ice removal from evaporator coils

Many a times , there is large ice built up on evaporator coils. We tried various means like water spray, use of blow torch etc to remove this ice.

Is there any other simple method & other means of removing this ice.

Whay this ice gets formed & how to reduce that is other issue. But we can not control these activities & have seen that many a times the evap coil is even unaccessible due to very very odd loading in the cold stores inspite of racking systems & defined methodology of stacking in the cold stores.

Hi from best practices manual:-

Types of Defrost

There are four common methods of frost removal and a fifth
hybrid method.

Hot-Gas Defrost
In a hot-gas defrost system, high-pressure, high-temperature,
refrigerant vapor is discharged from the compressor and routed
to and passed through the evaporator coil. The gas is often
managed by a pressure regulator at the coil outlet, maintaining a
pressure of 65 to 95 psig within the coil. In addition, there may
be a master pressure regulator on the main hot-gas line that
reduces pressure to about 100 psig. Any liquid or vapor
refrigerant leaving the coil is typically returned in the coil
suction line.

Water Defrost
In a water defrost system, warm water (typically 40 to 80°F) is sprayed over the coil surface.
Although well or city water is sometimes used directly, there is usually a tank or pit where defrost
water is stored. In a few cases, the water is heated by steam or electric resistance, but normally, it is
heated using heat recovered from the refrigeration system. In most cases, a remote condenser sump
serves double-duty as a defrost water tank, and water is heated
during condenser operation.

Air Defrost
Air defrost is used in spaces where the refrigerant is below
freezing and the air temperature is above freezing. The flow of
liquid refrigerant is interrupted, and the fans continue to operate,
blowing air over the coil surface to melt the ice.

Electric Defrost
Electric-resistance defrost is fairly uncommon in industrial
refrigeration systems. Resistance elements are located on the evaporator coil, in contact with the
metal. The elements heat the coil to melt accumulated ice. The size of the elements ranges typically
from 10 to 40 kW per coil.

Hybrid Defrost
Although uncommon, some systems use a simultaneous combination of hot-gas and water defrost.
A typical application would be a freeze tunnel where completely eliminating all frost quickly is
critical to productivity.

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Originally Posted by smpsmp45

Is there any other simple method & other means of removing this ice.

Whay this ice gets formed & how to reduce that is other issue.
.

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If your system is not defrosting correctly, automaticaly then the defrost system needs looking at and repairing, adjusting or replacing to ensure it does work.
If the system does defrost automaticaly but ice builds up in one area for no real reason then you need to look at what is causeing the ice.
If the evap is near a door that allows air to enter the room and go to the evap then this in my opinion would be the major cause.

Cheers taz.

Normaly one disign to have 4 defrost cycle every 24 hour.
If the evaporator is getting to much ice it is due to the fact a lot of moisture is getting in the freezer

Then you should increase the defrost cycle from 4 to 5 or to 6 . Of course you have to recheck the refrigeration load due to fact you are lowering the run time

Normaly you install a vestibulo (room) in each door at 5°C to reduce the humidity getting in the freezer

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Originally Posted by gwapa

Then you should increase the defrost cycle from 4 to 5 or to 6 . Of course you have to recheck the refrigeration load due to fact you are lowering the run time

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Or defrost longer on each cycle. You need to check the evap after a cycle to see if it is completely defrosted. To get the coil clean, you may have to run it through a couple of longer closed spaced defrost cycles. After this monitor the defrost for a week or so and adjust your times/cycles accordingly.

Also, make sure all of the defrost controls are working as designed.

Ken

We do have defrost system which is efficient. But many a times due to negligence of maintenance staff, this phenomenon takes place. Then we have to use some other means to remove the ice. If we try out some external heating methods, the wire gets hard due to cold temp inside the room. Blow torch is again a danger situation. People use screwdrivers & all that stuff to remove the ice & that can damage the fans etc.

Hi smpsmp45
A few questions.
How often does the ice build up and where abouts on the evap?
What type of defrost do you have?
How often do you defrost and how long is the defrost time?
What is the negligence of the maintenance staff you talk about?
Are the doos sealing properly?
Generally ice build up is due to a problem with the defrost system, moisture getting into the room or moisture from the product.
If you provide more info I am sure someone will solve your problem.
Paul

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Originally Posted by smpsmp45

We do have defrost system which is efficient.

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If you are requiring manual chipping and a blow torch, your defrost system is not operating properly.

