Envelope Thermal Performance Research Articles

Thermal Performance of the Building Envelope: Original Methods and Advanced Solutions

In the European Union, buildings are responsible for 40% of the final energy demand and approximately 36% of greenhouse gas emissions [...]

Cost Benefits of Net Zero Energy Homes in Australia

This paper presents a systematic analysis of energy savings and cost benefits associated with several options for integrating energy efficiency and renewable energy technologies. The primary goal of this study is to assess the cost-effectiveness of achieving optimal net-zero energy (NZE) designs for residential buildings in Australia. Specifically, the analysis combines a series of sensitivity analyses and multi-objective optimizations to account for a wide range of design strategies for detached homes in four cities representing different Australian climates. The results indicate that not only are NZE designs technically feasible for all the considered Australian cities, but they are also highly cost-effective. This cost-effectiveness is attributed to the lower installation costs of rooftop PV systems as well as the beneficial interactive effects of proven energy efficiency strategies. Indeed, it is found that the deployment costs of rooftop PV systems can be recovered in less than 4 years. Moreover, the addition of thermal insulation in walls and ceilings can reduce both HVAC capacities and annual energy end-use by up to 59%. Based on an optimization-based design, NZE homes in Australia can have lower construction costs and, ultimately, lower life cycle costs than dwellings built to meet current energy efficiency standards based primarily on stringent building envelope thermal performance.

Numerical Evaluation on Thermal Performance of 3D Printed Concrete Walls: The Effects of Lattice Type, Filament Width and Granular Filling Material

Three-dimensional concrete printing (3DCP) is of great interest to scientists and the construction industry to bring automation to structural engineering applications. However, studies on the thermal performance of three-dimensional printed concrete (3DPC) building envelopes are limited, despite their potential to provide a long-term solution to modern construction challenges. This work is a numerical study to examine the impact of infill geometry on 3DPC lattice envelope thermal performance. Three different lattice structures were modeled to have the same thickness and nearly equal contour lengths, voids, and insulation percentages. Additionally, the effects of filament width and the application of granular insulating materials (expanded polystyrene beads and loose-fill perlite) were also studied. Finally, the efficacy of insulation was established. Results show that void area affects the thermal performance of 3DPC envelopes under stagnant air conditions, while web length, filament width, and contact (intersection) area between the webs and face shells affect the thermal behavior when cavities are filled with insulating materials due to thermal bridging. The thermal efficiency of insulation, which shows the effective use of insulation, varies between 26 and 44%, due to thermal bridges.

Producing domestic energy benchmarks using a large disaggregate stock model

Within the UK, domestic buildings account for 16% of total national emissions. Considerable improvements to the performance of the existing building stock will be necessary in the context of the UK’s commitment to emissions reductions, and for this to be achieved successfully and efficiently will require an improved understanding of the current performance of the stock. This paper presents an analysis of metered gas and electricity use from 808,559 dwellings with detailed building characteristic data in London, showing how energy use can be examined using a highly detailed, fully disaggregate building stock model. New gas and electricity benchmarks have been produced for houses (split by the level of attachment) and flats, for both gas- and electrically-heated properties. The paper shows how energy use varies with form, and how the choice of units influences the relative performance of different types. Comparing gas use across the types, for example, when calculated as kWh/m2, consumption follows building compactness, but when calculated as kWh/household, the trends follow building size. Finally, the paper examines how energy use varies with building thermal performance, using the Heat Loss Parameter (HLP), a standardised measure which accounts for thermal transfer through building envelopes as well as via air flow. Practical Application: This paper presents domestic energy consumption benchmarks based on measured not modelled data, produced from a large sample of London houses and flats. Results are shown for different dwelling types and heating fuels. Additionally, the relationship between gas use and envelope thermal performance is explored. The results will hopefully be beneficial for researchers, policy-makers and designers interested in better understanding current domestic energy use, and informing decisions about future improvements to energy efficiency within the stock. This paper also provides details for anyone interested in the production of the domestic benchmarks for the CIBSE benchmarking tool.

