Wall Insulation Research Articles

Evaluation of insulation effectiveness for thermal comfort in summers: experimental and CFD numerical study

ABSTRACT We evaluate the thermal performance of PUF-insulation boards embedded in the roof of an office-sized room. Two rooms were constructed: one with and the other without insulation. The thermal comfort was evaluated by performing an experimental study according to ANSI/ASHRAE Standard 55-2017. The inside air temperature, humidity, wall and ceiling temperatures, air velocities and thermal flux were measured for the summer April–June 2023. Using these measurements, the PMV and PPD values were computed. The effectiveness of the insulation material with regard to thermal comfort is judged by the reduction in values of these indices. During a typical day, a reduction of around 30% is achieved just by adding the insulation. Nusselt number correlations are proposed to predict the convective heat transfer from the walls. Detailed CFD simulations were performed and a parametric study to understand the effect of insulation thickness, wall insulation, roof thickness and room dimensions on thermal comfort was undertaken.

Comprehensive Cost–Energy Evaluation of Wall Insulation for Diverse Orientations and Seasonal Usages

Comprehensive Cost–Energy Evaluation of Wall Insulation for Diverse Orientations and Seasonal Usages

Geopolymer-based insulated wall incorporating construction and demolition waste: Experimental assessment of thermo-physical behavior

The benefit of the application of geopolymers in the building sector is nowadays undisputed. In addition to good structural characteristics, these are characterized by interesting thermophysical properties, obtained through a production process, that reduces CO2 emissions and could incorporate recycled material, thus responding to environmental sustainability. However, it is noted the lack of studies regarding the in-field thermal performance. Thus, the aim of the present study is to investigate the thermal performance, under real conditions, of an innovative geopolymer-based insulated wall. It incorporates over 70% of net weight of Construction and Demolition Waste materials. The wall is conceived within the European project called “Green INSTRUCT” aimed to realize modular prefabricated building elements, for retrofitting and new construction of buildings. Two wall prototypes are analysed, which differ for the type of lightweight aggregate of geopolymer matrix, 3% by weight: expanded polystyrene or extruded polystyrene. The study refers to almost one year of continuous monitoring within a full-scale test room located in southern Italy. The method developed consists of 5 different phases and it involves also a normative-insulated reference wall. The results show higher insulation level of the proposed wall package, with a reduction of the heat flux of about 66% and more stable indoor thermal conditions, compared to the reference wall. Also the inertial properties are satisfactory, showing an experimental decrement factor equal to 0.05 and a time-shift of decrement factor higher than 6 h. All told, the experimental results can provide valuable insights into the real impact of innovative technology on energy efficiency and indoor thermal comfort.

Evaluation of thermal insulation capacity and mechanical performance of a novel low-carbon thermal insulating foam concrete

The use of building insulation materials is an effective measure to reduce building energy consumption. To improve the sustainability of insulation materials, desert sand (DS) was used to replace part of the binder, and rice husk ash (RHA) was incorporated to further improve the performance of foamed concrete. The fresh properties, strengths, thermal properties and thermal insulation function of DS-based foamed concrete (DSFC) were systematically investigated. The use of DS and RHA to replace part of Portland cement (PC) and fly ash reduces the flowability of the mixture when the water/binder (PC, fly ash, DS and RHA) ratio is constant. Although the incorporation of DS into foamed concrete increases its density and thermal conductivity, it improves the volume stability of the sample. The strength of specimen with DS decreases due to the low reactivity of DS, which also reduces the content of hydration products. Further incorporation of RHA not only improves the matrix strength by increasing the C-S-H content but also improves the pore structure of the DSFC by increasing the yield stress of the paste. The joint application of DS and RHA effectively reduces the heat storage coefficient and thermal inertia index of DSFC, which is beneficial to improve the thermal insulation capacity of buildings and reduce energy consumption. Incorporating DS and RHA can effectively improve the environmental and economic benefits of the foamed mixture, and the unit strength cost and carbon emission per cubic meter of the 5%–10% RHA-modified samples are reduced by 20.3%–39.1% and 20.2%–38.9%, respectively, compared with the DS35. This research provides a new approach and theoretical basis for building energy saving and external wall insulation.

