Evaluation of a hybrid personal cooling system using a manikin operated in constant temperature mode and thermoregulatory model control mode in warm conditions

In this study, the cooling effect of a portable hybrid personal cooling system (PCS) was investigated on a sweating manikin operated in the constant temperature (CT) mode and the thermoregulatory model control (TMC) mode. Both dry (i.e., no sweating) and wet manikin tests (i.e., sweating) were performed in the CT mode in a warm condition (30℃, 47% relative humidity (RH), air velocity v a = 0.4 m/s). For the TMC mode, two case studies were simulated: light work condition (30℃, 47% RH, air velocity v a = 0.15 m/s, duration: 60 min, metabolic rate: 1.5 METs) and construction work condition (30℃, 47% RH, v a = 1.0 m/s, 40 min exercise [5.5 METs] and 20 min rest [1.2 METs]). Four test scenarios were selected: fans off with no phase change materials (PCMs) (i.e., Fan-off, the Control), fans on with no PCMs (i.e., Fan-on), fans off with fully solidified PCMs (i.e., PCM+Fan-off) and fans on with fully solidified PCMs (i.e., PCM+Fan-on). Under the dry condition, the cooling rate in PCM+Fan-off during the initial stage (e.g., 55 and 50 W for the first 15 min and 20 min, respectively) was higher than that in Fan-on (i.e., 45 ± 1 W); under the wet condition, the cooling rate in PCM+Fan-off (e.g., 45 W for 10 min) was much lower than that in Fan-on (i.e., 282 ± 1 W). The hybrid PCS (i.e., PCM+Fan-on) provided a continuous strong cooling effect. Simulation results indicated that ventilation fans or PCMs alone could provide sufficient cooling while doing light work. For the intensive work condition, the PCS in all three scenarios (i.e., PCM+Fan-off, Fan-on and PCM+Fan-on) exhibited beneficial cooling, and the hybrid PCS showed an optimized performance in alleviating heat strain during both exercise and recovery periods. It was thus concluded that the PCS could effectively remove body heat in warm conditions for moderate intensive activities.