3651 -- Computational Frameworks for Numerical Assessment of Steady-State Conductive Heat Transfer Through Thermal Bridges PDF

Combined effects of heat transfer rates through exterior building elements and high relative indoor air humidities can lead to surface condensation. As a result, damage to the building as well as undesirable hygienic conditions indoors can occur. As a theoretical basis for adequate problem-preventing strategies, the relations between geometry and thermal resistance of building components (indoor) surface temperatures, water vapour pressure in indoor rooms and surface condensation risk are studied. The concept of "thermal coupling coefficient" is applied for the thermal description of building elements in the form of "L-value" matrices. These matrices are generated through computer-aided numerical analysis of steady-state heat transfer processes in construction. For the calculation of the minimum surface temperatures, the related concept of a "g-factor" matrix (temperature-weighting factors) is applied. A convenient evaluation method of the condensation risk based on temperature factors (f) and humidity factors (F) is considered. Results of simulation of heat transfer through building components demonstrate the relevance of the distinction between simplified (U-factor-based) calculations and more accurate numerical computation. Although a high degree of accuracy is not always required, there are many cases, e.g., thermal bridges), where only accurate calculations would lead to reliable results in regard to both heat flows (realistic prediction of heat loss quantities) and surface temperatures (evaluation of condensation risk).

KEYWORDS: calculating, steady state, heat flow, thermal bridges, geometry, heat loss, thermal resistance, buildings, components, surface temperature, water vapour, condensation, accuracy, computers.