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wta12
08-05-2012, 06:39 PM
hello,
For heating system, distribution(secondary) pump locate on return pipe is pretty popular but for chilled water system, i hadn't rarely (mostly never) seen secondary pump, which located on return pipe in primary/secondary. Please help me clarify about this difference and their advantage/disadvantage.
Thanks

aramis
08-05-2012, 09:32 PM
It is not popular, in heating you place them on cooler water so you can maximize NPSH.

In refrigeration water temperature is lower but you have the largest pressure drops usually at the HE so it is better to place them upriver not to produce cavitation inside the HE under any operating condition and the HE can absorb the pump heat so you get colder water for the process.

wta12
13-05-2012, 07:22 PM
Thanks for the comments. Here is my general schematic. For chilled water loop (from chiller to manifold) continuous line is supply, dash is return. Distributed Pump (4.2) on return along with flow meter (FM-2).
8959
Please give me some advices ?

The Viking
13-05-2012, 11:22 PM
Most pumps will operate with a much higher discharge pressure than suction pressure. One example of this is inline condensate pumps, typically these will be able to suck ~1m but be able to discharge up to a 30m head.

It therefore make sense to let pumps suck from a header and discharge towards the system and it's control valves.

But...
When it comes to hot water you get another factor to consider, heat.
The higher temperature the pump is rated at the more it will cost to buy.
It therefore makes sense to put heating pumps at the point in the system where the fluid is at it's coldest.

:cool:

.

MikeHolm
14-05-2012, 11:36 AM
Most pumps will operate with a much higher discharge pressure than suction pressure. One example of this is inline condensate pumps, typically these will be able to suck ~1m but be able to discharge up to a 30m head.

It therefore make sense to let pumps suck from a header and discharge towards the system and it's control valves.

But...
When it comes to hot water you get another factor to consider, heat.
The higher temperature the pump is rated at the more it will cost to buy.
It therefore makes sense to put heating pumps at the point in the system where the fluid is at it's coldest.

:cool:

.

That is old school thinking from back when seals were not very good. Now all the pumps are rated to 110C minimum and many of them higher than that so I would say that unless you have to operate close to the limits in temperature or on the curve, keep the pump on the supply to the load. Remember to keep your expansion tank on the suction side to keep the suction pressure stable.

aramis
16-05-2012, 05:40 PM
Unless your runs are extremely long or have high pressure drop, I don’t see the need for the extra pump.

If that pump does not work on variable speed you may overflow the tanks in the wrong direction.

The flow meter would be better placed at the suction of the chiller pumps provided you have slack NPSH-wise.

Why do you need this pump for?