Modelling a fixed minimum air flow rate on AHUs/VAVs

In large buildings with central air handling unit systems, it's common to have an effective minimum air flow rate that exceeds zero. A typical minimum zone air terminal flow rate is 40% of its maximum. It's considered good practice to aim for a 30% turndown, as this significantly reduces central plant energy consumption. This adjustment will have observable effects on annual fan energy consumption and supply airflow rates in the Design Day HVAC Nodes reports.

To model a 30% minimum airflow in an air handling unit system for each applicable Space, go to 'Space Sizing', select 'Cooling Supply Air', and adjust the 'Cooling Min. Air Flow Fraction' to 30%. Next, on the 'HVAC Schematic', select each applicable 'VAV Terminal. Go to 'Air Terminal Settings', then 'Sizing', and adjust the 'Constant Min. Air Flow Fraction' to 30%. Lastly, On the 'HVAC Schematic', select each applicable 'AHU Unit'. Go to 'Air Handling Unit Settings', then 'Setpoint Manager Settings', and adjust the 'Min. Turndown Ratio' to 30%.