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Implementation and validation of a long-wave heat exchange model

 
: Winkler, Matthias; Antretter, Florian; Radon, Jan

American Society of Heating, Refrigerating and Air-Conditioning Engineers -ASHRAE-, Atlanta/Ga.:
Buildings XIII Conference. Thermal Performance of the Exterior Envelopes of Whole Buildings XIII International Conference 2016 : December 4-8, 2016, Clearwater Beach, Florida
Atlanta, GA: ASHRAE, 2016
pp.636-644
International Conference "Thermal Performance of the Exterior Envelopes of Whole Buildings" <13, 2016, Clearwater Beach/Fla.>
Buildings Conference <13, 2016, Clearwater Beach/Fla.>
English
Conference Paper
Fraunhofer IBP ()

Abstract
The hygrothermal whole-building simulation software WUFI® Plus was extended with a new model: the calculation of longwave radiative heat exchange between surfaces inside a zone. This allows a more detailed calculation of the interior radiative and surface temperatures, which also results in a better simulation of indoor climate conditions. The model also takes into account the optical properties of indoor surfaces, such as low-e coatings. Further benefits are a more comprehensive comfort assessment, for example, for asymmetric radiant temperature. Radiant temperatures can also be calculated for every position inside a zone. The model uses Gebhart factors for the calculations of long-wave heat exchange between surfaces inside a zone. These factors describe the fraction of emitted energy from one surface that is absorbed at another. They are determined from view factors, which only describe geometrical relationships between surfaces. WUFI® Plus uses a numerical triangulation method to calculate the view factors. As the Gebhart factors also consider optical properties of surfaces, all possible radiation paths, including multiple and own reflections, are taken into account for the calculations. Single parts of the calculation process are successfully validated with analytical solutions: the view factor calculation of a nontrivial room geometry and the long-wave heat exchange between two parallel plates show only minimal deviations from the analytical results. The German standard DIN EN 13791 provides tests for the validation of interior long-wave heat exchange. The model was successfully validated with them. In an exemplary application case, simulations with the new model are used as a preliminary study to determine the required accuracy and positioning of measurement equipment of a future test room. The simulated surface temperatures were successfully used as a plausibility control. The measurements will later be used as an experimental validation test for the new model.

: http://publica.fraunhofer.de/documents/N-442444.html