Design, Simulation, and Performance Analysis of Multifunctional Solar-Assisted Heat Pump Systems for Residential Buildings

Residential buildings contribute about 22% of the national energy use in the U.S. Space heating, domestic hot water (DHW), and space cooling are the three major end uses, respectively accounting for 43%, 19%, and 8% of the residential sector’s total primary energy consumption. Currently, fossil fuels are the predominant source of energy in the residential sector. To address the problems caused by the combustion of fossil fuels, alternative renewable, low-emission, and energy-efficient technologies for heating and cooling applications in residential buildings are highly needed. In this respect, solar-assisted heat pump (SAHP) systems are a promising solution by coupling solar collectors with heat pumps that can complement each other to achieve high solar utilization and high efficiency of the heat pump.
This research proposes and evaluates a hybrid multifunctional SAHP system that can provide space heating, space cooling, DHW, and onsite electricity generation. The indirect expansion SAHP system supports both parallel and series configurations. Major components of the SAHP system include unglazed PVT collectors, a liquid-to-liquid heat pump, a thermal storage tank, a DHW tank, auxiliary electric water heaters, and pumps. Photovoltaic-thermal (PVT) collectors are used to serve three functions, including electricity generation (daytime), heat collection (usually daytime), and radiative cooling (usually nighttime). The system design and controls support fourteen operational modes involving different components for space heating, space cooling, and DHW heating.
TRNSYS software is used to model and simulate the multifunctional SAHP system. The system performance is evaluated in two locations (i.e., Baltimore, MD and Las Vegas, NV) with different climates. Based on the performance analysis of the system simulation, three potential performance improvement strategies, including replacing the thermal storage tank with an outdoor swimming pool or a tank having phase change materials for latent thermal storage, and replacing the liquid-to-liquid heat pump with a dual-source heat pump are explored. The TRNSYS simulation results are also used to calculate the simple payback period of the incremental investment associated with the multifunctional SAHP system relative to a reference air-source heat pump system.
With a 2 m3 storage tank and 30 m2 PVT collectors, the multifunctional SAHP system has a seasonal performance factor of 2.7 in Baltimore and 3.7 in Las Vegas. In comparison with the reference system, the SAHP system saves energy by 48% in Baltimore and 61% in Las Vegas. The seasonal performance factor of the SAHP system can be further improved by using a swimming pool to replace the storage tank in Las Vegas and using a dual-source heat pump in Baltimore.