Comprehensive Guide to Geothermal HVAC Systems for Contractors
Geothermal HVAC systems are a growing market in the industry, as homeowners and building owners look for green and energy-efficient alternatives.
Explore this comprehensive guide to learn about the different types of geothermal heating and cooling, the range of costs, tips for maintenance and troubleshooting and more.
What is geothermal HVAC?
A geothermal heat pump (GHP) uses ground loops to tap into the more consistent temperatures below the Earth’s surface. By exchanging heat with the Earth or water sources, they can keep buildings cool in the summer and warm in the winter. Geothermal heat pumps can be an energy-efficient option for residential homes and commercial buildings.
Types of geothermal HVAC systems
The different types of geothermal HVAC systems include open loop, which requires a clean water source year-round, and closed loop, which doesn’t require a water source.
The system you’ll want to choose for your customer will depend on several factors beyond that water source requirement. Learn details below:
Open loop vs. closed loop geothermal systems
Open loop geothermal systems draw on groundwater to regulate temperature. The water flows over the heat exchanger in the heat pump, and then the water is reinjected into the water source through a second well.
The water could also be discarded, which is sometimes referred to as “pump-and-dump geothermal” and is against the law in many areas. There are also creative and efficient uses for that discharged water, such as supplying a lawn sprinkler system or the hose bibb.
Open loop systems are the least expensive geothermal option because they can often draw from a well or other water source that doesn’t require drilling or excavating to run pipe. They require much less pipe than closed loop systems.
As simple as that sounds, installing an open loop system has several requirements. In addition to that supply of fresh water—at the correct flow of gallons per minute—the water quality should be high. Too many minerals in the water can cause deposits, and the pH level needs to align with the expected temperatures. Soil conditions, environmental regulations and permits also need to be considered.
If your customer’s water has too many minerals, you can use an intermediate heat exchanger between the ground loop and heat pump. This can help protect the primary heat exchanger, which is more expensive and labor-intensive to maintain and replace than the secondary exchanger.
A closed loop geothermal system, on the other hand, is more expensive but suitable for a wide range of site conditions. Just as it sounds, a closed loop is a pipe that bends in a U shape underground. In most closed loop systems, water or a water solution with antifreeze recirculates through buried or submerged plastic-type pipe. Because groundwater doesn't come into contact with a heat exchanger, a closed loop system eliminates concerns about water quality as well.
Pushed by a circulator pump, the water/glycol solution in the ground loop piping exchanges heat with the soil and flows to the water-to-air geothermal heat pump for distribution of warmed air in the winter. In the summer, the heat pump “reverses” the process to pump heat out of the home.
Closed loop works well for buildings without a suitable source of water. For closed loop configurations, moist and denser soil conducts heat well, and moist clay is typically best. If the soil is too sandy, it won’t retain moisture—and therefore heat—well.
A range of factors will determine which closed loop configuration is best for your customer’s building. The configurations that fall under the umbrella of closed loop are horizontal, vertical and pond/lake.
Horizontal, vertical and pond loop configurations
Horizontal geothermal systems have closed loop piping that doesn’t go very far below the surface of the Earth, from four to 15 feet. This makes them less expensive than vertical because the installer can usually avoid deep drilling, heavy excavation and those associated costs.
This system requires a large surface area of available land. The requirements will depend on the home size and heat pump capacity. Each ton of capacity needs 400 to 600 feet of piping, which means typically space from 800 to 3,000 feet of piping could be needed.
Depending on soil conditions and space of available land, there are a few ways to set up and place piping for a horizontal geothermal system: a single long circuit of pipe; two pipes either side by side or at slightly different levels; and an S-shape in which pipe loops underground to allow for less land area usage.
You’ll also run pipes from the ground loop to the geothermal heat pump at the building.
Once the pipes are installed, you’ll need to grout the loops to protect surrounding water sources from contamination or other issues and properly backfill the trench space to maintain good thermal contact.
A vertical geothermal system can work in areas without a lot of available land but adequate depth. While the loops don’t take up much horizontal space, they go very deep, typically from 125 to 400 feet deep or even beyond. Holes a few inches wide are drilled anywhere from 10 to 20 feet apart. When installation is complete, the holes will also need to be properly grouted.
To connect the vertical earth loops to the building’s heat pump, the vertical loop configuration still requires enough space for a trench to place the horizontal pipe.
