Frost elimination inside a cold storage room

Hi all, I been reading several threads and seems all have a strong knowledge in the field. Congratulations.
I’m having problems with the frost formation over the walls and ceiling inside the cold storage rooms (-20C). I’m aware that this frost is coming through the door from the lobby air with almost 85% HR and 25C. The cold room door already has plastic strips overlapping 2 inches, trying to block the air passage but the problem remains. Using air curtains or desiccants wheel is no option at the moment,due to lack of space. Some guy told me that increasing the air movement (via turbo axial fans) inside the room could reduce and even eliminate de frost.
Is it true? Some of you already try it?

Hi Frio1,

Is there any cooling in the lobby?
It would help a great deal to eliminate the humidity out side the freezer door.

Turbo fans can help too but then you will need more defrosts.

Air Curtain is no good as it pushes inside the freezer some 10%of the humid air.

Chemi:)

Hi Chemi-Cool:
The lobby is not refrigerated neither acondicionated, the outside air conditions are 30C and 80%RH. More defrost could be OK.

Frio1

Hi, Frio1 :)

Quote:

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Originally Posted by Frio1

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I’m having problems with the frost formation over the walls and ceiling inside the cold storage rooms (-20C). I’m aware that this frost is coming through the door from the lobby air with almost 85% HR and 25C. The cold room door already has plastic strips overlapping 2 inches, trying to block the air passage but the problem remains. Using air curtains or desiccants wheel is no option at the moment,due to lack of space. Some guy told me that increasing the air movement (via turbo axial fans) inside the room could reduce and even eliminate de frost.
Is it true? Some of you already try it?

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One question...frost formation are all around on panels or maybe more on connections of panels....

The best is to remove as much as possible humidity outside in manipulation corridor as Chemi-cool suggested using some additional coolers-dehumidifiers ...inside of freezer room is not easy


Best regards, Josip :)

I think the problem of humidity outside the cold room needs addressing as a matter of urgentcy to help stop excessive load of the evap but i don't think this is your only problem. What sort of frost and where is it forming? Moisture ingress into the room would cause 'snow' effect near to the doors and around evap and fan gaurds. If it is frost and ice build up on the ceiling I would check the defrost termination and fan delay. Usually too high a termination with little or no fan delay causes the heaters to get too hot causing steam and them the fans comming on and blowing the warm moist air around the room. Check for other holes in the panels (pipes)

Leture over. Take a breath and carry on!

Monkey spanners are you based in north west?

Hi Josip and Spoc, the frost formation is mainly in the middle of the panel not in the seams. The frost is like snow over the door and 2m away on the ceiling, also in the corners of the room. The frost in the evaporator is light and its defrosted every 8 hrs by hot gas, the fans have a 3 minute delay.

What size is the room? I have a feeling that it is only small an poss a Porkka or equiv.
You get what you pay for.

8 hours for hot gas is not enough and I would reccomend little and often. I usually set them for every 4 hours with a duration of 10 - 12 mins and a termination of about 8 - 10 deg C but this does depend on the size of room, equipment and where the Evap probe is sited asumming it is electronic.

Hi Spoc. The room dimensions are 30m long x 16m wide x 7m height. It has two recirculated evaporators FRICK, model SCA-463TL operating with a temperature difference of 10F.
I’ll reschedule the defrost times at your suggestions.

Snow is caused by moist air.Check off the likely causes,,gaps in door seals, ill fitting panels, large bore drain tubes,missing door sweeps,missing door curtains and excessive door opening frequency.Also over long defrost periods and fan delay periods.Go through the list and make sure every one is addressed.Put the unit into defrost and monitor the process and see when it clears.Set you controls so that you allow for total ice clearance and a couple of minutes extra, then wait to see how long the fans stay off.Bring the fans on when you get an even suede type frost on the coil.

I presume that the cold store is being used for storing frozen food and not being used to freeze warm product,

I doubt the problem is with the refrigeration system. In all probability the frost issue is from the warm moist air entering the doors. It will help if the area outside of the freezer is refrigerated to reduce some of the moisture content of the entering air. However, this will not completely eliminate the problem.

