What is a ground loop?
A ground loop is a U-shaped plastic pipe (a “u-bend pipe”) buried in a borehole deep enough to reach consistent year-round temperatures. It acts as a heat exchanger, allowing the geothermal heat pump to draw heat from the earth or release heat back into it.
How does a ground loop work?
About 6 feet underground, the earth stays at a steady temperature, unaffected by daily or seasonal air changes.The steady, mild temperatures underground allow the earth to act as a heat source in winter and a heat sink in summer. The geothermal heat pump, which is located inside the home, captures this energy by circulating thermally conductive fluid (aka water with a non-toxic antifreeze mixed in) through the ground loop.
In winter, water in the ground loop absorbs heat from the earth and delivers it to the heat pump, which concentrates it to warm your home. In summer, the system reverses, moving heat from your home into the ground to keep it cool.
Types of Ground Loop Systems
There are several types of ground loop designs, 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 loops, horizontal loops, and a water, or “pond loop” system. Because pond loops require the homeowner to have a large body of water on the property, they’re relatively uncommon, and we won’t discuss them in detail here.
Horizontal Ground Loops
Installers lay horizontal ground loops across a wide area, digging trenches hundreds of feet long and 6–10 feet deep. These systems work only when the yard has enough space and soil conditions make trenching easy.
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 works best for homes with limited yard space, shallow rock formations, or retrofit projects where homeowners want minimal disruption to landscaping.
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, installers insert a single U-bend pipe loop into the hole, then grout 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 heat pump extracts or adds heat, the system expels the water into a well, pond, or 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
Installers find open-loop systems the simplest to set up, and communities have used them successfully for decades where local codes allow. In this system, groundwater flows from an aquifer through a well into the building, transfers heat to a geothermal heat pump, and then returns to the aquifer through a discharge well set a safe distance away. Always consult local environmental officials before considering an open-loop system.
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?
The International Ground Source Heat Pump Association (IGSHPA) approves only high-density polyethylene (HDPE) and crosslinked polyethylene (PEXa) for closed-loop geothermal systems. Polyethylene, the world’s most common plastic, also appears in food packaging, bottles, bags, pool liners—and 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.
After construction, installers pressurize and leak-test the piping before putting it 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 hardens, place a sheet of plywood (or something similar) over the tire path to distribute the load of vehicles driving on it.
Can you plant trees over the area where ground loops are installed?
We don’t recommend planting trees over ground loops for two main 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?
Geothermal installation by itself should have no significant impact on radon levels inside the home. If any homeowner has concerns about radon in their home, we recommend they contact a mitigation professional.
What level of maintenance do ground loops require?
Ground loops are maintenance-free and don’t require cleaning or re-charging.
How Much Land Do You Need for Geothermal Heat?
The space you need to install a geothermal system varies. Particularly, it depends on whether you’re using horizontal or vertical loop systems.
As their names suggest, horizontal loops stay closer to the ground, and run parallel back and forth with it. Horizontal loops are less practical and can need up to 1200-1800 feet of underground space for a mid-sized home.
Vertical loops dive deep into the ground, taking up much less space but needing a greater depth of installation. Vertical loops need around 3-500 feet of depth. Don’t worry — installers can place these entirely from the surface, and they don’t require much space.
Does Geothermal Heat Work in Cold Climates?
It’s easy to think that geothermal heating only operates well in tropical destinations. This is probably because of the common misconception that all geothermal energy comes from the steamy byproducts of geysers or the intense heat of volcanic activity.
There are plenty of examples of this kind of energy harnessing with geothermal. The Mayacama Mountains in Northern California capture geyser steam to generate geothermal power. In Iceland, engineers capture supercritical water from volcanoes to generate energy.
This works because temperatures swing wildly above ground as autumn turns to winter, while the earth just a few feet below stays unaffected.
The sun’s heat energy is stored in the earth. So, rain, shine, sleet, or snow, it’s always around 55 degrees Fahrenheit at about 10 feet below ground. This is as true in Minnesota as it is in Georgia. So, it’s always easy for geothermal heat pumps to absorb the heat energy they need to get started.