Search Results (106)

This study empirically evaluates the energy and carbon reduction effects of an envelope retrofit applied to an aging public building in South Korea. Unlike previous studies that primarily relied on simulation-based analyses, this work fills the empirical research gap by using actual utility billing data collected over one pre-retrofit year (2019) and two post-retrofit years (2023–2024). The retrofit included improvements to exterior walls, roofs, and windows, aiming to enhance thermal insulation and airtightness. The analysis revealed that monthly electricity consumption was reduced by 14.7% in 2023 and 8.0% in 2024 compared to that in the baseline year, with corresponding decreases in electricity costs and carbon dioxide emissions. Seasonal variations were evident: energy savings were significant in the winter due to reduced heating demand, while cooling energy use slightly increased in the summer, likely due to diminished solar heat gains resulting from improved insulation. By addressing both heating and cooling impacts, this study offers practical insights into the trade-offs of envelope retrofitting. The findings contribute to the body of knowledge by demonstrating the real-world performance of retrofit technologies and providing data-driven evidence that can inform policies and strategies for improving energy efficiency in public buildings. Full article

This paper presents a comprehensive investigation to evaluate the impacts of air cavities between existing walls and insulated panels on the overall R-values of the retrofitted building envelope systems, addressing a key challenge in exterior envelope retrofitting. The effects of several factors are considered including the air cavity thickness (ranging from 0.1 cm to 5 cm), airflow velocity (varying between 0.1 m/s and 1 m/s), and surface emissivity (set between 0.1 and 0.9), in addition to the thickness of the insulated panels (ranging from 1 cm to 7 cm). It is found that any increase in the air cavity thickness increases the overall R-values of the building envelope assemblies when air is trapped within the sealed cavity. However, when air convection is prevalent, the overall R-value of the retrofitted walls decreases with any increase in air velocity and air cavity thickness. For sealed air cavities, the analysis results show a 9% improvement in R-value of the retrofitted walls. However, the R-value of retrofitted walls with unsealed air cavities can degrade by 76% and 81% for natural and forced air flows, respectively. Emissivity adjustment is found to be the most effective in improving the thermal performance of building envelopes with sealed air cavities, increasing the R-value of retrofitted walls by 13.6% when reduced from 0.9 to 0.1. Full article

China’s urban residential building stock is extensive and spans a wide range of construction periods. With the continuous enhancement of building energy efficiency standards, the chronological characteristics and variability of residential building envelopes are evident. Through field research and typological analysis of residential buildings in Jinan, a cold region of China, three construction eras were classified: Period I (1980–1985), Period II (1986–1995), and Period III (1996–2005). Building performance and economic benefits across these periods are modeled using Rhino 7.3 and Grasshopper. The NSGA-II algorithm, as the core of Wallacei2.7, is employed for multi-objective optimization. Through K-means clustering, TOPSIS comprehensive ranking, and Pearson correlation analysis, the optimized processes and solutions are provided for urban residential renovation decisions in different periods and target preferences. The results show that the optimal comprehensive performance solutions for Period I, Period II, and Period III achieve energy savings of 40.92%, 29.62%, and 15.81%, respectively, and increase annual indoor comfort hours by 872.64 h/year, 633.57 h/year, and 564.11 h/year. For Period I and II residential buildings, the most effective energy efficiency retrofit measures include increasing exterior wall and roof insulation, replacing exterior window types, and reducing exterior window k-value. The overall trend in energy savings rates and economic benefits across the three periods shows a decline. For Period III residential buildings, systematic strategies, such as solar thermal collector systems and photovoltaic technology, are required to enhance energy efficiency. Full article

Lecture halls are characterized by large spatial dimensions, deep floor plans, and high occupant densities. Lectures are typically conducted using multimedia and blackboard-based teaching, placing higher demands on the indoor light and thermal environment compared to standard classrooms. This study aims to simulate the interrelationships between multiple building envelope parameters and building performance, in order to improve visual and thermal comfort while reducing energy consumption in cold-region lecture halls. Based on seven key envelope parameters—including openable window area ratio, west-facing window-to-wall ratio, exterior insulation thickness, shading element spacing, angle and width, and window glass type—a multi-objective optimization framework was established. The optimization process targeted three key performance indicators—useful daylight illuminance (UDI), energy use intensity (EUI), and thermal comfort percentage (TCP)—in the context of a stepped classroom. The results show that increasing the thickness of exterior insulation and reducing the width of shading components contribute positively to photothermal comfort without compromising thermal and visual performance. Compared with the baseline design, optimized schemes that incorporate appropriate west-facing window-to-wall ratios, openable window areas, insulation thicknesses, and external shading designs can reduce annual energy consumption by up to 10.82%, and increase UDI and TCP by 12.79% and 36.41%, respectively. These improvements are also found to be economically viable. Full article

