Impact of atmospherical stability and intra-hour variation of meteorological data in the variability of building air change rates

Abstract

In contrast with structural engineering, where the focus for design is on extreme values, for the proper assessment and modelling of air change rates in natural ventilation and infiltration, one must use the full range of input variables. Most of the modelling in infiltration research relies on hourly datasets for air infiltration balance. This consideration overlooks the intra-hour variability on meteorological variables. Additionally, it is customary to assume unchanging neutral atmospheric conditions when modelling, which affects the calculated airflows. This work intends to detail and quantify these effects in a case study representative of an average single-family dwelling in a Southern European climate setup. By comparing four setups with an increasing degree of complexity, a median of 0.04 h(-1) of the hourly standard deviations in air change rates (ACH) is attributed to the time step effect. Approximately 43% of the occurrences experienced non-neutral atmospheric stability, skewing for stable conditions. This effect contributed to differences in the ACHs ranging from-0.202 to 0.131 h(-1) at the 5% and 95% quantiles. Overall, by using hourly uniform distributions and smart sampling of meteorological variables, one ensures that the values in between and others potentially occurring around the boundaries are being considered for air change rates calculation, and therefore providing a more detailed picture of actual conditions.