Variable Primary Chilled Water Distribution
Variable Primary Chilled Water Distribution
(OP)
Can anyone tell me what the preferred configuration for pumps in a variable primary chilled water distribtuion system? Is it better to have pumps dedicated to each chiller or is it better to have the pumps with a common heaher requiring that control valves be provided at each chiller? Please explain your answer.
I have asked this question to many people and seem to get a different answer each time.
Any help would be appreciated.
I have asked this question to many people and seem to get a different answer each time.
Any help would be appreciated.





RE: Variable Primary Chilled Water Distribution
RE: Variable Primary Chilled Water Distribution
RE: Variable Primary Chilled Water Distribution
In a headered configuration,assume that the first chiller is in operation.Before you start the second chiller,you need to open the motorised valve on it.This will divert part of the flow from the first chiller causing it to trip on low flow.By incorporating a time delay on the low flow cut out(normally a differential pressure switch),this can be avoided.
RE: Variable Primary Chilled Water Distribution
If redundancy is required there should be a redundant chiller/pump. With a dedicated pump to each chiller, if the chiller or pump fails then both will be out. And with motorised valves there is an additional item to potentially fail?
RE: Variable Primary Chilled Water Distribution
If this is a variable primary flow system, there would presumably be controls to prevent this scenario. Your description is valid for most constant primary flow systems.
No info is given on the chiller size, but most 100 - 200 ton aircooled chiller units typically used for office/commercial HVAC will tolerate a reduction in primary flow down to 50%. The problem is that the #1 chiller (already running) will then start to unload based on LWT. To prevent this the #2 pump should start just before the #2 chiller valve is opened and the chiller started (in a headered configuration). Both pumps are presumably under VFD control for variable primary flow operation.