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?

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.

 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.

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