Thermal Comfort and Cognitive Performance Under Peak Demand Air-conditioning Management Strategies

Abstract

This research focuses on university students’ thermal comfort and cognitive performance during direct load control (DLC) events in summer heat-waves. The specific indoor thermal environments resulting from three off cycle fractions, two cycling periods, two cooling setpoint temperatures, two different building envelope thermal performance conditions, and two ventilation rates were simulated within an EnergyPlus model of a university lecture theatre located in Sydney. Eight representative cases were selected from 48 simulations for examination using human subjects in a climate chamber. Fifty-six subjects in two separate experiments were exposed to three DLC conditions and one control condition. During the experimental periods, thermal comfort surveys and online cognitive performance tests were completed by the subjects. All the eight conditions yielded an average thermal acceptability of higher than the normative 80% limit. Subjects’ thermal comfort zone during DLC events was wider than predicted by ASHRAE’s PMV/PPD model. ASHRAE 55-2013 is overly conservative in defining the limits for temperature cycles, ramps and drifts. Analysis of cognitive performance tests confirmed that simpler cognitive tasks are less susceptible to temperature effects than more complex ones. In contrast with the prevailing belief about a single optimum temperature or thermal sensation for maximum performance, the present results indicated that the effects of thermal variations followed an extended-U relationship, with cognitive performance being stable across a relatively broad range of indoor temperatures. Results from this study reveal that as long as the DLC algorithms are judiciously designed and tailored to the specific building physics and occupancy conditions, DLC events can be readily accepted by university students without incurring thermal discomfort or performance decrements.