- BTU (British Thermal Unit): The quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit at standard conditions. (Equal to 252 calories.)
- Condensate: Water formed by the collection of warm moist air on a cool surface.
- Condenser: HVAC equipment that internally condenses refrigerant gas into a liquid state during the process of transferring heat.
- Closed-loop Heat Pump System: A heat-pump system that uses a loop of buried plastic pipe as a heat exchanger. Loops can be horizontal or vertical.
- COP (Coefficient of Performance): The ratio of heating or cooling provided by a heat pump (or other refrigeration machine) to the energy consumed by the system under designated operating conditions. The higher the COP, the more efficient the system.
- Compressor: The heart of a heat pump system. The compressor increases the pressure and temperature of the refrigerant as it circulates through the system during the process of moving heat from place to another.
- Cycling Losses: The actual efficiency of a heating or cooling system is reduced because of start-up and shut-down losses. Oversizing a heating or cooling system increases cycling losses.
- Desuperheater: A device for recovering otherwise lost heat from the compressor discharge gas of a heat pump for use in heating or pre-heating water.
- Efficiency: The ratio of useful energy output in direct relation to the amount of energy input.
- Geothermal: Of or relating to the Earth's interior heat.
- Geothermal Energy: The Earth's interior heat made available to man by extracting it from hot water or rocks.
- Geothermal Heat Pumps: Devices that take advantage of the relatively constant temperature of the Earth's interior, using it as a source and sink of heat for both heating and cooling. When cooling, heat is extracted from the space and dissipated into the Earth; when heating, heat is extracted from the Earth and pumped into the space.
- Heat Exchanger: A device for transferring thermal energy from one fluid to another.
- Heat Flow: Movement of heat from within the Earth to the surface, where it is dissipated into the atmosphere, surface water, and space by radiation.
- Heat Sink: The medium—air, water or earth—which receives heat rejected from a heat pump.
- Heat Source: The medium—air, water or earth—from which heat is extracted by a heat pump.
- Kilowatt: 1,000 watts—a unit of electric power. Abbreviated kW.
- Kilowatt-Hour: The energy represented by 1 kilowatt of power consumed for a period of 1 hour, equal to 3,413 Btus. Abbreviated kWh.
- Load: The simultaneous demand of all customers required at any specified point in an electric power system.
- Payback: A method of calculating how long it will take to recover the difference in cost between two different heating and cooling systems by using the energy and maintenance-cost savings from the more efficient system.
- Permeability: The capacity of a substance (such as rock) to transmit a fluid. The degree of permeability depends on the number, size, and shape of the pores and/or fractures in the rock and their interconnections. It is measured by the time it takes a fluid of standard viscosity to move a given distance. The unit of permeability is the Darcy.
- Porosity: The ratio of the aggregate volume of pore spaces in rock or soil to its total volume, usually stated as a percent.
- Thermal Gradient: The rate of increase or decrease in the Earth's temperature relative to depth.
- Tonnage: This is a measurement for cooling capacity of a system. One ton is equal to 12,000 BTUs.
