AHUs
Overview
The ahu tag is used model air handling equipment designed to heat or cool air. In Project Haystack, packaged rooftop units are considered a special class of AHU. Packaged units use the ahu tag, but should also specify the rooftop tag:
ahu // any type of air handler unit (built-up or RTU) ahu and rooftop // only packaged rooftop units (RTUs) ahu and not rooftop // only built-up custom AHUs
Tags
AHUs should always be marked as ahu and equip. The following tags are also used:
hvac: always specified to mark as an HVAC assetrooftop: if the AHU is a packaged rooftop unit (RTU)mau: if the AHU is a makeup air unitchilledWaterPlantRef: reference plant supplying chilled waterhotWaterPlantRef: reference plant supplying hot watersteamPlantRef: reference plant supplying steam
Heating and Cooling Method
AHUs should define their heating method using one of the following tags:
Cooling method should be defined using one of the following tags:
Constant vs Variable Volume
An AHU should be tagged as either constantVolume or variableVolume based on its ability to adjust the volume of air flow. Typically this distinction is based on whether the AHU's fan is single speed or a VFD.
Zone Delivery
The following tags define the system used to deliver air to the zones:
directZone: AHU supplies air directly to the zonevavZone: AHU supplies air to VAV terminal unitschilledBeamZone: AHU supplies air to chilled beam terminal unitsmultiZone: air is split into a duct per zone
A Variable Volume Temperature or VVT system is defined as a constant volume AHU with VAV terminal units. This is indicated by the presence of both the constantVolume and vavZone tags.
Ductwork
In multi-duct systems, the AHU discharges into multiple ducts for simultaneous cooling, heating, or neutral air:
singleDuct: AHU uses a single ductdualDuct: the AHU discharges to two ducts which is some combination ofhotDeck,coldDeck, orneutralDecktripleDuct: the AHU discharges into three ducts which are thehotDeck,coldDeck, andneutralDeck
Sections
Most points in an AHU are associated with one of the following sections of the unit:
discharge: air exiting the unit to be supplied to the zones/terminal unitsreturn: air returning from the zone back into the unitoutside: fresh, outside air entering the unit for air quality and economizingexhaust: air exiting the unit back outsidemixed: return and outside air mixed together before passing through the heating/cooling elementscool: cooling elements/coilsheat: heating elements/coilszone: conditioned space associated with the unit
The follow diagram shows the logical flow of air through an AHU:
Points
The following lists points commonly used with an AHU:
Discharge
dischargeairtempsensordischargeairhumiditysensordischargeairpressuresensordischargeairflowsensordischargeairfancmddischargeairfansensor
Return
returnairtempsensorreturnairhumiditysensorreturnairpressuresensorreturnairflowsensorreturnairco2sensorreturnairfancmdreturnairdampercmd
Mixed
Outside
outsideairtempsensoroutsideairhumiditysensoroutsideairpressuresensoroutsideairflowsensoroutsideairflowspoutsideairdampercmd
Exhaust
Conditioning
Misc
Zone (see zone points):