Development of Psi Factors for Thermal Bypass Due to Insulation Gaps in Low-Slope Roofing Assemblies

In commercial roofs, the presence or formation of gaps could be due to improper installation, thermal expansion, and dimensional changes in the insulation boards. The heat loss from these gaps could lead to higher thermal transmittance in the roof assembly. The current research study conducted around 70 experiments to investigate the effect of gap height, gap width and gap offset on the thermal transmittance of the roofing assembly. The measured data showed that in a staggered insulation layout with a joint offset of 610 mm (24 in), formation of 6.4 mm (1/4 in) to 12.7 mm (1/2 in) gaps at the insulation joints could contribute to an average decrease of 2% to 9% in the effective R-value of the roof assembly. As the insulation thermal resistance increases or becomes thicker, the thermal losses in the roof assembly increase. Generalized gap impact curves were developed to provide the relation between gap parameters (i.e., gap widths and height) and the thermal performance of the roof assembly. The experimental data were further analyzed using the psi factor approach of linear thermal bridging generating thermal transmittance data to support the calculation of thermal bypass from gaps in the thermal roof design.

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%.

Thermal Behavior of a Light Timber-Frame Wall vs. a Theoretical Simulation with Various Insulation Materials

The objective of this paper is to compare the thermal behavior of a light frame timber wall by measuring 15 test samples with various insulation materials versus a theoretical simulation with the use of a software. This work establishes the variance between the two different methods to measure the thermal transmittance coefficient of timber walls. It is verified that the mean percentage alteration between the two methods is 4.25%. Furthermore, this approach proved that with the use of a simulation software, additional readings (humidity, vapor flux, heat flux, and vapor pressure) can also be considered and measured, enhancing the overall development of a timber wall. This can provide additional information regarding to the characteristics of the masonry’s elements assisting in an improved design of a timber wall with upgraded performance.

Environmental and Economic Optimisation of Buildings in Portugal and Hungary

Life cycle assessment (LCA) is a scientific method for evaluating the environmental impact of products. Standards provide a general framework for conducting an LCA study and calculation rules specifically for buildings. The challenge is to design energy-efficient buildings that have a low environmental impact, reasonable costs, and high thermal comfort as these are usually conflicting aspects. Efficient mathematical optimisation algorithms can be applied to such engineering problems. In this paper, a framework for automated optimisation is described, and it is applied to a multi-story residential building case study in two locations, Portugal and Hungary. The objectives are to minimise the life cycle environmental impacts and costs. The results indicate that optimum solutions are found at a higher cost but lower global warming potential for Portugal than for Hungary. Optimum solutions have walls with a thermal transmittance in the intervals of 0.29–0.39 and 0.06–0.19 W/m2K for Portugal and Hungary, respectively. Multi-objective optimisation algorithms can be successfully applied to find solutions with low environmental impact and an eco-efficient thermal envelope.

Thermal Performance of LSF Wall Systems with Vacuum Insulation Panels

Lightweight Steel Frames (LSF) in building construction are becoming more popular due to their fast, clean, and flexible constructability. Typical LSF wall panels are made of cold-formed and thin-walled steel lipped channel studs with plasterboard linings. Due to the high thermal conductivity of steel, these LSF components must be well engineered and covered against unintended thermal bridges. Therefore, it is essential to investigate the heat transfer of the LSF wall of different configurations and reduce heat loss through walls by lowering the thermal transmittance, which would ultimately minimise the energy consumption in buildings. The effect of novel thermal insulation material, Vacuum Insulation Panels (VIP), their position on the LSF wall configuration, and Oriented Strand Board (OSB) and plasterboard’s effect on the thermal transmittance of LSF walls were investigated through numerical analysis. A total of 56 wall configurations and 112 finite element models were analysed and compared with the minimum U-value requirements of UK building regulations. Numerical model results exhibited that using plasterboards instead of OSB has no considerable effect on the U-value of the LSF walls. However, 77% (4 times) of U-value reduction was exhibited by introducing the 20 mm VIP. Moreover, the position of the VIP to the U-value of LSF was negligible. Based on the results, optimum LSF wall configurations were proposed by highlighting the construction methods. Additionally, this study, through literature, seeks to identify other areas in which additional research can be conducted to achieve the desired thermal efficiency of buildings using LSF wall systems.