Even with the external area being cooled the doors and walls inside the door will still accumulate frost.

The warm moist air entering the door flows through the top of the doorway when the door is open. Strip curtains DO NOT eliminate this, they simply reduce some of the effect. When the moist air enters the door the moisture in the air simply freezes onto anything cold enough to generate frost.

As the warm air rushes into the door (at the top) cold air rushes out through the bottom of the doorway.


Hopefully the evaporator coils are not mounted above the doors!:o This actually makes the problem worse!!!!

More defrosts cost money and is shutting the stable door before the horse has bolted. The answer is partly to ensure you have a rapid action insulated door with good controls (eg inductive loops, PIR, pullcords, etc) that limits the door opening time to around 7 seconds or less - when a door is opened it takes a while before the denser air inside the room overcomes it's inertia and starts (accelerating) to fall out at low level and at the same time is replaced by the much warmer air in your lobby. I would keep the strip curtains as a secondary back-up. The warmer the outside air the more unit volume of water vapour hence the snow on walls. Some of this vapour will condense also on the chamber floor and with prolonged door openings will freeze as ice which isn't a good idea with powered FLT's, etc. Even with all of the above you will still have a problem (reduced though) as has been said by others earlier because of the near ambient temperatures in the lobby. Ideally this should be refrigerated to say +1/+3oC so that the cold room incoming air has a much reduced water vapour content and a lessened wall snow affect. You might justify this additional capital expenditure through reduced cold store defrosts as well as reducing that room's plant energy consumption. In an ideal world I would also fit (to the new lobby refrigeration) a dehumidification system which would then result in virtually no frost inside the cold room - but no doubt you could not justify this in your situation. One last thought on lobby refrigeration - if it is big enough it might be possible to create an enclosed partitioned airlock. Hope all this may be of use.

Hi guys,

I plug for the fan delay being a likely caus , Id make it temp delay and not time delay. Im assuming there are no big holes in the coldroom or large crackes, also the door is not being left open alot.

There are cold rooms in much hotter countries and more humid countries that dont seem to have to much trouble.

Im a great beliver in 4 defrosts a day.

any pictures??

Quote:

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Originally Posted by Frio1

Hi Josip and Spoc, the frost formation is mainly in the middle of the panel not in the seams. The frost is like snow over the door and 2m away on the ceiling, also in the corners of the room. The frost in the evaporator is light and its defrosted every 8 hrs by hot gas, the fans have a 3 minute delay.

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Hi Folks
Where access to a room at -20 C is direct from an anti room at +25C/ 85% rh the laws of physics will cause quite rapid air exchanging with the resulting snow generation . The only fully successful method of ensuring a frost free space in the cold store is to condition the air in the load in load out area, but if the complex has not been built to accommodate this a retro fit is expensive . This topic has been responded to else where in this forum describing Desiccant Wheel technology through to refrigerated coils . If the provision of suitable conditioning of the load out area is not an option then the access door opening closing cycles will have to be addressed. I agree with US Iceman the location of the room evaporators and air flow have a big effect on the generation of the snow. If the evaporators are above the door and the air flow parallel to the air being induced the entrainment effect will make it worse. Snow build up in the corners of the wall where the door and on the ceiling 2 metres away is characteristic of the "S" flow of air through door ways which is fully explained by ASHRAE. These are the points where the velocity of the warm air , caused but the buoyancy effect is slowed down sufficiently to freeze and deposit the "snow". Extra defrosts will not necessarily solve the problem either. Here in NZ our local MAF come down hard on us in meat export stores if there is an ice build up. Most new stores are designed with an "ELA"; Environmental Load-out Area", with refrigerated air conditioning systems installed. If the design and installation is correct the initial extra cost is offset by a reduced operating cost of the cold store for its effective life.

Hi John Hunter:

Thanks for the comments. Your right with the snow pattern inside the room, and yes, I agree that the best way to avoid this problem is conditioned the hall, but at this moment there’s not an economical and practical way to supply treated air to it. Few years ago I read on some internet place, but I misplace the address, that installing fans facing the corners inside the room can eliminate the problem by sublimation of the frost. You are familiar with it?

