you can feel that there is something inconsistent here.
if you run a peltier 172W at 18V you get the best performance
if you run a peltier 172W at 12V you only get ~50W ??
12V= 2/3 of 18V
so you would only get 1.5 times 50W = 75W at 18V ???
the COP goes UP if if the voltage goes DOWN (TEC are more efficient at low voltages) so you gain cooling ability relative to
the amount of power used and not the other way around...
this guy used a tec 12V 6A 75W as load for 3 pelts 172W in a T at
8V......134W/3 = 44.66W
10V....185.1W/3= 61.66W
12V....242W/3= 80.66W
13V....306.9W/3 = 102.3W
from
http://homepage2.nifty.com/masamoto/DATA10.html
is in japanese but babelfish will translate it