View Full Version : Need help with Octagon shaped cheese display

11-03-2006, 03:15 AM
I am looking for design information on building an octagon shaped display mechandiser. I have built front facing grab and go ( air screen) type cabinets before but this will be my first 360 degree unit. Its approximate size will be 6 feet in diameter. The drawing I was presented shows a short tower, aproximatly 12" in diameter, in the center with a sloping deck toward the perimeter where the return air grills is located. It's load line is no more than 8-10 inches deep.

Of course pictures would be great but the ones I have seen so far leave lots of information out. Hussmann for example shows no more than a sales spec sheet with mostly dimensional info. I need a bit more info. Such as;
1 Compressor size
2 Evaporator size and placement
3 Fan placement
4 Are the decks perforated
And of course whatever other information you can supply that I have n't thoght of yet.

I am with a small company and as my name implys I'm flying by the seat of my pants with designing some of these projects, but I love every minute of it. When I finish some of this stuff and it gets cold there's some reward within yourself for it all.

You guys have helped me so much over the last few months I'd love to hear your thoughts on this one.


US Iceman
11-03-2006, 05:16 AM
Hey Ken,

Attached are some quick ideas for you. No AutoCAD drawings this late at night.;)

Not a very fancy sketch, but I think you will see the idea. If you want holes for return air you could drill or punch holes around the perimeter (in the 10" area) shown on the sketch.

I would look at a round coil, so that you have uniform air flow over the whole face area. Then the drip pan could be placed underneath the coil.

The fan motor could be secured in a belly band motor mount and removed from the top (which would have to be removable of course).

Air flow would have to be low so that water is not pulled off of the coil. Probably something like 200 CFM or less.

The sloped inside panels are shown this way so that when the air flow returns through the perimeter, the air flow is somewhat directly into the coil in a straight line. You could also connect a drain at the bottom of sloped area for cleaning.

360 degree air coverage of the counter through the tower. The top of the tower could have an opening at the top, say 3-4" for the exit air flow. Perhaps with some deflectors to channel the air flow on an angle.

I would not perforate the sloped decks. Let the airflow travel from the center tower and out to the entire perimeter.

Now all we need is the cooling load and equipment!

11-03-2006, 05:22 AM
Kengincopying? I don't think it is fair for you to blindly ask all the details of how to make something work that other people have designed. I like Kengineering much better.

I had a funny experience when I was designing a meat wedge that nobody could make work. I used an evaporator that went up higher in the back of the case than evaporators normally do. It worked so good, that my design went to headquarter engineering well before I was done with it and I was informed that I had a 30 psig pressure drop thoughout the evaporator. DUH!

You need to distribute your evaporating surface as well as you can within the space the design allows, and avoid my mistake: Use a distributor and individual circuiting to overcome the pressure drop that a single circuited evaporator will have. Squeeze the tubes and fins in and make them tall if you need to, but then distribute the flow as best you can.

Octogon cases don't require this attention to detail. But you need to think ahead and enjoy these less critical applications to be ready for the next more demanding request. Fresh meat and ice cream come to mind. :)

US Iceman
11-03-2006, 06:19 PM
...cases don't require this attention to detail

I believe any application should be well thought out with a lot of attention to detail. There are basic fundamentals that should be applied to any project.

Departure from these principles has the potential to make a simple project turn into one that will give you grey hair. ;)

11-03-2006, 09:01 PM
I believe any application should be well thought out with a lot of attention to detail. There are basic fundamentals that should be applied to any project.

Departure from these principles has the potential to make a simple project turn into one that will give you grey hair.

So true. And thank you for bringing my casual statement back to me. I was thinking of an enclosed octagon case when I made my statement. More or less I was speaking about what I thought was a forgiving application such as an enclosed case, versus an open air case. Now, after rereading the original question and your response, I am guessing that we are talking about an open multideck island cheese display case.

This style of case normally has a perforated wall to provide a low velocity, positive pressure cold air stream across the bottom deck of the case. You should also have a honeycomb discharge that directs air over the shelving and returns through a grill at the perimeter of the case. The evaporator design suggested by Iceman is not a bad idea, but expensive.

The flaw in this sort of design is that you will entrain a lot of ambient air. An old Hussmann case engineer once told me a thousand times that "Air does not spread."

So when you try to turn corners with air, or aim it at a larger perimeter, you will entrain ambient air in the process.

For an octagon with no shelving, I would suggest 4,000 btu/hr at a 15 deg F evaporator for compressor sizing and 200 fpm from the honey comb and half of that from the perforated tower. For one with upper shelving I would suggest 12,000 Btu/hr. Use solid pans and shelving. The corners are the weak spot, so if you can favor the air return to them, do so. Chances are, you can reduce the horsepower after tweaking.

Most importantly, use a 6-inch glass or plastic catcher on the outside perimeter of the case.

11-03-2006, 09:23 PM
I had a design I never implemented for an island meat display. I must have tossed it. But the corners are the killers in island displays. I drew up something that actually used a top discharge and a discharge where we normally see the return air with the air return through the bottom pans. Food for thought, Ken. It was a sheet metal experience.

12-03-2006, 03:31 AM
By far the round evap coil was the best I could come up with as well Ice. Even in spite of Dan's very sound advise

I believe any application should be well thought out with a lot of attention to detail. There are basic fundamentals that should be applied to any project.
Departure from these principles has the potential to make a simple project turn into one that will give you grey hair.
However I have a very short deadline on this one ( that usually spells trouble) so I have elected to go with 2-coils placed opposite of each other on the bottom of the towers circumfrnce while dividing the case in 2 in order to direct the return air through its coil. I do have an excellent metal man as long as it's drawn well.

Now the fans.. Would a tower fan as US Iceman has suggested be the only fan ? I've got only three weeks on this one...Ken

14-03-2006, 02:15 PM
Dear Sir ,

Kindly advise us on the brand name of absorbtion chiller
we are looking the 15 Kw , 22 Kw , 30 Kw. of absorbtion chiller



15-03-2006, 01:55 AM
A tower fan or two between the evaporators is what I would expect to see. Rely on a glass front with a return flue guard to help distribute the refrigeration and tweak your airflow with smoke testing. If you can get an under 40 deg return air temperature along with a 28 deg F discharge on the "non" refrigerated sides, You have a winner. You may choose to do some routing of the return air with underpan baffles in order to equalize return air velocities, but it just being cheese, you should be okay. Common mistake is moving too MUCH air. Good luck.

15-03-2006, 08:18 PM
You have all been helpful and encouraging. The structual shop is doing thier thing right now I expect to get started on the mechanical side of things on Friday.

Any ideas on controls? I was going to go with a T-stat but I'm not quite sure on bulb placement just yet.

I was also told to consider a rehostat to control fan speed. Is this a good idea?

Thanks , Ken

17-03-2006, 01:05 PM
Hi, Ken
May be these photos can be useful to you