# Ideas for refrigerator door design

## Main Question or Discussion Point

Hi all,

I just want to throw some ideas and get feedback from the community on refrigerator door design.
If anybody notices in supermarkets, etc, the frozen food are kept in glass-doored refrigerators. the prupose of the glass door is so the customers can see if the stuff they're looking is behind door number X, so, no opening door and got nothing, thus, increasing the temp in the compartment for nothing, where this would mean need to consume extra electricity to decrease the temp back to where it was for nothing.

now, the problem with this is that glass, even if it's not a good conductor, it still conducts heat. meaning, it heat from outside will still seep into the compartment, even when it's closed. I have 2 ideas:

1. in normal fridge in houses, we have 2 solid (non transparent) doors, top and bottom. I suggest we change this to a transparent material (glass, plastic, etc), but it a layered design. so the door is something like glass - vacuum - glass. the vacuum between glass is to prevent heat transfer from outside to inside compartment.

2. create more compartments in each section. so, right now, there are only 2 sections in a fridge --> freezer and refrigerator. normally, refrigerator section is quite big, so, I think it's better to further divide it to several compartment (tray level), so each tray is one separate compartment, so, when we open the compartment, we dont increase the temp for the other compartments.

the main objective is of course to save electricity, in tandem with inverter tech

any input ?
thanks

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256bits
Gold Member
You want to see through the glass what is in the fridge?

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You want to see through the glass what is in the fridge?
correct, see through the glass door what's inside. that way, less time looking for the item, which means less time the door is open, which would mean, less heat entering the compartment, which means less electricity to cool the temp down after opening the compartment door.
secondly, prevent as much heat as possible from entering into the compartments

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256bits
Gold Member
I suppose a comparison of the amount of time the door is open whether it ( the door ) is transparent vs non-transparent would be a place to start.
That would have to be done to see if type of door is a determining factor for the behavior of people, which includes those who who actually do like to open the door and stand there looking into the fridge.
And you would have to determine whether a transparent door would make retrieving items, or placing them into the fridge a time saver for the user and for electrical usage,
A table of time spent locating an item, retrieving the item, placing an item would quantify the results.

You could then record the amount of electricity used for both cases, if you find a substantial difference in the time the door is open.

russ_watters
Mentor
Have you looked into how windows are designed?

I would argue that transparency is actually not desirable for kitchen fridges, from a user's perspective.

billy_joule
I would argue that transparency is actually not desirable for kitchen fridges, from a user's perspective.
Well domestic fridges with glass doors are already available so presumably they're desirable to some consumers.

so the door is something like glass - vacuum - glass. the vacuum between glass is to prevent heat transfer from outside to inside compartment
Take a closer look at the supermarket next time, all the fridge doors are already double glazed. If they weren't, condensation would obscure the products and defeat the purpose of the glass doors.
In my country, most appliances have compulsory energy efficiency ratings with an annual running cost, glass door fridges cost a lot more to run than solid door fridges so that's probably one reason why market share is low.

An idea i quite like is having a small access port in domestic fridge doors, just large enough to grab the milk or butter while avoiding the energy loss associated with opening the door.

The door in door fridges are also an interesting idea;

anorlunda
Mentor
There are at least two simpler or less expensive ways I can think of to reduce energy losses when the refrigerator door is open.
They are both based on the principle that most of the energy loss comes when cold heavier air spills out onto the floor, and is replaced by warmer lighter air from above.

1) Make a horizontal refrigerator where the door opens from the top. That has a convenience cost.

2) Use a plastic strip curtain inside the refrigerator to slow down and reduce the spillage of cold air when the door is open.

An engineer in training should know that before presenting an innovative idea to management, that he should do some engineering analysis. For example,
• Where does a typical refrigerator's energy go? We are interested in the fraction of that energy that could be saved, and how much that is worth to the consumer in terms of cost savings per year.
• How much would the idea cost in design and manufacturing?
• How would the design affect customer service and warranty costs? (two doors = twice as many door-related problems)
• What is the cost/benefit ratio to the manufacturer? to the consumer?
• How would it impact consumer convenience?
• What similar ideas have been tried and rejected in the past by other manufacturers?
It is fine to filter ideas first with simple questions, "How much energy would the split door save?" If the answer comes back, "very little." then there is no need to investigate the other questions.

