchanger and absorbs heat from a relatively low-temperature heat source (air, water, or ground). The refrigerant evaporates as the heat is absorbed, becoming a gas.This refrigerant gas then passes through a compressor, where it is pressurized, raising its temperature to over 160 degrees Fahrenheit. The heated gas then circulates through another heat exchanger, where heat is removed from the gas and transferred to water or air, which is then circulated into your home via a hot-air duct system or a hydronic distribution system (the temperature of the heated air or water is about 100 degrees Fahrenheit). As it loses heat, the refrigerant gas changes back to a liquid. The liquid is cooled as it passes through an expansion device and the heat pump cycle is complete, ready to begin again.
Ground-Source Heat Pumps
Now I’m going to tell you how to heat your home with dirt and water. Of course, I’m talking about groundsource heat pumps. It’s ironic that we’ve literally been walking around on an unlimited source of heat for thousands of years without fully appreciating its potential. We’re finally starting to catch on. Ground-source (GeoExchange) heat pumps are not as common as their air-source cousins, but they have many advantages that a growing number of people are beginning to appreciate. One of the major remaining obstacles to wider use of these systems is that many people simply aren’t aware of them.
Savings from the Ground Up
The Earth is a huge energy-storage device that absorbs 47 percent of the solar energy that strikes its surface. This represents over five hundred times more energy than we need every year. Ground-source heat pump systems take some of this heat from the ground during the heating season at an efficiency of around 400 percent, and then return it during the cooling season. Spectacular efficiency figures like this can result in substantial savings. According to the U.S. Environmental Protection Agency (EPA), groundsource systems can save you 30 to 70 percent in heating costs and 20 to 50 percent in cooling costs, compared to conventional fossil-fueled systems. What’s more, studies have shown that approximately 70 percent of the energy used in ground-source systems is renewable energy from the Earth. Ground-source systems work well in almost any climate, especially more extreme climates where air-source heat pumps are less cost-effective.
How do these systems perform their magic? A ground-source heat pump uses the Earth, ground water, or surface water as sources of heat in the winter and as a “sink” for heat removed from your home during the summer. Heat is extracted from the Earth by a liquid, such as ground water or antifreeze. The heat pump components amplify this heat and transfer it to the air in your home.The process is reversed for cooling. Like their air-source counterparts, ground-source heat pumps can also filter your air and provide humidity control as well.
Ground-source heat pumps have three main components: a system of underground piping outside the house; a heat pump unit inside the house; and a heat distribution system, also located in the house. Since the heat pump unit in a ground-source system is located only inside a home, there are no problems caused by frost buildup or damage from ice, snow, or other severe weather conditions.
Some ground-source heat pump units contain all of the usual elements— blower, compressor, heat exchanger, and condenser coil—in a single cabinet. But in a split-system ground-source installation, the coil is added to an existing hot-air furnace and uses that system’s existing blower. In this case, the heat pump is the primary heater, while the existing furnace can provide supplementary heat during extremely cold conditions.