By Patrick F. O’Donnell
for East Penn Energy Solutions
Earlier this month we talked about air-source heat pumps and the potential energy savings they can provide. This week, we’re going to talk about geothermal heat pumps (GHPs).
Geothermal, or ground-source heat pumps, use the stable temperature of the earth to heat and cool a home. In the winter, just a few feet below ground level, the earth stays warmer than the air; in the summer, it stays cooler. The temperature rarely fluctuates more than a couple degrees. Because of this, ground-source systems are even more efficient than their air-source counterparts, which rely on constantly and widely fluctuating temperatures.
Like air-source pumps, geothermal pumps work by exchanging heat with the ground. In the summer, they pull heat from the air inside a home. In the winter, they pull heat from the ground.
There are several types of ground-source heat pumps. Most are what we call “closed-loop systems.” They rely on circulating a liquid through a loop of tubing buried in the ground or submerged in water. In the winter, the liquid picks up heat from the ground or water and transfers it to the house. In the summer, it’s just the opposite: The heat from the house is sent into the ground or water, cooling the liquid – which is then used to cool the house.
If there’s plenty of space available, a horizontal system can be employed. The loops are buried in trenches that range from 3 to 6 feet deep and 400 to 600 feet long. If the lot is smaller, a vertical system may be used. Holes are drilled from 100 to 400 feet deep, and the pipe loops are inserted in them.
Finally, if the house is near a pond or lake that’s large enough, both in surface area and depth, the loops can be placed at the bottom, using the water as a heating/cooling source.
There are two other types of geothermal systems to consider, but they’re less common than a closed-loop system. The first is called an open-loop system. Similar to the pond/lake system, it relies on well or surface water as the heat exchange medium, but unlike a closed-loop system, the water circulates directly through the open-loop system and is returned to the ground through the well or via a discharge from the surface of the ground. There has to be enough clean water for the system to work, and there are more regulations to meet because of the water discharge.
The second is a hybrid system, which might combine a horizontal system, a vertical system, and an air-source system or other options. These are usually used when the heating/cooling needs are quite large – for instance, in a school or other commercial building.
There are many benefits to geothermal pumps, but there’s one big drawback: the price tag. The systems cost several times more to install than their air-based counterparts.
The flip side, however, is that the cost can be recouped within five to 10 years through the savings on your energy bills.
So, what makes them so much better than air-based systems? For a start, they’re much more efficient. According to Energy.gov, using the earth instead of the air “allows the system to reach fairly high efficiencies (300% to 600%) on the coldest winter nights, compared to 175% to 250% for air-source heat pumps on cool days.” Some models can be equipped with two-stage (speed) compressors and variable-speed fans, which start out on a low speed and ramp up as needed. If a only a minor change in temperature is needed, the blower will run on low, using less electricity and increasing the life of your heat pump. This also helps reduce sudden blasts of cold air as the system comes on.
Another benefit is the longevity of the components. The Energy.gov article states that “System life is estimated at 25 years for the inside components and 50+ years for the ground loop.”
They’re also quieter than air-source models and need very little maintenance.
If you’re deciding on a geothermal system, you should look for a model that meets Energy Star specifications.
You also need to understand how a unit’s efficiency is calculated. This link is a good place to start.
If you have any questions about how a geothermal system works, or if it would be the right choice for you, feel free to contact us. We’re always willing to help!