Air vs. Ground Heat Pumps

There are two common types of heat pumps used in home systems. The ground source heat pump (GSHPs) and the air source heat pumps. At Shine Energy, we work with ground source heat pumps, but we are often asked about air source heat pumps due to some confusion in differentiating the two. This is a brief description of the differences between the two systems.

For useful and a more detailed description of the two systems, Natural Resources Canada has a great booklet .

An air-source heat pump absorbs heat from the outdoor air in winter and rejects heat into outdoor air in summer. It is the most common type of heat pump found in Canadian homes at this time. However, ground-source (also called earth-energy, geothermal, geoexchange) heat pumps, which draw heat from the ground or ground water, are becoming more widely used, particularly in British Columbia, the Prairies and Central Canada. p.6

GSHPs have a relatively constant coefficient of performance (COP) due to constant ground(or water) temperatures; whereas, air source heat pumps have a COP that declines with decreasing air temperature. For example, on a cold winter day, an air source heat pump has a lower COP as it is more difficult for the system to draw "heat" from the air to supply to your home. The reverse is true for cooling on a hot summer day.

Unlike the outside air, the temperature of the ground remains fairly constant. As a result, the output of an (GSHP) varies little throughout the winter. Since the (GSHP's) output is relatively constant, it can be designed to meet almost all the space heating requirement – with enough capacity left to provide water heating as an "extra." p.31

On average, an (GSHP) will yield savings that are about 40 percent more than would be provided by an air-source heat pump. This is due to the fact that underground temperatures are higher in winter than air temperatures. As a result, an (GSHP) can provide more heat over the course of the winter than an air-source heat pump. p.37

In addition, GSHPs are quieter and have a longer expected life (20 to 25 years) than air source pumps since they are not outside where they are exposed to the elements.

Know your products

In the geothermal industry, it is not uncommon for a supplier to make a product that is then re-sold under the banner of another company. Simply asking your installer who makes the product, especially when it comes to heat pumps, will help ensure you know who all is responsible for your product warranty.

You also have the ability to do some background reading on your recommended heat pump. Most suppliers have all their supplied technical information available over the internet. Like buying a car, don't hesitate to do some background reading on your recommended system. If your installer does not leave you with operational procedures (or you buy a home with an existing system), you can print out a copy and leave near your system to help you remember recommended maintenance schedules, troubleshoot, and assist in efficient operation.

Definitions

Ground Source Heat Pump Terminology

The field in which I practice has many different names for our product that can lead to some confusion. They all are used to refer to the same appliance (the first two are the most common).

1. Ground-source heat pump
2. Geothermal heat pump
3. Water-source heat pump
4. Well-water heat pump
5. Direct-expansion heat pump
6. Geo-exchange heat pump
7. Groundwater heat pump
8. Earth-coupled heat pump
9. Ground-coupled heat pump
10. Open-loop heat pump
11. Closed-loop heat pump

(Brumbaugh, J.E., HVAC Fundamentals, 4th ed., Audel, 2004, p.481)