A multi-life cycle assessment of external wall insulation strategies in an Irish domestic retrofit

European Union (EU) policy and initiatives are driving both building renovation and the uptake of low-embodied carbon and circular design in the construction sector. The European Performance of Buildings Directive (EPBD) recast (2021) introduces global warming potential (GWP) methodology, and the future state will likely be embodied carbon targets for which life cycle assessment (LCA) of buildings will be required. External wall insulation (EWI) will have an important role to play in meeting targets. In this context, this paper compares the carbon emission payoff of three alternative EWI strategies that address conventional, low-carbon and circular solutions to EWI respectively, in the retrofit of an existing dwelling. The circular strategy is based on design for disassembly (DfD). Whereas standard LCA is based on a single building life cycle, the literature reviewed shows that the environmental impact assessment of DfD requires a multi-life cycle approach. In the absence of standardised methods for assessment, four multi-cycle LCA methods are selected and applied holistically in a case study investigation. Three allocation methods, 100:0, linear degressive (LD) and enhanced linear degressive (CELD), provide a range of emissions from ‘conservative’ to ‘best case’ over three building life cycles and the fourth method, the Van Gulck method, assesses the benefits of circularity through the concept of ‘multi-cycling’ based on one building life cycle. As each method of assessment will deliver different results, carbon emission payoff is not a fixed value. Findings show that with multiple use, the circular strategy pays off due to avoided production emissions and benefits from end-of-life (EoL) processes that DfD facilitates, that the upfront carbon cost of the circular strategy is minor relative to the carbon emission savings that reuse brings, and that the margin of improvement relative to the alternative strategies increases with each subsequent reuse.

Solar PV vacuum glazing (SVG) insulated building facades: Thermal and electrical performances

As fire emergencies and energy saving demand of buildings have grown around the globe, concerns have been raised about the flammability of conventional external insulation materials in cold weather areas. In this paper, solar PV vacuum glazing (SVG) was proposed as a promising alternative to traditional external insulation layers of buildings due to its incombustible nature and superior thermal insulation performance. To assess the thermal and electrical performances of SVG-insulated facades, a heat transfer model and an effective absorptance calculation model for SVG-insulated façades were developed and validated against experimental data. Results showed that SVG-insulated facades exhibited significantly lower U values, ranging from 44.1% to 47.5% less than those of traditional concrete walls (without insulation layer). Additionally, the application of Low-emissivity (Low-e) coatings on the glazing could further reduce the U value from 2.05 W/(m2·K) to 0.647 W/(m2·K), making SVG-insulated facades competitive with traditional insulation walls. The secondary heat transfer factor (SHTF), defined as the ratio of indoor heat gain from solar radiation absorbed by building facades to incident solar radiation, was also reported for SVG-insulated facades with different solar cells (C-si, A-si, and CdTe), along with their respective efficiencies. Parametric analyses of eight parameters subsequently highlighted that their influence on the thermal performance of SVG-insulated façades was much greater than on the solar cell efficiency. Furthermore, considering the combined effect of optimal value of key influencing parameters, the lowest U value of 0.153 W/(m2·K) could be achieved, which represents approximately 24.6% of the U value of traditional insulation walls. This study provides compelling evidence for the adoption of SVG-insulated facades as replacements for traditional insulation walls and offers insights into optimizing their thermal performance.

