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

Abstract

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 °C) and four levels of environmental RH at two ambient temperatures of 36 and 40 °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 °C), HPCS presented good cooling performance with the maximum core temperature at around 37.5 °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 °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.

Personal Wearable Thermal and Moisture Management Clothing: A Review on Its Recent Trends and Performance Evaluation Methods

“…Hybrid-cooling wearable clothing is specifically engineered to optimize the benefits of various cooling techniques to achieve a superior cooling efficiency [22]. Figure 9 demonstrates a hybrid-cooling wearable clothing that combines microfans and PCM to improve cooling efficiency while addressing the drawbacks of air-cooling and phase change-cooling clothing [66]. Wang et al [25] designed a suit based on dry ice and ventilated fans, utilizing the sublimation of dry ice to reduce the wearer's load and reinforce air circulation to effectively alleviate thermal discomfort in mascot actors.…”

Advanced materials for personal thermal and moisture management of health care workers wearing PPE

“…Although the air permeability of PCM textiles can be improved, in the hot environment [ 225 ] [ 226 ], moisture condensation and sweat accumulation may occur on the surface of PCM garments due to the high microclimate RH inside PPE as a result of continuous sweat production and relatively low surface temperature of PCM. This may counteract the cooling effect and undermine thermal comfort.…”

Application of Combined Micro- and Macro-Scale Models to Investigate Heat and Mass Transfer through Textile Structures with Additional Ventilation

“…The velocity, temperature, and heat fluxes were found to vary significantly along the microclimate thickness, highlighting the limitations of space-average approaches [21]. Hybrid personal cooling systems (HPCS) incorporated with ventilation fans and phase change materials (PCMs) have been studied by Xu et al [22]. Siddiqui and Sun [23,24] developed finite element models that allow the prediction of the effective thermal conductivity of plain weft knitted fabric, MicroPCM-coated cotton, wool, and Nomex composite fabrics.…”