Research on Indoor Thermal Environment and Human Thermal Comfort in Office Buildings with Different Heating Ends

The energy consumption of heating and cooling systems is a major part of the energy consumption of building operation, accounting for about 30% of the total energy consumption of the whole society. In the context of China's “double carbon” goal, the main problem we face is how to strike a balance between reducing energy consumption and providing a comfortable indoor thermal environment. Proper indoor thermal environment parameters also affect human comfort and work efficiency. Radiant heating (radiators) and convection heating (air-conditioning systems) are common heating modes in office buildings in the cold climate zone of China. Different heating modes operate in different ways: radiator heating is to control the indoor air temperature by providing a hot surface, usually in continuous operation mode; air conditioning heating is to control the indoor thermal environment by providing hot air, and can quickly heat the indoor air, usually in intermittent operation mode. Different heating modes in the indoor thermal environment design standards there are also differences. GB 50736-2012 “civil building heating, ventilation and air conditioning design code” stipulates that: cold climate zones in winter radiator heating mode indoor design air temperature is allowed to be lower than the air conditioning heating mode 2 ℃. However, the international standards ISO 7730:2005 and ASHRAE 55-2020 do not make a clear difference in the indoor design air temperature for different heating modes, but both limit the indoor air temperature to a narrow range. There have been reports on human thermal comfort under radiant and convective heating modes at home and abroad, but most of the current studies are based on artificial climate chamber experiments, and there are few studies on different heating ends with a large number of actual building field tests.Zhou et al. investigated the thermal comfort of underfloor heating from the perspective of exposure duration, and found that the exposure duration had a significant effect on both subjective responses and physiological thermal comfort of the subjects. The results found that the exposure time had a significant effect on both subjective response and physiological thermal comfort. Wang Zhaojun et al. studied the change law of human thermal response in a microclimate chamber with radiator heating, and found that people staying at lower temperatures would be more likely to psychologically accept a colder environment, and have a lower preference for indoor temperatures.Su et al. experimentally compared the effects of radiator heating and underfloor heating on human thermal comfort, and found that asymmetric radiant temperature limits are different in different forms of heating. In addition, some scholars have found that radiator heating environments have small vertical temperature gradients, high heating efficiency and no noise during operation, but do not provide sufficient evidence that radiator heating is more comfortable than air conditioning. It has also been found that respondents complained more in radiator-heated buildings because they did not feel the air flow. In summary, human thermal comfort needs vary between heating modes. Although artificial climate chamber studies can accurately control environmental parameters, they can only reflect the unidirectional effects of environmental conditions on human thermal comfort, and usually do not reflect human adaptive behavior and regulation in actual buildings. As the standard of living improves, people spend their days in building environments with less fluctuating indoor air temperatures, which may also change their expectations and requirements of the environment. Therefore, it is necessary to conduct field research on the thermal environment of different heating modes in actual office buildings in cold regions, to clarify the impact of different heating modes on the indoor thermal environment and human thermal comfort needs, and to verify whether the indoor temperature design values in the standard for office buildings are applicable to cold climate zones. Based on this, the author's group selected 10 office buildings in Xi'an to conduct a large sample of actual field research and testing. By combining the measurements of objective physical environment parameters and the subjective questionnaire analysis of the office population, we compared the differences in the indoor thermal environment and the human body's thermal comfort needs under different heating modes, and compared the results of the study with the previous studies and standards, so as to provide a reference for the energy-saving and comfortable design and operation of the indoor thermal environment of office buildings under different heating modes in cold climate zones.