EXPERIMENTAL AND COMPUTATIONAL STUDY ON THERMAL PERFORMANCE OF WOOD-PLASTIC COMPOSITES IN BUILDING ENVELOPE

Wood-plastic composites (WPCs) are attractive material for enhancing thermal performance of buildings by acting as an insulation surface. A fast and reliable experimental method was devised using a simple quasi-steady heating film (QSHF) method to measure the thermal conductivity of locally manufactured WPCs in Kuwait. QSHF used two blocks of standard materials compared with the classic methods, although it does not require a fixed constant heating source nor a cooling source. QSHF had a 10 cm × 10 cm × 0.5 mm silicon heating film controlled by a temperature controller and several transparent acrylic square blocks of the same size with 10 mm thickness as the standard materials. The top surface of the WPC samples was the cold side of the system, which is open to indoor temperatures of 22-23°C. The bottom layer can be maintained at any desirable temperature ranges from 25° to 55°C using the heating film to simulate the real outdoor environment. The thermal conductivities of locally manufactured WPCs type, namely FB16, FB18W, CD, and TD, were 0.0912, 0.1174, 0.3453, and 0.3078 W/m.K, respectively, obtained within 1 to 3 hours, which all fall below the standard value of 0.414 W/(m<sup>2</sup>.K) for composite walls and 0.1-0.2 W/m.K for wood. Multiphysics CFD simulation for DP45 sample and TRNSYS simulation for FB18W WPC in the building envelop were conducted which showed strong 2D effects and 3.3&#37: reduction in maximum cooling load in Kuwait, respectively.

Infrared thermography application for in-situ determination of the building envelope thermal performance

During the phase of creating energy audit documentation, many calculations are needed when evaluating the thermal performance of building envelope components due to a large number of distinct components and junctions. Several computer programs are available to assess buildings’ energy consumption, using the thermal performance of building envelope elements as input data. These thermal performances are often provided with varying degrees of accuracy, typically only for the current field of the component, without considering the impact of thermal bridges. However, when using linear heat transfer coefficients ψ, the details provided in thermal bridges’ atlases do not cover all the case studies encountered in the current design, which often requires approximate details. In some cases, the technical documentation of the building is unavailable, which leads to various assumptions about the detailing of the building envelope and a non-realistic picture of the energy performance of the assessed building. The paper presents a methodology and accompanying software called THERMOG that evaluates the thermal performance of the building envelope under actual operating conditions using aerial and terrestrial thermography methods. The paper presents initial findings from some case studies used to calibrate the developed methodology.

Thermal performance of residential and non-residential sectors: describing differences and understanding underlying reasons

This paper presents a comparative analysis of thermal performance and heating demand for selected residential (single-family houses, SFHs and multi-family houses, MFHs) and non-residential sectors (Offices and Schools). The thermal performance and space heating demand of the Swiss building stock were analysed by a bottom-up element-based archetypal model. SFHs are characterised by the best envelope thermal performance (average envelope U-value = 0.62 W/(m2K)), followed by MFH (0.73 W/(m2K)), Schools (0.75 W/(m2K)), and Offices (0.84 W/(m2K). Results show significant differences regarding architectural features between building sectors: SFHs are characterised by the highest envelope factor (median value = 2.00), defined as the ratio between external surfaces and heated area, followed by Schools (1.50), MFH (1.30), and Offices (1.25). As a consequence of the above-mentioned differences, SFHs show higher specific final energy demand for space heating (on average 148 kWh/(m2year)), followed by Schools (117 kWh/(m2year)), Offices (100 kWh/(m2year)), and MFH (93 kWh/(m2year)). Moreover, a high potential for decarbonisation of heating systems in the Swiss building stock was identified: more than 70% of the ERA is heated by fossil fuel-based heating systems, with some differences amongst the studied sectors. This analysis serves as an important starting point to examine possible retrofit pathways and policies across sectors.