The role of passive, active, and operational parameters in the relationship between urban heat island effect (UHI) and building energy consumption

The energy performance of buildings located in urban areas is strongly influenced by the UHI phenomenon, which usually leads to higher cooling energy consumption and lower heating energy consumption. Despite the known effects of UHI on building energy consumption, there is a lack of detailed knowledge on the role of building design and operational parameters in determining the effects of UHI on building energy use. To address this knowledge gap, this study analyzes the impacts of UHI on annual, heating, and cooling energy consumption of 16 prototype buildings located in 16 climate zones in the United States. The objective is to determine the relative relevance of building types (e.g., residential, commercial, healthcare facilities etc.), occupancy parameters (e.g., occupancy schedule) and the Heating, Ventilation and Air Conditioning (HVAC) systems in governing the impact of UHI on the building energy use matrices. Additionally, the thermal properties of the building envelope were evaluated to determine their relative importance in mitigating the effects of UHI on building energy performance. We found that, among the studies building types, while the cooling energy use of restaurant and outpatient healthcare buildings was most affected by UHI (higher cooling energy demands), the outpatient healthcare buildings were most impacted by UHI in terms of their heating energy use (lower heating energy use). The selection of HVAC systems type was found to have negligible influence on the energy impacts of UHI. Lastly, with regard to the thermal properties of the building envelope, window insulation was noted to be the most influential thermal property, followed by roof and wall insulation. Also, the role of insulation as well as other thermal properties was higher in the context of UHI’s impact on heating energy consumption as compared to cooling energy consumption. Not only are the results of this study useful for urban planning purposes to determine the vulnerability of different buildings to UHI, but they also are beneficial to UHI-resilient building designs.

The influence of the climate, the materials of the walls, and the gas effects of double and triple-glazed windows in terms of energy evaluation and economic expenses

The computation of heating and cooling loads for office buildings is influenced by the significant population and diverse occupations of the users throughout various time durations. The first step in this investigation involves using specialized software to simulate a model office structure. To improve the thermal insulation of the building's outside covering and the arrangement of the windows, modifications are performed by considering the appropriate assumptions. Furthermore, this study examined samples of double- and triple-glazed windows using argon, xenon, krypton, air, and vacuum as insulating materials. In addition, the thermal efficiency of this construction was evaluated using common wall materials such as Autoclaved Aerated Concrete (AAC), Educational Credential Assessment (ECA), and Cellular Lightweight Concrete (CLC) blocks. This research conducted a comparison and analysis of four different climates, including Canada, Saudi Arabia, Greece, Sweden, and Iran, with the climate of the study location. The aim of this study is to enhance thermal loads and energy efficiency in a simulated construction. The research demonstrates that arranging windows correctly, implementing efficient wall insulation, and ensuring appropriate climatic conditions may result in a reduction in cooling and heating loads by around 4–8 %. Finally, the economic study demonstrates that the time it takes to recoup the investment for different configurations ranges from 2.4 to 9.3 years. In summary, this research provides significant insights on how to decrease energy consumption in buildings and highlights different approaches that architects and engineers could use to build energy-efficient and sustainable structures.

Evaluating building-level parameters for lower-temperature heating readiness: A sampling-based approach to addressing the heterogeneity of Dutch housing stock

The Dutch government aims to eliminate natural gas for residential heating in 1.5 million homes by 2030. One strategy is connecting existing dwellings to lower-temperature district heating (DH) systems, although these dwellings might require energy renovations. The heterogeneous dwelling stock causes varying renovation needs that complicate the energy transition. The present study addresses this issue by assessing the building-level parameters affecting the readiness of the Dutch terraced-intermediate and apartment types for lower-temperature heating (LTH) supplied by DH systems. A sampling-based approach was employed to capture variability within these dwelling types, addressing the limitations of archetype-based methods. The findings suggest a sample size of 1300 to represent the variations in these dwelling types. Parametric simulations and machine learning methods were used to identify significant building-level parameters for medium-temperature (MT: 70/50 °C) and low-temperature (LT: 55/35 °C) supply levels. These include heating setpoints (desired indoor temperature) and ventilation-related parameters (ventilation system type and air infiltration rate), followed by fabric-related parameters (roof, glazing, wall, ground, and door insulation) and geometric properties (orientation, compactness ratio, and window-to-wall ratio). Additionally, radiator oversizing also impacts LTH readiness. These results broadly apply to the studied dwelling types, although feature importance varies by supply temperature and dwelling type. The findings can guide stakeholders in assessing current conditions and prioritising renovation measures, aiding the development of targeted renovation solutions. Encompassing the representative variations within studied dwelling types enhances the robustness of the results. However, incorporating more refined data could improve the accuracy of the findings, better supporting the energy transition of these dwellings.

