Thermal Performance Of Windows Research Articles

Comprehensive Investigation of the Thermal Performance of an Electrically Heated Double-Glazed Window: A Theoretical and Experimental Approach

The thermal performance of windows is an important area of research to reduce the energy consumption of buildings and improve indoor comfort. The application of innovative glazing technologies can improve the energy performance of windows and transparent facades, resulting in significant energy savings. This paper presents research results on the energy performance of electrically heated windows. A comprehensive CFD and experimental analysis of the heat transfer processes in a window space depending on the size, power, and location of an electric heater was performed. The convective gas flows in the gas gaps and in the boundary layer were also analysed, and it is shown that a window with an electric heater can reduce the energy consumption of a room by 10–12%. This study is a pilot study to assess the feasibility and cost-effectiveness of electric local heating of a window or facade to minimise heat loss before full-scale implementation. The results of numerical modelling and experimental studies confirm the potential of the new technologies.

Thermal Performance Analysis of Windows, Based on Argon Gas Percentages between Window Glasses

Windows in new buildings in Korea are equipped with double or triple glazing, a low-E coating, and gas injection between the panes of glass, in accordance with the regulations for the reinforced insulation of windows. However, these windows have certain issues, such as thermal transmittance variations and injected gas leakage. In this study, we investigated the current status of double-glazed windows filled with argon gas and analyzed the actual deterioration degree in terms of insulation performance via field experiments and simulations. Accordingly, we manufactured a 26-millimeter low-E double-glazed window test specimen and conducted tests in accordance with the KS F 2278 standard. The test results indicated that the thermal performance decreased by 10.9% when the argon gas filling rate was reduced from 95% to 0%. The simulation results showed that the thermal performance of windows that were insulated using only glazing decreased by 22.6% with the decrease in the argon gas filling rate; the thermal performance of the double-glazed windows also decreased by 13.6%. A comprehensive analysis of the field surveys and simulations predicted a 92% probability that the argon gas filling rate of double-glazed windows would be below 65% by two years after completion, in addition to a ~4.3% decrease in thermal performance.

Thermal improvements of box-window using shading attachments. Hot-box measurements

This research explores shading potential for improving the thermal properties of a box-window. Two different types of shades along with three placements were considered. Ten configurations were tested in a hot-box apparatus and compared to base window performance. Condensation issues that may arise after shading installation were also studied.Measurements showed that shading installed along with the original box-window has a positive impact on the window thermal performance. The highest U-value reduction by 35% (from 1.9 to 1.0 W/m2K) was achieved by a roller-shade with low-emissivity layer and constrained airflow on shade perimeter, installed inside the window recess. Temperature analysis showed a higher risk of condensation on the indoor window surface due to shade introduction on the indoor side of the window.Shading placement within the box-window gave improvements of 34% (reduced U-value from 2.0 to 1.3 W/m2K) for reflective roller-shades placed between the window frames. Shades in this position do not increase the risk of condensation on the indoor surface of the window. The probability of condensation inside the box-window may be lowered by draught-proofing indoor frames and maintaining ventilation through the outdoor frame.Shades proved to be effective at improving the thermal properties of box-windows.

Modeling and analyzing the optical and thermal performance of window with transparent insulation slats

In order to achieve the sustainability of the built environment, extensive efforts have been made to improve the performance of glazed facade systems, thereby increasing indoor comfort and building energy conservation. A kind of window with transparent insulation slats (WTIS) is promising to achieve improved optical and thermal performance. In this study, an optical and thermal model of WTIS was established and the validity of the model was verified by experimental data. The impact of various influential factors on optical and thermal performance of WTIS was analyzed. The results show that the total transmittance decreases and the solar absorptance of transparent insulation slats (TIS) increases with the absorptivity of slat surface (αsl) and the ratio of slat width to the distance between two adjacent slats (W/L ratio). When the slat spacing increases from 10 mm to 25 mm and the slat width is 20 mm, the peak instantaneous heat flux and k-value of WTIS increase by 30.57 % and 17.54 %. When the transmissivity of slat surface increases from 0.1 to 0.7, the peak instantaneous heat flux and k-value of WTIS increase by 25.13 % and 5.31 %. Besides, the variation of shining factor has little effect on the total transmittance and the solar absorptance of TIS. The total transmittance and the solar absorptance of TIS have linear correlation with the proportion of diffuse radiation.

