Location Balance Valve on Secondary Circuits

[montgomerysj]

Hello, I a made a similar post of the below on the pump engineering forum, but got no replies.

We have a two pipe direct return cooling pipe system for a campus of buildings. Each building circuit is the secondary and the circuit between buildings is the primary. There are differing views as to whether the main balance valve for each building (secondary circuit) should be in the supply or return line.

1) One view is that for secondary circuits you place the balance valve on the supply. With the balance valve on the supply, it will be easier to set the flow into the building. (This is the perspective of the Test, Adjust, & Balance (TAB) technician from his experience.)
2) The other view is that having the balance valve on the return will reduce air and noise in the system.

1997 ASHRAE Fundamentals Handbook, page 33.4 says -- Compared with placement on the supply side, balance valves on the return side will reduce the amount of free air in the coil.

From ashrae above it is obvious that each individual coil should have the balance valve on the return. Would this also hold true for secondary circuits?

Is there any documentation stating that the balance valve for a secondary circuit should be placed on the supply?

 

[quark]

I don't think it is obvious as I always use them in supply lines. When you have a control valve in the return, issues related to air (or coil not flowing full) can be ignored.

Noise across a valve is a function of the pressure differential across it (and thus velocity). The PD across the valve is reduced only to the extent of drop across the coil and I am not sure how significantly it affects the noise.

The coils experience more fluid pressure when the balancing valve is placed in return than in supply.

 

[quark]

PS: My ASHRAE HOF is of 2005 and I didn't find your information. Can you scan a page and attach it here?

 

[montgomerysj]

I got the reference from the below link:

http://www.jmpco.com/balvalve.htm

--Steve

 

[montgomerysj]

What's the main advantage to installing the balance valve on the supply side?

 

[ChasBean1]

Does each building have its own pumping? If so, do pumps have triple duty valves at their outlets?

Is the setup like a typ. decoupled primary secondary loop (if so you're pumping way too much primary water)...

I don't have a clear enough picture of your configuration to come to any conclusions.

 

[Gunner777]

Hi montgomerysj,

I would personally always put the Balancing Valves in the return. The methodology behind this will be that this keeps the system behind the valve under pressure. This keeps air in suspention and coils and terminal units flooded. The moment the pressure drops the air will be released from suspension and interupt flow causeing noise as the pumps cavitate and the water flashes to steam. As for controling the amount of water entering the building, this can be set sucessfully by the valve in the return as the water leaving the building will be the same as the water entering the building....unless of cause you have puddles on the floors.

 

[montgomerysj]

The concern with locating the balance valve on the return is that it will create a high pressure zone upstream of the balance valve causing unwanted 'warm' chilled water return to recirculate through the recovery bypass.

See attched sketch.

 

[DuctHunter]

What does the effect of water temperature play into this. I've been told by some people that they put the valve on the return side because water temperatures are more moderate (at least in Hot water systems) which is less harsh on the valve itself. Is there any merit to this ?

 

[ChasBean1]

montgomerysj,

You need a check valve on the recovery bypass line to prevent direct supply-to-return short cycling. The system will move way too much primary water without it and you'll hurt DP for your other buildings.

Right now excess flow (as piped) will be a huge problem. With balancing valves, regardless if they're on supply or return, you can reduce excess flow to just a big problem. With the check in the bypass line, you'll eliminate the problem.

Assuming the check is in place, the deny (or choke) valve will limit building CHW use by maintaining a minimum return temperature. It is intended to allow return CHW to recycle through line, but only when the return temperature is too cool. This can hurt your supply temperature a little but it's a common configuration to keep from flowing excess water to the building.

Also, if you have three-way piping at coils in the building you'll want to change to two-way with this setup, esp. if the building pumps are on drives.

CB

 

[montgomerysj]

Yes, I was thinking it needed a check valve. I'm surprised one was not included in the original engineering design. Later a shut-off valve was installed on the bypass (still no check valve), so closing it will eliminate the short-circuit. But the energy recovery will have to wait for installation of a check valve. Thanks for the input.

 

[ChasBean1]

I recently had a building where it was in the design detail but then not installed because along the way, the contractor misinterpreted the intent as a typ. decoupled primary-secondary loop. The check (line size, swing persuasion) should do it. Has to be on the bypass line and has to stop water going from supply to return...

Good luck and try to get back to us with any results after doing this.

 

[montgomerysj]

Assuming a check valve is in place on the bypass line, does anyone have input on the possible negative impact of placing the balance valve as shown in my figure, downstream of the choke valve?

As I understand it, the ideal location for the balance valve would be on the return (i.e. after the load), but before the bypass recovery line. Unfortunately, the back up system for the load, which is a computer room, ties into the piping in this location, and, therefore, this was not allowed as a location option.

My two options are as below:
1) Install the balance valve on the supply before the bypass line.
2) Install the balance valve on the return after the bypass line.

ASHRAE says the former may cause cavitation, but it seems to me that the later will negatively impact the energy recovery.

Any thougths?

--Steve

 

[ChasBean1]

montgomerysj, I realize this question is to the rest of the field so I'll make my answer quick: no balancing valves where proposed. Pumps are in parallel and probably have triple-duty valves? No need for one in either location, esp. if (in addition) coils have circuit setters. In a system where there is a need, my vote is on the return side. Pls. others chime in...