Local heating and cooling effectiveness - an evaluation method based on calculated local and overall thermal state

Abstract

The application of Personal Comfort Systems (PCS) in the buildings demonstrated their potential to improve thermal comfort and reduce energy use by the space conditioning HVAC systems. With its personal controllability (on-demand) PCS is a practical solution to tackle the diversity in perceiving thermal comfort between occupants. The differences in thermal perception can be due to several physiological and psychological factors, such as metabolic rate, acclimatization, body composition, gender, and age. In addition to the primary purpose of improving individual thermal comfort, it allows for a wider set point temperature of the HVAC system conditioning the overall space, which may lead to an extensive reduction in energy use. Several PCS device options have already evolved, but incorporating these devices into building conditioning faces lots of restrictions. The PCSs are categorized between movable, portable, and fixed devices, and PCS devices can function with different means of heat exchange. In this study, the capability of local heating and cooling to correct the individual's thermal state toward thermal neutrality when the rest of the body is exposed to cold or heat was evaluated. For this purpose, a detailed physiology model was applied to evaluate the impact of the nonuniform environment from PCS on local skin, heat flux, and thermal comfort. Different locations of the human body (head, hands, feet, legs, thighs, back, and pelvis) have been tested since the heat exchanged at local body parts differs in its effectiveness in improving the overall thermal state. Different temperature relaxations have been tested with a base cooling setpoint of 25°C and heating of 24°C operative temperature. Multiple simulations have been conducted to account for multiple local environmental settings. In this study, we have evaluated the influence of local heating and cooling of different body parts on correcting the whole-body thermal state toward thermal neutrality. Results showed that the thigh could be a promising prominent body part for both cooling and heating, followed by the hands and feet, which are good responders to local heating. The percentage of correction toward thermal neutrality varies with background temperature and local heating or cooling power, and can range from 50–80% for hands and feet to 60–100% for the thigh.