Geothermal/Ground Source Heat Pumps

What are geothermal/ground source heat pumps?

Ground source heat pumps (GSHPs) are a form of renewable energy that uses the energy stored in the earth to heat spaces or water. The earth maintains a relatively constant temperature throughout the day and year. This can be used for heating in the winter and cooling in the summer.

Types and How do they work?Image

There are closed-loop systems, and open-loop systems. A closed-loop system circulates a fluid such as water or antifreeze or some mixture of the two through an underground piping system. The fluid warms as it passes through the earth, bringing heat into the building structure. It works the opposite for cooling applications. A closed-loop system can have piping in a shallow horizontal arrangement or if space is limited, it can be arranged in a deep vertical arrangement. Some systems are even installed in a pond or lake and use the temperature of the water instead of the earth.

An open loop system uses a well or surface water source and pumps the water directly from the source through the building, and back out into the same or a different source. It can be an issue with maintaining adequate stream flow or ground water quantity if too much of the water is not returned to the source it is taken from. System bleed is a term used to describe the portion of the return flow that discharged to a different water body from which it was withdrawn.

Legal Status

In Montana, there are currently no regulations specific to ground source heat pumps. Open-loop systems are regulated the same as traditional wells. There is a need for comprehensive legislation that will address the issues of construction, maintenance, operation, and abandonment of these systems.

Open-Loop Systems:
Most states regulate open loop (also referred to as geothermal injection wells) systems by the same standards as wells. In Montana this would mean that open loop systems can be authorized without a permit so long as the maximum amount of water used is 35 gallons per minute or less, not to exceed 10 acre-fee a year (MCA 85-2-306).

The US EPA also regulates these systems under the Underground Injection Control (UIC) Program, because the systems may have potential to contaminate or degrade groundwater quality. An inventory of the project is taken and if it’s determined no contamination or degradation will occur, then the project is usually authorized. If it’s found that there is potential to contaminate or degrade groundwater, than the system must go through a permitting process (US EPA).

System Bleed:
Many states regulate that the system bleed must not exceed a certain percentage of the quantity used to protect ground and surface water quantity and to ensure that water rights are not infringed upon.

Closed Loop Systems:
States have inconsistent laws and regulations regarding closed loop systems. Regulations that do exist focus on the type of fluid that is circulated through the piping. Usually, some mix of water and anti-freeze is used. States that have regulations usually state that the fluid must be non-toxic in the event that a pipe breaks and releases the fluid into the ground water. The International Ground Source Heat Pump Association recommends using potable water, water plus potassium acetate, or water plus propylene glycol and a number of states have adopted these as their standards as well.

Other Interesting Points:

Flathead Electric offers a $3,000 rebate for residential ground source heat pumps.

The Federal Government through the Energy Star program offers a of 30% of the cost of a geothermal heat pump with no upper limit.

Idaho has the Idaho Geothermal Resources Act that regulates the drilling, operation, maintenance, and abandonment of all geothermal wells in the state.

Utah has the Utah Geothermal Resource Conservation Act that can be applied to direct uses such as greenhouse heating, spas and pools, crop drying, aquaculture, and industrial processing.

Many other state regulate the construction of ground source heat pumps separate from other wells, but have little or no information on water rights or exemptions to permit requirements.

Additional Information and Resources

Montana Green Power – Geothermal Heat Pumps

Montana DEQ

Flathead Electric Rebate: Flathead Electric PDF

Federal Energy Star Tax Credit

Dept. of Energy EERE Geothermal Technologies Program

International Ground Source Heat Pump Association