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Converting a Chest Freezer to a Fridge [pdf] (mtbest.net)
42 points by andrewwhartion on July 8, 2016 | hide | past | favorite | 41 comments



Or there's this article about how to change the temperature range of a chest freezer with one simple screw adjustment.[1] Or this off the shelf external mechanical thermostat.[2] Designing your own analog electronic thermostat is not really necessary.

[1] http://www.homebrewtalk.com/showthread.php?t=249612 [2] https://www.amazon.com/Johnson-Controls-A19AAT-2C-Temperatur...


My goodness people. 12 hours of discussion and people are arguing about if it's actually more efficient or the best thermostat to use.

The reason no one wants a "chest freezer" style fridge (which the author of the article advocates) is because it's a pain the back to get stuff in and out, not to mention organizing your food.

Yes, this is great for home-brewing. But nobody should kid themselves that regular people would want this to replace their "normal" upright fridges.


I'm not sure the pain-in-the-back argument is necessarily true. Even for many upright refrigerators, you must still bend over or crouch to get things from lower shelves and drawers. I've never felt inconvenienced removing things from my chest freezer. Also, my chest freezer has some sliding racks that make it great for organizing its contents. It seems possible that the pain-in-the-back argument is great for marketing, because it sounds like there could be some truth to it. I would argue that a person that has back trouble would likely only be able to use the chest level shelves in fridges, but they could just as easily use the top level racks in a chest freezer.

My guess for why traditional upright fridges could be seen as more convenient is because they take up less floor space for the amount of volume they provide. Also, upright fridges would be easier for small/short children to access. If floor space is less of a concern, and there is no need for small children to access the fridge, a chest-freezer-style fridge sounds like a brilliant idea. Next time I need a new fridge, I will seriously consider this as an option. Perhaps by then some contrarian manufacturers will realize how much sense this makes and I won't even need to convert a freezer myself.


It's not about "back trouble". Digging through a chest freezer regularly is a pain even if your back is in great shape.

Most of the stuff people use frequently ends up on the top shelves or in the doors of fridges. Lots of fridges have really deep door shelves to maximize this utility. Similarly, nicer fridge/freezer combos have mostly moved the freezer to the bottom to increase the convenience of the fridge.

Most fridges also have quite a few shelves so that you can get out the thing you want without moving everything. In a chest freezer, the baskets don't hold most of the food. Most of it is stacked on the bottom. So to get the thing you want, you inevitably have to move other things off of it. Refrigerators minimize this hassle.

Plus the condensation is gross and extremely inconvenient to clean when the fridge is full. I can't imagine leaving the walls of my fridge wet for 2-3 months at a time. You can address that with a chest fridge that operates like a normal fridge (cooling and therefore dehumidifying the air directly), but I bet you lose most of the efficiency gains as soon as you do.


Lots of homebrew supply shops sell affordable, hobbyist thermostats to put between your chest freezer and the electrical outlet, or, with more work, to replace the freezer's built-in thermostat, in either case converting the freezer into a fridge. Good for lagering or serving small (~5 gal) kegs.


Usually those are shops don't sell what I'd consider affordable thermostats. The really affordable ones are meant for aquariums and are easy to pick up on ebay.


At around $20, something like an STC-1000 digital thermostat I'd consider pretty affordable for this type of application.


That would be the exact model I am talking about.


The article mentions that condensation collects on the bottom and has to be sponged out. It seems like what's missing is a system to deal with condensation.


Yeah I had a chest freezer fridge for a while. The condensation was a real pain.


Though, if you only have to deal with this every 2-3 months, like the article says, it might not be too much of a hassle.


I don't believe the claim unless the author lives somewhere with near-zero humidity all the time. People use these frequently for homebrew ("keezer" a la "kegerator"). The condensation is a frequent complaint. If you leave the walls of your fridge wet for months at a time, they will mold. It's cold, but not so cold that no molds can grow. And sponging out a chest freezer full of food is a giant pain in the ass because of, you know, all the food.


As someone who has done it.

TL;DR; How

Have zero knowledge about anything.

Buy part on eBay.

Spend 5 mins double checking what to do. Spend 30 seconds replacing part.

Because this is done by a lot of homebrewers, easy and lots of info out there.

