Bridge or No bridge for primary/secondary pumping

[cry22]

Hello all.
I have seen several arrangements in primary/secondary pumping systems.
Some utilize a suction from the primary and return to the primary with no devices of any kind.
Others use a bridge with a control valve.
Others use a 3-way valve.

I have used successfully primary/secondary pumping without using a bridge at all. Am I missing something? should I use a bridge? a 2-way control valve? whether in the decoupler or at the suction.

What is your pratice out there? any problems with any system you used? How reliable is the bridge and what does it add to the system?

Is it worth putting a bridge altogether? and why?

Thanks

 

[BigInch]

A bridge?

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[cry22]

Yes Big Inch, we call it a bridge in the HVAC world (at least in the US).
Basically, it consists of a parallel decoupler allowing secondary water to return to the secondary pump instead of going back to the primary system, thus achieveing a mixture of secondary water and primary water.
The question is: does the secondary water really need to be mixed with the primary water.

I think that Bell & Gosset came up with the "bridge" principal.

I will try to post a sketch of what I mean.

 

[BigInch]

Thanks, but I'm still not sure what it is, unless its a flow control valve, so I'll just hang around and see if anyone else here does. Alternatively, you might consider posting in the HVAC forum.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[quark]

The idea is not to take the secondary fluid flow back to the secondary pump suction but to take the excess primary fluid flow back to the primary pump suction (after mixing with secondary return).

When you have fixed primary flow and your secondary loop is operating below 100% then you do require to take back the excess primary flow (in excess of what is required at secondary loop) to the primary pump suction. The disadvantage with this method is that the chillers see very low dT and thus losing operating efficiency of chillers.

When you have variable primary, then you don't require this kind of arrangement.

Taking secondary flow back to secondary suction (though this is not possible hydraulically) is a bad idea as you can't maintain constant coil ADP and your primary objective of maintaining control space conditions is defeated.