Project no. 411
Hygrotermic Control of the Microclimate Around
C. K. Nielsen
DTU Architectural Engineering, Technical University of Denmark
The urban heat island (UHI) is a well-documented phenomenon, that increases the
temperature within a city. In hotter climate that leads to uncomfortable outdoor spaces.
Research shows that vegetation and trees can help decrease the temperature (Shashua-Bar
et al. 2009). Current tools, for investigating the effect of vegetation on the microclimate in the
urban space, are not well suited in an integrated design process. The objective of the thesis
is to develop such a method, which evaluates the influence of vegetation on thermal comfort
in the microclimate and apply it to a case study in Abu Dhabi.
For that purpose, two models were developed: The Soil Model and The Atmosphere Model.
The Soil Model computes the evapotranspiration from the ground. It is implemented as a
wrapper around the Catchment Modelling Framework (Kraft et al. 2011). The Atmosphere
Model is a simple air volume model, that turns the evapotranspiration into a change in air
temperature and relative humidity. The two models are written in Python and implemented in
the parametric design tool Grasshopper. It has been demonstrated how they can function in
an analytic workflow with Ladybug Tools to compute outdoor thermal comfort. The thermal
comfort metric Universal Thermal Climate Index (UTCI) was used to assess the thermal
A case study in Abu Dhabi, United Arab Emirates, was conducted. The case study was 20m
times 22m site, with a wadi running through and five trees. The thermal comfort was
evaluated with the proposed method and compared to an assessment method that neglects
evapotranspiration. The results showed that an average reduction of 3.7°C UTCI was
present, when evapotranspiration was included. During the daytime of June 1st, the
reduction would reach 15°C UTCI.
From this study it could be concluded that evapotranspiration has a substantial impact on
the thermal comfort in the microclimate and that it is possible include such an analysis in an
integrated design process.