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Hi everybody
In two week I will pull down the temperature in a cold room which will operate at -28ºC
The first Step is lower the temperature till +2ºC The question is:
How long must I keep the temperature at +2ºC before moving to -28ºC?
The cold room is 30x60x 12m (wxdxh)
apreciate your very kind coments
Gwapa
Hi gwapa.
With the room closed up run at +4 'C and check the amount of water coming out of condensate drain, measure it in a big bucket. When the rate slows right down it means you have dried out the concrete floor to a point, daily check for shrickage of floor, it will shrink a lot, had one recently of similar size and it shrank approx 20 mm at each wall, check for cracking as well. Could take a week or more.
Then run at -2'C for a week, and slowly bring down 5 degrees at a time, monitoring shrinkage daily.
The concrete of the floor must be at least 30 days old when you start the pull down.
Then I should cool down to 1°C for some days and then cool it down to the desired temperature with +/- 2°C/Day.
You will see that the system will hang around -10°C until all the concrete will be frozen. This can last for several days.
Hi Peter_1.
You must live in the perfect world, where the wear slab is poured and everyone stands around for a month.
Even after a month the concrete crust will powderize if frozen. Remember Gwapa is in Venezuela, probably not heard of special concrete mixes, fast cure ,what ever.
Thanks Magoo
It is a good method to check the dryness of the coold room.
I was thought to messure the Coldroom Dewpoint at a Drybulb of +2ºC
What do you think?
What product did you use to seal the shrank of approx 20 mm ???
What in the crank?
Finally I agree that shareholder do not wait one month the full the cold room with products
Aprreciate you coments
Regards
GWAPA
There's a difference between curing and drying of concrete. It was a typo: 3 days at temperatures you encounter in Venezuela.
Do you notice also a hanging point around -10°C?
If you get the client to sign away his rights and coving your own arse, then bring it down as fast as he wants.
turn the heater mat up so it runs [within reason]and set the room set point to 2-3 deg C for at least 3-4 days to dry / cure the concrete and pull the moisture out, i would pull it down in two more 24hr .stages, -10 then final setpoint.once its dry its down to how good the mix was :D over here it has to have a certain concentration of granite .:)
Hi Gwapa.
My method of pull down has developed over many decades, OK I am old.
But running room at + 4 , you operating evaps at or below O 'C which draws and accumulates moisture from concrete slowly, limited cracking. The idea of checking the condensate is a direct indication of moisture release from concrete.
OK after shrinkage has stabalized fill the void with construction foam fill. It comes in rolls and looks like a mile long sausage, insulation thing. Lightly pack into gap and cover top with selastic . Selastic will move and not crack open like silicon filler.
Remember that the outer metal skin of Coldstore is the vapour barrier, once you go low temp., check that there is no condensation anywhere on outer skin of coldstore.
Generally here in NZ the inner panel skin is selant free so as to draw any moisture out of panel, so outer metal skin seal is super important to stop moisture/ice building.
Hi guys,
Sorry to jump in, but yes I did noticed before when we started up a cold storage that the temperature did hang around a certain temperature for a few days before going to the final temperature.
I did not quite understand about the concrete freezing reference though. Is this referring to the absorption of the heat of fusion from the water in the concrete ? Why -10 C
Magoo
Thanks again
What do you think if we messure the dew point?
What would be the dewpoint temp. at +2ºC Db Temp. to restart to pull down the temperatur to negative range?
Could it be -21ºC??
Thanks
Gwapa
Hi Gwapa.
Generally I do not monitor wet bulb, as it will be high RH anyway, but log very closely the water coming out of evaps, as well walk around with an infa red thermometer and check the actual concrete floor surface temps., [you will be surprised how warm they are at start of pull down ] and shrinkage and possible cracking, until they have stabilized with room temps..
The balance ports will keep balancing with fresh air and resultant moisture.
Peter 1
Thanks for your advise
Could you tell me more about your experience regarding to:
"You will see that the system will hang around -10°C until all the concrete will be frozen. This can last for several days."
GWAPA
Hi Gwapa.
So what happened with the pull-down of your coldstore.
Share the process you actually followed, and the resultant profile.
Magoo
We low the temperature untill +3ºC and hold the procces till next year.
I will inform you all
Thanks
GWAPA
personal stuff sorry
hi jaysephus
Yes we do have heating mat in fron and inside the door and also we have a six inches coil underfloor in where atmosferic air is blowing at 30ºC to heat the underfloor.
We finally arrived to -28ºC
I have to thanks Magoo for the idea to monitor very closely the water coming out of evaps at +3ºC.
We observed it and when the water coming from evap become minimal we went below 0ºC.
We observed too that at -10ºC the temperature did not low as faster as over -10ºC.
At the begining when we started to low the temperature the ammoniac pump went out many times for the pressure diferential protection.
Every thing is now runnig perfect
Thanks for the advise of all you
Regards
GWAPA