Resilient or resistant to non-neutral environments? A comparative study on occupant thermal needs in buildings under natural ventilation, fee-free heating, and fee-charged heating modes

Occupant thermal needs may be various and can be met via different adaptive behaviors in buildings. However, few studies conduct an apple-to-apple comparison of thermal needs under different heating modes and explore the correlation among the ambient environments, occupant responses, and occupant thermal needs. This study aims to compare occupant thermal needs under natural ventilation (NV), fee-free heating, and fee-charged heating modes with the same group of occupants. A field study was conducted in three buildings (Building A: NV mode; Building B: feefree heating mode; Building C: fee-charged heating mode) of a university in winter. The obtained results indicate that (1) NV mode (averagely at 15.8 & DEG;C) and fee-charged heating mode (averagely at 15.7 & DEG;C) had similar cool indoor thermal environments while the fee-free heating mode had a warm indoor thermal environment (averagely at 21.2 & DEG;C). (2) Occupants under the three heating modes exhibited strong adaptation to the cool environment. (3) And occupant's adaptive behaviors exhibited obvious differences under different heating modes. Specifically, occupants mainly relied on non-air-conditioning-use (non-AC-use) behaviors under NV and fee-charged heating modes, while occupants under fee-free heating mode relied using air conditioners to maintain thermally comfortable. (4) Moreover, the needed temperatures of the occupants were similar under different heating modes (22.3-24.0 & DEG;C). (5) Also, the correlations between the needed temperature increases and subjective responses were similar. Specifically, every 10% increase in occupants who had cool sensations and thermal discomfort led to a 1 & DEG;C and 1.4 & DEG;C increase in the needed temperature, respectively. (6) Finally, fee-charged heating mode with a very low-price rate of electricity effectively reduced AC-use behaviors and activated non-AC-use behaviors, which was estimated to reduce 55% of AC-use energy compared to fee-free heating mode. This paper provided references for indoor temperature ranges in environmental design under different heating modes of real buildings in winter.