Ive been reading about the Helical coils being used in Water heaters , seems like a easy DIY project thought I would add a link to one paper on it in case its worthy of hacking
My thought is it can be used to scavenge heat from the heat pumps compressor or other parts or any heat source
This is a pdf file on it
https://www.google.ca/url?sa=t&rct=j...zUeGr5TuRuJgug