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AHUs
Overview
We define a wide range of equipment for air handling including:
ahu
: air handling unitdoas
: dedicated outside air systemmau
: makeup air unitrtu
: roof top unitfcu
: fan coil unitcrac
: computer room air conditionerunitVent
: unit ventilatorheatPump
: heat pump
All of these equipment types follow the same fundamental modeling techniques and subtype from airHandlingEquip
.
Choices
AHUs define a suite of choices that should be made on a per instance basis.
Heating Process
If the AHU provides heating, then it should add one of the following heatingProcess
choices:
Or if the unit does not provide heating, then add the coolingOnly
tag.
When applicable the heating choice marker should also be paired with the appropriate flow ref tag. For example if an AHU uses hot water heating, then the AHU should also define the hotWaterRef
tag to refer to its hot water plant.
Cooling Process
If the AHU provides cooling, then it should add one of the following coolingProcess
choices:
Or if the unit does not provide cooling, then add the heatingOnly
tag.
If using chilled water, then the chilledWaterRef
should be defined to reference the chilled water plant.
Air Volume Adjustability
One of the following airVolumeAdjustability
markers should be defined:
This choice models the AHU's 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
One of the following ahuZoneDelivery
choices should be defined to model how the AHU delivers conditioned air to the zone:
vavZone
: AHU supplies air to VAV terminal unitsdirectZone
: AHU supplies air directly to the zonechilledBeamZone
: 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 constantAirVolume
and vavZone
tags.
Ductwork
One of the following ductConfig
markers should be defined:
singleDuct
: AHU uses a single ductdualDuct
: the AHU discharges to two ducts, which is some combination ofhotDeck
,coldDeck
, orneutralDeck
tripleDuct
: the AHU discharges into three ducts, which are thehotDeck
,coldDeck
, andneutralDeck
Sections
Most points in an AHU are associated with one of the following ductSection
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
If the AHU has one duct used for both fresh air and economizing then use the outside
tag. If there are two dedicated ducts, then use the ventilation
and economizing
tags for the respective ducts.
The follow diagram shows the AHU sections and logical flow of air:
Examples
The following are examples of fully tagged AHUs:
// Built up AHU supplied by central plants with VAV zones id: @abc dis: "AHU" ahu equip hotWaterHeating chilledWaterCooling vavZone singleDuct siteRef: @xyz // Rooftop unit direct to zones id: @abc dis: "RTU-2" rtu ahu equip elecHeating dxCooling constantAirVolume directZone singleDuct siteRef: @xyz