# Peltier cell power calculation

#### Lolrapa

Joined Sep 19, 2018
15
Hello! I'm strugglin with the math of a proyect i'm trying to start.

I want to make a refrigerated carry-on trailer. Automotive cooling systems are way to expensive and I'm trying to figure out if I can use Peltier cells to achieve the same result. I must keep the content at 0ºC. By the design properties of the trailer 200W of power are lost through the isolation material of the walls. How can I calculate the power and quantiy of peltier cells neded?

I dont think the power of the peltier cell is its cooling capacity. I'm going to refrigerate the hot side of the cells using heatsinks and fans and the trailer must work at ambient temperatures of 40ºC

Thanks!

#### mvas

Joined Jun 19, 2017
538
An example ...
https://www.cui.com/blog/how-to-select-a-peltier-module

EXAMPLE: summary ...
20 watts of heat removed / transferred
20 watts of electric power consumed
==============================
40 watts of heat on the hot side

So, the heat sink needed to dissipate 40 Watts, for only 20 watts transferred

Power needed for the Cooling Fans is additional electric power consumed

Last edited:

#### wayneh

Joined Sep 9, 2010
16,114
I hate being the turd in the punchbowl, but I think TECs are a poor approach for several reasons. First, you need a ∆T of 40°C. You can't do that with a single TEC, so you'd need at least two in series and probably three or four. At maximum capacity, a TEC is very inefficient and will consume 10 units of power for every one unit moved from the cold to the hot side. All of that heat appears on the hot side and must be dissipated, or else the TEC can overheat and damage itself. (You'd usually mount a temperature probe on the hot side to to shut it down if it's overheating.)

So to move 200W from the cold to the hot side, you'd need perhaps 2000W of electricity. That would be a 3HP load on the engine!

TECs can be operated at much higher efficiency if they're run far below their rated capacity. But then the ∆T across the module goes down, and you'll need many more modules to achieve the same total heat removal.

If you can start with your trailer contents already frozen, and improve the insulation so that little cooling is needed, the TEC strategy could probably be made to work. I just wanted you to know the challenges.

By contrast, a traditional vapor recompression cooler can move ~10 units of heat for every one consumed, and can easily reach 0°C or less.