I live in the UK (where air conditioning units, and thought for where they'd go, is very uncommon in homes), and where the temperature in summer is increasing every year. I also live in an apartment where I'm not allowed to alter the exterior of the building.
I'm trying to figure out the best way to install A/C in my bedroom (~40㎥) for our impending summer.
TL;DR: Am I being dangerous/risky if I use my ventilation system's ceiling vents as a portable A/C's exhaust vent?
I've thought through a couple of possible approaches, and not had much luck.
Professionally installed split A/C units are unachievably complex/expensive
The quote I (and others in my building) have received is £20k/$25k and upwards for installation (beyond the unit). This is broadly because the only place for the external part of the split unit is the balcony, which is two full rooms away (along an external wall), and trapped on the other side of a floor-to-ceiling window and a load-bearing concrete pillar.
Window vents seem problematically complex
The two windows, next to each other, are large (1.5m x 1.5m each) and swing open from the middle either 10cm or a full 90º (when the child lock is off). They're a few mm off flush with the ceiling above them and the window sill below. I've experimented with making a seal above/below and have been unsuccessful so far (there's no room to work, or fix Velcro or similar). Besides, London can get noisy at night, so this isn't ideal either.
Venting into other rooms might work, but seems inefficient
The flat is incredibly well insulated, even internally. I might have some luck installing a portable A/C unit venting into a neighbouring room, but I'd definitely get heat leaking back in, so this would be inefficient (and would leave me with a hot flat to work in the next day)
Using the ventilation system's piping as an exhaust vent?
I do have a ventilation system set up in my apartment. The bedroom has an ensuite with a ceiling port for extracting damp air from the shower; I believe I could 3D print a connector for a portable A/C unit's exhaust that would allow me to vent directly outside via the ventilation system. The exchange unit has a summer bypass mode (which will stop it from capturing the extracted heat), and the ventilation inflow is slow enough that I don't believe it'll heat the room enough to cause serious inefficiency.
This last option is the interesting one. Am I setting myself up for any serious problems if I buy a portable A/C unit and get it working?