Solar responsive building glazing: Experimental analysis of the impact of photochromic glazing on indoor thermal and luminous conditions

Li Z., Wu Z.

The study investigates the impact of electrochromic glazing on indoor environments, providing valuable insights for the practical application of electrochromic glazing. Three rooms were constructed in Zhangjiakou City, China, equipped with different shading devices (electrochromic glazing, venetian blind, and base case of the glazing with no shading). Through experiments and simulations, the analysis of the overall indoor illuminance revealed that electrochromic glass, in its dark state, effectively reduces the average indoor illuminance while ensuring a uniform distribution of illuminance throughout the space, meeting the specified values for the discomfort glare index most of the time. During nighttime lighting, the average illuminance in room with electrochromic glazing was 42% higher than in the control rooms. In winter, the daily heat supply quantity in room with electrochromic glazing was 4.4%–21.9% higher than in the control rooms. In summer, the heat gain in room with electrochromic glazing was 19.1%–41.8% lower than in room with base case of the glazing. On a sunny day in winter, the room with electrochromic glazing exhibited more stable PMV values compared to the room with base case of the glazing, with a 20% increase in the duration of PMV thermal comfort compliance, but its Percentage of PPD values were inferior to the room with base case of the glazing. In summer, the room with electrochromic glazing outperformed both the room with venetian blind and the room wtih base case of the glazing in terms of PMV and PPD values.

Ghosh A., Hafnaoui R., Mesloub A., Elkhayat K., Albaqawy G., Alnaim M.M., Mayhoub M.S.

Globally building sector consumes a significant amount of fossil fuel-generated grid energy which emits a considerable level of carbon emissions. These scenarios can be an obstacle to sustainable or smart city developments. In a building which consists of various components, windows are the most influential to contribute to this energy consumption. To abate the excessive amount of building energy consumption, an alternative glazing system is paramount. Among the other available energy-efficient glazing, an active smart switchable is promising as it can be altered based on occupant choice. In this work, four active smart switchable glazings have been studied (electrochromic, suspended particle device, liquid crystal and gasochromic) based on their operating principle, glazing factors and energetic application. It is evident that EC has more material aspect investigation and overall energetic application for PLDC, SPD and EC needs more study. Gasochromic which can be a potential in future is not explored in higher order. However, these types of windows integration in buildings and how they will have an impact on urban heat islands, part of smart buildings, smart cities and digital twins have also been discussed.

Qahtan A.M., Almawgani A.H., Ghosh A.

Khaled K., Berardi U.

Driven by their low thermal resistance and static transmittance to solar radiation, existing static clear windows are often considered the least-efficient components in the building envelope, driving the heating and cooling demands and compromising the thermal and visual comfort of building occupants. Hence, window retrofit technologies that utilize innovative coatings are critical for enhancing energy efficiency and indoor daylight quality in the existing building stock. In particular, dynamic photochromic window films that reversibly modulate solar gains responding to the abundance of ultraviolet radiation are promising but received little attention. In this paper, five commercial flexible photochromic window films were experimentally characterized, and their energy and daylighting performance were numerically and parametrically evaluated in a representative office with different window configurations and orientations across six representative cities with a diverse range of climates. This is one of the first works dealing with photochromic window films as a retrofit technology. The results show that the films exhibit excellent colour-rendering and cyclic stability with rapid switching/bleaching rates. In addition, annual energy savings in the 1% − 4% range were observed for low window-wall ratios, reaching 10% − 14% in cooling-dominated climates with lower latitudes using PC-1, which resulted in the most significant cooling energy savings. Although the film influenced the quantity of light, resulting in lower daylight autonomy, improvements in the useful daylight illuminance and significant reductions in discomfort glare levels were the major benefits of retrofitting existing double-glazed clear windows with the photochromic film.

Gomes M.G., Santos A.J., Calhau M.

