Parallel Pumping Flow

[Buildtech2]

In primary / secondary chilled water system, we have 2 duty chillers and one standby chiller with corresponding primary and secondary pumps. Now, we want to provide air conditioning to the future expansion building without considering redundancy in the chillers and pumps. The pipe sizes are large enough to cater the additional chilled water flow for the third chiller and pumps. Is it advisable to start third chiller and related pumps to meet additional chilled water flow rate for the future expansion after modifying the control system. Appreciate,if anybody can advise on this.

 

[quark]

If you have common header for the chilled water primary, then you should check the primary pump head. In the new condition, the head requirement for each pump should correspond to the full flow rate.

 

[mk3223]

A little confused with the actual question...

But, to have a full loaded system without a spare or redundancy system can be a risk for the Operation and should be clearly understood and agreed with the Owner.
Or, is there an backup plan identified if the shortage of the chilled water flow due to the equipment shutdown?

 

[Artisi]

As quark has pointed out, you need a system hydraulic review to ensure pump head and flows can be met with the additional thru'put.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Buildtech2]

Thanks everybody for your valuable inputs. There are 3 primary pumps in a common header with 2 duty and standby configuration. 2 pumps in parallel should deliver 174 l/s at 36.7 m head. the new flow condition is 214 l/s with 3 pumps in parallel. Therefore as per pump laws:

HD2/HD1 = (flow2/flow1)2

HD2 = HD1 (flow2/flow1)2

HD2 = 36.7 (214/174)2

HD2 = 55.8 M.

Therefore, as per new flow condition, the head requirement for each pump corresponding to new flow condition is 55.8 m

Since the capacity of secondary pumps is same, we need to replace both primary and secondary pumps with higher head and flow.

Appreciate to receive comments on above.

 

[GT-EGR]

If your original design was for 2 running, then your header and possibly other main distribution items like flow meter or air separator may not be sized for your newly increased flowrate

Generally speaking you should have the flowrate and chiller capacity to serve your new load, you just have to ensure the main chiller piping and accessories are all sized to accommodate this 50% flow increase, and also the new branch you are taking to this new area doesn’t have a pressure drop that exceeds the runs to all your existing areas. There are a lot of other checks as well (system height/pressures, expansion tank size, does new run have freeze concerns, are operating temps the same) but there’s a starting point for you.

 

[SAK9]

Currently the third chiller and pumps are configured as a standby therefore your main electrical switchboard and mechanical equipment switchboard may not be designed for all chillers to work at the same time.Please recalculate your new electrical maximum demand and verify if the main incoming cable, breakers ,busbars etc can take a 50% increase in current.

 

[quark]

Buildtech2,

The way you calculated is not an optimized solution. We are unaware of the pumping and piping scheme. If your chillers have individual primaries, i.e common suction header connects to one pump, pump to chiller and chiller to common primary supply, then this portion of system resistance remains unchanged. System resistance in parallel circuits is non additive.


If your secondary pumps are feeding common in to a secondary header then you need to change them but if your secondary pumps and headers are separate then it is a different story.

 

[Buildtech2]

Both primary and secondary pumping systems are connected in corresponding common headered system. So both primary and secondary pumps need to be replaced with higher head pumps. As mentioned by SAK9 that third chiller and pumps are configured as a standby therefore main electrical switchboard and mechanical equipment switchboard may not be designed for all chillers to work at the same time. So this option may not be feasible at site.


Thanks once again everybody for your valuable inputs.