Pro tip: Keep common trenching and excavation hazards in mind to help you and your crew stay safe while installing geothermal systems.
Pond/lake geothermal systems tap into a nearby suitable body of water but don’t actually draw or discharge water like an open loop system does. If the pond is of a suitable depth (at least eight feet) and close to the home, this can be a great option to reduce the amount of trenching and pipe needed for installation.
Piping between the home and the pond is buried underground, and these pipes coil into circles at the pond or lake. The coils for the pond float out and sink to the bottom where temperatures are more stable.
Cost of geothermal HVAC system installation
Properly installed, geothermal heating and cooling is the most efficient and long-lasting HVAC system available for homeowners. A geothermal heat pump and components can operate for two decades or more, and the loop lifespan can be more than half a century.
However, initial purchasing and installation costs can be intimidating to some homeowners. Depending on a number of factors—including home size, region, permits, type of configuration, soil conditions or treatment and any ductwork considerations—those costs can range from around $15,000 to $40,000 or more.
Pro tip: Providing financing options to your customers could help you grow your contracting business. Learn how to offer financing.
While your customer likely will recoup this investment in energy savings, it could take more than a decade of efficient geothermal heating and cooling.
Geothermal HVAC piping and components
At the basic level, geothermal heat pump installation only requires the heat pump and piping and fittings for the loops. Additional “needs” for the system come from the type and size of heat pump is best for your customer and ducting considerations for their home.
Geothermal heat pumps come in single- or two-stage, and Ferguson offers brands with sizes from 1.5 tons to 10 tons.
In general, calculating ground loops depends on the size of heat pump capacity. Each ton of heat pump capacity requires 300 to 600 feet of piping.
As mentioned earlier, geothermal HVAC systems typically use plastic pipe for the durability, flexibility and resistance to corrosion that harder materials can’t offer. Three commonly used types for ground loops have appropriate temperature ratings as well: high-density polyethylene (HDPE), crosslinked polyethylene (PEX) and polyethylene of raised temperature (PE-RT).
In addition, you’ll need to select pipe fittings and manifolds rated appropriately for temperature and pressure.
Proper concrete grout will be needed to seal off the holes for the pipe, too.
Ductwork and thermostats for geothermal systems
If a home already has ductwork in good condition, it could be compatible with a geothermal heat pump. However, ducting that’s too small for the geothermal air velocity may cause drafts and create noise.
A geothermal heat pump will provide warmer air than a typical air-source heat pump does. Making sure ductwork is properly insulated can keep your customer’s system at its most efficient.
Not all thermostats are compatible with geothermal HVAC systems, so your customer may need a new one. Many heat pump thermostats will work for geothermal—simply check specifications when you’re ready to buy. A geothermal heat pump thermostat can be WiFi-enabled, smart and programmable.
Something for you and your customer to keep in mind when selecting a thermostat for a GHP is efficiency. It has long been best practice to use deep thermostat setbacks for customers to save on heating and cooling costs overnight and during unoccupied periods. With traditional electric, gas and oil systems, this method works well because their efficiency is unaffected by heating load.
But that method is less effective with geothermal heat pumps. Recovering from a deep setback may cause a GHP to use its second stage or supplement with a less-efficient backup heat source.
To ensure the heat pump system delivers the best possible performance and efficiency for your customer, recommend they use a small setback of 2-3°F, or provide a thermostat that allows for gradual recovery to minimize the use of backup heat sources.
Best practices for maintenance and troubleshooting
Geothermal HVAC maintenance is similar to other heating and cooling systems, with a few different steps. Ductwork should be regularly inspected, and air filters replaced or cleaned as needed. You’ll also need to check connections and make sure fans and motors are running cleanly.
In addition, you’ll need to check coolant levels in the closed loops along with pressure and temperature. Occasional soil tests can also alert you to potential leaks and environmental hazards.
If your customer calls you about problems with the system, a few troubleshooting steps are similar to other systems: electrical issues or air filters can affect most HVAC equipment.
With geothermal HVAC, additional troubleshooting tips include inspecting water valves and flow and making sure loop pressure is at the recommended level.
Shop geothermal equipment at Ferguson
We can help you find the right equipment and components for your geothermal HVAC projects. Shop geothermal equipment at Ferguson.