I am planning on using copper coils placed vertically in the storage tank for heat exchangers. I want to use the same coils for both heat input and output. Does the direction of flow matter with regards to whether you are storing or retrieving heat? I have been looking at some of the designs and it appears that some change direction between storage and retrieving. Nofossil's design for example. Is there any benefit to changing flow direction in the heat exchangers? If so, why?