Abstract: A heat exchanger element for exchanging heat between a fluid circulating in the element and a phase-change medium in a reservoir housing the element is formed of a plurality of spiral coils of flexible tubing disposed horizontally, one above the other, in a vertical stack. One end of each spiral coil is in communication with an inlet manifold and the opposite end is in communication with an outlet manifold. Preferably, the manifolds are disposed vertically, extending the height of the stack and side-by-side. Preferably, the manifolds are adjacent the outer periphery of the vertical stack of spiral coils. The spiral coils of the stack are wound alternatively clockwise and counterclockwise from a first radially outermost turn to a last radially innermost turn and arranged in pairs, one above the other. One spiral coil of each pair has the first radially outermost turn connected directly to the inlet manifold and the last radially innermost turn connected directly to the outlet manifold.

Abstract: A plurality of parallel heat exchange tubes are grouped together and connected at the ends to form a bank. One or more banks are positioned so that one end lies in a supply air stream and the other end lies in an exhaust air stream. Each bank of tubes is sealed and contains a working fluid of the type having a liquid phase and a vapor phase. At one end of each tube, the working fluid absorbs heat from one of said air streams to effect vaporization of said fluid, the vaporized fluid flows to the cooler end of said tube where said vaporized fluid gives up heat to the cooler air stream and condenses in the tube. The condensed fluid then flows back to the warmer end by means of gravity.One end of the lowest tube in each bank includes a reservoir connected thereto which communicates with the normally cooler air path and includes a heating coil operatively associated therewith for providing a modulated control of the system responsive to the temperature of the enclosed space being ventilated.