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• Sleeping thermal comfort using a bed-based ASHP was numerically studied. • A digital thermal manikin (DTM) was used to simulate a sleeping person. • The PTS - WPD model was used to evaluate sleeping thermal comfort. • Four factors affecting sleeping thermal comfort were numerically analyzed. Sleeping is an important human activity and heating system is needed for a comfort sleeping thermal environment in winter. By combining the merits from both an air source heat pump (ASHP) and a Chinese-Kang heating system, a prototype bed-based ASHP (B-ASHP) system has been proposed, and several design/operating parameters were experimentally and numerically studied previously. A numerical study using a digital thermal manikin (DTM) on the impacts of four influencing factors, i.e., operating mode, bed surface temperature (t bed), thermal resistance of mattress (R mat), and thermal resistance of quilt (R q) on sleeping thermal comfort was carried out, and the study results are reported in this paper. The numerical study results suggested that firstly, to maintain a suitable sleeping thermal environment, the use of only the Horizontal section (H-Section) of the bed-based heating terminal of the B-ASHP system was adequate; however using the Horizontal and Vertical section (H + V-Section) could minimize the temperature difference between the micro-climate close to the bed and outside environment, although with a higher energy consumption. Secondly, t bed of the bed-based terminal should be carefully selected, and a t bed of 44 °C could both meet the requirement of thermal comfort and acceptable operating efficiency of the B-ASHP system. Thirdly, the use of a mattress would reduce the heat transfer from the bed-based terminal to a sleeping person and indoor space, however an excessively higher R mat of mattress would reduce the heating capacity and operating efficiency, leading to a cold sleeping environment. Finally, the use of a quilt would help prevent the heat loss from a sleeping person, thereby maintaining a warmer sleeping thermal environment, however a higher-than-necessary R q of quilt would decrease the sleeping thermal comfort. [ABSTRACT FROM AUTHOR]

• Optimizing the design and operating of a B-ASHP system is numerically studied. • The operating/design parameters did impact indoor thermal environment. • A surface temperature of around 35 °C was recommended for high energy efficiency. • A higher emissivity was preferred when a lower surface temperature was to be used. 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. [ABSTRACT FROM AUTHOR]

• A novel bed-based air source heat pump (B-ASHP) system was proposed. • A prototype experimental B-ASHP system was established and tested. • The B-ASHP system can be operated at both nighttime and daytime modes. • Better thermal comfort and bed surface temperature distribution can be achieved. • A number of issues requiring further considerations were identified. Air source heat pumps (ASHPs) have been increasingly used for space heating due to their high energy efficiency and installation flexibility. On the other hand, in many rural areas in northern Chinese provinces, Kangs, a kind of traditional heating systems based on burning biofuels, are still being used for space heating in winter. Based on the pros and cons of both ASHPs and Kang-based heating systems, a novel bed-based ASHP (B-ASHP) system has been proposed to combine the advantages from both an ASHP and a Kang heating system. In this paper, a prototype experimental B-ASHP system was designed and established, and its dynamic and steady-state operating performances tested in four test cases. The test results from the four test cases demonstrated that the prototype experimental B-ASHP system can achieve quicker increases in indoor air temperatures and bed-surface temperatures than Kang-based heating systems. The use of experimental B-ASHP system can lead to a more uniformed vertical indoor air temperature gradient, thus a better occupants' thermal comfort, than the use of a conventional convection-based ASHP system. Furthermore, compared to using a Kang-based heating system, a more uniformed bed surface temperature may be obtained when using a B-ASHP system. Nonetheless, although currently the prototype experimental B-ASHP system can be satisfactorily operated, a number of issues related to the designs of a B-ASHP system such as choices of refrigerant, refrigerant tube layout optimizations, and the use of variable speed compressors for capacity control, should be carefully considered to further improve its operational safety and energy efficiency. [ABSTRACT FROM AUTHOR]