PDA

View Full Version : Temperature pull down in large cold stores( -25 deg c)







smpsmp45
29-09-2007, 07:00 AM
We are following a system of temperature pull down for large cold stores at the stage of commissioning. What are member's views / experience on that method. May be we may need to fine tune our method

Josip
29-09-2007, 06:21 PM
Hi, smpsmp45 :)


We are following a system of temperature pull down for large cold stores at the stage of commissioning. What are member's views / experience on that method. May be we may need to fine tune our method

Please can you tell us your method, in detail?;)

Best regards, Josip :)

TXiceman
30-09-2007, 02:13 AM
Are you talking about coolers or freezers?

Ken

smpsmp45
30-09-2007, 06:05 AM
It is -25 deg c & hence it freezer. I shall send what we are doing for this pull down. The files are over 200 KB & hence it is difficult to post those here. I shall try & reduce the size if possible.

Pooh
30-09-2007, 03:19 PM
In reality yo should be looking at a minimum of 14 days pull down may be longer if you have a concrete floor, if not you will damage the floor. I did a store several years ago and due to external control problems we took three goes at it as every time we got so far through the sequence somebody shut the plant down remotely and the temperature went to high.

Ian

TXiceman
30-09-2007, 09:14 PM
Like noted above, you need an extended pul down in a freezer. You need to pull it down to about 33 to 34 dF (1 or 2 dC) and hold it there fro several days and give it a chance to dry the place out. Lots of moisture in the wals and slab. Them you want to drop it slightly below freezing and hold it there. Continue on down in stages and give the room time to equalize.

If you rush it, you stand a chance of buckling the floors.

I had one large cooler in Houston the we tried to pull down in August. It took it the better part of 4 weeks to dry the place out to the point we could pull on down to 35 dF room. The coils had water literally pouring off the pans.

Ken

lana
01-10-2007, 04:23 AM
Hi there,

Have a look at the http://www.refrigeration-engineer.com/forums/showthread.php?t=8394 post #6 (attached file).

Cheers

smpsmp45
01-10-2007, 06:54 AM
Many thanks

bruceboldy
01-10-2007, 10:51 PM
I have seen schedules that limit your pulldown in many ways with freezers we have built. But, I agree with Tx Ice that taking the freezer to 35 to 36 degrees f relatively quickly works well, then holding there till no more moisture comes out of the evaporator drains. This may be 4 days or 20 days This is the important point. Once the drains do not flow any more then you can proceed to go below freezing at approx 5 to 7 degrees per day . This has worked without fail for over 20 years of construction on freezers of all sizes.

Best of luck

gwapa
06-10-2007, 10:10 PM
One important point when you pull down the temperature is to keep the door ajar. This evoid to have vacuon inside the frezer

NH3KIWI
20-10-2007, 02:56 AM
hi mate
just commissioned a large -25 store
set to +5c for a week or until coils stop freezing over (leave suction pressure as for operation)
set 0c and drop by 2 -5c every few days will be fine
make sure underfloor heating all ok