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Personal: Residential

Common Terms – Heat Pumps

Heat Pump Components

  • Refrigerant is the substance that circulates through the heat pump, alternately absorbing, transporting, and releasing heat.
  • Reversing valve controls the direction of flow of the refrigerant in the heat pump whether it heats or cools the house.
  • Coil is a loop, or loops, of tubing where heat transfer takes place. The tubing may have fins to increase the surface area available for heat exchange. The evaporator is a coil in which the refrigerant absorbs heat from its surroundings, causing the refrigerant to boil and become a low-temperature vapour.
  • Accumulator collects any excess liquid that didn't vaporize into a gas as the refrigerant passes from the reversing valve to the compressor. (Not a feature on all heat pumps.)
  • Compressor squeezes the molecules of the refrigerant gas together, increases the pressure, raising the temperature of the refrigerant, and circulates the refrigerant.
  • Condenser is a coil in which the refrigerant gives off heat to its surroundings and becomes a liquid.
  • Expansion device reduces the pressure created by the compressor. This causes the temperature to drop, and the refrigerant becomes a low-temperature vapour. It becomes liquid in the condenser.
  • Plenum is an air compartment that forms part of the system for distributing heated or cooled air through the house. It is generally a large compartment immediately above the heat exchanger.

Other Terms

  • Bels: A-weighted sound power level is expressed in bels. A-weighted decibels, abbreviated dBA, or dBa, or dB(a), are an expression of the relative loudness of sounds in air as perceived by the human ear. In the A-weighted system, the decibel values of sounds at low frequencies are reduced, compared with unweighted decibels, in which no correction is made for audio frequency. This correction is made because the human ear is less sensitive at low audio frequencies, especially below 1000 Hz, than at high audio frequencies. The sound rating is a tone corrected. The lower the value, the lower the sound power emitted by the outdoor unit. Select a heat pump with an outdoor sound rating in the vicinity of 7.6 bels or lower if possible. These ratings are available from the manufacturer and are published by the Air Conditioning and Refrigeration Institute (ARI), 4301 North Fairfax Drive, Arlington, Virginia, U.S.A. 22203.
  • Btu/h (British thermal unit per hour) is a measure of the output of a heating or cooling system, the amount of heat required to raise or lower the temperature of a pound of water by a single degree fahrenheit. One Btu is the amount of heat energy given off by a typical birthday candle. The heat energy released by a candle over the course of one hour is the equivalent of one Btu/h.
  • Heating degree days is a measure of the severity of the weather. One degree day is counted for every degree that the average daily temperature is below the base temperature of 18oC. For example, if the temperature on a particular day is 12oC, six degree days are credited to that day. The annual total is the sum of the daily totals over a year.
  • kW (kilowatt): 1 000 watts; the amount of power required by ten 100-watt light bulbs.
  • Ton is a measure of heat pump capacity, equivalent to 3.5 kW or 12 000 Btu/h.
  • Coefficient of performance (COP) is a measure of a heat pump's efficiency. It is determined by dividing the energy output of the heat pump by the electrical energy needed to run the heat pump, at a specific temperature. The higher the COP, the more efficient the heat pump. This number is comparable to the steady-state efficiency of oil- and gas-fired furnaces.
  • Heating seasonal performance factor (HSPF) is a measure of the total heat output of a heat pump over the entire heating season (in Btu) divided by the total energy it uses during that time. This number is similar to the seasonal efficiency of a fuel-fired heating system.
  • Energy efficiency ratio (EER) measures the steady-state cooling efficiency of a heat pump or air conditioner. It is determined by dividing the cooling capacity (in Btu/h) by the electrical energy input in watts at a specific temperature. The higher the EER, the more efficient the unit.
  • Seasonal energy efficiency ratio (SEER) is a measure of the cooling efficiency of a heat pump or air conditioner over the entire cooling season. It is determined by dividing the total cooling provided over the cooling season (in Btu) by the total energy used by the heat pump during that time in watt hours. The SEER is based on a climate with an average summer temperature of 28oC.
  • Balance point is the temperature at which the amount of heating provided by the heat pump equals the amount of heat lost from the house. This is the point at which the heat pump meets the full heating needs of the house. Below this point, supplementary heat is required.

Energy Efficiency Terminology

The efficiency ratings for different types of heat pumps use different terminology.

  • Air-source heat pumps have seasonal heating and cooling ratings. The heating rating is the HSPF; the cooling rating is the SEER. However, you may still see COP or EER ratings in manufacturers’ catalogues. These are steady-state ratings obtained at one set of temperature conditions and are not comparable to the HSPF or SEER ratings.
  • Ground source heat pumps or earth-energy systems use only COP and EER ratings. HSPFs are not typically used to express the efficiency of earth-energy systems.
  • There are ENERGY STAR qualified models of both kinds of heat pumps available.

Certification and Standards

The Canadian Standards Association (CSA) verifies all heat pumps for electrical safety. A performance standard specifies tests and test conditions at which heat pump heating and cooling capacities and efficiency are determined. The performance testing standard for air source heat pumps is CSA C273.3-M1991. There is also a CSA installation standard for add-on air-source heat pumps (CSA C273.5-1980).

CSA publishes standards to test the efficiency of ground-source heat pumps (CSA C13256) and to ensure that they are installed properly (C445-1992). Minimum efficiency standards are stipulated in both the air-source and ground-source performance standards, and these levels are currently regulated in Canada by the Energy Efficiency Act and Regulations.