Modelling of Long Wave Radiation Exchange in Enclosures with Building Integrated Heating

Paper in proceeding, 2005

Today, radiant floor heating is the most frequently used heating supply system in newly built Swedish single-family houses. Most simulation tools for heat transfer calculations in whole buildings are simplified regarding the distribution of long-wave radiation (LWR) dominating the total heat transfer from a radiant floor heating system. In this paper, two calculation models for the LWR distribution are explored in terms of radiant floor heating. Moreover, two levels of thermal insulation standard are tested. An advanced LWR-model (Net Radiation Exchange Model) that includes exact computation of view factors is used as reference for the LWR exchange inside the building. Additionally, non-uniform surface temperatures for all construction parts are calculated using the NRE-model. The second LWR model (TX-model) represents a simplified model that is commonly used in energy simulation software. In order to quantify the accuracy of the simplified LWR-model, calculated surface temperatures over time for both models are compared. Results indicate that the TX-model is unable to accurately calculate the whole set of surface temperatures that occur simultaneously in the building. This holds even if the radiant heat transfer coefficient in the TX-model is optimised to give the smallest overall temperature difference for the building.