Meeting Abstract

25.11  Monday, Jan. 5  A heat-conserving ventilator for buildings based on nasal countercurrent exchangers VOGEL, S.; Duke University svogel@duke.edu

Respiratory ventilation in warm-blooded animals causes loss of both heat and water. Small mammals and birds commonly minimize such losses cyclic storage and release of heat plus condensation and evaporation of moisture during exhalation and inhalation respectively. Such single-passage, reciprocating flow, countercurrent exchangers can recover well over 80 percent of exhaled heat and water according to measurements done long ago by Schmidt-Nielsen and his collaborators on small desert rodents. Well-insulated, sealed buildings in cold places face an equivalent problem of heat and moisture loss through ventilators; unfortunately, as constant volume systems, they cannot use directly analogous devices. A biomimetic version for a building is nevertheless applicable, one based on paired exchangers operating in opposite phase at opposite ends of the structure. A very crude model house, consisting of a 0.8-m styrofoam box heated up to 50° C above room temperature, permitted exploration of at least the thermal aspect of the problem. Ventilating it at opposite corners were paired exchangers, 5.0 cm square by 41 cm long, in which air passed between 20 closely-spaced, parallel, aluminum plates 0.61 mm thick, drawn by small electronic cooling fans at their outer ends. With a full cycle about every 10 seconds and an average air exchange time (flow relative to box volume) of 250 seconds, the device recovered somewhat over 25 percent of the heat that would have been lost were ventilation unidirectional. Changing the operating conditions pointed to poor thermal interaction between moving air and aluminum plates as the chief limitation of this particular model.