Thermal Performance of Facades Based on Experimental Monitoring of Outdoor Test Cells in Tropical Climate

The high cost of energy consumption in buildings highlights the importance of research focused on improving the energy efficiency of building’s envelope systems. It is important to characterize the real behavior of these systems to know the effectiveness in terms of energy reduction. Therefore, the aim of this paper is to characterize the thermal performance of facades based on experimental monitoring of outdoor test cells in tropical climate. To carry out this research, a case study was presented to compare two construction systems. One of them is a light façade (M1) and the other a reference façade (M2). A thermal simulation was performed for the opaque and glazed facades. In addition, several parameters were measured with different types of sensors, as well as environmental variables to evaluate the thermal and lighting behavior of multiple facades systems under real conditions. The findings show that light façade behavior was the opposite of what was expected, since by incorporating a window in the façade it has allowed solar radiation to increase the interior temperature in both modules. In the case of the light facade the penalization was higher than the reference facade, which has a lower thermal transmittance than M1. Doi: 10.28991/cej-2021-03091773 Full Text: PDF

Thermal Performance Assessment of a Wall Made of Lightweight Concrete Blocks with Recycled Brick and Ground Polystyrene

Hollow concrete masonry blocks made of low strength self-compacting concrete with recycled crushed brick and ground polystyrene as an aggregate (RBC-EP blocks), and their expected structural role as masonry infill in steel frames, has been confirmed in previous research studies, thus the extensive investigation of thermal properties is presented in this paper to fully approve their potential application in practice. The Heat Flow and Temperature Based Method was used to conduct in-situ measurements of the wall thermal transmittance (U-value). The experimental U-values of the wall without insulation varied from 1.363 to 1.782 W/m2·K, and the theoretical value was calculated to be 2.01 W/m2·K. Thermal conductivity of the material used for making RBC-EP blocks was measured in a laboratory by using a heat flow meter instrument. To better understand the thermal performance characteristics of a wall constructed from RBC-EP blocks, a comparison with standard materials currently used and found on the market was performed. Walls constructed from RBC-EP blocks show an improvement of building technology and environmentally based enhancement of concrete blocks, since they use recycled materials. They can replace standard lightweight concrete blocks due to their desired mechanical properties, as well as the better thermal performance properties compared to commonly used materials for building walls.

Circularity concepts for offsite prefabricated energy renovation of apartment buildings

Deep energy renovation includes the realisation of the full potential of energy performance. A circular deep renovation, which contributes to a circular built environment, is based on 100% life cycle renewable energy, and all materials used within the system boundaries are part of infinite technical or biological cycles with the lowest quality loss as possible. In the current study, the circularity potential was assessed for deep energy renovation from different aspects: circularity of materials, building component and building structure. Careful selection of materials as well as connection, position and disassembly possibilities are needed to increase the degree of circularity. This shows a good possibility to increase energy performance by using circularity principles. The window glass circularity analyse showed that, at best, the thermal transmittance of a new circular product can be more than three times lower than the original. The circular use of materials, components, and structures pose new challenges for the building physic design of building envelope structures.

In-situ measurements of the U-value of a ventilated wall assembly

The walls in a building envelope have the largest contact area with the exterior environment, and, therefore, a considerable portion of the thermal energy can be lost through the walls compared to the other parts of the building envelope. For energy-saving purposes, the thermal transmittance of walls is typically limited by building energy performance standards at the national level. However, the presence of a ventilated air-space behind the external cladding, which has variable hydro-dynamic behavior, can differently affect the total thermal transmittance of the entire structure. This paper aims to provide an experimental analysis of the total U-value of a ventilated wall assembly measured in a building prototype following the average and dynamic methods defined by ISO 9869-1. Differences between the calculated theoretical U-value and the measured U-value are compared. The contribution of the thermal resistance of the ventilated air-space in the total thermal transmittance of the wall assembly is also analyzed. The results show that the air movement and the enthalpy change in the ventilated cavity can affect the thermal performance of the wall structure to a certain extent.

A multi-year comparative analysis of green and conventional roof thermal performance under temperate climate conditions

Research suggests that—relative to conventional roofs—green roofs can significantly reduce rooftop heat exchange in moderate climates; however, limited research exists on the performance of green roofs in colder climates. This paper analyzes the comparative performance of two side-by-side roof assemblies: a conventional roof and a green roof located in the temperate climate of Ottawa, Canada. Using two years’ worth of temperature and solar radiation data, we analyze variations in the incremental thermal benefit of the green roof relative to the conventional roof. We discuss factors contributing to these variations, such as precipitation and ambient temperature. Our results indicate that the green roof under investigation reduced thermal transmittance by 31.5% on average across two years. Although the percent benefits were much higher during the summer months, reductions in thermal transmittance were consistently above 7.7% throughout both years, indicating green roofs may be an appropriate alternative to conventional roofs in climates with hot, humid summers and cold, snowy winters.