Analyse des thermischen Verhaltens von Substraten in Pflanzgefäßen

Master thesis by Andrea Heil

[Excerpt]

Abstract

In response to the consequences of the climate crisis, there is a growing call for increased greening in urban areas. To address the lack of space in conurbations and the competition for land between greening, infill development and underground infrastructure, urban trees can be planted in planters rather than in the ground. This thesis examines the effects of frost on planters during winter. To date, there has been no comprehensive analysis of this issue. This master’s thesis is designed as preliminary work for a larger research project at the Technical University of Munich. Initial findings and foundational principles are being established to support a targeted approach within the research project. The focus of this study is on the influence of the water content in the substrate and the influence of container insulation on the cooling behaviour of the substrate. A literature review, experiments under controlled conditions and simulations using ANSYS Fluent were carried out. The experimental results indicate that an increased water content in the substrate has a positive effect on plant survival. The phase change and the associated freezing enthalpy of water have a significant influence in this regard. The application of insulation also has a positive effect on plant survival, as can be concluded from measurement results in the specialist literature and from our own freezing experiments. Insulation significantly delayed the time taken to reach sub-zero temperatures in the freezing test (by 16–32 hours, depending on the measurement point). Temperature stratification was observed within the substrate during the tests. The upper regions tended to be warmer. This paper discusses possible reasons for this. Based on the findings from the freezing tests, further possible test set-ups for the research project were developed. The simulation was unable to realistically replicate the experiment. The simulated temperature curves drop too rapidly and the freezing enthalpy is underestimated. Potential causes for this include modelling errors and differing boundary conditions. In the simulation, -25 °C was set as a constant external temperature, whereas in the experiment the freezer warmed up significantly due to the introduction of the warm mass.