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Experimental and theoretical study on the effect of window films on building energy consumption
Abstract
Solar control films are designed to absorb or reflect the incident solar radiation, in order to reduce solar transmission through window glass. In the present study, the glass surface temperatures were measured for selected solar window films on various applications, and compared to the cases of the same window glass types without solar window films. Dynamic simulation models are also developed with the aid of the building energy simulation program EnergyPlus. After experimental validations, the computer models are used to evaluate the energy saving potentials of the subject samples of solar window films as applied onto glazing of three different function rooms in Hong Kong, namely office, shopping mall and hotel guest room. The results show that the thermal performance of the film applications on clear glass is better than on tinted or laminated glass windows. Solar films have very good energy saving potential when applied to all three functional areas in commercial buildings, and the best results are found in office applications.
... A web-based search of existing studies was carried out covering scientific engineering databases such as Science Direct, Scopus and Google Scholar. Very scarce studies have investigated the impact of solar control films (SCFs) on the performance of buildings using numerical [34][35][36][37][38][39][40], experimental [19,[39][40][41][42][43][44][45][46][47][48][49][50][51] or computer simulation [35,[43][44][45][46]48,49,[52][53][54][55][56][57] approaches, singly or in combination. Table 2 resents a brief description of the existing studies that assess the performance of SCFs installed in building glazing organized by the type of climate (Köppen-Geiger climate classification [58]: Aw, tropical monsoon; Bsk, cold arid steppe; Bwh, hot desert; Cfa, humid subtropical with a hot summer; Cfb, temperate oceanic; Csa, hot-summer Mediterranean; Cwa, monsoon-influenced humid subtropical; Dfb, warm-summer humid continental). ...
... A web-based search of existing studies was carried out covering scientific engineering databases such as Science Direct, Scopus and Google Scholar. Very scarce studies have investigated the impact of solar control films (SCFs) on the performance of buildings using numerical [34][35][36][37][38][39][40], experimental [19,[39][40][41][42][43][44][45][46][47][48][49][50][51] or computer simulation [35,[43][44][45][46]48,49,[52][53][54][55][56][57] approaches, singly or in combination. Table 2 resents a brief description of the existing studies that assess the performance of SCFs installed in building glazing organized by the type of climate (Köppen-Geiger climate classification [58]: Aw, tropical monsoon; Bsk, cold arid steppe; Bwh, hot desert; Cfa, humid subtropical with a hot summer; Cfb, temperate oceanic; Csa, hot-summer Mediterranean; Cwa, monsoon-influenced humid subtropical; Dfb, warm-summer humid continental). ...
... Also, considering the monsoon-influenced, humid subtropical climate (Cwa [58]), Li et al. [49] conducted an experimental study in two test cells with different combinations of glazing systems and SCFs facing southwest. The authors reported that installing SCFs on single glass induces higher indoor glass surface temperatures for clear glass (increase of up to 10 • C) than for tinted or laminated clear glass, proving the higher ability of solar films in absorbing and reflecting radiation when applied to clear glazing. ...
Buildings with a high window-to-wall ratio tend to suffer from excessive solar gains/losses that usually result in high energy demand and discomfort for occupants. Solar control films (SCFs) are a passive solution with the potential to increase the performance of new or refurbished glazing they are applied to. This paper presents a comprehensive literature review of the performance of SCFs applied to glazing systems of buildings. Research studies with experimental, analytical and computer simulation approaches were gathered and analyzed, identifying glass and film systems, climatic conditions, energy savings and comfort performance. The research approaches and main findings of existing research studies were compared and discussed. The presence of SCFs significantly reduced indoor solar radiation and illuminance levels, particularly with reflective films applied to south-oriented glazing (northern hemisphere). Glazing systems with SCFs were reported to promote cooling energy savings compared with clear glazing in hot climates. Few studies have explored the visual and thermal comfort performance of SCFs, concluding that these films promote thermal comfort, and reduce excessive illuminance and potential glare. Furthermore, this paper helps to highlight areas of guidance for future studies on the topic.
... Windows have huge impact on thermal comfort level in buildings as well as the buildings efficiency [4], [5]. Thermal comfort and proper air ventilation is also provided by windows in buildings [6], [7]. ...
... Additional advantage of window films is that it provides and maintains privacy for occupants as well as protecting furniture from the exposure to excess solar radiation for long times [11]. Preventing harmful UV radiation and rejecting solar radiation are two of the main purposes of installing window films [4]. Window films designs are different depending on the location of installation. ...
... Interior films therefore are cheaper than exterior films, and this characteristic was mentioned in many literature [4], [12], [13]. In a study conducted by Li et al. [4] where they applied window films during the hot weathering condition in Hong Kong on a commercial building, suggested that clear glazing have better energy saving in comparison to tinted one [4]. ...
Thermal comfort studies are very important during the early stages of the building's design. If this study was ignored, problems will start to occur for the occupants in the future. In hot climates, where solar radiations are entering buildings all year long, occupant's thermal comfort in office buildings needs to be examined. This study aims to investigate the thermal comfort at an existing office building at the Australian University in Kuwait and test its validity and improve occupant's thermal satisfaction by covering windows with a heat rejection tint material that enables sunlight to pass through the office while reflecting solar heat outside. Environmental variables were measured using thermal comfort data logger INNOVA 1221 to find the predicted mean vote (PMV) in the selected location. Also, subjective variables were measured to find the actual mean vote (AMV) through surveys distributed among occupants in the selected case study office. The results of this study showed improvement in both PMV and AMV. The mean value of PMV based on the original design before installing the window film was 0.691 which dropped to 0.1 after installation. Also, the mean value of the AMV has improved for the first occupant, where before it was 0.25 and it became-1.5 which is cooler. For the other occupant, it was slightly warm with a mean value of 0.75 and it was improved and became cooler with a-0.25 mean value.
... Windows and window panels have great impact on comfort and efficiency of buildings (Li et al., 2015;Wang and Greenberg, 2015). Windows provide sunlight and visual to outside environment, thermal comfort and air ventilation and also escape from fire (Huang, Niu et al., 2014;Cuce and Riffat, 2015). ...
... Two main effects of window films are to reject solar radiation (heating band) and to prevent harmful UV radiation from entry to the building. Window films also maintain privacy and protection of interior furniture (Li et al., 2015;Plummer, 2015). ...
... Applications of window films were reported in several publications (Yin et al., 2012;Yousif, 2012;Li et al., 2015). Li et al. (Li et al., 2015) applied window films on a commercial building in a warm weather condition of Hong Kong who suggested clear glazing have better energy saving than tinted one. ...
This research attempts to develop a systematic method to address climate changes by studying temperature-humidity patterns as the two major meteorological parameters and to moderate these effects using a commercially available window film on interior windows of an office building with double-glazing. A three-floor educational building at Australian College of Kuwait (ACK) was equipped with temperature, humidity and illuminance sensors for two similar size offices, one with 3 M Neutral 20 window films. Total readings of 50,000 entries from each sensor was recorded every 3 min by a home-designed microprocessor-based logging system for three months of June, July, and August 2019. In parallel, the ACK building was simulated in EnergyPlus and DesignBuilder software and calibrated with the experimental measurements. Histograms and a probability density function (PDF) of temperature and humidity are built by a representative rational function as a model of main climate parameters variations. By examining min-mean-max values of data, it is observed that the office with window films has increased indoor humidity and, in most instances, reduced temperature by 2–5 °C compared to double-glazed bare windows which can significantly reduce cooling loads in extreme hot-arid climates. Simulation results are presented on the energy saved and the reduced CO2 footprints by applying the solar window films in the ACK building.
... The relatively scarce studies that investigate the impact of SCFs on the performance of buildings through experimental [16][17][18][19] or numerical [20][21][22][23][24][25] approaches, or both [26][27][28][29][30], generally conclude that the installation of SCFs can promote better thermal and visual performances and result in energy savings. ...
... When analyzing the performance of glazing systems with SCFs in office rooms, significant reductions in the solar radiation income (up to 60%), the indoor illuminance (up to 65%), the cooling energy needs (up to 29%) and consumption (up to 13.1%) were obtained in the presence of films by previous studies [16][17][18][26][27][28]. Considering previous studies of the performance of single- [29] and double-glazing [30] systems with SCFs conducted in the city of Lisbon, Portugal, a better performance was obtained for SCFs installed on the external glass surface, and films with low solar transmittance made it possible to significantly reduce the cooling energy use (up to 86%). ...
