Low Thermal Transmittance Research Articles

Evaluation of heterogeneous core sandwich panels for energy efficiency and fire safety in warehouse buildings

Sandwich panels are extensively used in the construction industry because of their superior thermal insulation performance and ease of installation. However, panels with combustible cores are prone to fire, whereas those with mineral-based cores exhibit lower thermal insulation capabilities. Therefore, to address these limitations, this study proposed a composite core approach to enhance both fire resistance and thermal insulation performance. A surface layer incorporated phenolic foam (PF), which fulfilled the fire resistance requirements and delivered excellent thermal insulation properties, and 30–40 mm of glass wool (GW) and mineral wool (MW) with exceptional fire resistance were applied. The heterogeneous core sandwich panels exhibited excellent flame-retardant performance, with a maximum peak heat release rate of 0.712 kW/m2 and a total heat release of 0.18 MJ/m2. This satisfied the semi-non-combustible flame retardancy level and ensured sufficient time for residents to evacuate safely. Moreover, based on its low thermal transmittance of 0.114–0.125 W/m2·K, when applied to warehouse-type buildings, heating energy consumption was reduced by approximately 10 % compared to sandwich panels based on inorganic core GW and MW. Heterogeneous core sandwich panels can exhibit excellent flame retardancy and thermal performance owing to the use of inorganic materials and PF, respectively.

Hygrothermal Performance of Prefabricated Insulation Elements for Serial Renovation of Apartment Buildings in a Moderately Continental German Climate

The reduction of energy use in the buildings is expected to be reached by fulfilling several requirements of the low- and nearly-zero energy buildings (nZEB) policy. The improvement of the energy performance of the building envelope and the service systems of the existing buildings offers great potential for energy savings as the annual replacement of the existing stock is only 1 to 2%. The efficient way to accomplish the purpose and global goals of the nZEB is to apply the integrated design process, development, and application of prefabricated insulation elements on a large scale. In this project, in the Berlin area of Germany, prefabricated timber frame insulation elements were designed for the external insulation of the envelope of the apartment building in the serial renovation process, with the thermal transmittance of the external envelope U external-wall = 0.14–0.16 W/(m2·K). In the current study, the potential hygrothermal risks and their effect on highly insulated multi-story apartment building envelope were analyzed. The study contained a set of hygrothermal analyses to ensure the moisture safety of highly insulated facade structures and the selection of materials from the perspective of hygrothermal performance and low risk of degradation. This research found that the risk of mold growth is high if timber elements are installed without protective measures against drying-out built-in moisture, wind-driven rain, and other weather conditions. The initial moisture content of the external concrete slab, to be considered critical, is 90 kg/m3, and the drying out period is longer than the covered with new layers constructions can sustain if a proper vapor control layer is not added between the existing moist wall and installed insulation elements. Furthermore, the wind barrier layer with high thermal resistance and vapor permeability of the installed insulation element helps to minimize the risk of mold growth. A careful analysis and selection of materials allow to design moisture-safe timber frame insulation elements and provide low thermal transmittance of renovated building envelopes. The results showed that before the final design and installation of the insulation elements, a thorough hygrothermal analysis of the original external envelope with actual climatic conditions and moisture loads must be realized.

Robust multi-objective building design optimization approach using NSGA-II algorithm considering weather and occupant uncertainties