One of the most important concerns when designing buildings as liveable spaces is the indoor comfort. This depends on different factors, including daylight availability and discomfort glare conditions. The increasing use of glazing areas in the building's envelopes can lead to high energy consumption and problems such as visual discomfort. The use of shading devices stands out as a sustainable design strategy to reduce energy consumption in the buildings. This work presents an experimental analysis of the impact of an innovative shading device, a double-tilted venetian blind (DTVB) with different positions of upper and lower slats, on the indoor daylight conditions. Moreover, discomfort glare evaluation, through DGPs metric, is performed. The experimental campaign was conducted in an outdoor test cell during three periods of the year: summer solstice, winter solstice and autumn equinox. Experiments were carried out with both white and grey DTVBs, for several positions of upper and lower slats, under clear and overcast sky conditions. This comprises the measurement of indoor and outdoor horizontal and vertical illuminances and irradiances and solar and visible transmittance of the fenestration. It was concluded that DTVBs can achieve a higher performance, regarding solar protection, daylighting and glare control, when compared with more traditional venetian blinds systems. • Experimental daylight performance study of an innovative shading device. • A double tilted venetian blind (DTVB) with different slats angles was studied. • Daylighting parameters were measured in a test cell. • White and grey DTVB slats were evaluated under clear and overcast sky conditions. • DTVB have higher daylight efficiency than traditional Venetian blinds.

Nicoletti F., Kaliakatsos D., Ferraro V., Cucumo M.A.

Windows have a considerable influence on the thermal balance of buildings. The aim of the present work is to evaluate the performance of a photochromic window (PCW) in terms of building's energy demands and natural lighting. In these windows, a fundamental role is played by the solar transmission coefficient, which can change depending on the incident solar radiation. A comparison is made with the case of using clear double glazing and low emissivity (Low-E) windows. The analysis is performed using EnergyPlus, where a laboratory of DIMEG, University of Calabria (Rende, Italy) is modelled. The model is calibrated to be representative of reality and can be used to compare different types of windows under the same external conditions. Results are obtained for a south-facing window, varying its size. The results show, for this location in southern Italy, that the PCW allows a reduction in annual energy consumption compared to the clear window (up to 9.3%) and compared to the Low-E window (up to 4.1%). The daylight provided by the PCW is greater than the other two solutions and, in some cases, also reduces the risk of glare. • PCWs in buildings are an energy-efficient and visually comfortable solution. • Results are closely related to the size of the glazed area. • For large window areas, PCWs allow energy savings of up to 4.1%. • For low WFR values, PCWs are not recommended over Low-E windows. • Daylight is always favored by PCWs and, despite this, the risk of glare is reduced.

Cannavale A., Zampini G., Carlucci F., Pugliese M., Martellotta F., Ayr U., Maiorano V., Ortica F., Fiorito F., Latterini L.

• A novel photochromic (PC) film was developed and tested for smart windows. • Building integration in a standard medium office building was modelled. • Energy saving were assessed, comparing PC glazing with standard compliant glazing. • Up to 4 MWh/year of energy saving and 40% of visual comfort increase were reached. • The dynamic behaviour of the PC film is the best choice for visual comfort. The study of chromogenic materials and systems is particularly promising for innovative, transparent building envelopes, with thermo-optical properties adaptable to surrounding environmental conditions. This work spots light on the multiple effects of photochromic glazing on the energy consumption of buildings and on the impact that such technologies would have on the visual comfort of occupants. To our knowledge, this is the first work dealing with building integration of spirooxazine-based photochromic films. This experimental and theoretical work aims helping to fill this gap by reporting the results of a study concerning the spirooxazine photochromic molecules, integrated in transparent matrices of polymethylmethacrylate. This work discloses the potential of specific photochromic materials, especially as a function of spectral peculiarities. The figures of merit of this technology have been studied by assuming its integration in an ideal multi-storey office building, and by studying the effects in terms of energy consumption and visual comfort and proposing a comparison with several static commercial glazing technologies. The photochromic glazing demonstrated to offer significant reduction of energy use for cooling, compared to a clear glass (with yearly saving of 4079 kWh, on the Southern facade), and for artificial lighting (with a saving of 3711 kWh), if compared to the commercial solar control glazing. Furthermore, the dynamic behaviour of the photochromic glazing represented the best choice in terms of visual comfort.

