Abstract: A heat storage tank is provided to receive a spent liquid from a heat transfer mechanism, to reconstitute the liquid and to return the reconstituted liquid to the heat transfer mechanism for another heat transfer cycle. The tank is divided into at least two compartments. Spent liquid is discharged into a first compartment near its lower portion. Means are provided for passing liquid from the first compartment to a second compartment by drawing liquid from the upper portion of the first compartment and discharging it near the lower portion of the second compartment. The liquid is then drawn from the upper portion of the second compartment and returned to the heat transfer mechanism.