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 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 central part of a heat pump system - the compressor increases the pressure and temperature of the refrigerant and simultaneously reduces the volume while causing the refrigerant to move through the system

Cycling Losses
The actual efficiency of a heating or cooling system is reduced due to startup and shutdown losses – over sizing a heating or cooling system increases cycling losses

EER (Energy Efficiency Ratio)
The ratio of cooling provided by a heat pump (or other refrigeration machine) to the energy consumed by the system under designated operating conditions (the higher the EER, the more efficient the system)

Fossil Fuel
Any of several types of combustible fuels formed from the decomposition of organic matter – examples are natural gas, propane, fuel 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 moving heat from one location to another. Heat pumps can extract heat from air, water, or the earth – they are classified as either air-source or ground-source (geothermal) units

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

Hot Water Generator
Device for recovering superheat from the compressor discharge gas of a heat pump or central air conditioner for use in heating or preheating potable water

Open-loop Heat Pump System
A heat pump system that uses groundwater from a well - the water is returned to the environment.

Payback
A method of calculating how long it will take to recover the difference in costs of two different heating and cooling systems by using the energy and maintenance 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 – may be in the form of electric resistance or fossil fuel