BTU (British Thermal Unit)
The amount of heat needed to raise the temperature of one pound of water one degree Fahrenheit. BTU is used to signify the heating and cooling capacity of a system and the heat losses and gains of building and homes.
The number of BTU’s produced in one hour.
Closed loop system
A heat pump system that uses a loop of buried plastic pipe as a heat exchanger.  Loops can be horizontal or vertical.
Coefficient of Performance (COP)
A measure of efficiency in the heating mode that represents the ratio of total heating capacity to electrical energy input.
The central part of a heat pump system. The compressor increases the pressure and temperature of the refrigerant and simultaneously reduces its volume while causing the refrigerant to move through the system.
A heat exchanger in which hot, pressurized (gaseous) refrigerant is condensed by transferring heat to cooler surrounding air, water or earth.
Cycling losses
The efficiency of a heating or cooling system is reduced due to start-up and shut-down losses.  Over sizing a heating or cooling system increases cycling losses.
A device for recovering superheat from the compressor discharge gas of a heat pump or central air conditioner for use in heating or preheating water.
Energy Efficiency Ratio (EER)
A measure of efficiency in the cooling mode that represents the ratio of total cooling capacity to electrical energy input.
A heat exchanger in which cold, liquid refrigerant absorbs heat from the low-temperature source (fluid from the ground loop).
Fossil Fuel
Combustible fuels formed from the decomposition of organic matter. Examples are natural gas, propane, fuel oil, oil, and coal.
Geothermal heat pump
A heat pump that uses the earth as a heat source and heat sink.
Heat exchanger
A device designed to transfer heat between two physically separated fluids or mediums of different temperatures.
Heat pump
A mechanical device used for heating and cooling which operates by pumping heat from a cooler to a warmer location.  Heat pumps can extract heat from air, water, or the earth. They are classified as either air-source or geothermal units.
Heat sink
The medium – air, water or earth – from which heat is extracted by a heat pump.
Open Loop System
A heat pump system that uses groundwater from a well or surface water from a lake, pond, or river as a heat source.  The water is returned to the environment.
A method of calculating how long it will take to recover the difference in costs between two different eating and cooling systems by using the energy and operating cost savings from the more efficient system.
Supplemental heating
A heating system used during extremely cold weather when additional heat is needed to moderate indoor temperatures, maybe in the form of fossil fuel or electric resistance.