Development of an Energy Rating Tool for Australian Existing Housing

Australia aims to achieve net-zero emissions by 2050, and its building sector needs rapid change. The Nationwide House Energy Rating Scheme (NatHERS) is supported by the Australian Government to expand the current building envelope thermal performance energy star rating to a whole-of-home (WoH) energy rating. The NatHERS Administrator supports CSIRO to develop a benchmark WoH energy rating tool for new and existing housing, respectively. The tool for new housing was released in June 2023. This study presents the tool development for Australian existing housing. A case study was conducted using the tool for the eight capital cities of Australian states and territories. It shows that with a detached house built in the 1900s being updated to six or more stars and replacing old equipment and appliances with high-energy-efficient ones, more than 50% of energy can be saved in all the eight cities. To be zero-energy (carbon) housing, 5 kW solar PV needs be installed in Darwin and Hobart, 4 kW in Melbourne and Canberra, 3.5 kW in Adelaide and Sydney, and 3 kW in Brisbane and Perth. It demonstrates that this tool can be used for housing retrofitting to be low/zero-carbon emissions and low operational cost.

A New Method of Building Envelope Thermal Performance Evaluation Considering Window–Wall Correlation

This study proposes a new method to accurately evaluate the overall building envelope thermal performance considering the window–wall correlation, providing a new tool for building thermal design. Firstly, a non-stationary room heat transfer model is established based on the Resistance-Capacity Network method. The influence of solar heat gain through the windows on the heat transfer process of the walls in the actual environment is considered, and the room’s integrated thermal resistance and integrated heat capacity indexes describing the overall room thermal resilience performance are proposed. Then, a field research test is conducted around Lhasa to obtain the local dwelling information, climate conditions, and indoor thermal environment. Numerical simulations using EnergyPlus are made to verify the effectiveness of the indexes in describing the overall building (maximum difference within 3.67% MBE and 2.92% CVRMSE) based on the field test results. Finally, the proposed envelope thermal performance index is used to analyze the local residential buildings around Lhasa. The results show that the lack of consideration of window–wall correlation has led to the failure of a local newly built building’s actual envelope performance to meet the design requirements. These findings could help to develop the thermal design method of the building envelope.

Feasibility Analysis of Nearly Zero-Energy Building Design Oriented to the Optimization of Thermal Performance Parameters

The effective control and reduction of building energy consumption are major global focuses. The building sector is responsible for over 40% of all direct and indirect CO2 emissions. Nearly zero-energy buildings have been the subject of aims and regulations from several developed nations. An office building located in the severe cold region of China was chosen for this case study. The building was equipped with multiple NZEB technologies. Building indoor environment parameters and energy efficiency indexes were used as performance targets, and a performance-based design approach was used to optimize building design parameters. Thermal performance of the building envelope, airtightness, energy demand, and indoor thermal environment were tested according to different evaluation criteria. The total energy demand was as low as 53.93 KWh/(m2·a), and this can be attributed to the exceptional insulation of the building. In this test, the indoor thermal environment comfort was satisfactory. This study can be used as a reference for the design and evaluation of low-carbon buildings and low-energy buildings.

Prediction of urban residential energy consumption intensity in China toward 2060 under regional development scenarios

With global commitments to carbon neutrality, restraining the rapid growth of building energy consumption becomes crucial. Several building energy consumption predictions for China were conducted, but the regional heterogeneity and urban residentials’ special characteristics were not considered in these models. Thus, a “bottom-up” physical model with regional scenario assumptions was proposed for existing, newly-built, and renovated urban residential energy consumption prediction in five building thermal zones in China. Large-scale investigations were conducted for regional energy-use status and energy-use-related advanced technology development status both in China and developed countries. Regarding building envelope thermal properties, types, possession quantities, and performance of energy-use equipment, occupant energy-use behavior, and renewable energy utilization, Benchmark (B), Medium control (M), and Strict control (S) scenarios were assumed considering the spatial differences among each zone and temporal difference between 2020 and 2060. Results showed fluctuating trends, but all zones peak in 2035 under the B scenario, and before 2025 under the M and S scenarios. The intensity for newly-built urban residentials under the S scenarios in Severe cold, Cold, Hot Summer and Cold Winter, Hot Summer and Warm Winter, and Mild zones by 2060 are 4.07 kgce/(m2·a), 6.8 kgce/(m2·a), 6.53 kgce/(m2·a), 6.5 kgce/(m2·a), and 5.21 kgce/(m2·a), respectively.

