Chilled water Increased flow in 1-1/2" pipe
Chilled water Increased flow in 1-1/2" pipe
(OP)
I am working on a system that has a 1-1/2" common header from 3 individual pumps. We didn't do the original install but the 9 air handlers that were originally selected didn't perform so we re-did the heat load calculations for the new units and the chilled water to nearly all of the units has increased. The total GPM we are now looking at with a full load is close to 110 GPM. We have plenty of head from the pumps, I think the inlet was around 30 and the outlet sits at about 70ish on the original system. This is a constant flow system with 3 way valves at each air handler. I am thinking with the increased flow the velocity and pressure loss will obviously increase but the 1-1/2" header should still "work" its not ideal I know, but the customer doesn't want to have to rip out a bunch of piping to upsize to a bigger header as space is at a premium as well. What would the negative effects of leaving the 1-1/2" piping in vice up-sizing be, any thoughts would be appreciated.
Side note there are two air handlers near the pumps (within 30ft of pipe or so) that have about 30 GPM running through them, so the main section of header will run closer to 80 GPM after these branches.
Thanks
Side note there are two air handlers near the pumps (within 30ft of pipe or so) that have about 30 GPM running through them, so the main section of header will run closer to 80 GPM after these branches.
Thanks





RE: Chilled water Increased flow in 1-1/2" pipe
Q2/Q1^2. Not knowing the original flow you will need to calculate the new losses.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Chilled water Increased flow in 1-1/2" pipe
all depends on how much "spare" the systems had and where the 3 way valves went - are they modulating or on/off?
YOu say the total flow is now close to 110 gpm. What was it before??
A network diagram or schematic with before and after would help a lot to understand what has changed and whether the flow in the system is actually higher or not.
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RE: Chilled water Increased flow in 1-1/2" pipe
I will have to look up the numbers to be sure, but the original flow was closer to 90 GPM so its about a 20 to 30 GPM increase.
RE: Chilled water Increased flow in 1-1/2" pipe
If it is too high then you are wasting power and maybe eroding the piping.
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RE: Chilled water Increased flow in 1-1/2" pipe
110/90^2 = 1.49 which is a 50% increase - lots of luck.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Chilled water Increased flow in 1-1/2" pipe
In addition to what the others said, you can also expect problems with noise and water hammer at the proposed velocities.
RE: Chilled water Increased flow in 1-1/2" pipe
RE: Chilled water Increased flow in 1-1/2" pipe
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Chilled water Increased flow in 1-1/2" pipe
Is it a 2" NPS pipe or 2" OD?
Only then can you work out if the pressure / head differential of your pump, which could drop by 10-15% depending on the pump curves, is sufficient for your new load. The length of the pipe to the furthest AHU could be critical.
It's the system that counts, not just this bit of pipe.
Let us know how it gets on.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Chilled water Increased flow in 1-1/2" pipe
jtimmer, can you show the pump curve?
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Chilled water Increased flow in 1-1/2" pipe
Not all the increase comes from the pipe so increase in required pressure isn't as much as a pipeline. my point about pump curves is what ids the differential head/pressure at the new higher flowrate? It won't go up....
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Chilled water Increased flow in 1-1/2" pipe
However, you need to determine if the pump has adequate head to pump against the higher system head caused by the increased velocity.
Note that the pumped flow will decrease as the system head increases. The change in pumped flow can be determined by plotting the system curve onto the pump performance curve.
RE: Chilled water Increased flow in 1-1/2" pipe
For this increase in flow, if the original designers did their job properly and optimized the pumps and flow control then you may not have enough and may need to swap out your pumps for some bigger ones.
Let us know how it goes.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.