Session: 02-01 Heat Pump and Building Waste Heat Utilization

Paper Number: 107445

107445 - An Optimization Study of CO2 Heat Pump Water Heaters Using NSGA-II 

Due to growing concerns about the environmental impact of refrigerants, CO2 heat pumps have been increasingly evaluated as efficient alternatives for conventional heat pumps. Performance analyses of CO2 heat pump water heaters (HPWHs) have been the subjects of many studies, but these are typically limited to parametric analyses of air-source heat pumps. The interrelated behavior of the supercritical and subcritical thermodynamic properties, component operation, and efficiency means that a parametric study cannot adequately capture the inherent nonlinearity. Therefore, this paper, for the first time, aims to perform a multi-objective optimization on water-source HPWH performance in order to maximize the coefficient of performance (COP) and minimize component costs using three different scenarios. The decision variables are defined as compressor suction pressure (20 to 35 bar), compressor discharge pressure (85 to 135 bar), and gas cooler (GC) CO2 outlet temperature (16 to 22°C). The model performance is constrained by the practical ranges of GC and evaporator water inlet and outlet temperatures. A coupled simulation-optimization model through Python is developed using Engineering Equation Solver software (EES) and the non-dominated sorting genetic algorithm II (NSGA-II). The result of the optimal Pareto front showed that the COP changes from 3.58 to 3.94, with the lowest cost of $11,607 to the highest cost of $12,425, respectively. In addition, the variation of the GC water mass flow rate is negligible compared to the variation of the COP and cost values for different optimization scenarios.

Presenting Author: Kashif Liaqat Rice University

Presenting Author Biography: Name: Kashif Liaqat

Institution: Rice University