Double Regulating Valves on Supply or Return Piping

[mechanical3010]

Double Regulating valves provided in chilled water branch lines for balancing and achieving systems flows are sometimes seen on supply and sometimes on return piping. Is there a strong technical reason or preference for locating them on supply or return? Do these work equally well regardless of which line they are on and is balancing achievable equally well?

 

[cdxx139]

I believe you place the control valve on the return side for AHU coils, so the coil "sees" the expansion of the expansion tank.

knowledge is power

 

[ChrisConley]

Valve placement on hydronic systems is a matter of preference. Most of my designs place the control valve on the return side of the coil. Control valve placement is based on traditional steam control valve placement, which needs to be on the supply side.

I have one client that insists that they be placed on the supply side. They have dozens of buildings and no problems related to control valve placement.

 

[mechanical3010]

The shop drawing detail shown for fan coil units and air handling units depicts the balancing (double regulating) valves on the return. But another balancing valve on the branches coming from the main and supplying chilled water to 3 or more fan coil units is shown installed on supply pipes and not the return. This inconsistency is of concern and whether it will have any negative impact on balancing?

 

[Drazen]

We have two issues put together here. There is difference between balancing and control function.

What you call double-regulating, I assume it is valve with presetting feature.

During balancing, you preset valve, and in operation it works as control valve.

For hydronic terminal units, I exclusively put control valves on supply side if radiators are in question, to enable possible adding of thermostaic head if it is not intended in original design.

For fan coils, double-regulating valves are strange as control is mostly on-off, and pre-balancing is done on separate return valve.

For branches, balancing valves should be logically put on return side if control valve is placed on supply side, but that is not carved in stone.

 

[mechanical3010]

I think there is some miscommunication about terminology. I understand that Double Regulating Valves are the same as Balancing Valves, which simply put is to pump the flow rate of water in the branches as per the GPM requirements of fan coil units. Pre-setting or not is a detail that I am not addressing at the moment. I do not decipher either what is the control valve in this context.
To do the balancing with an ordinary DRV we assume that all the fan coil units are ON with a bypass line in the three way valve leg. When they are actually off, the balancing valve in the bypass line takes over to simulates the pressure drop of the coil. This of course is different from the 2 way valve that is either on or off, but the application in question is of 3 way valves.

 

[KiwiMace]

I don't think that the branch balancing valves being in the supply will cause any problems. The flow will change with the setting either way, and net differential pressure across the control valve will be the same. There should be no effect on CV authority.

Valves for pressure control are a different story. Like steam as mentioned.

I agree that I typically detail them in the return, but can't think if I have a reason why, maybe draining down in some instances.

I just checked a reference (Total hydronic balancing, Robert Petitjean) which agrees, no hydraulic difference.