Air tightness freezer

[Peter_1]

Does someone know if a standard exists how airtight a freezer must be and more specific a freezer at -70°C and eventually the procedure how to test this?
We did in the past testing for ULO rooms but these are probably other standards.

[US Iceman]

Hi Peter,

I am not aware of any standard for freezer construction here in the US. The actual construction is not something I normally work with.

However, it seems your question relates to the moisture transfer through the building walls as it relates to the temperature difference. And also, as the vapor pressure difference increases, with the temperature difference and humidity levels increasing, across the insulated walls.

This appears to be a requirement for defining the minimum vapor barrier requirements for the structure. Which would essentially mean we want no water vapor transfer through the freezer wall.

Is this what your are looking for?

Best Regards,
US Iceman

[Brian_UK]

Peter, I have no idea at all. I assume there is a concern about the product either leaking out or contamination leaking into the freezer.

Most -70°C cabinets that I worked on had over-centre clips to secure the doors in the closed position. Providing the door seal was in good condition the pressure exerted by the clips made sure that the seals were compressed and (in theory) air tight.

Leakage around the pipe and sensor access holes was down to the quality of the sealant used !!

[Peter_1]

Well, I'm helping someone - posted here previous - with a problem he has.
Capacity seems too small to reach the desired -70°C.
Or the installed capacity is too small or the enclosure is leaking more than allowed. Both contractors (cooling/enclosure) are different so it's nobodies fault.
Both have to be investigated very precisely because

[frank]

Not my line of work Peter, but a question.

If you have a -70C freezer(I'm assuming walk in) that is airtight without a pressure relief device, how is it possible to open the door?

[US Iceman]

Hi Peter,

Have you found anything new on the freezer problem? This sounds like an interesting problem. I would like to hear what you find.

Best Regards,
US Iceman

[Peter_1]

As a matter of fact, I just received a mail today from the responsible engineer that they will perform tomorrow some tests on the units.

This engineer came first for help via this RE forum and because he's from Belgium and I'm doing often work for the Belgium courts, we discussed further via regular email.

I advised him to take some necesarry readings on both the compressors (LP, HP, subcool, superheat, discharge temperature, suction temperature, liquid temperature, ambient temperatures, in/out temepratures of the water codenser of the high stage... as much as possible readings)

He also made already a paper for the air tightness tests - he first had to make a proposal because he can't just perform these tests before first explaining every step he will taken - and this paper has to be agreed first. These rooms are installed in rather important facilities - as far as I have understood - for the European Community.

I advised him how we did these tests it in the past and he will follow most of the guidelines I think. (which I learned by making many mistakes in the past)
So, me too am very eager to learn how it all went.

He promised me to send me tomorrow after alle the values.
I keep in touch and share what I learn.

[Lancer]

Hi Peter,
I am a little curious as to why the control temp is -deg C, is there a specific reason for this that you know of?.

Lance

[Peter_1]

Hi Peter,
I am a little curious as to why the control temp is -deg C, is there a specific reason for this that you know of?

What do you mean with 'control temp is -deg C' and reason for what?
Sorry, my English is not that perfect.

[US Iceman]

Peter,

Has there been any progress on the freezer testing? I realize if this is in the Belgium courts you may not be able to share the information.

I am interested in the testing procedure you use to determine the air tightness of the freezer.

Thanks in advance for any information you can share.

[Peter_1]

I haven't heard Sven anymore.
I will contact him tomorrow.

How we test it?
There are two ways I know: the 1st one is how they test here ULO cooling rooms.
The door is closed, tighten the 6 locks on the door and blow up then the inflatable door seal.

Then drill one small hole of 6 mm to insert the plastic tube of the inclining manometer (don't know if this is the correct expression)

Then vacuum the room via the drain with an industrial vacuum-cleaner till a certain under-pressure. When desired vacuum is reached, remove the hose and duct tape the drain so that no air can enter the room.
You just have to look then how pressure rises versus time and look in a graph if it's falling within the given specs.


Second way like we did it already some times to the test the tightness for the Belgium Army after we installed Munters absorption dryers.
In the room you install a smoke generator like you see in disco's.
You then close every door like it should be closed in normal operating way.

One door is replaced with a wooden (hardboard, OSB..) plate. We duct taped it from inside and outside so that no air could escape via this plate. Negative point is that we don't measure then this door but it was not allowed to make additional holes in the wall.

On that plate, we installed via a small hole the tube of the inclining manometer and a larger hole for an in-line centrifugal fan.

At the inlet of the fan we installed an iris valve (like in a photo-camera) to adjust precisely the airflow.

At the outlet of the fan (between fan and plate) is a venturi special made for measuring flow via a DP reading over the venturi (Law of Bernouillie)
You only have to connect a pressure manometer over the diaphragm to translate this to flow.

The Army stated in their specs that their may not be an air change per day larger than the internal volume of the building at a pressure differential of ..Pa (I forgot the specs for this but can find them back if I search long enough)

When we first did the test, smoke was coming out of every corner of the building. The supervising engineers laughed loud and said that their chimneys at home were even not smoking that much.

If any English expression I used is not understandable, please tell me, I wil ltry to clarify.

[frank]

Hi Peter

Your explanation was spot on and very understandable

[US Iceman]

Peter,

The explanation was clear. Thank you for taking the time to reply to my request.

I also sent you an email with some additional information that may be helpful, but I may have forgotten to include my RE screen name. If I did, I apologize for my oversight. At least now you will know who sent it.

Regards,
US Iceman