Center for the Built Environment

Large amounts of energy are consumed by air-conditioning systems to maintain tight control of air temperature in rooms--a narrow range of temperature excursion from neutral, and a uniform temperature in the ambient space. However, both field and lab studies are showing that neither narrow range nor uniformity is really necessary for providing occupant comfort. Data from several large field studies shows occupants accepting a much wider temperature range than is typically applied in practice (Arens 2009). In addition, if occupants have access to a personal environmental control (PEC) system, the acceptable ambient temperature range can be further extended, to as much as 18-30ºC (Zhang H 2009, Amai 2005, Zhang Y 2008). By targeting specific body parts, PEC systems produce equivalent comfort using much less energy than is needed to condition the entire ambient space.

Energy is also required consumed in fans and mixing diffusers to produce uniform room temperature conditions. To assure complete mixing, diffuser manufacturers specify minimum supply volumes that are as high as 50% of maximum volume. Some engineers have been successfully operating buildings well below these volume minima, and research is now underway to quantify the acceptability of their non-uniform environments to their occupants. Substantial fan energy savings are possible, and recent changes to energy standards (ASHRAE 2009) have begun to require a lower minimum.

This paper simulates the energy savings possible from through these two approaches to providing comfort in less tightly controlled spaces. Their savings are substantial and justify looking into how they might be incorporated into building design and operation.