The first thing one should probably do is attach an amp meter to the fridge power cable, and see how much additional power is consumed after a normal access to the fridge. Alternatively, you could measure the temperature inside the fridge, and see how long it takes to go back to operating temperature.

Another, wild idea would be to do something like stores do when they blow warm air from the ceiling when you enter the store, in order to prevent cold air from entering. Maybe you could push cold air out when the door is opened!

Stephen Tashi
Cameras inside the fridge and an LCD display on the outside of the door - which could show reminder messages when the owner wasn't browsing the contents of the refrigerator.

rbelli1
Gold Member
OmCheeto
Gold Member
According to my calculations, I would have to open and shut my refrigerator door 36 times before it would cost me a penny's worth of electricity.

Based on:
the volume of my fridge: 0.37 m^3
difference in air temperature: 17.8K
my last electric bill: $0.122/kwh and all those universal constants​ Although saving energy is always a good idea, I like to do a tad bit of maths before I invest too much money in things that will save me virtually nothing. The first thing one should probably do is attach an amp meter to the fridge power cable, and see how much additional power is consumed after a normal access to the fridge. ... This sounds like a very good experiment. I purchased a Kill-A-Watt meter last summer. I think it will pay for itself in what it's made me aware of. My above calculations were based solely on the heat capacity of air. Heat losses, I am sure, are higher, due to both convective and radiant energy transfers. Though, I doubt they will be significant. But, you can never be sure. The experiment has started. And right off the bat, I notice a problem. My refrigerator has a power factor of 0.5 Volts: 121.4 Volt Amps: 413 Watts: 208 PF: 0.50​ I may have to look into this. Although I may not pay for un-utilized current flow, I have a feeling it makes the entire grid less efficient, which I would imagine we are all paying for. ... see through the glass door what's inside ... I suspect most homeowners don't want to have the contents visible. They'd rather see a nice enameled or stainless surface, not a bunch of drippy bottles and Tupperware full of yesterday's beans. ok, so there are 2 issues here: • see through fridge door --> already a concept by samsung (pretty sure it's not on sale yet, or is it?). the reason I brought this point up is that I've observed the behavior of normal people when opening the fridge : 1. open door 2. aristotle's pose when pondering which leftover food one wants to eat now 3. turn the fridge upside down in an attempt to locate said leftover 4. close door (#1 to #4 takes around 10 seconds) • multi compartment --> now, I think an experiment is in order. @OmCheeto , you're already conducting experiment? lets compare data later. I'm in asian country where electricity is quite high and dry season can be really hot and humid, so I dont know if this will affect the speed of heat transfer when door is opened. OmCheeto Gold Member ok, so there are 2 issues here: • see through fridge door --> already a concept by samsung (pretty sure it's not on sale yet, or is it?). the reason I brought this point up is that I've observed the behavior of normal people when opening the fridge : 1. open door 2. aristotle's pose when pondering which leftover food one wants to eat now 3. turn the fridge upside down in an attempt to locate said leftover 4. close door (#1 to #4 takes around 10 seconds) • multi compartment --> now, I think an experiment is in order. @OmCheeto , you're already conducting experiment? lets compare data later. I'm in asian country where electricity is quite high and dry season can be really hot and humid, so I dont know if this will affect the speed of heat transfer when door is opened. Preliminary results are inconclusive: I either opened my refrigerator door 356 times last night, or I have not collected enough data, or I have not accounted for all significant variables​ Thank you for mentioning humidity. As everyone knows, warm humid air will condense on everything in the refrigerator. This may be significant. I will attempt to ascertain the humidity in my house. ok, so there are 2 issues here: • see through fridge door --> already a concept by samsung (pretty sure it's not on sale yet, or is it?). the reason I brought this point up is that I've observed the behavior of normal people when opening the fridge : 1. open