Hygric properties of porous building materials are important for hygrothermal analysis. Their experimental determination is however not always reliable, shown by the discrepant results from different laboratories on the same materials. In this study, a recent round robin campaign initiated by KU Leuven (Belgium) and participated in by eight institutes from different countries is reported. Ceramic brick was selected as the target material. The bulk density and open porosity from vacuum saturation tests, the capillary absorption coefficient and capillary moisture content from capillary absorption tests, and the vapor permeability from cup tests were measured. Results were analyzed statistically and compared with a previous round robin project, EC HAMSTAD. The reproducibility errors for determining the capillary absorption coefficient were noticeably reduced when compared with the EC HAMSTAD project, and the different laboratories in the present study obtained similar results from vacuum saturation tests and capillary absorption tests without a common protocol. For cup tests, large inter-laboratory discrepancies still exist. However, with a stringent common protocol different laboratories achieved consistent results. For all properties a common protocol did not change the average results of all laboratories.
Hygrothermal simulations are of major importance for critical problems in building physics, such as the application of internal insulation in heritage buildings. These simulations require numerous material parameters that are challenging to determine. We present measurements of typical internal insulation materials, calcium-silicate and autoclaved aerated concrete, which we expose to a warm, humid climate on one side and a cold temperature on the other side. We measure the moisture gain over time and determine the moisture profile at experiment end. In an inverse modelling approach, the measurements are used to identify material parameters, in particular vapour conductivity and capillary conductivity as a function of moisture content. We found the measurements of crucial importance for the accurate determination of these parameters. When the parameters rely only on isothermal measurements such as the drying experiment, the model fails to predict the capillary condensation process. We demonstrate this on a dataset from another study with interior insulation subjected to changing boundary conditions. The model calibrated with capillary condensation data reliably reconstructs measurements while the drying-calibrated model drastically underestimates the moisture content.
The District Energy Simulation Test (DESTEST) is a series of common exercises about modelling building stocks and district heating networks aiming at testing, benchmarking and verifying different urban-scale energy system simulation tools. For each common exercise, participants are modelling a case with well-defined characteristics, grid topology and boundary conditions. The DESTEST allows participants to discuss common mistakes and pitfalls and define guidelines from the experience and feedback. These common exercises can also be used for training purposes. This article discusses the development process of these common modelling exercises and presents the main lessons learnt during the creation of the DESTEST.
In recent years, building energy systems have become an important area of application for Modelica. However, few components, such as ground heat exchangers, remain difficult to implement in Modelica, and thus require co-simulation with an external model. We present a method for coupling a building energy system modeled in Modelica with an external ground heat exchanger model. The so-called waveform relaxation method (WRM) realizes co-simulation by exchanging arbitrary time-series data, instead of constant/polynomial values, as currently possible with the FMI standard. This may allow for performance improvement compared to FMI under certain conditions. A major advantage of this method is the applicability to simulation tools that do not yet support FMI. First, we briefly explain the energy system model (implemented in Modelica) as well as the ground heat exchanger model (implemented in external software DELPHIN). Next, we present different implementations of the WRM coupling method and their results. Finally, we discuss the performance of WRM under certain conditions and compare it to the FMI-co-simulation approach.
We conducted numerical simulations of a heat pump system connected to a horizontal ground heat exchanger (HGHX), using a coupling of the hygro-thermal simulation software DELPHIN with Modelica. The aim was to study the influence of different HGHX sizes and assemblies as well as the impact of passive cooling on the systems efficiency. We found that the required ground area could be reduced by up to 70 % compared to the recommendation of German standard when the pipes are placed in multiple layers. Passive cooling is possible but has a negligible effect on the systems efficiency.
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