What is your room temperature and the coil temperature? Also, what is the temperature and humidity of the space that opens to the freezer?

You have one of two issues here. There is too much moisture getting into the room due to doors not properly sealed, infiltration from poorly sealed seams or doors being left open too long.

Your coil is not being completely defrosted when you terminate defrost and go back into operation.

What type defrost are we dealing with here? Air, hot gas, electric or water wash?

If it is hot gas, is the hot gas pressure set correctly and is the coil getting hot enough to fully defrost the coil? Next is the valve sequence proper for the coil to sequence and isolate and clear the coil? What controls your defrost termination?

If you are on electric defrost, are all of the heaters working? Is the defrost cycle long enough to clear the coil?

There is no hard and fast rule for defrosting times or cycles. Typically you will start with 4, but some times you will have more or even fewer.

If it is air defrost, what is the box temperature and how long do you cycle the liquid feed off?

Using a heat source is a bad idea as it creates a thermal shock on the coil and can cause serious damage or failure. Also, using picks and chipping at the ice is dangerous as you could damage the finned surface or even penetrate a tube.

In either case, these are not acceptable methods for a normal defrost.

Ken

Quote:

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Originally Posted by smpsmp45

We do have defrost system which is efficient. But many a times due to negligence of maintenance staff, this phenomenon takes place. .

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How many evaps are in the room?
If there are more than one do they defrost at the same time?
Make sure that all evaps defrost at the same time and see if the problems persist.
Somtimes when evaps defrost at seperate times, the moist air from the defrosting evap can go straight to the running evap and cause ise to build up on it.

taz.

smpsmp45, in order to get some help, you need to answer a few questions which have been ask in the above post. We can't help anymore at this time until you provide the responses.

Ken

may be the evap is under sized according to load

Well Well. The defrost cycle works good in normal conditions. It is hot gas defrost system. & we do not face problems when it is operational. The issues come in when
1. When the product is loaded at temperatures of more than -20 deg c. That also carries lot of water as we can see the cartons are wet. It is a typical mcdonalds distribution center.
2. The loading in the cold store is generally at specified temperatures & the problem is not seen then.
3. many a times Mcdonalds import some items which come in container loads. Then loading into the cold stores takes time due to earlier product inside. So they keep in the ante room till they rearrange the cold store products.
4. The negligence now comes into play. The team on site is not checking at this time wherein max moisture goes in the cold store along with the wet cartons. They should manulaly defrost the system when this happens. But like all the mainteneance team, they wait till the problem becomes exceptionally bad.
5. The only alternative left is to clean up the coil then.

Hi

Its seems to me that the coldroom is being missused,I had a situation where a freezer coldroom was to small for the stock at certain times of the day.The store would over stock the freezer cold room then store the excess in an ht coldroom until the shop floor freezers had been stocked.The moisture from the continuall door opening and wet boxes from Ht coldroom went straight for the coil.

They kept calling me out until I said no more,I told them they needed a refrigerated trailer to empty and defrost coldroom.After four times in 6 months they soon got fed up and have now changed they delivery times and guess what,no more call outs.

So I would spend some time in there taking pictures to prove its missuse.If you show them where there going wrong and give them a solution it may solve your problem.

Regards Bernards

Dear Bernards,

Many thanks for the practical view. We shall do that

Now we are beginning to see the issues. As noted above, the room was not designed for the way it is being used so you need to address how to use the room or how to adjust your procedures to make the room work.

One easy solution may be to make it part of the standard procedures to have the "Operators" take the coils through a couple of manual defrost cycles to help clear the frost before it becomes a problem.

Ken

Infact we issue a standard procedure for daily/ six monthly checks etc. But that is kept in the files.

Anyway issue still remains as to how to clean up the coil eventually.

Hi

If you must defrost the coil then I would valve the liquid line off and set defrost for 30min every hour for as long as the other evaps can hold the temp.Return with back mounted hot water sprayer and remove whats left if any.

Lets face it,defrosting a freezer coldroom blower is one of the down sides of our job.:(

Regards bernard

You should change length of defrosting or/and frequency of defrosting. Coil should be defrosted before it is frost plugged(no space between fins). Additional frost on the coil require additional time to melt it.

Gentlemen

I am from the tropics and was just posted to work in a brewery cold-cold Mongolia. We have an NH3 system with evaporative condenser using fan (winter mode) and fan+water (summer mode). Cutoff for winter/summer is -9.9 deg C (14.2 deg F). The water is pump from an indoor sump to the evaporative condensor outside.

