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Iced-T
27-04-2016, 10:24 AM
Hi,

I need to pull down a cold room which will operate at -24. The cold room is about 20 years old and it has not been operational for the last 6 months.

should I bring down the temperature in 2 stages??
from ambient to 0C ( hold for how long?)
and from 0 to -24

any help is much appreciated

Thanks.

smpsmp45
28-04-2016, 05:23 AM
Panellised Cold store Temperature Pull down procedure >>>>

In short,

1. Temperature pull down 1 degree per 15 minutes as per standards, but slowest could be 1 degree per 30 minutes.
2. Doors BE KEPT OPEN 50% till temperature drops to +05C, then 25% till it drops to -05C.
3. Door can have a small gap till room stabilizes at -20C if required.
4. Ensure that Pressure relief valves are operative and connected to power.
5. Try cycling of evaporator fans to reduce the pull down speed by selective operation of fans.
6. Check for ceiling / wall panels and the ceiling suspension rods / mupro channels for any visual stress.

A typical program as below ,

1. 9am > start cold store at inside temperature of say +25C
2. Set temperature to +15C with 1degree=30minutes rate and hold till 6PM > Observe defrost water
3. Set temperature to +05C with 1degree=30minutes rate and hold till 6AM next day > Observe defrost water
4. Set temperature to 0C with 1degree=60minutes rate and hold till 9AM next day > Observe defrost and concrete
5. Set temperature to -10C with 1degree=30minutes rate and hold till 6PM > Observe defrost and concrete
6. Set temperature to -20C with 1degree=30minutes rate and hold till 9AM next day > Observe defrost and concrete
7. Hold the cold store at -20C for next 2 days. The defrost water should have reduced by now and concrete totally dry.

Say around 4 to 5 days program.


This is a typical procedure.

Few parameters can be different though.

Important point is as much water in side cold store should be pulled out before we go below Zero Deg C. That way we minimize the damages to panels( Buckling etc) plus icing in the flooring / cracks in the flooring etc.

PaulZ
28-04-2016, 07:48 AM
Hi Iced T
The schedule provided by smpsmp45 could be a bit quick, O oC to -20 oC in 18 hours is a bit quick.
You need to give the concrete time to cool down throughout gradually, if you drop the surface temperature too quickly the top layer of the concrete will get small cracks and start to breakup under traffic.
This is the time frames we would use on a new freezer.
Given the room is old and has been off for only 6 months you may be able to speed up a bit.
Regards
Paul



Day

Freezer Temperature

Notes



Day 1

5C (3-6C)





Day 2

2C (3-6C)





Day 3

2C (1-2C)





Day 4

2C (1-2C)

Check that no condensate is on coils before lowering to negative temperatures.



Day 5

-2C





Day 6

-4C





Day 7

-8oC





Day 8

-12C





Day 9

-18oC





Day 10

-23C





Day 11

-25C

Iced-T
29-04-2016, 06:04 AM
Thank you for your replies. Its day 3 now of the cooling down process and I have brought down the temperature slowly to 0C. I will hold it at this temperature for 24 hours and then will slowly bring it down to -10C depending on the room condition. When I bring the temperature down I drop it as slow as possible (1 degree every 30 minutes)

There is an exposed suction pipe that goes to the compressor that is condensating a little bit inside the cold room. For that I have wrapped some armaflex insulation with ducting tape.

I am using a Bitzer compressor and the discharge temperature is reading 230 PSI (compressor cut off is at 250PSI). It is recorded that the compressor used to have a discharge of 205 PSI during normal operating conditions.

I am guessing that because the suction is higher could be the reason that I am getting readings like this. The discharge should drop as I slowly bring down the temperature further.

smpsmp45
30-04-2016, 06:02 AM
Yes. This is the usual condition of higher pressures in the pull down conditions

Recoilzn
01-05-2016, 04:46 PM
Forgive me for asking but at -24 deg c, those are pretty low temps for cold room panels, wouldnt the panel thickness play a role in how fast the room comes down to temp and how long it retains that temp. Would you also start to see condensate forming on the outside of the cold room due to insufficient thermal breaks?

RANGER1
01-05-2016, 11:04 PM
Forgive me for asking but at -24 deg c, those are pretty low temps for cold room panels, wouldnt the panel thickness play a role in how fast the room comes down to temp and how long it retains that temp. Would you also start to see condensate forming on the outside of the cold room due to insufficient thermal breaks?


I think it's more to do with concrete slab, especially if relatively new, as it can generate heat.
The concrete & everything contracts, if to quick damage will occur.
Cold room panel would be thick enough so no condensation.

Stories of people who close doors & reduce temperatures way to quick & building implodes also.