Simple cooler

[zoner21]

This is my first post on this board, but it looks like I've found the right place!

I brew my own beer at home. In making beer, one may 'lager' the beer to make lager. This involves fermenting the beer at a low temperature (between 30-60F) for a long time. The traditional way to do this is to buy an old fridge and swap out the temp controller.

I had something else in mind.

I would like to build a dedicated cooler for a 5 gallon container that would regulate the temperature at around 45-50F when kept in a cool place. Basically this would be a box made of styrofoam with thermoelectric cooler(s) with heat sinks and fans up top hooked up to a thermostat. My first instinct was to do what I usually do and buy a bunch of parts, halfass it together until it may or may not work, and either use it or let the parts sit on my desk until my wife yells at me to get rid of it all.
I thought it better to ask some folks who may know what the hell they're doing.

I am handy with a soldering iron, not afraid of 12 volts, and I can do pretty much anything with my hands that doesn't require schooling.

Does anybody have any advice for me? Specifically, I'm looking for the best way to get enough amps at 12v out of the wall to run my cooler/s and fan/s, what sort of relays to use off of the thermostat, and any reasons this would not work.

I know that most thermoelectric units have a max deltaT that may make this project not so functional during extremely hot weather, but it would be usable most of the year where I live (MA).

Thanks!

 

[Sceadwian]

Define cool place, if you know the ambient temperature you know the temperature differential required which will allow you to value your TEMs.
Just an FYI, even if you insulate the heck out of the container you're still going to need some pretty beefy TEM modules, and they aren't cheep

Just keep in mind a brand new mini fridge I randomly looked for on a web store was 1.8 cubic feet, which would hold over 13 gallons of liquid, would cost you 80 dollars, and would be useable the day you got it only cost about 85 dollars. The time, research and limitations of the TEMS modules themselves would probably net you a less useful more expensive cooler.

 

[zoner21]

The size of the fermentation vessels used in beer making limit the usability of small refrigerators. Granted, it may be less expensive to simply find a suitable fermentation vessel that would fit in a 1.8 cubic foot fridge, but there is a fair amount of standardization for equipment. Using a custom fermentation vessel would require fabrication of custom equipment to use with it.
Beermaking vessels are either 5-gallon buckets (fridges are shorter and wider than a bucket, so a fridge with a larger volume is required to meet the height) or glass or plastic carboys, even taller and narrower.
My goal was to make a small, energy efficient enclosure that would not be harmed by being left unplugged for long periods of time as a mechanical refrigerator can.

 

[MrAl]

Hi,

I have to agree with Scead completely. The complexity of what it sounds like you want to do will be more more than just hooking up some modules.

Another point is that if you intend to use those thermal Peltier devices you'll also need a nice hefty power supply as they do take quite a bit of current to operate for the heat transfer operation to work to maximum. 12 amps wouldnt be unusual. You'd have to build or buy a power supply. You also need large heat sinks on BOTH sides of the Peltier device, one to absorb heat and one to radiate it away externally.
One of these things i think can cool 1 can of beer, but i havent yet experimented with these devices.

A little refrigerator would cost less as Scead pointed out, and would last a long time. If you cant fit your setup into a small one, buy a bigger one. I really dont think you'll get better than that for what you have to spend both financially and chronologically

 

[KeepItSimpleStupid]

That's the problem, the TEM flunks the efficiency test. It passes the SMALL test. A delta T of 60 deg C is attainable.
Mechanical Fridge with a UPS is my suggestion.
You could design the custom enclosure and canabalize and re-arrange the parts of a small fridge to meet your other goal.

I have used these devices with a water and fan cooled side. The newer controllers use PWM for temperature control. We were primarily using them to control at 25 deg C when under a heat source.

 

[zoner21]

OK. Maybe I'm easily discouraged, but I think I've been talked out of it. My basic problem was the power supply. If I would have to build my own, then this really isn't worth it. I wasn't expecting any spectacular efficiency, and was aware of the need for heatsinks, fans, etc. If it is going to be super expensive and requires a DIY power supply, I'll likely skip it and just find a crappy old fridge on Craigslist. BTW, you can't really cannibalize a mass-market mechanical fridge. They aren't made to ever be taken apart/serviced. The whole evap system is brazed in place and is very fragile. I have a number of fridges for other purposes, some modified. Modification of these tin cans is iffy.

 

[MrAl]

Hi again,


In addition to post #4 above, you would also need fans both on the hot side heat sink and on the cold side heat sink.

Yes, another option is to extend a small refrigerator by keeping the door open and building a bigger box attaching it to the front.

 

[Sceadwian]

How about this, buy the cheapest air conditioner you can find and build a wood cabinet with thick Styrofoam insulation. Even the smallest of room air conditioners should easily handle what you need. You can build to suit any shape and a room AC should easily be able to meet those cooling requirements in that volume without modification.

 

[zoner21]

I like that thinking Sceadwian, but I think the simplest solution (if all I'm looking for is simplicity) is to find any old chest freezer and add to its height with a wood collar. This is a common method in homebrewing when making a kegerator(which I have experience with already). Any fridge-based solution will require the replacement of the temperature controller. I believe this would also be the case with an A/C unit, as those thermostats don't go below 60.

