Abstract: An improved dual-pressure dual-compartment tank for transferring heat energy between two solutions while physically isolating the solutions from each other is disclosed. The tank has one fluid compartment positioned within a second fluid compartment such that the transfer of heat energy between the compartments is facilitated. One of the compartments is structured to maintain a substantially higher pressure than the other compartment so that if a physical divider between the compartments were to fail, the lower pressure fluid would not contaminate the higher pressure fluid. Additionally, the divider may take a variety of shapes to improve fluid mixing by accelerating or decelerating the fluid, and/or to provide an amount of surface area between compartments that is inversely proportional to the local temperature gradient between the compartments.