A system and method for providing hot water to a point of use such as a shower. Waste warm water from said point of use passes through a heat exchanger, where it initially warms incoming mains water, typically to about 34 C. The initially warmed water is heated to its final temperature, typically about 42 C., in a smart boiler. The smart boiler, which typically has a volume of about 40 liters, comprises two chambers with a flexible barrier therebetween. Each chamber is separately heated as needed. Hot water is drawn from one of the two chambers; simultaneously, the other chamber fills with initially warmed water and is heated to its final temperature. When the volume of water in the chamber from which water is being drawn reaches a minimum, the system begins to fill that chamber and to draw water from the other one.

A system for heating water in a hot water storage tank, comprising a heater; and means for drawing water onto the heater to be heated from beneath the heater.

The present invention relates to a fuel cell system comprising: a fuel cell configured to generate electricity and heat by a reaction between hydrogen and oxygen; a heat storage tank provided therein with a storage heat exchange unit configured to perform heat exchange between the heat recovered from the fuel cell and a fluid contained in the heat storage tank; a heat media supply line and a heat media recovery line configured to interconnect the fuel cell and the storage heat exchange unit to form a circulation flow channel of heat media; a bypass line branched from the heat media supply line and connected to the heat media recovery line; a flow channel switching device configured to selectively switch the flow channel of the heat media flowing along the heat media supply line to the storage heat exchange unit or the bypass line; and a controller configured to control the flow channel switching device such that the flow channel of the heat media flowing along the heat media supply line is connected to the storage heat exchange unit when the fuel cell generates power, and the flow channel of the heat media flowing along the heat media supply line is connected to the bypass line when the fuel cell stops power generation.

A hot water returning system according to the present disclosure includes a hot water generator that generates hot water, a hot water line that supplies the hot water to a source of demand, a water returning line that returns the hot water to the hot water generator for preheating the hot water in the hot water line, a pump which pumps the hot water for returning of the hot water, and a processor electrically connected to the pump, and the processor is configured to determine a need for preheating corresponding to whether it is necessary to preheat the hot water and a status for use of hot water corresponding to whether the hot water is supplied to a source of demand, and control the pump based on the need for preheating and the status for use of hot water.

A system and method for heating water are provided. The system includes a first subcooler for receiving a first water flow, a second subcooler for receiving a second water flow, a first condenser in fluid communication with the first subcooler and the second subcooler for receiving water from both subcoolers, and a second condenser in fluid communication with the first condenser. The method involves receiving a flow of water, and transferring heat to the water using the system.