Optimal Placement for Portable Air Conditioner Exhaust Pipe in an Attic Apartment

Ladies and gentlemen,
I apologize in advance for the complete lack of knowledge and orientation on the topic I am discussing. I am a single mother of two kids and unfortunately I have no one to ask for help in this topic - that's why I allow myself to write here.
I live in an attic apartment where the temperature reaches 35 degrees at night during hot weather. Last year I bought a portable air conditioner, unfortunately I led the pipe out of the window (which had to be slightly ajar), and as a result, a lot of warm air fell into the apartment.
The gentleman who sold me the air conditioner recommended that the window sash be replaced with one with an additional small "window" to which the air conditioner can be connected. Unfortunately, I called many companies producing windows and you can not order any such sash - you have to replace the entire window.
I heard that you can supposedly drill a hole in the wall of the building and connect the air conditioner there. And here is my question: is it really possible to do it, what does it look like, does this hole need to be prepared somehow and how to protect this hole for the winter so that no cold air enters?
Thank you very much in advance for your answer.
Anna.

maxine wrote:

And here's my question: can it actually be done

Not only you can, but you must, otherwise it doesn't make sense.

maxine wrote:

or somehow this hole needs to be prepared

It usually needs to be carved into the wall the size of a pipe.

maxine wrote:

how to protect this hole for the winter

A plastic plug is best with polystyrene or some kind of insulation inside.
For example, yes.

Read this more Link the topic is not new .

I will join this topic:
- why this pipe cannot be bent?
I have such a portable air conditioner, but the problem is, of course, with the open window.
I came to the conclusion that I could use such a PVC elbow at the end of the pipe as here: http://www.lub-went.pl/pl/p/Kolano-lacznikowe-90-75x150mm125/235
and fix it in the floor under the threshold of the balcony window (there is no balcony - there is only a balcony grate).
The round part would remain in the apartment to be connected to the air conditioner pipe and the rectangular part would pass under the window sill and would direct the warm air outside.
Will it work in this case, will the efficiency of the air conditioner decrease or risk the compressor boiling?

In my opinion it should work, to be sure compare the diameter of the pipe with the area of the rectangular hole.

Thank you for your answer,
I even thought to install such an elbow with a larger rectangular cross-section, because I have a lot of space under the window sill ...

Thanks a lot for the answers I will definitely use the advice and make holes in the wall to connect the pipe. Unfortunately, two "experts" from the renovation with whom I talked do not want to drill holes in the building on the 3rd floor - I am still looking :)

Added after 3 [hours] 50 [minutes]:

I am also asking for information on how to carefully protect the drilled hole in winter, if there is no leakage during autumn rains, so that no leakage or fungus appears.
Thank you and best regards

sell a portable air conditioner, add a bit, buy a split, though used (PLN 500-800), if not a new one with an inverter ~ PLN 1200 + assembly. Somehow I can't imagine drilling a fi100 hole for such a noisy box at home. massacre

You can build an "artificial sash" in place of an open window. I had the same problem and in this video I present the end result: https://www.youtube.com/watch?v=RFqcocKqaWQ
In this case, it makes no difference whether the air conditioner works in the room (as in most cases) or on the balcony (as in my case).

No need to drill large holes or break windows. In the simplest and cheapest form it would simply be an 18mm cut-to-size board with a cut-out hole. Everything that is needed for this can be purchased in a DIY store, and if the window has more than one sash, such a panel can be easily inserted and removed.

You can also purchase a material sealant, which can be found under "Window Sealing for Mobile Air Conditioner"