door 2. aristotle's pose when pondering which leftover food one wants to eat now 3. turn the fridge upside down in an attempt to locate said leftover 4. close door (#1 to #4 takes around 10 seconds) • multi compartment --> now, I think an experiment is in order. @OmCheeto , you're already conducting experiment? lets compare data later. I'm in asian country where electricity is quite high and dry season can be really hot and humid, so I dont know if this will affect the speed of heat transfer when door is opened. just want to clarify, I meant was quite expensive berkeman Mentor Sorry if this has been already suggested (TLDR), but do you have a barcode reader in your door? Sorry if this has been already suggested (TLDR), but do you have a barcode reader in your door? in my door? as in fridge door? I dont think so. why? 256bits Gold Member ok, so there are 2 issues here: • see through fridge door --> already a concept by samsung (pretty sure it's not on sale yet, or is it?). the reason I brought this point up is that I've observed the behavior of normal people when opening the fridge : 1. open door 2. aristotle's pose when pondering which leftover food one wants to eat now 3. turn the fridge upside down in an attempt to locate said leftover 4. close door (#1 to #4 takes around 10 seconds) • multi compartment --> now, I think an experiment is in order. @OmCheeto , you're already conducting experiment? lets compare data later. I'm in asian country where electricity is quite high and dry season can be really hot and humid, so I dont know if this will affect the speed of heat transfer when door is opened. As I mentioned in post #4 you will have to do obtain some data, if your premise that a glass door will save electricity in the long run. That is your biggest issue here. Just making the assumption is not enough. You have to back it up. With a glass door, all the convenient placeholders will be lost for eggs, milk, etc. Final result could be a larger fridge with more surface area to lose "coolness", so the gain in electrical usage can end up negative just from that. OmCheeto Gold Member As I mentioned in post #4 you will have to do obtain some data, if your premise that a glass door will save electricity in the long run. Yes! It would be interesting to see how other people approach this problem. Mostly, I've been trying to not open my refrigerator at all. It is more difficult than one would expect. So far, I've accidentally opened the door 4 times, and 4 times on purpose, for a total door open time of 30 seconds. I've now collected 48 hours worth of data, and have come to no conclusions. I will probably do some more tests tomorrow. Things I originally overlooked: The unit is a frost free type, so it must have a defrost cycle. I have not determined how much power that consumes. I have a feeling that when I'm done, I will have discovered that this is more of a psychology test, than a science experiment. I think I will post a sign on my refrigerator: Are you really hungry, or just bored? 256bits Gold Member Yes! I think I will post a sign on my refrigerator: The addition of several doors for different trays containing different food items, could solve that problem to some extent. A separate tray for legumes and fruits, one for meats, another for condiments, ...., as TE had mentioned, does seem practically pleasing. People can choose to open whichever door to whichever food they like to stare at in the hope of become psychologically satisfied. To his credit, and your insight, TE may have discovered a design feature that the refrigerator people have overlooked. DrClaude Mentor The addition of several doors for different trays containing different food items, could solve that problem to some extent. My upright freezer is like this, with a transparent plastic "door" in front of each shelf. ok, so there are 2 issues here: • see through fridge door --> already a concept by samsung (pretty sure it's not on sale yet, or is it?). the reason I brought this point up is that I've observed the behavior of normal people when opening the fridge : 1. open door 2. aristotle's pose when pondering which leftover food one wants to eat now 3. turn the fridge upside down in an attempt to locate said leftover 4. close door (#1 to #4 takes around 10 seconds) I would be curious to know how much heat is lost in the first few instants of the door being opened. Is there a big difference with the door being opened 5 seconds vs 30 seconds? Window insulation is a big business. They are rated by "U-value" Watts/m2/K (the inverse