Geothermal Loop Field & Design
Loop fields, like heat pumps, are measured in units called “tons”. Each loop in a field is designed to provide 1 ton of energy for the system. So if your geothermal system requires a 4 ton heat pump then it calls for 4 loops. Earth loops come in two basic types. Closed loops are buried in the earth or submerged in a lake or pond. They transfer heat by circulating a solution of water and environmentally safe antifreeze. Open loops use ground water pumped from a well as a heat source. Which type you use depends on the terrain, the cost of trenching or drilling, the availability of quality ground water, and what space is available.
3 Major Considerations For Designing a Geothermal Loop Field
- Thermal Conductivity of the Soil
Space for the Loop Field
The amount of space required for the loop field is often a determining factor of which loop field to use for your geothermal system. There are three choices of loop designs which we will educate you on!
- Vertical Geothermal Loop Field
- Vertical loops are drilled straight down so they require the least space to install.
- Vertical loops can be spaced as close as 10 feet apart, allowing them to be installed in a space as small as the driveway on a city lot.
- Horizontal Geothermal Loop Field
- Horizontal loops require the greatest amount of space because the loop installed and horizontal to the surface.
- Depending on how they are configured, loops can range from 100 to 800 feet in length.
- If you have enough useable land, horizontal loops can be installed. This is done by digging trenches with a backhoe or a chain trencher. Then, you insert polyethylene pipes backfill the trenches. Various horizontal loop configurations are possible, using one, two or three circuits per trench. The more pipes you have in each trench, the shorter the trench can be. Trenches normally range from 100 to 300 feet , depending on the design. A typical home requires 1⁄4 to 3⁄4 of an acre for the trenches.
- One of our geothermal loop installations showing a vast horizontal loop field can be seen here
- A variation on the horizontal loop is the horizontal bore loop. This type of loop is most often used in a retrofit situation to minimize disruption to the landscape. It requires special equipment to bore holes horizontally under the surface. The operator can “steer” the drill head to go deeper or shallower, or turn right or left. This machine drills at a slight angle down to a typical depth of 10-12 ft., then back to the surface, typically 200 ft. away. At that point, two ends of pipe are attached to the drill bit and pulled back through the hole until the pipe is buried. This technique allows the loop to be placed.
- Pool/Lake Loop Field (pictured here)
- This requires a body of water that is at least 1/3 acre in size and at least 12″ deep. This helps to keep the pipes from freezing in the cold weather.
- If an adequately sized body of water is close to your Atlanta home, we at EcoMech can install a pond loop. A series of sealed pipes containing a mixture of water and antifreeze can be coiled and sunk to the bottom. Using pond water directly is never recommended. A 1⁄2-acre, 8-foot-deep pond is usually sufficient for the average home. Ideally, the pond should be close to the home (less than 200 ft.). If the pond is farther from the home, the benefit of using a pond loop is reduced due to added trenching, materials and pumping costs.Pond loop coils are connected together on dry land, then floated into location. Once filled with fluid, they will sink to the bottom and remain there. Generally, a 300 ft. coil is used for each ton of capacity. This is less pipe than is used in an earth loop, because water is a better conductor of heat energy. Pond loops are a cost-effective way to install a geothermal system, because trenching is limited to only the supply and return piping from the pond to the house.
This is the property of a material to conduct heat. Materials with high thermal conductivity conduct heat much better than materials of low thermal conductivity. Since a loop field relies on conductivity to move the heat from the ground into the solution in the loop, it is also a major consideration when designing a loop field.
Different soil types have different levels of thermal conductivity. For example, Dry sand/gravel has some of the lowest thermal conductivity while “saturated clay” has a high level of thermal conductivity. This difference in thermal conductivity means a loop in dry sand/gravel would have to be more than twice as long as a loop in “saturated clay” in order to deliver one ton.
If you don’t know how well your thermal conductivity is, then give us a call to assist you!
Cost of Loop Fields
Cost is always a consideration with just everything in life and geothermal cost is no different, but when all other factors are equal, costs becomes the final determining factor in choosing a loop field. EcoMech offers many financing options too!