05CH11231, the CEC under the Califoarnia Energy Commission contract No. EPC-15-037 and Aereco SA under Contract No. FP00003428. The contribution of Cerema is funded by the French Ministries in charge of sustainable development, transports and urban planning, and by the Région Auvergne Rhône-Alpes.

Explicit algebraic equations for calculation of wind and stack driven ventilation were developed by parametrically matching exact solutions to the flow equations for building envelopes. These separate wind and stack effect flow calculation procedures were incorporated in a simple natural ventilation model, AIM-2, with empirical functions for superposition of wind and stack effect and for estimating wind shelter. The major improvements over previous simplified ventilation calculations are: a power law pressureflow relationship is used to develop the flow equations form first principles, the furnace or fireplace flue is included as a separate leakage site and the model differentiates between houses with basements (or slab-on-grade) and crawlspaces. Over 3400 hours of measured ventilation rates from the test houses at the Alberta Home Heating Research Facility were used to validate the predictions of ventilation rates and to compare the AIM-2 predictions to those of other ventilation models. The AIM-2 model had bias and scatter errors of less than 15% for wind-dominated ventilation, and less than 7% for buoyancy ("stack-effect") dominated cases.

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Synopsis Although the power law has been broadly accepted in measurement and air infiltration standards, aI!d in many air infiltration calculation methods, the assumption that the power law is true over the range of pressures that a building envelope experiences has not been well documented. In this paper, we examine the validity of the power law through theoretical analysis, laboratory measurements of crack flow and detailed field tests of building envelopes. The results of the theoretical considerations, and field and laboratory measurements indicate that the power law is valid for low pressure building envelope leakage.

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