Numerical Simulation of Heat Removal from a Window Slab Partition of a Radiative Coil Coating Oven

In this work, fluid flow and heat transfer performance of a radiative coil coating oven is numerically investigated. In the coil coating oven concept under consideration, porous radiant burners provide the required energy to evaporate the volatile species (solvents) from the applied coating and to promote curing reactions. To avoid the mixing between burners flue gas (with a non-negligible oxygen content) and evaporated (combustible) solvents in the oven (which could lead to a catastrophic oven failure), a semi-transparent window in between both atmospheres is applied. To ensure the window thermal stability during the oven operation, window cooling by wall jets is considered. Different turbulence models were compared against available wall jet heat transfer correlations to select the most suitable for three-dimensional (3D) numerical simulations. Convective heat transfer correlations purposefully developed were embedded in a one-dimensional (1D) window energy model for fast performance characterization, analysing the most influencing parameters—window radiative properties, thickness, inlet temperature and velocity of wall jets, and cooling strategy. The 1D window thermal performance is compared with literature and 3D results considering the full coil coating oven, providing satisfactory confidence on the developed strategy. The 1D model is used for an optimisation study to find the minimum energy consumption while ensuring the safety requirements (maximum window temperature and thermal gradient) are met.

АВТОМАТИЗАЦИЯ РАСЧЕТА ТЕПЛОЗАЩИТНЫХ ХАРАКТЕРИСТИК ОКОН

The use of information modeling tools at all stages of the life cycle of a capital construction object allows you to analyze design information in order to make the most correct decision, while significantly reducing the uncertainty of processes by increasing the amount of data available for analysis. One of the labor-intensive processes at the design stage is the selection of the most suitable structural elements, including translucent structures. As part of the work, the normative and reference information related to the calculation of the heat-shielding characteristics of building structures has been analyzed, scientific developments and publications devoted to the automation of the implementation of heat engineering calculations using various software tools are considered. For the purpose of the study, two indicators were calculated: the normalized value of the reduced heat transfer resistance and the reduced heat transfer resistance of the window. To solve the problem, such automation tools as the Dynamo visual programming tool and the Python programming language were used, with the help of which a script was developed for calculating the thermal performance of windows for use in Autodesk Revit (Autodesk, Inc., USA). As part of the study, it was determined that the combined use of the Dynamo visual programming tool and the Python text programming tool, expanding the functionality of Autodesk Revit, made it possible to automate the task of calculating the reduced heat transfer resistance of a window and the normalized heat transfer resistance, taking into account conditions of a specific construction region.

Parametric Energy Simulation Methods for Solar-NIR Selective Glazing Systems

Solar near-infrared (NIR) selective glazing systems have been proposed by incorporating photothermal effects (PTE) of a nanoparticle film into building windows. From an energy efficiency perspective, the nanoscale PTE forms unique inward-flowing heat by heating up the window interior surface temperature under solar near-infrared, significantly improving the window thermal performance. Also, the PTE-driven solar heat gains are dynamic upon solar radiation and weather conditions. However, the PTE on annual building energy use has not been investigated thoroughly, due to the lack of an accurate and appropriate energy simulation method. In this study, we used the EnergyPlus energy management system to develop a parametric energy model and simulation approach in which a solar-temperature-dependent thermal model was embedded into the parametric energy simulation workflow. Applying this method, we examined the solar near-infrared-dependent PTE-induced thermal performances of glazing systems and their effects on annual heating energy use in representative cold climates (i.e., Zones 4, 5, and 6). The results show that the dynamic model considering the PTE demonstrated more heating energy savings, up to 11.64% in cold climates, as opposed to the baseline model that ignored the PTE. This work presents a method to model and simulate the dynamic thermal performance of windows with PTE.

Optimization of Thermal Performance of Windows in Intermediate Housing in Cold and Dry Climate of Tabriz

Windows in the building are the biggest elements of heat loss through convective heat transfer. The purpose of study is to select appropriate dimensions for windows relative to shell and appropriate glazing for windows, in order to achieve optimal pattern to reduce energy consumption. The research method is based on the simulation and research tool is DesignBuilder software. Therefore, amount of natural gas consumed annually in the studied building was received from the National Iranian Gas Company and then the basic research was modeled by software and after converting unit from kWh to m3 and validating simulation results. In the next step, the range of 20% to 80% of window-to-wall-ratio, types of glazing and window height is considered and through parametric optimization, all conditions in the windows are simulated and analyzed for sensitivity index. The calculations confirm that in an intermediate residential building with a rotation of 12 degrees to the southeast in Tabriz, by reducing window-to-wall-ratio from 50% to 20% and replacing triples-glazed-glazing with a low-emission coating filled with argon gas with a transparent single-glazed glazing and UPVC frame and a canopy with a depth of 48cm and windows height of 1.5m, the heat losses were reduced by 60.34% and 75.24%, respectively.

