Airtightness Predictor

Has anyone tried to model airtightness for a building and predict the buildings overall air change rate at the design stage?  I’ve done this by making educated guesses for each element, such as walls, floors, roof and windows and then multiplying by the areas to give a whole building infiltration rate and then comparing against the ventilation volume.  I’m looking for some pier review to see if it could be used reliably.  Any thoughts…?  I’m happy to email my model to anyone who’s interested.  Please get in touch