VAV Boxes (Cooling and Heating Coils)

[duck1221]

I work for Bell & Gossett and was wondering if I could pick your brains here for some Voice of the customer questions to help improve some of our products.

I was wondering how contractors measured flow across VAV-Boxes and cooling/heating coils...

Do you measure across the flow limiter or coil itself?

It is pretty easy to measure across a Venturi or a Calibrated Ball Valve, but in the case of a pressure independent valve, how is the flow being measured? Thanks for any input you can give.

[TriSTar]

I believe measuring across the coil is the best method. The point is to be able achieve full flow at design conditions. I assume you are talking about a pressure independent characterized control valve. Most other pressure independent valves, flow limiters, provide the maximum coil flow rate when the control valve is 100% open. The reality is that calibrated balancing valves are not really needed in a variable flow system as they do nothing but add head to the pump. Flow limiters are great as they prevent overflow in the event that the control valve fails and is open 100%.