Machine and method for the manufacture of an air-to-air heat exchanger
 A heat exchanger for transferring heat from stale air evacuated from a building to incoming fresh air employs a core made of a stack of spaced aluminum sheets that are joined along opposite edges in an alternate arrangement to define two separate sets of air passages for the respective outgoing and incoming flows, while providing good thermal contact between the two flows. This contact is improved by generating a measure of turbulence in the air flows by forming the sheets with surface nodules. The core is mounted in a frame that can be readily slid into a housing containing fans for generating the air flows. In an alternative construction, each air flow can be caused to travel in series through two parts of each set of air passages, rather than in parallel. This series arrangement has the advantage of reducing the temperature drop across any one part of the core below the total temperature difference between the inside and outside of the building. A machine is also disclosed for manufacturing such a core. It employs sliding tools for quickly forming lap joints between adjacent sheets to space them apart and form the sides of the air passages. 
Nutech Energy Systems, Inc.
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James H.
Lewis