A Numerical Analysis of the Cooling Performance of a Hybrid Personal Cooling System (HPCS): Effects of Ambient Temperature and Relative Humidity

Hybrid personal cooling systems (HPCS) incorporated with ventilation fans and phase change materials (PCMs) have shown its superior capability for mitigating workers' heat strain while performing heavy labor work in hot environments. In a previous study, the effects of thermal resistance of insulation pads, and latent heat and melting temperature of PCMs on the HPCS's thermal performance have been investigated. In addition to the aforementioned factors, environmental conditions, i.e., ambient temperature and relative humidity, also significantly affect the thermal performance of the HPCS. In this paper, a numerical parametric study was performed to investigate the effects of the environmental temperature and relative humidity (RH) on the thermal management of the HPCS. Five levels of air temperature under RH = 50% (i.e., 32, 34, 36, 38 and 40 degrees C) and four levels of environmental RH at two ambient temperatures of 36 and 40 degrees C were selected (i.e., RH = 30, 50, 70 and 90%) for the numerical analysis. Results show that high environmental temperatures could accelerate the PCM melting process and thereby weaken the cooling performance of HPCS. In the moderately hot environment (36 degrees C), HPCS presented good cooling performance with the maximum core temperature at around 37.5 degrees C during excise when the ambient RH <= 70%, whereas good cooling performance could be only seen under RH <= 50% in the extremely hot environment (40 degrees C). Thus, it may be concluded that the maximum environmental RH under which the HPCS exhibiting good cooling performance decreases with an increase in the environmental temperature.