Frost elimination inside a cold storage room

[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.

[Spoc]

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.

[Frio1]

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.

[John Hunter]

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.

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.

[Frio1]

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?