Does Any One Know The Equation To Determine
The Size Of A Freezer Relief Port
It Is 2800m3 And -22 ????
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Does Any One Know The Equation To Determine
The Size Of A Freezer Relief Port
It Is 2800m3 And -22 ????
If you give me your personal address, I can send that data. The file is over 200KB & hence it can not be uploaded here.
Pl. send me PMS.
So also the location of these valves is very important & critical. If installed in the suction path of the evap fans, can cause lots of problems too.
CHEERS MATE
prostheteks@xtra.co.nz
Mail sent with the details
My curiosity has outweighed my ignorance: what is a "Freezer Relief Port"?
When we start the frezer room, there is a possibility of vacuum being developed inside as the moisture in the air gets sucked out & to balance the pressure differential we put up these valves. These are spring actuated valves & work on pressure differential. With this extra air from outside is sucked inside & the pressure is balanced.
Hi Expat
They can also be a small flaps that can swing either way and generally have a heater around the opening to stop ice build up.
Do we really need them?
Thanks for that guys, but I'm still a little in the dark as I don't know why a depression within a freezer would be bad,...is it less air flow and therefore less heat exchange or what?
Thanks
Expat (we may make a fridgey of me yet)
I've seen coldroom panels blown out because of excess pressure inside the coldroom caused by defrost and a sealed room.
The pressure relief allows the equalization of the pressure.
I have never known a room to implode due to lack of pressure.
In my oppinion this is not as common or as much a risk as the excess pressure.
Cheers taz
In the Blast freezers we ha installed the wall panels collapsed due to malfunction of the relief ports.
it is very important to put these.
we allways fit them next to the door [hanging flap type]or on the roof above or ajacent to the door,[larger rooms]. just for the last post,when you open and shut a freezer door there is a big pressure differance and theese valves allow it to ballance out,if you do not fit them air will get in where it can,ie gaps in pannels,door seals,pipe holes,drains, etc,in some cases i have seen the walls pulled inwards[distorsion].
think its safe to say if you fit one near each door on a large store you will be o/k.but obviousley a calc is in order.
Can anybody give the size of damaged rooms? Most likely these rooms for commercial refrigeration but not for industrial refrigeration.
Hi all,
Also have a look at the Fermod website for the pressure relief valve models.
Regards,
last one was a 5mtr x 5mtr x two storey freezer 6mtr high, loosened all the wall panels into the floor,told the customer it has to come down before it does it on its own.!!
If the air in the freezer collapses, you form a lower pressure inside than you do outside. This results in a pressure being exerted on the freezer walls or panels. If the pressure difference is great enough, you can get wall panel to buckle.
Ken
We have also come to a conclusion that the rate of moisture abosrption in the freezer is also an important factor. If the vacumm is created fast enough, the walls still collpase. That we have observed that if the moisture content is high enough & if the freezer starts & condesnes that air, still the relief valves fail short of proper air intake & still it creates huge pr differential between inside / outside.
Hello Sergei.
I have seen rooms as small as 5mtr by 6 mtr by 3 mtr have the wall panels seperated from the roof.
I have seen 3 or 4 large cold romms about the size of tennis courts with the wall pannels pushed out.
Finaly I have seen an industrial cold store about the size of a football pitch with a fork truck size hole init from one careless drivers speeding:eek:.
All the best.
taz.
This is issue for commercial(walk-in) freezers, because the doors can be tight. Industrial(drive-in) freezers don't this problem.
cold store collapse- the ceiling panels caved in. THe reason being thee are 12 fans of the evaporators & all start together. After cycling the fans, the pressures were OK.
Based on our recent experience & lots of data finding, we have compiled a small explaination on this point. May be it is interesting.
I remember my Uni teacher talking about relief vents for freezer rooms. If you do not use these the exerted pressure on the outer sides of the walls can equate to the weight of a meduim sized car sitting on the roof of the freezer room!
Hi Guys. PRESSURE EQUALISATION VALVE
You need them because of the pressure temperature relationship.
When the temperature within the cold room drops so does the pressure. Ask any Enginneer who services butchers cold rooms. They will of at sometime had the situation where " The door won't open" (the vaccum inside is keeping the door shut.) Because the heater element on the PRESSURE EQUALISATION VALVE has failed and the flaps have frose shut.
DO NOT underestimate the power developed if the presures are not equalised. I have seen very large cold store walls that have moved due to this problem!
Cheers Steve.
Hi, Sergei :)
O, yes...I am sorry cannot upload a photo of collapsed ceiling in one huge cold room due to missing pressure regulating valves....Came there later when they almost repair all damage...the reason was someone forget to leave the cold room doors open during pulling down...funny...but very expensive..
Just try to think about the Force (under pressure-vacuum) when you close the door (A=1 m2)of your kitchen freezer (V=150-500 lit) and try to open it again few seconds later :eek:...and the force in one cold room for ice-cream (-28C) size of 32,3m x 22,7m x 10,6 m (LxWxH) = almost 8300 m3....
I will not dare to not install those valves....
Best regards, Josip :)
I have the solution to the problem. No relief ports are needed.
