Observations and model evaluation of building wall temperatures for outdoor thermal comfort applications

Longwave radiation from the surroundings is an important part of the human comfort in urban areas. While the distribution of longwave radiation from the sky is fairly known, this is not the case with regards to the longwave radiation emitted from the surrounding buildings in complex urban settings. In this study we present observed as well as simulated data from two sites in Gothenburg, Sweden: 1/ a wall with one storey of plastered brick and one of wood and 2/ two brick walls facing southeast (SE) and southwest (SW) respectively.  We also show how wall temperatures can be simulated based on estimations of the radiation balance using a single-layer step heating equation.

Under clear skies in summer, the daytime wall temperatures of the wooden wall exceed air temperature with, on average, 20 °C while the plastered brick wall did not reach 15°C. During the night the wooden wall  was on average 2°C cooler than the air whereas the plastered brick wall  was on average, 2°C warmer. These differences depend on the heat properties of the wall materials but also of its thickness. The heating of the SW-looking brick wall was delayed by four hours compared to the SE-looking but in spite of this the maximum temperature was almost the same.

Net radiation, modelled by the SOLWEIG model, and air temperature are the input variables in simulations of wall temperature. Material parameters are thermal effusivity of the wall and a time constant related to its thickness. In the afternoon, the simulations underestimate wall temperature, probably a result of heat stored within the wall during the warming phase. However, the diurnal march of wall temperatures with max and min are over all well described by the simulation.