Differential pressure control valves for Chilled Water System
Differential pressure control valves for Chilled Water System
(OP)
We are going to install VSD's on some existing pumps for cooling. These pumps are all constant speed. Most of the loads have two-way control valve. To make sure there is a minimum 30% flow rate for VSD's, differential pressure control valves are needed. My question is whether we should install the valves on the suction and discharge headers or the end of the loops?





RE: Differential pressure control valves for Chilled Water System
Regards
Dave
RE: Differential pressure control valves for Chilled Water System
Is this a primary-secondary pumping system (with separate pumps for circulating through the chillers) or one single loop?
Assuming you have a primary-secondary, I would take one of the air handlers, and install a 3-way valve. Pick a valve that will give you whatever minimum flow you're trying to achieve, and you're done, and you have no control system to worry about.
If your system is large and diverse enough and you have some year-round cooling loads, you probably will always acheive your minimum flow anyway. You might want to wait and see how the system operates before installing anything.
More importantly, you should make sure that you choose your method of VSD control carefully. Pick a couple of remote points in the system, and install differential pressure sensors between supply and return. Modulate the VSD to satisfy the differential setpoints of each of the zones.
---KenRad
RE: Differential pressure control valves for Chilled Water System
If there is no constant cooling load, i.e. there is no core area, my feeling is that we should install a differential pressure relief valve in the end of the loop, not a by-pass on pumps. What are the pros and cons of these two configurations?
RE: Differential pressure control valves for Chilled Water System
KRB
RE: Differential pressure control valves for Chilled Water System
I always prefer the header bypass(for minimum flow) to be at the end of the headers to avoid possible short circuiting(particularly at low loads) when it is installed in the pump discharge.
Regards,
RE: Differential pressure control valves for Chilled Water System
A bypass near the secondary pump must be set to allow your minimum flow when loop DP increases to calculated maximum for a minimum demand state. Under maximum demand the DP due to the increased flow(dynamic head press) and pump speed will invariably be close enough the setpoint to result in unwanted bypass.
RE: Differential pressure control valves for Chilled Water System