I am way out of my league and need some help. I have a thermoelectric project but do not have a clue how to determine the "horsepower" needed to accomplish the task with some reserve in case I forgot something.

 

Goal...keep a can of liquid cold (between 33 and 39 degrees F). It will start cold and must stay cold...24/7

 

The can is 3 inches in diameter and 14 inches long. It will be stored in a heavy aluminum pipe (maybe 1/4 inch walls) covered on one end (the bottom of the pipe) and open on the other end. I expect to mount a plat on the side of the pipe to add some mass along the length of the pipe. The Peltier will be mounted to the plate.

 

The pipe will have 1.5 inches of insulation all around it except for the open end. Spray foam insulation will be used.

 

The unit will be powered by a 110vac to 12vdc power supply.

 

The entire mechanism will be contained in a small cabinet made of sheet metal approximately 8x10x22 inches

 

The ambient temperature of the room is <80 degrees F and humidity no more than 50%.

 

My question is what size peltier chip do I need (size and wattage) and how large of a heatsink and fan would be recommended.

 

I would like to have a unit that would be capable of doing 150% of the basic task so I have some reserve cooling power.

 

The necessary power is hard to estimate because the essential heat leak occurs at the open end, where not even natural convection is expected, so wind will be the primary cause. You foam can be thinner.

 

I suggest that you measure it. Bring your can of liquid at a known (measured) cold temperature, put it in the intended place, wait for an hour or more until you observe a measureable temperature change. Knowing the mass and considering the liquid is nearly pure water, you can deduce the leak power. Reproduce during the experiment the expected air movement: door movements...

 

Then the specs of Peltier cooler will tell you which might fit. Don't expect to supply them 12V DC: they need additional supply electronics.

 

Peltier coolers are deplorably inefficient. Are you sure of your choice?

Thanks for the reply, You raise a good question about Peltier being my best option. I know that the open end needs to be addresses because of condensation concerns. Is there some other way of maintaining the cold temp in an efficient yet affordable way...I have considered micro compressors but they are cost prohibitive.

 

The affordable option would be an ice cube from the fridge, but supposedly this is what you don't want... Dry ice (=solid CO₂) is commercially available; not more capacity than water, but it leaves no liquid behind.

 

Could you put a cap on the open end? A transparent plastic maybe? Pmma, Pc.

 

I expect miniature cold machines to be expensive. Peltiers weren't cheap last time I used them, during the upper paleo semiconductor era.