... Most of the reported studies [16,17,[20][21][22]24,26,27] tend to assess the luminous and thermal performances of windows with SCFs and give a special focus to the energy performance, while the evaluation of the effect of SCFs on indoor comfort [24,25,[28][29][30] is still very scarce. Since people spend, on average, 90% of the time indoors, in Europe [31], the indoor comfort assessment becomes significant and that is why it was taken into account in the present experimental study. ...
The global increase in energy needs and environmental awareness for a more efficient energy use have boosted building rehabilitation to decrease energy consumption. The installation of solar control films (SCFs) in buildings with large glazing façades makes it possible to reduce excessive solar gains through the glazing. The main purpose of the work is to assess, with field experimental data, the thermal and luminous performances of double-glazing units with SCFs installed in office rooms, in Lisbon. An experimental campaign was carried out simultaneously in three adjacent offices: one with a highly reflective SCF (external installation), one with a reflective SCF (internal installation) and one without an SCF. The exterior SCF showed the best thermal performance with reductions in the peak indoor air temperature of up to 6.9 and 2.3 °C during the representative days of the heating and cooling periods, respectively, increasing thermal comfort mainly during the cooling period. The interior SCF had a poorer thermal performance since it contributed to solar radiation absorption that is then emitted as heat into the indoor environment, increasing the greenhouse effect of the office. The presence of SCFs reduced the indoor illuminance levels, having a positive impact on thermal comfort and glare reduction in the cooling period.
... In [10], the glass surface temperature was measured for selected window films on different applications and compared to a window without films. Dynamic simulation models were developed using EnergyPlus, which were employed to calculate the possible energy savings from window films installed on glazing in three distinct rooms in Hong Kong: office, shopping mall, and hotel guest room. ...
... The second technique included setting up a separate frame, laminating a PDLC film between two glass substrates, and attaching a new window to the interior side. According to their findings, the building's energy consumption was reduced by 3.1-17% and 18. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22].4% considering the first and second methods, respectively. ...
Recently, there have been several advancements in the field of sustainable energy solutions, particularly in the selection of solar window film sheets. In this research, a multi-criteria decision-making approach was applied to compare three different types of window film sheets, Silver 35, TrueVue 15, and Sterling 40, to aid in selecting the most suitable window film based on the United Arab Emirates market. The primary aim of this work is to provide decision-makers with a structured approach to enhance their choices for selecting window film sheets. The methodology employed involves evaluating various criteria, including visible light transmittance, solar energy rejected, energy transmittance, energy absorptance, cost, glare reduction, visible light reflectance interior, and fade reduction. These criteria are assessed using the Analytic Hierarchy Process (AHP) and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). The results demonstrate that Sterling 40 is the best choice followed by Silver 35. Based on the final TOPSIS results, the difference between the scores of these two window film sheets was not significant, while they were far from the score of TrueVue 15.
... The temperature distribution, the boundary heating flux of SSAF coated glazing systems and T in were numerically calculated by using FORTRAN computer language. In order to quantitatively evaluate the impact of SSAF on energy-saving, building performance softwares such as EnergyPlus, eQUEST and ESP-r were used to simulate energy consumption [15][16][17][18][19][20][21], which put forward the need to verify the model of energy consumption. Gijón-Rivera et al. [15], Li et al. [18], Moretti et al. [19], Teixeira et al. [16] and Pereira et al. [17,20] validated or calibrated entire models with experimental data. ...
... In order to quantitatively evaluate the impact of SSAF on energy-saving, building performance softwares such as EnergyPlus, eQUEST and ESP-r were used to simulate energy consumption [15][16][17][18][19][20][21], which put forward the need to verify the model of energy consumption. Gijón-Rivera et al. [15], Li et al. [18], Moretti et al. [19], Teixeira et al. [16] and Pereira et al. [17,20] validated or calibrated entire models with experimental data. ...
Spectral selective absorption film (SSAF), a solar control film, has a special energy-saving mechanism. In the previous studies of SSAF coated glazing systems, thermal parameters (global thermal transmittance (U) and solar heat gain coefficient (SHGC)) calculated by traditional algorithms were not verified. In order to evaluate the energy-saving effect of SSAF coated glazing systems accurately, U and the SHGC were calibrated and then used for energy consumption simulation. Firstly, the simulation models of the heat transfer process of SSAF coated glazing systems were established by COMSOL Multiphysics, considering simplified linear attenuation of radiative transfer. After being validated, the simulation models were used for the calibration of U and SHGC by the Multiple Linear Regression (MLR) model. As a result, the calibration coefficients of U and SHGC are 1.126 and 1.689, respectively. Secondly, the thermal parameters of SSAF coated glazing systems calibrated by the calibration coefficients were used for a building energy consumption simulation case. The result showed that the inner surface is the best coating position for single glazing systems (SG), while the outer surface is the best coating position for double glazing systems (DG) in hot summer and cold winter zone, hot summer and warm winter zone and the moderate zone of China.
... Hard coatings, on the other hand, have higher emissivity, are thicker, but more durable. Low-emissivity coatings and their application in different climates have been studied by Aguilar et al., Li et al., Kumar et al., and Laouuadu et al. [24][25][26][27]. The study by Kumar et al. [26] showed that the gray reflective glass has the highest cost savings in annual net cooling and heating for all orientations across three climatic regions in India. ...
... The study by Aguilar et al. [24] showed that for Mexican climate, the combination of clear glass and reflective glass provided the highest energy benefits. The study by Li et al. [25] showed that the use of coatings in the climate of Hong Kong can lead to energy savings and that the best results are obtained when the coatings are applied to clear glass rather than tinted glass. The study of Laouadi et al. showed than in winter period in Canada, energy can be saved by using the low-emissivity coatings. ...
Glazing elements are an important part of the thermal envelope of a building. Therefore, good thermal performance of glazing elements can improve indoor comfort and reduce annual maintenance costs and CO2 (carbon dioxide) emissions by reducing heat loss. Reducing heat loss through glazing elements during the heating season can be achieved by combining low thermal transmittance with high solar heat gain. Using standardized calculation methods and measured climate data for three Slovenian locations representing typical continental, mountainous and Mediterranean climates, this study predicts the best combination of optical properties (emissivity, transmittance and reflectance) of glass panes in double and triple glazing systems that contribute to minimal heat loss. It was found that for the double glazing system, the minimum heating and cooling demand for buildings with low solar gains or high solar gains and applied shading is achieved by an inner pane with high transmittance without low-emissivity coating, and an outer pane with low-emissivity coating with minimum possible emissivity. In Maribor and Portorož climatic zones, the panes with low emissivity coating should be used as inner panes in buildings with high solar gains. For triple glazing, the minimum heating and cooling requirements are achieved with two or three panes with low emissivity. For buildings with low solar gains, an emissivity of the coating of 0.03 is preferable, but for buildings with high solar gains, lower emissivity values should be used.
... Several studies have examined the performance of window films in terms of energy savings (Hui & Kwok, 2006;Li et al., 2015). Hui's work focused on the thermal, solar, and visual performance of window films, finding that films effectively limit the transfer of infrared solar heat. ...
In recent years, window films have emerged as a popular solution for managing solar heat gains across diverse climatic conditions, ranging from extreme to moderate weather. While these films effectively reduce unwanted heat gains, they often compromise daylight availability and modify the colour quality of natural light. This study quantifies the spectral irradiance of windows films, serving as a basis for energy, daylight, and colour assessment. We looked at high and low transmittance levels for correspondingly moderate and extreme weather conditions.
A comprehensive analysis was conducted on 14 different window films, with visual transmittance spanning from approximately 6% to 89%. The spectral power distribution (SPD) of each film was meticulously measured using a spectrometer. The collected data provide a holistic visual and non-visual evaluation of the films' performance.
The results reveal significant insights into the trade-offs between visual transmittance and correlated colour temperature (CCT). High transmittance films allow more natural light penetration but can lead to unwanted heat gains. Low transmittance films effectively block solar heat but often at the cost of reduced daylight and altered colour rendering. The study discusses the advantages and disadvantages of the evaluated films.
