Water Balance of FCU's

[iken]

I have been heard (from somewhere, can't remember) that if I set up an IR valve, say at a FCU to achieve the design flow rate, and then the availble pressure increases (flow increases) this will have an effect on the original FCU flow rate.

Is this so? If it is, how can it be, as I am under the understanding that the flow rate through the IR valve is dependant on the Kvs value, and not other external factors.

The reason I ask is because I am about to start the water balance of a large complex (160 FCU's) with no as builts, and the only IR valves are at the FCU's themselves (no on branches).

And not knowing the exact layout of pipework, I do not want to revisit ecah FCU to ensure that things do not change on me.

Any comments would be great.

Cheers

 

[vpl]

iken

please spell out your abbreviations. I read "FCU" as a flow control unit which I usually take to be a globe valve with associated instrumentation to measure flow and provide feedback to open/close/throttle the valve. "IR" is the name for our item reporting system and "Kvs" is kilovolts. Somehow, when I put these three together, your question doesn't make sense. Sometimes, the everyday shorthand used in one company, industry, or even country doesn't "translate" even to someone who speaks the same language.

Patricia Lougheed

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[friartuck]

I assume this is an existing system??

Start on the index run...usually the longest (but not always)

Measure the flow of the last fan coil unit and then compare it with the next in line. Balance one to the next...i.e. if you need .1l/sec at FCU1 and 0.1l/sec at FCU2 then vbalance both units until they read the same. Even if they read 0.2l/sec each...9Sounds daft but it works).

Work your way back through the system comparing flow rates and keeping them in proportion.

You will end up with all FCU's probably over duty by say 12% or whatever. You can then reduce (or increase if you have the facility) the flow rate at the pump.

All fcus will keep in balance and their individual flow rates will change by 12% etc.

Its hard, slow and boring but it works.

(balance all sub-circuits the same way)

good luck...(or hire a commissioning engibneer...or nbuy self bvalancing valves which are realy quick......Hattersley make then in uk)

Friar Tuck of Sherwood

 

[iken]

vpl,

FCU = Fan Coil Unit
IR Valve = Isolating Regulating Valve

Friartuck,

Thanks, does sound long winded. This is an existing system.

Will give your approch a go, and see what happens (we do have IR vlaves in plant room to throttle flow back if required.

Thank you

 

[friartuck]

If the system is existing, I would take readings over the whole system first to see what I was getting. The system may already be in balance??????

If so, whoopy

If not....good luck, its a big system and will take a few days to do

Friar Tuck of Sherwood

 

[quark]

Iken!

You can control high flow only and if your system is already starving then you won't have anything to do.

If you have high flowrates in your system then pressure drop across IR valves will operate your pump to the left of its present operating point and will balance your entire system flowrate.

Danfoss manfactures some good balancing valves.

It took me 3 days to balance 40 AHUs. You shuold be as patient as Buddha

Good luck,