Comparison of measured and simulated Mean Radiant Temperature. Case Study In Lisbon (Portugal)

Abstract

Mean Radiant Temperature (MRT ) is one of the most relevant humanbioclimatic indices, particularly suitable for assessing the influence of climatic parameterson thermal comfort outdoors. MRT can be calculated either from physical measurements,carried out using a globe thermometer or a pyranometer and a pyrgeometer, in order toquantify short and long wave radiation fluxes, or through computer simulation. The firstmethod, although accurate, entails the measurement of radiant fluxes from six directions,therefore it is time consuming, complex and it requires the use of expensive equipment. Thesecond method is based on RayMan, ENVI-met and SOLWEIG computational models,often employed in urban climatological research. The present research deals with thecomparison of MRT data obtained by measurement and computational simulation inCampo de Ourique, a denselypopulated city quarter of Lisbon. The measurements werecarried out in a park and in the surrounding canyon streets during four summer days in2006. The three computational models present some differences regarding their viabilityin estimating MRT compared to measurement: in case of direct solar exposure RayMan andSOLWEIG provided particularly good approximation (with an average difference of 6 and9%, respectively), whereas the average overestimation of MRT obtained by ENVI-metis around 20%. However, in shaded locations ENVI-met provided the most acceptableagreement between measured and simulated MRT ; in contrast RayMan and SOLWEIGoverestimated MRT by 15% on average.