PRESSURE INDEPENDENT VAV - ISSUES

[VEEKRISH]

Hey Everyone,

I encountered a peculiar situation at one of our sites. Using Pressure Independent VAVs with a Centralized Air Handler. Noticed that on a few VAVs, when the AHU is shut-off, the Controller is registering a negative flow on the BMS. In a System with about 35 VAVs, this is happening on about 3-4 VAVs. Has anybody experienced this ? What do you reckon is the issue ? Faulty Controller ? Would appreciate any thoughts / suggestions.
Thanks
Veekrish

 

[HVAC-Novice]

Flowmeter not calibrated/measuring correctly.

Use Accutrol airwaves and not hose pito-tube VAV boxes.

 

[SAK9]

If I understood you correctly some of the VAV boxes have air flowing in reverse direction when the AHU is shut off. This means the space is at a higher pressure/temperature than the duct and air is flowing out of the space through a path of least resistance. The exfiltration could be due to number of reasons such as a temperature differential or pressure differential due to a leaky facade etc. Why should you be bothered about it as the AHU is shut off and there is no requirement to condition the space?

 

[HVAC-Novice]

SAK9: flow read in BAS =/= actual flow

And most flow stations don't measure reverse flow.

OP should measure actual flow. Also tell us what type of flow station this is.