The Measured Energy Impact of Air Leakage on Frame Wall Systems

Abstract

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 frame wall systems. Calorimetric measurements conducted on a small test cell and on a well characterized stud-cavity wall specimen with measured amounts of air leakage introduced under a variety of controlled conditions and configurations show convincingly that infiltration can lead to a much smaller change in the energy load than is customarily calculated. The data also suggest that the phenomenon occurs in full-sized houses as well.

Infiltration Heat Exchange Effectiveness {IHEE), €, is introduced as a mea­ sure of the effectiveness of a building in 'recovering' heat otherwise lost {or gained) because of infiltration. Measurements show that € increases as: a) flow rate decreases;

b) flow path length increases;

c) hole/crack size decreases.

€ also generally increases as the pressurization exponent, n, increases; so fan

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pressurization results may be useful in predicting E for buildings. An analytical • model based on fundamental heat and mass transfer principles has been

developed and all the predicted values of E as a function of air flow rates and effective path length for the different stud-cavity wall specimen test configurations were remarkably consistent with the experimental results.

Significant experimental results include:

a) E values as high as 0.9 and as low as 0.05 for the test cell configurations tested indicate an energy impact of the air leakage as low as 10% of customary values;

b) E values in the 0.16-0.7 range in the stud-cavity (vs. theoretical maximum

of 0.5); and

• c) E values of 0.16 to 0.34 for air exiting the stud-cavity directly across from the entry.

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