[Bldg-sim] Constant air volume systems

[Bishop, Bill]

Hi Rathnashree,
You need to know more about the air handling unit and system (controls, ductwork and zone dampers, if any) to know how to simulate the minimum flow associated with a VFD. An AHU may be designed as a constant volume unit and still use a VFD to balance the system at a fixed flowrate. You don’t automatically get energy savings by using a VFD, and you actually incur a small energy penalty associated with drive losses. If the system does not have any adjustable zone dampers that are automatically controlled, it may be designed to operate at constant volume, and you would use a minimum flow ratio of 1. If the unit only handles a small number of zones, it may be designed to run at constant volume. I suggest you ask the design engineer how the unit will be controlled. You can also look for a controls drawing or talk to a factory rep for that unit.
Regards,
~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:image003.png at 01D690BB.2FB08530]         Ask me why Carbon Fee & Dividend may be right for you.

From: Bldg-sim <bldg-sim-bounces at lists.onebuilding.org> On Behalf Of Rathna Shree via Bldg-sim
Sent: Tuesday, September 22, 2020 7:39 AM
To: bldg <bldg-sim at lists.onebuilding.org>
Subject: [Bldg-sim] Constant air volume systems

Dear All,

In many of our projects, we have Air handling units with VFD and no VAV system. When simulated with minimum flow ratio as 1 and AHU with VFD, there is no difference in energy consumption. The impact of with and without VFD is negligible. Since there will be a small amount of variation in Airflow in zones due to VFD in AHU, can we reduce the minimum flow ratio from 1 to about 0.8 or 0.7?

Regards,
Rathnashree
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20200922/a9e57ad2/attachment-0002.html>
-------------- 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/bldg-sim-onebuilding.org/attachments/20200922/a9e57ad2/attachment-0004.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image003.png
Type: image/png
Size: 1554 bytes
Desc: image003.png
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20200922/a9e57ad2/attachment-0002.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image004.jpg
Type: image/jpeg
Size: 1903 bytes
Desc: image004.jpg
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20200922/a9e57ad2/attachment-0005.jpg>