# Designing a working refrigerator storage unit



## theTheme (Dec 18, 2013)

Hi all, I live in New York and have very little control over the temperature of my building. I'm considering a DIY project for a refrigerator storage unit and I'm trying to address the issues that come with them.

From my research it seems there are 2 issues that come up with fridge storage:

1. Fluctuations in temp due to compressor coming on and going off.
2. Lack of humidity.

Other than these issues, the box itself seems like it would be an idea storage instrument since it is heavily insulated and sealed.

To take on the second issue first, if the correct level of humidity is achieved in the unit before hand and then the door is closed (and subsequently not opened) it would seem to me that humidity would stay relatively constant. A well insulated fridge should have little to no leakage (remember the warning as kids, don't play in those things) and by not running the compressor (step 2 below) it would seem that it would stay that way. Thoughts?

Now the temperature issue. There are kits that allow you to somewhat regulate the temperature inside the unit by taking a more direct control of the compressor, but I'm looking for inexpensive storage (used cheap fridge) and replacing the compressor every year and paying more in electricity doesn't sound cheap (and running compressor would lower humidity).

What I'd like to do is get a fridge freezer combo (the kind with the freezer on top), turn off the fridge part of the unit, leave the freezer on, and circulate water through brass tubes so that it runs through the freezer compartment down through the fridge and back. The end goal would hopefully be to lower the ambient temp of the fridge without the air flow.

Before I go too far down this road, what do you think of the theory?

From a technical point of view, I'm thinking fish tank with water on top, small low voltage pump to continuously circulate the water, 2 holes drilled through the top of the freezer for input and return (then sealed), 2 holes drilled into the floor of the freezer (then sealed), and then the brass coiled in some way as to be the max distance from the bottles themselves and allow cool water to circulate in and out.


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## sour_grapes (Dec 18, 2013)

I think there may be a problem with your plan. You seem to be assuming the use of a dual-evaporator (or perhaps a dual-compressor) fridge. I could be wrong, but I don't think you will find a cheap used one.

Also, what makes you think that you will pay less in electricity this way? Also, are temperature fluctuations with a conventional setup actually significant? If they indeed are, you could always moderate them by putting thermal insulation around the object that you are cooling.


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## botigol (Dec 18, 2013)

I have been using a mini-frig as my primary wine storage for almost 15 years; same unit still doing it's job. I bought an external thermostat into which the refrigerator plugs to receive power when the temperature probe indicates (I've since built one for $40-$45). For seven years of it's time I lived in a townhouse without air conditioning; 90s are the norm in summer here with some days reaching the 100s. I don't recall it running that much which may or may not mean anything given that it is now years in the past and a minor detail. In any case it is still working. Refrigerators are naturally relatively humid. I live in a ridiculously dry climate and my wine frig always has some humidity. It definitely doesn't stay around the recommended 70%, but I've never had a cork dry out. The longest that I've had a bottle in there was 8 years.

The reason I start with a description of my set up is that even though I think that your idea would work, it seems overly complicated for the situation. If the compressor failing is a major concern, then it could be justified, but from my perspective it seems to be too much. 

As a tangent of your idea, if you were to leave the temperature control on for both the freezer and refrigerator and drill large holes/remove most of the barrier between the two compartments, the cool air from both areas would take care of your temperature control, thus reducing the amount of time that the compressor would have to run and the additional humidity generated from the freezer cycling on/off would help to maintain your humidity level. Reds on top, whites on the bottom and a temperature probe in the middle set around 50 should do it.

I hope that this helps!


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## botigol (Dec 18, 2013)

A tangent thought...even though maintaining temperature is a major concern in wine storage, please make sure to install a sufficiently sturdy rack to hold the bottles. My first attempt was not up to par and I was very fortunate to not lose a bottle, but it very easily could have turned out differently.


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## theTheme (Dec 18, 2013)

sour_grapes said:


> You seem to be assuming the use of a dual-evaporator (or perhaps a dual-compressor) fridge. I could be wrong, but I don't think you will find a cheap used one.



You are correct, I didn't really understand how the cooling unit was getting to the fridge. Single evaporator means no way to selectively turn off the fridge while leaving the freezer on. Unless...I cut the wire for the fridge fan which would technically stop the cooling air from going between the freezer and the fridge, drill the holes as suggested below in ever increasing size until a stable temp is reached... but then I don't know how the compressor would react and we are definitely in the territory of over complication, as botigol points out 



botigol said:


> I have been using a mini-frig as my primary wine storage for almost 15 years; same unit still doing it's job. I bought an external thermostat into which the refrigerator plugs to receive power when the temperature probe indicates (I've since built one for $40-$45). For seven years of it's time I lived in a townhouse without air conditioning; 90s are the norm in summer here with some days reaching the 100s.
> ...
> I hope that this helps!



It definitely does! I think my biggest fear is that I will sink all this time into making the first batch (and the second and the third) and then it will be ruined because I didn't store it properly afterwards (I can't cool my apartment below about 72 now. It's a steam heat building so my choices are outside temp with windows open, 72-78 with strategically cracked windows, or 90+ windows shut up). At least if I ruin it some other way, I won't have to wait 6 months to find out and be left with several dicey batches...

Can I ask what brand thermostat and mini fridge has worked so well for you?


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## WI_Wino (Dec 18, 2013)

My thoughts:

- I think it's overly elaborate. Drilling holes to run pipes and have a pump to cycle cool water through out is getting pretty crazy. Think KISS

- It's the wine temp that is most important to remain stable, it doesn't really matter if the air temp in the refrigerator fluctuates some. You will get less swings as you put more wine in (as there is more thermal mass).

