Understanding occupant behaviour: The use of controls in mixed-mode office buildings

A mixed-mode building is heated in winter, free running in mid-season, and has cooling available in summer as required. It is likely to use less energy than a fully air-conditioned building. However, the energy consumption of a mixed-mode building depends greatly upon how the occupants use the available controls, such as windows, fans, heating, and cooling. Hitherto, for the purpose of building thermal simulation, rather arbitrary assumptions have often been made about occupant behaviour. Using thermal comfort field data sets from Europe and Pakistan that include mixed-mode buildings, the occupant behaviour with regard to the building controls is analysed. The results indicate that the mixed-mode buildings were generally controlled as if they had been naturally ventilated buildings, but with the provision for cooling if needed, rather than as normal air-conditioned buildings. Equations are developed to relate the probability of using the various controls to the indoor and outdoor temperature, and to relate the indoor comfort temperatures to the outdoor temperature. Such equations may be useful for estimating comfort and energy use.