Thanks! I think the idea you outlined would definitely work, but it is different than current refrigerants a few ways. For example: the secondary liquid loop you mention would probably vary in temperature with time. Right after the pulse starts the fluid would be very hot (or cold). As the solid material changes trends back toward the mean temperature, the secondary loop would follow. The secondary loop would need to then exchange heat with the system being heated or cooled. This would require the heat exchanger to work over a variety of temperatures for the fluid loop. This in itself is obviously not impossible but it does prohibit important optimizations to efficiency that you can get by assuming more steady operating conditions.