Optical and thermal performance analysis of aerogel glazing technology in a commercial building of Hong Kong

Abstract Improving the thermal insulation of glazing units is a common strategy of reducing building energy use for spacing cooling. This paper newly examined the application of aerogel glazing technology in Hong Kong by the means of laboratory testing and simulation. Nine prototypes of granular aerogel glazing were selected to examine their optical properties, and the measured optical properties of aerogel were used to calculate the total window thermal performance indices. A typical 40-story commercial office building was chosen for energy simulation to compare the thermal performance of aerogel glazing with different glazing technologies in Hong Kong. The results showed that aerogel glazing could achieve the promising reduction of window heat gain up to 57% and cooling energy up to 8.5% compared with double glazing. The heat insulation performance of aerogel glazing is even better than the double glazing with low-E coating in Hong Kong. Therefore, aerogel glazing can be a good alternative of glazing to comply with the existing local Overall Thermal Transfer Value (OTTV) requirement and to reduce the building energy use for space cooling in Hong Kong and other regions.

Study on the Cooling Effect of Window Gardens

Window gardens are known to provide a window view with psychological and physiological benefits, whether they can be used for passive cooling of buildings remains to be investigated. This paper aims to supplement the impact of window gardens on the thermal performance of windows, walls, and even indoor air temperatures, which previous research has ignored. A field experiment was conducted for two classrooms with integrated planting troughs outside the windows, with and without living plants. The indoor air temperature and the interior surface temperature of the two classrooms were measured on a typical hot summer day, with windows closed and air conditioners switched off. The results show that: Window garden with living plants can not only reduce the average temperature of the indoor air by 1.1 ℃, but also reduce the average temperature of the interior surface of the building envelope by 2.8 ℃, the reduction of interior surface temperature is more obvious, which is due to the formation of a cold bridge. Therefore, Window garden can improve the summer indoor thermal environment in hot summer and warm winter area in China.

A Study on Changes of Window Thermal Performance by Analysis of Physical Test Results in Korea

The interest in zero energy buildings is increasing in South Korea. Zero energy buildings need to save energy by using passive technology. The window performance is important to the thermal insulation of the building. Also, the government regulates the window performance through regulation and standards. However, it is difficult to predict window performance because the components of the window have become complicated due to the various materials used in the glass and frame. Based on window performance standards and regulations, the quality of window performance was managed. In this research, to consider thermal performance in proper window design in South Korea, we confirmed the impact on the thermal performance of the window through various kinds of materials and shapes. The authors also propose a window shape classification and frame calculation method based on actual test results. The authors analyzed the thermal performance data of the windows provided by the Korea Energy Agency and confirmed the change in the thermal performance of the windows by year and by frame material. The average U-value of the window decreased from 2012 to 2015 and maintained similar values until 2017. In 2018, this value was decreased to comply. Also, the authors confirmed the U-value of the windows through actual physical experiments and confirmed the change in thermal performance by the construction of the windows based on the results. The results show, in the case of aluminum windows, the U-value corresponding to Grade 3 (1.4–2.1 W/m2·K) was as high as about 60%. Regarding the analyzed results of the U-values of PVC windows, Grade 3 (U-value of 1.4–2.1 W/m2·K) accounted for about 35%, and Grade 2 (U-value of 1.0–1.4 W/m2·K) for about 29%. This paper also confirmed that the frame U-value of the PVC windows is lower than the frame U-value of the aluminum windows. Therefore, the authors proposed the performance index of the glazing part in PVC and aluminum window design. The results of this research can be used as basic data to identify problems in the method of determining the performance of windows in Korea.