However, I find that the evaporative condenser may be undersized (high discharge pressure +18-19 bars!), and sometimes turn on the water pumps while the outside air temperature is -15 to -18 deg C (5 to 0 deg F).

What I would like to learn from your experience is: at what lowest outside air temperature do you continue to spray water without fear of the condensor coils developing ice?

We do not have any defrosting device installed or heater in the water basin. Could anyone point me to the right direction on this.

Thanks a million.

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Originally Posted by stepperider

Gentlemen

I am from the tropics and was just posted to work in a brewery cold-cold Mongolia. We have an NH3 system with evaporative condenser using fan (winter mode) and fan+water (summer mode). Cutoff for winter/summer is -9.9 deg C (14.2 deg F). The water is pump from an indoor sump to the evaporative condensor outside.

However, I find that the evaporative condenser may be undersized (high discharge pressure +18-19 bars!), and sometimes turn on the water pumps while the outside air temperature is -15 to -18 deg C (5 to 0 deg F).

What I would like to learn from your experience is: at what lowest outside air temperature do you continue to spray water without fear of the condensor coils developing ice?

We do not have any defrosting device installed or heater in the water basin. Could anyone point me to the right direction on this.

Thanks a million.

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Condenser coils will never develop ice, because their temperature are above 0 deg C. Condenser water has positive temperature as well. Make sure that pump will cut off first, otherwise you have opportunity to freeze fan blades.

Hello Sanjay,

I had gone through your thread. First thing is that I fully agree with Ken. You have set the timing of the defrost cycle after assessing the ice formation. Forming of ice to such an extent so as to defrost with blow torch is not correct. In addition to other problems, it will damage the coil fins.

While designing the cold room, you must have been provided with some requirement details. If loading in wet boxes were not there, you should make it very clear to your customer that what he is doing is wrong and harmful to the plant and that you can not be held responsible for such things.

I would advice you to reassess the time period of defrost and and also the time required for running the defrost. I hope the it is electrical defrost that you have.

smpssmps45
I note that you started your thread in the middle of september.
From all the advise you have had have you been able to resolve anything?
It is a real pain when evaps freeze up isn't it. You can be the most diligent Engineer and still get caught out sometimes, so don't be to hard on your maintenance staff. Unless of course you suspect that they really are the problem?
I myself have been in cooler pods Kangoing the sheet ice off of the pod floor. BUT.. As has been said! If it is the evap coils that are blocked. That's a different story!
You don't say how your coldstore chamber is designed, with regard to how the evaps are mounted.
Are they suspended (eisier to deal with), or pod mounted with access from the side of the pod. Via a INSULATED DOOR ( that can be relevant).
Anyway a practical solution is to isolate the evap from it's cold enviroment. Not so easy sometimes, so if it is the pod type. Get some large suitable sheets of polystrene or similar.
Place these across the face of the pod and retain in place. Only you can decide as to how.
On the suspended type ( these are much more common. Particularly on smaller applications) Borrow from despatch a roll of shrink wrap. Wrap up the whole evaporator in the cling film.
Once either method has achieved thermal isolation.
Initiate manual defrost and cook ( sit down, put the kettle on and wait.)
Basically only you will be able to tell when "cooking is complete" by visually checking the coil status.
The beauty of this method is you can apply the heat locally without to much heat introduction to the rest of the chamber.
Hope this is of help?
Grizzlyhttp://www.refrigeration-engineer.co...ons/icon14.gif

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Originally Posted by Sergei

Condenser coils will never develop ice, because their temperature are above 0 deg C. Condenser water has positive temperature as well. Make sure that pump will cut off first, otherwise you have opportunity to freeze fan blades.

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True Sergei, but if you have a condenser that is last on the lead list it is certainly possible to freeze the sump. I know, because we made a nice ice cube out of the sump of one condenser last year when the temperature dipped below 0f for a few days. There was a pool of liquid water extending about 12" around the sump heater but the rest of the pan was frozen. Looking back through the logs we found that the pump had not been called for in over 48hrs.

Now we drain 1-2 of our 3 condensers for the winter.

Winter is also a good way to find minor water leaks on condensers - I have seen some really nice ice flows build up from a drip a minute leak!

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Originally Posted by brian_chapin

True Sergei, but if you have a condenser that is last on the lead list it is certainly possible to freeze the sump. I know, because we made a nice ice cube out of the sump of one condenser last year when the temperature dipped below 0f for a few days. There was a pool of liquid water extending about 12" around the sump heater but the rest of the pan was frozen. Looking back through the logs we found that the pump had not been called for in over 48hrs.

