The basic index of heat pump performance evaluation is a transformation coefficient COP (abbr. from English “coefficient of performance”). Terms “heat transformation coefficient” and “efficiency factor” are also met.
The COP is determined by the relation between heating capacity and consumed power:
where Qc - condenser capacity (heating capacity), kW; N – consumed power, kW
In view of this formula, it is obvious that the higher COP value is, the less electric power is needed for a heat pump to perform heating.
The COP is often confused with a coefficient of efficiency, but it is not correct. The COP value exceeds one, because this coefficient only points to how effectively the heat pump transfers heat from the surrounding environment to the object to be heated.
As an example, let us consider the heat pump operation based on Bitzer 4FES-5Y-40S compressor of Ecoline series.
Table 1.1 The technical characteristics of Bitzer 4FES-5Y-40S compressor at operation modes.
|Parameter name||Value||Measurement units|
|Discharge temperature without cooling||100.7||129.5|
|Condenser performance (heating capacity)||10.43||5.08|
|Refrigerant mass flow rate||226||91||kg/h|
As can be seen from the technical characteristics of one compressor at two different modes, in view of COP values, the unit operating efficiency much depends on use conditions and environment. The boiling temperature corresponds to the particular temperature of heat take-off source and the boiling temperature change has a sufficient effect on compressor operating indexes and, as a consequence, on COP values.
Table 1.2 The energy efficiency classes.
|Energy efficiency classes||A||B||C||D||E||F||G|
The EER coefficient (EER – Energy Efficiency Ratio) is equal to the ratio of refrigeration capacity to consumed power:
where Q0 - refrigeration capacity, kW; N – consumed power, kW
The equipment is labeled in accordance with a class (see fig. 1.1).
Figure 1.1 – The sticker (label) fragment detailing the energy efficiency class of equipment.