Geothermal Ground Loop Frequently Asked Questions
What is a ground loop?
A ground loop is a series of pipes buried underground at a depth where temperatures stay consistent year-round. It serves as the critical link allowing geothermal heat pumps to use the earth as a heat source or heat sink, depending on if heating or cooling is required.
How does a ground loop work?
Just a few feet below the ground’s surface, the earth maintains a steady 50-55 degrees no matter what the temperature of the outside air. This difference in temperature allows the earth to act as a heat source in winter and a heat sink in summer. A geothermal heat pump (located inside the home) captures this energy by circulating thermally conductive fluid through the buried ground loop.
In winter, the fluid absorbs heat from the warmer earth and carries it into the heat pump, where it enters a heat exchanger and is used to warm your home.
In summer, the process is reversed when the home’s heat is captured and released into the cooler ground, leaving your home comfortably air-conditioned.
Types of Ground Loop Systems
There are several types of ground loop designs that can be made, but they all fall under two basic categories: closed loop and open loop.
Closed Loop Geothermal Systems
There are 3 types of closed loop geothermal systems: vertical, horizontal, and pond / lake. Because pond/lake loops require having a water source on the property, they’re relatively uncommon, and we don’t discuss them in detail.
Horizontal Ground Loop
A horizontal ground loop is installed over a wide area of ground and requires enough space to dig trenches hundreds of feet long and 6-10 feet deep. Horizontal ground loops can only be used when adequate yard space is available and trenches are easy to dig.
Horizontal Ground Loop Installation
To install a horizontal system, workers utilize trenchers or backhoes to dig trenches 5-10 feet below ground and then install a series of plastic pipes that comprise the geothermal heat exchanger. They will then backfill the trench, taking care not to allow sharp rocks or debris to damage the pipes. A common practice is to coil the pipe into a slinky shape to fit the loop field in a smaller area. While doing this reduces the amount of land area needed, it will require installation of more pipe.
This configuration is usually the most cost effective because it requires trenching rather than drilling.
Vertical Ground Loop
A vertical ground loop is installed in one or more boreholes about 200 to 500 feet deep in the ground. Each hole is 5 to 6 inches in diameter, and if you have more than one, they’re about 20 feet apart. This configuration is ideal for homes where yard space is limited, when rock formations are very close to the surface, or retrofit applications where minimum disruption of the landscaping is desired.
Vertical Ground Loop Installation
To install a vertical loop, a contractor will use well-drilling equipment to bore a 6-8 inch diameter vertical hole in the ground 200-500 feet deep. Next, a single pipe loop with a U-bend at the bottom is inserted in the hole. After the pipe is inserted, the hole will be grouted, filling it from bottom to top.
The grout serves two primary functions:
- Ensures contact between the pipes and the earth to promote heat transfer.
- Seals the hole off from any aquifers or groundwater supplies that may have been penetrated during the drilling process. Protecting the deep earth environment with a proper grouting material is just as important as providing heat transfer between the piping system and the surrounding earth.
Vertical loops are generally more expensive to install, but require less piping and less land area than horizontal loops. Dandelion Geothermal currently only installs vertical ground loop systems. This type of geothermal system is ideal for urban or suburban areas across the Hudson Valley and NY’s Capital Region where space is at a premium.
Dandelion developed an innovative and proprietary sonic drill suite that’s lighter, cleaner, and can install 14x faster than a conventional well drill.
Open Loop Geothermal Systems
Open-loop geothermal systems extract water directly out of a water well or pond and run it through the water-refrigerant heat exchanger in the geothermal heat pump unit. After the transfer of heat between the extracted water and heat pump takes place, the water is then expelled back into a well, into a pond, or into a drainage ditch depending on local codes.
This type of ground connection method is used less frequently, but may be employed cost-effectively if groundwater is plentiful.
Open Loop Installation
Open loop systems are the simplest to install and have been used successfully for decades in areas where local codes permit. In this type of system, ground water from an aquifer is piped directly from a well to the building where it transfers its heat to a geothermal heat pump. After the water leaves the building, it is expelled back into the same aquifer through a second well, called a discharge well, located a suitable distance from the first. Local environmental officials should be consulted whenever an open loop system is being considered.
