Description:

For HVAC systems with variable air volume (VAV) systems, reducing the zone supply airflow during periods of low cooling and heating load will result in measurable energy savings at the central equipment (e.g., boilers, chillers, air handlers). In addition, reducing or resetting the duct static pressure setpoint will also result in energy savings. Specific zone control energy conservation modifications will vary by HVAC system type and the specific needs and capabilities of each facility. In general, for centralized HVAC systems, it’s important to integrate the controls of both the central equipment and the distribution system for maximum energy efficiency and occupant comfort.

Special Considerations

• Lowering the VAV box minimum flow setpoints mostly involves TAB (testing, adjusting and balancing) work. If a system already has DDC control at the distribution level, the minimum flow setpoints can be lowered at the main operator workstation.
• Prior to lowering the duct static pressure setpoint or implementing an automatic reset strategy, it’s a good idea to verify the integrity of the duct system. Check to see if there is excessive leakage in the system. If a certain area has recurrent comfort complaints, check to see if there are obstructions in the ductwork (e.g., duct liner that has peeled away from the duct, closed fire dampers). Also check to see if there are an excessive number of duct elbows in the ductwork serving that area.
• VAV box damper position is a good input variable to use for resetting the duct static pressure setpoint: raise the setpoint if a certain number of dampers are 100% open, lower the setpoint if most of the dampers are less than 100% open.

Estimates for this measure come from the Department of Energy's Advanced Energy Retrofit Guide.