The use of fans are not a guaranteed solution. The fans that have been used were high velocity units designed to entrain the warm incoming air into the main body of the room . Their placement depends on the location of the existing evaporators and the room air flow direction. Be very aware that this set-up will add to the overall heat load and frequency of frosting on the coils and an increase in operating costs. The reason I used such a system in the past was to stop Snow and Ice forming on a ceiling above meat carcasses. The Snow and ice , started to drip during defrosts and the local MAF shut the room down until we rectified it. The fans were only a compromise they solved some of the problems but created others and I never considered it a success. The store in which this was used was closed down about 10 years ago .
The fans were semi - mobile as I remember it took a bit of time to locate them correctly placed either side of the door with the flow directed at just less than 90 degrees to the incoming air so that the diverging air from the fans induced the warm air into the body of the room. When the door closed the fans were obviously stopped.

I'm in agreement with Mr. Hunter. Adding fans in an attempt to solve this problem is very questionable at best. The problem you face is infortunately a difficult one to solve without major surgery.:(

Mr Hunter and Mr Iceman, I've just carefully read my way through this thread thinking all along, wow theese guys are clever but I think I've got an idea:- placing fans either side of the doors to get the new air circulating better.

You've both just burst my bubble:(. Apparentely it's only a quick fix. So we're saying no other feasable way other than reducing humidity before entry to the room. If this is the case I'm glad I'm not the bringer of bad tidings to the customer.

By the way, Mr Hunter did you like our avenge for you on Saturday in Paris? I'm not sure how we will avail against the spring bocks however.

Sorry.

The only thing I have seen that seems to work decently is from this link...

http://www.hcr-inc.com/productinfo/physicalforces.htm

I've seen some of these in practice and can say they work pretty well.

However, these are more expensive than just placing panel fans (etc) in some position to gain questionable results.

Hi Expat
It would have been better if the All Blacks had done the Job right in the first place.At least the beer fridge kept the beer cool to console us after the defeat.
Any way all the best for Saturday, will be watching Sunday morning our time
Regards

John H

Sorry to intervene in this thread. I have a similar problem with one of my projects. In this case there are two ante rooms and three Cold Rooms. From the first Ante Room you enter into a 4oC Room. Then you enter another Ante Room. From this you enter into a -35oC Room. From this room you enter into a -40oC room. Now the problem is that the puf insulated panel manufacturer has made a complete mess of his work, due to which there are leakages. This is resulting in frost formation at the bottom edges of the the second ante room. We have tried to seal every pint but even then the frost is forming. It is possible that the low temperature of -35oC and -40oC is being transmitted to the wall by metal, as there is no slot on the alumunium floor. What I feel that there should be a thermal break. To make it now will be difficult.

Can some one suggest some means, by which the frost formation is elliminated.

Hi Samirjit.Sen
"We have tried to seal every pint but even then the frost is forming. It is possible that the low temperature of -35oC and -40oC is being transmitted to the wall by metal, as there is no slot on the aluminium floor."
Am I reading this correctly, is the aluminium floor common to the anti room at 4.0C and the cold store at -35.0 C.
The Coefficient of heat transfer of Alum is very high in the region of 200 W.M.C.
Regards
John Hunter

Hello John Hunter.

You are correct. The al. floor is common. There is no cut where the vertical panels are located. It was a very big mistake to have given the panel work to a person who has no experience. Now there is nothing that we can do about the panels. We are attaining the temperatures in all the rooms except that there is a great deal of frost on the floor in the Ante Room. Is there any thing by doing which we can reduce the frost.

Hi Samirjit.Sen
The fact that a complex was designed with a Ali. floor with no thermal insulator between areas of such vast temperature differences would indicate incompetence in the designer. The Ali floor must be the wear surface of a sub structure I presume and the ali floor must have insulation and vapour menbrane between it and the sub structure. Iam trying to picture the construction, but what ever the only positive solution is to create a thermal insulator in the floor surface. This will no doubt be costly and very disruptive to the current operations but I see no other realistic engineering solutions . Others may .

