air-conditioninginstallation
I really like this A/C unit and its width is exactly the width of my window panel (21.5"), but the "Window opening minimum width" in the specs is 23". From what I've seen in the Q&A for this Frigidaire unit, is that The side panels, fully compressed, add 2" to each side. However, other A/C units (LG), on the same retailer site, have their width equal to the window open minimum.
Are side panels necessary?
You could build a wood frame that fits in the window with an interior hole large enough to accommodate the AC unit. This also has the advantage that you won't have to hold the window open, while juggling the unit into place. You can install the light weight frame, then slide the unit into place.
I built one when I lived on the second floor of an apartment building, because I was always afraid I would drop the unit out the window while installing it. I used foam tape around the exterior and interior of the frame, to make sure I got a good seal around the window and AC unit.
For a unit that only vents through the window (not sits in it), you could build a smaller frame with a port to allow the vent to pass through. Filling the interior of the frame with Lexan will reduce the amount of wasted window space.
(You could always use smaller lumber for your frame, if you want it to have a lower profile. The frame size in the image is just an example, to illustrate the idea).
You may be able to rig up something whether the compressor-side air intake and exhaust are piped outside, but the efficiency will be low and you may risk burning out the compressor by working it too hard.
If you want something you can install in a small opening, you might consider wheeled portable AC units which come with a flexible duct.
If you're still determined to try it, note that window AC units have two sets of air intake & exhaust:
On a typical window AC unit the "outside" air comes in through vents on the side and top of the unit and is blown out the coils at the back. So you will need to make sure both of those parts are getting the airflow they need. And they can't be the same duct, or else you will just get super hot air recirculating through the unit.
Best Answer
In my opinion, no they are not. they are conveniences added to the unit to fill the space of various window sizes.
Their main thing is to stop the transfer of air into the room
If you remove them, be sure that the openings (louvers) on the sides of the AC unit are not blocked by the thickness of the wall since the fillers used for a wider window opening would maintain some space automatically.