# Design of Liquid-Air Hybrid Cooling Garment and Its Effect on Local Thermal Comfort
## 1 Introduction
The most important thing is that the ventilation device embedded in the clothing can greatly increase the convection heat dissipation [14; 15; 16]. Over the years, many scholars have studied the ventilation efficiency and cooling performance of ventilation clothing. The effects of body movement and wind speed [17], garment design [18], fabric properties, and body posture [19] on the ventilation rate of garments have been investigated using tracer gas methods. Numerous studies [20; 21; 22; 23] have studied the cooling effect of ventilation clothing under forced ventilation in different environments and different motion states. [PERSON] et al. [24] designed a ventilation jacket, and the cooling effect was examined using a thermal manikin. The results showed that significant increases in dry heat losses (through convection) were brought for the trunk thermal zones, of which the percent changes greatly exceeded 100% for the thermal zones close to the fans. The air ventilation determined significant decreases in the total thermal insulation (IT) values (up to 35%) compared with the fans-off condition, confirming and quantifying the cooling effect of the ventilation jacket. Apart from these research studies, many studies have performed subject trials to study the cooling effect of air ventilation garments. [PERSON] et al. [25] showed that subjects wearing a ventilated garment over a soldier's combat uniform had significantly reduced heat stress. [PERSON] et al. [26; 27] studied the effect of wearing ventilated clothing on thermal comfort for outdoor workers in Hong Kong during the summer and showed that subjects experienced a significant reduction in heat stress. [PERSON] [28] used a fan-cooled garment to test its cooling effect on athletes after exercise, confirming that air-cooled clothing can effectively alleviate heat stress and discomfort during and after exercise in a humid and hot environment. [PERSON] et al. [28] showed that the using of fan-cooled clothing while walking under compensable heat stress was effective in attenuating increases in core temperature, skin temperature, and heat rate compared with no cooling, but [PERSON] et al. [29] showed that when the air temperature exceeds the skin temperature, the cooling effect provided by the ventilated garment may not be sufficient to dissipate the excess body heat. [PERSON] et al. [30] designed a personal cooling system (HPCS) by combining a phase change material (PCM) with an electric fan. Results demonstrated that the control of electric fans could suppress the mean skin temperature rise to 34.0 \({}^{\circ}\)C by over 15 min. Although there are some differences in the cooling methods of various types of cooling garments, most of them aim to reduce the skin temperature of the microclimate zone. In previous studies, some scholars have put the cooling source in direct contact with the surface of the human body. Although this cooling method can significantly improve the cooling effect, it tends to cause local hypothermia [31]. In addition, the cooling source in some cooling garments can cause mobility inconveniences to the wearer due to its excessive size [12]. Furthermore, from the aforementioned studies, it can be concluded that both liquid cooling and air ventilation cooling had a good application point, but the use of both cooling methods in one garment was quite few. Therefore, in this study, hybrid cooling garments using both liquid and air cooling were designed and made. The cooling garments combined both liquid cooling and air ventilation cooling. They were aluminum tube combined with fan cooling (AAL), silicone tube combined with fan cooling (SAL), silicone tube with inner yarn fabric combined with fan cooling (YAL), and a control garment without a cooling source (CON). This study was conducted by human trials, in which a summer indoor working environment with an ambient temperature of 32 \({}^{\circ}\)C and relative humidity of 50% was set in the climate chamber, and the subjects simulated a sedentary working condition for 45 min and rest for 20 min.