It actually doesn't when humidity is above 80% and air temp is above 85F.

CAN be very expensive. If you are doing it with a car radiator and a hose pipe it costs very little and there isn't even a heat pump involved.

You can take it up a step by using a heat pump of course. Which you can also do fairly cheaply if you are willing to modify a portable AC unit or tbh anything else with a heat pump in it. All you need to do is water cool the hot side of the heat pump and send that water through your ground loop.

Depends how much you want out of it. Are you heating and cooling the entire house year round along with providing hot water. Or are you just taking a few degrees off the peak summer temperature in a room or two?

Look up succulent roofs sometimes and you might change your preconceived and mostly false opinion about green roofs 🤷

Those are cheap, low maintenance and last forever.

And how does the heat or coolness get distributed? Magic.

Some ancient middle-eastern architecture (can't remember the name) is a low-tech and permanent air-conditioning tower. We gotta go low tech. We also need trees everywhere, white buidlings and roofs, rain water collectors, etc etc.

Unnecessarily reductive. It's both the ceilings and walls. There is no single solution. We also have no idea of they have an attic or vaulted ceilings. An attic full of hot air is a heat bank that will radiate into the living space all night. All insulation will do is slow the transfer. Really good attic floor insulation will help retain heat in the attic, so you still want to improve attic ventilation. But, if you reduce the amount of heat going into the attic in the first place, you reduce how much insulation and ventilation you need to reach a certain cost/benefit ratio. It's usually more feasible to do half a job addressing each than it is to make just one variable perfect. So, when it comes to replacing a roof covering that needs replacing anyway, doesn't it make sense to do that as best as feasible?

Tour a home with an infrared thermometer camera in summer. I promise you, the ceiling is warm, too. You just don't hang out 3 meters up.

We grow a grape vine on the south wall, over a large window, using a set of stand-off cables. Warmth and light in the winter and green shade in the summer.

We are growing it for the foliage, but the delicious table grapes are a nice bonus.

Yeah, if you build with conventional stick and fibreglass.

Thermal mass and earth-cooled air and shading can achieve a lot.

Asian architecture too, it's layered in a certain way so that the warm air can escape and the cool air can enter and doesnt have as many windows as the regular apartment