Coolling tower converted to vfd

[Peztoy]

Some company converted the closed loop cooling tower to vfd.
Vfd controlled by loop temperature.
Used to be a two speed motor.
They ignored the tower dampers and spray pump .
Now I have the tower dampers, spray pump and a vfd that don't work together.
Anyone know if BAC or Marley has docummentation on how to make this work properly.

[DDC_Dan]

I've done several closed loop towers (sometimes called fluid coolers here), never seen one with dampers.

I always do the same sequence. On rise in temp above SP, spray pump on. Further rise, fan on, min speed, then modulate speed up. On fall in temp, modulate speed down to min. On fall below SP (approx. 2 deg.), fan off. On further fall, spray pump off.

How are the dampers arranged? Do they have actuators? What controls them now? Something new to me...

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[Tech Rob]

I would use the same control sequence described above and lock the discharge dampers open or cut them out altogether.

[DDC_Dan]

Are the dampers a cold weather thing? We dont see them here in sunny Phoenix.

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[Tech Rob]

Modulating discharge dampers are used on forward curved fans as a means of condensing temperature control in cold weather.

[DDC_Dan]

Modulating discharge dampers are used on forward curved fans as a means of condensing temperature control in cold weather.

Got it. Then yes, it would make sense to just lock open or remove with a VFD retrofit.

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[hotrodrob]

The dampers might not be modulating. Ive worked on several towers where the dampers are used to retain the heat in the tower in the winter to aid the sump heaters. If these are this type of damper i would use the call for spray pump to open them and the end switch to enable vfd. Then use loop temp to start and control vfd with a 4-20 signal.

[ncboston]

The dampers might not be modulating. Ive worked on several towers where the dampers are used to retain the heat in the tower in the winter to aid the sump heaters.

x2

[Tech Rob]

I guess that could also be what they're for. Especially up there in Ontario. I have never seen a setup like that.

[hotrodrob]

I also forgot to mention not just aiding the sump heaters but keeping the heat exchanger from freezing in a closed loop tower. Ive seen this setup more on evapco's than anything. of course the damper motor will fail in the middle of summer and will stump you if you have not seen this before.

[jnsrose]

The dampers always tend to lock up and rust open or closed.

[Peztoy]

Got back to the site.
The new vfd is set to maintain 80*f. The sensor is down in the mechanical room.
On the roof the rest of the control system remains. The sensor is at the cooling tower.
Modulating discharge dampers at the fans were still in operation. I disconnected them and left fully open. These were to control capacity, but now the vfd does it.
In the next few weeks I'll be putting water back into the tower sump and the spray pump will come into play.
Nice if they'd use one temperature sensor to control everything.

[buford]

I would use the dampers as stage one then as DDC dan says stage on the rest.You would think the dampers would be up on the outlet of the tower to keep as much heat in the bundle.What protects it from the cold weather now? With no sump water and sump heat there must be a 3way valve thats left cracked opened or is the bundle drained also?

[wcsmith]

What type of fluid cooler and what type of dampers? If this is an older centrifugal cooler this may have dampers inside the fan housings near the fan wheels used for capacity control. If this has dampers as part of a discharge hood these are called positive closure dampers designed for specific process designed to reduce heat loss, typically used in colder climates.
If your dampers are the capacity control type then the dampers can be locked in the open position or removed since you would be using the VFD as capacity control. If these are positive control dampers they would/should work of a controller that is set-up to maintain the required heat and to open as the motor starts.
The pump for a fluid cooler should not be set on a VFD since lower water coverage than what is designed to cover the coil will causing scaling and/or icing depending on the location.

[Peztoy]

Glycol in a closed circuit tower. Pump run at 100 %.
Dampers inside the fan housing are disconnected as noted. No dampers on top.
I put water in the sumps. Spray pump is working. So far so good.
One common temperature sensor would be nice.