Experimental and numerical evaluation of the crystalline silicon PV window under the climatic conditions in southwest China

Windows integrated with PV can provide electrical energy and control the energy flow (heat and light) through the windows. With the objective of evaluate the potential application of window integrated PV in southwest China, the performance of silicon PV windows was comprehensively studied. A test unit was developed to monitor the performance of window integrated PV, then a validated comprehensive approach integrated with heat transfer, optical, electrical and building simulation model was used to comprehensively evaluate the performance of the window integrated PV under various climatic conditions in southwest China. The effects of the air gap on window thermal performance, window orientation, different window-to-wall ratio and coverage ratio of PV cells are evaluated. It was found that a maximum energy saving could be achieved, when the PV window is installed on the south facing façade with a PV cell coverage ratio of 0,87, air gap of 9 mm between the two glazing panes. It was found that a maximum energy saving of 983 kWh was achieved in Lhasa. A highest energy saving ratio of 83% was found in Kunming. The window integrated PV shows good energy saving potential under different climatic conditions in Southwest China.

Thermal Performance of Window with Vacuum Glazing. Case Study

This document deals with the determination of thermal transmission properties of wood-aluminium window with vacuum glazing. Test measurements are performed with guarded hot-box method at defined temperature difference. They describe how the support pillars influence temperature distribution on the surface and how the edge vacuum glazing influence the heat flow through window. The deformation of the temperature field due to support pillars is surprisingly small and its range is from 0.40 K to 0.51 K with temperature difference on both sides of approximately 33 K. Decrease of internal surface temperature from the middle of glass to the edge is about 18.92 °C – 12.37 °C = 6.55 K, and so it is considerable effect. The effect of the edge on the glazing is not explicitly quantified in the term of heat flow in this document, but is implicitly documented by means of surface temperature. Thermography was used to check if there are touching points between glasses where distance is from 0.15 to 0.2 mm. The vacuum glazing measured in this work was a sample, which was fabricated in Asian producer. The window was tested two years after delivery from the producer.

Thermal performance evaluation of low-income buildings based on indoor temperature performance

In South Korea, about 40,000 buildings of low-income households have been diagnosed and remodeled annually by the Energy Welfare Program, using the normative method. The normative method is based on the heat gain elements of a building. In contrast, the performance-based method is based on the output derived from the thermal performance of each building part. In the normative method, there is no other building in which the input conditions of a building are perfectly matched. Further, cost-effective energy remodeling strategies vary according to the capacity of the diagnosis engineer. In this paper, we analyze the thermal performance of buildings by the performance-based method using indoor temperature, and examine the possibility of a database for the optimal remodeling method. For this, we analyzed more than 2500 simulation cases by combining thermal performance of each building part. The indoor temperature pattern can be similar even when the thermal performance of each building part is different. In buildings with similar indoor temperature patterns, the coefficient of variation of the root mean squared error of energy demand falls within the acceptable error range. Furthermore, changes in energy demand and predicted mean vote are similar when window thermal performance is changed.

Analysis of Window Components Affecting U‐Value Using Thermal Transmittance Test Results and Multiple Linear Regression Analysis

Currently, global warming is accelerating, and many countries are trying to reduce greenhouse emission by enforcing low energy building. And the thermal performance of the windows is one of the factors that greatly influence the heating and cooling energy consumption of buildings. According to the development of the window system, the thermal performance of the windows is greatly improved. There are simulations and tests for window thermal performance evaluation techniques, but both are time consuming and costly. The purpose of this study is to develop a convenient method of predicting U‐value at the window system design stage by multiple linear regression analysis. 532 U‐value test results were collected, and window system components were set as independent values. As a result, the number of windows (single or double) among the components of the window has the greatest effect on the U‐value. In this research, two regression equations for predicting U‐value of window system were suggested, and the estimated standard errors of equations were 0.2569 in single window and 0.2039 in double window.

Optimisation of the thermal and structural performance of an integrated patio door

Frames for glass doors and windows need to be designed to be both thermally insulating and structurally strong, and there are computer programs which accurately determine the required properties. However, these programs are complex and expensive to use and are not useful for initial design work. By identifying the structural and insulating roles of the various layers within the frames we obtain simple results for the thermal transmittance and structural properties of frames. These results can be used for design guidance. More accurate (but still simple) results were obtained and coded in Excel for easy processing. References R. J. Roark ``Formulas for stress and strain'' McGraw-Hill (1965), 4th ed. ``Thermal performance of windows, doors and sharing devices–-Detailed Calculations''. iso 15099:2003(E) ``Thermal performance of windows, doors and shutters–-Calculation of thermal transmittance–-Part 2 Numerical Method for Frames''. bs eniso 10077-2-2003 ``Thermal performance of windows, doors and sharing devices–-Part 1 General''. bs en 10077-1:2006

