Cooling Water System
Cooling Water System
(OP)
I have been performing a cooling water system calc in Excel. The system is being pressure balanced using butterfly valves. I have always heard that in real life it is incredibly difficult to actually balance a cooling water system this way. I am wondering if the calculations that I am performing would actually give me something that sort of resembles the actual system. Say I put in the pipe length, size, fittings, flows that I want to go through and use the butterfly valves to take the excess pressure drop I need to balance everything, would the flow rates that I have specified resemble what would happen out in the field? Thanks for any help!





RE: Cooling Water System
A better choice than the butterfly is a globe valve for reasonably steady flow. I would estimate, as a rough rule of thumb, that the valve absorbs at least 30% of the total DP available.
It's very hard to provide advice when the details of the problem are not known.
RE: Cooling Water System
RE: Cooling Water System
As far as using excel to calculate the network, you are brave! With correct modeling it can be done it is a case of iterative application of pressure loss calculations for each branch given desired flows. ensure there is continuity of mass (volume) for each distribution network and it can be done. If losses without the valve are found then the pressure loss diferences between parallel branches represent the required "trim" pressure drop across the balancing valve.
Mark Hutton
RE: Cooling Water System
Depending on the number of branches you have, it could be tedious doing the simulation with Excel. But by no means impossible. The valve manufacturers will supply charts of K value (or Cv) vs % opening, so once you have done your calcs you will be able to get starting points for the settings on each valve and then do the fine tuning on site using local pressure gauges.
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RE: Cooling Water System
Mark Hutton
RE: Cooling Water System
RE: Cooling Water System
I agree with dcasto. If the system sizing is properly done, butterfly valves can be OK. However, if the user points are more and very close flow control is required then reversed return piping will complement the balancing action of the valve.
RE: Cooling Water System
Your real problem, of course, will be finding a proper way to characterize the hydraulic resistance of partially open butterfly valves. The pressure drop changes dramatically over just a few additional degrees of opening when you are in the effective regulation range for this type of valve. Unless you spend umpteen hours "fine-tuning" the parameters, I wouldn't be too optimistic about the results, as far as matching field results, even if you have programmed correctly.