TL;DR; Why, if not for homebrew.

Because a fridge will lose a lot of air when opening. 600 liters of air weights 600 grams. This ~ needs to be re-chilled on each opening.


Abstract:

"This article describes a household refrigerator that requires about 0.1 kWh per day to operate. The refrigerator offers excellent food-preserving performance, because temperature fluctuations in its interior are naturally minimized during everyday use. This fridge is 10 to 20 times more energy efficient than typical household fridges on the market today. It seems that the biggest obstacles in increasing the energy efficiency and food- preserving performance of household refrigerators are strange human habits and lack of understanding of Nature, not technology or cost."


Hang on, how is it we've spent hours arguing over thermostats, and no one has mentioned this is the work of dr tom chalko inventor of the cancer curing bioresonant t-shirt: https://bioresonant.com/tshirts.html

as seen in the authors head shot at the end of the pdf.

that's no mere dead head tie dye you're seeing folks


"Vertical doors in refrigeration devices are inherently inefficient. As soon as we open a vertical fridge door – the cold air escapes, simply because it is heavier than the warmer air in the room."

Okay, so the author proposes that the thermal losses from the cold air being replaced with ambient air make up for the hundreds of extra kWh/year consumed by a vertical fridge.

While chest freezers typically have better thermal insulation and larger evaporators than fridges...

So shouldn't we be comparing a chest fridge to a vertical fridge with a comparable insulation system and condenser/evaporator capacity before declaring that lower air losses are the reason chest fridges work better?


Hm.

Air has a heat capacity of approximately 1 kJ/(kg K). Its density is 1.2 kg/m^3.

I don't know how big the fridge is, but someone elsethread said 600 litres, so I'll use that. (And assume that it's empty.) That's 0.6 m^3, and so has a mass of ~700 grams. Assuming ambient air temperature of 20°C and a fridge temperature of 4°C, that's a temperature delta of 16 K. Therefore the energy required to chill that air is 0.6 * 16 = ~10 kJ.

10 kJ is 0.003 kWh. Electricity costs about 20 US cents per kWh. Assuming a factor of ten fudge factor for cooling efficiency, then we can be reasonably confident that opening and closing the fridge would cost less than 0.03 * 0.20 = 0.006 dollars = 0.6 cents.

That's not a lot.

Does anyone have any figures on how good fridge insulation is, for comparison?


Don't forget that refrigerators have a coefficient of performance greater than 1. So it takes less than 1 Joule of work to cool the interior by 1 Joule.


This is nonsense (what the author said, not you). The heat capacity of the air contained in a fridge is insignificant when compared to that of the contents. Opening and closing the door occasionally has almost no effect.

The two important variables are thermal mass and insulation.


The relative heat capacity of the air and the content is irrelevant. The thermal mass of the content is irrelevant as well since it's the same for a chest fridge and an upright fridge.

The relevant comparison is how much heat escapes through the walls of the fridge relative to the heat loss via escaping air. Since fridge insulation has improved massively in the last decade that might actually be a significant share. The paper also mentions that an imperfect seal (due to imperfect closing or plain wear) on a vertical door leads to a constant trickle loss, while it does have much less of an effect on a chest freezer.


Consumer fridges also consume a lot more energy in the interest of keeping humidity (and, subsequently, frost) out of the compartment. They also run defrost cycles with heaters to keep the evaporators from icing over and locking up the system.

That lack of humidity control is what builds up a secondary layer of insulating frost/ice inside a normal chest freezer. It results in that "cleaning flow" of water inside the chest fridge, which doesn't sound as sanitary or healthy as the author proclaims once it builds up to a significant level.

"The amount of condensation depends how much moisture is in the ambient air and how often and how vigorously we open and close the fridge lid."

Wait. I thought less to no ambient air mixed into a chest fridge cavity according the author.


> Consumer fridges also consume a lot more energy in the interest of keeping humidity (and, subsequently, frost) out of the compartment.

Yep. I'm pretty sure if you had an upright fridge built to modern standards but cooled conductively (convectively?) it would be about as efficient as the chest fridge here, but it would also have the same condensation problem.


I think you misunderstood.

There's this urban myth that opening the fridge door is a problem because it let's the cold air out. The author of this article falls for that one as well.