 

[KeepItSimpleStupid]

Brazing is brazing. It's a necessary evil of refrigeration repair. If the tubing is Aluminum, the connections can be flared. I've installed, from scratch, an AC in the car and I do hold an EPA license for Auto/Small appliance. The cars used O-ring aluminum tubes. With the right torch, brazing is easy if clearances permit.

You can, if you want to get fancy buy a refrigeration thermostat with digital setpoint, alarm contacts and defrost control, but fridge should not require defrost.

A TEC temperature controller for just cooling really isn't bad. If you can get by with an unregulated power supply without regulation, you should be fine, but i would protect against overvoltage. i.e. at least add an overvoltage detect and temperature alarm. With the TEC, I'd also look at an overtemperature alarm for the "hot" side.

 

[MrAl]

Hi,

I dont think i would try an A/C unit though, as the fins could ice up if you restrict the output air and also lower the thermostat setting lower than factory standard. You could do an experiment i guess.

My refrigerator goes much lower than 60, down to at least 40 deg F.

 

[Mr RB]

5 US gallons is under 20 litres, that would be pretty easy to cool with a decent Peltier device if the whole setup is in a "cool place" as you describe and surrounded with a decent amount of insulation. It's only a couple of cubic feet to cool.

I like Scaedwians idea of a small fridge, you can get a Peltier DC fridge or a small 12v DC compressor fridge and use the internals and temp control from that.

Or buy a couple big Peltiers, 2 big heatsinks and fans, and a big 12v DC PSU. Then make your own control circuit. But besides the extra work that might cost more anyway!

 

[zoner21]

I'm not afraid of a little work. It was the solid state design that appealed to me. Modifying refrigerators leads to early compressor death. The thermoelectric coolers shouldn't have that limitation.
The problem with fridges is that they don't go warm enough (as high as 60, usually mid 50s) and an AC unit wouldn't go cold enough.
An advantage of the Peltiers would be that I could also use the cooler as a heater to ferment ale at 70F+ in the winter when I keep my house at ~65 and my brewing space ends up being considerably cooler (it is in the worst heated part of the house as that space is largely unused). I find the prospect of having a temp controlled box that isn't just a cooler very appealing.
Where could I find a beefy 12v transformer if I ended up going for this?

 

[Sceadwian]

You seem to have a basic lack of understanding of what a cooling unit does. It is impossible to create cool, it's the first law of thermodynamics... Compressor or thermoelectric modules are nothing more than heat pumps. Thermoelectric coolers have VERY limited temperature differentials, and it being solid state will mean nothing if you don't fully engineer the cold/hot side to properly dissipate the modules heat pumping capacity. This is ALL that AC units do, they have a hot side and a cold side exchange, I'm not sure why frosting was brought up as a problem if your cooling requirements are 55 degrees...

The logistics of this are NOT that hard to grasp. You're over analyzing, virtually any room AC unit wil do, you don't even have to redesign the temperature controller, you just have to move the sensing element to the most important spot in your cooler. Keep in mind air flow.

 

[ronv]

You can probably make the peltier work if you insulate it well.
Consider a PC power supply and a couple of small fan heatsink assemblies. If one is not enough I'm pretty sure two would do it. I used some inexpensive ($10) heatsinks for my golf cart cooler. Let me know if you want to pursue it and I'll try to find them again on line. Do you mind the noise of the fans?

 

[MrAl]

Hi again,

Im still waiting for thermoacoustic cooling, which i havent see yet although it started in the 1980's. Basically a sound wave produces the cooling effect.

A modified refrigerator if done right could work for a long time i think. Just requires thicker insulation due to the larger space that's all.

To experiment with a A/C unit perhaps you can put a cardboard box in front of an air conditioner and see how that works first.

 

[Pommie]

I had a peltier cooled coolbox. It easily maintained a 25°C (45°F) differential and didn't take that much current (can't remember but it didn't worry the car battery).

Let's do some calculations,
A box of 1m x 0.5m x 0.5m and a wall thickness of 25mm of styrofoam would have 2.5m² of wall area. At an Rsi value of 1.25 it would require 2.5/1.25/1 = 2W per °K to cool it. So for a temperature differential of 20°C (36°F) would require 40W of cooling. Two reasonable sized units would easily suffice. An aircon unit would be total overkill.

Note, the R value is in m²·K/(W·in) hence 25mm = 1".

Edit, two of these should manage to move 60W at a 20°C differential and use 8A at 12V.

Mike.

 

[KeepItSimpleStupid]

Went googleing and found this: **broken link removed**

 

[Pommie]

They are much cheaper on EBay. For example, **broken link removed**.

Mike.

 

[Mr RB]

...
A box of 1m x 0.5m x 0.5m and a wall thickness of 25mm of styrofoam would have 2.5m² of wall area. At an Rsi value of 1.25 it would require 2.5/1.25/1 = 2W per °K to cool it. So for a temperature differential of 20°C (36°F) would require 40W of cooling.
...

I've done incubators heating 2 cubic feet by 30 degrees C with about 40W to 50W, so I agree 40W or so would probably be enough for the beer although the cabinet only needs about 2 cu feet for that beer container.