Multi-zone Room Operation Coupling Thermal Condition Profile and Occupants’ Thermal Preferences

Description

Thermal comfort is an imperative aspect of indoor wellbeing and significantly affects occupants’ health and productivity. The air conditioning system, which is widely used to provide a thermally comfortable indoor environment, consumes the most energy in buildings (around 50%). To reduce energy use, vertically non-uniform air distribution methods (e.g., displacement ventilation, stratified ventilation and stratum ventilation) have been proposed. Vertically non-uniform air distribution methods focus on thermal comfort in occupied zones, and saves energy used to condition unoccupied upper zones. However, two issues limit their performances in thermal comfort and energy efficiency in a shared room: (1) the horizontal non-uniformity of the thermal conditions, and (2) the different thermal preferences of occupants. The thermal condition in an occupied zone is conventionally assumed to be uniform horizontally, and the average thermal condition of an occupied zone is controlled within a certain range for thermal comfort. However, thermal conditions are inevitably non-uniform. Conventional methods overlook horizontal non-uniformity which largely contributes to thermal discomfort complaints and low energy efficiency in practice. Another issue is that while occupants’ thermal preferences are inherently different, occupants are conventionally regarded as typical persons and their thermal preferences are assumed to be identical. Since the thermal preference of a typical person cannot represent the thermal preferences of actual occupants, conventional methods fail to effectively track the actual demand for thermal comfort. Considering the horizontal non-uniformity of thermal conditions and the different thermal preferences of occupants, the novel idea of coupling thermal condition profiles and thermal preferences to improve thermal comfort is originated. The proposed coupled operation strategy (1) divides an occupied zone into subzones horizontally, (2) instructs occupants preferring cool conditions to sit in cool subzones and those preferring warm conditions to sit in warm subzones, and (3) controls the thermal conditions of the subzones to maximize the satisfaction of thermal preferences. According to the thermal adaptation theory, occupants play an active role in thermal comfort management. When informed of the thermal condition profile of the room (i.e., the ranking of thermal conditions of the subzones from cool to warm), occupants tend to instinctively choose the subzones with thermal conditions consistent with their thermal preferences for thermal comfort. Therefore, the coupled operation strategy innovatively takes advantage of both the horizontal non-uniformity of thermal conditions and the active role of occupants in thermal comfort management to improve thermal comfort. With improved thermal comfort, energy efficiency can also be improved by reducing unnecessary cooling.  There are three core tasks in developing the coupled operation strategy: (1) developing a control algorithm that couples thermal condition profiles and thermal preferences; (2) characterizing robustly thermal conditions under different operation conditions; and (3) optimizing the division of subzones considering how well the thermal condition profile matches occupants’ thermal preferences. The coupled operation strategy will be validated in our unique environmental chamber which conveniently allows for experiments with offices and classrooms with different modes of air distribution (e.g., stratum ventilation and displacement ventilation). A set of guidelines will be compiled for the application of this coupled operation strategy for thermal comfort and energy saving.