coldroom not pulling down on temp?

[knight rider]

hi everyone
maybe some light can be shed on a discussion i had with a refrig engineer ,
is it possible for a cold room NOT to come down on temperature eg -18c UNLESS it is full off stock which has arrived frozen

the story goes --
cold room breaks down ,frozen stock removed , engineer arrives on site finds compressor contactor faulty , replaces , starts up system , unable to bring tempuretue down below -13c,
spends around all day checking system to find out why it will not pull down, new frozen stock arrived ,cold room filled up , -18c achived and maintained as cold room is used as normal no problems last 3 months

i would have thought it would have been easier to achive pull down without stock

any thought ?

many thanks

[Andy]

hi everyone
maybe some light can be shed on a discussion i had with a refrig engineer ,
is it possible for a cold room NOT to come down on temperature eg -18c UNLESS it is full off stock which has arrived frozen

the story goes --
cold room breaks down ,frozen stock removed , engineer arrives on site finds compressor contactor faulty , replaces , starts up system , unable to bring tempuretue down below -13c,
spends around all day checking system to find out why it will not pull down, new frozen stock arrived ,cold room filled up , -18c achived and maintained as cold room is used as normal no problems last 3 months

i would have thought it would have been easier to achive pull down without stock

any thought ?

many thanks

Hi Knight Rider

in this case it is the air volume that has been reduced but I would say you system is under sized or has a problem.

Get it checked and ask for a load calculation to be carried out.

I have commissioned a lot of rooms without witnessing this myself.

Kind Regards Andy

[Latte]

i would have thought it would have been easier to achive pull down without stock

Not always, If the stock is put in at the correct temp (-18 to -20) then this will help cooling effect.

With coldrooms their are so many factors that can effect it, it is difficult to know where to start. How old a room is it. Is the insulation OK, when the coldroom broke down was their any water which could have penatrated the insulation. Is the coldroom indoors or outdoors. What size is the coldroom, what are the units on it.
Is the sight glass flashing. has the coldroom got a light, strange question i know but the amount i go to without working lights and the staff keep the door open when loading/unloading, are their any curtains on the door.
This is probably one of those questions that would be difficult to give a diffinative answer to online but if you can post as much information as possible we can do the load calculations and possibly rule out certain things

Regards

Raymond

[Dan]

Although I agree with Rdocwra and Andy for the most part, my supermarket experience has been similar to what you describe. It is obvious in empty display cases that you will never achieve temperature until they are properly shelved out and stocked.

Cold rooms share this to some degree. As Rdocwra points out, there are many conditions that can affect proper pull down.

In my mind, I see an empty room as a room primarily cooling air. I see any change in the air temperature as a new load that immediately impacts the load on the refrigeration equipment.

I also see a full room as a room with ballast, or flywheel effect. Conditioned product that fills the air space where air intrusion has less effect upon the loading of the coils, simply because air intrusion is less, and refrigeration effect is greater from the cold product displacing the air.

It is entirely possible that an empty room is more difficult to maintain temperature in than a full room.

[Andy]

. It is obvious in empty display cases that you will never achieve temperature until they are properly shelved out and stocked.

It is entirely possible that an empty room is more difficult to maintain temperature in than a full room.

Dan is ofcourse correct. Cabinets are designed to have product in them. When product is absent the velocity between the air off and air on grills/ducts drops and the air throw is lost. To increase the velocity cross sectional area must be reduced.
Maybe this is the problem with your cold store, the coolers have low throw fans fitted and are unable to create the velocity necessary to send the volume of air necessay to the far end of the cold store. When you add the product you are creating a duct to send the air to the other side of the room.
Most coldstores are controlled on the return air. If your were reading a thermometer or a electronic thermostat at the far end away from the cooler this would explain why with low throw fans you were seeing poor temperatures.

Kind Regards Andy

[old gas bottle]

i would be worried if a cold room would not pull down empty or not, how could it be commisioned and data loged to hand over to the customer, all the ones we fit pull down and maintain good temperature unless loading etc,
i tend to think that the cold room in question may have been off for a while ,possibly un noticed and it just took a while to remove to heatload from the stock,walls,floor etc,but andy states ,get the kit checked out for size if in dowbt.

[LRAC]

You didn't mention wether it was a cheap packaged unit or a designed fridge plant, most of the package units we come across state in their design that they are hold rooms and do not allow for product pulldown. Most package kit states product must not enter 3c above room temp.

I believe the fridge kit you have is undersized if everything else checks out, or the evap fan has been changed at some stage and may be incorrect for the application.

Regards
Lrac

[knight rider]

thank you for the excellent reponce and comments,
as i said it was another engineer who had expreienced this ,
as far as i know the cold room is around 8 years old ,
by the time the engineer had got to site , the stock had been removed and placed in the other coldrooms , the temp was up to around -5c ,he found contactor for compressor faulty , fitted new contactor to unit , started up and found it was struggling to come down to -18c ,it was holding around -13c,he check for gas , fans ect and said it was running as normal, as the day went on, new stock had arrived (frozen) which was placed in the cold room ,and temp fell to -18c
and as far as i know it seemed to be ok , no further calls on that coldroom recived

i agree with the other comments , i would have siad it was under sized ,or maybe designed this way ?