Measuring thermal comfort of courtyards by mobile measurements - a case study

Cities are currently becoming more densely built almost everywhere, thus reducing the possible amount of areas for public green spaces, which are even more relevant in light of climate change as they can mitigate thermal stress during hot summer days. Here, optimizing existing courtyards concerning their green structure might be an option in order to provide conditions of low thermal stress during these days. However, there is no vast amount of studies addressing this issue for temperate and cold climate and related typical urban structures by measurements. We present mobile measurements recorded in Erfurt (Germany) during a hot summer day in 2018. These measurements also covered three courtyards of different design and geometry. Differences in air temperature between the three courtyards were small, but larger differences in mean radiation temperature existed, which mainly contributed to differences in thermal stress for human beings. We used the Universal Thermal Climate Index (UTCI, Jendritzky et al. 2012; Błażejczyk et al. 2010) to assess human thermal comfort. Out of the three investigated courtyards the smallest courtyard with established trees showed the lowest thermal load providing conditions of no thermal stress almost throughout the whole day (UTCI range: 18°C – 28°C). Highest values of thermal stress were recorded for the most open spaced courtyard with a value of 31°C after midday. Thermal loads of the different courtyards were related to general aspects (size of courtyard, ratio of unvegetated and sealed areas to vegetated areas). However, the sample size is too small to draw general conclusions and underlines the necessity for further measurements. We hope that our work will help to broaden the base of available measurements for climatic conditions and typical urban structures for Middle Europe concerning courtyards.

References

Błażejczyk, K., Broede, P., Fiala, D., Havenith, G., Holmér, I., Jendritzky, G., Kampmann, B., and Kunert, A.: Principles of the New Universal Thermal Climate Index (UTCI) and its Application to Bioclimatic Research in European Scale, 14, 91–102, https://doi.org/10.2478/mgrsd-2010-0009, 2010.

Jendritzky, G., Dear, R. de, and Havenith, G.: UTCI—Why another thermal index?, Int J Biometeorol, 56, 421–428, https://doi.org/10.1007/s00484-011-0513-7, 2012.