Location Balance Valve on Secondary Circuits
Location Balance Valve on Secondary Circuits
(OP)
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?
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?





RE: Location Balance Valve on Secondary Circuits
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.
RE: Location Balance Valve on Secondary Circuits
RE: Location Balance Valve on Secondary Circuits
I got the reference from the below link:
http://www.jmpco.com/balvalve.htm
--Steve
RE: Location Balance Valve on Secondary Circuits
RE: Location Balance Valve on Secondary Circuits
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.
RE: Location Balance Valve on Secondary Circuits
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.
RE: Location Balance Valve on Secondary Circuits
See attched sketch.
RE: Location Balance Valve on Secondary Circuits
RE: Location Balance Valve on Secondary Circuits
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
RE: Location Balance Valve on Secondary Circuits
RE: Location Balance Valve on Secondary Circuits
Good luck and try to get back to us with any results after doing this.
RE: Location Balance Valve on Secondary Circuits
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
RE: Location Balance Valve on Secondary Circuits