Will a Peltier cooler work for my application?

The temperature of an object is dependent on the amount of heat energy it contains. In this case, the object is the perishable item in the refrigerator. To lower the temperature, heat must be removed. To add temperature, heat must be added. If the refrigerator was perfectly insulated (it’s not), it would be a matter of removing just enough heat from the perishable to get to the temperature of interest, then you could turn the Peltier device off and the temperature would remain the same.

In an imperfectly insulated refrigerator, there is always heat coming in. To reduce the temperature of the perishable, the Peltier must remove heat at a rate in watts that greater that the rate of heat in watts coming into the refrigerator. The Peltier would also need to remove a certain amount of heat from the object in a specified amount of time.

Peltier devices are designed to move a given amount of heat when the hot side of the device is at a given temperatures and the cold side is at a given temperature.

STEP 1: Find the delta T needed

The cold side for the refrigerator will be around 2.7C for perishables. The hot side would be room temperature so about 21C. The delta T would be 18C but add about 20C to be safe due to temperature drop and rise on the heat sinks you’ll need on the hot and cold side. The delta T you need would be 48C if the assumptions are correct.

STEP 2: Find the heat transfer rate in watts needs to be removed from the refrigerator

Without some knowledge of heat transfer, it would be difficult to calculate the rate of heat transfer coming into the refrigerator so it will need to be done with trial and error. A starting place for the number of watts coming in is 85 watts based on an educated guess of what some refrigerators need.

STEP 3: Find the spec sheet for a thermoelectric cooler

Based on it’s spec sheet, the cooler in the URL below will pump a about 100 watts of heat at 48C delta T. This would be a good start. If that does not work for the application, then the delta T assumption is off or the number of watts coming in assumption in is off.