Calculating Operating Pressure!!!
Calculating Operating Pressure!!!
(OP)
Guys,
I'm pretty new to the field, and I have a simple question..I think. I have a closed chilled water loop going to cased chilled water coils...w/ a 40 ton chiller ewt=45 lwt=56...is it as simple as converting my head on my pump to psi? it seems more involved.
I'm pretty new to the field, and I have a simple question..I think. I have a closed chilled water loop going to cased chilled water coils...w/ a 40 ton chiller ewt=45 lwt=56...is it as simple as converting my head on my pump to psi? it seems more involved.





RE: Calculating Operating Pressure!!!
What is ewt=45? lwt=56?
What Operating pressure are you looking for? The water pump's circuit? Where, exactly on the circuit?
Are you at the design stage (i.e., are you process designing the system)? Or is the system existing and operating? If it is operating, install a pressure gauge.
If you are in the process design stage, you have to define the system and where in that system you are interested in the "operating pressure". It might be as simple as looking at your pump curve and converting, as you suggest, your system head to psig. However, assuming you have a centrifugal water pump, you will have to generate a system curve and overlay it over the pump's performance curve to find out the pump's operating pressure under your system's definition. Once you identify the operating point, you can make the hydraulic calculations for the pressure drops involved until you get to the place in your system where you want to find out the operating pressure.
I hope you can see what is involved and what I've explained.
Art Montemayor
Spring, TX
RE: Calculating Operating Pressure!!!
RE: Calculating Operating Pressure!!!
RE: Calculating Operating Pressure!!!
RE: Calculating Operating Pressure!!!
RE: Calculating Operating Pressure!!!
25362, in my opinion, is correct in mentioning your pump shutoff pressure (maximum, "deadhead" pressure) as the value to design upon. If you hold a HazOp, that is what will come out of the discussion. It is very credible to have a blocked-in pump discharge and, as a result, attain deadhead pressure.
Therefore, go to your pump's performance curve and read off the deadhead pressure and design around that value. This is normal procedure when applying a centrifugal pump.
Art Montemayor
Spring, TX
RE: Calculating Operating Pressure!!!
I appreciate your time that you put in and answered my question, and I thank you. Some of the reasons why I asked this question is becuase I only have an AS in mechanical engineering, and I'm working on the rest...would fluid dynamics cover alot of these typical questions? And are you saying that my shut-off pressure can be applied to mostly all of my design water loops as a "operating pressure"? most likely not huh
RE: Calculating Operating Pressure!!!
The initial fill pressure will fill the system, and push the air out. This pressure only needs to be high enough to fill the system to it's highest elevation, plus 5 or 10 PSI to make sure the lines are full. This pressure might be 20 or 30 PSI, or maybe 100 if there's a big elevation change. That's the pressure that exists in the system, even with the circulating pump is off. It's maintained by a pressure reducing valve, or small high head pump, that will make-up water lost by small leaks, or minor repairs. The circ pump will typically be a relatively large, low-head pump, because it's just moving the water around in a circle, like a Ferris wheel. The weight of water going up is the same as the weight coming down. The difference in system pressure, whether the circ pump is running or not, will likely only be a few PSI.
RE: Calculating Operating Pressure!!!
My elevation should only be around 15-25 ft. My longest run will be in the crawl space, but my shortest will be in the attic of the house. Bascially Here are my parameters:
40 ton gas fired chiller
600' to my furthest coil.
11F delta T
96 gpm
pump will be located far away from the house near the chiller.
20-30 psi would do it?
RE: Calculating Operating Pressure!!!
RE: Calculating Operating Pressure!!!
RE: Calculating Operating Pressure!!!
When you design a system, such as a centrifugal pump, you have to take into consideration the credible possibility of the pump reaching it's maximum possible pressure - the deadhead pressure. That may not be the ultimate design pressure in the case where other events can also occur - such as a hydrostatic test on the entire system (in situ) or a high pressure source of fluid connected to the system.
Yes, if you're lucky and get a good, hands-on fluids prof who takes the pain to take through a side bar adventure into Fluid Transport (pumps & compressors), you should be able to really soak up all the input you will need in the future to resolve this type of problems (really, applications). Lots of luck in Fluid Dynamics.
Art Montemayor
Spring, TX
RE: Calculating Operating Pressure!!!
RE: Calculating Operating Pressure!!!
RE: Calculating Operating Pressure!!!
Don't ever go with name plate data. Once you install the pump in the system, you will directly get your pressure (no need for any conversion
Regards,
RE: Calculating Operating Pressure!!!
RE: Calculating Operating Pressure!!!