Evaluation of component interactions in heat pumps on the base of advanced exergetic analysis

Advanced exergy-based analysis provides information concerning interdependencies among components of an energy-conversion system. Exogenous parts of exergy-based parameters can indicate how an improvement in one component affects (positively or negatively and by how much) the remaining components. This paper presents the evaluation of component interactions in air-source and water-source heat pumps using exogenous parts of exergy-based parameters and proposes possible ways for their simultaneous thermodynamic and economic enhancement.

It has been found that for the air-source and water-source heat pumps about 53% and 39% of avoidable exergy destruction, respectively, are due to interdependencies among components. Almost the whole amount of avoidable exogenous exergy destruction belongs to the compressor and to the throttling valve.

However, the share of the costs due to avoidable exogenous exergy destruction is smaller than the part avoidable exogenous exergy destruction. For the air-source heat pump this share accounts for 23% of costs due to exergy destruction, which can be avoided. For the water-source heat pump it accounts for only 8% of costs due to avoidable exergy destruction.

Furthermore, the results of advanced exergoeconomic analysis have shown that for the air-source heat pump system exogenous investment costs of the compressor, as the most expensive component, are positive and caused by irreversebilities within the evaporator and condenser. Thus, in order to decrease the cost of this component, the thermodynamic efficiency of both heat exchangers needs to be increased.

In case of water-source heat pump, the exogenous expenditures for the compressor due to irreversibilities occurring within the evaporator are negative, whereas the ones related to the condenser are positive. Therefore, in order to decrease investment expenditures for the compressor, thermodynamic efficiency of the condenser needs to be increased.

On the contrary, decreasing irreversibilities within the evaporator increases investment costs of the compressor and thus it is not recommended.