A numerical study on evaluating the thermal environment in a space served by a bed-based air source heat pump (B-ASHP) system

Abstract Both air source heat pumps (ASHPs) and traditional Chinese-Kangs heating systems are widely used. However, they have their pros and cons. By combining the merits from both an ASHP and a Chinese-Kang heating system, a prototype bed-based ASHP (B-ASHP) system has been proposed, and its operating characteristics experimentally obtained under a fix set of design/operating parameters for the bed-based heating terminal. Therefore, a follow-up numerical study was carried out to numerically evaluate the impacts of optimizing these design/operating parameters, including the location, dimension, surface temperature and surface emissivity of the bed-based heating terminal, on the indoor thermal environment and the operating efficiency of the B-ASHP system. The numerical study results suggested that the variation in these parameters did impact both indoor thermal environment and the operating efficiency of the B-ASHP system, in terms of the uniformity of indoor thermal environment, indoor air velocity distribution and the output heating capacity, as well as the installation space requirement and cost implication. Therefore, care must be exercised in properly balancing all influencing parameters. Also, to both maintain an acceptable indoor thermal environment that can meet the Chinese National Standard, and achieve the best possible operating efficiency of the B-ASHP system, the bed surface temperature of its bed-based heating terminal may be set at around 35 °C. Furthermore, although the changes in surface emissivity did not significantly impact on indoor thermal environment, a higher surface emissivity should be preferred when a lower bed surface temperature was used, so as to further improve potentially the operating efficiency of the B-ASHP system.