Head loss across an Idle pump.

[khan644]

In a typival DATA Centre chilled water cooling application, we have two pumps in series

one for emergency chiller work.
Other at a regular District plant supply.

In emergency situation, motorised valves are actuated in such a way that the one pump has to complete this closed hydronic loop by passing through a Idle pumps.

Pump: Its a normal horizontal mounted centrifugal pump.
With ahead of 30 meter and flow around 15 l/s.

Excatly, one must say "it should be provided by supplier" but thats taking too long for a comeback reply from them.

Is there any like such situation one came across?
What could be the head loss for assumption basis. May be 2 90 Elbow.

Can we determine in any way?

 

[quark]

I am not sure even manufacturers give such data. Use a manometer if you have pressure gauge tappings at both suction and discharge. 2x90 elbows can be close approximation.

 

[hollandhvac]

I am a bit surpriced with two pumps in series.

If I am getting this correct, than you have got a chilled water system with a duty/standby pump?

Now the systems I have seen in this that the two pumps (duty/standby) are allways in parallel. In this situation the standby pump does not need to pump through the other.

But, maybe I do not understand the question.

 

[Artisi]

Yes, a bit more explanation of the instalation or a sketch would be helpful.

 

[RossABQ]

I've seen a similar arrangement in a data center (didn't think it was a really great idea). As I recall, there was a bypass line with check valve around the pumps that are idle in emergency mode. When those pumps are running (normal operation) the check valve would be closed by their discharge pressure. Details at the emergency pump elude me...Probably similar?

The reason for this arrangement was that city water or water from some other source was used in emerg. mode; i.e, it switched to open-loop mode, with water going to drain, and the head requirements were greatly different than in closed-loop mode. It was an old building that had been retrofitted for data center use (small by today's standards).

 

[khan644]

QUARK: I agree with u, a repeated push to supplier came with a wild guess of 5Kpa.

For holland and artisi check out the attached schematic. The 43-42 are in operation.

RossABQ idea have opened my thought... is discuusing same but seems very difficult.

Thanks everyone who made gave penny

 

[hollandhvac]

Khan,

Have checked the attached PDF fiel, but I see only pump 41 and no 43 or 42?

I guess there is a part of the drawings missing?

 

[khan644]

Holland,

Yes its a mistake by my draughtman, Actually PUMP 19 should be read as 43 please!

And the Idle pump (which is the issue) is at the bottom passing through chilled water tank.

 

[hollandhvac]

Khan,

Ok got it and the air handling units are on each floor of this building? and what is connected to the two pipes next to the chilled water tank the pipes after the NC valves?

Being honest with you I would look for a system where you did not have to go through an idle pump. I guess there is a lot of resistance, because if it was not the pump would not work when running.

 

[IRstuff]

seems like someone might design something as described, but one can easily imagine a pump head with essentially infinite head, i.e., no water can be pushed through it without the pump motor running.

TTFN

FAQ731-376

 

[RossABQ]

I doubt it; that is the reason check valves are provided on multiple pump installations. For a typical double-suction split case horizontal pump, I would expect quite a bit of flow (say 50% of design) is possible with modest losses.

 

[Artisi]

I would think that the head loss thru a stationary pump would be dependent on the pump configuration and the relative size in relation to the flow rate, therefore there is no rule to establish what the head loss would be for this condition.
Testing the individual installation would be the only way to come up with a realistic number - not that difficult, either a differential pressure gauge to measure across the pump or a gauge on each side of the pump.