Because open-loop systems utilize water on a “once through” basis, they are often referred to as “pump and dump” systems. The performance of the GSHP system may degrade over time if water quality issues are present (high mineral or dissolved solids content, etc) or if the water supply diminishes for any reason.
How are geothermal ground loops sized?
The ground loop size is based on the geothermal heat pump size, the property’s soil conditions, and the overall climate. The larger a home’s heating and cooling load, the larger the geothermal heat pump required, and therefore the larger the ground loop needed.
What’s the lifespan of a ground loop?
Geothermal ground loops can last 50+ years — even up to 100 years!
Once installed, the buried ground loop will be a permanent fixture on the property for as long as there is a building to heat and cool.
What material is used to make ground loops?
High-density polyethylene (HDPE) and crosslinked polyethylene (PEXa) are the only materials formally approved for closed-loop geothermal systems by the International Ground Source Heat Pump Association (IGSHPA). Polyethylene, the world’s most common plastic, is used in a wide range of applications such as food packaging, plastic bottles and bags, pool liners, and of course, geothermal piping.
Polyethylene pipe is durable, corrosion-resistant, and can even withstand damage due to an earthquake, according to the Plastic Pipes Institute.
Dandelion Geothermal uses HDPE, a food-grade plastic often used to make milk jugs.
What liquid circulates through the ground loops?
Closed loop geothermal systems typically circulate a mixture of water and a small amount of antifreeze to lower the solution’s freezing point. Dandelion’s mixture is just 22% propylene glycol.
Dandelion Geothermal uses a mixture of water and propylene glycol, a food-grade, non-toxic antifreeze commonly used as an additive in drink mixes, dressings, cake mix, soft drinks, popcorn, bread, and dairy products.
Where does Dandelion get the water used to fill the ground loop system?
We use the homeowner’s water to fill the loop. This is done only one time and requires a moderate amount of water. The same water is used again and again in a closed loop.
Can geothermal ground loops become damaged underground or leak?
HDPE ground loops are extremely robust against corrosion and chemical insult, which means the normal (or abnormal) movement of water and fluids underground will virtually never harm them.
When construction is complete, the entire piping assembly is pressurized and leak tested before being placed into service. This ensures that no leaks are present in the system prior to startup.
There are, however, some rare conditions where they can become damaged:
- Mechanical injury. Any mechanical work done in the loop field can injure the ground loops, particularly when drilling deep post holes.
- Leaks from Bad Fusion Joints. This is an installation error where the ground loops are “cold fused”, but the iron wasn’t held on the fittings long enough.
Dandelion Geothermal requires that all piping joints/connections be made via heat fusion and doesn’t allow the use of buried mechanical fittings.
Can you drive over ground loops?
Yes, they are safe to drive over once buried in the ground. That said, if the ground is still soft from installation, it won’t be highly compacted.
Until the ground is hardened, we recommend placing a sheet of plywood (or something similar) over the tire path to distribute the load of any vehicles driving over it.
Can you plant trees over the area where ground loops are installed?
We would not recommend planting trees over where ground loops are installed for 2 primary reasons:
- Tree root systems can grow into the loops. It may be difficult to repair or add to the piping system without damaging the tree.
- Freezing pipes. Given the fluid temperatures the system is designed to reach, it’s possible the soil around the pipes will freeze. This may have a negative impact on the tree.
Ask your geothermal installer about the safest distance you can install trees near your ground loops.
Can radon enter a home as a result of ground loop installation?
Radon generally enters the home through cracks in the foundation. It can come into the home through a water well (and be found in drinking water) if levels in the soil are high.
Vertical geothermal bores are completely sealed from bottom to top with a low permeability grouting material, which eliminates the possibility of radon coming into the home as a result of the ground loop installation.
What level of maintenance do ground loops require?
Ground loops are maintenance-free and don’t require cleaning or re-charging.