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Kind: Marker
Used With: equip, rooftop

Air Handler Unit which heats and/or cools air.

From: AHUs


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


AHUs should always be marked as ahu and equip. The following tags are also used:

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:

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.


In multi-duct systems, the AHU discharges into multiple ducts for simultaneous cooling, heating, or neutral air:


Most points in an AHU are associated with one of the following sections of the unit:

The follow diagram shows the logical flow of air through an AHU:



The following lists points commonly used with an AHU:








Zone (see zone points):

active ahuRef