Finally, this research highlights the need for a balanced approach when choosing window films, considering energy efficiency and daylight quality. The findings serve as a valuable resource for architects, building engineers, and environmental designers seeking to optimise building performance with visual and non-visual aspects of daylight through informed decision on spectral evaluation of windows films.
... The use of window filters might be an economical and fast solution to improve glare protection, privacy levels, thermal comfort, cooling savings (Li et al., 2015) in indoor spaces. However light also influences cognitive performance, alertness, and circadian rhythms of building occupants (Duffy & Czeisler, 2009). ...
Visual, thermal and spectral properties of translucent facades can have a significant impact in occupant’s visual comfort and thermal sensation in near-window zones. Moreover, the use of translucent window filters used to vary the color temperature and intensity of the incident radiation through windows also has impact on the non-image forming (NIF) responses of light. The aim of this investigation is to explore the circadian stimulation, visual comfort and thermal sensation of different window filters on office users in a calibrated simulation study. We considered the spectral properties of 10 window filters to conduct daylight and thermal simulations were performed on the LOBSTER model with different window filters to assess the circadian stimulation, visual comfort, and thermal sensation considering both with and without direct sunlight. We used the metric Melanopic Equivalent Daylight Illuminance (MEDI) to evaluate NIF, while Predicted Mean Vote (PMV), and Daylight Glare Probability (DGP) were used to evaluate thermal sensation and visual comfort, respectively. Point-in-time simulations were performed for both equinoxes and solstices during working hours (8:00-16:00). Our results showed that the selection of window filters significantly influences predicted visual comfort, circadian stimulation, and thermal sensation of building occupants, underscoring the importance of performing both, daylight and thermal simulations to ensure healthy and comfortable evaluation of buildings when selecting appropriate window glazing filters.
... Some studies have used comparisons with standard test cases to demonstrate the reliable performance simulation capability of Honeybee based on EnergyPlus [42,43]. Li et al. conducted experimental validation of the annual energy performance for five different tested film-and-glazing combinations, showing good agreement between EnergyPlus simulation results and measured data, with a maximum deviation within 3.0 °C [44]. Similarly, the accuracy of daylighting tools has also been validated through comparisons with standard test cases and experimental measurements in multiple studies [45][46][47]. ...
Bifacial photovoltaic sunshade (BiPVS) is an innovative building-integrated photovoltaic (BIPV) technology. Vertically mounted BiPVS is capable of converting part of the incident solar radiation into electricity, regulating the indoor heat gain from solar penetration and improving daylighting. An excellent BiPVS design should comprehensively consider its impact on building performance and economic viability. This study aims to address this issue by proposing a parametric design-based multi-objective optimization (MOO) framework to maximize indoor useful daylight illuminance, minimize air-conditioning energy consumption, and shorten the payback period by optimizing BiPVS design parameters. The framework utilizes the Ladybug, Honeybee, and Wallacei plugins on the Rhino-Grasshopper simulation platform. It validates the optimization potential of BiPVS in a typical office located in a hot summer and warm winter zone. The results indicate that BiPVS has significant energy-saving and daylighting potential. Compared to the baseline model without BiPVS, useful daylight illuminance is increased by 39.44%, air-conditioning energy consumption is reduced by 12.61%, and the economically satisfactory payback period is 4.80 years. This study provides a practical solution for the competing objectives of daylighting and energy saving in buildings with significant renewable energy utilization. The developed framework is highly efficient and versatile and can be applied to other BIPV designs, which benefits the realization of carbon-neutral goals in the building sector.
... Moretti and Belloni (2015), in their study to evaluate the effects of SCFs on the thermal, and daylight performance for moderate climate, reported a reduction of 60.00% in the incoming radiation, about two to three o C of the indoor temperature, increase of artificial lighting, decrease of the cooling demand by 29.00% while the heating demand increased by 15.00%. Li et al. (2015) investigated the effect of solar films on building energy consumption and concluded that solar films have good potential for energy saving. Rezaei et al. (2017) presented a review on various types of glass coatings and glazing systems and evaluated the potential of using different window technologies for hot, cool, and temperate climates. ...
On a global level the building sector consumes about 45.00% of energy consumption, contributes about 40.00% to emission, uses 30.00% of water and impacts the environment by generating 30.00% of waste. Although windows are important components of a building that provide natural lighting and ventilation and establish necessary contact with the external environment necessary for healthy indoor ambient, they permit entry of undesirable solar heat in summer and allow escaping heat from the indoor ambient in cold seasons, which aggravate the building needs for energy and increase its contribution to atmospheric emissions. The present investigation provides a review on research, development, and applications of advanced windows in the building sector. The introduction highlights the importance and contribution of advanced glazing technology to improving energy, comfort, and thermal performance of buildings. The review includes natural illumination and ventilation, thermal comfort and discusses the effects of window to wall ratio on natural illumination and ventilation of windows and façades. The review also covers recent developments in glazed windows and façades including performance enhancements by using reflective solar films, vacuum glazing, windows with filling materials, windows with water flow, window with phase change material, window with stagnant inert gas filling, ventilated windows and façades and windows with aerogel. A special section was also included on smart glazing for windows and façades showing the new tendencies and applications in the building industry. Since commercial programs and open access codes are handy tools for simulation and performance calculations a section is dedicated to these codes. The conclusion section contains the most relevant conclusion of the review as well as future trends in research and developments in the area. The topics included in this review can be helpful for experienced and young researchers, practicing engineers and general readers interested in windows and façades.
... In Li et al. [12], the glass surface temperatures of several kinds of film were measured and compared with those of similar windows without film. EnergyPlus was also used to evaluate the energy-saving potential of the films applied to the glass of three different functional rooms in Hong Kong. ...
The objective of this study was to evaluate the effects of window films on indoor environmental conditions and electricity consumption of air conditioning. The research focused on the performance of different window films (HAG, RG), taking into account variations from different building orientations. The findings of this research indicated that building orientation could significantly influence the duration of direct sunlight entering the interior, with the areas closer to the glass being more susceptible to the effects of outdoor temperature and solar radiation. The clear glass with heat-absorbing film (HAG) and reflective film (RG) both reduced the indoor temperature and indoor illuminance while increasing indoor comfort. The RG could accumulate less heat on the glass surface compared with the HAG. The glass temperature of the RG will be lower than the HAG. The electricity-saving ratios of the HAG were 1.4%, 1.9%, 1.4%, and 1.2%, respectively, when facing the east, south, west, and northwest orientations compared with the clear glass (OG). The electricity-saving ratios of the RG were 3%, 4.2%, 4.2%, and 10.3%, respectively.
... They found that the film can reduce heat gain by about 52% in hot climates. Li et al. [106] reported the results of a study to evaluate the effects of window films on the energy consumption of buildings. The results showed that the thermal performance of films on clear glass is better than on colored glass and has significant energy-saving potential in office applications. ...
The building sector is rated as a big consumer of electric energy and emissions, responsible for about 40% of final electric energy consumption. As a result, the Paris Agreement 2015 set a goal for buildings and the construction sector to reach a nearly zero-carbon stage by 2050. This urged most countries to create regulations for the construction sector and invest in energy efficiency programs. The present paper aims to present an updated review of building energy-saving solutions and techniques to contribute to carbon emission mitigation in the building sector. The high energy consumption of a building is mainly due to heating and cooling, which is directly related to the thermal properties of the materials used. Natural ventilation and illumination are other aspects that contribute to the high energy consumption. Considering these issues, the review covers energy-efficient construction materials such as mortars, concrete with PCM, new construction materials with PCM such as 3d printing concrete and geopolymer concrete, and bricks usually used in buildings. Also, the review covers the methods and solutions for energy saving for building heating and cooling. Since transparent windows and façades are essential for structures, their thermal and visual performance is crucial. Established and under-development techniques for windows and façades are presented and discussed. Walls and roofs are usually rated at the top of the weak barriers against a building's heat losses and energy gains. The present paper reviews existing and still under research and development techniques to improve the thermal performance of walls and roofs, such as cool roof and cool walls, walls and roofs with phase change materials (PCM), and ventilated walls and ceilings.Some authors’ comments are presented at the end of each topic. Some possible opportunities for future research and developments are also presented.
... A complex smart window was combined with an SPD and LGG to maintain the indoor environment at optimal conditions. SPD reduces heat loss in a building by varying the transmittance according to the external conditions of the building [19,20]. LGG refracts light from the sun to increase the amount of light entering a building, thereby reducing the lighting energy in the building. ...
