water balancing accuracy/tolerances
water balancing accuracy/tolerances
(OP)
Hi Guys,
I am looking at the CIBSE code W for flow tolerances. if my coil needs a flow of 0.1574XXXX l/s and I have a tolerance of +- 10%, what decimal point goes in the coil schedules? I am thinking at if the flow needs to be within 10% then I need the third decimal place, ie 0.157 l/s, because +10% would be 0.172 and -10% would be 0.142 and without the third decimal place you could be anywhere between 0.140 and 0.149. Am I correct in concluding that if a accuracy of 10% is required, three significant numbers are needed? Does this make sense in that Kv numbers on balancing valves only go to three significant figures?
Would someone be nice enough to confirm or explode my understanding?
Thank you
I am looking at the CIBSE code W for flow tolerances. if my coil needs a flow of 0.1574XXXX l/s and I have a tolerance of +- 10%, what decimal point goes in the coil schedules? I am thinking at if the flow needs to be within 10% then I need the third decimal place, ie 0.157 l/s, because +10% would be 0.172 and -10% would be 0.142 and without the third decimal place you could be anywhere between 0.140 and 0.149. Am I correct in concluding that if a accuracy of 10% is required, three significant numbers are needed? Does this make sense in that Kv numbers on balancing valves only go to three significant figures?
Would someone be nice enough to confirm or explode my understanding?
Thank you





RE: water balancing accuracy/tolerances
RE: water balancing accuracy/tolerances
You can figure out from the pipe size and configuration, fluid velocity, measuring instrument accuracy, and measuring instrument precision what sort of precision in flow rate can be realistically expected at those low flow rates.
Or, just call it 0.16 - 0.2 l/s so they err on the upper side for safety.
Good on ya,
Goober Dave
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RE: water balancing accuracy/tolerances
At a 1Kpa dp accross the smallest valve, the smallest measureable change in flow is 0.00X l/s which is .6kw or so, which is clearly significant on a small terminal unit.
At this point I am leaning towards four decimal places for the smallest flows of 0,0Xl/s, that way on the smallest measureable flows on the smallest stad valves the flow can be checked to be within 10%.
any other toughts on this?
RE: water balancing accuracy/tolerances
While you may be able to "measure" 5dp, you will have no accuracy or repeatability even at 3dp. Secondly, even if you could measure it, you can't control to it. Fluid flow itelf is not that stable. Watch the meter for a while. Try closing the valve and opening it back up to the same position.
RE: water balancing accuracy/tolerances
I usually try to err on the upper side of the spec, in order to insure that I don't leave a coil with under-capacity, which leads to call-backs. But not too much, which may lead to not enough available flow to satisfy all coils. Hopefully, there is enough excess pump capacity to push all coils above spec a few percent.
Good luck on your project!
Good on ya,
Goober Dave
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RE: water balancing accuracy/tolerances
RE: water balancing accuracy/tolerances
My conclusion at this point is three significant figures so you have the resolution to see the +-10% effectively.
I will keep everyone posted.
thanks