Efficiency indexes comparison of heat pumps operation depending on the running conditions

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:

COP=Qк /N,

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
1 2
Refrigerant R134a -
Boiling temparature 7.00 -10 °C
Condensing temperature 70.0
Discharge temperature without cooling 100.7 129.5
Power supply 400V-3ph-50Hz -
Refrigeration capacity
(evaporator performance)
6.86 2.86 kW
Consumed power 3.56 2.22
Condenser performance (heating capacity) 10.43 5.08
Current (400В) 7 5.58 A
СОР 2.93 2.29 -
EER 1.93 1.29
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.

Depending on COP and EER values, refrigeration equipment (heat pumps and conditioners in particular) are currently divided into energy efficiency classes (see Table 1.2) from A to G.

Table 1.2 The energy efficiency classes.

Energy efficiency classes A B C D E F G
EER >3.2 3.0-3.2 2.8-3.0 2.6-2.8 2.4-2.6 2.2-2.4 <2.2
COP >3.6 3.4-3.6 3.2-3.4 2.8-3.2 2.6-2.8 2.4-2.6 <2.4

The EER coefficient (EER – Energy Efficiency Ratio) is equal to the ratio of refrigeration capacity to consumed power:

EER=Q0 /N,

where Q0 - refrigeration capacity, kW; N – consumed power, kW

The equipment is labeled in accordance with a class (see fig. 1.1).

Шкала классов энергоэффективности

Figure 1.1 – The sticker (label) fragment detailing the energy efficiency class of equipment.

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