I don't know any cheap cures for this Samarjit. The floor construction seems to be continuous and without the use of tongue & groove joints for the partition panels. The tongue and groove joints into the floor create the thermal break necessary to prevent the problem you describe.

I'm in agreement with Mr. Hunter. The supplier/designer of this insulated building only thought in terms of room size and insulation thickness in the panels.

If they understood what was required they would not have been selected to provide the building as this would have increased their price.:o

Price is a poor indicator of quality!

I am stuck with this problem. I propose to cut about 50 mm of the alumunium strip on the floor from the edge of the common wall panel and another 50 mm strip from the bottom of the wall panel. I presume this will create a thermal break and should reduce the frosting. I tried to have the common wall removed so that I could get the alumunium sheet cut and removed from the space the wall is standing. But it was not possible as the Unit Coolers are fixed.

Please advice if this would give some relief.

Since the wall panels are constructed this way and there is not much else you can do, your suggestion is as reasonable as any I can think of.

I might suggest some type of protection for the area where the metal is removed though, otherwise the isulation will be exposed.

Hello Mike,

What would you suggest to cover the exposed puf insulation. I was planning to pour some more puf soltion over the edges and cover the same with bakelite sheet.

What would you suggest would be better ?

Hi Samarjit,

I think you need something to seal the cut edges to maintain a vapor barrier of sorts. Secondly, I like a higher density plastic rather than bakelite.

If you can install the plastic like a floor to wall coping then it might also look nice too.

Hi Samarjit
I agree with Mike , the more I think of your problem I wonder where the vapour barrier actually is . It is normal practice to have the barrier create an envelope right round the sub zero room. With the continuous Ali floor how is the vapour barrier maintained up on to the warm side of the insulated panel dividing wall with the anti room. I agree with your idea of creating a thermal isolation by cutting the continuous Ali floor but if the vapour barrier is not maintained there is the danger of "Frost Heave" which could lead to much bigger problems with the general structure.
Regards
JH

I think as suggested by both of you, I shall have a layer os high density polythene sheet put at the edges and over whih I shall have a strip pf 50 mm x 50 mm puf poured in and duly covered with again high density polythene sheets.

I completely blame my self , as the contractor to whom I gave the job is absolutely impompetent. In my effor to help him to regain his business I tried to help him, and he has rewared me with a complete mess up. You do not know to what exdtent I had to get the work rectified.

Subsequently in my other projects, I gave the panel jobs to professionals from out side the country and they have done a wonderful job and never had any complaints.

Now I somehow want to get out of this mess at any cost.

I had installed more tham 55 fast freezer doors in Argentina and with the save of energy cost, the investment required for this doors had ben re-paid in less than three years.
Infiltration of warm and humid outside air throught bigs industrial overhead doors is a non predictable heat load, and according with my experience in field is very important to do a big ante chamber, put a big refriferation equipment, choiced in a low suction pressure of -15ºC, with capacity for reheating for control HR.
The basic sentence is ; if there is not water, no ice .
If you want some help mail to
arceyasoc(arroba)arnet(dot)com(dot)ar
Luis Arce

How is underfloor heating effected at that warehouse?

If its forced draft or even barometric stack, there's a huge vapor pressure drive toward the inside. If you interior air circulation is pretty good, it doesn't even have to be great, there shouldn't be any identifiable frost distribution except within a few feet of the doors and within a few feet of the air unit, if its near the ceiling.

And you won't find a singularly vapor pressure introduction by tracking air flow...Though if this is a forced draft system, or probes inside conduit, you probably will find it by air flow.

Are the panels showing presence of moisture? Take an infrared sensor and "shoot" a pattern on the outside skin, just before the sun comes up in the morning..You might find some interesting temperature distribution, which would indicated frost forming in the panels....

As a real quick visual: I have done this on a white panel at the right time of day and year with Portland cement dust....Blow it on the damp panels, take a photo of all the gray patterns, wash it off.

When we fit ducting to chilled rather than cold rooms, we direct a continual stream of air (only 5% of the total air volume) across the ceiling to prevent condensation build up. This increased circulation may do a similar thing for frost build up.
http://80.165.29.186/uk/files/referebcer/I~000021.jpg