Infiltration heat recovery, Part II - Laboratory studies of two test panel geometries

The flow of air through the porous media that is used as building insulation has the potential to recover energy normally lost through the building envelope via conduction. In essence, the walls of a building can be used as a crude heat exchanger, the effectiveness of which depends on the flow
direction, flow rate, and material thermal properties. In theory, the largest effects will be seen in the situation where the airflow is counter to the conduction loss and is distributed uniformly over the entire envelope surface. In theory, this form of distributed heat exchanger, at the appropriate flow rate, should be capable of recovering all of the energy that crosses the inner gypsum board boundary. To examine the potential for energy recovery, a research project, supported by ASHRAE, was undertaken in two parallel studies: laboratory work with carefully constructed wall sections and field studies with a well-instrumented test building. This paper presents the results of the laboratory studies and shows that the energy recovery potential is strongly dependent on airflow rate, crack geometry, and flow direction. The work indicated that air flowing through insulated cavities could result in significant changes in the apparent thermal resistance of the wall sections.