Types of Geothermal Loops Common in Residential Heating Systems
As you learn more about geothermal heating and cooling, you’ll soon hear that there are several types of geothermal loops in use in systems today. The type of loop used on your system depends on the type of system or the amount of land available for the loop itself.
This Geothermal Guide article provides information on the types of geothermal loops and when they are used.
Closed Loop Geothermal Configurations
Closed systems are filled with water, antifreeze, or a water/antifreeze blend. They do not lose water or take in water. There are several types of closed loop geothermal heating systems.
Horizontal Geothermal Ground Loops
These are used where land is abundant. Trenches are dug 4-6 feet deep, usually with a backhoe or trencher. From 300 to 500 feet of pipe is used for most residential systems. The pipe is high-density polyethylene, or HDPE, with a lifespan rated up to 200 years. A typical warranty is 25-50 years. Joints are heat fused rather than glued. Horizontal geothermal ground loops are used most often in geothermal heating and cooling systems in new homes. Where ground frost penetrates deeply, as in some northern climates, or in southern sunny climates where the ground 6 feet down can be quite warm, ground loops may not be appropriate. Where they can be used, they are often the most affordable choice because the installation cost is less.
Vertical Geothermal Ground Loops
These are used on small lots and for geothermal cooling and heating in very hot or very cold climates. The loop is buried in narrow well shafts, sometimes lined with well casing for stability. The shafts can be several hundred feet deep. Not as much HDPE pipe is used because the temperature of the earth is more stable at deeper levels. The holes are produced with a drilling rig which may add to the labor price for the job.
Horizontal Coil Loops
Instead of long runs of horizontal pipe, these geo thermal systems use overlapping coils. They conserve space and are often used where space is limited and deep drilling is difficult due to bedrock. They also are less invasive to the landscape than standard horizontal loops. For these reasons, they are gaining popularity.
Geothermal Pond Loops
Sometimes ponds are dug for the purpose, where allowable by environmental regulations. Most often, an existing pond is taken advantage of as a source for geo thermal energy. Loops in water can be very efficient because heat transfers more quickly from water to water. This improves the geothermal energy system’s heating and cooling. It requires a ½ acre pond minimum that should be at least 10 feet deep. Coils of pipe are laid out on the bottom of the pond and a trench is dug back to the home for connecting pipes.
DX or Direct Exchange Loops
Rather than containing water, DX loops contain refrigerant. They employ copper pipe and use less of it than systems using HDPE. The use of DX systems is typically limited to homes with very little yard space. They are not preferred because the refrigerant poses a threat to the environment if it leaks and the piping does not have the same durability as HDPE.
Open Loop Geothermal Configurations
There is only one type of geothermal open loop. These geothermal energy systems use a continually refreshed supply of well water rather than the same enclosed water and anti-freeze mix. Fresh well water is pumped into the system through one open-ended pipe and released from the system through a second, returning to the ground. Open loop geothermal cooling and heating is the most efficient. Open loop geo thermal systems are not allowed in some areas due to concerns over ground water quality or the depletion of aquifers.
In closing, these are the primary types of geothermal loops currently in use. When you speak with geothermal contractors, they will be able to tell you which types are suitable for your area and for your property, as well as the relative prices for each type. Some soil testing may be required to determine the best geothermal loop for your geothermal heating and cooling system.