A geothermal heat pump (GHP) is similar to an all electric heat pump in that it can both heat and cool your home. But instead of using the air to dissipate and gather heat energy, a geothermal heat pump uses the constant thermal energy underground.
There is a large “loop” that makes up any heating and cooling system. Even with a traditional air conditioner installation this loop exists, but is referred to as an outdoor coil and an indoor coil. The air conditioner contains the outdoor coil, and an evaporator coil (or fan coil) contains the indoor coil. This coil contains refrigerant, and this refrigerant is used to move heat energy out of the home during the summer. An air conditioner dispenses heat energy into the outside air, chills the refrigerant, and sends it back into the home.
With a geothermal heat pump installation, your HVAC contractor installs an “earth loop” which replaces the outdoor coil in a traditional system. Earth loops are made of durable, high-density polyethylene pipe and contain a water based fluid. For cooling, heat energy is dissipated into the ground from the earth loop instead of the air. The cooled fluid is pumped back inside to the indoor coil
In the heating season, this process is reversed. Heat energy from the constant thermal temperature of the ground is used to heat the fluid, and then in turn is used to add heat energy to the air inside your home.
When you own enough land around your home, horizontal loops can be the ideal earth loop system to install. Depending on the exact system needs and space available around your home, pipes are placed in trenches that range in length from 100 to 400 feet. We say they are ideal, because trenching is typically cheaper than a vertical installation which requires a well-drilling rig. In colder climates, a normal trencher can’t be used because frost depths reach down to 7 feet.
Can a pond covered with ice actually be used to heat your home? Yes! The principal, according to the MNGHPA is this: When water is 39 degrees it is in its heaviest stage, and will often rest in an isolated temperature layer at the bottom of a pond or lake during the winter season. The geothermal loop extracts heat energy from this area, and the resulting cooled water ascends out of this zone. Remember, even low temperatures still have heat energy, whether air, ground or water.
When not much yard or land is available, a vertical earth loop can be the way to go for your GHP installation. These are still a closed loop system like horizontal and pond/lake loops. Small diameter holes are bored into the ground using well drilling equipment. The polyethylene piping is then installed into these holes that range from 150-250 feet deep! Geothermal installations will often have one bore hole per nominal ton of GHP capacity, and the holes should be spaced about 15-20+ feet apart. This type of install is the most expensive due to the drilling.
An open loop system uses local water, and does not use a closed/buried loop system like the above methods. This eliminates a lot of cost, however, water usage in some areas can be a concern, and might be illegal or require a special permit. This type of installation is not as common, but when the stars align, it can definitely be the least expensive way to implement geothermal energy for your home!