A novel methodology is presented to evaluate how real-world operational uncertainties impact multi-objective building design optimization process. NSGA-II algorithm is applied across nine distinct operational scenarios, considering diverse weather datasets and energy usage patterns to optimize energy efficiency and thermal comfort in a residential building within India's hot and dry climate. The analysis considers 382,400 possible design options for each scenario. Using (10.5–12.5) % of model evaluations, NSGA-II significantly reduces Annual Cooling Energy Demand (ACED; 46.7%–58.7%) and Cooling Set-point Unmet Hours (CSUH; 70.92%–86.93%) to identify nine Pareto–Optimal solution sets. The final robust optimal design is confirmed by selecting the most repeated parameter settings, representing the highest robustness. Low thermal transmittance walls, double-glazed windows with a 10% window-to-wall ratio (WWR), deep overhangs, and a low solar heat gain coefficient are recognized as robust optimal building components. However, Air Conditioner (AC) sizing lacks robustness in minimizing energy demand across scenarios, requiring case-specific evaluation due to its sensitivity to weather and operational variations. Further, PAWN sensitivity analysis highlighted the substantial impact of WWR (KSWWR ∼ (0.46–0.66)) and wall type (KSWall ∼ (0.31–0.46)) on ACED and CSUH in chosen climate. AC operation is more important for predicting CSUH (KSAC ∼ 0.35) than ACED (KSAC ∼ 0.10).

Experimental and numerical study on a new thermal masonry block by comparison with traditional walls

The present work concerns an innovative construction system consisting of brick blocks with micropores and multiple air cavities which confer to the material a very low thermal conductivity combined with a high thermal inertia. The aim of this research is to experimentally compare the performance of these single-layer inertial walls with a traditional super-insulated lightweight wall, characterized by similar and very low steady thermal transmittance. The walls were monitored in the summer season in two adjacent test rooms in a free dynamic regime, i.e. without the use of mechanical cooling systems. The test rooms were built without windows to evaluate only the heat transfer through the opaque surface. The incidence of solar gains, of ventilation and of the dispersing surface area was evaluated by means of numerical analyses using the hourly dynamic method of EN ISO 52016-1. The results demonstrated that the new single-layer blocks with low conductivity and high thermal inertia guarantee excellent performance by substantially limiting the internal air temperature compared to the other solutions. This makes it possible to reduce the summer peak loads and cooling energy consumptions, especially in the case of night ventilation.

Influence of green roof systems on the energy performance of buildings and their surroundings

The thermal behavior of green roofs may vary according to climate and substrate and plant characteristics. This study aimed to analyze the influence of green roof systems on the energy performance of buildings and their surroundings under three different Brazilian climates. For this, 1944 combinations of green roof parameters were simulated. An initial validation of the thermal balance model was performed reaching RMSE of 2.17 °C and 2.85 °C, for substrate and vegetation temperature, respectively. It was obtained that, in temperate climate, low leaf area index (LAI), combined with high substrate thickness and low thermal transmittance, provided 5.6% of reduction with climatization when compared with cool roofs, and high transfer of latent heat to the exterior. In semi-humid tropical climate, 4.9% of savings was achieved with high LAI, intermediate substrate thickness, and high thermal transmittance. In equatorial climate, although there was high transfer of humidity, green roofs resulted in higher energy consumption than cool roofs, indicating that low thermal mass systems are more favorable for climates with low temperature fluctuations. The results showed that green roofs play a fundamental role in improving energy efficiency and outdoor air quality. However, an inadequate system may produce detrimental effects depending on climatic conditions.

Use of sunspaces to obtain energy savings by preheating the intake air of the ventilation system: Analysis of its main characteristics in the different Spanish climate zones

Novel solutions need to be further developed to continue to improve the energy efficiency of buildings achieved over the last few decades. One of these innovative systems is the use of sunspaces to preheat the ventilation intake air and reduce heating consumption. The main goal of this research is to determine the optimal configuration of these sunspaces. For that purpose, a prototype was built to calibrate a simulation model. Once validated, the model was used to calculate the energy savings obtained with 96 sunspace configurations in the different Spanish climate zones. Different key factors were analyzed and the optimal configurations were established in each zone. The results show that, although these systems are based on solar gains, a low thermal transmittance of the glazing has a higher impact on the energy savings than a high solar heat gain coefficient. In addition, introducing inertia tanks is not convenient when the ventilation includes a heat recovery system. While combining sunspaces with heat recovery ventilation is not interesting in warmer climates; in cold climates, heat recovery becomes a determining factor to reduce energy consumption. The use of sunspaces is more efficient as the winter severity increases: while in the warmest Spanish climate zone, only 2.51 kWh·m −2 ·year −1 savings are achieved; in the coldest zone, 39.54 kWh·m −2 ·year −1 savings are obtained, which represents important energy savings of 60%. This research contributes to evaluating and quantifying the impact of key variables on the design, configuration, and operation of sunspaces to improve the energy efficiency of buildings. • Sunspaces to heat ventilation air entail great energy savings if properly designed. • A energy simulation model for sunspaces was validated with experimental results. • Savings of 96 sunspace configurations were quantified for different climatic zones. • Optimal sunspace configurations for maximum energy savings have been established. • In the coldest Spanish climatic zone savings of 60% in heating were achieved.

