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cooltrain
02-08-2003, 03:55 PM
Hello to everyone. I'm just new in this forum and have read enough to be convinced that I can really learn alot here.

I need your advice on this subject.

We have a high failure rate (leakage) on our chiller barels.

One reason that I can think of is freeze-ups that may occur during loss of charge and water flow failure.

During loss of charge, freezing could occur at the outlet of the EEV extending into the tubes in the barel and causes contraction leading to stress and eventually leakage. Similar thing could happen during water flow failure.

But this freeze-up is suppose to be prevented by the freeze stat.

The stat is set to cut-out at 38deg F. but no trip-off so far has been registered by the stat. It is also proven functional.

The chiller barel is a two-pass counter flow type. I think this is mostly typical.

Refrigerant inlet and outlet are on the same end. The water "IN" is near to the refrigerant inlet and outlet while the water "OUT" is at the other end. Both water lines are on one side.

The stat sensor is located near at the water "OUT" side.

Could this be a wrong location of the sensor? It may not be able to sense the freeze-up near the EEV outlet? Is it supposed to be installed near the EEV outlet where freeze can favourably occur?

i'll be more than happy to hear your comments.

frank
04-08-2003, 08:37 PM
I'm a little concerned that you could get freezing with a loss of charge or water flow - these 2 items should be protected by a flow switch and an LP switch in the control circuit. Standard items on all chillers and items which should be tested during routine servicing.

The freezing after the EEV indicates that either the EEV is not working right (causing too much of a restriction) or that you have a short gas charge. Normal frosting can be eliminated by insulating the liquid line up to the point that it enters the evaporator.

Maybe you should have someone who is familiar with chillers take a look at the machine before you lose it. :eek:

herefishy
04-08-2003, 10:54 PM
Hi cooltrain :)

I get the impression that you are engaged with the mfgr of such product that you are discussing.

First of all, I think that your logic regarding the freeze stat location is entirely backwards. If you are short-charged, you will have very cold (flashing gas) at the inlet of the refrigerant (gas) circuit. Mind you, that if you are short-charged, you will only be freezing the water when there is no load on the machine (no water flow). In effect, when no water is being called for.... the compressor is running, because the operating thermostat is not satisfied, and the only effective cooling that you are doing is at the point of the EEV outlet, with no water flow. The water oulet temperature does not see this cooling going on on the other side of the evap, becuase the superheat is (so) high by the time it gets there (and there is no water flow anyway). :)

In a freeze-up situation, there is no water movement. the freeze stat location must be near the outlet of the expansion device (sensing the water circuit temp) in order to protect against the long run times of short-charge, dirty condenser, etc.

'hope that helps.

cooltrain
06-08-2003, 10:58 AM
Thank you Frank and Herefishy for your reply.

Actually, I am investigating the cause of this failure. We are getting this barrel from a vendor and need to know where the fault originates e. g. material weakness, application mistakes or technicians fault.

The result is a valuable info for us in the service and maintenance and perhaps I can recommend modification to the manufacturer.

The barrel is not suppose to break on the event of freeze-up or flow failure if it is properly protected.

My quick guess was the stat sensor. We will start on this before we finally conclude that it is a materials failure.

Thanks a lot.

P.S.
I think I posted under the wrong category (training). Sorry, I'm just new here.

lin
06-08-2003, 02:10 PM
On the situation of shortcharge or liquid line restriction, the evaporating pressure will drop down, and the temp of EEV outlet would be lower than freezing point. maybe there will be some ice built up arround upstream tube in evap. but the tube temp rise quickly follow the stream(because of high temp diff between tube &water, and low cooling capacity), ice cann't develop any more.

So unless the flow fail, low evap temp mostly wouldn't break system. many chillers have their LP switch setting on 2 bar(R22), saturated temp is -15C.

Andy
06-08-2003, 07:58 PM
Hi:)
I would agree with Marc, L.P set just about or slightly below freezing. Water off cut out at 1.5 deg C and flow fail straight out at anything much less than full flow. You could add a 10 sec establishment timer to short out the flow fail, but no more.
It's not rocket science you know, just common sense:D :D
Regards. Andy:)