VAVs – Project Haystack

VAVs

OverviewChoicesSectionsExamples

Overview

The vav tag is used to model variable air volume terminal units. VAVs are supplied conditioned air from an AHU and use a damper to modulate the air flow to the zone. Typically VAVs are supplied cool air at a temperature of around 55°F (13°C). Some VAVs support reheat which allow them to heat this cool air to a warmer temperature.

A VAV without reheat must define the coolingOnly tag, otherwise it must must define one of the heating process tags. Some reheat VAVs contain a fan in which case they should also define the fanPowered tag.

VAVs should define the airRef tag to reference their supply AHU. When there are multiple supply AHUs, then the airRef tag should be a list of all the upstream AHUs.

Choices

AHUs define a suite of choices which should be made on a per instance basis.

Heating Process

If the VAV provides reheat, then it should add one of the following heatingProcess choices:

Or if the VAV does not support reheat, then add the coolingOnly tag.

When applicable the heating choice marker should also be paired with the appropriate flow ref tag. For example if a VAV uses hot water for reheat, then it should also define the hotWaterRef tag to refer to its hot water plant.

Modulation

One of the following vavModulation markers should be defined:

vavAirCircuitType

If the VAV is fan powered, then one of the following vavAirCircuit markers should be defined:

Ductwork

One of the following ductConfig markers should be defined:

Sections

We associate points with sections of a VAV using these tags:

  • inlet: air entering the unit from the AHU
  • discharge: air exiting the unit to be supplied to the zones
  • zone: conditioned space associated with the unit

Since most points are not clearly associated with the inlet or discharge ducts, we typically omit a section tag for most points. However any points which would conflict with the zone points however must be qualified with either inlet or discharge.

Examples

The following are examples of fully tagged VAVs:

// Cooling only VAV
id: @vav
dis: "VAV-Example"
vav
equip
coolingOnly
pressureDependent
singleDuct
airRef: @ahu
siteRef: @site

// Fan powered VAV with hot water reheat
id: @vav
vav
equip
fanPowered
hotWaterHeating
pressureDependent
singleDuct
hotWaterRef: @hot-water-plant
airRef: @ahu
siteRef: @site