I was investigating it from a home heating cooling perspective.
But I was not able to find the wax that phase changed at 22 deg C.
I had also some scrap radiators. Fill them up, it absorbs the head during the day and releases it during the night. Solar heated water can be pumped through it during the day in the winter. And house water supply can run through it in the summer.
Or just fill beer bottles and stack them next to the walls
But that idea probably belongs in the home eco modding section of the forum.