Performance analysis and multi-objective optimization of the high-temperature cascade heat pump system

Abstract

This paper presents a high-temperature cascade heat pump system with a high compression ratio for recovering the waste heat of the chemical plant and replacing the steam. To analyze the economic and the thermodynamic performance of the high-temperature cascade heat pump, a mathematical model, considering energy, exergy, economy and environment, has been developed under different heat source inlet temperature. The proposed system here indicated good stability and feasibility under various operating conditions according to the simulation results. However, as the heating capacity and the annual net profit were found to be conflicting with each other, a multi-objective optimization method was developed to solve this problem. In addition, the technique for Order of Preference by Similarity to Ideal Solution method was selected as the decision-making method to search for the final optimal result of the system. The optimization results showed that if the optimized heating capacity project was selected, the average heating capacity and the average annual net profit were 2.8% and 6.7% lower than their maximum possible values. At the optimal heat source inlet temperature of 71 °C and condensing temperature of 145 °C, the heating capacity of the system was 498.9 kW and the payback period was 3.9 year.