Cooling Tower Isolation

[CascadeControl]

Is there any good reason to isolate a cooling tower, other then for service?
It seems more efficient to let the water flow over them.
Is there a minimum water flow I should be concerned about?

[freddy-b]

Sump warmup in a large app would be one.

[tlp261]

Are you talking about isolating one cell or tower while another is on? If so, you isolate so you don't loose capacity in the one that the fan is running on.

[NINAX]

Is there any good reason to isolate a cooling tower, other then for service?
It seems more efficient to let the water flow over them.
Is there a minimum water flow I should be concerned about?

Every tower has a minimum flow rating. Having at least the minimum flow through a tower will provide even water distribution and full wetting of the fill to prevent scaling.

[willf650]

I always thought there was no reason to isolate the towers but after we got some info from some engineers who design nothing but large chiller plants we got the same info Ninax said. Was also told one tower with the correct water flow is more efficient than two with not enough flow. Still don't know if I believe it but in the case of the last plant I did I changed the programing to run one cell per chiller as requested.

[simsd]

What we've been doing is running two towers at the same time and modulating the tower fans together rather than ramping one up to full speed and then bringing on the other. VFD company says two towers at half speed is more efficient than one at full speed. Of course this is assuming you have VFD's on the tower fans.

I know this doesn't have anything to do with scaling or isolation, but thought I'ld
throw in my two cents.

[CascadeControl]

I just completed a controls upgrade of a large central plant and I changed the sequence from dedicated towers to running the towers together. I appreciate all our comment and will use them going into functional testing. Thanks

[simsd]

VFD's on the fans?

[CascadeControl]

2 big towers 6 cells each.
Four of the 12 cells have VFD's

[HVAC-DDC-Guy]

I just completed a controls upgrade of a large central plant and I changed the sequence from dedicated towers to running the towers together. I appreciate all our comment and will use them going into functional testing. Thanks

Ninax is right, it is the spray heads ability to properly wet the fill. If you have multiple chillers with dedicated condenser pumps, you will not have sufficient condenser flow with both towers on and one chiller. When you check it, observe the spray nozzles. If they dont spray the fill properly, then one tower is warranted. If they do, then you probably have too much condenser flow through one chiller.