A heat pump’s efficiency is often referred to as a “Coefficient of Performance” (COP) and all heat pump manufacturers are giving this value for nominal conditions of 7 °C outdoor temperature and 35 °C flow temperature.
The Coefficient of Performance (or COP) describes the ratio of electrical power used to heating power produced under fixed input and output conditions by the heat pump unit only. A COP is used for examining the performance of a heat pump unit at ideal test conditions, usually in a laboratory.
COP of 4 means for every 1kW of electrical energy used, 4kW of useful energy is produced – a net 3kW of useful energy will be ‘free’ generated by the heat pump.
COP decreases with falling ambient air temperatures and rising flow temperatures
The Seasonal Performance Factor or Seasonal Coefficient of Performance (SPF or SCOP) describes the ratio of the amount of electrical energy used by all components associated with the heat pump system, to the amount of heat energy delivered to the heating system, over a long period of time (e.g. season or year).
SPF is a better indicator of performance for the purposes of examining the “real-life” performance of a heat pump than COP and takes in account the type of heating system installed.
Under the new EU regulation SEAI has implemented this in the New Heat Pump Methodology and by using their proposed Heat Pump Calculation Tool we can get accurate SPF’s based on data that every heat pump manufacturer has to provide.
SPF values may vary depending on the type of heat emitters used and aiming for a low flow temperature will result in high SPF figures. Ideally with an Air-to-water heat pump we should use an UFH – underfloor heating system because this only requires flow temperatures up to 35 °C, resulting in SPF’s over 5.
We can also use low temperature radiators, aluminium or steel panel or fan coils which require flow temperatures up to 55 °C, resulting in SPF’s around 400%. Comparing these two figures we can see that the UFH system compared with a Low temperature radiator / fan coil system is circa 20% more efficient.
The DHW production efficiency though for any heat pump it is not that high due to the high flow temperature required to heat the DHW cylinder. This figure is in around the 200% mark and takes in account that most air-to-water heat pumps require an electrical immersion to raise the temperature in tank to 60 °C, as an anti-legionella protection.
Both Monobloc (water connection) and Split (refrigerant connection) heat pumps have their advantages and where the Monobloc scores well for the ease of installation the Split has slightly higher efficiencies and can be used with integrated cylinder units, giving a more compact and small footprint solution, having all components built-in the indoor module.