Thermal Performance and Building Energy Simulation of Precast Insulation Walls in Two Climate Zones

Traditional concrete buildings exhibit low energy consumption and high heat loss, which results in a larger environmental problem. Precast insulation walls are proposed for strengthening thermal insulation efficiency and mitigating heat loss. Numerous studies have investigated the thermal performance of insulation walls over the past decades. However, gaps remain in practical engineering applications. This study aims to bridge these gaps by providing practical design recommendations based on experimental research. Nine different types of precast insulation walls were tested to examine the thermal performance, and the parameters of the insulation material, insulation form, insulation layer thickness, and concrete rib width were investigated. Then, numerical models of these walls were developed for simulating the thermal performance of the tested specimens. Finally, a six-story student apartment model using designed walls was developed to assess energy consumption in two distinct climate zones: the hot summer and cold winter zone of Changsha City, and the cold zone of Harbin City. The results indicate that the precast insulation wall with external insulation form shows better thermal performance than the sandwich insulation form. It is recommended to use precast insulation walls with 50 mm extruded polystyrene (XPS) external thermal insulation form in Changsha City and 80 mm XPS external thermal insulation form in Harbin City. Furthermore, buildings using precast insulation walls can significantly reduce energy consumption by 49.25% in Changsha and 49.38% in Harbin compared to traditional concrete wall buildings. Based on these findings, suitable design suggestions for this precast concrete wall panel building composed of insulation walls are given.

Experimental study on energy saving and thermal insulation of AAC walls and sandwich structures

Autoclaved aerated concrete (AAC) materials are increasingly being recognized as an effective method of improving the thermal efficiency of buildings. This paper uses a bolted AAC sandwich wall with rock wool to measure the indoor temperature enhancement and energy savings achieved by applying AAC and autoclaved aerated concrete sandwich (AACS) to building surfaces without ventilation. In addition, the energy efficiency and insulation of sintered brick (S) walls, AAC walls, and AACS walls in three test rooms are discussed in the fall and winter seasons. The study showed that the average daytime room temperatures of the AAC and AACS walls were reduced by 9.11 % and 14.31 %, and the heat load levelling was reduced by 28.41 % and 46.76 % compared to the S walls. The study concluded that compared to the S wall, AAC and AACS walls were reduced by 0.64 W and 0.8 W, respectively, and CO2 emissions were reduced by 11.78 g/m2day and 14.69 g/m2day.Under the premise that the building life cycle is 50 years, the energy consumption of the building electricity bill is saved by 157.14 RMB/m2 and 195.84 RMB/m2 for AAC wall and AACS wall, respectively, compared with S wall. Therefore, AAC shows a growing trend in the building material market due to its low-carbon insulation, green energy saving, and policy support, and it should be promoted in the construction industry.