- External temp controller is probably needed. You get components for a DIY build easily enough (google STC 1000 and you'll find a ton of info), cost is about $30 or so. Or you can buy complete units (Johnson Controls has a couple options, Ranco is another brand) starting at $50 or so I think. Basically you turn your fridge to it's coldest setting so it "always" runs when it has power, then use the external controller to control the power as needed. I have something similar (freezer that I run at 33F for lagering beer). I have the temperature probe in a mason jar of water. That has enough thermal mass to avoid larger swings in the temperature and keeps the compressor from running too much.

- Very good point on older refrigerators costing way more to run, I feel that people completely ignore that. W/o doing math I would hazard a guess that in some cases you would pay for a new fridge with the extra electrical cost a free but older one would use. I think your ideal is a fridge w/o a freezer.

- I don't know what to do about humidity. One thought would be to put in a humidity meter in your current fridge to set what is "normal". Is it sufficient? If it's too high you could use a larger, reusable desiccant dehumidifier. If it's too low, you'll need to add humidity somehow. Not sure on that. Or just use synthetic corks...


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## richmke (Dec 18, 2013)

It is my understanding that all fridges have a drain line. As such, you cannot have a perfectly sealed fridge.

This is what some people use instead of the fridge's thermostat:
http://www.midwestsupplies.com/johnson-digital-temperature-controller.html

A typical fridge thermostat cannot be set for a high enough temperature. Hence the need for the external unit. Cheaper ones are available. I have not heard about it burning out compressors. The risk to a compressor is if it cycles off->on too quickly. Hopefully it has a built in time delay to prevent that.


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## theTheme (Dec 18, 2013)

WI_Wino said:


> Or just use synthetic corks...



I fear that simple is (simply) not in my nature (although I'm working at it). I spent an hour wondering and researching if I could get one of those commercial screw top applicators at home to solve the humidity issue. Synthetic corks, so much simpler.

Do you know if I can get synthetic in the same size as the regular (#8, I'm going to be using the cheap red hand press).


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## botigol (Dec 18, 2013)

I have a Wine Stat external thermostat on a Danby mini-frig. I doubt that I did much more research on the frig other then it was the right size for my use and that it was on sale at the time. Although the Wine Stat works fine and looks decent (professional finish) I wouldn't buy it nowadays. At the time I didn't have enough DIY knowledge, nor knowledgeable friends to attempt such a thing, so I didn't have much choice. Now there are so many detailed instructions and videos that you should probably be able to build one very easily and for much less; I think that the Wine Stat is now $150...way too much. As WI wino suggested, do a search for STC-1000 temp controller build and you will be good to go.


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## jsiddall (Jan 9, 2014)

I have already done what you are thinking of, using an antique fridge I was getting ready to throw out, so it is definitely possible. Because it is so old it isn't fancy and doesn't even have any drain. The freezer part is small and is internal to the fridge itself (not a separate compartment) so minimal lost space there. Also, I hooked and energy monitor on it and it keeps a steady 13 C for just over $1/month of electricity.

I built a custom temperature controller for it, partially because I didn't want to shell out for a commercial one, and partially because I wanted to integrate it with my home automation server also. The results are better than I expected. To prove it is working correctly and alert me if there are any problems I log the temperatures (bottle and ambient) every minute. Attached below is a graph from a few days ago. The nominal bottle temperature variance is about +/- 0.1 C which I am happy with, and the compressor runs less than once per hour.

I put a dish of sanitized water in the freezer compartment to keep it from getting too dry but it turns out that added too much humidity and it was constantly condensing on the sides of the fridge. Since it is so well sealed I now just leave it without any extra humidity. YMMV on that though.

Jeff


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## sour_grapes (Jan 9, 2014)

Umm, wow! That is impressive! Nice work, Jeff!


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## theTheme (Jan 10, 2014)

Jeff, this is amazing! I'd like to hear more about how you hooked this up to a home server. How did you get the temp output to the server and what kind of server are you running?


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## jsiddall (Jan 10, 2014)

Starting from scratch this would have been rather ambitious so I would not generally recommend you take the same path I did. However, I already had most of the pieces I needed and I was curious to see how well I could make this work.

My home automation is run by misterhouse (http://misterhouse.wikispaces.com/) on a normal linux PC but you could also run it on a Windows box or something as inexpensive as a Raspberry Pi. Misterhouse isn't the easiest thing to start with unless you are familiar with perl scripting so keep that in mind also.

For the temperature control bit I used a couple of high precision 1wire thermometers (MAX31820PARMCR+ less than $3 each) and for reliable control of the compressor I used an Insteon dual band OutletLink (less than $50).

Of course you also need the iButton reader and Insteon powerline modem to talk to these devices, but I already had all that.

The perl code to control the whole thing isn't that long and most of it is error checking/handling. I can share that if anyone is interested.

The graphs are courtesy of gnuplot using a "tail -n 1440" of the temperature log file and a pretty simple config.

For comparison, I also put a thermometer in the Cuisinart Wine Fridge which I use more for temporary storage. It's internal temperature varies about +/- 1 C (see graph below)


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## sour_grapes (Jan 11, 2014)

jsiddall said:


> Starting from scratch this would have been rather ambitious so I would not generally recommend you take the same path I did. However, I already had most of the pieces I needed and I was curious to see how well I could make this work.



Again, just wow.



> For comparison, I also put a thermometer in the Cuisinart Wine Fridge which I use more for temporary storage. It's internal temperature varies about +/- 1 C (see graph below)



+/- 1 C? The horror. The horror.


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## jsiddall (Jan 14, 2014)

sour_grapes said:


> Again, just wow.
> 
> +/- 1 C? The horror. The horror.



Yeah, +/- 1 C isn't the end of the world despite what some might suggest.


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