Systems and methods are directed to water heater systems, including combi boilers and instantaneous water heaters, for initiating pre-heat and energy savings operations. Embodiments of the present invention can include at least one heat exchanger configured to heat water; and a control system in communication with the at least one heat exchanger. The control system can be configured to at least determine an expected flow demand for hot water; sense water temperature at one or more locations, including at a domestic hot water outlet; determine an end to the expected flow demand for hot water; upon receiving an indication to end the flow of hot water, initiate a recovery demand determination; and initiate a pre-heat operation based on the recovery demand determination.

A medium for energy storage includes a plurality of capsules. Each capsule contains a phase changing material (PCM) configured to undergo a liquid-solid phase transition at a solidification temperature, T.sub.S. The PCM undergoes a relative volume change due to the phase transition. A shell is filled with the PCM. The shell contains a first heat-conducting material, and is configured to comply to the relative volume change. The relative volume change is configured to cause a buoyancy force, which acts on the capsule when the capsule is disposed in water at a water temperature, T.sub.W, to be larger than the capsule's weight for T.sub.w>T.sub.s, and equal to or smaller than the capsule's weight for T.sub.w<T.sub.s. The T.sub.s can be within ±5° F. of a design water temperature T.sub.o at the outlet of a water tank. The capsule can be neutrally buoyant in water at T.sub.o.

The disclosure includes a hot water circulation device, and a hot water device monitoring system including a circulation passage; a circulation pump circulating hot water in the circulation passage; a closed expansion tank in which a water chamber communicating with the circulation passage and an air chamber filled with a predetermined pressure in initial state are partitioned by a diaphragm; and a control unit controlling hot water circulation. The hot water circulation device includes an air chamber pressure sensor detecting pressure in the air chamber; a closing valve cutting off water chamber from the circulation passage; and an open valve opening to atmosphere from between closing valve and water chamber. The control unit closes closing valve and opens opening valve during hot water circulation, detects pressure in the air chamber by the air chamber pressure sensor, and issues a warning notification when the pressure is not within predetermined pressure range.

A dual fluid heat exchange system is presented that provides a stable output temperature for a heated fluid while minimizing the output temperature of a cooled fluid. The heated and cooled fluids are brought into thermal contact with each other within a tank. The output temperature of the warmed fluid is maintained at a stable temperature by a re-circulation loop that connects directly to the mid portion of the tank such that the re-circulated fluid flow primarily warms only a re-circulation section of the tank. The other, lower flow rate, section of the tank may be positioned so that it has a cooler temperature and thus serves to increase the efficiency of the heat exchange by extracting extra heat energy out of the cooled fluid before it leaves the tank. Alternatively, the low flow rate section of the tank may be warmer than the re-circulated section, and thus allow the re-circulated section to be cooler than the output temperature of the warmed fluid.

A heat distribution system, method and computer program product, including an unpressurized tank configured for holding a heat transfer fluid; and one or more submersible heat transfer fluid pumps configured to pump the heat transfer fluid to one or more heat load loops respectively connected to the one or more heat transfer fluid pumps.

A dual fluid heat exchange system is presented that provides a stable output temperature for a heated fluid while minimizing the output temperature of a cooled fluid. The heated and cooled fluids are brought into thermal contact with each other within a tank. The output temperature of the warmed fluid is maintained at a stable temperature by a re-circulation loop that connects directly to the mid portion of the tank such that the re-circulated fluid flow primarily warms only a re-circulation section of the tank. The other, lower flow rate, section of the tank may be positioned so that it has a cooler temperature and thus serves to increase the efficiency of the heat exchange by extracting extra heat energy out of the cooled fluid before it leaves the tank. Alternatively, the low flow rate section of the tank may be warmer than the re-circulated section, and thus allow the re-circulated section to be cooler than the output temperature of the warmed fluid.

A tank-type water heater includes a storage tank and a heating circuit outside of the tank. The heating circuit includes at least one heat engine and at least one pump for circulating water from the bottom of the tank through the heat engine and back to the top of the tank. A stratifier introduces the heated water from the heating circuit into the top of the tank in a diffuse manner to promote stratification of hot water in the tank.

The application pertains to, for example, novel processes and systems for heat transfer, refrigeration, energy storage, and various cooling and heating processes. Such processes may include cooling or mixing various liquid-liquid phase transition liquids to release and/or energy. Additionally or alternatively, such processes may include charging and/or discharging thermal storage reservoirs with layered liquids of various temperatures.

There is described an apparatus for storing heat. The apparatus comprises a thermal mass for storing heat, the thermal mass having a first surface and a second surface. Fins are provided on the first surface and the second surface for accelerating heat transfer to and from the thermal mass. A displacement mechanism is secured to the thermal mass for translating the first surface to a first environment, e.g., a duct, while removing the second surface and its fins from a second environment, e.g., outside, and for translating the second surface to the second environment while removing the first surface and its fins from the first environment.

A dual fluid heat exchange system is presented that provides a stable output temperature for a heated fluid while minimizing the output temperature of a cooled fluid. The heated and cooled fluids are brought into thermal contact with each other within a tank. The output temperature of the warmed fluid is maintained at a stable temperature by a re-circulation loop that connects directly to the mid portion of the tank such that the re-circulated fluid flow primarily warms only a re-circulation section of the tank. The other, lower flow rate, section of the tank may be positioned so that it has a cooler temperature and thus serves to increase the efficiency of the heat exchange by extracting extra heat energy out of the cooled fluid before it leaves the tank. Alternatively, the low flow rate section of the tank may be warmer than the re-circulated section, and thus allow the re-circulated section to be cooler than the output temperature of the warmed fluid.