Thermal-economic analysis of a heat pipe heat exchanger for energy recovery in air conditioning applications

Abstract

The computer simulation and working fluid selection of a heat pipe heat exchanger (HPHE) system appropriate for both heating and cooling modes in air conditioning applications are performed in this article. The studied heat pipes had a screened mesh wick and methanol as the working fluid. Various numbers of heat pipes and different values of return to the total outlet air mass flowrate ratio were considered. The heat transfer rate in HPHE was computed by the ε—NTU method by considering appropriate heat pipe thermal resistance. Because of its higher evaporation enthalpy and appropriate working limits, methanol was selected as the working fluid. Checking the heat transfer limits showed that the minimum heat transfer rate was well above the required heat transfer rate. Furthermore, the economic analysis of the HPHE was performed considering initial (investment) and operational costs as well as annual savings due to energy recovery for different numbers of heat pipes and various values of return air ratio. The results showed that there was a design point at which the savings of energy recovery was the maximum. The characteristics of this point at various values of return air ratio were determined and reported for the most economical HPHE design and for manufacturing purposes.