Mould on walls in chiller room?

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28 Aug 2016
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I'm involved with a local off-licence/deli which has a chiller/refrigeration room where cold drinks and serve yourself fruit and veg are kept. The room was originally referred to as the cellar as we used to store kegs of beer in there as we sold it by the pint in jugs to take away.

The problem we have is mould forming on the walls and ceiling, near the chiller unit. The walls are all dry lined and insulated with 75mm Kingspan, the ceiling is also insulated as it was designed and built basically to be a big fridge.

As I understand it the way to avoid mould is heat and ventilation, obviously we can't turn up the heating and I don't want to leave a window open as we would then be trying to chill the whole universe! Does anyone know if these chiller units produce moisture? Is the way forwards some kind of de humidifier (using more electricity :rolleyes: )? The mould doesn't look great when food is stored in there, we do get the decorator in quite often who cleans it all down properly and repaints with what he says is the best paint for the job but it would be nice if the mould just didn't come back.

Pics below, any thoughts?

chiller room 1.jpg

chiller room 2.jpg
Pics below, any thoughts?

Thinking about your question, "does anyone know if these chiller units produce moisture?" we would need to consider how this might be possible and the source of the moisture.

How do they work? They have a cold coil (which is cooled by a closed refrigeration system) in front of a fan which blows the room air over said coil. So the chiller cannot produce moisture, only cool the air in the room to such an extent that it can no longer contain its moisture in gaseous form.

Where does the condensate (the pipe with a triffid growing up it) drain to? Hopefully outside the room.

A proper chiller room generally has plastic or metal walls, not painted ones. I do not use Dulux inside my domestic fridge.

Putting the fruit and veg, which are the main source of moisture, inside airtight boxes may reduce the problem.

A dehumidifier in a room full of lettuce might lead to some disappointed pet rabbits.
Thank you, some great points there.

The condensate pipe does drain to the outside.

I never considered it could be the fruit and veg giving off the moisture but thinking back I don't remember this being a problem when it was just casks of beer in there.

It doesn't actually get that cold in there, think it's set at 11 C.

Good idea about the airtight boxes but don't think it will go down well as everything is in rustic wooden crates for that farm shop type look.
Probably needs a bit of a clean down more often. Humidity could be cause. A lot of stuff grows even at 10ºC
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A proper chill unit will have a period where it seems to kick out warm air. I dont know exactly why, but the chills ive worked in from the butchers sometimes had you'd walk in and it would be a bit of a warm breeze blowing. Maybe something to do with defrosting the pipes or such now I think about it.

When did you last wash out the chill ?. We used to do it every week on a Monday, as that was a quiet day

I say 'we' but its always muggins here :LOL:

Big bucket of hot water with a splash of bleach and wash down the walls, floor and any shelves. Be thorough.

" It doesn't actually get that cold in there, think it's set at 11 C "

Then it isnt really a chiller. Normal temp for a chill is about 3c (As in meat)

I've just had a little look at what cold storage is temp wise for veg and fruit. -
" Most fruits and vegetables are stored in positive cold rooms. As a general rule, the storage temperature is between 3 and 6°C to prevent the products from losing their freshness too quickly."

I think at 11c what you have is less chiller and more greenhouse :LOL:
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What paint are you using? I'd use kitchen / bathroom paint as a minimum or exterior / floor paint better still. Some exterior wall paints have antifungal properties.
I'm told that it's 11°C as some things in there are better stored at room temp so it's a bit of a compromise.

I will check what paint the decorator uses but I seem to think it was a Johnstones durable eggshell.

I guess the answer is to wipe it down more often but it means moving a lot of stuff around and you can't have staff balancing on the top of step ladders these days.

I will try and keep on top of it but it would be nice if it just didn't keep coming back!
What is possibly happening is that the chiller unit is blowing out cold air onto the near by surfaces, causing the local surfaces to drop below the dew point of the air entering the room, condensation is forming on these cold surfaces, attracting dust etc and allowing mold to grow. Avoiding the door being open too often thus keeping fresh moist air out would help, as well as keeping fresh fruit and veg in air tight boxes.

However, the other option is that the other side of the plasterboard is getting condensation forming and the damp has slowly penetrated through. To my eye there seems to be a pattern of studwork amongst the mould. For me this could indicate its condensation on the other side penetrating through. Although you have kingspan on the other side if you don't have a moisture barrier on the warm side of the kingspan then warm moist air can get to the coldside of your pasterboard.
Firstly the paint you want off the shelf is zinsser perma white, its great antifungal, expensive and thin but does the job.
alternatively you can mix borax (banned but available online) into standard paints to make them antifungal.

Bleach does not kill mould it just discolours it, most mould is not visible and when you spray mould with anything to try and kill it, it just throws out spores to survive the attack you actually make the issue worse. to actualy kill mould you need to fill the atmosphere of the room with a denaturing chemical (think vinegar) so that the mould and any spores thrown out when it senses an attack are killed in the air.
I agree the mould does seem to favour spots between your studs, probably because the insulation is doing its job and keeping the cold from passing through the walls. I doubt a vapour barrier as described before is going to of any use, the world beyond your walls is warmer thus more humid than the inside of your room, any vapour issues withing the makeup of your walls will be from the outside.

Your insulation is to keep the room cold not to keep cold out. when you and/or anyone else enters the room they introduce warm moist air, continually breath out even warmer and vastly more moist air into the room, once this new air settles into equilibrium and drop to the rooms lower temperature this moisture is in part condensing on the walls which are colder. combine that with a complete absence of airflow and you have a recipe for mould.

I think the real issue is that your walls are not suitable for purpose, they should be similair to that of a fridge with anitfungal properties.
A chiller is basically what a dehumidifier is hence why its got a condensate drain. In larger installations the amount of dehumidification is controlled to suit the type of produce being stored as if excessive moisture is removed you get dessication/ drying of the produce etc - normally its done by the temp drop over the coil being increased or decreased to cause more or less dehumidification at design stage. Chills tend to be damp as the air in the chill is normally cooler than the air outside so for example if the air outside is say 20 deg C and 60% RH by the time you cool it to your storage temperature the RH of the air increases as cold air cant hold as much moisture if the outside air is humid enough it will condense out on the cooling coil in the evaporator and to a lesser degree the walls etc due to doors opening and the cold air being displaced with warm etc. Have a look at a psychrometric chart and you will see the change in RH for change in dry bulb temperature.
The other issue could be vapour barrier as water will migrate from (generally) hotter area to colder area due to daltons law of partial pressures. The partial vapour pressure of water vapour in warm humid air will often be higher than that of the air in the chill so the water vapour will try to migrate to the colder surfaces and may build up in the walls.
Chill wall panels frequently consist of a sandwiched layer of insulation with plastic coated steel sheets to try and prevent water vapour passing through the construction. If the panel fails the insualtion can become completely sodden due water vapour transport.
Fruit and veg do give off heat also - heat of respiration- but doubt if thats your issue.

Keeping the door closed as much as possible/ fitting a PVC curtain to minimise fresh air load would help. But think main issue is that it would have been better with coldroom panels. It may be less of an issue as weather cools.
Give it a washdown with some anti mould cleaner and paint it with a good anti mould paint. I did this in my bathroom and it really worked quite well, I forget the exact paint now but it was sold as a bathroom specific paint in Brewers.
Of course it would be good if the source of the moisture could be sorted out but the paint will definitely help.


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