Numerische Simulation des Mikroklimas im Innenhof

Abstract

It is widely accepted that the courtyard concept can modify the climate and with moderating the extreme hot or cold climate condition is considered as one of the old passive design strategies. However, despite the effect of the courtyard on climatic variables, the heat loss calculation methods mostly consider the weather file of the courtyard the same as the ambient weather file. Regarding the low thermal resistance of the courtyard surrounding glass envelopes against heat conduction, these façades are more sensitive in front of the environmental parameters and this simplification in the calculation can overestimate the heat load for the surrounding rooms of the courtyard. This study seeks to understand the effect of the courtyard and its various configurations on the environmental parameters and to suggest appropriate adjustment factors to consider the courtyard’s special microclimate in the calculation of the heat loss through the building’s envelope. In this way, the parametric analysis was implemented using the three-dimensional computational microclimate model “ENVI-met”. Hence as a first step of the research processes, the numerical simulations were validated by experimental in-situ investigations and the accuracy of the computational model in predicting air temperature, wind speed, relative humidity and mean radiant temperature inside the courtyard was evaluated. The next steps following the linking the climatic variables inside the courtyard in the thermal balance of surrounding building envelopes and the heat loss calculation. Since the biggest advantage of the courtyard semi-closed space related to the wind protection offered by the courtyard and its heat island during the winter, this study was focused on the effect of the courtyard and its configuration on two building physics parameters including the convective heat transfer coefficient (CHTC) and temperature adjustment factor (Fx, heat load). The outcomes of the research, which were calculated for the experimental case in the Hanover climate region, showed that the CHTC through the façade inside the courtyard is less than exposed building envelopes. This decrease is particularly noticeable at higher ambient wind speeds. In addition, the aspect ratio of the courtyard has a great effect on wind speed inside it. So that, inside the deep courtyards (H/W ≥ 2.67) the wind speed is almost zero at low levels of the courtyard and CHTC can be considered with the minimum value and is about 4 (W m-2K-1) according to DIN EN ISO 6946. Investigating the air temperature difference between the courtyard and outside standard temperature for Hanover also proposes an Fx, heat load between 0.9 and 2.2 for courtyard semi-closed space, which varies depending on the courtyard aspect ratio and glazing percentage of the surrounding envelopes.