Water heating tank with thermosiphonic circulation for improved heat recovery rate

In a water heater having an elongated vertically disposed water tank adapted to be normally filled with water, a cold water inlet conduit for delivering cold water to a lower region of the tank, a hot water outlet conduit for removing heated water from an upper region of the tank, and at least one elongated heating element positioned in the tank so as to be immersed in the water between the upper and lower regions, the at least one heating element extending generally horizontally into the tank from an inner sidewall of the tank to heat water in the tank, the improvement comprising a thermosiphonic apparatus for improving the efficiency of the water heater, the apparatus comprising:

• an elongated tubular sleeve having a closed end and surrounding each of the at least one heating element, each sleeve having a first plurality of upper openings for providing waterflow communication between the sleeve's inside and outside, the first plurality of openings being distributed along substantially the entire length of the sleeve and being normally positioned above the heating element within the sleeve, and a second plurality of lower openings for providing waterflow communication between the sleeve's inside and outside, the second plurality of openings being distributed along substantially the entire length of the sleeve and being normally positioned below the heating element, the total area of the upper openings being greater than the total area of the lower openings, whereby upon operation of the at least one heating element, the sleeve generates along substantially the entire length thereof an upwardly directed transverse waterflow through the sleeve and in a direction from the second plurality of openings to the first plurality of openings;
• a bypass conduit positioned externally of the tank and positioned to cause delivery of heated water from the hot water outlet conduit to the cold water inlet conduit, the bypass conduit having an upper end connected to the cold water inlet conduit and a lower end connected to the hot water outlet conduit, said bypass conduit extending upwardly from its connection with the hot water outlet conduit to its connection with the cold water inlet conduit, so that hot water will rise in the bypass conduit, from the hot water outlet conduit to the cold water inlet conduit;
• and
• a flow control valve in the bypass conduit having an open position and a closed position, such that in the open position hot water flows from the hot water outlet conduit to the cold water inlet conduit and in the closed position waterflow is obstructed from flowing from the hot water outlet conduit to the cold water inlet conduit;
• wherein the cold water inlet conduit is substantially immersed within the tank and comprises sidewalls and an open lower end, said sidewalls extending generally vertically downwardly within the tank from an upper wall of the tank to the lower region of the tank, whereby the operation of the bypass conduit cooperatively with the at least one heating element surrounded with the sleeve causes heated water to be circulated by thermosiphonic action in the tank through the bypass conduit from the upper region to the lower region.