To put it another way sand is not a good PCM material for example in green houses they use calcium chloride and sodium sulfate decahydrate to absorb heat during

To put it another way sand is not a good PCM material for example in green houses they use calcium chloride and sodium sulfate decahydrate to absorb heat during day and then give off that stored heat at night. Sand is operating in reverse as it absorbing heat near freezing and releasing it as temps get above freezing... Sorry I did have quite a bit of physics once upon a time..