Peltier units are simply heat pumping devices and have really low COP compared to conventional vapor compression cycle based units. To estimate, how much amount of heat is pumped, I did a simple experiment. I bought a simple Peltier unit from Adafruit and glued it to a heat sink with thermal tape.
I put the heat sink in the measured amount of water (160 gm) and recorded temperature with TMP 35 sensor. Initial temperature of water was 31 deg C and final temperature after 300 seconds was 44 deg C.
Resistance of the Peltier was around 3.1 ohm from the current (2.6 A) and voltage (9.6 V) measurement.
- Amount of total energy energy dissipated (Qd) in water is 8706 J from m*Cp*(Tf-Ti)
- Energy supplied (E) over the 300 seconds was found to be 7488 J from V*I*t
- Heat generated to resistance (Qr) is small 21.9 J from I^2*R loss.
- Amount of heat removed from cold side = Qd – Qe – Qr = 1197 J or about 4 W
- This comes to COP = 4 W/(2.6 A*9.6 V) = 0.16
This calculation is rough estimate of the COP as thermocouple was +/- 2 deg C accuracy. Also this test does not indicate the performance of peltier in other operating conditions. It was done just to know how good is the peltier performance.