Thermal performance of double-layer pipe-embedded envelope with low-grade energy for heating

Heat dissipation through a non-transparent envelope contributes significantly to the heating load during winter. The traditional single-layer pipe-embedded external wall (SPEW) can utilize low-grade energy to reduce the heat transfer through the envelope but can hardly be used for direct room heating. This study proposes a double-layer pipe-embedded external wall (DPEW) to utilize low-temperature hot water to reduce heat loss and provide indoor heating in winter. A numerical model of DPEW is developed to analyze its heat transfer performance. After experimental validations, the model is used to investigate the heat transfer performance of DPEW with different water temperatures, ambient temperatures, and envelope structures. The results show that (1) for the outer pipes of DPEW, water with a temperature lower than the room temperature (e.g., 12 °C) can be employed to reduce heat loss through the wall; for inner pipes of DPEW, water with a temperature slightly higher than the room temperature (e.g., 22 °C) can be employed for direct room heating; (2) the insulation layer thickness of the DPEW can be reduced to be significantly smaller than that of a conventional wall; an insulation layer between the two layers of embedded pipes is necessary to reduce heat transfer between water pipes; (3) the effect of water temperature on the heating capacity of DPEW is more significant than that of ambient temperature; increasing the pipe diameter and decreasing the pipe spacing can improve the heating capacity of DPEW.

The Energy Saving Renovation of Regional Buildings Based on Bayesian Estimation

With China's new urbanization vision and existing urban renewal and building energy efficiency improvement project, large-scale energy conservation renovation of regional buildings has become an important content of ecological environmental protection and low-carbon and an important means to improve the regional energy efficiency level. Of energy-saving reform foundation database is presented in this paper, including construction, power consumption, equipment, operation, technology and willingness to word stock, statistics obtained the regional energy complex parameter (envelope thermal performance, elevator equipment, power and efficiency of cooling and heat sources, etc.) statistical rule and can use the benchmark, build the regional buildings energy consumption prediction model based on bayesian estimation, The probability matrix of large-scale reconstruction of regional buildings is obtained. At the same time, the global sensitive parameter analysis method and the single parameter regression model of energy saving transformation factor are established, and it is found that the internal load factor has the most significant effect on energy consumption. By adjusting energy parameters, the probability distribution curve of energy saving and the distribution of normalized value under the constraint conditions of different reconstruction scenarios were simulated, and the discrete MC simulation method was used to predict the regional overall energy saving reconstruction based on renovation intention, which could realize the trade-off judgment and gradual optimization of the strategy package of energy saving measures combination.

Research on Envelope Thermal Performance of Ultra-Low Energy Rural Residential Buildings in China

Rural energy consumption plays an important role in energy consumption due to the improvement of rural residents’ living quality requirements in China. Ultra-low energy rural residential buildings are proposed to decrease rural energy consumption. First of all, this paper aims to provide the definition of ultra-low energy rural residential buildings, which is to reduce 50% of the building energy consumption of the rural residential benchmark building according to the Chinese standard for energy efficiency of rural residential buildings. Secondly, this paper presents the heat transfer coefficients of building envelopes of ultra-low energy rural residential buildings in the severe cold zone, cold zone and hot summer and cold winter zone in China. Based on optimized design and simulation analysis, the heat transfer coefficients of building envelopes are determined by the construction cost, energy efficiency and retrofit feasibility. Thirdly, the suitable combination of a high-performance external wall and internal wall is recommended based on carbon emission and cost efficiency. As an achievement, a technical specification for ultra-low energy rural buildings has been proposed by the China Academy of Building Research. It is beneficial to design ultra-low energy rural residential buildings in China and other countries.