A CFD study and measurements of double glazing thermal transmittance under downward heat flow conditions

Fenestration systems are important elements of building facades. Although there are fenestrations placed at different angles in facades, not only vertical and roof glazing, there is little information about calculating procedures of thermal resistance and thermal transmittance for reversed glazing in which heat flows in a downward direction. The aim of this paper is to propose some amendments to EN 673–Glass in building – Determination of thermal transmittance (U value) – Calculation method [1] as well as to ISO 15099 – Thermal performance of Windows – Detailed calculations [2] to improve calculation accuracy for glazing under downward heat flow direction. In the paper CFD modeling of glazing thermal transmittance is presented. CFD calculated data were then validated by measurements performed in a calorimetric chamber in a test stand prepared for thermal transmittance measurements under different glazing angles resulting in a downward heat flow direction. Measurement data are then compared to simulation results. After achieving satisfactory agreement, some additional simulation results are presented and some amendments to glazing thermal resistance calculation procedure given in EN 673 and ISO 15099 standards are proposed.

High-Tech Solutions for Building Retrofit: Investigation of Window Systems with Vacuum Glazing

The retrofit of the historical building stock has gained significance due to energy efficiency requirements in the building sector. Major attention is drawn to windows as they are typically the building components with the highest heat transfer coefficient of the building envelope. Therefore, vacuum glazing is a potential option for improving the thermal performance of casement windows. In this context, specific considerations regarding building physics and heritage protection regulations are required.The present contribution describes the current progress of the research project VIG-SYS-RENO. New double glazing products with durable vacuum layer are emerging on the market. Such developments can be regarded as a major step toward energy-efficient windows with U-values close to conventional opaque building elements. Small thickness and excellent thermal resistance of vacuum insulation glazing renders it an attractive option in thermal retrofit of historical buildings. Vacuum glazing systems could potentially offer a feasible balance between conservation and thermal performance of windows. However, prior to any application, a set of aspects and potential issues have to be assessed and explored. These include: (i) thermal bridging effects in different joint positions, for instance the glass edge seal and the frame & wall joint; (ii) the positioning of tight layers in composite or casement windows; (iii) aspects of structural integrity of windows equipped with vacuum glazing. The present contribution structures the different aspects that need to be considered in utilization of vacuum glazing in thermal retrofit, describes applied evaluation methods, first results of the ongoing research project, and illustrates the influence of various rebate depth and length of the edge seal on thermal transmission of the window.

Impact of Growing Conditions of Spruce Wood on Thermal Performance of Windows

In order to eliminate this wood handicap comparing to other material bases, chiefly PVC, which are used for window production, it is inevitable to know the thermal transmittance values of wood grown in Slovakia region, eventually in Czech Republic, to be able to modify the calculated or measured values of window thermal transmittance. Solution for the research problem is documented by the spruce or fir wood example, which are used the most in window production in SR.

Modeling and thermal performance evaluation of a switchable triple glazing exhaust air window

A concept of switchable triple-glazing exhaust air (SEA) window is proposed. The window is characterized by two air cavities with one being a ventilation channel for exhausting indoor air to the ambient. The other cavity is enclosed and, together with the adjacent two glass panes, acts as a conventional double-glazing unit. Venetian blinds are imbedded in the ventilation cavity which is located to the outer side in summer and is switched to the inner side in winter. Such a design makes the window able to reduce its heat loss/gain by utilizing the heat/coolth inherent in the exhaust air. An unsteady state numerical zonal model is developed and validated by comparison with the measured data reported in a published literature. The model is used to calculate the temperatures of the glass layers for evaluating the hourly thermal performance of window. Numerical simulations are carried out to investigate the SEA window, double and triple glazing window at a hot-summer and cold-winter city. Simulation results show that, in comparison with the double and triple glazing windows, the SEA window reduces 73.5% and 71.9% of the heat gain in summer, respectively, and 74% and 46.8% of the heat loss in winter, respectively. Further analysis reveals that the advantageous performance of the SEA window pertains to other orientations. A discussion on the difference of using steady state model and unsteady state model for the window is included.