Uncertainties due to the use of surface averaged wind pressure coefficients

A com~nonp ractice, adopted by several buildingenergy simulation (BES) tools, is the use ofsurface averaged wind pressure coefficients (Cp)instead of local Cp values with high resolutionin space. The aim of this paper is to assess theuncertainty related to the use of surfaceaveraged data, for the case of a cubic buildingwith two openings. The focus is on wind-drivenventilation and infiltration, while buoyancy isnot taken into account. The study is performedusing published empirical data on pressurecoefficients obtained from wind tunnel tests.The method developed to calculate theuncertainty is based on comparison of: the flowrate calculated using the averaged values (?AV),and the one calculated using local values (?LOC).The study considers a large number ofcombinations for the opening positions in thefacade. For each pair of openings (i), the valuesof ?LOC_I and ?AV_I , are calculated. Based on theratio between ?LOC_I and ?AV_I the relative error(ri) is calculated. The relative error is presentedstatistically, providing probability densitygraphs and upper and lower bounds for theconfidence interval (CI) of 95%. For this CI, theconclusion is that 0.24 ?AV