Energy efficiency of occupant controlled heating, ventilating and air conditioning systems for office buildings.

Occupant controlled HVAC systems offer inhabitants of open office spaces some degree of control over their immediate microclimate typically by control of air supplied at floor or desk top level. Productivity gains have been attributed to these systems but it is unclear whether these systems will use less energy than conventional HV AC systems. It is also not clear what the controlling parameters will be. To study energy consumption, a simplified model of the thermal environment was created for an occupant controlled system. Th.is model was combined with a model of the central HV AC plant and ambient weather conditions to simulate the annual energy usage for several climates. The HVAC control behavior of the occupants (e.g. comfort preferences) and the occupancy of each work station in the space were modeled as random processes. Factors affecting energy use are identified with this model. Typical occupant controlled systems are shown to offer HVAC savings of 5-16% depending on climate. Savings are achieved by occupancy sensors, properly selected plant and local supply temperatures, reduced cool air supply requirements due to thermal stratification, and reduced conditioning in areas which do not contain a workstation. The influence of occupant behavior, minimum temperature limits, local fan design and task lighting on energy savings is presented.