Center for the Built Environment

Over-cooling happens commonly in air-conditioned buildings that costs energy and results in discomfort complaints. There are many reasons causing overcooling, and HVAC engineers and researchers have proposed several approaches to prevent it from happening. In this paper, we describe a field study to show how the overcooling and energy use were significantly reduced by lowering maximum and minimum supply air flowrate setpoints, while providing personal comfort systems for occupants. The study was conducted over 16 months in two office spaces of a campus building with high HVAC energy expenditure and frequent cold complaints. The initial visit and measurements showed that the spaces were over-ventilated, causing cold discomfort in several workstations. We provided personal comfort systems to 26 occupants (heated/cooled chair, footwarmer, legwarmer based on occupants’ own choices) to maintain comfort, and gradually reduced the maximum and minimum supply air volume setpoints, to reduce the air-conditioning intensity and to let the office ambient temperature float. We increased occupants’ satisfaction rate from 56% to over 80%, meanwhile lowered HVAC zone energy use by 60% in heating and 40% in cooling.