Technical room boundary construction, air source heat pump suction

The idea is good. Only the distance between both devices could be too long. I believe the limit was 10 m.

The maximum length depends on the device manufacturer and can certainly exceed 10 m by a wide margin.

I think that's a good approach. If necessary, the indoor unit would have to be placed at the lower end of the equipment room. The connecting line surely has its price as well. Spare your neighbor. Especially since he has already allowed you to build 15m of the shared boundary (whether he really knows what he's getting himself into ...)

Especially since he has already approved you to build on 15m of the shared border (whether he really knows what he's getting himself into ...)

A 15 m long wall.

On paper one thing, in reality right in front of your nose maybe something else entirely

I think that's a good approach. If necessary, the indoor unit would have to be placed at the lower end of the technical room. The connection line surely has its price as well. Spare your neighbor. Especially since he has already approved you to build on 15m of the shared boundary (does he really know what he's getting into ...)

Only the authority grants permission. @TE: has it already said yes to your boundary construction?