A Guide to Key Terminology in the Ground Source Heat Pump Industry

In the growing ground source heat pump (GSHP) industry, understanding the specialized terms can be essential for both newcomers and seasoned professionals. This glossary is designed to clarify key concepts and terminology, offering a valuable reference tool for anyone interested in or working with GSHP systems. From foundational definitions to industry-specific terminology, this guide aims to make the language of GSHP energy accessible, helping readers gain confidence and precision in their work and conversations within the industry!

Heat pump: An electrical appliance designed to remove heat from a low-temperature source to produce higher temperature heat for use in space heating, domestic hot water heating, or by other processes. Heat pumps may include a reversing valve that reverses condenser and evaporator operations to produce either heating or cooling from a common source.

Ground source heat pump (GSHP): A system that uses the ground, groundwater, or surface water as a heat source and sink.

Note: Other terms used in the industry include “earth-coupled heat pump”, “geothermal heat pump”, “geoexchange”, “ground-coupled heat pump”, and “water source heat pump”.

Geothermal heat pump (GHP): SeeGround source heat pump system. NOTE: The U.S. Department of Energy (DOE) and the U.S. tax code uses “geothermal heat pump” when referring to GSHPs.

Groundwater heat pump (GWHP) system: A term used in GSHP ratings, designating a ground source heat pump system connected to a groundwater/water well, operating as an open-loop system.

Ground loop heat pump (GLHP) system: A term used in GSHP ratings, designating a ground source heat pump system connected to a closed-loop system.

Direct exchange (DX) heat pump: A ground source heat pump system that uses a heat pump and a refrigerant charged ground heat exchanger.

Ground heat exchanger (GHX): A buried heat exchanger that uses the ground, groundwater, or surface water as a heat source and sink. Ground heat exchangers include vertical ground heat exchangers, horizontal ground heat exchangers, submerged heat exchangers, and groundwater heat exchangers.

Horizontal ground heat exchanger: A ground heat exchanger that is buried in a trench, open excavation, or installed by horizontal drilling.

Vertical ground heat exchanger: A ground source heat exchanger installed in a vertical or inclined borehole with insertion of the piping to the bottom of the borehole, and grouting via tremie method from the bottom of the borehole to the ground surface.

Borehole: A drilled, bored, cored, driven, hydraulically advanced, or otherwise constructed hole mechanically created in the earth. Boreholes may be vertical, horizontal, or angled.

Borehole heat exchanger: See vertical ground heat exchanger.

Loop: The component of a ground heat exchanger where energy transfer occurs between the ground and a mechanical system via a heat transfer fluid.

Building loop (or indoor piping): Piping that connects the heat pump(s) in the building to the ground heat exchanger.

Closed-loop system: A continuous, sealed, underground, or submerged heat exchanger through which a heat-transfer fluid passes to and returns from a heat pump.

Water well: An excavation that is drilled, cored, bored, washed, driven, dug, jetted, or otherwise constructed for the purposes of extracting groundwater, monitoring groundwater, using the geothermal properties of the earth, or injecting water into an aquifer or subsurface reservoir.

Open-loop (surface water or groundwater) system: A system designed to use groundwater for the purpose of extracting or rejecting heat by use of a ground source heat pump.

District Energy System: A system characterized by one or more central plants distributing ambient water, hot water, and/or chilled water, which then flows through a network of pipes to provide hot water, space heating, and/or air-conditioning for multiple buildings. Systems include Ambient Temperature Loop Systems, Combination Systems, and may include site-generated power or energy storage.

Note: Other terms include District Heating and Cooling Systems, District Geothermal Systems, Community Heat Pump Systems, 3G/4G/5G Heating and Cooling Network Systems, Thermal Energy Networks, and Utility Thermal Energy Networks.

Ambient Temperature Loop Systems: A piping network that distributes fluid at low to moderate temperatures sharing heat between buildings, to/from ground heat exchangers, and to/from other sources and sinks, generally operating in the range of 39˚F (4˚C) to 104˚F (40˚C).

Thermal Energy Network (TEN): See District energy systems.

IGSHPA created this glossary to clarify and simplify the language of geothermal/ground source heat pump systems and provide a helpful resource for both newcomers and industry veterans. By defining these essential terms, we aim to support greater understanding and communication within our field. In addition to terms, consistency of messaging also helps avoid confusion in the industry. Below are some common scenarios where the terminology should be used within the proper context based upon IGSHPA’s brand guide.

1. When discussing the heating and cooling unit: At the heart of the system is a heat pump that is connected to the ground heat exchanger or groundwater piping. This device should be referred to as a “ground source heat pump” / “GSHP” (typical usage by IGSHPA, CSA, ASHRAE and other standards/technical manuals, and documents), or a “geothermal heat pump” / “GHP” (typical usage by the U.S. D.O.E. and in legislation/tax code). The words “heat pump” should be included with describing the unit to avoid confusion with other geothermal technologies like geothermal power generation.
2. When discussing the system: The system includes the GSHP(s) and ground heat exchanger(s). It can be a geothermal heating and cooling system, which includes a GSHP(s) or GHP(s). It can also be called a GSHP system.
3. When discussing the ground heat exchanger: The ground heat exchanger (GHX or GHEX) is defined above. IGSHPA training materials use “ground heat exchanger” as a term instead of “ground loop”. The words “heat exchanger” are more descriptive of the actual function. “Ground loop” is not incorrect, but it is not consistent with technical materials.
4. When discussing a vertical ground heat exchanger: It is extremely important that the term “bore” is used to describe the vertically drilled portion of the GHX in a closed loop application. A bore is not a well, and could cause confusion, especially among code inspectors and other regulating bodies. Depending upon the regulations in the state or province, water well requirements may be different than GHX bore requirements (e.g. grouting requirements, casing requirements, etc.)
5. When discussing groundwater systems: A groundwater system, as defined above, uses water wells. “Open loop” or “pump and dump” as terms can be confusing. The term “groundwater system” is more accurate and easier to understand, since the system is connected to a water well and uses ground water.