High Humidity in Cool Room

[Miehadtje]

Hi All,

Long time reader of the forum, first time poster!

We have an issue with a cool room on site where meat is being stored. The room is served by a single condensing unit, located outside and single evaporator. The room is being maintained at 2deg C and currently runs around 90-95% humidity.

This is creating problems and the site would like to see humidity levels brought back to 80-85%. The room is accessed quite frequently and it is difficult to keep the doors closed for significant period of time. Curtain strips have been installed to reduce the infiltration load, but the room is still prone to high humidity.

I am going to visit site soon to get some more details, but am thinking the evaporator may be over-sized, enabling the unit to operate at low TD and reducing dehumidification.

I want to get an idea about the pressure control setup of the compressor and how often the unit cycles on/off. The client is keen to try to make the existing setup work before doing any equipment changes.

Some ideas I have currently:
- Change pressure controls (increase differential pressure setting) so that unit cuts out at lower pressure/temperature, runs longer and provides more dehumidification.
- Blank off a part of the evaporator air inlet to reduce heat transfer area of the evaporator and achieve a higher TD.

Any thoughts on this? Anyone who's seen similar issues and tried solutions? What would be a typical design TD (I know rule of thumbs can't be relied on, but would be good to get an idea) for a system like this?

Thanks a lot!

[mikeref]

More info required. Wait one while i search my ute for the appropriate hat..By the way, welcome.:)

You have to see this room, and the condition of the refrigeration equipment. (Kit) Ask the person who is in charge for a history of this room. Check for faults. IE: gas, fans, TX etc
Meat storage should not be controlled by an LP switch.

[Magoo]

Hi and welcome to forum.
High humidity in chiller means that the sensible heat ratio of evaporator is too high. hanging fresh meat will sweat and get slimmy. Lower air flow and increase latent cooling/ dehumidification. Or as Mike Ref suggested re assess whole system.
magoo

[Miehadtje]

Hi guys,

Thanks for the quick responses. I'm going to visually inspect the system, but won't be able to get any readings from it. Apparently, the humidity in the room goes down when the doors are open (with curtain strips).

This indicates to me again that the evaporators may be somewhat oversized, resulting in a higher evaporative temp and high sensible heat ratio of the evaporator. Is lowering air flow the only way we can achieve a higher TD and remove more latent heat? Not sure whether the fans are EC Fans, and can be reduced in speed.

[Magoo]

Basically yes, you could consider fitting air on fabric filters which will obviously need cleaning but they will slightly reduce air flow across coil and increase latent cooling. An out of left field suggestion.
magoo