Customer has a w/i freezer, about 30ft to ceiling. Box runnin at -18deg F, plant guys in/out all the time with forklift storing product on pallet racks. Complaint is alot of moisture/ice build-up on ceiling in front of evap. coils(2 coils). My boss checked coils and end bends on both coils, all clear of ice! We went in and ran her through a defrost, and waited to check fan delays to make sure they were working, both are good. What we did notice was alot of moisture evaperating off of coils during defrost! My boss decided to shorten defrost time and watch for next while to see any differance, I'm thinkin that 3 wire defrost terminator may be rated at too high a temp. I did'nt get up there to check the rating on the 3 wire so I'm just guessing. Any other suggestions, or is this just somthing the client will need to live with?
Ive seen the same problem but on a smaller walk-in. about 20'w x 40'L x 8'H. They are also in and out alot. Moisture all on the ceiling and ice forms all around the fan guards and usually ends up destroying the fan blades. I too have checked the time delay on the fans and they are working. They even have a 1min delay every time the door is opened. Have never figured it out yet either.
- Too long of a defrost time.
- Staggered defrost times on different coils.
- Air infiltration through the threaded rods, conduits, and/or piping penetrations.
- Defrost cycles too frequent.
- Fan delay too short. (Common with pressure control operated fan delays.)
- Fan delay too long to turn off.
There are other things, but these are the common ones.
You could also ban them from entering or leaving the freezer, but most customers frown on that.
A lot of traffic in this freezer,huh...
Are these electric or propane fired forklifts?
Are they bringing a lot of unfrozen products into this freezer?
Does the freezer have door curtains?If so what is the condition of these curtains?
Have you checked all the joints on this freezer,is it airtight to the exterior?
Has there been a large amount of precipitation in your area lately?What is the humidity level in the rest of the building?
Is this case contained within a building?If so have you checked around and on the top of the case for excessive moisture?
In my opinion you have an excessive humidity problem.....
Keep us posted...
Thanks for responses!
Hussmantech: 1. Electric lifts
2. There is a Air-curtain but nothing else
3. up in Vancouver lots of percipitation(rain-rain go away.)
4. Box is located inside a wherehouse
5. Did poke around on ceiling of box, and did not find any cracks or gaps. Also none were found on box walls.
Sounds like BJS wholesale clubs...............i think its the same as Dave said!
Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced
yup i agree with dave also, it sounds like a deforst problem not humidity, humidity makes snow n frost, defrost creates water droplets, water droplets turn to ice, excessive defrost and early fans would be where ild look first. my suggestion would be to go there when its going through a normal defrost and observe whats going on even if you gotta get a boost from one of the fork lifts. ps bring some coveralls with you
Did you check everything Dave sugested?
Originally posted by gas-n-go
yup i agree with dave also, it sounds like a deforst problem not humidity.
my suggestion would be to go there when its going through a normal defrost and observe whats going on even if you gotta get a boost from one of the fork lifts. ps bring some coveralls with you
Oh, and when you get lifted up there to wait it out ... bring a thermos of something warm to drink.
Oh .. and make sure U P B4 U go up!
I haven’t run across this problem but just reread this thread and had a brain fart. Now that is a dangerous thing for me because I usually only have them in the shower... But see what you think about this. When the unit goes into defrost the system steams some - the ice thawing turns to steam which floats up to the ceiling. Well the ceiling is very cold so the steam freezes to the ceiling or fan blades or fan shrouds etc. Someone said humidity will make snow on the freezer - that is true - but steam will make ice. So how many ways can we keep steam from forming in a freezer that is cold? As I see it maybe the defrost system is getting things a little too hot to long. Maybe you should shorten the defrost time and have more of them each day. This would cause the system to go into defrost before allot of moisture freezes on the coils. Thereby, cutting down on the moisture available to make steam. I think you are on the right track by shortening the defrost time and maybe raising the termination temp.
Another thought - are the fork trucks coming directly into the freezer from the outside ambient or are they coming from a cooled space. You might have to consider putting in a drive through cooler ahead of the freezer just for humidity control. Also is the product really wet – is the customer bringing in a lot of moisture? Maybe he should pre-cool the product to get some of the moisture out. I would give the application of this freezer a good eyeball. It might be a customer education thing.
Interesting problem – good luck.
It’s possible you have the wrong heat elements, or your high limit is not working. Coils should not produce significant amounts of steam.
A Diamond is just a piece of coal, that made good under pressure!
I suspect the problem is with the termination/fan delay t'stat. Most standard units have a termination temp of 50-55ºF and a delay temp of about 20ºF. While this generally works OK for a 0ºF box, at -18ºF that 50+ºF will create a lot of steam. That steam will deposit itself on the nearest and coldest surface it finds.....the ceiling.
Since this is a temperature terminated system, when you say that the boss shortened the defrost time, what he really did was shorten the failsafe time. The terminator determines the actual time.
I'd suggest trying an adjustable terminator. Ranco makes one. If the termination temp were dropped to say 45ºF and the delay temp dropped to 10-15ºF, less moisture would be steamed off during defrost and less moisture would be blown out of the coil on fan restart.
Shorter more frwequent cycles
I have run into that abit here as well, our problem is that they are low profile Bohn units which only have the terminator in one side, and as access is an issue (%$#$%^ engineering) as well as parts availability(way out in the boonies and budget stuff) I have been running shorter and more frequent cycles. Not really the best answer but I don't have time to hit every user with a stick to get them to close the darn door!! I am considering putting a terminator in each side of the coil?
Check the stampings on the elements if you can, and compare them to coil specs if possible.
You have received some good advice so far, if this does not resolve the problem your element is to big (watts). The only permanent solution I have found is new high limit (if bad), or smaller heaters, longer duration.
A Diamond is just a piece of coal, that made good under pressure!