VAV Box Minimum and Maximum Airflow
The most and the least air a VAV box may deliver to a zone.
Example
You enter
- Zone sensible load (Btu/hr) 12000
- Supply-to-room deltaT (°F) 20
- Ventilation minimum (cfm, ASHRAE 62.1) 100
- Turndown fraction (default 0.30) 0.3
You get
- Maximum airflow 556 cfm
- Minimum airflow 166.7
Details, formula, and sources
Max = zone sensible / (1.08 x supply deltaT), min = max(ASHRAE 62.1 ventilation, turndown x max). 12,000 Btu/hr, 20 F, 100 CFM vent, 0.30 turndown -> 556 max, 167 min (turndown governs); a denser zone at 250 CFM vent is driven to 250 by fresh air. The box range and ventilation calc govern.
cfm_max = load / (1.08 x supply_dt); cfm_min = max(ventilation_cfm, turndown x cfm_max).
The VAV box maximum and minimum airflow from the zone load and the ASHRAE 62.1 ventilation minimum, by name.
The sensible-airflow maximum and the ventilation/turndown minimum are standard published VAV design relations.
Estimate. AHJ and licensed professional govern.
Field names used by the API: zone_sensible_btuh, supply_dt_f, ventilation_cfm, turndown, cfm_max, cfm_min
- Maximum cfm_max = load / (1.08 x supply deltaT)VAV design
- Minimum max(ASHRAE 62.1 ventilation, turndown x max)ASHRAE 62.1 / VAV practice
- Box range the manufacturer's controllable range governsscope of this tile