of "R-value" In the USA, R-values are given in hr.ft2/BTU). Adding double panes helps by about a factor of 2. Adding a "fill gas" (typically argon) is common. And another gain is adding a transparent conductive coating to reduce radiation transfer (Low-e coatings). These coatings are typically either a couple of microns of SnO2:F or dielectric/Ag/dielectric where the Ag is ~12 nm and the dielectrics are ~ 40 nm or "1/8 wave" layers for antireflection. Software to calculate such things is available. LBNL has their "Berkeley Lab WINDOW" program that allows engineers to try out various scenarios. There you can find how frames are also a big part of the problem making the "small doors" idea work less effectively than one might first imagine But it turns out that in commercial freezer doors there is more concern with "fogging" than with energy savings! So the coatings (which are electrically conducting) are used as resistors in a heating circuit!!! Not only does opening the door dump cold air out on the floor but it also activates the heater to reduce condensation which would make it impossible for the next customer to clearly see the products! Vacuum insulation panels are real - Vacuum windows are also being offered but have many issues that will need to be solved Bowing of the sheets requires "pillars" at about ever 10 cm or so Differential thermal expansion between "in" and "out" sheets means the seal should not be rigid or at least sheets not too big Thermal expansion can also shift the pillars "scratching" the glass OmCheeto Gold Member The addition of several doors for different trays containing different food items, could solve that problem to some extent. A separate tray for legumes and fruits, one for meats, another for condiments, ...., as TE had mentioned, does seem practically pleasing. People can choose to open whichever door to whichever food they like to stare at in the hope of become psychologically satisfied. To his credit, and your insight, TE may have discovered a design feature that the refrigerator people have overlooked. I don't think refrigerator designers have overlooked anything. If you google for any feature you think might be a good idea, you will find that someone makes it. refrigerator with windows refrigerator with drawers refrigerator with the most doors refrigerator with doors in their doors​ From personal experience, a water and ice dispensing door would reduce my door opening activities by 90%. After I affix my "Are you just bored?" sign, of course. I would be curious to know how much heat is lost in the first few instants of the door being opened. Is there a big difference with the door being opened 5 seconds vs 30 seconds? I can do that. But the results won't be available for another 2 days. One complicating factor with my refrigerator[1], along with it being very cyclic[2] is that instantaneous power consumption varies between 213 to 228 watts. And there is that dreaded "defrost cycle", which according to wiki, should be consuming between 350 and 600 watts, for about 15 minutes, for an indeterminate number of times a day. And that dreaded measurement at t=20.95 hours: Watts = 1.3 [???????] Does that infernal light bulb in the refrigerator really go out? Or, is it a quantum light bulb, that is both on and off? hmmmm.... Ah ha! [1] Hotpoint model CSX20EKC, mfg 10/88 (29 years old!). If anyone has a schematic, it would be greatly appreciated. [2] Duty cycles, measured on the hour, vary from 28% to 100%. OmCheeto Gold Member ... And that dreaded measurement at t=20.95 hours: Watts = 1.3 [???????] Does that infernal light bulb in the refrigerator really go out? Or, is it a quantum light bulb, that is both on and off? hmmmm.... Ah ha! ... Refrigerator light bulb: 60 watts Freezer light bulb: 45 watts This may take me a few minutes to calculate. Everyone else is free to join in: ## Homework Statement If OmCheeto opens his refrigerator door for 30 seconds, and stares thoughtlessly into the abyss, wishing he'd gone to the store yesterday, but instead sees just a half a loaf of bread, does the light bulb or the exchange of air consume/impart more energy? th 291.5 K tc 273.7 K delta t 17.8 K air 1,000 joules/(kg K) air cap of fridge 0.3718 m^3 measured air 1.225 kg/m^3 air 0.4555 kg air 8,107 joules conversion 3,600,000 joules/kwh air 0.00225 kwh electricity 0.122$/kwh
air 0.000276 \$
air 36.25 times air replaced to cost a penny

ps. see previous posts for more data

## Homework Equations

just google them like I did

## The Attempt at a Solution

will take me a few minutes