[Equest-users] Setting DOAS system type airflow rates

[Bishop, Bill]

Thanks, Brian! You make an important point on design sizing of DOAS systems - the hourly ventilation rate is determined by the systems/zones that the DOAS serves, and the corresponding ventilation controls for those systems.
Some additional observations:

  *   If you enter the DOAS SUPPLY-FLOW (Design cfm):
     *   The design fan power will be based on the SUPPLY-FLOW multiplied by SUPPLY-KW/FLOW (if entered).
     *   Any central airhandler coils will be autosized based on the SUPPLY-FLOW. (See the SV-C report in the SIM file.)
  *   If instead, you let the DOAS SUPPLY-FLOW (Design cfm) default by leaving it blank:
     *   The design fan power will be based on the design ventilation rate determined by the served systems multiplied by SUPPLY-KW/FLOW (if entered).
     *   Any central airhandler coils will be autosized based on the design ventilation rate.
  *   If you enter zone ventilation as OA/FLOW-PER (cfm per person), to simulate DCV or to size the ventilation per ASHRAE 62.1 guidelines, the design ventilation rate will be based on the highest hourly value in the occupancy schedule. So you have to have at least one hour with 1.0 occupancy either in the weekday, weekend and/or CDD/HDD schedules. Otherwise, the design ventilation rate will be reduced.

~Bill

William Bishop, PE, BEMP, BEAP, CEM, LEED AP
Senior Energy Engineer

[Pathfinder-EA-logo-2]T: (585) 698-1956                        F: (585) 325-6005
bbishop at pathfinder-ea.com<mailto:wbishop at pathfinder-ea.com>        www.pathfinder-ea.com<http://www.pathfinder-ea.com/>
134 South Fitzhugh Street
Rochester, NY 14608               [cid:image006.png at 01D50A44.052C4960]         Ask me why Carbon Fee & Dividend may be right for you.

From: Equest-users <equest-users-bounces at lists.onebuilding.org> On Behalf Of Brian Fountain via Equest-users
Sent: Monday, May 13, 2019 5:47 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Setting DOAS system type airflow rates

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:image007.jpg at 01D50A44.052C4960]

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<mailto:Brian.Fountain at sa-footprint.com>

100 Sheppard Ave Suite 800 Toronto Ontario M2N 6Z1
t 416 218 7025 f 416 487 9104  sa-footprint.com

Vancouver  Calgary  Edmonton  Winnipeg  Kitchener  Toronto  Ottawa

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20190514/c8dfcdc2/attachment-0001.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.jpg
Type: image/jpeg
Size: 9336 bytes
Desc: image001.jpg
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20190514/c8dfcdc2/attachment-0009.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image006.png
Type: image/png
Size: 1554 bytes
Desc: image006.png
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20190514/c8dfcdc2/attachment-0003.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image007.jpg
Type: image/jpeg
Size: 31943 bytes
Desc: image007.jpg
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20190514/c8dfcdc2/attachment-0010.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image003.jpg
Type: image/jpeg
Size: 1903 bytes
Desc: image003.jpg
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20190514/c8dfcdc2/attachment-0011.jpg>