Note: Flat vs. Nested

Diagrams on this page are presented in both a flat and nested structure. Use the toggle in the top right to switch between the two.
A nested structure is the way forward for the modelling of building equipment, however as many systems still use flat representations both option are presented here for ease.

VAVs

The following diagrams divide VAVs into six key types. It is contended by the author that all VAVs can be entirely defined as one of these key types.
  • Type 1: Single duct
  • Type 2: Single duct with reheat
  • Type 3: Dual duct
  • Type 4: Series (fan powered)
  • Type 5: Parallel (fan powered)
  • Type 6: Bypass
Each diagram shows the core points that are useful to model an instance of the VAV type and deploy meaningful analytics. There are typically many more points exposed by a VAV controller - for a full list of points that are typically found for each type please see the full points guide section of this site.

Single Duct

VAV comprises of a single inlet duct with damper.

Single Duct with Reheat

VAV comprises of a single inlet duct with damper and reheat components - electric or HHW.

Electric Reheat

HHW Reheat

Dual Duct

VAV comprises of two inlet ducts with a damper per inlet.

Fan Powered: Series

VAV comprises of an inlet duct with damper, a 'return' or 'induced' air opening/duct, a fan, damper, and reheat components - electric or HHW. The fan is inline (in series) with the discharge air flow and must run for the VAV to deliver air to the zone.

Electric Reheat

HHW Reheat

Fan Powered: Parallel

VAV comprises of an inlet duct with damper, a 'return' or 'induced' air opening/duct with fan (and backdraft damper), and reheat components - electric or HHW. The fan in not inline (parallel) with the discharge air flow and typically only runs when heating is required - either independently or to supplement the primary air flow.

Electric Reheat

HHW Reheat

Bypass

VAV comprises of an inlet duct, two outlet ducts - one to supply the zone and one to exhaust unwanted air into the plenum, and a bypass damper (which controls the bypass/discharge split).