Abstract

Thermal comfort standards, such as ASHRAE Standard 55, prescribe a thermal comfort zone based on operative temperature, which includes both dry-bulb temperature and mean radiant temperature in the calculation. However, the built environment, regulated by a dry-bulb temperature based thermostat, will quite often maintain a space outside of its thermal comfort zone. The problem is more pronounced in a space open to a large window surface when the influence of the mean radiant temperature is not considered. The objective of the research is to develop control strategies that can maintain the space within the thermal comfort zone and offer energy savings.
The work is based on energy modeling and simulation of the five thermal zones (core, south, east, north, and west) of a prototypical small office building for four different climate zones (represented by Miami, San Diego, New York, and Montreal) under the influence of various window sizes (ranging from window-to-wall ratios of 10% to 80%). EnergyPlus software is used to simulate indoor environmental conditions and calculate the energy demand to maintain such conditions. Fanger's Predicted Mean Vote (PMV) model is used to estimate occupants’ thermal sensations in the space operated under the control of conventional dry-bulb thermostats. A performance indicator is developed to facilitate the calculation of new thermostat setpoints (and subsequent development of control strategies) that could ensure the space is maintained within the thermal comfort zone and operated with some energy savings for all occupied hours.
Simulation results reveal a monotonic correlation between window size and the number of hours outside of the thermal comfort zone. The proposed control strategies are not only able to maintain the space within the thermal comfort zone and offer energy savings but also can be implemented with no modification to existing HVAC equipment or building fabric.