The 3D Printing Potential for Heat Flow Optimization: Influence of Block Geometries on Heat Transfer Processes

The building envelope is a crucial element in the regulation of thermal energy in the indoor environment, from which comfortable living inevitably depends. Designing a low-dispersion envelope represents a fundamental strategy to minimize the energy demand and HVAC systems’ consumption. To this end, the need to select suitable insulation has become increasingly important, and the search for new solutions is constantly evolving. This justifies the great interest in the study of energy-efficient and sustainable insulation materials that are able to provide the low thermal transmittance values of multilayer components. To date, 3D printing has experienced a growing popularity for the research of alternative building materials (e.g., concrete). Conversely, it still appears to be very uncommon for the research of purely energy-efficient solutions. The aim of this work is to compare the thermal performance of three 3D-printed PLA (polylactic acid) blocks, characterized by different internal geometries and air cavities: (i) a multi-row structure; (ii) a square structure; (iii) a honeycomb structure. The study was conducted theoretically, with two-dimensional heat transfer modeling, and experimentally, by means of a heat flow meter and infrared thermography. The results showed that the configurations of the 3D-printed blocks reduced the flow of heat exchange. In addition, as the complexity of the blocks’ internal structure increased, a heat flow reduction could be observed. In particular, the honeycomb structure showed a better behavior than the other two blocks did, with an experimental transmittance value that was equal to 1.22 ± 0.04 W/m2K. This behavior, which was mainly due to an attenuation of convective and radiative internal heat exchanges, suggests that the 3D printing has great potential in this field.

Wpływ kształtu wzmacniających profili okiennych na wytrzymałość i sztywność skrętną okien

Leading European manufacturers of profiles intended for the production of construction joinery currently use mainly PVC profiles with various configurations of external and internal shapes, allowing the production of functional products due to their intended use, shape, possibility of building them, maintaining color and maintaining low thermal transmittance coefficients of profiles. It is important to obtain high cross-sectional strengths, especially for torsion and bending. It is related to high wind loads of structures. A profile is made of a PVC with a low Young’s modulus compared to other materials, and thus it has low stiffness and strength indicators. This leads to relatively easy deformation of the joinery profiles during assembly. To avoid this unfavorable effect, the PVC profiles are reinforced with steel sections. Currently, in the industry producing PVC profiles, open steel reinforcement profiles are almost exclusively used. This solution is very disadvantageous for reasons of stiffness. However, manufacturers use such profiles primarily for technological and price reasons. Closed profiles pose many technological problems in their production and are approx. 30% more expensive compared to the corresponding open profiles. This paper presents research on the use of closed steel stiffening sections in place of open profiles. The main advantage of stiffening closed profiles is many times greater bending and torsional stiffness compared to open profiles. The theoretical and experimental studies carried out for selected cross-sections have shown that the stresses in a closed profile are several times lower than in an identical open profile, and the torsional stiffness of a closed profile is even several dozen times higher than that of an identical open profile.

