Question-and-Answer Resource for the Building Energy Modeling Community
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I agree with a comment above, that no matter which model you choose in an energy model, there will be coefficients/constants that are not attainable without further testing such as blower door and tracer gas tests. And if you enter a constant infiltration rate, you don't capture the effects of weather and system operation on infiltration. In real life, infiltration is not constant.
I published an article in the July issue of ASHRAE Journal which outlines equations to calculate coefficients in one of the EnergyPlus infiltration models. You use building height, surface-to-volume ratio, and net system flow (supply-return-exhaust) normalized by surface area, to calculate those coefficients. You do have to assume a baseline leakage value (like m3/s/m2 @ 4Pa) but having these coefficients allows infiltration to vary with weather and system operation (building pressurization, essentially). In the buildings I simulated, sometimes doing this saved energy, sometimes it increased energy. But it was still better than using a constant infiltration.
