VAV CALIBRATION AFTER NOT MATCHING FLOW READINGS IN FIELD ND BMS

[Ajender]

Hi Freinds,

Good Evening, In my site am facing vav calibration after flow readings not matching field side and Bms graphics.What we did calibration time not installed AHU Final filter and Isolation room inside Hepa Filter.This one high rise building. After installation we applied AHU Static pressure .But Before also not getting same reading VAV is titus and bms is Honeywell calibration.Now what can i do . I need support from your side.Another thing One AHU serving 2 floors .

Anybody Face side like this problem. I need your suggestions ASAP.

 

[Drazen]

it's hard to grasp your grammar, but how do you expect to do design flow if you did calibration before filters were in place? do you know how much of overall static pressure goes on hepa filters??! it may be in range of half of all static pressure drop!

 

[Ajender]

Hi,
I want know ahu static pressure process.can you tell me.is it correct vav calibration time they are not installed hepa filter and ahu inside final filter ,fresh air filter .

 

[willard3]

Start at the beginning and find out how to calculate static, velocity and total pressures. Ameroican Conference of Governmental Industrial Hygienists "Industrial Ventilation" is a good place to start SMACNA and ASHRAE volumes also cover this.

 

[GT-EGR]

Not sure what exactly you are asking, but it is very typical that factory calibration does not line up with the field inlet conditions - you almost always have to recalibrate your airflow sensor readings based on actual measured airflow delivered by totaling it at the diffusers, and then set your minimum/maximum damper positions accordingly.

As far as not having filters in when you balanced - if this is a VAV system, it shouldn't matter, the only impact that has is that you will have less static pressure available as the filter dirties up. Unless your system isn't designed for any filter static at all - in which case you likely need a new fan.

 

[ChasBean1]

Ajender, if I grasp your original post, final filter installation or anything related doesn’t matter. When you balance each of the system VAV boxes, you only need the system to deliver a static pressure range that satisfies the VAV boxes. This might be 0.3” to 2” for regular VAVs or 0.6” to 3” for a Phoenix type system.

But I would argue, to the dismay of my friends in the TAB field, that there is a sort of competition between an installed DP transducer at a VAV box with a known inlet area and flow hood measurements at diffuser outlets, taken one at a time.

If the installed DP transducer at the VAV box is in a pretty straight run (say a 12” round duct with a straight inlet without turns/bends), and the DP sensor reads a steady 0.05”, and the DP transducer is somewhat accurate, the velocity really is ~900 fpm and the flow really is ~700 cfm. If the guy with a flow hood reads something way off (e.g., something creating a K factor outside 0.8-1.2), there is an issue either with the pressure transducer reading or the measurement method.

The problem is not always clear, but K factors outside this range indicate an issue either with the mathematical conversion on the BAS or the measurement method.