Is a multisplit air conditioner suitable for heating?

no mosquito screen fits on the roof window and at 7 p.m. the sun is still shining on it, which lets in more heat.

Ok. Then the roof window was planned incorrectly ;). No, seriously, of course there are situations where airing out is not possible. It hadn't occurred to me, since I wouldn't plan rooms with only a roof window, at least not as a permanent living space, if there was any other option.

With tropical nights, an open window doesn’t help, apart from the possibly existing noise and humidity.

I think humidity is often underestimated.
We have air conditioning installed, have been using it for 2 years now, and will build it the same way again in the house 2.0.
We usually ventilate in the early morning when it's still cool, but the time in summer when it is cool is not enough for me to bring the house to a reasonable temperature. And to maintain it, you would also have to heavily shade every day, practically the entire living area for us. You can do that, but then you also feel a bit like a hobbit.
To avoid drawing electricity from the grid for the air conditioning, we have photovoltaic panels. When the sun is blazing, we run the air conditioning, and that keeps the cost reasonable.

I will soon have a 4-unit split system installed. I'm curious!

The system is now running. The costs amount to around €11,700 for the outdoor and indoor units. 4 acquaintances are now also getting quotes from the installer, because the system turned out really great, but the subsidy will also be significantly reduced from 14.08. With the Panasonic system, I can schedule each room individually, which is really useful to save money. Now I am in a 4**** hotel and sweating at night. No air conditioning and windows open everywhere during the day. Uncool xD I'm already looking forward to the cool nights at home. The Russians are burning off our gas, the sea of flames can be seen from Finland. Really messed up! At the same time today still over €100 electricity refund and lower installments thanks to the elimination of the Renewable Energies Act. Gas will be used as little as possible for now, I am already being milked enough by the state and social system as a driver and employee.

The system is now running. The costs amount to around €11,700 for the outdoor and indoor units. Four acquaintances are now also getting quotes from the installer because the system turned out really great, but the subsidy will be significantly reduced from 14.08. With the Panasonic system, I can schedule each room individually, which is really useful to save money. Now I am in a 4**** hotel sweating at night. No air conditioning and windows open everywhere during the day. Uncool xD Looking forward to the cool nights at home. The Russians are flaring off our gas, you can see the sea of flames from Finland. Really messed up! At the same time, today still over €100 electricity refund and lower installments thanks to the elimination of the Renewable Energy Act. Gas will be used as little as possible for now; as a driver and employee, I am already being milked enough by the state and social system.

Great, which model did you get for outdoor and indoor? I want to equip 6 rooms with air conditioning: 3 x bedrooms upstairs, 1 x bedroom, living room, and kitchen downstairs. The living room and bedroom on the north side of the house will get a two-zone multi-split, but on the south side I’m still undecided! Either a four-split or a three-split for the two bedrooms upstairs and one downstairs, and a single for the kitchen. I’m trying to minimize the piping and also prefer the outdoor unit location close to the ground; otherwise, the service technician will need scaffolding/lift every time for maintenance!

Great, which model did you get for outside and inside?
I want to equip 6 rooms with air conditioning: 3 x bedrooms upstairs, 1 x bedroom, living room, and kitchen downstairs.
A two-split multi will be installed on the north side of the house for the living room and bedroom, but on the south side, I haven’t decided yet! Either a four-split or a three-split for the 2 bedrooms upstairs and one downstairs, and a single unit for the kitchen.
I try to minimize the lines and also prefer the location of the outdoor units closer to the ground, otherwise the service technician needs a scaffold/lift every time for service!

Panasonic CU-4Z68TBE
4 Etherea indoor units