Micro AC?

[larswik]

Hi First post here.

I know very little about AC's I am a computer programmer by nature and I have wanted to do a project for a while and thought I would ask a question.

Is it possible to create / build an AC unit the size of a Coke can, a micro AC? That might sound crazy and useless but I was getting to build my own humidor for cigars as a hobby. I enjoy cigars and my current humidor gets hot in the summers and can ruin cigars if to hot.

I can use a heating pad to keep it 70 degrees in the winter time but there is no Micro AC options to cool something that is only 1'.5"w x 1'D x 1'H that I have seen.

There is no demand for something like this which is why I have never seen anything like it. But my question is it physically possible to have an AC unit that small? From what I understand the refrigerant is compressed, turns to liquid, and cools. It then runs through the coils which the fans blow through to cool air. The refrigerant in liquid form is pushed through a small hole which the expands the liquid to a gas form again and the cycle continues.

Sorry if this is a silly question. I was just wondering if parts an manufactured that small if it would work, or if AC units must be a certain size to function.

Thanks!

[Helioson]

Ever consider a portable cooler such as the ones that go in your vehicle? No refrigerant, just fans and heat sinks.

[larswik]

Thanks for the response. I have not considered that and that might work. Again this is just a hobby and I wanted to see if it were possible to build one, or if any exist. If heat sinks can offer efficient cooling then that might be worth a try. The humidor tends to be the exact temp inside as the surrounding ext temp.

I will look into it but I am just wondering if it is physically possible to have an AC the size of a coke can?

[CraziFuzzy]

Might be best to go with something like a peltier cooler for such a small load. they aren't as energy efficient as a mechanical refrigeration system, but it is small, simple, and would work decently enough. Still have to figure out how you are going to control the system of course. (this is, I believe, what most the small portable electric coolers use).

[mark beiser]

The smallest cooler you could make using a traditional refrigeration cycle would be in the 500w range, using an Aspen mini compressor, but that would be massive overkill.

Might be best to go with something like a peltier cooler for such a small load. they aren't as energy efficient as a mechanical refrigeration system, but it is small, simple, and would work decently enough. Still have to figure out how you are going to control the system of course. (this is, I believe, what most the small portable electric coolers use).

A peltier cooler was my first thought too.
Not very efficient, but a small <100w peltier wouldn't cost much to operate.

[larswik]

WOW. That is crazy, I never heard of those before but a quick Google search reviled lots of info and youtube videos like this one http://www.youtube.com/watch?v=3x-wxLEfLEQ

So on side gets hot and the other gets cold. That sound perfect for directing air flow over the hot side to warm up the humidor or the cold side to cool down the humidor. Perhaps this is the reason I never found any micro AC's. When the application is so small it may switch from AC to these peltier coolers.

I am glad I asked this question. Thanks for helping me with a great solution!

[mark beiser]

For cooling a small box with a peltier, you could incorporate a small cold plate into the box for the cold side of the peltier to mount to, and have a heat sink on the hot side, with a small fan blowing air over it.
Some experimentation would be needed, but peltiers are fairly cheap.
You would also need a 12v power supply, and some sort of temperature control.

You will also see peltiers call TEC coolers(ThermoEleCtric).
They are used a lot in computer/electronics cooling, either directly mounted to the components being cooled, or as part of a TEC chiller to supply cold water for cooling, with the hot side either air or water cooled.

One important thing to keep in mind, if the heat load on the cold side ever exceeds the heat removal on the hot side, both sides will get REALLY hot, then it will burn out.

[Moonrunner]

Saw a TEC cooler for $7.40 at DX. Might get one for a small project

[CraziFuzzy]

WOW. That is crazy, I never heard of those before but a quick Google search reviled lots of info and youtube videos like this one http://www.youtube.com/watch?v=3x-wxLEfLEQ

So on side gets hot and the other gets cold. That sound perfect for directing air flow over the hot side to warm up the humidor or the cold side to cool down the humidor. Perhaps this is the reason I never found any micro AC's. When the application is so small it may switch from AC to these peltier coolers.

I am glad I asked this question. Thanks for helping me with a great solution!

It is really hard to make a single peltier work for both heating and cooling. When on, it constantly pushes heat from one side to the other, and you can't switch directions, so it really would be set up for cooling only, or heating only, with the cold or hot side, depending on use, thermally connected to the inside of the compartment, and the other outside. For the prices, it might be easier to purchase two coolers, and then connect them up side by side on the inside and outside plates, but reversed, then just choose which one to turn on for heating, and which one for cooling.

[larswik]

I created a crude 3D model but if the air is pushed in there could be a flap (in blue) that could flip up or down. This would divert the air above or bellow for heating or cooling. That would then push open a door (in orange) allowing air flow to heat or cool?

[CraziFuzzy]

You have to remove the heat from the other side though as well. As it turns out, after some research, it looks like peltier modules ARE reversible, so all you have to do is switch the current through it, and it switches direction.

[larswik]

I see. So you can't trap the heat like that. If I vent it to the outside then it would draw in air from the edges of the box. The humidifier would run more then keeping the humidity level at 70%. So it sounds like flipping polarities would be the best. I am guessing if I apply a heat sink to to it it could radiate hot and cold through the fins and have the fan blow over that.

I will order one tonight and test it out.

Thanks again!

[Moonrunner]

I am guessing if I apply a heat sink to to it it could radiate hot and cold through the fins and have the fan blow over that.

Something like this?

[larswik]

How large is that? what site is it from?

I placed an order for a few of the Peltier Cooler plates. It will be fun to see how well they perform. I'm guessing they get hot and cold pretty fast.

[mark beiser]

I am guessing if I apply a heat sink to to it it could radiate hot and cold through the fins and have the fan blow over that.

You have to be able to pull heat off of the hot side faster than heat flows into the cold side.
The heat being rejected by the hot side is the total of the heat flowing into the cold side + the heat generated by the TEC itself.

[Moonrunner]

How large is that? what site is it from?

I placed an order for a few of the Peltier Cooler plates. It will be fun to see how well they perform. I'm guessing they get hot and cold pretty fast.

That's the Arctic Cooling Freezer 7 Pro Rev.2 CPU Cooler. The metric dimensions are 104 L x 58 W x 126.5 H mm (divide by 25.4 to get inches, so in the 5 x 2.5 x 6 ballpark). The fan is ultra-quiet (I know as I got one of those sitting on top of my CPU as we speak) and flows 45CFM. Got it on sale for $15, typical price $20-25. Try newegg