Inline VFD duplex booster pump to house pumps
Inline VFD duplex booster pump to house pumps
(OP)
There is a situation at this building where they installed new duplex booster pumps(VFD) in series (Pumps A) with these old booster pumps (Pumps B). Pumps B pump the water to a roof tank. Pumps A pump water to these Pumps B and to the first 6 stories of the building. The fuse keeps failing in the new pumps (Pumps A). The pump manufacturer thinks the suction line between pumps A & B is not getting enough volume and/or pressure when pumps B turns on and pumps A cannot satisfy the demand so it is overworking itself causing the fuse to fail. I have come up with these possible solutions:
1. There is an electrical/controls problem causing the fuse to fail requiring a simple electrical fix.
2. I noticed they installed a by-pass line with an isolation valve closed so the water only travels through the new booster pumps (Pumps A). I think maybe installing a check valve in lieu of or next to this valve and opening this valve could certainly resolve this issue.
3. The new pumps (Pumps A) are simply not large enough to handle the demand of both the old booster pump (Pumps B) and the the demand of the first 6 stories of the building. The new pumps (Pumps A) either need to be replaced or the old pumps (Pumps B) will need to be replaced with a new dedicated pipe line running to them prior to the inlet of pumps. This way pumps A only feed the first 6 stories as maybe originally intended.
Personally I am leaning towards 2 or 3 but I would like to see from other engineers eyes what other causes and solutions are out there that I may be overlooking. The pumps are centrifugal and pump domestic cold water (55 deg F).
1. There is an electrical/controls problem causing the fuse to fail requiring a simple electrical fix.
2. I noticed they installed a by-pass line with an isolation valve closed so the water only travels through the new booster pumps (Pumps A). I think maybe installing a check valve in lieu of or next to this valve and opening this valve could certainly resolve this issue.
3. The new pumps (Pumps A) are simply not large enough to handle the demand of both the old booster pump (Pumps B) and the the demand of the first 6 stories of the building. The new pumps (Pumps A) either need to be replaced or the old pumps (Pumps B) will need to be replaced with a new dedicated pipe line running to them prior to the inlet of pumps. This way pumps A only feed the first 6 stories as maybe originally intended.
Personally I am leaning towards 2 or 3 but I would like to see from other engineers eyes what other causes and solutions are out there that I may be overlooking. The pumps are centrifugal and pump domestic cold water (55 deg F).





RE: Inline VFD duplex booster pump to house pumps
With just the generic, somewhat abstract situation you've presented, anything more than a good guess just isn't possible.
As a guess..... Pumps A could be flowing "off the end of the curve", or as you state "are simply not large enough to handle the demand of both the old booster pump (Pumps B) and the the demand of the first 6 stories of the building".
Then again it could be #1 or #2, or a myriad of other reasons.
RE: Inline VFD duplex booster pump to house pumps
It should be fairly simple though to see if the rated flow of the A pumps is bigger than the B pumps. If you can't monitor current though it will be difficult to see if 1) is happening or not..com
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Inline VFD duplex booster pump to house pumps
RE: Inline VFD duplex booster pump to house pumps
Do you have a clear understanding of your system curve (min case, max case) versus the different operation conditions ?
Difficult to not speculate without some diagram or sketch.
RE: Inline VFD duplex booster pump to house pumps
Inherently this looks wrong and if the old pumps were doing their job, then adding head by means of the discharge of pumps A, then they will start to pump a lot more water, maybe more than pumps A can handle. Who knows?, supply some data and we might be able to give some help.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Inline VFD duplex booster pump to house pumps
Pump motors are generally overloaded due to too much flow through the pump. Throtle the discharge of pump B. It is supplying a storage tank so you do not have to fill it so fast.
RE: Inline VFD duplex booster pump to house pumps
Usually a sign of system design flaw when you see centrifugal pumps in series...not always...just mostly.