Considerable amount of frost/ice on ceiling of cold storage

[stanthonycold]

Hi Guys,

Im working in a considerably large cold storage(5000 TON capacity (shrimp)) that is divided into 2 parts.Our main part is the one we keep at -27 c at all times and the second part is around -10 c.Our problem is that up on the ceiling of #1 cold storage is a lot of ice/snow buildup.Would this be because Cold storage #2 is only -10 were #1 is -27? Would the "warmer" -10 air from #2 cold storage cause this ice to form on the -27 cold storage ceiling if air was leaking out into #1 from #2 ??

Regards,

Kirby

[gregd1401]

Do you have fast acting doors between rooms 1 and 2? Is the product allowed to pre cool in the -10 room before it is placed in the -27 room? Is there a refrigerated loading dock attached to the facility?

[gregd1401]

Also what type of defrost system do you have and is it allowing the coils to drain completely before restarting fans?

[smpsmp45]

The reasons could be many. Is there any ante room. There must be a source of Hot air / outside air to get inside, which is freezing on the top.

[stanthonycold]

Should of stated this better.All product that we store is typically at -18 to -25 c before it is placed in the cold storage.My question is will air coming from the -10 cold storage form frost in the -27 cold storage?The door hardly gets opened going into #2.No product stored in there.

[smpsmp45]

If there is no ante room this can yet happen. May be there is a leak in the panels itself.

[Pykester1]

Where is the ice build up? If it is in the air off path of the evaporators check defrost termination settings, fan delay and drain down times. Excessive ice on ceilings is often caused by too high defrost termination settings. Also check all heater rods are operating correctly, (assuming the coils are electric defrost). You may have a faulty rod in there somewhere causing the unit to stay on defrost too long.

[stanthonycold]

Where is the ice build up? If it is in the air off path of the evaporators check defrost termination settings, fan delay and drain down times. Excessive ice on ceilings is often caused by too high defrost termination settings. Also check all heater rods are operating correctly, (assuming the coils are electric defrost). You may have a faulty rod in there somewhere causing the unit to stay on defrost too long.

The frost is forming on the ceiling above the 3 evaporators and on the ceiling and also where the CS is divided into 2 sections.We use hot gas for defrosting.We defrost each evap for 50 mins,pump down is 6 mins, fan delay is 5 mins i believe.Any sugestions ?

[Pykester1]

50 minutes seems quite a long time, especially for hot gas defrost. What are the termination settings?

[stanthonycold]

The frost is forming on the ceiling above the 3 evaporators and on the ceiling and also where the CS is divided into 2 sections.We use hot gas for defrosting.We defrost each evap for 50 mins,pump down is 6 mins, fan delay is 5 mins i believe.Any sugestions ?

Pump out time - 6 mins

Deforst time - 55 mins

Bleed time - 1 min

Cool coil time - 3 mins

Alarm delay time - 2 mins

[stanthonycold]

50 minutes seems quite a long time, especially for hot gas defrost. What are the termination settings?

Pump out time - 6 mins

Deforst time - 55 mins

Bleed time - 1 min

Cool coil time - 3 mins

Alarm delay time - 2 mins

How long is the norm for defrosting with hot gas ? This section of the cold storage can hold 2500 Tons of -25 frozen shrimp using 3 evaps.

[icecube51]

if you don't have plastic flaps on the doors, you can try a cold air curten to keep the hot air out.
what about the RH outside the coldstore and inside? maybe you bring to mutch moisture in when loading the fridge.

Ice

[ref717]

Indeed 55mins. defrost time is too much, this may be the cause of ice/frost accumulation on your ceilings. What are the sizes of your aircoolers?,45 KW gross cooling capacity aircoolers operating on -27deg.C system can be defrosted for only 25-30mins.,the other datum you provided seems fine,but still all your defrost settings depends on your operation and aircooler size.

You can try to observe your 3 aircoolers and defrost them 1 at a time every 8 hrs. depending on the ice accumulation on the evaporator coils. Check also your valve stations, defective liquid,suction,regulating,relief or defrost valves can make your aircooler operate abnormally.

Installation of plastic curtains in all doors between CS divisions will also help in keeping moisture out.

[Scramjetman]

Hot gas defrost is a very efficient defrost method and should usually get rid of ice in 20 min or so unless it is unusually heavy build up. Might pay to look at how many defrosts are being performed in a 24hr period. More defrosts of less duration can help.

[Segei]

Probably your roof is leaking. Moisture content difference between -10 and -27 is not significant and this is not a reason of the frost. Hot gas defrosting should be done when you have a frost on the coil. Do not over defrost. How often do you do defrost? Did you notice any difference in ceiling frost formation between summer and winter?

[stanthonycold]

We have three evaps in each of the storage rooms, the capacity of each evap is 25.6 TR. The evaps are scheduled to defrost every eight hrs, but at different times.

[sterl]

The moisture that makes frost can be coming in from any part of your building enclosure; from exposed product that has "free moisture" on its skin; by infiltration of warm moist air from outdoors via the traffic openings; or it may remain entrapped in the space because its either not draining during the defrost or is being recycled within the space by high coil surface temperatures and extended defrost periods.....Of these:

You probably aren't getting it from the product cause that would cause freezer burn; and all your production and QC people would be chasing that topic.

If its on the ceiling but not near the door openings: its either no from the traffic openings or its being picked up and distributed so quickly by a nearby evaporator that it never accumulates on any surface between the door and the air unit....

If it was simply drainage related: your pans would have considerable slabs of ice in them 15-minutes after the unit reverted to refrigeration following a defrost cycle.

If it was being recycled due to the chimney effect of an overheated evaporator you would have a lot of fog on one side or the other, not both, of the evaporator during the defrost, especially the late stages of HG injection...

If it was coming through the roof membrane, and your roof is directly on top of the cold space, there is no ceiling space between: you would probably be able to find icicles hear and there...especially after it rains.

If its coming through a traffic opening to a minus 27 deg space while doors are open: it would play hell with the door seals as well as make considerable fog on the warm side....

If you have a drop ceiling and this increases and reduces seasonally according to whether its hot and humid outdoors or not: you either have a bad vapour barrier, no circulation in the false ceiling space, or your insulation sytem of the drop ceiling has failed.

Ditto for the walls: But that's pretty easy to spot, look for condensation on the face exposed to the outdoors or warm area, early one morning: You will have some, its the pattern of thick/ thin that you are looking for.

So, tell us, what if any of this do you see or think might be in the midst of failing?



Has this thing always had an accumulation of frost or has this

[Mild Bill]

Schedule all three evaporators to defrost at the same time. IMHO, The formations are caused by each coil in defrost, releasing its moisture onto the ceiling of the cold box and freezing in place.

[savoc]

defrost time to long. set to 30 mins. monitor coils for ice build. 55 mins way to long. are all the pressure valves working and set correctly.

[R ALLATT]

defrost each evaporator for a max time of 30 mins seperately and check the fan restart temp. 4 defrosts per 24 hours should be enough