A method of operating a thermal storage system that includes one or more thermal storage tanks that include a tank body that defines a tank cavity configured to hold a tank thermal storage medium, and one or more ports. The thermal storage system also includes a heat exchanger assembly disposed in the tank cavity of the one or more thermal storage tanks and comprising a heat exchange coil connected to inlet and outlet lines that extend through at least one of the one or more ports of the thermal storage tank, the heat exchanger assembly configured to run a flow of working thermal storage medium through the one or more thermal storage tanks so that heat exchange occurs between the flow of working thermal storage medium and the tank thermal storage medium disposed within the tank cavities of the thermal storage tanks.