Heating and defrosting performance assessment of dual-source heat pump operational modes under various ambient conditions

Abstract

Multifunctional dual-source heat pump systems, featuring two sets of heat exchangers (air-to-refrigerant and water-to-refrigerant) in series or parallel, aim to boost efficiency. However, these systems often require extensive piping, leading to power losses, higher energy consumption, and increased installation space requirements. Furthermore, few comparative studies have assessed the effectiveness of dual-source versus single-source heat pump systems under various ambient conditions. This study introduces a novel air-water dual-source evaporator design that enables efficient heat exchange using air, water, or both. With this design, the heat pump system can be tuned according to three distinct modes: pure water-source mode (WSHP), pure air-source mode (ASHP), and dual air-water-source mode (AWSHP). The heat pump's efficiency across these modes was evaluated under various weather conditions, adhering to the CNS15466 and GB/T21362 standards. The findings reveal a strong correlation between the operational modes and ambient temperatures, indicating that maximum efficiency is achieved with the WSHP mode below 7 °C, AWSHP mode between 10 °C and 35 °C, and ASHP mode above 35 °C. Moreover, three defrosting methods were evaluated: hot gas bypass, hot water bypass, and a combination of both. The hot water bypass, in conjunction with the proposed dual-source evaporator design, efficiently performed full defrosting, boosting system efficiency. The ability of the heat pump to switch between operating modes enhances the overall energy efficiency during space heating and defrosting, reduces installation space requirements and compressor oil loss, and facilitates hot water production. The proposed system is ideal for various industrial applications requiring efficient operation under diverse ambient conditions.