Stress grading system optimisation for an inverter‐fed rotating machine

AbstractStress grading systems using non‐linear resistive coatings are a key component to suppress surface corona in the end‐windings of rotating machine. Compared to a sinusoidal‐fed motor, the high slew rate of the voltage at the flanks of the repetitive square voltages from the inverter cause large capacitive currents to flow in the main wall insulation. These large currents, if not properly considered in the design phase, lead to severe electrothermal stress of the grading system. Experiments and simulations were conducted on a stress grading system whose structure arises from limitation posed by the motor structure. Measurements performed with different rise times show that the maximum potential along the conductive armour tape (CAT) increases non‐linearly with increasing axial distance, and the potential at the edge of the CAT reached nearly twice the peak‐to‐peak voltage at 500 ns rise time, leading to corona inception. As metal plates are used in the machine to dampen vibrations in the end‐winding, similar plates were also fastened to the stress grading system, worsening the already inadequate corona suppression performance. The stress grading system was therefore modified, avoiding the surface corona while, at the same time, reducing the temperature in the grading system to acceptable levels.

Hygrothermal performance of multilayer wall assemblies incorporating starch/beet pulp in France

This work focuses on the investigation of the hygrothermal performance of four different wall insulation assemblies including starch/beet pulp composite for an office in France under two climatic conditions. Subsequently, a comparative performance analysis is made on all studied assemblies by substituting the Starch/beet pulp composite with hemp concrete (HC). For each design, the overall energy performance, total water content, drying rate and condensation risk were evaluated through hygrothermal simulations using the WUFI® Plus software and mold growth risk assessment was conducted with WUFI®Bio software. Results showed that insulation assemblies based on Starch/Beet pulp exhibited a slightly improved effectiveness in potential energy savings and higher dryness rate while having a higher condensation risk, a lower dynamic thermal performance, and a higher susceptibility to mold growth risk. Moreover, insulation assemblies based on Starch/Beet pulp demonstrated better hygrothermal performance under Nancy’s climate compared to that of Marseille. Wall assemblies based on hemp concrete reduced total energy consumption by up to 35 % in Nancy’s climate and 24.9 % in Marseille’s climate. In comparison, starch/beet pulp concrete achieved reductions of up to 37.5 % and 26 % respectively. However, the mold growth risk for starch/beet pulp was 1.2–7.2 times higher than for hemp concrete. In Marseille’s climate, this risk was 2.3–8.9 times higher for starch/beet pulp and 4.7–17.8 times higher for hemp concrete compared to Nancy’s climate. The findings from these room-scale studies enhance the understanding of the hygrothermal behavior of the Starch/Beet pulp bio-composite material by comparing its performance, under the same conditions, to that of the well-studied hemp concrete material in the literature. Additionally, these studies provide greater insight into the impact of water on the overall energy consumption, service performance of a building and health hazards. Finally, this research also tackles the challenges of integrating innovative materials into the established construction industry.

Multi-objective optimization of rural residential envelopes in cold regions of China based on performance and economic efficiency

Building envelope renovation solutions are critical to building performance and post-renovation economics. Building renovation is easier to carry out if the impacts of building envelope renovation solutions on building performance and post-renovation economic efficiency can be foreseen and a more sustainable and efficient renovation design can be achieved. This paper explores the optimal design of building envelope renovation using genetic optimization algorithms and statistical analysis methods, taking the performance of the renovated building and the economic efficiency of the renovation solution as the starting points. In Qingdao, a cold region of China, a survey was carried out on typical rural areas in seven regions. The selected design variables include the external wall and roof insulation material type(TWall, TRoof), external wall and roof insulation thickness(δWall, δRoof), type of window construction(TWc), and area radio of the window to the wall(WWR). Minimization of total building energy consumption(E) and renovation cost(COSTRE) and after renovation maximization of the combined incremental cost-benefit ratio over a 20-year life cycle(CICBR20-year life-cycle), effective natural daylighting illuminance(UDI), and percentage of time spent in indoor comfort(PTC) were considered in the optimization of the envelope. The results show that in cold regions, different envelope renovation solutions affect the optimization objectives to different degrees; changing the south-facing window-to-wall ratio(S_WWR) has a bigger effect on E, PTC, and UDI; and choosing different TRoof has a bigger effect on COSTRE and CICBR20-year life-cycle. Renovation of the selected typical rural residence with the optimal solution results in an energy-saving rate(Re) of 53.08 %, an increase of 940.86 h/year in annual indoor comfort hours(HIC) and 377.00 h/year in annual effective natural lighting hours(HUDI).

