The drawing at right is the schematic of an air conditioner based on phase change.  In this case wax that melts at 22C (72F).  The wax is encapsulated in tiny spheres and then mixed with water to create a fluid.  That slurry is pumped thru the radiator (labeled: cool-phase condensing rods).

At night cool outside air is used to solidify the wax, and during the day inside air is cooled by melting the wax.  This is analogous to how I cool my house; cooling it at night and sealing it up during the day.  I let the building provide the thermal mass.

They claim you can use it to store heat over night, but I assume that’s only going to work if you warm the house over 72F during the day.  But maybe the slurry is a mixture of wax for different temps.

They can store about 4kWh of energy the slurry.  That’s not a lot as air conditioning loads go (a medium sized room?); but they claim the capital cost per cubic meter and much lower operating costs.

The manufacture is currently testing units around London.  The box looks like a clunky old steam radiator.

So, interesting that a daily cycle, room sized, phase change scheme might show up in the market soon.  There are daily cycle, office building, phase change schemes where in a block of ice is frozen each night.  I’ve thought it would be a hoot to build something similar that was yearly cycle, and house sized.  More here.