The Energy Impact of Air Leakage Through Insulated Walls

Infiltration is customarily assumed to increase the heating and cooling load of a building by an amount equal to the mass flow rate of the infiltration times the enthalpy difference between the inside and outside air—with the latent portion of the enthalpy difference sometimes neglected. An experimental and analytical investigation has been conducted on the actual energy impact of air leakage on a well-characterized insulated stud-cavity wall specimen. Calorimetric measurements conducted on the specimen with measured amounts of air leakage introduced under a variety of controlled conditions and configurations verify earlier test cell measurements showing that infiltration heat exchange can lead to a much smaller change in the energy load due to infiltration than is customarily calculated and show the dependence of infiltration heat exchange on flow rate and path length. An analytical model based on fundamental heat and mass transfer principles has been developed and the predicted values of Infiltration Heat Exchange Effectiveness, ε, as a function of air flow rates and effective path length for five stud-cavity wall specimen test configurations were consistent with the experimental results. Significant experimental results include: (i) ε values in the 0.16–0.7 range in the stud-cavity and (ii) ε values of 0.16 to 0.34 for air exiting the stud-cavity directly across from the entry. These results indicate that significant heat recovery is probable for most leakage occurring through insulated stud cavities.