Center for the Built Environment

When building occupants become sufficiently hot or cold and have exhausted all coping behaviors available to alleviate their discomfort, they often complain to the facility manager. These complaint events trigger maintenance service calls. This paper focuses on predicting the frequency of hot and cold complaint events so that control policies and decisions that affect both energy utilization and comfort-related service calls can be formulated. A mathematical model of the mean frequency of hot and cold complaint events in buildings is developed that is based on the level-crossing theory of stochastic processes. The model quantitatively relates the statistical behavior and performance of the temperature control system to the mean complaint frequency. When combined with the labor rate and with estimates of the mean time to respond to complaints, the model becomes an estimate of the mean cost of service calls resulting from hot and cold complaints. Data from a commercial facility are used to determine parameters of the model. The relationship between this model and the Predicted Percent Dissatisfied (PPD) model is discussed. The economic consequences of operating buildings at the limits of the ASHRAE comfort range are illustrated. Examples illustrate how the model may be used to optimize the operational performance of buildings by balancing the energy-saving benefits of uncomfortable conditions with the cost of service calls caused by complaints arising from uncomfortable conditions, and for the cost-benefit analysis of retrofits.