Open air refrigeration

Hello,
I've got some great feedback from this group before, let's what people know about this one...
I'm curious about those refrigerators you see in businesses like take out restaurants and cafeterias. They have things like bottled soda, fruit, yogurt, and other things you can just grab and consume, without opening any door. They are fully exposed to the elements. My curious question is how they can be efficient and effective, while leaving the refrigerator at home open for more than a minute is "so bad." I was always told not to leave it open for more than a few seconds. Yet save for some plastic perforated sheeting, these things never are fully closed.
Is there some intricate fan device that keeps the cold air in? Or are these just a conservationist's nightmare?
-Elliott
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Elliott P wrote:

Obviously they're not as efficient as an enclosed refrigerator. It's a convenience trade-off. The main difference in the open display case is that it doesn't have the opening at the very bottom like an open refrigerator door. There's usually a lip at the bottom that helps keep the cold in so it can be collected. The refrigerated air is recycled, pumped into the case at the top and sucked out at the bottom. With that arrangement of air cycling there isn't as much mixing of air as you might think.
R
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Elliott P wrote:

Conservationist's nightmare? Have you noticed what these things are dispensing?
Designer water, mostly.
The main purpose of the gizmo is to sell product - energy efficiency is way down the list of desirable features.
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Maybe I'm not thinking about the same display cases, but what about almost every grocery store? The entire row where the milk, juice, eggs, cheese etc? THOSE are open cases. What about the aisle that has the open FREEZER cases. The kind that are about waiste high that have frozen orange juices and stuff? or are we talking about something else?
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#1 they aren't very efficient. You can feel the cold air around these coolers as soon as you get near them. It's a trade-off to the owner. The convenience of having the products easily accessible to the customer means the customer is more likely to buy them, but having it in the open will cost the owner more in electricity. Apparently, it must pay off since these things are everywhere.
#2 they probably aren't as cold as a refrigerator. They're not meant to keep food preserved for long periods of time. They exist only to keep food cool (in the case of drinks); and fresh for a couple of hours (fruit, etc.). It takes less energy to cool air from 70F down to 45F than it does to cool it down to 35F.
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#1 they are NOT efficient. You can feel the cold air around them when you get near them. It's a trade-off for the owner, and having the products in the open where people are more likely to buy them is the winning strategy apparently, since many businesses are willing to pay for the higher electrical cost of running these coolers
#2 they probably do not run as cold as a refrigerator. They only have to keep drinks cool and food fresh for short periods of time. It takes less energy to cool ambient air to 45F than it does to cool it to 35F.
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I have worked with these for years. They are only good for drinks. Meats and dairy products will never keep until use by date. They are fine for a busy suoermarket that turns food over quickly, but nit good for storing anything over a period of time. Also you will need a good refrigeration man and deep pockets to keep it running well.
--
jackpona

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they have an "air curtain". problems occur when improper stocking of goods blocks the curtain. look at the display cases when your shopping next time, you'll find a stocking line which is not supposed to be crossed with product.

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If you look overhead at the front of the cabinet you will see what looks like a bundle of straws, just the ends... this creates whats called in the business a high velocity laminar flow air screen as the fans in the case blow air into a plenum above these bundles creating the 'air screen' when cold air tries to leave the case it is drawn into this air screen down to the cold air return and recirculated.
"case parts' company in LA Calif will sell you the media used to create such air screens.
when warm outside air tries to enter the case it hits the outside of the air screen is and is drawn down and away.
cross flow ventilation, or even people walking by and disrupt the air screen and it will mix warm outside air with the refrigerated case air.
yes they are less efficient than a case with doors... but products sell better with open cases. A closed case, thats with glass doors, 10' long might have a 1/2 or 3/4 hp refrigeration package on it... an open case that long might have a 1 hp refrig package on it.
They are most viable for tightly packaged and sealed foods that can stand the occasional excursion to 40F or a little higher... they are not viable for say fresh meat, that idealls should be kept as close to freezing as possible 32 or 33 def F.
So you see these on cheeze, and packaged process meats...a lot in the vertical configuration (the worst but sells product the best)...
You see horizontal open cases for package meats running close to 34F....because cold air is denser than warmer air and will lay low in a horizontal case. those do not have air screens... but gentle low velocity air drifting across the top from back to front.
Packages that sit into this flow will disrupt this air flow, creating turbulence that involves the warmer ambient air and its heavy moisture load...this warms the case, causes ice to develop on the evaporator coil... generating more defrost cycles... the case warms a bit during defrost... shelf life of the product is reduced proportionally.
Phil Scott Refrigeration contractor since 1450

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Phil Scott wrote:

Phil, it's come to our attention that your resume states that you've been a refrigeration contractor since before the industrial revolution. Well, what with the CEO of RadioShack resigning due to his fabricated qualifications, some board members reviewed your employment application. Admittedly, it is a bit belated, but we have discovered some discrepancies. To wit:
- you do not in fact hold the patent for ice - Moses parted the Red Sea, not you - if you stop dreaming, we don't all die, as you've threatened numerous times
Although we have no proof on the last item, we're pretty confident we're right...if not - we're only kidding!
R
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I think he's trying to get his name on a tree in Sequoia National Park.
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The pharohs used ice from that mountain in africa at the source of the nile river. floated it to the palaces on barges, and stored it underground insulated with hay. Then used bellows to blow air through it on hot days to keep the pharoh cool.
I have my resume out these days... trial balloon mostly to test the larger market and get over going ballistic when recruiters call... I had to figure out what the hell is going on with those people.
I tell some of the recruiters that if the company is as lame as their position requirements and HR staff that they need to locate a moron if they want a good fit... these are real concerned with fit these days.
. That hasnt been working out real well... but its satisfying.
I read where Manpower inc says there is a world wide shortage of talent in the sales rep and the engineering and technical areas..due to get worse fast.
Ive seen some of that lately but not much...if it gets to be a disaster as many have predicted it will be a good chance for some of us to become complete pains in the ass.
that will be good.
Phil Scott

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