Microclimate Load: Transformed Weather Observations for Use in Durable Building Design

Abstract: This study investigates the microclimate load, i.e. conditions prevailing in the immediate atmospheric environment of a building, to establish the natural conditions of degradation for a building surface at a specific location. To achieve this, in situ microclimate measurements were carried out at a test building at Fiskebäck Field Station, of Chalmers University of Technology, Göteborg, Sweden. Although the weather parameters studied related primarily to driving rain striking the building surfaces, the parameters of wind, precipitation, air humidity, ambient temperature, solar radiation, and total net radiation were also observed. Since the microclimate measurements describe the weather situation, the external wetting and drying conditions for the building can be studied. Comparing the results of two types of driving rain gauges mounted on building surfaces demonstrated the importance of metering equipment. The microclimate measurements were also compared with nearby standard meteorological observations, taken to represent macroclimate conditions. These comparisons showed the need to take into account the widely divergent scales in time and space of different atmospheric processes, as well as the effects of topography, vegetation and land use, urban and industrial activities, while keeping in mind the influences of the building itself. Hence, the customary long term climatic statistics should not be used since these are based on integrated atmospheric processes representing a larger area and showing only minor local deviations.

In addition, the microclimate measurements were compared with simulations of driving rain, solar radiation, and air temperature. In the transformation models used, the interaction between the climate parameters was included to refine the estimated microclimate load. First, with the aid of potential flow theory, the driving rain variation over wall surfaces was calculated from transformed, standard meteorological observations of wind and precipitation. Second, solar irradiance on a building surface was derived from an existing anisotropic sky model improved with meteorological information about clouds and precipitation. Third, the urban modification of air temperature, including information about wind speed and the amount of clouds, was calculated. Finally, the comparison of measured and calculated results showed that the transformation models can be used successfully to estimate the microclimate load.