Peltier coolers....?

[MJG]

Does anyone one the Board know about Peltier coolers? Has anyone used one to cool a vivarium? What conditions do you need in order for them to be effective (external temperature, size of vivarium)? How much of a temperature difference can they make?

Etc. etc. etc. with the questions. Thanks in advance!

[Ray]

A peltier cooler is basically a thermocouple run in reverse.

When two dissimilar metals are joined at a point, a temperature difference between the joined end and the loose ends creates a voltage potential. A Peltier device applies a voltage in order to drive a temperature differential. Voltage applied in one polarity cools the junction; reverse it and it heats it. The technology is used in portable heaters/coolers that plug into your car's lighter outlet.

So basically, a bunch of junctions are "buried" in an aluminum heat sink, and air is blown over it to cool it.

The amount of heat removed is determined by the voltage potential applied, the mass of the heat sink and the air flow.

A Peltier cooler typically has two heat sinks, and transfers heat from one to the other, so you have to have air flow to bring air in to be cooled and to blow away the heat on the other.

Sorry, but I cannot be more specific than that.

[estación seca]

How much of your terrarium glass surface do you want to cover with coolers? Remember heat is pouring in through the glass and air leaks. I read quite a bit about Peltiers at one time, and the people with the best results got their terrariums down by 2-3 degrees F / 1.5C.

Aquarists and carnivorous plant people who want cool aquaria and terraria use an ice chest containing ice to cool water pumped into the terrarium through a pipe under the terrarium substrate.

[DirtyCoconuts]

This is very helpful info.

I want to ask if the air outside the terrarium is not hot but close to the terrarium temp would the cooler work more? Also, if I have a waterfall running from a reservoir can I put the cooler in the water and use that as the fluid instead of air resulting in more cooling across the whole tank and more efficiency bc it does the heat is not really much hotter than the cool side?

[Ray]

Pettier coolers can be quite effective, but as EC pointed out, balancing the heat transfer with the size and other heat gains of the chamber can be an issue.

DC - I’m sure the heat transfer to water would be better than to air and it would give you a larger, cooled mass to absorb heat from the air, but I think you’d have to find a way to chill the water outside the tank and circulate it, otherwise the extracted heat would end up being dumped right back into the air in the chamber.

[DirtyCoconuts]

I see. Thanks for the info, Ray!

I have done a bit more research and it seems that I would be looking at either a very small decrease in temp OR I’d need to set up an entire separate chilling tower lol

Thanks for the science all!

[Ray]

FWIW, I know several folks who have purchased small, dormitory-type refrigerators and built terrariums on top of them.

There seems to be two, primary application methods - Either a larger hole is cut in the top of the fridge and a small muffin fan blows the cooled air up into the growing chamber, or water is recirculated through the fridge to do the job.

Plus, you now have a dedicated, handy place to store KelpMax and Quantum!

[DirtyCoconuts]

Ha! That’s hilarious!

And brilliant. I was already thinking about how I could use my garage fridge for this but I don’t want the terrarium in the garage....

[Draikan]

Hey, I'm an electrical engineer with a background in robotics and control systems. I usually work with motion control, but also have experience with temperature, humidity, light, etc. Been keeping miniatures for a couple years after getting hooked on dendroboard. I saw this thread and thought I should jump in!

Others have touched on it already, but cooling is complicated. Temperature, pressure, humidity, and airflow are all related. Try to control or modify one and you probably mess up two others! It is possible though.

The first step is to limit the amount of cooling you need. Drop the ambient temp of the room as much as possible (or use a basement if you can), then insulate the tank as much as possible. Minifridge is a good start, you can also look at wine coolers since they tend to come with a glass door. Cork and great stuff expanding foam are also great insulators, so backgrounds made from these materials will help.

Peltiers really have two problems for this application.
1) They are small compared to the size of the tank you are trying to cool. So they have to remove all the heat leaking in from all the walls of the tank. This is why you need to insulate those walls!
2) They are not efficient coolers. This means that It takes a large amount of electrical energy to remove a small amount of heat energy from the tank. You can think of a peltier cooler like a heat "pump". You give it some electrical energy, and it "pumps" some heat energy out.

Evaporative coolers, and refrigerators can both be more efficient. Heat pump and refrigeration cycle - Wikipedia

I'd recommend looking into aquarium chillers (especially used) as a cheap way to get a lot of cooling power. How you use all that cold water to cool down the air without messing up humidity is another problem!

Hope this is helpful.

[DirtyCoconuts]

thanks!