Using thermostats for indoor climate control in offices: The effect on thermal comfort and heating/cooling energy use

Abstract

The most commonly used thermostat control variable in heating, ventilating and air-conditioning systems is air temperature. However, people's thermal comfort responds to operative temperature more directly than air temperature. Will the adoption of operative temperature based control lead to better thermal comfort and how will this affect the energy use? To get a better understanding about these questions, simulations have been performed based on three heating and cooling systems in three different geographical locations (Copenhagen, Denmark, Paris, France and Rome, Italy). The three systems are fan-coil system representing convective system and two radiant systems: floor heating/cooling system and radiant ceiling heating/cooling panel system.The results show that air temperature based thermostat control and operative temperature based thermostat control had different impacts on fan-coil system and radiant systems. For fan-coil system, the use of operative temperature based thermostat control had better thermal comfort conditions and higher energy use than that of air temperature based thermostat control. For the two radiant systems, the results were the opposite. The results were almost the same in different locations. Besides, the thermal comfort difference between the two controls of north office was smaller than that of south office. For fan-coil system, in south office, compared with air temperature based thermostat control, the hours of Cat. I (−0.2≤PMV≤0.2) increased 8.3% for building in Copenhagen, 8.8% for Paris and 14.2% for Rome and hours of Cat. IV (PMV<−0.7 or PMV>0.7) decreased 2.5%, 3.9% and 7.1%, respectively, when operative temperature based thermostat control was used. Meanwhile, total energy supply increased 13.7% in Copenhagen, 14.3% in Paris and 12.7% in Rome. For radiant systems, the total energy use reduced 3.3% to 8.3% depending on location and type of system when operative temperature based control was used. With this reduction of energy use, PMV index in south office was still within the range of ±0.7 in most cases, which satisfied the thermal comfort requirement of Cat. III (−0.7≤PMV≤0.7) of EN 15251. Based on the results, it is suggested that air temperature based thermostat control be used in fan-coil system and operative temperature based thermostat control be used in radiant system in north office. For south office, operative temperature based thermostat control was considered better for fan-coil system and could be more energy efficient when used in radiant heating and cooling systems.