The interest in zero-energy buildings has increased in Korea recently. Following the significant increases in cooling and lighting energy consumption in offices, various studies have been conducted to implement energy-saving measures. The purpose of this study is to reduce lighting and cooling energy consumption in the summer through the dimming control of a complex smart window system. To achieve this, the optimal dimming control algorithm has been derived and applied in simulations to analyze the energy consumption for lighting and cooling. A smart window incorporates suspended particle display glass that actively responds to changes in indoor and outdoor environments and controls light transmittance. It also includes a light-guiding glass that can actively control solar reflectance. Simulations of office buildings were conducted to develop optimal control algorithms and controllers based on solar radiation. Subsequently, we installed this complex smart window in a test room along with the developed control algorithm and controller, which responded to the amount of insolation and time. To ensure the accuracy of the experiment, we constructed separate test and reference rooms. The experimental results obtained under the same conditions showed a reduction of approximately 36.9% in cooling energy consumption in the test room compared with the reference room and a 54.5% reduction in lighting energy consumption. Furthermore, based on additional simulations and experiments, we confirmed that the application of complex smart window systems in office buildings could reduce considerably the energy consumption for cooling and lighting.
... The use of low-emissivity (low-E) window films have captured the attention of researchers as a simple, non-intrusive method of retrofitting windows. These films can be applied to the existing windows without requiring the replacement of the glass ( [1], [3]- [6]). They are spectrally selective, meaning they can reduce unwanted solar heat gain by blocking near -infrared radiation from the sun in the summer while retaining indoor warmth by reflecting longwave radiation back to the indoor environment in winter ( [1], [7], [8]). ...
Low-emissivity (low-E) window films are designed to improve the performance of buildings. These films can be applied to different glazing systems without replacing the whole window. For most of the existing windows, it is not possible to apply these films on the surfaces inside the cavity. Placing them on the outer surface is not usually recommended by manufacturers. Therefore, these films need to be attached to the indoor-facing surface of the windows. These films help to prevent the longwave radiation from escaping the building, thereby lowering the U-value of the glazing. However, they may cause single-glazing systems to be at risk of condensation by reducing the temperature of the indoor surface of the glass. The literature review revealed that most of the studies focused more attention on single-glazing systems and considered standardized outdoor conditions (e.g. standardized temperatures and surface heat transfer coefficients). While in reality, the outdoor conditions are dynamic an d changing with the geographical locations. This study aims to investigate the impacts of outdoor conditions on the U-value and condensation risk of double-glazed systems. The investigation has been conducted with the help of the simulation tool WINDOW in such a way that first a double-glazed system with an indoor-facing low-E film is modeled, then validated against the manufacturer's technical data. In the next stage, different scenarios are created to include the outdoor conditions of different cities wit h diverse climates (the main focus is on outdoor temperatures and surface coefficients). Then the U-values of the created scenarios are compared against each other. In addition, condensation analysis is conducted following ISO 13788:2012 to discover which climates and outdoor boundary conditions could hinder the application of the low-E films. The study results showed utilizing a low-E film on the interior side of a double-glazing system can result in a reduction in the U-value. Nonetheless, as the outdoor temperature drops, the effectiveness of the low-E film appears to diminish. In addition, applying a low-E film on the interior side of the glazing can lower the temperature of the glazing's indoor surface when compared to not using the film. Meaning that applying these films in cold climates like Stockholm can lead to condensation on the glazing's indoor surface (especially, during the coldest hours of the year) resulting in apparent weaker energy performance of glazing and weaker visual comfort.
... The solar and visible transmittances of window glasses also are the properties that determine the heat gained by radiation. Glazing with low solar and visible transmittances could decrease the cooling load of the building by curbing the gaining heat, while it increases the heating demand in cold seasons (Li et al. 2015). ...
Buildings consume about 40% of global energy. It is essential to use various measures to reduce the energy consumption of the buildings as much as possible. This research investigates the impact of using a new combination of thermochromic (TC) materials in the building envelope of educational buildings. A case study building at Razi University was selected, and a 3D model was created in DesignBuilder software. Firstly, TC coating for external walls was entered into the base model, and several simulations were performed to find the effect of this coating on the energy consumption of the building. Then, a low-emissivity thermochromic (LETC) window was defined using energy management system (EMS) scripting and was entered into the base model. Finally, these two measures were combined, and the cumulative effect of using both TC coating on the external walls and LETC window was identified. Results indicated that the simultaneous application of these two measures reduced the heating demand of the building more in Tabriz, with the least cooling degree days (CDD). Also, simulation results revealed that the simultaneous use of these measures decreased the cooling demand of the building more in Bandar Abbas, with the highest CDD. Using TC coating on the external walls and LETC windows together reduced the energy consumption of the building more in Bandar Abbas. Consequently, integrating these measures can reduce the heating demand of educational buildings more in heating-dominated climates. Also, the simultaneous use of these measures can reduce cooling demand more in cooling-dominated climates.
... If placed on the outside and inside of window frames, the layers can minimize the SC (Shading Coefficient) and solar heat gain factor by 44 and 22 percent, respectively. The building cooling load through the use of the glass on design day can be minimized by 27% and 2.2% for exterior and interior window films, correspondingly, for the double-pane, low-E glazing system [12]. The weather data are also very essential for the calculation of the cooling load and have a high impact on the solar load by glass. ...
Heat loss through the building envelope comprises air leaks through the cracks and largely through the windows, which is the weakest link of the thermal envelope. Therefore, it is necessary to devise a systematic approach to analyze the rightful selection of glass for buildings. The investigation is to analyze the energy-saving potential of different glasses and their comparisons to the initial capital cost to find the payback time in terms of energy saving by using two different types of equipment. The quantitative simulation study was completed on the Hourly Analysis Program (HAP) to analyze the annual energy consumption of the HVAC system for seven glasses and two types of chilled water equipment. The results show that the performance glasses with a tint had better efficiency in terms of energy saving, with a payback time of 3–7 months. A comparison of all glasses illustrated that float glass contributes the most to the total cooling load among all glasses, which were 5.04%, 5.7%, 7.6%, and 8.9% for the N, S, E, and W orientations, respectively. Moreover, the lowest contribution of glass to the total cooling load was given by tinted double-glazed glass, which was 2%, 2.3%, 3.0%, and 3.01% for N, S, E, and W orientations, respectively.
... A possible solution is to equip the windows with infrared screens, as reported in some studies in the literature such as [19,20]. There are different types of films, depending on their use, i.e., when glare, sunlight or heat loads need to be reduced. ...
Increasing global warming is largely attributable to human activities. International strategies have already been implemented to reduce emissions to zero, thus reducing energy consumption. Given the current world situation and the rising costs of raw materials (gas and oil), it is incumbent on us to find savings solutions that can also be implemented in our own small way; there are many solutions, especially in the domestic sphere. In this paper, the focus is on building energy savings that can be achieved using modern technologies and starting with the simplest solutions. In particular, this paper shows how the conscious use of natural lighting can lead to significant electricity savings. Moreover, it describes the effect of innovative building insulation materials and the effect due to the installation of a local photovoltaic power generation system; at the end, it illustrates the new horizons that are opening with the introduction of new building control techniques. Some studies are also reported where the extent of achievable savings can be understood.
... These films are designed and optimized for various climates around the world. For instance, a warm and sunny climate requires a film with more tinting and near-IR reflection, whereas a colder and less sunny climate requires more visible light transmission and less near-IR reflection, in order to optimize the balance between solar heat gains in winter and rejection in summer (Hui & Kwok, 2006;Li et al., 2015;Sedaghat et al., 2021). As such films are fabricated in a cost-effective way and can be applied to existing window panes, they are an appealing and easy-to-install renovation option. ...
The type of glazing implemented in a building plays an important role in the heat management of a building. Solar heat entering through glazing causes overheating of interior spaces and increases building’s cooling load. In this work, the energy saving potential of window films based on Cholesteric Liquid Crystals (CLC) is explored. This emerging technology allows for the fabrication of static and thermochromic solar heat rejecting window films and can provide a simple renovation solution towards energy efficient buildings. Simulations on a model office showed that static CLC-based window films can save up to 29% on a building’s annual energy use in warm climates. In climates with distinct summer and winter seasons, static solar heat rejecting windows films cause an additional heating demand during winters, which reduces the annual energy savings. In these climates, the benefit of thermochromic CLC-based window films becomes evident and an annual energy saving up to 22% can be achieved.
