Abstract
The quality of a building envelope has a significant influence on the energetic behavior of the respective building. It decisively decidesto what extent external climatic loads are filtered before they reach the inside of the building. This aspect is of particular relevance, especially in climatic zones with hot summer periods, mainly if an energy‐efficient control of the room air conditioning is desired. In this case, the merely stationary consideration of heat transfer processes through envelope components is not sufficient. Dynamic effects, such as time shift and damping of the heat flux amplitude reaching the building interior are to be considered in detail here. Some researchers have already focused on the numerical determination of thermal response parameters. However, the developed models are very dependent on the accuracy of the input parameters used, which have a strong effect on the accuracy of the results. In addition to numerical analyzes, there are some studies focusing on the experimental determination of dynamic thermal properties. However, no reliable standard measurement methodology has been defined yet.
The present work addresses this gap and focuses on the holistic assessment and improvement of a corresponding measurement methodology for the reliable and accurate determination of dynamic thermal characteristics of opaque envelope components. The starting point of this work is a detailed literature review on the state of the art, especially with regard to experimental investigations of the dynamic thermal behavior of opaque building envelope components. Existing gaps in the applied measurement procedures are analyzed and evaluated.
In a first step, a numerical model for mapping the heat and mass transfer processes is developed by means of the hygrothermal simulation tool “Delphin”. In addition, the convective processes occurring at the component surface are analyzed with a flow simulation model and implemented with the software tool “Fluent”. The coupling between flow simulation and Delphin model defines an initialsimulation model. This model is then analyzed for its simplification possibilities, utilizing statistical methods to prove model robustness. The simplified simulation model developed in this way is then used to investigate the influence of different boundary conditions and parameters on the simulation results. From this, conclusions are made for an initial measurement setup for the component analysis under stationary climatic boundary.
Ten stationary experiments are carried out on a multi‐layered wooden wall in order to analyze and evaluate the influence of different climatic and structural boundary conditions on the measurement results. In doing so, at the same time, a comprehensive database is created, which is used for the later numerical model validation. From these ten test setups, the experimental model with the best performance and lowest measurement error is determined. This model is then considered for an experimental test under dynamic conditions. Furthermore, three laboratory tests are carried out under transient conditions in order to obtain a comprehensive database for the later validation of the dynamic simulation model.
Based on the data obtained from laboratory tests, an adjustment of the respective stationary and dynamic numerical simulation model is carried out. Subsequently, the validation of the simulation models is conducted, which shows in all cases a very good agreement between measured and simulated values. In a further step, a device for carrying infrared emitters is designed and implemented. The application of this device to a laboratory test under dynamic conditions is investigated and thus it can be stated that the homogeneity of the surface temperature distribution is positively influenced. This contributes to the reduction of measurement errors. Finally, two further wall structures are investigated both, experimentally and numerically, with regard to their stationary and dynamic thermal behavior. Again, a good correspondence between measured and simulated values can be achieved. This allowsthe applicability of both models, experimental and numerical, to a wide range of opaque building components and materials. The present work contributes to the standardization of an experimental measurement setup for the determination of dynamic thermal parameters of opaque envelope components. In addition, the applicability of a numerical model developed to determine steady state and dynamic characteristics of envelope components could be demonstrated. For the first time, several experimental tests for determining steady state as well as dynamic thermal characteristics could be modeled in this work with a high accuracy using a single numerical simulation model. With the hygrothermal simulation model developed in this work, it will be possible in the future to determine the dynamic thermal parameters of opaque building envelopes taking into account different moisture conditions. An analysis of the influence of material and ambient moisture on the dynamic thermal characteristics of components is thus also feasible.