Prefabricated components inevitably generate numerous assembly joints during installation, with each 1 mm increase in joint width correlating to a 15–20% elevation in the annual occurrence frequency of the frost formation risk. In the Inner Mongolia Region, the water migration at wall connection interfaces during winter significantly exacerbates freeze–thaw damage due to persistent thermal gradients. A coupled heat–moisture transfer model incorporating gas–liquid–solid phase transitions was developed, with the liquid moisture content and temperature gradient as dual driving forces. A validation against internationally recognized BS EN 15026:2007 benchmark cases confirmed the model robustness. The prefabricated sandwich insulation walls reconstructed with region-specific volcanic ash materials underwent a comparative evaluation of temperature and relative humidity distributions under varied winter conditions. Furthermore, we analyze and assess the potential for freezing at connection points and identify the specific areas at risk. Synergistic effects between assembly gaps and indoor–outdoor environmental interactions on wall performance degradation were systematically assessed. The results indicated that, across all working conditions, both the temperature and relative humidity at each wall measurement point underwent periodic variations influenced by the outdoor environment. These fluctuations decreased in amplitude from the exterior to the interior, accompanied by a noticeable delay effect. Specifically, at Section 2, the wall temperatures at points B2–B8 were higher compared to those at A2–A8 of Section 1. The relative humidity gradient remained relatively stable at each measurement point, while the temperature fluctuation amplitude was smaller by 2.58 ± 0.3 °C compared to Section 1. Under subfreezing conditions, Section 1 demonstrates a marked reduction in relative humidity (Cases 1-3 and 2-3) compared to reference cases, which is indicative of internal ice crystallization. Conversely, Section 2 maintains higher relative humidity values under identical therma. These findings suggest that prefabricated building joints significantly impact indoor and outdoor wall temperatures, potentially increasing the indoor heat loss and accelerating temperature transfer during winter. Full article

As energy-efficient buildings become central to climate change mitigation, the opportunity for interior and interstitial moisture accumulation and mould growth can increase. This study investigated the potential simulation-based mould growth risks associated with the current generation of insulated low-rise timber framed external wall systems within southeastern Australia. More than 8000 hygrothermal and bio-hygrothermal simulations were completed to evaluate seasonal moisture patterns and calculate mould growth potential for nine typical external wall systems. Results reveal that the combination of increased thermal insulation and air-tightness measures between the 2010 and 2022 specified building envelope energy efficiency regulations further increased predicted Mould Index values, particularly in cool-temperate climates. This was in part due to insufficient moisture management requirements, like an air space between the cladding and the weather resistive layer and/or the low-water vapour permeability of exterior weather resistive pliable membranes. By contrast, warmer temperate climates and drier cool-temperate climates exhibit consistently lower calculated Mould Index values. Despite the 2022 requirement for a greater water vapour-permeance of exterior pliable membranes, the external walls systems explored in this research had a higher calculated Mould Index than the 2010 regulatory compliant external wall systems. Lower air change rates significantly increased calculated interstitial mould growth risk, while the use of interior vapour control membranes proved effective in its mitigation for most external wall systems. The addition of ventilated cavity in combination with either or both an interior vapour control membrane and a highly vapour-permeable exterior pliable membranes further reduced risk. The findings underscore the need for tailored, climate-responsive design interventions to minimise surface and interstitial mould growth risk and building durability, whilst achieving high performance external wall systems. Full article

Based on the resource conservation requirements of GB/T 50378-2019 “Green Building Evaluation Standard”, this study constructed a BIM–Ecotect collaborative analysis model and proposed a “four-dimensional integration” green performance optimization method. Taking a high-rise office building in Wuhan as an example, a LOD 300-level Revit building information model was established, and a multidisciplinary collaborative analysis was achieved through gbXML data interaction. The lighting simulation results show that the average natural lighting coefficient of the office area facing south is 2.4 (the standard 85%), while in the meeting room area, due to the optimized design of the curtain wall, the average natural lighting coefficient has increased to 2.6 (the standard 92%). In terms of energy-saving renovation, a three-dimensional collaborative design strategy was adopted. Through the optimization of the envelope structure, the cooling load of the air conditioning system was reduced by 25.3%, and the heat load was reduced by 23.6% (the u value of the exterior wall was reduced by 56.3%, the SHGC of the exterior windows was reduced by 42.9%, and the thermal resistance of the roof was increased by 150%). The ventilation optimization adopts the CFD flow field reverse design, adjusting the window opening rate of the exterior windows from 15% to 20% to form a turbulent diffusion effect. Therefore, the air change rate in the office area reached 2.5 times per hour, and the CO₂ concentration decreased by up to 27.1% at most. The innovative adoption of the “composite sound insulation curtain wall” technology in acoustic environment control has increased the indoor noise compliance rate by 27 percentage points (from 65% to 92%). The above research data indicate that digital collaborative design can achieve an overall energy-saving rate of over 20% for buildings, providing a replicable technical path for enhancing the performance of green buildings. Full article

Due to moisture migration effects, thermal and moisture bridges tend to form at building joints, thereby increasing the thermal conductivity coefficient of construction materials. To examine the influence of moisture transfer on the thermal performance of ‘one-line’ vertical joint walls, this study establishes a thermal–humidity coupling numerical model at the vertical joint of sandwich insulation composite walls. This model is employed to analyze the effects of various joint filling materials (aerated blocks, glass wool, concrete), insulation layer thicknesses, and environmental conditions on the thermal transfer properties of the wall joint. The results indicate that when filled with aerated blocks, the joint is most significantly affected by moisture transfer, exhibiting a heat flow loss rate of 8.08%. In high-temperature environments, the thermal transfer performance at the connection of the composite wall is particularly susceptible to humidity, with heat flow loss rates ranging from 6.17% to 8.74%. Furthermore, an increase in the thickness of the insulation layer leads to a reduction in the “heterogeneity” of the sandwich insulation wall, which reduces the wall’s effects to moisture transfer; however, this is accompanied by a rise in the heat loss rate at the connection. After accounting for the effects of hygrothermal bridging, the mean heat transfer corrected coefficient of the wall in areas with hot summers and cold winters ranges from 1.10 to 1.18 during the summer and from 1.12 to 1.16 during the winter. This finding holds significant relevance for aiding researchers in predicting thermal transfer analysis in scenarios involving wall moisture transfer. Full article

With the increasing global demand for sustainable energy, energy conservation and efficiency in buildings located in severe cold climate regions have attracted considerable research attention. Conventional exterior wall insulation and energy utilization strategies in such environments often fail to achieve the desired levels of efficiency, energy conservation, and productivity. To address these challenges, this study proposes a thermoelectric power generation–wall system (TEPG–Wall System) designed specifically for prefabricated buildings. The system utilizes Ni₉₀Cr₁₀-Ni₄₅Cu₅₅ thermoelectric material, integrated with a wall collector cavity design, to harness the temperature difference between indoor and outdoor environments for electricity generation. Through software simulations and experimental investigations, the thermoelectric performance of the system under severe cold climate conditions was analyzed. With only 15 parallel devices, the system achieved an average output power of 0.02 W under typical operating conditions, corresponding to an annual energy output of approximately 0.0586 kWh. Such an energy output is sufficient to power low-power building equipment. Full article

This paper presents research concerning simulating the thermal firebrand effect due to its accumulation in exterior construction wall elements by developing a 3D finite element model (FEM) via ABAQUS (2022) software to analyze the exterior walls commonly applied to the exterior of dwellings in southern Europe and South America. A non-linear thermal transient analysis is undertaken, in which the results are directly compared with a previous experimental campaign, in which firebrands are deposited on localized surfaces of construction wall specimens, and the temperature is measured in the several layers of the construction elements. The walls are composite elements, made of different layer combinations of masonry brick and wood, varying the type of thermal insulation in the internal core from cork to classical rigid rockwool and polystyrene foam (XPS). It can be summarized from the results that the FEM effectively simulates the thermal response of brick, normal wood (NW), and cross-laminated timber (CLT) walls when insulated with materials like cork or rockwool coated with mortar against firebrand accumulation. However, the lack of accounting for uncontrolled combustion leads to inconsistent results. Additionally, for walls using XPS as the insulation material, the model requires further refinement to accurately simulate the melting phenomenon and its thermal impact. Full article

With growing concerns over global warming and the significant contribution of buildings to energy consumption, reducing energy demand in buildings has become crucial. This study addresses this issue by investigating the integration of phase-change materials (PCMs) with wall insulation on the inside surface of building exterior walls as a strategy to reduce energy consumption. The methodology involved conducting simulations using OpenStudio and EnergyPlus software to assess the thermal performance and energy savings of this approach. The parameters evaluated include energy consumption reduction, material selection and thickness, cost savings, and payback period. The results show that combining a 100 mm Celotex TB4000 Insulation Board with a 1 cm PCM RT24HC layer can reduce energy consumption by 65.4%, save approximately GBP 1645.67 annually, and achieve a payback period of 13 years. Additionally, the selection of the PCM phase-change temperature, thickness, insulation layer thickness, and indoor temperature settings are crucial to optimizing the combined effect. Based on these results, it is recommended that designers and practitioners consider these factors when conducting pre-retrofit simulations to ensure that PCM-enhanced insulation operates within its optimal temperature range. Full article

