Human thermal comfort under dynamic conditions: An experimental study

Although thermal comfort has been a research topic since the 1960s, some knowledge gaps still affect understanding of the human response to changing thermal environments. To enhance knowledge in this regard, an exploratory study is presented, which aims to understand human response to monotonic thermal variations by describing its relationship with covariates of interest. Thirty-eight participants (29 females, 9 males) worked in an office-like climate chamber and were exposed to dynamic and controlled heating and cooling ramps of the operative temperature with different speeds. Participants' perception, evaluation, preference and acceptability of the indoor thermal environment were recorded by filling in dedicated questionnaires. Additionally, participants could indicate when an uncomfortable event occurred during these temperature ramps by clicking a digital button on a dedicated app. This discomfort event was defined in behavioural terms as the decision to "take action to restore a comfort condition". Survival analysis was used to study participants' reactions to the dynamic thermal stimuli. It showed that two distinct mechanisms caused discomfort events due to overheating and undercooling: warm discomfort is driven by the absolute value of the achieved operative temperature, while the relative change in operative temperature mainly causes cold discomfort. Compared to the current recommendations regarding temperature cycles, drifts and ramps, this result shows that current standard recommendations underestimate the risk of thermal discomfort during a cooling process while overestimating it during a heating one. The new knowledge of human reaction to a dynamic thermal environment can lead to more energy-efficient and satisfactory building control strategies.