Construction and Case Analysis of a Comprehensive Evaluation System for Rural Building Energy Consumption from an Energy–Building–Behavior Composite Perspective

A comprehensive evaluation system for rural building energy consumption from an innovative composite perspective was established, suitable for southwest of China. The index system was established by brainstorming and the Delphi method, the weights of the comprehensive evaluation model were calculated by the analytic network process (ANP) method, and the scoring criteria of all evaluation indexes were levelled based on fuzzy evaluation theory. The system model was verified by case analysis, in the countryside around Chengdu Second Circle. Taking into account the highest weight, lowest comprehensive score, and widest range of comprehensive scores, three key factors were identified, namely percentage of clean energy use, thermal performance of exterior walls, and implementation rate of energy-saving measures. The distribution of comprehensive indicators and evaluation factors had certain spatial distribution characteristics, and the overall spatial distribution was characteristically high in the southeast and low in the northwest. Finally, based on key factors and regional distribution characteristics, energy-saving measures are proposed from three aspects: increasing sunrooms, adding wall insulation layers, and standardizing air conditioning temperature settings.

Investigating on thermal insulation in concrete partition wall with insulation-material-infilled Voronoi sections: Feature impact analysis and efficient assessment approach

Reducing energy consumption in building operations, occupying 27 % of total carbon emissions, is crucial for decarbonization. Concrete partition walls with insulation-filled hollow sections, offer high thermal resistance, reducing air conditioning needs. Voronoi pattern represent a space being subdivided into polygonal regions and can be incorporated as the cavity pattern of the hollow section. However, the existing studies on Voronoi sections focus on porosity and pore quantity, with limited research on other feature metrics. This research addresses this gap by quantifying additional feature metrics of Voronoi sections using Bayesian inference, determining their collective influence on insulation. Findings reveal that feature metrics like cavity distribution and standard deviation of cavity areas affect insulation. Additionally, to improve time-consuming simulations, we proposed a model using Graph Neural Networks (GNNs) for accurate and rapid thermal assessments of complex Voronoi sections. Our GNN model, which uses graph-structured data rather than design parameters as training inputs, outperforms another four widely used models, achieving over 85 % prediction accuracy. In this research, two novel approaches are introduced: a Bayesian-based statistical model to understand the relationship between multiple feature metrics and insulation, pinpointing the most promising search space affiliated with certain values ranges of various feature metrics, and a rapid and accurate GNN-based model that uses graph representations of Voronoi sections in building components, preserving detailed geometric information for insulation prediction. Both approaches collectively improve the design process for building components with material-filled Voronoi sections by narrowing the search space and enhancing evaluation efficiency, respectively.

Research on new technology of resource-saving ultra-thin stone curtain wall

Ultra thin stone curtain wall technology is a resource-saving innovation. This article explores the application of ultra-thin stone in building exterior wall decoration, including pasted curtain walls, self insulated walls, AAC walls, and decorative insulation composite board exterior wall insulation systems. This technology has advantages such as thin thickness, light weight, low cost, convenient construction, and excellent self insulation performance. The key construction points include waterproofing, rust prevention treatment, use of high standard adhesives, embedding of steel wire mesh in the plaster layer, and small mortar joint technology. The future development direction should focus on innovation in the production technology of ultra-thin stone panels and new directions for stone products.

