In case of Micropelt devices, one side is placed near the heat source and the other side has a fixed heat-sink on top of it.
The top part, as seen in the picture above, is soldered “upside-down” through a hole in a PCB. This is the hot end.
The bottom part, as seen here, is the cool end. It sits over the PCB and requires a heat-sink. Here’s what it looks like implemented.