Shifting viewpoints on flow controls can cause disagreements where balancing valves should be located in closed loop systems. Many (including us at Hays Fluid Controls) agree that the balancing valves should be placed on the return side, whereas other companies may choose the supply side.
The role of balancing valves are to control the flow rates in each of the buildings branches to deliver the desired flows in low temperature, chilled, or hot water applications. At each heat exchanger the balancing valve is set to provide the desired flow rate to maintain comfort and energy.
The ASHRAE Handbook 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.” When comparing the location of installing Mesurflo valves, the one on return side will help in reducing the amount of free air in the coils and hence decrease the potential for noise. Another benefit being that you want to balance after the friction loss of the coil not before the loss.
With that in mind, there is not a right or wrong order to place the balancing valves because both location have been proven to be effective. Placing a balancing valve on the supply side will give you satisfactory results, but choosing the return side can be more effective because it can reduce air and noise problems while achieving better heat transfer across the coils. Moreover, the coils can remain fully flooded and there will be less turbulence due to less free air trapped in the coils. Due to several above benefits, Hays highly recommends to install the Balancing Valves on the Return side of the coil whenever possible.