High humidity in cold room

[nimamu]

Hi Everyone,

I have been requested by a client to check a cold room with a high humidity problem. The water condenses on the ceiling and walls. When the air curtain installed on the warmer side of the door is switched on while the door is open, the condensation is worse.

Any ideas what causes the above.

Regards

nimamu

[Samarjit Sen]

What are the required RH and the temperature of the Cold Room. Further how is the high humidity being achieved. Once these are known, some solutin can be advised.

[lana]

Hi there,

This is because the moisture content of the area you are located is very high. When the air curtain starts, outside air goes into the cold room. This high moisture condenses on cold surfaces.

Cheers

[bruceboldy]

I have always found that air curtains are of little help in moisture control between a warm area and a cold area, that is open much of the time.

The room air acts like a cold front moving into an area that is warm. the cold area moves outward near the ground or in this case near the floor and the warm air with high humidity comes over the top to replace the volume of cold drier air leaving the cooler. Remember everything in nature seeks to be in balance. espically the vapor pressure..

We have used an ante room design between the two areas always open and then put a cooling evaporator blowing towards the warm side opening or door.
This allows the incoming air replacing the escaping cold air to be partially dehumidified before entering..

In addition, if you use cooling evaporators blowing near the ceiling they tend to wipe the high humidity from the cold surfaces, alleviating some of this moisture problem

Try to understand the vapor pressure issue between the two areas and yo will then solve your moisture delimma.

Hope this helps
Bruce.

[nimamu]

Hi Bruce,

Many thanks for the analysis. Will keep all advised with update once the issue is solved.

Regards

nimamu

[PaulZ]

Hi
Does the room have condensation in there all the time or does it only appear when the door is open.
Air curtains are a waste of time and I have found that clear plastic strips work better if the door is left open a lot.
Another cause could be the product in the room.
What is stored in the room and what is the desired room temp.
If the evap is close to the roof of the coolroom and you are running a very cold evap temp the roof of the room will get very cold and if the product is hot and gives off a lot of moistue condensation will occur.

[Magoo]

Hi Nimamu, I tnd agree with Paulz that air curtain is waste of time, add slatted curtain instead. Secondly, sounds like sensible cooling ratio is too high, either add more compressor HP to decrease suction, or slow evap fans with filters or speed control. Basically you have to condense moisture on coil fins to remove it from room.
regards Magoo

[Psychro]

Hi Nimamu

A conventional air curtain is a waste of time as this can often introduce more moisture into the cold room - despite manufacturers claims.

The modern method of reducing ingress of moisture into cold stores is to use very dry air from a desiccant dehumidifier. A number of leading UK supermarket chains are now using this method in their cold storage depots The dry air duct outlet is designed to produce a curtain of dry air down across the face of the doors (on the warm side). I have recently supplied a number of desiccant dehumidifiers for use in supermarket cold stores where the DH units supply air at minus 25°Cdp. This system dramatically reduces ice build up on door frames, ceilings and floors (health & safety) and also improves efficiency of dx cooling coils (reduced latent load and defrost cycles). If the dehumidifiers are located in the loading area (2-5°C) then these areas also benefit from a much reduced humidity.

[nimamu]

Hi Psychro,

Your idea to use dry air is excellent. Thanks a lot for that idea. Will recommend this to the client.

Regards

Nimamu

[Psychro]

Hi Nimamu

Please let us know how you get on !

[smpsmp45]

Dear Psychro,
Can you throw more light on this & what is that system The air needs to made dry? You need separate compressors for air? We too are desperately loking for a sustainable solution. We tried rapid doors, & the problems got reduced drastically. but your suggestion seems more efective.

[Psychro]

Hi smpsmp45

When cold store doors are opened, a turbulent exchange of air occurs across the door space. Moisture from outside air condenses on the cold store floor and other surfaces producing ice, frost and even snow. Moisture entering a cold room will also freeze on evaporator coils. Frosted coils are inefficient and defrosting is expensive.

A desiccant dehumidifier operates by extracting moisture in its vapour state so is able to effectively remove moisture without producing condensation (or frost). It is capable of supplying air at a very low dewpoint (< -35°Cdp). Provided the dehumidifier process air inlet is already at a reasonable humidity ratio (7 to 10°Cdp), a dry air outlet at -20°Cdp is easily attainable. In industrial drying systems this is normally achieved by using a pre-cooling coil.

In large cold storage depots, there is often a loading area which separates the cold store from ambient. The loading area is normally cooled to 2 to 5°C. If a desiccant dehumidifier is installed in the loading area and takes its suction from this space, the dry air outlet will be around -25°Cdp. This air is then ducted to above the cold store doors (loading bay side) to produce a curtain of very dry air. The unwanted moisture vapour from the dehumidifier is ducted to ambient.

The dehumidifier is effectively dehumidifying the loading bay area whilst also supplying the driest air to where it is needed (above the cold store doors). The system is better used in conjunction with fast closing doors and whilst it greatly reduces ice build up, the biggest advantage is energy savings by allowing evaporator coils to do what they were designed to do - sensible cooling.

If you want to know more about desiccant dehumidifiers there is a fair bit available on the web (Google search) but please spell desiccant correctly – one S, two C’s !!!! :D

Regards
Psychro

[smpsmp45]

Many thanks Psychro

[Giannis]

A desiccant dehumidifier is the best solution but you can try also to set the evaporatior fans in continious mode (only stop at defrost) this will help a little.

[hendry]

but, strange in Asia, eventhough is highly humid, situations are rather different.

could you advise?

i've not receive info on installation of desiccant drier.

[bernard]

Hi
It could also be the defrost termination set to high,with the fans switching on to early blown warn air around cold room.Also when was the last time the coldroom was closed down, defrosted and dried.

Regards Bernard

[Nightmare]

Sounds like the ingress of warm moist air into the room when the doors are opened... strip curtains help but if the door is left open for too long, the inevitable will happen.
fitting a "bubble" or additonal entry that is dehumidified will help this, although it can be costly and should really have been thought about during the desgn stages.
somebody posted earlier that hot products will cause high moisture also... very true, should your client be blast chilling their product before it goes into cold storage?

[sidhartha]

Hi
pl can any one will paste here

wet bulb , dry bulb chart to calculate the humidity
i will appricate it
sidhartha

[liptow]

Hello all,
Better late then never?
I deal in alot of 4C cold rooms.
We have something we call "cold fingers".
It is bare copper coil without fins added just upstream
of the evap coil. We get water in the air to condense without as much heat transfer. Refrigerant to the DH coil and the EVAP coil is controlled independently. There you have it........my 2 cents.

[Gary]

http://www.owlnet.rice.edu/~phys203/handouts/Nautica_SI.pdf

[Gary]

Hi Everyone,

I have been requested by a client to check a cold room with a high humidity problem. The water condenses on the ceiling and walls. When the air curtain installed on the warmer side of the door is switched on while the door is open, the condensation is worse.

Any ideas what causes the above.

Regards

nimamu

What are the temperatures of the air entering/leaving the coil?

What humidity level are you trying to achieve?