Keeping buildings cool without air conditioning

I was just daydreaming about a residential development where houses were all underground. They would be in a permaculture-style food forest with an artificially circulated stream. Each home would just have a little bit of a clearing around it.

Underground homes don't require much energy for heating and cooling as far as I know. Of course it is more difficult to build underground. Also my idea just now had something like skylight over the entire ceiling, with insulated covers (solar panels on top of those) that would automatically slide to adjust the temperature.

5 days ago: http://www.bbc.com/future/story/20190822-are-there-alternati...

Discussion: https://news.ycombinator.com/item?id=20776815

These are all really cool, but none of the ideas address reducing humidity, and water evaporation will increase it. ACs lower temperature, but also reduce humidity, and both are what make for comfortable environments.

If only their outbound links weren't to Elsevier...