A heat pump is a device for transferring energy in the form of useful heat from one place to another. It cannot store, make or destroy heat energy it simply moves it. There are a number of techniques that exploit heat transfer; the commonest in use is the Refrigeration Cycle. A heat pump is capable of transforming a large quantity of low grade, low temperature heat. Some air source systems will operate in winter ambient conditions down to -15ºC. Heat pumps are available that can operate in a variety of media Air, Water, glycol, etc.
A European standard for testing and rating heat pump performance, EN 14511 Part 1, defines a heat pump: [a] heat pump [is an] encased assembly or assemblies designed as a unit to provide delivery of heat. It includes an electrically operated refrigeration system for heating. It can have means for cooling, circulating, cleaning, and dehumidifying the air. The cooling is by means of reversing the refrigeration cycle?
A heat exchanger is a device for the transfer of heat energy from one medium to another. It can take a variety of different forms; the commonest in everyday use is a central heating radiator where hot water is circulated through pipes or plates and gives its heat up to the surrounding air.
Inverter or Variable Speed Drives (VSD)
Rarely are heat pumps required to run at full duty for significant periods of time, mostly due to variable load conditions such as external temperature conditions and hence varying building heat loss. By varying the speed of the compressor the output of the equipment can be varied and lead to increased efficiency because both the evaporator and condenser are sized for peak duties and able to conduct heat even more efficiently at part load. Such drives are used in most electrically driven vapour compression heat pumps, whether two piece âsplit systems? multi split or VRF and use Inverter technology. Variable speed drive is also possible with Gas Engine Heat Pumps by conventional throttling of engine speed via the carburettor.
The SI unit of power. It is used to specify the thermal performance of a Heat Pump as well as the power it consumes. It is a Kilojoule of energy per second (kJ/s).
Kilowatt Hour (kWh)
The standard unit (Not SI) for the of sale of electrical energy; it is the equivalent power consumed by a purely resistive load of 1000 Watts (1kW) for 1 hour. Because a kW is kJ/s, a kWh is equivalent to 1 kJ/s for 1 hour. Therefore 1 kWh = 3600 kJ. Your electricity supplier will specify the price in your supply contract.
A heat collection system whereby water is extracted from ether the ground or an open water source (lake, river or sea) and is passed directly through a water source heat pump. This water may be re-injected or passed to waste, in the latter case water charges may be incurred. Environment Agency approval is required for all systems extracting more than 20m3 which restricts use to domestic small to medium size without such approval.
The heat transfer fluid contained in a heat pump refrigeration circuit. Normally this is a chemical contained in a hermetically sealed circuit that has a low temperature boiling point. Refrigerants can be one of a number of man-made Fluorocarbons(e.g. HFC) or a Hydrocarbon compound (refined Propane or Isobutane). All refrigerants currently used have Zero Ozone Depletion potential, but many have quite high direct Global Warming Impacts if released to atmosphere. All refrigerant handling should be undertaken by qualified and certified personnel.
All heat pumps use the refrigeration cycle in some way. Heat is extracted from a source, upgraded in temperature and delivered to a use. The most popular method is the vapour compression cycle.
Reverse Cycle Heat Pump
A reverse cycle system is a refrigeration system that can, by means of a valve that reverses the flow of the refrigerant fluid, change the operation of the system from heating to cooling. This process can also be used to facilitate defrost.
Seasonal Coefficient of Performance (SCoP)
An efficiency metric of heat pumps which describes performance of the unit over a typical season where the source temperature varies. Used mostly with Air Sourced Heat pumps where the source temperature varies considerably over the year and hence efficiency and/or output varies. Thus SCoP is dependant on the local climate. In order to compare units the EU has been divided into 3 principle regions and is defined in BSEN 14825 and will be used for the Energy Using Products directive (ErPEner Lot 1 and 10). Often referred to as SPF.
(See also CoP, CoSP, SPF and SEER)
Seasonal Energy Efficiency Ratio (SEER)
An efficiency metric of reverse cycle heat pumps which describes performance of the unit over a typical cooling season where the source temperature varies. Used mostly with Air Sourced Heat pumps where the source temperature varies over the year and hence efficiency and/or output varies. Thus SEER is dependant on the local climate. In order to compare units the EU has been divided into 3 principle regions under BS EN 14825 for both heating and cooling functions.
(See also CoP, SCoP and EER)
Seasonal Performance Factor (SPF)
Seasonal Performance Factor is similar to SCoP in that it is a ratio expressing the efficiency of a heat pump by describing heat output to total energy input taking into account variations in performance over the heating season. Under BS EN 15316, input energy includes auxiliary energy which may be all or part of pump/fan power. Care must be exercised as to whether this is intended to include any additional boost heat from other sources (e.g. electric immersion heater) and the full pump/fan power to overcome all resistances of circuits (i.e. not just the heat exchangers of the heat pump). For this reason the predictive SPF, if based on say CoSP or SCoP, may vary greatly from an empirical SPF based on actual data measured on site because this may include the total power consumed by circulating pumps/fans and direct electric additional low ambient boost heaters, all of which are bespoke to predict in advance.
The term is used in a wider sense than it’s specific definition under BS EN 15316 and is being widely adopted in UK and EU.
A heat pump system whereby heat is extracted from water which is either directly extracted from the ground (e.g. a buried aquifer) called ‘open loop’ or from an open water source such as a lake, river or sea. These systems are invariably indirect and need careful filtration to remove particles from the water source before it enters the heat exchanger. This term is sometimes used interchangeably with Ground Source with a sub designation of âopen loop? In the UK permission is usually needed for extraction of ground water.
Water to Water
A heat pump where the collecting medium (source) is either ground water or a glycol solution and the destination medium is also water or glycol. These systems are invariably indirect.
Water to Air
A heat pump where the collecting medium (source) is either ground water or a glycol solution and the destination medium is air. Hence the source side is indirect but the delivery side is likely to be direct.
CO2 Emission Comparisons with other Technologies