Try steady state. Maybe the transient time isn't long enough to see a large temperature change.
I would also take a look at your mesh size. Is it too large? You want finer elements around and through the pipes. Try Local Initial Mesh.
I don't exactly understand what temperature goal you're trying to apply. Try a volume goal for fluid temperature in the housing. Model in a dummy solid and use component control to keep it out of the analysis.
Let me try to reduce mesh.
This looks like a very detailed model, will take a lot of compute time to model and sim accurately. I would recommend starting out with a simplification, replace the pipes with a porous medium and see how to best gage the heat transfer with the trapped hot air.
Actually i do with simple model and it work good.
Now when i add more Real wall condition, it works now.