Numerical Analysis to Understand Influence of Ventilation Systems on Thermal Comfort Parameters, Quality of Air, and Local Sweating

Abstract

The body’s heat exchange mechanisms include sensible heat transfer at the skin surface (also called “Dry Heat exchange”) due to temperature differences (via conduction, convection, and radiation (long-wave and short-wave)), latent heat transfer (via moisture evaporating and diffusing through the skin, and through sweat evaporation on the surface), and sensible plus latent exchange via respiration from the lungs as the breathing process involves humidifying exhaled air with around 34◦C in normal resting person with more or less constant core temperature at 36◦C. It is important to predict comfort temperature in a built environment because the thermal comfort model has great potential for energy saving as well maintain a good well-being both at home and workplace and provide building sustainability. Hence, local sensation and local phenomenon (temperature gradients and velocity distribution) are gaining more popularity as CFD has become a very reliable and easy tool for in-depth analysis. Understanding this phenomenon is very crucial in understanding the adaptive thermal comfort. One of the most important physics that had been ignored for a long period of time which influences the thermal comfort of the occupant i.e., actual sweat analysis (modelling sweat as droplet or layered) based on local conditions. These local conditions are highly influenced by mechanical ventilation systems like using of fans and ac vents. Also, the quality of air determines the health and productivity of the occupant in any indoor environment. The higher concentration of carbon-dioxide causes dizziness, headache, and potential death in case it reaches a hazardous level. Similarly, air exchange from the outdoor to the indoor environment is necessary to remove bacteria, and viruses and to maintain fresh air for healthy breathing. The energy consumption in indoor environments is directly dependent on the ventilation systems that are used to maintain supposed Comfort Temperature and Air Quality. In this research, various ventilation methods are applied in indoor environments including Car Cabins, Conference Rooms, and Office Cubicles which are simulated in ANSYS CFX and FLUENT software using the κω-SST model.The use of a combination of a fan and ac vent or a fan with windows is found to be better in saving energy, maintaining air quality as well as keeping the temperature of the skin low. The Sweat is modelled as a combination of water (99 per cent) and NaCl (1 per cent) on a 1 cm X 1 cm area of skin surface to understand the effect of sweating on the skin temperature due to local conditions around the skin. Fans and AC vents are modelled in indoor environments to comprehend the influence of mechanical systems. This thesis aims to provide insights into the role of local conditions (velocity and temperature of the air) around the skin in determining the local skin temperature and the influence of mechanical ventilation systems on the quality of air as well. The concept presented in this paper has the potential to improve the popular thermoregulation models like FIALA, TANABE, and UCB or at least provide some idea about the possible incorporation of the sweating phenomenon considering the local environment to enhance their functionality. Likewise, the research aims to encourage further combined study on air quality and thermal comfort for energy efficient and safe design of indoor environment.