Would it be practical to use a Peltier device to keep five gallons of water above 40°F and below 60°F in an environment where the ambient temperature fluctuates from 20°F to 80°F?

 

Yes it would. The efficiency of cooling is not so great but in the heating mode you get more heat transferred than you use in electrical power to do it.

 

Here is a sloppy calculation to get you started.

I think I have a 5 gallon bucket of drywall compound. It measures 12" tall and 12" diameter. If I add 2 inches of styrofoam all around, the dimensions change to 16" dia and 16" tall. Surface area = Pi 8 squared x 16 + 2( Pi 8 squared) = 2.1 ft squared.
The styrofoam has about R5 per inch (depending on what brand and style) so your math goes: BTU = (area dt)/R where a watt second per second provides 3.413 BTUs per hour.

A worst case load is (20 degrees times 2.1 square footies) over (R10 and 3.413) = 1.23 watts to keep it warm. You are easily within the limits of a practical device.

Please correct my math as necessary to compensate for any stupid math errors I made and for the particulars of your shapes and materials.

 

I have an incubator about that size, and it takes a LOT more than 1.23W to keep it warm.

I can't compare it directly because it is not insulated anywhere near as good as 2" thick styrofoam, but maybe you made an error in the surface area?

If it is a cube 16" on each edge the outer surface is approx 10.7 sq feet.

 

I have an incubator about that size, and it takes a LOT more than 1.23W to keep it warm.

I can't compare it directly because it is not insulated anywhere near as good as 2" thick styrofoam, but maybe you made an error in the surface area?

If it is a cube 16" on each edge the outer surface is approx 10.7 sq feet.

My homemade incubator is a styrofoam cooler that is 1.5" thick; I use a 24 watt forced air heater to keep the interior at 99.5°F with an exterior ambient temperature of about 75°F. However, it is thermostatically controlled and runs only about 10% of the time.

As you may have guessed, the Peltier project is to keep drinking water for my chickens above freezing in the winter and reasonably cool in the summer.

 

maybe you made an error in the surface area?

If it is a cube 16" on each edge the outer surface is approx 10.7 sq feet.

I was talking about a round bucket that drywall mud arrives in, but I just got out of hospital 2 days ago and have quite a brain fog going on. That's why I put the disclaimer in at the end. Shape makes a lot of difference in insulation quality, every pipe makes a difference, and being altered with drugs can mess up the whole calculation.

 

I think I found it. I used 1728, the factor for cubic feet. I should have used 144, the factor for square feet.

 

I think I found it. I used 1728, the factor for cubic feet. I should have used 144, the factor for square feet.

Take another Percocet.

 

And get well soon.

Chicken water temperature math is less important than your health.

 

the peltier units we use here have a maximum heat diferential of 40 degrees, in other words, maximum of 40 degrees heating or cooling. you have to bond two together to get more than that.

 

I'd consider using an immersion heater for heating and a swamp cooler (evaporative cooler) for cooling. Both could be easily controlled with simple thermostats, and I think the overall project would be much easier. I think peltiers are cool (unintentional pun!) but I'm not a fan of them when any other technology will do. They're so inefficient.

 

the thermostats are simple, and there are NO moving parts to a peltier cooler.

 

...there are NO moving parts to a peltier cooler.

That's not always quite true, when you consider the heat exchangers that are inevitable parts of a complete system. A heating element has no moving parts, and evaporative cooling could be accomplished with something as simple as one of those little sealed pumps they put in pet drinking fountains.

You can make a peltier work for this application. I'm just pointing out that there may be better options.

 

the peltier units we use here have a maximum heat diferential of 40 degrees, in other words, maximum of 40 degrees heating or cooling. you have to bond two together to get more than that.

Are you sure? I've had no problem getting one sided iced up (well below 0'C) and the other side hot to the touch (well above 40'C) so I think they are capable of at least a 50'C differential. 60'C would be closer to what I have seen.

Maybe the "40 degrees" is one of those worst case max spec where you require full power under any possible condition?

Even so, +/- 40'C from ambeint should be enough for the chicken water application anyway?