Abstract: A cool storage system comprising which includes a plurality of heat pipes. Each of the heat pipes has a lower evaporator section, a hybrid evaporator/condensing section, and an upper condensing section. The hybrid evaporator/condensing section positioned between the lower evaporator section and the upper condensing section. Each of the heat pipes contains a selected amount of a heat transfer fluid adapted to transfer heat from the lower evaporator section to the hybrid evaporator/condensing section and the upper condensing section through a vapor/condensation cycle, or the heat transfer fluid is vaporized in the hybrid evaporator and condensed in the upper evaporator section. A thermal storage medium is provided in thermal engagement with the hybrid evaporator/condensing section. A heat source is located in said lower evaporator section, and a cooling source, located in said upper condensing section.

Abstract: A thermal energy storage system includes a phase change composition including a phase change material. The phase change composition has a first melting temperature at a first hydration level and a second melting temperature at a second hydration level. The phase change composition stores thermal energy by converting from a solid to a liquid. The thermal energy storage system also includes at least one compartment containing the phase change composition and at least one tuning medium receiving water to adjust the phase change composition from the first hydration level to the second hydration level and supplying water to adjust the phase change composition from the second hydration level to the first hydration level. A method of storing and releasing thermal energy is also disclosed.