Simplified Model of Heat Load Prediction and Its Application in Estimation of Building Envelope Thermal Performance

This study provides a reference for estimating the building envelope thermal performance at the initial stage of design for nearly zero-energy buildings in different climate zones. A simplified model of heat load prediction, which combines the quasi-steady-state thermal balance calculation procedure in ISO 52016 and the variable-base degree-days method, was proposed. Therefore, a building energy performance evaluation tool BPT V1.0 was developed. Subsequently, the simplified model was validated through comparative analysis with the Building Energy Simulation Test (BESTEST) standard procedure. To conduct a feasibility analysis of the development tool, case studies were performed on the performance evaluation of building envelopes of residential and office buildings in different climate zones in China. Compared to the simulation results from EnergyPlus, the deviation of heat load calculated by BPT V1.0 was within 10%, which further verifies the applicability of the tool under different climatic conditions. Annual heat load under different thermal performance building envelopes was calculated through BPT V1.0. The building energy efficiency improvement rates were found to range from 30 to 60% in nearly zero-energy buildings in different climate zones in China. The study results can provide a reference for energy managers and a basis for estimating the building energy efficiency performance with different envelope thermal properties in the region.

Challenges and opportunities in quantitative aerial thermography of building envelopes

The use of small unmanned aerial vehicles (UAVs) equipped with an infrared (IR) camera has created opportunities for qualitative and quantitative thermal assessments of building envelopes. However, it is currently unclear how successful this method is at quantifying heat losses through the building envelope. The inconsistency in findings indicates that sources of error that affect the accuracy of surface temperature measurements are not well understood by thermographers and that recommendations to minimize the errors in aerial thermography measurements have yet to be determined. In this study, laboratory and field experiments were conducted to investigate the scientific reasons for discrepancies between aerial (i.e. dynamic) and conventional stationary infrared thermography (IRT) observations. A set of practical approaches were presented to minimize the sources of error in UAV-IRT measurement. The results of field experiments showed a non-linear and dramatic variation of measured surface temperature during flight, where the deviations of results between dynamic and stationary thermography were beyond the manufacturer-reported accuracy of ±5 °C. Additionally, the results indicated that induced convection from drone propellers affects microbolometer stabilization with surrounding environmental conditions, which significantly influences the IR camera measurement accuracy. Finally, subsequent investigations utilized a shield around the camera to minimize the convective turbulence on the lens and thermal sensors, successfully achieving temperature deviations of less than 1 °C. These findings may inform manufacturers about the limitations of current IR camera technology during aerial surveys and therefore provide opportunities to define a more robust thermal imaging protocol for the quantification of building envelope thermal performance.

OTTV'S Assessment on Thermal Performance of High-Rise Apartment Buildings in Penang

This study evaluates the envelope thermal performance of high-rise apartment buildings in Malaysia, which are being largely dominated due to the high economic development and increased population. The evaluation was conducted using the Overall Thermal Transfer Value (OTTV), which is the key tool used in the Green Building Index to assess the Energy Efficiency of buildings. Different high-rise apartment buildings were selected with different architecture styles, to account for several periods of building construction. The OTTV value was calculated for the west-oriented façade of the selected buildings, which is considered as a critical orientation that receives high solar radiation. The results showed that four out of the five investigated buildings achieved the minimum requirements for the OTTV, i.e., less than 50 W/m². The maximum and minimum OTTV values with the buildings’ original design were 82.60 W/m² and 41.54 W/m², respectively. However, one of the buildings achieved a lower OTTV value with the installation of shading devices by the owners, i.e., decreased from 48.39 W/m² to 37.60 W/m². The solar radiation penetration through the fenestration was found to be the major contributor to the total OTTV, while it can be controlled by the shading devices. Besides, using dark paints increased the heat conduction through the opaque walls by more than double compared to light paints. This study shows that some design considerations, such as paint colour, shading devices, and glazing material, can have a great influence on the heat gain in buildings.