Now we drain 1-2 of our 3 condensers for the winter.

Winter is also a good way to find minor water leaks on condensers - I have seen some really nice ice flows build up from a drip a minute leak!

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Hi, Brian.
Water sumps of your refrigeration plant are outside, but stepperider's water sump is inside. This is a huge difference. I'm surprised that somebody designed the plant in Pennsylvania and located condenser sumps outside.

Sergei.
In U.K. All our evaporative towers are outside, or at least I have never seen one inside yet!
I have not seen anything as harsh as Brian describes, although some of my colleages in the colder regions of our isles may disagree!
I have seen ice damaged sumps due to faulty frost stats though.
Brian you refer to leak identification due to ice forming.
Try 2 young "Chlorination Experts" trampling through the sump in their "Hob Nail Boots". Quote "it wasn't Me"
Grizzly

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Originally Posted by Grizzly

Sergei.
In U.K. All our evaporative towers are outside, or at least I have never seen one inside yet!
I have not seen anything as harsh as Brian describes, although some of my colleages in the colder regions of our isles may disagree!
I have seen ice damaged sumps due to faulty frost stats though.
Brian you refer to leak identification due to ice forming.
Try 2 young "Chlorination Experts" trampling through the sump in their "Hob Nail Boots". Quote "it wasn't Me"
Grizzly

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Grizzly.
I'm talking about water sump, but not about evaporative tower. Condenser itself, certainly, should be outside. Water sump can be located at the bottom of condenser(outside) for warm climate and inside the warm building for cold climate.

Sergei
Sorry crossed wires. I have never seen one with a remote sump. Have I got that correct?
The design is different to anything I have seen.
Have you or anyone reading this a photo?
Iv'e led a sheltered life you see! Pun Intended!
Respect- Grizzly.

We are getting off-topic a bit guys. Ice removal from evaporator coils is different than indoor remote water sumps.;)

Grizzly, a remote sump (or indoor sump) is simply a water tank and pumps for the evaporative condenser water supply (located in a warm environment like the engine room). This is very common in colder climates where the system operates year round.

smpsmp45,

1] curious to me that you depend on maintenance person to handle defrost. aren't that to be automatically done?
2] storage management is poor; has to improve the method.
3] have u considered lowering ante room temp?
4] can u check on SST of system?
5] can u check incoming product temp against design assumptions?

above will define your focus point in troubleshooting.

We use a steam heater like this one http://www.cleanstore.co.uk/images/large/2255a.JPG

As I had noted in an earlier post, defrosting with a steam system is not a good approach. If you hit the coil too fast or too hard with the steam, you can thermally shock the oil which can lead to premature metal failure.

Your best bet is to either get the defrost working properly or get the humidity source under control.

ken

Ken with all my respect but I don't think we can heat that much the oil that it reaches a higher temeprature then discharge temperatures.
Because that's the temperature for what's it designed for
Further, we use it to melt the ice, not to heat up the copper or the steel of the evaporator.
We direct it to the ice of course and you heat of course the fins but you always can touch the fins with your bare hands. It doesn't become that hot.
Also, the heat is spread very equal over the fins and it distributes the heat equally.

Peter if you have an untrained operator (and we all know that there is no such thing), they can put so much steam on the coil that it can thermally shock it, especially if it is not heated evenly. Too much heat in one area can create thermal stress which can lead to a material failure.

So yes, in the hands of a properly trained person, a steam generator can be used. But look at the steam again....more humidity in the space where you do not need it, for the other coils or the only coil to deal with. I still say that the correct procedure is to locate the design or operating problem.

I have in a rare situation, used steam to get rid of ice, but I still located the problem rather than continue to use steam for a crutch.

Ken

Ken, I agree with you for 100%, the cause of the problem must be solved.
And certainly, steam as a standard is not done.
We only use this small device from Karcher to defrost after a resistance failure or something similar when the coil has blocked up with ice.
If you use water in a freezer, then the whole floor becomes an ice-skating rink.
In a small counter, sometimes the sewage are too small to use water.
We use it also to disinfect the small drain pans in counters.
You sometimes find strange creatures in the drain pans.

In a case like these ones

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Originally Posted by Peter_1

In a case like these ones

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Oh ! This needs a new cold room !!!! Defrost all !:eek: