Energy 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.

Passive Window Energy Performance in Buildings: Modeling of Apartment Buildings in Indonesia

Along with urban growth in urban areas and energy consumption, which continues to increase every year, the selection of windows in the initial design is essential to obtain buildings that are not energy intensive. Selecting the correct window in the blueprint design reduces building energy consumption. Smart windows, especially thermochromic windows, are one of the most promising window technologies because they are the most economical and have passive control with zero energy input, which holds good promise for energy-saving applications. Apart from that, double-glazing windows are also frequently used in energy-saving applications. Therefore, a study compared the energy-saving potential of thermochromic and double-glazing windows to clear glass windows, using computer modeling through EnergyPlus, in high-rise apartment buildings in cities throughout Indonesia's diverse climates. From the modeling results, total energy consumption can be reduced by around 8.91% to 10.96% of total building energy consumption by replacing the conventional clear glass with double-glazing windows or more able to reduce about 20.22% to 24.19% by replacing the conventional clear glass with thermochromic windows. Furthermore, this potential varies depending on geometric shapes, materials, building facades, local climate, and building orientation. Nevertheless, considering the potential benefits, these windows are highly suitable for application in buildings seeking to reduce their energy consumption and improve energy efficiency.

Evaluation of Numerical Methods for Predicting the Energy Performance of Windows

Windows are important structural components that determine the energy efficiency of buildings. A significant parameter in windows technology is the overall heat transfer coefficient, U. This paper analyzes the methods of numerical determination of the U-value, including for windows that use passive technologies to improve thermal performance. The analysis was intended to evaluate the heat flux and temperature distribution across glazed surfaces and the accuracy of traditional approaches to the determination of heat loss through window structures. The results were obtained using the heat flux measurement method described in the international standard ISO 9869-1:2014. The paper shows that the non-uniformity of the heat flux density on a window surface can be as high as 60%, which in turn generates an error in the calculations based on stationary heat transfer conditions.

Experimental and numerical analysis of the energy performance of building windows with solar NIR-driven plasmonic photothermal effects

Thin films made of metallic nanoparticles can exhibit strong photothermal effects (PPE) on near-infrared light irradiation, paving a way for new designs of spectrally selective building windows for solar infrared modulation that operates without the need to compensate for visible transmittance. More importantly, the surface plasmon-induced light-to-heat conversion creates strong localized heating effects with a much smaller fraction resulting in the heating of the substrate. Incorporating such nanoscale PPE into the design of complex building fenestrations, this research conducted a comprehensive analysis to better understand the PPE-induced heating effect and conductive, convective, and radiative heat exchanges between windowpane surfaces and the surrounding indoor and outdoor environments. The authors first developed and then validated a numerical analysis method to incorporate spectral features, solar spectral irradiance, and nanoscale PPE. Subsequently, using the established numerical method, two-dimensional windowpane temperature profiles and solar heat gains were yielded under different boundary conditions. To understand the energy performance of windows with solar near-infrared-dependent PPE, a series of parametric energy simulations was employed. The results show the photothermal coating can be used as a new energy-efficient retrofit technology for single-pane windows, with heating energy saving 16.2–20.8%, which performs similar to the double pane windows. Notably, these energy savings were not achieved by increasing the thermal insulation via additional layers or insulating materials, but rather by the spectrally selective design of glazing materials and utilization of solar near-infrared energy. This work presents the energy saving mechanism on an architectural scale due to the nanoscale surface plasmon-induced photothermal effect and associated heat gain coefficient enhancement. It also poses a fundamental reference for the future integration of this novel nanoscale phenomenon into the building envelope systems.

A Comparative Analysys of Window Energy Performance According to the Difference Between Actual size and Standard size

A Comparative Analysys of Window Energy Performance According to the Difference Between Actual size and Standard size

창호 에너지소비효율등급제에 따른 공동주택의 열성능 평가

The Korean fenestration energy consumption efficiency rating system only considers thermal performance of the heat transfer coefficient (U-value) and airtightness excluding optical characteristics of the solar heat gain coefficient (SHGC). This study analyzed annual heating and cooling energy requirements on the middle floor of apartment by optical and thermal performance of windows to evaluate the suitability of the rating system. One hundred and twenty-eight windows were analyzed using THERM and WINDOW 7.4, and energy simulation for a reference model of an apartment house facing south was performed using TRNSYS 17. The results showed that window performance was the main factor in the heating and cooling load. The heating load of the reference model was 539 kWh to 2,022 kW, and the cooling load was 376 kWh to 1,443 kWh. The coefficient of determination (R2) of the heating and cooling loads driven from the SHGC were 0.7437 and 0.9869, which are more compatible than those from the U-value, 0.0558 and 0.4781. Therefore, it is not reasonable to evaluate the energy performance of windows using only the U-value, and the Korean fenestration energy consumption efficiency rating system requires a new evaluation standard, including SHGC.

Roadmap for improving roof and façade windows in nearly zero-energy houses in Europe

Windows are central for the development of liveable nearly zero-energy homes and require careful consideration. Various studies have indicated that the effect of windows on energy consumption may change significantly with improved building insulation levels. Current guidelines on windows may therefore not apply in very well-insulated buildings, and more up-to-date information is needed about window solutions that are appropriate for the new conditions. This study maps the effect of multiple combinations of window size and basic glazing—and frame properties on energy, daylighting and thermal comfort in nearly zero-energy houses located in the European cities Rome and Copenhagen. The aim was to identify options that can support the easy and robust design of future homes with typical use of roof and façade windows. Hourly daylight levels were calculated in DAYSIM, while space heating demand and operative temperatures were calculated in EnergyPlus. The results support previous findings on the limited ability of nearly zero-energy buildings to utilise solar gains. It was found that U-values are becoming increasingly important for the energy performance of windows. The paper sketches the increased flexibility and related possibilities that may appear with improved roof window frame constructions and glazing U-values far lower than currently standard levels.

Optimization of Energy Performance of Windows by Applying Self-Adjustable Shadings

The paper studied the thermo-physical properties of the windows with self-adjustable jalousie and consequent cooling load reduction for the buildings in 60-degree North latitude throughout the year. We focused on using different types of innovative materials and window structures and specified possible ways of improvement for modern and conservative windows. The paper discussed main factors that induce choosing specific window type. First, we investigated quantity of solar radiation energy that is taken into account while calculating the cooling load. Then this dependence was analyzed with different scenarios for specific window structures facing to corresponding cardinal direction. The results provide useful information for optimizing the thermal response of an enclosure to periodic solar heat gains.

Energy performance of windows in office buildings considering daylight integration and visual comfort in hot climates

In hot climates, the exterior envelope of office buildings can significantly contribute to the building's energy consumption. Windows are considered as a major source of heat gain and can contribute to the reduction of energy when daylighting is integrated with artificial lighting. However, with daylighting, the possibility of visual discomfort is likely to arise due to the uncontrolled light. The present study focuses on investigating the energy savings when daylight and artificial light are integrated while maintaining visual comfort. In order to assess visual comfort, both glare index and DaylightFactor are studied. A typical office in a hot climate is modeled using the simulation program, DesignBuilder. We predict the energy and visual performance for three different types of glazed windows. For all types of modeled windows a significant reduction in the annual cooling and building energy consumption was observed. For example, a 14% reduction in total building energy consumption was obtained with daylight integration for the double-glazed clear glass windows and a 16% reduction was obtained for double-glazed low-E windows. It has been observed that in all cases visual comfort was not achieved. By employing automatic interior shading control, visual comfort was achieved with no significant reduction in energy savings.

Energy performance of windows under climate change in Turkey

Windows are one of the thermally weakest parts of a building envelope and climate change is becoming an increasingly important parameter in evaluating the energy performance of buildings. This study investigated the effect of various window configurations on the energy behaviour of school buildings in three cities in Turkey based on climate change, orientation, glazing type and window size. Detailed parametric simulations were used and the results were compared in accordance with ISO 18292. The simulations indicate that the contribution of windows to cooling loads is highest when the value of the solar heat gain coefficient (SHGC) is high and its contribution increases due to climate change. The U-value of glazing is not as significant as the value of the SHGC for cooling. Orientation and window size are other important parameters that affect the energy performance of windows. In addition, in terms of energy costs and performance, it is more efficient for a building to be orientated in south or north directions.

The energy performance of windows in Mediterranean regions

The paper focuses on the assessment of the windows’ contribution to the energy performance of buildings in the warmer regions of Europe. This is derived by calculating the cooling energy index qc and the area weighted energy needs for different window configurations installed on a reference room for two different building uses, office and residential. The examined window types differed with regard to their thermophysical and optical properties (U- and g-value), geometry (frame and window fractions) and orientations. The energy parameters used for the performance assessment were calculated with the help of a dynamic simulation tool for a location with a representative Mediterranean climate. The extensive multi-parametric analysis exhibited interesting results. It was found that for the cooling mode the energy performance of windows in warm climates is influenced significantly by their thermophysical properties. More specifically, the impact of solar transmittance is significant and its optimal selection can contribute in minimizing the energy consumption, especially in environments with controlled ventilation, such as offices. On the contrary, advanced fenestration products with low thermal transmittance seem to behave unfavorably, since their extremely low thermal transmittance prohibits the dissipation of heat toward the ambient environment and results ultimately in higher cooling energy loads.

Energy balance calculation of window glazings in the northern latitudes using long-term measured climatic data

This article examines long-term patterns in energy performance of windows. It presents energy balance calculation results of window glazings in cardinal directions in the Estonian climate representing the Nordic climate in general. Measured climate input data of 43years were used in addition to standard energy calculation years. The energy balance of five different glazing types was compared during the heating period of October to March. Calculations were made according to the EU standard ISO 13 790. It was found that southern facing glazings with reduced solar to thermal transmittance ratio higher than 0.63m2K/W can have positive energy balance over the sum of the heating period. Two of the selected glazings exceeded this level and achieved positive energy balance over the heating period in all years. On the other hand, glazings in the other cardinal directions predominantly were found to experience negative mean energy balance over the sum of the heating period. In the maximization of energy and economic efficiency, this sends the message to architects that, under certain conditions, optimization constraints are more important in some cardinal directions than in others. Such results support scientifically-informed decision making by practitioners at early design stages, for optimal energy efficiency.

Windows thermal resistance: Infrared thermography aided comparative analysis among finite volumes simulations and experimental methods

The correct estimation of the energy performance of windows represents a fundamental issue in the buildings heat losses assessment, since both accuracy and simplicity requirements have to be fulfilled.The most common approaches proposed consist of finite element simulations and laboratory measurements. The reliability of numerical methods results is still an open issue: the general policy of Standards requires for the calculated values to be on the safer side but it is not clear if this assumption is always verified and which is the difference between measured and simulated values. Standards allow the implementation of numerical simulations also in a two-dimensional domain, while windows are composed by zones with a definite three-dimensional geometry such as corners.Two types of windows (wood and aluminum framed) were analyzed, showing that the difference between two-dimensional and three-dimensional simulations is not so high to justify the vast difference that exists instead in terms of calculation time.By means of a hot box apparatus, a comparison term was given to evaluate the finite volumes method adherence to the experimental values. Infrared thermography gives the possibility of a better understanding of the differences between the simulation results and the measured values.The experimental measurements indicated a good data coincidence with simulations for both types of windows, with an expected thermal window performance underestimation of the numerical approach. The reasons lie in the use of thermal conductivity cautionary values in simulations, and on the stratification phenomenon (highlighted by the infrared camera), that brings a decrease to the convection heat transfer. It emerges therefore that, if a window manufacturer strives for achieving high performance certified products, the test on an experimental hot box setup becomes more appropriate, since it brings to a thermal resistance evaluation around 10% higher than the one obtained from a simulation procedure.

Assessing cooling energy performance of windows for residential buildings in the Mediterranean zone

Heat transfer through windows accounts for a significant proportion of energy used in the building sector for covering both heating and cooling needs, since the optical and the thermal characteristics of conventional fenestration products constitute them more “vulnerable” in energy flows when compared to opaque building elements. In this study, an approach for evaluating the cooling energy performance of residential windows is presented. It is based on a parametric study, which aims at highlighting the impact of the window configuration on its energy behavior in terms of geometrical characteristics, thermophysical and optical properties, as well as orientation and shading levels. The results underlined the magnitude of the relationship between the thermal and optical properties of the transparent elements with respect to their orientation; especially for residential buildings, the solar transmittance determines at a considerable extent the cooling energy performance of fenestration, at least in the warmest part of Europe. Furthermore, the statistical analysis of the derived data provided mathematical expressions, which can be used in praxis for predicting the cooling energy performance of windows with respect to their thermal and optical characteristics.

Assessing cooling energy performance of windows for office buildings in the Mediterranean zone

Fenestration has always been regarded as the weak element in the building envelope due to its role in determining of the energy balance of a building. At the same time, cooling performance is becoming a significant parameter for evaluating the energy performance of buildings in Europe. Due to the plethora of window products with advanced properties currently existing on the market, it is not always easy for engineers to select the optimum solution. In this paper, the cooling performance of windows in the warmest part of Europe is evaluated with regard to their geometrical, thermophysical and optical characteristics, as well as their shading provisions. The analysis shows that the contribution of the windows in determining cooling loads is maximized when their solar transmittance is high and their thermal transmittance is low. Moreover, in the Mediterranean regions the increased thermal efficiency of transparent elements in buildings with controlled ventilation, such as offices, prohibits the dissipation of heat toward the ambient environment and ultimately result in higher cooling energy loads.

A generalized window energy rating system for typical office buildings

Detailed computer simulation programs require lengthy inputs, and cannot directly provide an insight to relationship between the window energy performance and the key window design parameters. Hence, several window energy rating systems (WERS) for residential houses and small buildings have been developed in different countries. Many studies showed that utilization of daylight through elaborate design and operation of windows leads to significant energy savings in both cooling and lighting in office buildings. However, the current WERSs do not consider daylighting effect, while most of daylighting analyses do not take into account the influence of convective and infiltration heat gains. Therefore, a generalized WERS for typical office buildings has been presented, which takes all primary influence factors into account. The model includes embodied and operation energy uses and savings by a window to fully reflect interactions among the influence parameters. Reference locations selected for artificial lighting and glare control in the current common simulation practice may cause uncompromised conflicts, which could result in over- or under-estimated energy performance. Widely used computer programs, DOE2 and ADELINE, for hourly daylighting and cooling simulations have their own weaknesses, which may result in unrealistic or inaccurate results. An approach is also presented for taking the advantages of the both programs and avoiding their weaknesses. The model and approach have been applied to a typical office building of Hong Kong as an example to demonstrate how a WERS in a particular location can be established and how well the model can work. The energy effect of window properties, window-to-wall ratio (WWR), building orientation and lighting control strategies have been analyzed, and can be indicated by the localized WERS. An application example also demonstrates that the algebraic WERS derived from simulation results can be easily used for the optimal design of windows in buildings similar to the typical buildings.

Influence of windows on the energy balance of apartment buildings in Amman

The influence of windows on the energy balance of apartment buildings in Amman is investigated by using self developed simulation software (SDS) based on the ASHRAE tables for solar heat gain calculation and coaling load factor for latitude 32°, where Amman city is located. The calculations of energy saving are made to find out the influence of windows on the energy balance of apartment buildings in Amman. Also, the present investigation aimed to study the energy performance of windows of an apartment building in Amman in order to select the most energy efficient windows that can save more energy and reduce heating load in winter, the percentage of saving energy and saving fuel and money through time. Variations of type of glazing using eight types of glazing (clear glass, types A, B, C, D, E, F, and G) are made to find out the most appropriate type of glazing in each direction. Also the orientation of window is changeable in the main four directions (N, S, E and W). The area of glazing varies also in different orientation to find the influence of window area on the thermal balance of the building. The results show that if energy efficient windows are used, the flexibility of choosing the glazed area and orientation increases. It has been found that choosing a larger area facing south, east and west can save more energy and decrease heating costs in winter using certain types of glazing such as glass type A and clear glass, while decreasing the glazing area facing north can save money and energy. However, it has been found that the energy can be saved in the north direction if glass type B has been used. In the apartment building, it is found that certain combination of glazing is energy efficient than others. This combination consists of using large area of glass type A in the east, west and south direction, and glass type B in the north direction or reducing glazing area as possible in the north direction.

A Simplified Calculation Method for Seasonal Accumulated Solar Heat Gain through Windows

To estimate the energy performance of windows, the seasonal accumulated solar heat gain through the windows has to be calculated. A simplified method for calculating seasonal accumulated solar heat gain through windows with arbitrary azimuth and tilt angle is proposed. The method was tested using weather data from seven locations in Japan. The proposed simplified method provided good simulations of detailed hourly calculations.

Energy performance of windows in high-rise residential buildings in Hong Kong

At the present time in Hong Kong in its hot and humid climate, a single pane, clear glazing is most often used in windows of tall residential buildings. During this study, we employed HTB2, detailed building heat transfer simulation software, to evaluate a decrease in the yearly cooling load ( Q) and in the peak cooling-load ( D) in two residential flats due to different glazing single pane types and different flat orientations. The investigated glazing types were clear glazing, tinted glazing, reflective glazing, and tinted and reflective glazing.

A simple model for assessing the energy performance of windows

A simple model for the annual energy balance of the window taking solar radiation and heat losses into consideration has been further developed and analysed. Hourly meteorological data for the solar irradiation and the outside temperature are used together with the optical and thermal performance of the window to evaluate the net energy heat flow through a window. The model renders a very simple way to compare different advanced windows in different geographical locations, orientations and buildings using basically only the balance temperature as building input. The energy balance and the cost efficiency for several glazing combinations are evaluated for buildings with different balance temperatures in a typical mid-Swedish climate. This model has a potential to be used for energy rating of windows.