Development of Lightweight Steel Framed Construction Systems for Nearly-Zero Energy Buildings

Light steel frame (LSF) building systems offer high structural resilience, lower costs due to fast prefabrication, and high ability to recycle and reuse. The main goal of this paper was to provide state-of-the-art main components for such systems with the intention to be implemented for use in nearly-zero energy buildings (NZEBs). A brief historical outline of the development of LSF systems was given, and the key parameters affecting the design and use of LSF systems were discussed. The influence of the individual components of the LSF system (steel studs, sheathing boards, and insulation materials) was then thoroughly discussed in light of relevant research on energy efficiency and other important properties (such as sound protection and fire resistance). Web of Science and Scopus databases were used for this purpose, using relevant key words: LSF, energy efficiency, sheathing boards, steel studs, insulation, etc. Several research gaps were identified that could be used for development and future research on new LSF systems. Finally, based on the analysis of each component, an innovative LSF composite wall panel was proposed which will be the subject of the authors’ future research. Conducted preliminary analysis showed low thermal transmittance of the system and indicates the path of its further research.

Passive cooling strategies to optimise sustainability and environmental ergonomics in Mediterranean schools based on a critical review

This article identifies and compares the passive cooling strategies used and their relationship to optimising sustainability and environmental ergonomics based on 47 case studies. The analysis of the schools has resulted in the identification of 20 passive strategies, eight parameters related to sustainability and six related to environmental ergonomics. The results show that the most used passive strategies are natural ventilation, green roofs, low thermal transmittance windows and solar shading. In contrast, the least used strategies are ventilated façades and evaporative cooling systems. In terms of sustainability, energy efficiency is present in most case studies; in contrast, the circular economy is hardly considered in schools. In terms of environmental ergonomics, thermal comfort is present in most case studies, while acoustic comfort is not assessed. Furthermore, the results show an absence of optimisation of acoustic and visual comfort, climate change adaptation measures and involvement of the educational community. This work provides a detailed understanding of the status quo for researchers, practitioners and policymakers and predicts the dynamic directions of the field. It highlights the need to incorporate passive design protocols explicitly applied to schools to achieve a sustainable and climate-resilient educational building stock within the principles of the circular economy.

Effect of Clay’s Multilayer Composites Material on the Energy Efficiency of Buildings

Climate change and resource and energy depletion are already impacting ecosystems and societies around the world. As a result, environmental sustainability has become one of humanity’s priority challenges. This study aims to use ecological multilayer material in order to reduce the impact of carbon and energy needs of heating in severe climates in which people die each year from cold. The combination of the investigated multilayer material gives a low thermal transmittance (U = 0.361 W·m−2·K−1). A simulation using the software TRNSYS was established to estimate the yearly heating and cooling needs in the building with the developed multilayer material in a semi-arid climate. The yearly energy demands for heating and cooling were compared to a normal wall with conventional bricks; 47% of energy was saved by the use of the multilayer material wall. The use of the multilayer material permits a low ratio of energy needs of 24 KWh/m2/year for cooling needs and 43 KWh/m2/year for heating.

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 Optimization of Double and Triple Glazing Systems for Slovenian Climate Conditions

Glazing elements are an important part of the thermal envelope of a building. Therefore, good thermal performance of glazing elements can improve indoor comfort and reduce annual maintenance costs and CO2 (carbon dioxide) emissions by reducing heat loss. Reducing heat loss through glazing elements during the heating season can be achieved by combining low thermal transmittance with high solar heat gain. Using standardized calculation methods and measured climate data for three Slovenian locations representing typical continental, mountainous and Mediterranean climates, this study predicts the best combination of optical properties (emissivity, transmittance and reflectance) of glass panes in double and triple glazing systems that contribute to minimal heat loss. It was found that for the double glazing system, the minimum heating and cooling demand for buildings with low solar gains or high solar gains and applied shading is achieved by an inner pane with high transmittance without low-emissivity coating, and an outer pane with low-emissivity coating with minimum possible emissivity. In Maribor and Portorož climatic zones, the panes with low emissivity coating should be used as inner panes in buildings with high solar gains. For triple glazing, the minimum heating and cooling requirements are achieved with two or three panes with low emissivity. For buildings with low solar gains, an emissivity of the coating of 0.03 is preferable, but for buildings with high solar gains, lower emissivity values should be used.

