Single-Duct Constant Air Volume System Supply Air Temperature Reset: Using Return Air Temperature or Outside Air Temperature?

摘要

The supply air temperature set point for a singleductconstant air volume air handling unit (AHU)system is often reset based on either return airtemperature or outside air temperature in order toreduce simultaneous cooling and heating energyconsumption. Both reset strategies make engineeringsense as long as the reset schedules are reasonable.Quite often the decision to use one over the other ismade with the assumption that they will all achievesome sorts of energy savings. However, the impact ofthese two strategies on AHU energy consumptioncould be very different. A comparison of these twocommonly used supply air temperature resetstrategies for a single-duct constant air volumesystem is presented in this paper. It is shown thatfrom either the building energy consumption orbuilding comfort point of view, the reset strategybased on outside air temperature is inherently betterthan that based on return air temperature. Significantamount of heating energy savings can be achieved byswitching from return air temperature based reset tooutside air temperature based reset. The reset strategycan also benefit variable air volume (VAV) AHUs.An improved supply air temperature set point resetcontrol strategy is proposed by combining andstaging the outside air and return air temperaturebased resets.