Hello Stefan,
You didn't mention which ZWO camera, but I read a thread (elsewhere*) on a ZWO 120 camera which showed a large reduction in noise following the addition of custom cooling. See the before (LHS) and after (RHS) image from that thread attached below and the thread link here....
https://stargazerslounge.com/topic/1...wo-asi-120-mc/
Best
JA