Double Regulating Valves on Supply or Return Piping

Whenever possible, balance valves should be placed on the return side of coils to reduce air and noise problems. ASHRAE states that "water velocity noise is not caused by water but by free air, sharp pressure drops, turbulence, or a combination of these, which in turn cause cavitation or flashing of water into steam" (1997 ASHRAE Fundamentals Handbook, page 33.4). Compared with placement on the supply side, balance valves on the return side will reduce the amount of free air in the coil. Result is less noise and better control of the coil. Flow will be controlled using supply or return. Do what is best for your system.