It's snowing in my walk in freezer!

[Matt]

We installed a combo. You walk into the first freezer (12x12), from there through another door into what they call a blast freezer (10x12).
The problem is the blast freezer has 3 inches of snow in it. The evap fans regularly get stuck in ice around the venturi.
They put fresh (warm) blood plazma in it through two reach in doors in the front.
Bitzer 7.5 hp two stage compressors.
During start up we dehydrated the box in stages as per Masterbilt.
We used 60 tubes of caulk while biulding the box.
The drains are trapped outside the box.
I have never seen a frost or snow problem like this.
Can anyone explain this?
What can I do to correct it? Matt

[shogun7]

Matt this seems to me to be your problem.
When they open the doors to put in the blood samples in you are apparently getting warmer air with enough moisture in it so that as soon as it hit the cold blast it turns into snow flakes. I would try to isolate the outside doors where you put in the blood samples from the blast freezer and try to figure a way to keep from so much humidity. maybe another room connected to the door openings that is refrigerated.
Roger

[Peter_1]

When I see snow on the ceiling, then you have mostly somewhere an airleak.

Drain trap filled with water? Try to install a trap of 3 or 5 feet long outside the chamber. It can be sucked out when opening and closing a door or after a defrost when the fan starts.

Pressure equalisation valve somewhere in the wall? Isn't this leaking?

Seals of door completely tight?

You didn't drilled somwewhere as small hole you forget to seal afterwards?

Shut down the unit and the light in the freezer, stand in the freezer for some time with closed door so that you're eyes become sensitive and look around if you see somewhere light.

Do you wait not to long with starting the fans again after a defrost (pressure decrease).

For these kind o problems, we have a special device for this: an ultrasonic leak tracer of SDT (Belgium)
You put in the freezer an ultrasonic transmitter and you can start on the outside with searchin for a leak.
I can make a picture of this device if you're interested.

[Gary]

Following defrost, the fans should be delayed until the coil is frozen, else moist air will be blown out into the room. This is usually accomplished with a fan/termination thermostat.

Your defrost timer has both temperature termination and solenoid termination. It MUST terminate on the solenoid, not the time. Time termination is for backup in case the termination solenoid fails. If it is terminating on time (fans start immediately), lengthen the time duration setting.

If the timer will not terminate on solenoid, then check the fan/termination thermostat, timer solenoid, and wiring.

[Matt]

Thanks for all the input. I haven't been back to the job yet but I will look into everyones ideas.
I will check for a fan delay after defrost. I'm assuming it is terminating on temperature not time. I have the time set for 50 minutes.

[Peter_1]

Thanks for all the input. I haven't been back to the job yet but I will look into everyones ideas.
I will check for a fan delay after defrost. I'm assuming it is terminating on temperature not time. I have the time set for 50 minutes.

Let us know what you found. I bet on an airleak.

PS Webram: nice change since yesterday evening. Fantastic layout, it's just looking around now a little bit on the screen where all the previous buttons can be found.
Let's all applaud for Webram.

[WebRam]

thanks Peter there are loads on new toys for you all to play with and check out the calender options

[Matt]

Thanks Peter
I'm keeping the air leak in mind. We had a hell of a time biulding the box. Even the guy from Masterbilt was scratching his head as to why it wasn't going together easier. My biggest problem looking for an air leak is, the back and one side wall are not accessible from the outside, and there is only two feet above the box!!! What fun it was piping and insulating up there.The front and one side wall are accessible.
Thats ok, work would be boring if it wasn't for things like this! I'll let you know how it goes.

[shogun7]

I was wondering about the vapor barrier and how extremely important it is to properly install vapor retarders and seal all joints in the vapor retarder material to ensure continuity from one surface to another (i.e., wall to roof, wall to floor, or wall to ceiling).
Many times the failure of vapor retarder systems for refrigerated facilities is almost always due to improper installation so the contractor must be competent and experienced in the installation of vapor retarder systems to be able to execute a vaportight system.

Roger

[Matt]

Just a quick update,I went back to the job today.Here is my summary,see what you think!
I verified that I'm terminating on temperature (not time). The termination/fan delay klixon is working properly.What I did find is: because the two systems for this freezer are controlled by their own thermostat, naturally one becomes the lead, the other the lag. The defrost times are identical for each system, both defrost at the same time. But since the lead sys. does most of the work it also requires more time to defrost.What I saw today was the lag sys. terminated after 25 minutes, the lead sys. continued for another 15 minutes during which time the lag sys. nullified some of that because it's fans came on after the delay and was the cause of the ice biuldup on the lead evap. because it didn't get the time to drip dry so to speak like it should. I may not have mentioned the fact that due to space constraints the evaporators were hung one underneath the other. The lead sys. is the top evap.
On top of that I think there are some air leaks in the box.I plan to shut the sys. down thaw everything and caulk all the panels from the inside.
I'm also tossing around two other control changes. Either shut one system down all together and use it (if needed) as a backup system. Or, control both systems with the same thermostat to equalize run times, defrost times etc.
I hope I didn't ramble on too much.
Am I on the right track?

[RogGoetsch]

It will do you no good to caulk the inside of the box. Water vapor pressure is highest outside of the box and lowest on the coil surface. If there is infiltration into the insulation from outside the box, the moisture will condense and freeze inside the walls, compromising the insulation and eventually causing bulges in the walls. Caulking the inside is at best useless.

I doubt that the snow is the result of such infiltration.

I recommend using a control relay so a single thermostat controls both systems. Even so they will probably build frost unevenly so I would use a single defrost time clock to ensure simultaneous defrosting, with selector relays so each coil's termination control shuts off its own heaters. When both are satisfied, the system restarts.

If you want a lead-lag system, I suppose you could leave the separate thermostats and still use some means to ensure neither system can start while the other is defrosting.

I have seen hot gas defrost systems with two evaporators in a low-temp cold storage facility where one coil always runs while the other is defrosting in order to maintain enough hot gas for defrost. But the coils are never close enough for the air from one to affect the other.

Rog

[Peter_1]

Matt,
Is problem arlready solved or are you skiing now inside the freezer?

[dallan]

Dixell and Eliwell manufacture a twin evaporator controller with seperate defrost termination probes if you want to run both systems off one thermostat.

[Peter_1]

which types from both?

[dallan]

Both produce a similar product. It's a controller designed for coldrooms with two evaporators that you want to control as one. The basic logic is a common cooling output and two seperate defrost termination probes which prevents a lead/lag scenario that was described earlier in this thread.

[Peter_1]

OK, but do you have types?

[dallan]

The Dixell was a version of a XR170C, this is the one that I would normally use. I am not sure of the exact model for the Eliwell version, it was an old EWPC type.

[Toolman]

I reckon make all systems run off the same controller ,same defrost times same termination , same cut out temp . That will stop these systems fighting each other when its down to temp .

[Toolman]

Yet again I have posted a reply on a REALLY old posting . ( sigh ) everyone would have forgotten about this job by now .

[rbartlett]

Yet again I have posted a reply on a REALLY old posting . ( sigh ) everyone would have forgotten about this job by now .

part of the appeal of AU is that it's so far behind the times ;-)

cheers

richard