Human Thermal Comfort and Indoor Air Quality

This chapter deals with numerous important issues pertinent to designing indoor air environments conducive to human comfort and health. These are largely based on the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Comfort Standard 55-2013 and the ASHRAE Ventilation Standard 62.1-2013. Environmental parameters such as temperature, humidity, and wind speed that are critical in maintaining thermal comfort are presented. We introduce the concepts of clothing level insulation (clo) and metabolic rate (met) and discuss their effect on indoor human comfort characterized by the predicted mean vote (PMV) and percentage of people dissatisfied (PPD). The ASHRAE comfort chart is then introduced, and pertinent correlations that allow extrapolations to other environmental conditions are presented and illustrated by way of solved examples. We then describe basic concepts of air quality and commonly found indoor pollutants and their threshold limits. Next, we discuss the role of outdoor ventilation air in controlling the indoor air quality (IAQ) and widely accepted design procedures to determine the necessary outdoor ventilation amounts for different building types and occupancy densities are presented. The effects of short-circuiting of the supply air within the room, the role of filters, and the impact of recycling some of the return air on IAQ are also discussed. Finally, we present a few pertinent studies that deal with the increase in unsolicited complaints (and their financial penalties on operations and maintenance), the reduction in worker productivity, and the increase in sickness and absenteeism if the right indoor environment is not maintained.