Abstract: A storage fluid heater for heating a fluid, employs a heat storage unit, a heating element thermally coupled to the heat storage unit, and a heat recovery tube thermally coupled to the heat storage unit. The recovery tube is made from a material having a coefficient of thermal expansion so that as the average temperature of the heat storage unit near the heat recovery tube increases, the surface area of gaps between the heat recovery tube and the storage unit increases, causing the contact resistance between the heat storage unit and the heat recovery tube to increase. The temperature of the fluid flowing within the heat recovery tube is thereby limited to a predetermined maximum. A structure that relieves excess pressure when the flow of fluid through the tube is stopped has an expansion tank connected to the fluid inlet of the tube.

Abstract: A storage heater for storing heat and for heating a fluid, such as water, has an enclosure defining a chamber therein. The chamber has a lower portion and an upper portion with a heating element being disposed within the enclosure. A tube through which the fluid flows has an inlet and an outlet, both being disposed outside of the enclosure, and has a portion interconnecting the inlet and the outlet that passes through the enclosure. A densely packed bed of phase change material pellets is disposed within the enclosure and is surrounded by a viscous liquid, such as propylene glycol. The viscous liquid is in thermal communication with the heating element, the phase change material pellets, and the tube and transfers heat from the heating element to the pellets and from the pellets to the tube. The viscous fluid has a viscosity so that the frictional pressure drop of the fluid in contact with the phase change material pellets substantially reduces vertical thermal convection in the fluid.