Abstract: Methods and apparatus are disclosed for high-efficiency thermal storage with a fluid-filled “battery” tank positioned within a fluid-filled “reservoir” tank. Fluid loops couple the tanks to a heat pump and a building. The heat pump can charge the battery tank or deliver thermal energy (cold or heat) to a building, using the reservoir tank or ambient air as a thermal energy source. The battery tank can discharge energy to the building jointly with the heat pump or, at periods of peak electricity usage, with the heat pump switched off. Operating modes allow significant savings in electricity usage and mitigate the “duck curve.” Low duty cycle usage of the reservoir enables efficient underground thermal storage with less digging than conventional geothermal technologies. Additional efficiency is achieved with phase change materials installed inside a tank or in a tank wall, providing temperature regulation. Control methods are disclosed.

Abstract: Methods and apparatus are disclosed for high-efficiency thermal storage with a fluid-filled “battery” tank positioned within a fluid-filled “reservoir” tank. Fluid loops couple the tanks to a heat pump and a building. The heat pump can charge the battery tank or deliver thermal energy (cold or heat) to a building, using the reservoir tank or ambient air as a thermal energy source. The battery tank can discharge energy to the building jointly with the heat pump or, at periods of peak electricity usage, with the heat pump switched off. Operating modes allow significant savings in electricity usage and mitigate the “duck curve.” Low duty cycle usage of the reservoir enables efficient underground thermal storage with less digging than conventional geothermal technologies. Additional efficiency is achieved with phase change materials installed inside a tank or in a tank wall, providing temperature regulation. Control methods are disclosed.

Abstract: A guard for a valve upon a buried fluid line prevents earth entering the opposed arches or the bottom of a conventional casing during installation about and above the valve permitting access after filling of the excavated cavity for the fluid line. Alignment of the casing with the valve and the fluid line is also facilitated with an upward facing bore of an upward extending upward portion of the guard which permits insertion of the end of a length of conduit during installation and allows passage of the end of a wrench in operation of the buried valve. A longitudinal cavity open at the bottom and ends and continuous with the bore is defined by a lower portion of the guard. Opposed ends extend into the opposed arches of the casing, protect the fluid line from a descendant arch, and serve as guides for casing disposition. Two lateral pairs of stabilizers extending outwardly from either end stabilize the guard with respect to the casing and the fluid line.