... Relative to incandescent lights, LEDs use ~85% less energy and have 50 times longer lifetimes 16 and are likely to remain as the dominant source of illumination in the future. 17 Glass composition has also become increasingly sophisticated in recent years, such as through multipane glazing, 18 tinting, 19 lowemissivity coatings, 20 anti-reflective coatings, 21 and vacuum glazing, 22 compared to the single pane and compositionally simple glass types that used to be more common. 23 These changes will undoubtedly affect levels of indoor lighting and hence indoor air chemistry. ...
The importance of photolysis as an initiator of air chemistry outdoors is widely recognized, but its role in chemical processing indoors is often ignored. This paper uses recent experimental data to modify a detailed chemical model, using it to investigate the impacts of glass type, artificial indoor lighting, cloudiness, time of year and latitude on indoor photolysis rates and hence indoor air chemistry. Switching from an LED to an uncovered fluorescent tube light increased predicted indoor hydroxyl radical concentrations by ~13%. However, moving from glass that transmitted outdoor light at wavelengths above 380 nm to one that transmitted sunlight above 315 nm led to an increase in predicted hydroxyl radicals of more than 400%. For our studied species, including ozone, nitrogen oxides, nitrous acid, formaldehyde, and hydroxyl radicals, the latter were most sensitive to changes in indoor photolysis rates. Concentrations of nitrogen dioxide and formaldehyde were largely invariant, with exchange with outdoors and internal deposition controlling their indoor concentrations. Modern lights such as LEDs, together with low transmission glasses, will likely reduce the effects of photolysis indoors and the production of potentially harmful species. Research is needed on the health effects of different indoor air mixtures to confirm this conclusion.
... Moreover, the rise of full glass curtain walls is further contributed to energy loss/gain including heat and light through windows [131]. Conventional window technologies such as roller blinds [132], blinds [133], roller shade [134], window films [135] and multilayer pane windows [136] mostly focused on static performance improvement through keeping the inside separate from the outdoor, which resulted in overheating or overcooling effects by the diurnal and seasonal variation. Generally, to overcome these negative effects, extra electricity load will deteriorate energy consumption. ...
Thermal comfort has a substantial implication for human health. Achieving thermal comfort requires not only thermal regulation of the building's macroenvironment, but also personal thermal management. Radiative cooling, which could pump thermal radiation through atmospheric window, is a promising passive cooling option in energy-efficient green buildings and personal thermal management. However, these fixed and monofunctional properties cannot adapt to highly dynamic weather and even result in overcooling. Therefore, it is necessary and urgent for dynamic radiation regulations (DRR). In this review, an overview is presented about latest technological advances and the prospects in this burgeoning field. First, the fundamental principles of DRR are presented. Then the emerging materials and strategies of DRR are introduced, adapting to the varying environment under the external stimuli like electricity, strain, temperature, etc. Afterwards, we present the latest applications of DRR in energy-efficient green buildings and personal thermal management, particularly the smart windows and dynamic responsive textiles. Finally, the challenges and opportunities of DRR are presented and future directions are identified.
... Numerical studies were conducted to investigate the thermal transmittance and heat transfer processes of double [15], triple [16], and quadruple pane windows in relation to gap width, filled gases, and emissivity [17]. The experimental and theoretical studies on installing solar control layers [18], reflective-PVC, and absorptive-PVC films [19], over clear glazing in office, commercial and accommodation buildings have shown a significant saving in electricity. As seen in the literature [20], thermal processes through innovative polymer-dispersed liquid crystal (PDLC) films of glazing were shown to regulate the heat flux through their assembly adequately through the variable transparency. ...
Building glazing is a weak thermal envelope that admits too much solar heat, resulting in increased air conditioning expenditures. An optimal glazing system must be chosen to promote the thermal and visual comfort of building interiors. The current study examines how different glass retrofits affect the air-conditioning cost savings of an office building in a hot and dry region of India. To assess the thermal performance of the building, the apertures of the office building were retrofitted with brick glass, stained, tinted, reflective, laminated, polymer dispersed liquid crystal film glazing, and double-glazed window systems. The spectral characteristics of the studied retrofit glazing systems were measured experimentally, and a mathematical model was developed to estimate the heat gain, cooling cost demand, and energy savings for air-conditioning. The polymer dispersed liquid crystal film glazing retrofit provided the highest average air-conditioning cost savings (5.11 /m²), relative to the original glazing installation among the other retrofits tested. The examined retrofit glazing systems have a colour rendering index of more than 80, indicating appropriate lighting quality. The findings of this study are critical in determining the most energy-efficient retrofit glazing solutions for energy-conscious building design.
... Utilizing window films could reduce the building cooling load in the Shanghai, 3 and the increment of the building heating load was slight. In Hong Kong, a solar film on single clear window glass would save 44−57 kW h/m 2 per year for the shopping mall and the hotel guest room, 22 and it could save up to 15.22% of electricity per year in comparison with the normal glass. 12 But the comparative study of the SSAF's performance in different climate zones has not been reported and there is some confusion about the appropriateness of the SSAF for the specific climate in China. ...
The transparent envelope structures in existing buildings have caused so much energy consumption. As one kind of the energy-saving technologies and strategies, the solar spectrum selective absorption film (SSAF) is considered suitable for the retrofit of glazing systems. The energy-saving performance of the SSAF in different types of glazing systems under different climate zones in China was investigated via a field study and simulation experiment. The results indicated that SSAF slowed down the rise of indoor air temperature in the daytime and reduced the total energy entering the room. The effect of the SSAF on the single glazing system was more potent than that on the double glazing system. In the hot summer and cold winter zone, moderate zone, hot summer and warm winter zone, the SSAF could reduce the energy consumption of windows. The highest energy-saving rate reached 35.0% for the single glazing system and 28.3% for the double glazing system. However, the SSAF does not have the energy-saving potential in existing buildings that already have low-E double glazing systems.
... The results of another field test carried out to investigate the impacts of solar films on the energy performance of windows in an air-conditioned office building in Hong Kong's climate showed that the solar heat rejection of the filmtreated window was 30% for diffused radiation and 50% for beam radiation. These reductions proved the AC-energy-saving potential of solar films [29]. The effectiveness of solar control window films depends on several factors, including the location of the installed window film, the type and configuration of the original glazing system and the climate [14,22,27]. ...
Low‐emissivity (low‐E) window films are designed to improve the thermal comfort and energy performance of buildings. These films can be applied to different glazing systems without having to change the whole window. This makes it possible to apply films to windows in old and historical buildings for which preservation regulations often require that windows should remain unchanged. This research aims to investigate the impacts of low‐E window films on the energy performance and thermal comfort of a three‐story historical stone building in the cold climate of Sweden using the simulation software “IDA ICE”. On‐site measurements were taken to acquire thermal and optical properties of the windows. This research shows that the application of the low emissivity window film on the outward‐facing surface of the inner pane of the double‐glazed windows helped to reduce heat loss through the windows in winter and unwanted heat gains in summer by almost 36% and 35%, respectively. This resulted in a 6% reduction in the building’s annual energy consumption for heating purposes and a reduction in the percentage of total
occupant hours with thermal dissatisfaction from 14% (without the film) to 11% (with the film). However, the relatively high price of the films and low price of district heating results in a rather long payback period of around 30 years. Thus, the films seem scarcely attractive from a purely economic viewpoint, but may be warranted for energy/environmental and thermal comfort reasons.
... In the past, coatings on windows that reduced the solar gain also reduced the visible transmittance and were hardly accepted by occupants. However, new high-performance tinted glass and low solar-gain (or low-E) coatings make it possible to reduce the solar heat gain with little to no reduction in the visible transmittance (Padiyath and Seth 2007;Jitka 2009;Chunying et al. 2015;Mainini et al. 2015). ...
