I'm doing a take-off on a chilled beam and chilled water system where both systems share a common chilled return. I've already requested main branch balance valves on the heating hot water system and the general contractor asked me to review the chilled water piping. I don't see asking for main branch valves on the common returns. Does anyone have any reason why I shouldn't request that they install the balance valves on the supply sides so I can differentiate flow rates between the chilled beam and chilled water loops? I never see balancing valves installed on the supply side of systems and was wondering if there is a logical reason for this.
Sorry if this post seems vague, I didn't want to get to wordy.
In a closed system keeping the coils full of water isn't a problem. There is a thread that discusses balance valves versus control with equal percentage control valves that gets fairly detailed.
No man can be both ignorant and free.
Thomas Jefferson
I'm doing a take-off on a chilled beam and chilled water system where both systems share a common chilled return. I've already requested main branch balance valves on the heating hot water system and the general contractor asked me to review the chilled water piping. I don't see asking for main branch valves on the common returns. Does anyone have any reason why I shouldn't request that they install the balance valves on the supply sides so I can differentiate flow rates between the chilled beam and chilled water loops? I never see balancing valves installed on the supply side of systems and was wondering if there is a logical reason for this.
Sorry if this post seems vague, I didn't want to get to wordy.
Thanks for the input and manual that I will eventually get around to looking at. However, in my case, does anyone see an issue with installing them on the supply side as installing one on the common return will not tell me how much flow is chilled beam vs chilled water. I kind of understood why they install the CBV's on return side at the coil.
Not to confuse the original question but here's another one that I don't understand:
If both pumping system share a commons return and both the chilled water and chilled beam pump control to a differential pressure via VFD, wouldn't they fight one another as each different system pump ramps up and down?
Control of the pumps should be by differential pressure not GPM. The pumps will ramp up and down to maintain set point.
The pumps are modulating based on differential pressure and not flow. Both the chilled beam and chilled water share a common return. This is why i presented my initial question regarding installing the balance valves on the supply side of the main branches, it is to differentiate between flow on the chilled beam and chilled water system. If I had one installed on the common return, I wouldn't be able to do this. The second half of my question was regarding the controlability (is that a word?) of the systems independently with each system sharing a common return pressure for differential pressure control. I imaging that I would have to establish both of the differential pressure set points at the same time once the systems are balanced in a full open scenario (minus any diversity). Just seems to me that as one of the systems is modulating it would have an impact on the other. Maybe not.
They will impact each other but the pump VFD'S will modulate to maintain differential pressure set point. As long as both pumps are maintaining DP set point you will have design flow to each system. That's why DP is used instead of discharge and or return header pressure.
Most closed systems have the balance valves on the supply but if you want them on the return no problem. I like your thought process though.
No man can be both ignorant and free.
Thomas Jefferson
id do discharge of any chiller or pump. its better to keep the impeller loaded then not on the pump.
And by keeping pressure on the chiller reduces the possibility of any cavitation.
Variable volume pump? Constant volume pump? 2 way valves? 3 way valves? Design pressure drops across the coils, and across the beam? Bypass designed into the system? Direct return, or reverse return piping? Primary variable? Primary / secondary? Your post #9 kinda suggests a primary variable, but?
Way too many missing parts and pieces in your system description. For a simple start, it's customary, and preferable, to install control valves, and circuit setters on the return, downstream of the coil. At the pump, the circuit setter should be on the discharge side of the pump, and if not installled, you use normally the discharge isolation valve to set the pump.
On large systems, large coils, or systems that have elevation differences, it becomes even more important to install your flow control devices downstream of the coil. Yes, depending on the system operating conditions, and, or design, water has a tendency to seperate near the top of the coil. (Also depends on coil design. There is more than one design for different coil characteristics) If you install a control valve on the inlet of a coil, when you close the valve, you have the suction head of the pump, as well as gravity working to seperate the water in your coil. And, we haven't discussed anything about air seperators installed in the system, and how they might affect this potential issue.
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Originally Posted by stanbyyourword
