Caution note when using DOAS systems - you cannot simply define the OA volume in the flow parameters tab of the DOAS fan.

In DOE-2.3, there is now a system type 'DOAS' that will properly provide outdoor air either directly to zones or to the mixing section of the system it serves. The volume of outdoor air delivered by this system is determined by the outdoor air flow rates of the zones that take air from this system. The screenshot below suggests that the unit will be delivering 6,545 cfm of OA but in fact this system was only delivering 500 cfm as the served zones did not have their OA volumes set properly.

[cid:image003.jpg at 01D509B3.D8F50570]

When the OA was defined in the zones taking air from this system, the volume of OA in the DOAS was as expected.

Today's lesson - define outdoor air rates properly, and hourly reports are your friend.

Footprint

Brian Fountain P.Eng., LEED AP BD+C, BEMP
Associate
Brian.Fountain at sa-footprint.com

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