Abstract
The paper describes an hourly simplified model for the evaluation of the energy performance of heat pumps in cooling mode maintaining a high accuracy and low computational cost. This approach differs from the methods used for the assessment of the overall energy consumption of the building, normally placed in the so-called white or black box models, where the transient conduction equation is deterministically and stochastically solved, respectively. The present method wants to be the expression of the grey box model, taking place between the previous approaches. The building envelope is defined using a building thermal model realized with a 3 Resistance 1 Capacitance (3R1C) thermal network based on the solution of the lumped capacitance method. The simplified model evaluates the energy efficiency ratio (EER) of a heat pump through the determination of the hourly second law efficiency of a reversed Carnot cycle. The results of the simplified method were finally compared with those provided by EnergyPlus, a dynamic building energy simulation program, and those collected from an outdoor test cell in real working conditions. The results are presented in temperatures and energy consumptions profiles and are validated using the Bland-Altman test.
Highlights
The increasing demand for building services has persuaded the EU to take decisive measures for energy efficiency
The calculation of the hourly consumption of the heat pump is based on the evaluation of the coefficient of performance in winter (COP) and the energy efficiency ratio in summer (EER), which is calculated through the values of the hourly average temperature of the refrigerant fluid in the condenser and in the evaporator of the heat pump
The first evaluation concerns the calculation of the EER
Summary
The increasing demand for building services has persuaded the EU to take decisive measures for energy efficiency. Equivalent RC schemes are broadly used to represent thermal systems This method of representation arises from the lumped capacitance solution of transient heat transfer equations, a well-known consequence of the thermal-electric analogy. This is clearly not the case of the building envelope, where sparse temperature distributions come along with heat sinks (thermal bridges, air gaps, etc.) and gains (solar radiation, etc.). The calculation of the hourly consumption of the heat pump is based on the evaluation of the coefficient of performance in winter (COP) and the energy efficiency ratio in summer (EER), which is calculated through the values of the hourly average temperature of the refrigerant fluid in the condenser and in the evaporator of the heat pump These temperatures are calculated using some complex relations starting from the energy needs of an envelope [29]. To evaluate the suitability of the model, a comparison with the results obtain with EnergyPlus [31] are presented, which is one of the widespread building energy simulation (BES) programs, an expression of the black-box approach
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