Windows are often pointed to as the weakest elements in building facades, given their low thermal resistance. Consequently, they are a main focus during building retrofits, when their substitution is often considered an expensive but necessary choice. This article describes a new high-performance glazing coating, which can be used for the in situ retrofit of existing windows. The easy application of this new liquid-applied coating on the internal side of the glazing makes it possible to reduce the solar heat gain coefficient of an existing window substantially and quickly, without interrupting the building occupancy. Experimental characterizations of light transmittance and thermal characteristics are presented in this article. Although the new coating allowed a reduction in the visible transmittance (VT) of only 0.1 compared to nontreated insulating glass units (IGUs), it proved to reduce significantly the solar heat gain coefficient (SHGC) of the investigated IGUs to values below 0.45. This article also reports the results of aging studies aiming at assessing the risks of long-term performance reductions of this new liquid-applied coating. Finally, the results of energy simulations investigating the energy-efficiency improvements when this coating is applied to different kinds of windows in Canada are reported.
... Application of window films were investigated in a humid and warm climate by Li, et al. [25] where they found clear glazing performed better than tinted windows for energy saving. In another study, it was found that exterior window films saved energy by 44% whilst interior window films merely saved 22% [26]. ...
The electricity consumption in residential/office buildings reported 45% of the
total annual electricity demand in hot-arid climates. This accounted 27.2 TWh of
electricity consumption with 14.2 MWh/capita/year in Kuwait. In this research,
four offices in an educational building are equipped with a meteorological data
logging system using temperature, humidity and illuminance sensors. All four
offices use double-glazed windows. Moreover, two offices were equipped with
two types of commercially available window films. Two million data was stored
in iCloud using Wi-Fi and an IOT system for the three months of June, July, and
August 2019. Here, histograms and the kernel density estimation (KDE) of
temperature/humidity are analyzed and compared for the two offices with/without
3M Neutral 20 window films. Two floors of the same building consist of 31 offices
were also modelled and simulated to study energy saving and CO2 footprint
reduction using various window films. The results of simulations for the month of
July 2019 using SOL101 and SOL102 window films, respectively, shows that
about 250 kg and 255 kg of production of CO2 can be reduced and energy saving
counts 416 and 422 kWh. Measurements from offices with 3M Neutral 20% and
3M Neutral 70% window films for the month of July 2019 indicate that the carbon
footprints can be reducing about 82 kg and 0.43 kg and energy saving counts
147.11 and 0.71 kWh, respectively. It is observed that annual energy saving and
CO2 footprint reduction of 2.76% can be achieved using window films in a hot arid climate.
... In a theoretical-experimental study, effects of different glazing types and film materials on the energy consumption of a building were investigated [16]. The results indicated that the film applications on clear glass tend to enhance the thermal performance of the window, as compared to tinted or laminated glass windows. ...
Energy saving is one of the challenges of today. In recent years, growing concerns about the environmental impacts of energy consumption and global warming has doubled the importance of this issue. The contribution of building sector to the energy consumption is significant at a country-wide scale, so that various measures have been taken to help save the energy, including the codification of regulations in accordance with local climate conditions. In this research, using DesignBuilder software, a building in Semnan (Iran) with hot arid climate was modeled with various window configurations. To generalize the results, the two cities of Tabriz and Bandar Abbas with different climates were added to the study. One of the important strategies for optimizing energy consumption in a modeled building is to improve the heat transfer coefficient of the window glass based on local climate conditions. In this work, investigations were performed on a variety of single-pane and double-pane windows with argon gas, krypton, and air as the insulator. By changing the gap between the panes and glass thickness, the cooling/heating load of the modeled building were analyzed to find optimum window configuration for the dominant climate condition at Semnan. Finally, an economic assessment was performed by estimating the required capital cost and payback period for different window configurations.
... Tinting glazing panes help to retain material transparency from the internal layer of the window, absorbing a portion of the solar heat whilst blocking daylight [26]. Glass tinting involves the addition of metallic components on the glass during the floating process. ...
Windows are one of the significant indicators of the energy efficiency of a building and have undergone extensive research since the last decades. This paper reviews the performance of various window technologies covering the physical and optical properties of traditional windows and advanced window technologies. In window technologies, one of the most critical parameters is its thermal transmittance value or also known as U-value. In this paper, we discuss the relationship between the physical and optical parameters of the different types of windows and its U-value. Additionally, this paper will also provide interested readers with a wide range of information, including the research gaps in window technologies. Among the main conclusions, we found that, although several advancements have been achieved in this field in the last decade, further research is needed to develop window technologies that not only have high insulating properties but also can generate power.
... Many attempts have been made including shutter technology (Cuevas et al. 2010), coating technology (Nilsson and Roos 2009), and thin film (Li et al. 2015). Recently, transparent wood has attracted wide attention as a potential window candidate Jia et al. (2019). ...
With the shortage of global fossil energy resource and the emergence of ecological crisis, concerns toward energy issues have risen to an unprecedented level. People have begun to seek potential and sustainable solutions to energy problems, developing energy materials with green blocks, so as to provide technical support for the reliability and advancement of future living environment. As an alternative method for constructing sustainable materials by assembling scattered nanocellulose building blocks using bottom-up technology, the integrated nano-architectonic from wood has attracted more and more attention in energy areas. Based on the current hotspots of high performance batteries, solar steam generation and building energy efficiency, this review describes the significance of wood nanotechnology for sustainable energy development.
... Recent studies analyzed the use of solar control absorbing film in double-glass windows under warm and cold climate conditions, with a focus on the effect of varying the spacing between the glass sheets, indoor temperature, and solar radiation. Experiments on solar window films in various applications, compared with cases without solar films, indicated that the thermal performance of the film on clear glass is better than that on laminated or tinted glass windows (Noh-Pat et al. 2011;Gijón-Rivera et al. 2011;Xamán et al. 2014Xamán et al. , 2016aXamán et al. , b, 2017Li et al. 2015). Gan (2001) numerically predicted the total energy transmitted through a multiple glass window and found an optimal gap thickness of 25 mm. ...
This investigation is focused on assessing the thermal performance of a ventilated double-glass reversible window with reflective film for building applications. The window is composed of two glass sheets separated by a gap forming a channel. One glass sheet faces the external environment while the second glass sheet faces the internal environment. A solar reflective film is attached on the internal surface of the first glass sheet for hot climates or attached on the internal surface of the second glass sheet for cold climates. A home-built numerical code is developed, using the finite volume method for the discretization of conservative equations, and validated against available numerical and experimental results. The simulations were done hourly for representative days of the summer and winter seasons. Three possibilities were examined in this study: a ventilated double-glass window without a reflective film, a ventilated double-glass window with a reflective film for hot climates, and a ventilated double-glass window with a reflective film for cold climates. Based on the results, for the hot climates, the use of a reflective film is highly recommended because the ventilated double-glass window with a reflective film was able to reduce 57% of the energy gain in comparison with the same window without a reflective film. For cold climates, the ventilated double-glass window without a film is better than the same window with a reflective film.
Human thermal comfort in buildings is an increasingly important topic. Improvements to system efficiency will bring about considerable benefits to power consumption and thermal comfort of building occupants. This work examines the use of an adaptive vent system (AVS) within a university classroom. The system will use directional cooling to lower the temperatures of occupied regions, reducing cool air supply to unoccupied regions and thus waste. Computational fluid dynamics simulations were conducted to characterize the behavior of the AVS and compare it against a standard diffuser system. The simulations show that directed cooling from the adaptive vents reduces the temperature and relative humidity surrounding the occupants approximately 3.3 times faster than the standard system. However, the draft rate has also increased significantly. Despite this, the simulations indicate that the AVS is capable of greatly increasing the cooling efficiency of the overall system, especially if the supply airflow rate were to be lowered.
Purpose
This purpose of this paper is to address the problem of reducing energy consumption in existing buildings using advanced noninvasive interventions (NVIs).
Design/methodology/approach
The study methodology involves systematically developing and testing 18 different NVIs in six categories (glazing types, window films, external shading devices, automated internal shades, lighting systems and nanopainting) to identify the most effective individual NVIs. The impact of each individual NVI was examined on an exemplary university educational building in a hot climate zone in Egypt using a computational energy simulation tool, and the results were used to develop 39 combination scenarios of dual, triple and quadruple combinations of NVIs.
Findings
The optimal 10 combination scenarios of NVIs were determined based on achieving the highest percentages of energy reduction. The optimal percentage of energy reduction is 47.1%, and it was obtained from a combination of nanowindow film, nanopainting, LED lighting and horizontal louver external. The study found that appropriate mixture of NVIs is the most key factor in achieving the highest percentages of energy reduction.
Practical implications
These results have important implications for optimizing energy savings in existing buildings. The results can guide architects, owners and policymakers in selecting the most appropriate interventions in existing buildings to achieve the optimal reduction in energy consumption.
Originality/value
The novelty of this research unfolds in two significant ways: first, through the exploration of the potential effects arising from the integration of advanced NVIs into existing building facades. Second, it lies in the systematic development of a series of scenarios that amalgamate these NVIs, thereby pinpointing the most efficient strategies to optimize energy savings, all without necessitating any disruptive alterations to the existing building structure. These combination scenarios encompass the incorporation of both passive and active NVIs. The potential application of these diverse scenarios to a real-life case study is presented to underscore the substantial impact that these advanced NVIs can have on the energy performance of the building.
The bi-facial photovoltaic sunshade (BiPVS) is an innovative solution that utilizes vertically mounted bi-facial photovoltaic modules to provide shading. The BiPVS is capable of converting incident solar radiation into electricity on both the front and rear sides of the module, resulting in higher electrical efficiency compared to traditional mono-facial PV sunshades. The BiPVS has great potential as a sustainable solution for building shading and energy generation, which allows for improved indoor light/thermal environment and building energy efficiency. In this study, the bi-facial photovoltaic sunshade (BiPVS) was implemented in an office under typical hot summer and warm winter climate of Shenzhen, China. The energy performance of the BiPVS was analyzed using Energyplus. The comprehensive building energy saving was evaluated by comparing the energy consumption of the office with and without the BiPVS. Results showed that the total annual photovoltaic power generation was 133.19 kWh, while the comprehensive building energy savings were 159.65 kWh. Additionally, carbon dioxide emissions were reduced by 83.29 kgCO2 per year. The proposed method can help optimize the design parameters of BiPVS according to specific climate conditions, building types, and orientation, and contribute to the development of high-efficiency BIPV technology and support efforts towards carbon neutrality.
A variety of dynamic window and glazing systems with variable solar heat gain control features reacting to seasonal weather conditions and indoor space heating and cooling demands have been investigated in the past several decades. However, the modulation of solar heat gain has to affect the solar light transmittance in most existing dynamic glazing and window systems. In this work, a new type of dynamic window concept was proposed: reversible photothermal windows based on nanoscale solar infrared-induced plasmonic photothermal effects, which can modulate solar heat, independent of visible light conditions. This study provides the underlying technical characteristics and the thermal and optical features under solar irradiation via experimentally validated analytical models. The reversible photothermal windows exhibit a substantial ability to control solar heat gain coefficient with a range between about 0.2 and 0.6 and a stable visible transmittance of 0.32, A whole-building energy simulation demonstrates the potential for energy savings offered by reversible photothermal windows could reach over 18% in mixed climates, as compared to baseline models built using the most recent energy efficiency standards. This research illustrates technical and numerical evidence and mechanisms for energy savings that will support future research and development of this new dynamic window technology.
Sustainable construction has been the main priority in the global construction industry. For that reason, Malaysia is moving towards green building approach to promote built environment sustainability. Therefore, it is essential to raise awareness about the environmental-responsible practice among construction players particularly on the implementation of green engineering-based technology. This study aims to explore the existing green engineering-based technology and to investigate the preferred green engineering-based technology to upgrade the sustainability of existing residential buildings. The study focuses on the existing technology to be incorporated in the operation of buildings. A comprehensive literature review was carried out and 384 feedback was collected from questionnaire survey distribution among respondents in Johor Bahru. Various green engineering-based technology includes solar energy, wastewater treatment, rainwater harvesting, window shading, housing landscape, natural ventilation, smart PDLC film glasses, roof thermal insulation, and smart home control panel are discussed in this paper. From this study, it was found that that the housing landscape is the most preferred with the highest mean index value followed by daylighting system and solar panel. The results indicate the preferred green engineering-based technology is because of low cost and familiarity among users. The future study should consider relating the awareness of individuals on sustainability with their preferred green technology. Perhaps, the coverage of this study should be extended by involving respondents from all over Malaysia.
The present experimental study is dedicated to investigate ventilated windows with and without reflective film for hot climate applications. The experimental findings are used to validate a thermal model and its numerical code developed in a previous study and also to validate developed correlations for predicting the windows thermal performance. The experimental rig was built and instrumented for outdoor tests of windows of different configurations. Experiments were conducted on three window configurations which were assessed numerically using the numerical code. The configurations included a traditional single glass window, ventilated window with reflective film and ventilated window without reflective film. The numerical predictions were compared with the experimental results showing good agreement. The results indicated that the temperature decrement increased with the increase of the gap between the glass sheets and that a spacing more than about 0.03 m has marginal effect. The experiments confirmed that the ventilated window with film is more efficient and that it can reduce the energy gain by almost 57% and hence can be recommended for hot climate. The developed correlations showed maximum deviation for the case of the window with film of about 13% and about 7% for the case without film.
The conjugate heat transfer in a triple glass window (TG) is presented to determine the air-gap width that improves its thermal performance under a warm Mexican climate. Five different air-gap widths (Hc = 6, 10, 14, 18, and 22 mm), 4mm of thickness for each glass, and 80 cm in height are considered. Hourly climatic data of the coldest and the warmest day of Merida were used to assess the thermal behavior of the TG, and the results were compared against a double glass (DG) and a singles glass window (SG). A validated numerical code based on the Finite Volume Method was developed to model the windows. We found that an air-gap width of 10 mm reduces the hourly heat flux to the indoor during the warmest day up to 17.7 and 38.7 % compared to the DG and SG, respectively. Moreover, the daily total heat flux, electricity cost, and CO2 emission on the TG are up to ≈ 40 % lower than an SG, respectively. Therefore, we recommended a TG to improve the thermal performance on windows under weather conditions of Merida, Yucatan.
The spectral selective absorbing film is suitable for the renovation of windows and curtain walls of existing buildings to improve building energy efficiency due to special optical and thermal properties. The thermal and energy performance of the spectral selective absorbing film strongly depends on the environmental conditions, but the present performance study is mostly focused on moderate or warm climate conditions. In this paper, the thermal and energy performances of the spectral selective absorbing film in a cold climate region were investigated by the temperature test chambers installing spectral selective absorbing film glass and normal glass, exposed outdoor to acquire the air temperature and calculate the energy consumption. The results show that the spectral selective absorbing film can not only not increase the heating energy load in winter, but also significantly reduce the cooling energy load in summer. Furthermore, it can be predicted that the annual energy loads can be reduced when using the spectral selective absorbing film in a cold climate region. In addition, the heating energy-saving performance of spectral selective absorbing films in the residential building is more effective than in the office building.
The incorporation or the replacement of materials in buildings may decrease the energy use during the operational stage but increase the embodied energy in a building's life cycle. In this study, three different solar control films (SCFs A, B and C) with application on the existing windows of a building are investigated through an energy, environmental and economic perspective over a defined life cycle period. The full replacement of the existing window with a new one is also analyzed as an alternative retrofitting solution. Retrofitting solutions with higher light-to-solar gain ratios showed higher energy savings during the use stage by decreasing the solar gains in a higher proportion than the decrease of the visible transmittance. The best retrofitting solution, SCF C, showed a life cycle energy (LCE) (embodied plus operational energy) and a carbon footprint of 4447 MJ/m²/40y and 380 kgCO2eq/m²/40y, respectively, whereas the least performant solution, new window, showed a LCE 1.5 times higher than the average of the three SCFs. The higher LCE value of the new window was found to be related to the higher value of the embodied energy when compared to that of the three SCFs (∼9 times higher than the average of the films).
An evaporatively-cooled façade system, composed of a Photovoltaic thermal (PVT), evaporative cooler, and evaporatively-cooled façade, was previously developed. In this study, a control algorithm for the system parameters is implemented and applied on spaces with evaporatively-cooled façade to generate the least possible façade temperature, and consequently maximum possible energy savings. The optimization of the system parameters is expected to overcome the limitations of using evaporative coolers in humid countries. The application of the control algorithm managed to increase the reductions in the façade heat gain from 33.5% to 38.3%.
The system, integrated with the control algorithm, is then applied throughout the year on spaces located in Doha (Qatar) and Riyadh (Saudi Arabia), mimicking cities with harshly hot humid and dry weather conditions, respectively. The daily and monthly performances are further investigated in four different space orientations (i.e., north, east, south, and west). It was found that the application of the system can halve the highly glazed façade heat gain during the summer, in all orientations, and may have adverse, yet desirable effect during the winter. The integration of the control algorithm managed to reduce differences in system performance between dry and humid locations, thus generating total annual savings of up to 21.8% in any typical city of the Arabian Gulf.
Passive solar design is an effective strategy to alleviate the energy-intensive status of the building sector. Identifying passive solar design parameters that significantly impact office buildings’ energy performance can further understand sustainable design principles and prioritize energy efficiency measures. This study proposes a holistic methodology integrating data mining techniques and parametric energy simulation to explore the critical design parameters in passive solar office building envelopes in hot and humid climates. The data mining module incorporates Extreme Gradient Boosting Decision Tree (XGBoost) and association rule mining to measure feature importance and extract strong correlations, respectively. A case study, using a typical office building in Guangzhou, China as a reference building, is conducted to demonstrate the implementation procedure and feasibility of the proposed approach. In total, 115,200 design scenarios are created and simulated in EnergyPlus software. The results of XGBoost show that the glazing system, window-to-wall ratio, and roof coating are the most critical design factors, with importance scores of 0.4858, 0.3197, and 0.1297, respectively. Similarly, based on a confidence threshold of 30% and a lift threshold of 3.0, the extracted association rules indicate that the above three factors have the strongest correlations with the energy consumption level. Findings of this study will provide practical passive solar design guidance for office buildings in hot and humid climates to achieve energy-saving targets. Also, the developed simulation-based data mining method can be applied to other building types in different climates.
A model of heat transfer through low-emissivity windows was developed. The two most important performance parameters including overall heat transfer coefficient and solar heat gain coefficient were calculated and analyzed. The factors that influence these parameters were discussed and the mechanism of that why low-emissivity windows can save energy was described. An example was given for the simulation of the impact of low-emissivity windows on air-conditioning and heating energy costs in four typical climates in China. Based on the results of simulation, the most eligible class of low-emissivity windows was proposed for each climate to obtain the best energy-saving effect.
In this paper the thermal analysis by natural convection of a double glazing unit (DGU) is presented. One of the sheet glasses may or may not have a solar control film (SnS–CuxS) on its surface. Solar radiation falls on the outside surface of the DGU at 32°C, the opposite sheet glass interacts with the inside environment at 24°C. The governing equations of mass, momentum and energy of the air enclosed between the two sheet glasses are solved, as well as the heat conduction equation for both sheet glasses. The effect of varying the separation distance between the glasses (1.0≤b (cm)≤10.0) and the incident solar radiation is analyzed (500.0≤G (W/m2)≤800.0). From the results, it was found that in order to reduce heat gains towards the inside environment, the optimal separation distance between the sheet glasses was b≥6.0cm. It was also observed that, the use of a solar control film in this type of system (double glazing unit) is highly recommended; due to energy gain was reduced by 55% compared to the traditional DGU without solar control film.
To calculate the energy performance of buildings, one must know the heat-transfer characteristics of the windows as functions of environmental variables, such as temperature and wind speed. Window designs are becoming more complex in response to the need for energy conservation. In this paper, we develop a general procedure for calculating the net energy flux through the glazed area of a window composed of an arbitrary number of solid layers. These layers, which may have thin-film coatings, can have any specified solar and thermal radiation properties and enclosed spaces between solid layers can contain either air or other gases. We verified our results by comparing them with experimental measurements of heat flow using a calibrated hot-box.
In subtropical Hong Kong, solar heat gain via glazing contributes to a significant proportion of the building envelope cooling load. The principal fenestration design includes eliminating direct sunlight and reducing cooling requirements. Daylighting is an effective approach to allow a flexible building façade design strategy, and to enhance an energy-efficient and green building development. This paper studies the lighting and cooling energy performances for a fully air-conditioned open-plan office when solar control films together with daylight-linked lighting controls are being used. Measurements were undertaken at two stages including the electricity expenditures for the office using photoelectric dimming controls only (first stage) and together with the solar control film coatings on the windows (second stage). Electric lighting and cooling energy consumption, transmitted daylight illuminance and solar radiation were systematically recorded and analysed. The measured data were also used for conducting and validating the building energy simulations. The findings showed that the solar film coatings coupled with lighting dimming controls cut down 21.2% electric lighting and 6.9% cooling energy consumption for the open-plan office.
The building area in northern heating areas accounting for 70% of the total land area in China is 6,500,000,000 m2. The average heating energy consumption in northern China is 100–200% times more than developed countries in the same latitude. This paper introduced firstly the heat metering and energy efficiency retrofit background of existing residential buildings in northern heating areas of China organized by mohurd and MOF, and then put forward the total principle and contents of retrofit. Through analyzing some retrofit cases in Germany, Poland and China, some technological experiences were summarized and finally a technology line suitable for heat metering and energy efficiency retrofit of existing residential buildings in northern heating areas of China which involved retrofit for heat metering and temperature regulation of heating systems, heat balance of heat source and network, and building envelope was described to provide a systematic, scientific, technological guide for the retrofit projects of 0.15 billion m2 in “the Eleventh Five-Year Plan” period.
In subtropical Hong Kong, the principal objectives of fenestration design include eliminating direct sunlight and decreasing cooling loads. To avoid the problems of glare, excessive brightness and thermal discomfort, occupants may block the windows with internal shading devices, resulting in poor daylighting performance and very small amount of electric lighting energy savings. Recently, the advances in thin film coatings for window glass products provide a means of substantially reducing heat gain without proportionally reducing daylight transmittance. It has been suggested that film coatings together with photoelectric lighting control systems could minimise the electric lighting and cooling requirements without causing undue visual and thermal discomfort to the occupants. This paper presents field measurements on solar control film coatings in fully air-conditioned offices in Hong Kong. Solar heat gains, indoor illuminance levels and the electricity consumption by the fluorescent luminaires were systematically recorded and analysed. Measurements were made for two cellular offices, one with solar control film coating on the window glass and the other without. The findings showed that the solar film coating could cut down energy expenditures for air-conditioned buildings, especially for spaces with large glazing areas subject to substantial amount of direct sunlight. Results are presented and the design implications discussed.
Green roofs are a passive cooling technique that stop incoming solar radiation from reaching the building structure below. Many studies have been conducted over the past 10 years to consider the potential building energy benefits of green roofs and shown that they can offer benefits in winter heating reduction as well as summer cooling.This paper reviews the current literature and highlights the situations in which the greatest building energy savings can be made. Older buildings with poor existing insulation are deemed to benefit most from a green roof as current building regulations require such high levels of insulation that green roofs are seen to hardly affect annual building energy consumption.As over half of the existing UK building stock was built before any roof insulation was required, it is older buildings that will benefit most from green roofs. The case for retrofitting existing buildings is therefore reviewed and it is found there is strong potential for green roof retrofit in the UK.
Heat metering and energy efficiency retrofit of existing residential buildings in northern heating areas of China is organized and implemented in a large scale by local government in 15 provinces of North China with the unified guidance and control of central government. Firstly, this paper introduced the target of energy-saving reformation of existing residential buildings in North China and the importance of check and evaluation on this target, then pointed out the necessity of building up an evaluation system for energy-saving retrofit. According to the analytical hierarchy process (AHP), three-grade evaluation system was built up for heat metering and energy efficiency retrofit of existing residential buildings in northern heating areas of China. Also, based on multi-index comprehensive evaluation method combined with life cycle assessment (LCA) theory, post-evaluation thought and successful degree evaluation method, a mathematical model was established. Finally, a set of scientific method for evaluating heat metering and energy efficiency retrofit of existing residential buildings in northern heating areas of China systematically, scientifically, comprehensively and objectively was created.
American Society of Heating Refrigerating and Air-conditioning Engineers
- Ashrae Fundamentals Ashrae
- Handbook
ASHRAE, ASHRAE Fundamentals Handbook, American Society of Heating
Refrigerating and Air-conditioning Engineers, 2001.
The research on the energy efficiency of glazing system with low radiation rate
- Y Yang
- H F Di
Y. Yang, H.F. Di, The research on the energy efficiency of glazing system with
low radiation rate: 2001, Acta Energiae Sol. Sin. 22 (3) (2001) 296-301.