When you open the fridge door a small amount of cold air is replaced by a small amount of room air. Yet, even if it was open long enough for all of the cold air to be replaced (use a fan to push room air into it) it would have zero effect.

In a nicely filled fridge the mass of items cooled to the set temperature has, by means of it's heat capacity and the mechanism involved in heat transfer from solid to gas, a thermal inertia that results in negligible effects from occasional door openings.

For example, I'd be surprised if opening the door to a well-stocked fridge and leaving it open for five minutes caused a 1 gallon jug of milk to drop in temperature even as much as 0.1 degrees at the core.


You're misunderstanding the point I (and the author) make. It's not a problem that cold air gets replaced by warm air because that might heat up the milk in the fridge (this is where thermal capacity of the fridge content would be relevant). It's an issue because the warm air needs to be cooled down to fridge temperature and that costs energy. So the relevant question is "how much of the total energy loss of the fridge is caused by cooling down warm air repeatedly after every opening)


We know the important fact already -- the chest fridge consumes much less power than an upright. The author has demonstrated that clearly. His reasoning as to why that's true is really secondary, almost irrelevant.


> His reasoning as to why that's true is really secondary, almost irrelevant.

It's really not. I'd wager that the vast majority of the efficiency is due to the lack of condensation control rather than the fact it's in a chest orientation.


> In 2004 I became really curious just how efficient a “chest fridge” can be.

Pretty sure you couldn't easily get a chest fridge back then. I know, I looked for one a few years later.


What constitutes a chest fridge to you? A Google image search on the term yields exactly what I expected and those have been around as long as I can remember (30+ years).


Something I can buy in a store or have delivered to my house and isn't an order of magnitude more expensive because it's "design"


So you're saying that "design" chest fridges are a new occurrence? I'm thoroughly confused as to what you're trying to say.

Chest fridges are not new and have been around for decades. If by "design" you mean designer, then ok maybe designer chest fridges are a new thing. I wouldn't know because I've never actually seen one. Most people keep chest fridges in their basement or garage and wouldn't care if it's designer or not.


> Chest fridges are not new and have been around for decades.

I'm saying that they might "have been around", but they weren't in any of the stores that sold fridges when I went looking for them. The only thing resembling a chest fridge I have seen in real life in the last decade was some kind of fancy designer-drawer in an upper-class house.


Just make sure to get a freezer with a drain plug. They are normally used for defrosting. "Some GE and HP chest freezers have a convenient drain at the front with hose adaptor. Check Owner's Manual for specific model information. Download a copy of the Owner's Manual." http://products.geappliances.com/appliance/gea-support-searc...


Non-PDF Google Cache Copy (for people like me, who don't like clicking on unknown PDFs):

http://webcache.googleusercontent.com/search?q=cache:_wPrLjU...

Missing the diagrams of the circuits but totally readable.


I'm struggling to find the reason for the battery backup / UPS. It has to be charged occasionally by the system, so doesn't make it's consumption zero standby... Why not drive the circuit directly from the A/C via a DC transformer? Is it to keep the memory of the last cycle to not over cycle the compressor?


An easier way could be to take a fridge and lay it horizontally.


The compressor has a coil with oil in it. The oil must settle in the right places or the thing could stop functioning. It can ruin a compressor to store the unit in the wrong orientation.


Yep. There's lots of scary warnings when buying even mini fridges that you can't operate it for at least 24 hours if the unit was rested on its side during transport to you.


Also, chest freezers are much, much cheaper than refrigerators. The last time I bought one, I paid around $300 for one that was quite large, vs. twice that or more for a typical upright refrigerator. Partly, I expect that's because they are so much less complicated, and partly it's because the demand is much lower.


Shouldn't bigger demand lead to efficiencies of scale, and thus lower price---at least for manufactured goods like fridges?


Consumer kitchen refrigerators have a higher BOM cost. They have two separate regulated champers, auto-defrost for the freezer compartment (chest freezers typically don't), shelving, ice makers, external ice/water dispensers, ice crushers, and cosmetic features.

And the cosmetic features for a kitchen, rather than the work-a-day ugliness of chest freezers probably means a larger profit margin too.


Why doesn't anybody sell this in shops?




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