Thank you for reply Hanno,
That is what i was waiting for i think, I can clearly see it works very well as a bufer for home against the cold water being supplied straight to home. I think i am sold for that solution, on other hand i do not have many defrost cycles, on reverse. there are reverse defrosts only when outdoor temp is below 2.6C, otherwise heat pump is doing passive defrosts i which it does not compressor to defrost.
Thanks a lot for reply