Comparing geothermal heat pumps
Last updated 8/7/2019
Ground source heat pump (GSHP) system designs are customized to each property. The solution that’s best for your home or business depends on the existing systems in place, as well as your unique heating and cooling needs.
First step: closed-loop vs. open loop systems
There are two general types of geothermal heat pumps: closed-loop and open-loop systems. A closed-loop ground source heat pump is separated from the environment, meaning that it cycles a mixture of antifreeze and water in a completely closed loop of piping. In comparison, an open-loop setup uses naturally occurring groundwater as the refrigerant and returns the water back to the environment once it has cycled through the GSHP’s heat exchanger.
While open-loop systems tend to have lower upfront costs and higher efficiencies, closed-loop installations are more practical and common for most situations. Generally, open-loop systems are only practical if there is an adequate supply of clean groundwater, and may require greater efforts to comply with local regulations and codes regarding water discharge and water quality.
Comparing geothermal heat pump equipment
There are two main factors to consider when comparing geothermal heat pump equipment: efficiency and ground loop type.
An important piece of selecting the right heat pump is choosing the right equipment from a performance perspective. In general, more expensive heat pumps will have higher efficiency ratings, but it’s always a good idea to check the specifications of your geothermal options and compare various models.
A geothermal heat pump’s EER rating is a measure of its ability to cool efficiently. The number is a ratio of the heat removed from your property to the amount of electricity used, meaning that a heat pump with a higher EER rating is more efficient. Geothermal heat pumps typically have an EER rating between 13 and 18. A heat pump’s heating efficiency is rated by COP, which is another ratio of heat produced to electrical energy used. Ground source heat pumps typically have COPs between 3 and 5. In general, ground source heat pumps with higher EER and COP ratings will cost more.
You can be sure you’re installing a high-quality product if your geothermal heat pump is a certified ENERGY STAR product, meaning that the federal government has determined that it meets certain efficiency standards. Geothermal heat pumps with an ENERGY STAR rating are over 45 percent more efficient than conventional heat pump options.
Ground loop type
Closed-loop ground source heat pumps are far more common than open-loop heat pumps and come with three main loop varieties: horizontal, vertical, and pond/lake.
Horizontal loop systems are often best for residential installations and involve laying a ground loop horizontally underground, usually between four and six feet below the surface of the earth. A vertical loop system is better suited for commercial buildings, or those looking to minimize alteration to existing landscape on the ground level. In these systems, the ground loop runs directly into the ground for 100 to 400 feet and then returns to the surface. This type of ground loop installation often requires specialized drilling equipment to make the appropriate path through underground rocks, which can require a longer and more expensive installation process. Vertical ground loop systems are also applicable in areas where the soil is too shallow and/or difficult to trench.
Lastly, a pond/lake system involves laying the ground loop under a nearby water source at least eight feet below the surface. This option is typically the least expensive, but only feasible if there is a suitable body of water nearby.
While air source heat pump systems are somewhat susceptible to outside temperatures (as they use the temperature of the air to collect and disperse heat), ground source heat pumps are almost completely unaffected by cold or warm climates. This is because the earth maintains close to a constant temperature underground regardless of the above ground temperature. Extreme climates can have an impact on the type of heat pump you’ll want to install, but in general, geothermal heat pumps work well in all climates.