Geothermal Heat Pumps: How They work and Types

The new renewable energy technology that has gained acceptance worldwide is the geothermal heat pumps. It is also known as earth-coupled, water-source heat pumps, geo-exchange or ground source heat pumps. So, what are geothermal heat pumps, their types and how does it function?

The geothermal heat pumps work by transferring the heat to and from the ground or water. These units are more efficient as they concentrate on the naturally existing ground and water temperatures. This heat is more constant compared to air temperatures.

What is a Geothermal Heat Pump?

A geothermal heat pump is responsible for transferring energy to and from the earth with an electrically powered refrigeration unit. Some geothermal systems are available with variable fans and two-speed compressors for better comfort and energy savings.

In comparison with air-source heat pumps, geothermal or water-source heat pumps are quieter, do not depend on the temperature outside of air, and last longer. It can provide a source of energy for space heating, domestic hot water and a heat sink for space cooling.

You may come across a dual-source heat pump, which is a combination of both air-source and geothermal heat pumps. The benefit of such a system is that it works just as well as a single geothermal unit but costs much less in terms of installation.

How Does a Geothermal Heat Pump Work?

Most geothermal technologies focus on electricity generation. A geothermal heat pump takes advantage of the constant 50 to 60 F of heat beneath the earth’s surface. Any typical geothermal system consists of some ground loop system that is filled with a water solution, heat exchanger, and ductwork into the building.

The system mainly has three parts:

  1. The air handling system to distribute air within the spaces either being heated or cooled.
  2. The ground or groundwater heat exchanger that can either absorb or discharge the heat from or to the earth.
  3. A reversible refrigerant loop responsible for transferring heat in the middle of the air handling system and the ground.

During winter, heat is absorbed by a water solution that circulates through pipes in the ground. This warm water solution is carried to a water-to-air heat pump in your home that can concentrate the thermal energy. It is later transferred to the air in a conventional ductwork system to circulate the heat in your home.

In summer, the process is reversed and heat is pumped from your house to the ground. It is done with the help of a heat pump leading it to the water solution in the ground pipes. The ground pipes then carry excess heat into the ground.

Types of Geothermal Heat Pump System

Here are some of the types of geothermal heat pump systems available today.

  • Closed-loop Systems
  • Open-loop Systems
  • Hybrid Systems

1. Closed-loop Systems

A closed-loop geothermal heat pump system circulates an antifreeze solution or a refrigerant through a closed-loop made out of copper or plastic tubing. It is buried into the ground or submerged in the water. Many closed-loops even use radiant heating alongside a fan and ductwork.

A heat exchanger allows the exchange of heat in between the refrigerant and an antifreeze solution in the closed-loop. Although one of its variants, namely direct exchange, pumps the refrigerant through copper tubing instead of using a heat exchanger.

This loop can be horizontal, vertical, and pond/lake configuration.

  •  Horizontal

If you’re looking to install the system for residential purposes and have sufficient land, the horizontal type of installation is the most cost-effective. The trenches on this one must be at least four feet deep.

Commonly, the layouts use two pipes, buried at six feet and four feet, or simply two pipes buried side by side at five feet with trenches that are two-foot-wide. Mounting these pipes inside your walls or floors can help to prevent cold floors.

  • Vertical

Most schools and large commercial buildings generally use vertical systems because the area required for horizontal loops would be restrictive. Such loops are used in shallow soils as they minimize the disturbance to existing landscaping.

To install a vertical system, the holes are drilled almost 100 to 400 feet deep and  20 feet apart. Then two pipes connected at the bottom with a U-bend form a loop. These vertical loops are connected to each other with horizontal pipes, placed in trenches, connected to the heat pump of the building.

  • Pond/ Lake

This is the lowest cost option if you have an adequate water body. A supply line pipe runs underground from your building to the water and is coiled into circles. It should be placed in a source that has minimum volume, depth, and quality criteria and at least 8 feet under the surface to prevent freezing.

2. Open-loop Systems

An open-loop geothermal heat pump system uses water from well or some surface body water. It functions as a heat exchange fluid circulating between the pipes and the water source. This system can even work as water heaters eliminating the worries of replacing your existing unit.

Simply placing pipes underwater costs much less than digging up holes for underground pipes.

3. Hybrid Systems

A hybrid geothermal heat pump system uses different geothermal resources or a combination of those resources with outdoor air. This option is suitable for people who have larger cooling needs rather than heating needs.

Geothermal Heat Pump: Pros and Cons

Pros Cons
Environment-friendly Surface Instability
Highly-efficient Greenhouse emissions
Highly Sustainable Depletion of geothermal sources
Reliable Source of energy Requires a large amount of land
Low maintenance cost High investment cost

Final Words,

The geothermal heat pumps can eliminate the need for a displeasing outdoor unit. If you want to recycle the waste heat from a heat pump compressor, you can add a device called a desuperheater to your geothermal system. This device can supplement the solar thermal water heater and allows you to enjoy domestic hot water.

A desuperheater is highly convenient during summer when it can channel the removed heat from your house and redirect it into a hot water tank instead of the earth.