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). Specific zone control energy conservation modifications will vary by HVAC system type and the specific needs and capabilities of each facility. 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

• During periods of no heating and cooling, VAV boxes must still deliver air to the zones in order to provide ventilation air for the occupants. For commercial office buildings, this airflow rate, the “minimum airflow”, is almost always a fraction of the peak airflow rate required during peak cooling periods. Oftentimes these minimum airflow rates are set higher than needed – a common strategy is to set the minimum at 50% of the maximum, even though less than 50% of maximum airflow is required for ventilation. Energy savings can be realized by lowering the minimum airflow rate to a level that still provides adequate ventilation air for the occupants, but will result in reduced fan and reheat energy used by the system.
• The minimum airflow rates should be calculated for each zone, since each zone will have different requirements.
• Lowering the VAV box minimum flow setpoints mostly involves TAB (testing, adjusting and balancing) work. If a system already has direct digital control at the distribution level, the minimum flow setpoints can be lowered at the main operator workstation.

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