Performance Evaluation of Thermal Bridge Reduction Method for Balcony in Apartment Buildings

Most apartment buildings in South Korea use internal insulation systems to reduce building energy demand. However, thermal bridges such as balcony slabs in apartment buildings still lead to significant heat loss in winter, because the internal insulation system is not continuous in the balcony slab structure, and floor heating systems are commonly used in residential buildings. Therefore, this study investigates two types of thermal break elements, namely thermal break (TB) and thermal break-fiber glass reinforced polymer (TB-GFRP), to improve the thermal resistance of a balcony thermal bridge. To understand the effects of balcony thermal bridges with and without thermal break elements, the linear thermal transmittances of different balcony thermal bridges were analyzed using Physibel simulations. Then, the heating demand of a model apartment under varying thermal bridge conditions was evaluated using TRNSYS simulations. To understand the effect of insulation systems on heat loss through a balcony thermal bridge, apartments with internal and external insulation systems were studied. Whether the apartment was heating was also considered in the thermal transmittance analysis. Thus, the linear thermal transmittance of the thermal bridges with thermal break elements was reduced by more than 60%, and the heating energy demands were reduced by more than 8%.

MATHEMATICAL MODELING OF THERMAL EFFICIENCY OF BUILDING EN-VELOPE OF MULTI-STOREY BUILDINGS WITH ACCOUNT OF INDIVIDUAL INSULATION

At present, the problem of general thermal modernization of building envelopes is given much attention both at the level of scientists and consumers. This is one of the effective ways to reduce natural gas consumption, reduce the negative impact on the environment, maintain and improve comfortable indoor conditions. Over the last decade, the population has rapidly begun to insulate their homes in order to raise the indoor air temperature to a comfortable level in the multi-storey residential sector. Due to insufficient attention of the authorities in the housing and communal sector, the lack of scientific research and widespread public awareness, there is a massive thermal insulation of building by residents of multi-store buildings within their own apartments. But the study of thermal processes that occur in individual thermal insulation of enclosing structures is currently not fully completed. Therefore, in the context of significant increases in gas and electricity prices, this problem is relevant. In the study was carried out mathematical modeling of a fragment of a partially insulated wall of an enclosing structure with determination of heat flux by solving a three-dimensional differential equation of thermal conductivity with boundary conditions of II, III and IV kind and distribution of characteristics of building structures and insulation. These results can be used in the analysis of the efficiency of insulation of the building taking into account the fragmentary insulation and of comparison with systemic thermal modernization. As a result of modeling, the three-dimensional temperature fields of wall surfaces, are determined, there are additional heat fluxes (thermal bridges), which are not considered in the simplified one-dimensional calculation. In one-dimensional calculation, the heat flux from the wall is reduced by 2.43 times during insulation. Taking into account the total heat flow from the side surfaces near the window (thermal bridges) and system insulation - by 1.75 times. With fragmentary insulation and considering the total heat flux from the side surfaces near the window - by 1.6 times. The next stage of calculations is the determination of the actual air temperatures in the premises of a multi-storey building considering the actual condition of enclosing structures and heating systems, heaters, mode parameters of the coolant and outdoor air parameters. The methods and means of this analysis can take into account the final data of heat loss adjustment after the mathematical modeling presented in this paper. In consequence, the results will be taken into account in the projects of thermal modernization of buildings, reconstruction of heating systems, rational placement of sources, selection of equipment and regulation of devices.

Simplified Infinite Fin Method to Model the Heat Transfer Associated with Slab Edges and Balconies

As building codes become more stringent in terms of thermal performance of building envelopes, and higher insulated wall assemblies are becoming more common, the heat flow due to major thermal bridges can contribute to a significant portion of the total heat transfer through a building façade. Characterizing different thermal bridging elements is essential not only to capture the thermal resistance of wall assemblies and understand the thermal efficiency of buildings, but also in terms of understanding the impact of each thermal bridging element and mitigation strategies that can be used. Numerical simulations are used widely to characterize different thermal bridging elements. However, not all designers have access, technical skills or time to complete numerical simulations to calculate the heat transfer loss through thermal bridges. In this study we propose an analytical method to integrate the effect of adding a slab edge/balcony/eyebrow into a clear-field wall assembly. The additional heat transfer due to the slab edge is calculated by considering the slab edge to be an infinite fin. The additional heat transfer is integrated into the clear-field as a quasi-convective heat transfer coefficient. The overall thermal resistance of the wall assembly is calculated by employing the parallel path method. Comparing the results obtained from this method with the numerical simulations which were benchmarked against guarded hot box results, an overall deviation of 1 to 8 percent was observed.

Heat and moisture transfer in wall-to-floor thermal bridges and its influences on the insulation performance

The moisture modifies the characteristics of heat transfer in building envelopes. Multiple factors, including the distinct hygric properties of various material, gravity, etc., affect the moisture content, resulting in a non-uniform distribution of water vapour in different parts of the envelope (e.g. column, beam, the main part of exterior walls). Usually, the more water vapour in a material, the higher the thermal conductivity, resulting in more heat transfers here. Moreover, condensation easily occurs where there is wet, marking such parts have risks both on structural safety and mould growth. The wall-to-floor thermal bridge (WFTB) occupies the largest area among all kinds of thermal bridges that formed by frame structures. In this study, we aimed to quantify the influence on heat loss through WFTB when the moisture transfer in envelopes is considered. The average apparent thermal resistance of WFTB (R TB, ave) was defined to access the insulation performance of WFTB in practical application. The results of transient numerical simulation indicated that when the moisture transfer is considered, the insulation performance of building envelopes decreases significantly, while the adverse effect of WFTB on heat insulation becomes less pronounced. The results indicated that the measures of insulation for WFTB should be reconsidered when the moisture transfer is considered.

Minimization of a point thermal bridge by a roof restraint system holder

Roof restraint systems are designed for flat roofs for safe maintenance and repairs. By anchoring them, considerable point thermal bridges are created, which can also lead to condensation in the roof cladding. We deal in this work with the design of minimization of these point thermal bridges.