Simulated performance of a borehole-coupled heat pump seasonal solar thermal storage system for space heating in cold climate

Abstract

The performance of a seasonal solar thermal energy storage system for space heating in cold climates was investigated. The system includes a double U-tube vertical borehole thermal energy storage integrated with a ground coupled heat pump and evacuated tube solar collectors. A validated TRNSYS model for six cold climate locations: Lukla, Dras, Sivas, Harbin, Ulaanbaatar and Verkhoyansk was applied. The hourly typical metrological year (TMY) data of each location was used. The house model for each location was based on the typical local dwelling. The annual heating loads per unit floor area (GJ m−2) was found in the range of 0.71–2.59 (1.71, 1.79, 0.71, 1.19, 1.45 and 2.59 for Lukla, Dras, Sivas, Harbin, Ulaanbaatar and Verkhoyansk respectively). The sizes of the system components such as solar collector area, borehole length, number of borehole and heat pump capacity were determined for each location. The analysis covered both heat charging and discharging. It was found that the average ground temperatures were stable in each location with solar charging. However, if the system was not charged by solar energy, the average ground temperatures were decreased over the years. The seasonal compressor heating coefficient of performance coefficient of performance were found to be more than 5.8, that shows the potential benefit of the system. The proposed system could fulfil more than 93% of the space heating demand in all selected locations. The results of the study reveal the potential benefits of utilising seasonal solar thermal energy storage system in cold climate locations.