The study aimed to investigate the thermal storage potential of oak tree bark as a natural and easily accessible material and to examine the possibility of incorporating this raw material into external prefabricated walls. The U-values of oak tree bark were compared with mineral wool (MW), which is a standardized and well-known insulating material. Oak tree bark, a residual material, is mainly used as an energy source. However, in light of actual green policies at the European Union (EU) level, raw wood and its components, e.g., bark, should be used for long-lasting products and not as an energy source. According to the Croatian Technical Regulation on the Rational Use of Energy and Thermal Insulation in Buildings, the maximum U-value for external walls in Croatia is 0.30 W/m²K. Here presented test results show that the U-values of the experimental wall compositions were 0.22 W/m²K for the wall with mineral wool (MW) and 0.29 W/m²K for the wall with oak tree bark. Despite mineral wool having a thermal conductivity (λ, W/mK) 53% lower than the experimental tree bark, walls with bark fulfill the national insulation requirements; therefore, they present an alternative and sustainable insulation option. Furthermore, the Blower door test (n50 value) of the bungalow was measured to be 3.75 h^−1, proving the potential of tree bark as an alternative eco-friendly insulation material in exterior walls. However, further investigations are necessary in order to create and optimize the panel, its thickness, density, adhesive technology, the size of bark particles, production parameters, etc., as these influence properties of the final product to be placed on the market. Full article

Wood is the most commonly used material for framing single-family houses in the USA, yet alternative materials like Insulated Concrete Forms (ICFs) offer potential advantages in energy efficiency and thermal performance. This study evaluates ICFs as a viable alternative by analyzing the energy performance and indoor temperature stability of five single-family houses in Oklahoma, USA, monitored over 12 months. The sample included a total of five single-family houses: two wood-framed houses with blown fiberglass insulation, one wood-framed house with spray foam insulation in the attic, and two houses with ICF exterior walls. Results demonstrated that ICF houses consumed up to 41% less electricity and at least 5% less natural gas compared to wood-framed houses, with improved indoor temperature stability. Occupants also saved approximately USD 270 annually on energy costs, highlighting the advantage of ICF’s efficiency. This study provides empirical evidence of the benefits of ICF construction, which previously relied heavily on simulations or anecdotal claims. However, findings are limited by the specific geographic focus of the study. Future research should expand on these findings by incorporating a wider range of climates and housing designs to better understand the broader applicability of an ICF as an alternative to conventional wood-framed construction. Full article

Employing thermal insulation in buildings’ exterior walls is an effective technical measure to reduce energy consumption and carbon emissions of buildings. A multi-objective optimization method is presented for exterior wall insulation in buildings based on the equivalent full-load hours-based energy consumption (EFLHEC) prediction method, comprehensive analysis(economic, energy, and carbon emission) models, and assessment indexes. The presented optimization design method consists of an EFLHEC-based energy consumption prediction module, a comprehensive analysis model-based quantitative evaluation module, and a balanced index-based optimal design scheme determination module. Comprehensive analysis models are developed to evaluate economic performance, energy, and carbon emissions of external wall insulation. The balanced index method is extended to cope with economic, energy, and carbon emission factors of buildings’ external wall insulation. The research results showed that the EFLHEC provided an accurate and simple energy consumption prediction method for buildings’ exterior walls. The optimal design scheme was determined by comparing the values of balanced indexes for different design schemes of external wall insulation. Cooling and heating source type had important influences on the optimal insulation layer thicknesses, economic performance, and carbon emissions of external wall insulation in buildings. The largest variations in the balanced index for different types of insulation and different types of cooling and heating sources were 0.14 and 0.41, respectively. The cooling and heating source type should be considered in optimizing the design of external wall insulation in buildings. The best solution was obtained by EPS and natural gas for an office building in Zhengzhou city in China. The presented multi-objective optimization method is very helpful in solving the complex engineering problem of optimizing external wall insulation. Full article

The external walls of a building represent the interface between the interior and exterior environments. Insulating external walls represents the most cost-effective means of ensuring indoor comfort. Despite the prevailing assumption that insulation will increase the cost of the building, this study has demonstrated that this is not the case. Notwithstanding the increase in investment costs, the application of insulation to the external walls has been demonstrated to result in a reduction in fuel consumption and operating costs. In accordance with TS 825, there are five distinct degree-day zones, with the requisite heat loads in these zones exhibiting variability. Accordingly, a cost-based methodology is required to ascertain the optimal insulation thicknesses for the various degree-day zones. In this study, the gains to be obtained in the case of using three different insulation materials for five different wall types to be used in the buildings to be built instead of the buildings destroyed in the earthquake in Turkey in 2023 were analyzed. Samples from three degree-day zones affected by earthquakes were assessed for insulation, wall structures, and fuel types. The study assesses optimum insulation thickness, investment cost, annual fuel savings, annual economic benefits, and investment payback period. Full article