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Grizzly
23-03-2013, 09:57 PM
Hi Guys.
I was on an Industrial site last week that was using a Danfoss controller.
Which loaded both multiple compressors and the condensers 4 fans.

These fans load one after the other in short bursts, starting at the gas intake and liquid discharge end.
Whilst the short cycling is more evident whilst we are experiencing the very cold ambients of late!
Apparently when the ambients are warmer, a Fan will take the lead and the others will load up and down around it.

I had been told that especially with the Blend refrigerants that we now have, it is better to have the fan nearest the inlet and outlet pipework as lead!
This the reduces the situation where the hot discharge gasses have travelled through the condenser. Until reaching the duty fan and being cooled.

This cooled refrigerant Liquid then travels back through the condenser before exiting.

En_route it can be influenced by the warm / hot gasses travelling towards the cooling condenser fan!

In short.
You have hot gasses travelling through the condenser and below it you have the cooled liquid flowing in the other direction.

Could you get a situation where a blend may split?

Either way it is not an ideal scenario!

I am told the rotational and sequenced start up maintains balanced fan running hours.
With none stopping for long periods the bearing wear and seizures are reduced.

Both are fair comments, any thoughts?
Grizzly

The Viking
23-03-2013, 10:59 PM
:D

Now then dear old bear,
Interesting that you should ask that question now when I'm working for a company flogging, amongst other heat rejection systems, condensers and their associated controls...

But to answer your question, the manufacturer we represent recommends all fans being inverter driven and speed controlled together as one, just to minimise the risk of blend fractionation.

(Need a quote for new controls? )
:cool:

.

Grizzly
24-03-2013, 07:46 AM
:D

Now then dear old bear,
Interesting that you should ask that question now when I'm working for a company flogging, among st other heat rejection systems, condensers and their associated controls...

But to answer your question, the manufacturer we represent recommends all fans being inverter driven and speed controlled together as one, just to minimise the risk of blend fractionation.

(Need a quote for new controls? )
:cool:

.

Sadly I no longer hold the purse!

But the issue I have is VSD's don't like power fluctuations or unclean supplies. (More so the larger the motor)

The further you travel to the extremities of this fair isle. usually the further you are from the power station.
Therefore in my case VSD's are susceptible in parts of Devon and Cornwall.

So there may be merit in considering which fans lead then?

Thanks for the input.
Grizzly

Nico
24-03-2013, 02:29 PM
I always thought that the VSD can handle and correct most power supply problems.
Ever minor undervoltage can.
Am I wrong in that? and where can I learn about that?

monkey spanners
24-03-2013, 04:36 PM
I think the first fan to start needs to be the one by the outlet of the condenser, often this is the same end as the inlet, this prevents the hot gas coming in from causing the condensed refrigerant to warm up and possible vapourise again.

I prefer to run all the fans off one speed control, but it does mean there is potential for one fan to fail and damage the vfd so nothing will run. I have a system where i run the fans independantly for this reason as a failure would cost 7k a day in spoiled product.