I will send you a couple of our forklift drivers. They will have all your doors "vented" in a matter of days.:)
Even I have few photographs which had the ceiling issues. Even the suspension arrangement too was bent by almost 25mm or so.
One has to see that to believe it.
But Again the file is too big to be uploaded.
Hi, Sergei :)
What Grizzly wrote is true, but overpressure pressure is able to open the doors or to distort the walls/panels too ;)
It is not the question about tightness, no need to dream about, but some of them are gas tight for example ULO cold stores;), it is more about temperature and pressure change...Quote:
Originally Posted by Grizzly
....for example having cold room doors at size 2,5 x 3,2 m (8 m^2) open with automatic close from 0-120 sec or manual close....try to imagine how many cubic meters of warmer and humid air will get in during that time rising the pressure....then we close the doors and start to freeze water vapour causing air pressure fall....
defrosting....freezing...cause pressure change....
...., but pressure changes we can have and we have due to weather change causing change of atmospheric pressure...eg.storms
Temperature change of 1 degree Celsius can cause approximately pressure change of 40 mm WC (water column) 40 kg/m^2....what is evenly distributed load of 29 metric tons :eek: on the cold room ceiling from my previous post...
....seems, it is not so bad idea to install pressure relief valves....
for more info about doors, please, see here...
http://www.ems-isolier2.de/gb/downlo...iebetueren.asp
Best regards, Josip :)
This is only question of doors tightness. I agree that possibility of vacuum in refrigeration room exist, but only if the doors are tight. I think that these ports should be installed for walk-in freezers, but for industrial cold rooms(drive-in) impossible to get doors tightness.
Industrial Cold Store Doors are airtight. IF NOT the warm higher pressure air from outside. Flowing into the cold store chamber condensates and freezes, causeing the door to be sealed against the door jamb
(frame in common english). ( There are also periferal heaters within the frame and embedded into the floor)
Obviously most of the doors do not remain perfectly sealed. Especially as previously mentioned, when they have been hit by a fork truck or 2.
The average UK Cold Store is 600,000 to 1,000,000 Cubic feet PLUS. with an average of 3 to 4 doors.
With -18c the required minimum chambers are kept at anything between -25c to -20c ( -13 to -4f ) so there is a thermal buffer. 1, I used to look after had a chamber at -29c ( -20.2f ).
So even during the winter months were we average say 8c there is a difference of 30c ( -22f).
Therefore the pressures pushing in ie. Forces pushing the door shut can be quite large. Not forgetting as originally mentioned the walls themselves!
The temperature differances between inside a store chamber and outside can be huge.
A moist product can have its weight reduced
dramatically through being stored for long enough.
Sometimes consignments are reduced by TONS.
ANYWAY THATS ANOTHER STORY.
remember leaking doors are money being thrown away.
Cheers Grizzly
Sorry for the rant guys but the doors are kept as airtight as possible. The primary concern is to limit heat introduction into the store. Also on larger stores the reason there is not normally an issue is because of the volumes / area 's involved and the constant operational traffic
equalises out the pressures faster than large pressure differentials can be achieved.
But as I have tried to explain there is huge potetial for problems if the need for pressure relief valves is not considered.
Hi Every body
It is clear when we have a closed volume and we lower the internal temperature then the presure will also lower
Pv=RT
PV=mRT
P=(R/V)mT
v=V/m
Where v is especific volume
and V is the Walkin Room
So the internal presure depend of the internal temperature and the air mase.
The air mase is a mixture of N2,02 and vapor of water . When we lower the internal temperatura and we condensate the humidity, both term of the equation m and T lower so the internal pressure will low dramaticaly. It cause an internal heavy vacuom.
That is the reason why we have to protect with safety valves the freezer. Our friend Smpsmp45 post the formula to estimate the number of valves
Now it is very import too, the location of the valves.
Some time we located the valves in a place where the outside wind velocity is high and it produce a static pressure over the valve pushing humidity inside the room and creating some frost araund the valves.
So I would like to hear from you your expirience in the location of this safety valves
Regards
Gwapa
Incidently the doors on the cold stores were from EMS!!!.
I shall try & split the Photos in small size & try & poet them up.
yes the location is very important. The valves should not be fitted in the air path as otherwise, the valves shall be forced open due to the air pressure. So also they should not be in the suction path of the fans. That also makes them open inwords causing considerable leaks into the cold store. So also they should be located preferably in the ante room wherein no ambient air is taken inside incase the valves operate.
We have as a precaution started putting up an indicator in series with the heater on the valve. So that one knows that heater is operating.
smpsmp45, otherwise via megaupload.com.
Sergei, a well service door is always gas-tight.
Why can an industrial freezer-door not be gas-tight?
I don't see the difference with a commercial freezer.
If not ,you will see a lot of snow forming on the ceiling above your door. This snow falls down on the entrance in front of the door and the reach-trucks will melt this due to the high weight. So this will become an ice-rink instead of a freezer.
Dear Peter_1,
Megaupload has no uploading available from India for timebeing as it has exhausted its limits.!!!
smpsmp45
I think it is not a good idea to install the safety valves in the wall between the freezer and ante room
I prefer select a wall to the outside o maybe the roof panels