Room Temperature Control During Season Switchover with Single Duct Variable Air Volume System Without Reheat

Abstract

The Langford “A” building houses the College of Architecture on TAMU campus. There are ten singleduct variable air volume (VAV) air-handling units (AHUs) without reheat serving the building. The local pneumatic thermostats modulate the dampers of VAV boxes to maintain room temperature at their setpoints. The thermostat action is switched from direct acting (DA) to reverse acting (RA) when the season changes from fall to winter and vice versa from winter to spring, based on the out side air temperature, when season changes. This results in various parts of the building ether too cold or too hot during the season change. This paper presents that the thermostat action will be switched according to cooling loads or discharge air temperature, instead of outside air temperature. For the interior zone, thermostat action does not need to be switched at all. The comfort is improved and savings is achieved by the new control scheme. Because some air-handling units (AHUs) serve both interior and exterior zones, this system never worked as intended. The system must be modified to have zone reheat and the AHUs discharge air temperature is set below dew point for humidity control.