Heat Pump, Solar, Thermal Storage, Solar Thermal, TRNSYS
Solar assisted heat pump systems offer an attractive method of reducing the energy used for space heating and cooling, while efficiently using low temperature renewable energy from the sun to reduce the degradation of heat pump performance at low ambient temperatures. However, the majority of these systems use sensible storage to bridge the gap between thermal supply and demand, with the maximum storage capacity limited by physical constraints within the building. Latent storage has the potential to significantly reduce the required tank volumes in these types of systems. Previous work has demonstrated the benefit in heating mode of combining a solar heat pump system with ice based latent thermal storage, with this type of system achieving an up to 86% reduction in space heating energy use compared to a conventional system. The objective of this paper is to expand upon these findings and examine annual system performance in various Canadian climate regions through the evaluation of an innovative new operational mode providing space cooling to the building. The proposed system has distinct heating and cooling modes of operation. In heating mode, energy obtained from the solar collectors is stored in the ice tank. Thermal energy is then extracted from the ice tank using a heat pump, and delivered to a warm water tank acting as the distribution point for heating and DHW loops. An innovative new cooling mode is also presented, where the heat pump is used to build a cold storage reservoir for cooling purposes during the summer months. Excess thermal energy is then dissipated at night using radiative cooling (via solar collectors) or an air cooled condenser. Anticipated system benefits include increased energy storage densities, improved solar collector efficiencies, and potential utility cost savings by operating the heat pump during off-peak hours. To perform the analysis a computer model of the proposed system is developed using the TRNSYS energy simulation program, and integrated into high performance homes in three Canadian regions (Montreal, Toronto, Vancouver). Annual simulation results are presented and compared with typical base case designs in order to assess the viability and potential energy savings. A sensitivity analysis on several system variables is then presented in order to identify key design parameters for improved energy performance.