Development of Structural Insulated Panels Made from Wood-Composite Boards and Natural Rubber Foam.

An experimental study was carried out to develop and examine the properties of a new type of structural insulated panel (SIP). SIP prototypes conducted from this research consisted of insulated foam manufactured from natural rubber filled with wood particles as the core layer and three kinds of commercial wood-composite boards (plywood, cement particleboard, and fiber-cement board) as the surface layers. Polyurethane was used as an adhesive bond between the surface and the core layer. This preformed panel was placed into a clamping device and compressed until adhesive curing was achieved. The physical and mechanical properties of the SIP prototypes were consequently evaluated. The test results indicated that the types of surface layer materials played a significant effect on the SIP properties. The SIP covered with cement particleboard and fiber-cement board revealed high mechanical properties and high water resistance. The SIP prototype covered with plywood showed desirable properties (such as low density, high resistance of screw withdrawal, and low thermal transmittance). However, high water absorption and low fire resistance were drawbacks of the SIP covered with plywood. These properties should be improved.

Pontes térmicas em estruturas de concreto

A importância de considerar as pontes térmicas e seus impactos no cálculo de transmitância térmica é um assunto que tem sido discutido em regiões de clima com estação fria no Brasil. A presença de pontos vulneráveis no envelope do edifício pode ter consequências no desempenho térmico, além das implicações nas paredes e coberturas do edifício, como por exemplo a formação de fungos filamentosos. Várias normas e regulamentos tratam da temática. Esse estudo tem por objetivo discutir, por intermédio de simulação computacional, a necessidade das normas Brasileiras de desempenho considerarem a possibilidade de formação de fungos filamentosos nas edificações com baixo e elevado isolamento térmico. Na análise examina-se as condições termo-higrométricas próximas a estrutura de concreto armado do modelo da edificação onde ocorrem as pontes térmicas, e as superfícies dos fechamentos vertical, de alvenaria, para todas as fachadas. Os resultados mostram que existe uma elevada probabilidade de crescimento dos fungos filamentosos nas pontes térmicas quando o edifício é mais isolado, ou seja, apresenta baixa transmitância térmica.

Thermal Transmittance (U-value) Evaluation of Innovative Window Technologies

Calculation of heat transfer in windows has a direct impact on the thermal transmittance on highly insulated glazing components. A series of experimental tests were carried out in order to calculate the U-value of active insulated windows using the Heat Flux Meter method (ISO 9869-1); this to compare the insulation properties of traditional single glass, double glazing with different aerogel fillings and vacuum glazing windows. The use of this heat flux method utilised an environmental chamber to provide a temperature difference of 15 °C reporting the U-values as follows: traditional double glazing 3.09 W/m2·K, vacuum glazing 1.12 W/m2·K, and double glazing with aerogel pillars 2.52 W/m2·K. On the other hand, double glazing with KGM wheat starch reported 3.40 W/m2·K, double glazing with granulated aerogel 2.07 W/m2·K and heat insulation solar glass 1.84 W/m2·K. Vacuum glazing recorded optimal results under these experimental conditions, describing a U-value 78 % lower when compared to traditional single glazing window units (5.15 W/m2·K). Installation of windows with lower thermal transmittance are expected to increase in the global market to meet the current construction codes, aimed for achieving net zero carbon buildings.

