I have a 300L hot water tank. It's heated from an air-to-water heat pump. The hot water tank is connected to a heat exchanger. When any hot water faucet is opened, a circulation pump is turned on which pumps hot water from the tank through the heat exchanged, at the same time cold water runs through the heat exchanger, is warmed up and goes to the faucet.
So far everything works as described.
But if no hot water is being used and the circulation pump is turned off, gravitational forces lead to a hot water circulation flow through the heat exchanger. Thus the hot water tank loses it's heat much faster than I liked (sure, some insulation will be added when I think that all is set).
My understanding was, that one needs to add a "thermosiphon" where the hot water would cool, fall to the bottom of the siphon and could not clime up the other side of the siphon. Well, I did not read any technical specs for such a thermosiphon, I simply added a siphon like pipe-loop to the hot water loop from the tank to the heat exchanger. However, I seem to have missed some important sizing or leveling or something else, because my thermosiphon still seems to circulate hot water - at least that's what my impression is - purely based on the speed of temperature drop and the touch on the heat exchanger which is warm also in the morning when no hot water has been used for hours. The U shaped pipe in the picture is supposed to be my thermosiphon. Any advice on better thermosiphoning?
UPDATE: Emphasis is on BOTH (in- AND out-let of the water tank) that need the "siphon" to prevent heatloss. I added a 4 foot high loop to only one end and while this reduced the heat loss it does not stop it. I will add a siphon to the other end aswell, else I am loosing 1C of water temperature every hour (additionally added insulation to the pipes - but I cannot insulate every piece )