Detailed modeling of a novel photovoltaic thermal cascade heat pump domestic water heating system

A domestic water heating system that combines photovoltaic thermal (PVT) solar collectors with two heat pumps, in a novel cascade arrangement, is presented and analyzed in this paper. The goal of this analysis is to determine and compare the annual thermal energy output of the PVT cascade heat pump system with an evacuated tube and simultaneous consumption PVT single heat pump water heating system. The computational technique that was developed to analyze the PVT cascade heat pump system, which determines solar panel energy outputs, and heat pump operating characteristics, is described in detail. Case study simulation results are also presented, which include transient power output profiles, temperature profiles, and yearly energy output results. Hourly weather data, including air dry-bulb temperatures and solar flux values, from locations with a range of climates was used in these simulations. The results of this study show that the PVT cascade heat pump system has an annual thermal energy output improvement over the evacuated tube heating system ranging from 37% to 68%, depending on the selected simulation location.