Solid and Homogeneous Thermal Wall of Cored Lightweight Concrete Blocks Solidarized in situ

Abstract: The exterior walls of buildings play a major role in the road for a near-zero energy building. Nowadays, in Portugal, the ETICS system is the most used technology to ensure the thermal insulation of exterior walls of buildings. However, the ETICS system has low resistance to impacts and requires a self-supporting sheet of wall, among other disadvantages. Here, the concept of new technology for exterior walls of residential and commercial buildings is presented. It consists of a hybrid technology for the easy and quick execution of a single sheet wall, which may provide high thermal efficiency for buildings. This hybrid technology relates to parallelepipedshaped cored lightweight concrete blocks comprising two parallel sides separated by one or more solid connectors in which the connectors allow the filling of the block core with lightweight concrete. No bed or head joints are used to connect the blocks because the wall made of cored blocks gets solid and homogeneous when filled with lightweight concrete. When the block thickness is 30 cm and the thermal conductivity of the lightweight concrete is lower than 0.09 W/m.ºC, in Portugal, this type of exterior wall does not require the application of extra thermal insulation materials.

Investigation of double-PCM based PV composite wall for power-generation and building insulation: Thermal characteristics and energy consumption prediction

The integration of phase change material (PCM) with building-integrated photovoltaic (BIPV) presents a compelling approach to enhance solar energy utilization and mitigate indoor thermal loads, contributing to energy-efficient and low-carbon building development. Traditional BIPV-PCM structures, however, struggle to balance PV efficiency and thermal insulation, particularly with varying PCM wall positions. To address this situation, this study introduces a novel double-PCM BIPV composite envelope (BIPV-dPCM). An experimentally validated dynamic heat transfer model was developed and used to perform a comparative simulation analysis with three reference systems to quantify the energy-saving potential of the BIPV-dPCM, focusing on PV output and wall insulation effectiveness metrics. Further dimensionless parametric analysis were carried out to investigate the systematic performance of the two PCMs at different relativities. In addition, the coupled working mechanism of the BIPV-dPCM system concerning the power generation performance and thermal insulation performance under transient variations is explored. It was found that the BIPV-dPCM showcases superior thermoelectric coupling performance compared to three alternative enclosures. Incorporating two PCMs significantly enhances electrical exergy efficiency by 11.66 % and thermal exergy efficiency by 1.54 %, surpassing other reference systems. The increase in PCM latent heat ratio has a limited effect on performance gain. Notably, as the PCM thickness ratio exceeds 1, the decline in P value decelerates, for every 0.5 increment in the g, the P value diminishes by merely 0.2 %. The ideal h is identified between 1 and 1.5, with 1.5 being optimal for energy conservation objectives. Additionally, the self-sufficiency coefficient (SSC) of the BIPV-dPCM remains robust, sustaining a range of 55 % to 65 % over prolonged periods. This study offers novel perspectives and serves as a design reference for optimizing building energy systems and enhancing cooling efficiencies in subtropical climates.

Multi-objective optimization of buildings in urban scale for early stage planning and parametric design

Passive design of buildings in early design stage is essential for energy efficiency and sustainability. In this study, a streamlined tool for parametric study and passive design of buildings in urban scale considering thermal loads and natural lighting performance is presented, which markedly enhances the efficiency of early-stage urban planning. The tool is comprised of three sub-models, including (1) degree-month based annual building thermal load prediction model, (2) simplified climate modification model that takes into account the effects of building layout on solar heat gain and urban heat island, (3) multi-objective optimization algorithm NSGA-II, which optimizes both energy-saving and natural lighting performance. Model validation results show that this tool has an average error of 11.44% and 15.82% in simulating building thermal load compared with Dragonfly and CitySim, and has an average error of 9.9% in predicting average daylight factor compared with Radiance. Multiple optimization scenarios and sensitivity analysis in 10 typical climatic cities were conducted. It is found that in cold and hot climatic cities, it is more beneficial to set energy target as the optimization objective, meanwhile, establishing natural lighting as a constraint, rather than solely minimizing thermal loads. In contrast, the inherently lower thermal loads of buildings in milder climatic cities help to achieve both energy-saving and natural lighting goals, and it is also found that the increased thermal loss due to a higher window-to-wall ratio can be offset by employing thicker wall and roof insulation or by improving building layouts.