Computational fluid dynamics analysis of convective heat transfer coefficients for a sleeping human body

Task/ambient air conditioning (TAC) systems have been introduced to solve the problem of thermal comfort in bedrooms during night. The key point of this problem is the thermal environment or heat transfer between a sleeping human body and the surrounding environment. Therefore, a numerical study on the convective heat transfer between a thermal manikin and the surrounding environment was carried out in a bedroom equipped with a TAC system. Firstly, the influence of supply conditions on indoor environment was investigated. Based on this section and previous studies on the convective heat transfer coefficients (hconv) between the human body and surrounding environment, equations depending on temperature difference between the thermal manikin and the environment or the air velocity in the surrounding environment were respectively established. Considering the effects of temperature difference and air velocity on the hconv, the equations were modified to be a function of both temperature difference and air velocity. The further analysis of the new equation indicated that this modified equation can tackle with variations of both temperature difference and air velocity, and can also give a good prediction. Besides, the hconv distributions on the 16 body segments were presented. Higher hconv values can be obviously found at body segments of heat, neck, hand and trunk. Due to the importance of clothes to thermal comfort level, the influence of coverage (blanket) was studied. When the thermal manikin was covered with blanket, the hconv values were about 0.5-1.0 W/(m2 K) higher than the naked ones and the temperature differences were much lower than the naked ones.