Peltier air conditioning project

allanschon · #1 (**permalink**) 05-10-2007, 02:20 AM

Well, I've seen this idea tossed around a bit, but I've never seen anyone who claims to have implemented it. Being a sadist, I've decided to give it a go.

I'm new to dart frogs, but I want to make sure that my frogs have the best environment that I can provide. I've just completed my first vivarium, and the first thing I've noticed is that the temps are way too high. My apartment is on the top floor, and faces west, so all afternoon heat builds up. It was 76 degrees outside today, 82 in my apartment, and 87!@ in the viviarium. Unfortunately, the heat sticks around too... As I write this, the outside temp has fallen to 66, and it's still 80 inside. Luckily, I haven't picked up any frogs yet.

I have air conditioning, but I'm cheap, and I'd rather not cool the entire apartment when I'm at work, and I'm only concerned about the 6 cubic feet that make up my exo-terra. So, I've decided to tackle a DIY air conditioner for the frogs.

For those who are unfamiliar with peltier coolers, read Peltier FAQ.

Essentially, I'm going to going to install a peltier cooler in the wall of a watertight enclosure. On the outside of the box, a large heatsink and fan will dissapate the heat, and two ducts and a fan will carry hot air from the terrarium and cool air back. Power will be supplied by a surplus computer power supply I had lying around. Condensation from the cooler will be routed to the terrarium's sump tank.

I've just ordered the heatsinks, fans, and peltier. I'll post pics once the parts come in.

Dancing frogs · #2 (**permalink**) 05-10-2007, 04:32 AM

They have been experimented with a little before, but probably not enough.
I started too, but lost interest fairly fast, as I have frog tanks in all but two rooms of my apartment, so AC is probably the cheapest way for me.

Good luck with you're experiment, and please do post results.

defaced · #3 (**permalink**) 05-10-2007, 05:25 AM

Sounds like a cool idea, but can you post a drawing? I'm not seeing this at all.

Dancing frogs · #4 (**permalink**) 05-10-2007, 05:38 AM

One of the roadblocks I encountered in my limited experimentation was finding a nice big heatsink for the cold side (for heat collection) that didn't cost an arm and a leg...that and trying to figure out how to best insulate the cold side from the hot side.

allanschon · #5 (**permalink**) 05-10-2007, 04:38 PM

I'd be glad to post a diagram. I just have to draw one.

If you google 'peltier air conditioner' you'll come across sites that detail the peltier + heatsink assembly, which might help you picture what I'm talking about.

Haroldo · #6 (**permalink**) 05-10-2007, 10:49 PM

I've familiar with these cooling solutions as I used to do custom waterblocks and phase change systems for computers. Chances are, the power supply you'll need to juice this peltier up is likely to near what a small air conditioner might be pulling. I'd consider figuring out wattage needs before ruling out an entire room. Good luck in your search and project and be sure to post updates...

defaced · #7 (**permalink**) 05-11-2007, 06:29 AM

Power out ~= power in. Most peltiers are in the range of 60 watts. In order to supply that 60 watts from line voltage, his supply would consume about the same power as a 75 watt light bulb (which accounts for losses in the power supply). That's far from what is used by an air conditioner of any size. You're probably thinking that at 12v this thing is going to need 5 amps, which is right, but the supply won't be operating at 12v, but at 120v, so it'll need more like .6 amps.

allanschon · #8 (**permalink**) 05-11-2007, 01:06 PM

If I could cool the room, that would be an option, but the viv is in my apartment's main living area. I'd have to cool about 800 square feet of living area, which would cost >$75/month. I think I can build this whole thing for less than $125. At that rate, It'll pay for itself in less than two months.

In order to make sure I bought an appropriate cooler, I used the sizing software from here to estimate the total amount of heat I'd need to dissapate. I figured on about 80W, so my power supply will be pumping out around 7A@12VDC. With the losses from the power supply and the small power draw for the fan, I figure total energy usage will be just less than for my lights.

At first, I'll just leave it turned on all day, but my other project is building a controller for the whole climate system. I'll start another thread on it when I'm closer to starting, but in essence, I'll have my water heater, humidifier, and (hopefully) my AC unit attached to relay circuits which will in turn be controlled by a PIC microcontroller and a temp/humidity sensor.

alifer · #9 (**permalink**) 05-11-2007, 02:18 PM

Do you think it would make your project easier by buying a small peltier refrigerator and modifying it with a temp controller and ductwork with a low voltage fan for air circulation? My wife bought a peltier refrigerator/cooler for my son at Target or Walmart so he could keep cold drinks in his room and it works well if the drinks are cold before placing them in the cooler. It's big enough to hold a 6-pack of sodas.

Rick

allanschon · #10 (**permalink**) 05-11-2007, 03:32 PM

I considered doing that, but for the following reasons, it probably wouldn't work:
1) the fridges and coolers are insulated, thus don't require as much power to cool.
2) Most of them enclose less space than the size of my xxxl exo-terra.
3) I have lights pumping heat into the tank; I doubt these coolers would work if you left them sitting in the sun.

As a result of the above factors, I think that the peltier unit in those fridges would be underpowered for this application. On the other hand, they might be appropriate for a smaller tank, such as a 29g.

In either case, the cost would be the same or higher than the DIY approach.