Impacts of Static Pressure Set Level on the HVAC Energy Consumption and Indoor Conditions

Air static pressure must be maintained at a certain level leaving the air-handing unit (AHU) to force a suitable amount of air through the terminal boxes. However, an excessive static pressure level is often used due to ( 1 ) lack of a control device in a constant volume system (CV); (2) malfunctioning control device in a variable volume (VAV) system; and (3) fear of failure to maintain room temperature. High static pressure often develops excessive damper leakage in older mixing boxes. This results in an inappropriate mixing of hot and cold air and an excessive amount of air entering the space. Consequently, the actual fan power, heating and cooling energy consumption all become significantly higher than the design values. Even worse, the system may not be able to maintain room conditions due to unwanted simultaneous heating and cooling, and may be noisy due to the excessive static pressure. This paper proposes to control the hot duct pressure and the Variable Frequency Drives ( VFD's) to control the fan static i.e. the cold duct pressure. Both a theoretical analysis and a case study results are presented in this paper