Development of a short duration method to assess the envelope thermal performance of multi-family housings

Development of a short duration method to assess the envelope thermal performance of multi-family housings

Envelope design for thermal performance in residential buildings under hot arid climate conditions

In a typical hot arid climate, heat gains throughout the building envelope are responsible for more than 70% of the total thermal load. Furthermore, the thermal behavior of a building depends on the formal and constructive choices implemented in the envelope design. Since the envelope is exposed to outdoor conditions, it is crucial to give a major interest to the thermal characteristics of its structural components (i.e., walls, roof and windows). These elements are in charge of thermal exchanges between the building and its environment that occurs by heat transmission, thermal heat storage, solar heat gain and air infiltration. In return, implementing proper climatic responsive design strategies could potentially improve the envelope thermal performance while significantly reducing the building’s energy needs. The present study addresses the thermal behavior of the envelope under hot arid climate conditions by focusing on residential buildings. The research was conductuted in the city of Biskra (Algeria); it deals with the thermal investigation of the urban individual self-produced houses as the most widespread housing type in Ageria. The study explores the potential of improving the climatic adaptability of the envelope while respecting the specific characteristics of this self-produced dwelling. To achieve this goal, optimization scenarios of the building envelope were examined by implementing a set of selected passive design strategies. The process of optimisation was initiated by performing a simulation using TRNSYS 17 software, followed by a sensitivity analysis of the envelope design elements relating to their material characteristics (architectural and constructive to evaluate their effect in regulating indoor air temperatures and providing comfort condition. The results demonstrate significant improvements in the thermal responsive of the envelope and a consequent decrease in indoor temperatures. Moreover, the study defines the most prominent strategies in the process of optimization of the envelope. Accordingly, using suitable constructive systems and materials for walls and roofs in addition to adequate orientation and judicious ratios of openings, while implementing insulation and exterior light colors found to be the most efficient design strategies.

Building-integrated photovoltaics in hot climates: Experimental study of CIGS and c-Si modules in BIPV ventilated facades

Buildings, especially mid- and high-rise ones, offer the opportunity to incorporate Photovoltaics (PV) on their vertical surfaces in addition to their roofs. This is achieved through Building Integrated Photovoltaic (BIPV) solutions. Ventilated facades in buildings can facilitate PV integration and improve the envelope's thermal performance. However, research on BIPV ventilated façades is lacking in the Gulf and MENA regions. Considering the area's harsh climate, investigating these facades is critical. Therefore, the authors of this paper conducted comparative experimental research on the energy performance of BIPV ventilated facades in the hot climate of Dubai. For a year, they monitored the energy yield and temperatures of Copper Indium Gallium Selenide (CIGS) and monocrystalline silicon (c-Si) modules on the south, east, and west facades. In addition, the study analyzed the effect of the modules' characteristics, orientation, temperature, and solar angle on the energy yield. Despite the hot temperatures, the monthly area-normalized energy yields of the c-Si modules were consistently higher than the CIGS modules across all orientations, with an average difference of 13.6%. The modules in the south facade produced the highest annual yield. Also, from October to February (the coolest period), the energy yield of the south modules surpassed the east and west modules by 41.6% and 48.5%, respectively. However, from April to August (the highest energy demand period), the east and west energy yield exceeded the south by 40.9% and 32.5%, respectively. In addition, the west-facing modules experienced higher temperatures than those in the east, resulting in an average of 12% lower energy yields. Hence, the east façade has performed the second best. The west façade production, nevertheless, closely coincides with Dubai's peak periods curve. Thus, the combination of modules on the west and south facades achieved the strongest generation-consumption correlation.