Abstract: Disclosed is a heat exchanger, and a method for heating a working fluid. The heat exchanger includes a burner, a combustion section, and a condenser section positioned below the combustion section such that exhaust from the burner passes through the spiral coils and to the condenser. In an example of this disclosure, the combustion section includes a plurality of spiral coils radially spaced apart relative to one another, and the condenser section includes a plurality of U-bend coils.

Abstract: A battery charging method and system with a temperature-compensated charge profile requires that, during a ‘bulk stage’, a regulated constant charge current is provided to the battery until the voltage across it increases to a predetermined ‘absorption stage voltage limit’, at which time charging transitions to an ‘absorption stage’. During the absorption stage, a charge current is provided which maintains the voltage across the battery at the absorption stage voltage limit, until: 1) the charge current falls to a predetermined current threshold, 2) the charge delivered to the battery during the absorption stage reaches a predetermined charge threshold, or 3) the difference in charge between two successive intervals of equal duration becomes zero, at which time charging transitions to a ‘float stage’. During the ‘float stage’, a regulated constant charge current is provided, such that the voltage across the battery varies with the temperature of the battery.

Abstract: Disclosed is an economizer including a plurality of coil stacks. Each coil stack includes a tube coiled such that adjacent layers of the tube contact one another in a radial direction. Further, the coil stacks are axially spaced from one another to allow exhaust to flow between adjacent coil stacks.