Integrated environmental, energy and cost life-cycle analysis of windows: Optimal selection of components

There is an increasing need for energy-efficient windows; however, these windows can have high embodied impacts and can be costly. This has not been thoroughly analyzed and the literature has mainly focused on the operational performance of windows. It is important to wisely select optimal windows that minimize energy consumption, costs, and environmental impacts throughout their life cycle, considering the influence of window orientation and climate data. This article presents an integrated cost and environmental life-cycle assessment (LCA) of window solutions, combining alternative glazing and framing options. Optimal window solutions were selected using a Pareto bi-objective optimization (costs vs. environmental impacts) for three different European climate regions, considering various window orientations. The influence of each window component (glazing and framing), as well as window properties (thermal transmittance and solar factor) on the overall environmental and cost life-cycle impacts was studied. Pareto optimal window solutions for warm climates highlight low solar factor windows, while for cold climates they highlight low thermal transmittance value. The glazing is the component with the greatest influence on the total environmental impacts (mainly operational). The impacts depend to a very great extent on the thermal transmittance values and solar factors. The life-cycle cost analysis shows that the initial investment in the windows has a high impact on the overall cost, even when a lifespan of 30 years is considered. This article provides insights into and recommendations for the design of windows by addressing different climatic conditions and window orientations.

Numerical and experimental study on metamaterials featuring acoustical and thermal properties

Metamaterials can be defined as materials which, for their peculiar composition or structure, exhibit characteristics that are not normally found in nature. “Multifunctional” metamaterials could be used to optimise different characteristics at the same time. In this paper the authors try to apply them for thermal and acoustic optimization of external building walls. Thermal optimization consists in obtaining a low transmittance, important in winter, and a low periodic thermal transmittance, important in summer. Acoustic optimization consists in obtaining high sound transmission loss, to respect the law prescriptions, and a good sound absorption coefficient, if possible. In this way should be possible enhance the comfort conditions in buildings and reduce the energy demand for winter heating and summer cooling. The proposed solution consists of several layers with different suitable characteristics: the sequence of the layers has been chosen with particular care. The thermal analysis has been performed by means of a self-developed code based on the ISO 13786 standard. The acoustic behaviour of the single layers has been determined following the procedure given by the ASTM E2611-09 standard using a four-microphone impedance tube and the transfer matrix method has been used for the complete assembly. This preliminary combined study showed encouraging results.

Experimental Evaluation and Numerical Simulation of the Thermal Performance of a Green Roof

In the building sector, both passive and active systems are essential for achieving a high-energy performance. Considering passive solutions, green roofs represent a sustainable answer, allowing buildings to reach energy savings, and also reducing the collateral effect of the Urban Heat Island (UHI) phenomenon. In this study, a roof-lawn system was investigated by means of an extended measurement campaign, monitoring the heat transfer across the roof. Heat-flow meters and air- and surface-temperature probes were applied in a real building, in order to compare the performance of the roof-lawn system with a conventional roof. This experimental approach was followed to quantify the different thermal behaviors of the building components. Moreover, an equivalent thermal model of the roof-lawn system was studied, in order to obtain the equivalent thermal properties of the roof, useful for setting building models for yearly energy simulations. The roof-lawn system revealed its advantages, showing a higher thermal inertia with no overheating in summertime and a lower thermal transmittance with energy savings in wintertime, and, consequently, better indoor conditions for the occupants of the building.

Slim building envelopes using vacuum glazing and high-performance insulation

To get a slim building envelope with low thermal transmittance, and hence a low energy consumption, vacuum glazing and high-performance insulation material have been combined. Preliminary investigations both experimental and numerical have been carried out to determine thermal, hygric and mechanical properties of these building components according to either existing standards or to best knowledge procedures. This includes measurement of the center-of-glass U-value, the simulation of the influence of support pillars on the glass surface temperature and comparison of measured and calculated results. Several specimens were measured under different temperature gradients to get more information about accuracy and deviation in the production of the vacuum glazing elements. Further, mechanical stability of larger specimens was tested by the standard pendulum tests for flat glass and compared to identical tests on conventional double-glazing elements of the same size. Finally, a one-dimensional hygro-thermic analysis has been conducted to determine the temperature and moisture distribution within a thin wall construction containing high-performance insulation when submitted to climatic conditions in the Swiss Midlands.