Density controlled phase-changing material (PCM) spheres for increased heating power and optimal delivery temperature in hot-water tanks

A system for heating water, the system comprising:

• one or more tanks, each of the tanks configured to hold water;
• an inlet coupled with one of the tanks to receive water at an input water temperature Twi;
• means for changing the temperature of at least a portion of the received water to a target water temperature Twt;
• an outlet coupled with one of the tanks to output the water at an outlet water temperature Two;
• and
• a plurality of capsules, each capsule comprising
• a phase changing material (PCM) configured to undergo a liquid-solid phase transition at a solidification temperature, Ts, wherein the PCM undergoes a relative volume change due to the phase transition,
• a shell filled with the PCM, wherein the shell comprises a first heat-conducting material, and wherein the shell is configured to comply to the relative volume change;
• and
• wherein 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, Tw, to be larger than the capsule's weight for Tw>Ts, and equal to or smaller than the capsule's weight for Tw<Ts;
• the capsules being immersed in the water held by the tank coupled with the outlet,
• wherein, when heating the water in the tank causes the temperature inside the capsules to rise to or above TS,
• the PCM undergoes a solid-to-liquid phase transition to create a charged capsule, and
• the charged capsules are configured to float above the level of the outlet, and store latent heat captured during the PCM's solid-to-liquid phase transition, and
• wherein when cooling the water in the tank causes the temperature inside the capsules to drop to or below TS,
• the PCM undergoes a liquid-to-solid phase transition to create a discharged capsule, and
• the discharged capsules are configured to float adjacent to the level of the outlet, and release the stored latent heat.

A method of heating water, comprising the steps of:

• providing a tank for the water, the tank having an upper portion and a lower portion, and a water outlet and a water inlet, the water outlet being positioned between the upper portion and the lower portion;
• providing in the tank a plurality of capsules, each capsule comprising:
• a phase changing material (PCM) configured to undergo a liquid-solid phase transition at a solidification temperature, TS, wherein the PCM undergoes a relative volume change due to the phase transition,
• a shell filled with the PCM, wherein the shell comprises a first heat-conducting material, and wherein the shell is configured to comply to the relative volume change, and
• wherein 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, Tw, to be larger than the capsule's weight for Tw>Ts and equal to or smaller than the capsule's weight for Tw<Ts;
• and,
• heating the water in the tank to a target water temperature Twt;
• withdrawing water from the water outlet while inputting water through the water inlet, the withdrawn water having a temperature Two that is higher than the temperature Twi of the inputted water and lower than Twt, creating a stratified water temperature tank with a graduated water temperature decreasing from the upper portion to the lower portion;
• wherein the PCM in the capsule will solidify and the capsules will sink in the stratified tank.