Pereira J., Teixeira H., Gomes M.D., Moret Rodrigues A.

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.

Teixeira H., Glória Gomes M., Moret Rodrigues A., Aelenei D.

Highly glazed buildings are typically responsible for significant solar heat gains/losses and, consequently, considerable cooling and heating energy needs throughout the year. Thermochromic glazing is an innovative passive technology, which autonomously and reversibly modifies its thermal and optical properties when direct sunlight heats it, potentially improving both energy efficiency and comfort. However, there is scarce evidence about the global performance of this glazing when installed in commercial buildings. Therefore, this study aims at assessing the annual visual, thermal and energy performance of a thermochromic glazing (12 + 12 + 6 mm) against a conventional clear glazing (6 + 12 + 4 mm) with and without a reflective solar control film installed in an existing office room, considering different European climates. To this aim, a building simulation model calibrated with experimental data obtained on a previous study was used. The results showed that in respect of the percentage of working hours with useful illuminance levels the thermochromic glazing (80%–88%) is better than the conventional clear glazing (64%–74%). However, the glazing with the reflective solar control film is more effective in reducing potential glare. Regarding the thermal performance assessment, under free-float conditions (no mechanical heating/cooling), the thermochromic glazing shows a better performance (20%–48% working hours within comfort conditions) when compared to conventional glazing (1%–42%). The results also show significant total energy savings (climate control and artificial lighting) in the case of the thermochromic glazing, particularly in the hot climate of Lisbon (50%). • Comfort and energy performance of thermochromic versus conventional static glazing. • Building simulation model of an office room calibrated with experimental data. • Up to 88% of working hours with useful illuminance with thermochromic glass. • Up to 48% of working hours within thermal comfort with thermochromic glass. • Up to 50% of energy savings with thermochromic glass when compared with clear glass.

Ascione F., Bianco N., Iovane T., Mastellone M., Mauro G.M.

• High-efficient buildings and NZEB need operable and adaptive building components. • Multi-objective requisites are energy-saving, use of renewables, and indoor comfort. • DSF and responsive components can be useful for both retrofits and new buildings. • Recent examples of applications to both new and retrofit designs are reviewed. • Experiments and numerical studies should optimize design and management. The building sector is – directly or indirectly – the first pillar for application of technologies aimed at reducing energy wastes. To achieve sustainable growth goals, worldwide, the building stock needs to be re-developed from the energy viewpoint. This study focuses the attention on the building envelope, since it is the primary subsystem through which energy losses occur between inside and outside environments, by reviewing and discussing the most recent and cutting-edge researches in matter of double-skin and responsive façades for the building retrofit. Each study is investigated by characterizing the technology, the location (i.e. , the climatic conditions) and season of analysis, the building intended use and the main findings. The objective is identifying potentialities and recurrent benefits related to the discussed retrofit solutions – such as reduction of energy consumption and CO 2 -equivalent emissions, exploitation of renewables, conceptual transformation of the building envelope – but also barriers and criticalities – such as overheating risk, lower efficiency of transparent photovoltaics compared to traditional ones, high cost of responsive elements – which have to be addressed and solved in the future. In this vein, a comprehensive snapshot of the evolution of building envelope retrofit solutions is provided with original insights into current and future trends with a view to low- (or zero-) energy buildings. Despite the critical aspects and barriers to overcome, the potential advantages make most of the addressed technologies an important tool to achieve the sustainable renovation of the existing building stock, and therefore their potentialities must be deeply investigated and understood.

Chun S.Y., Park S., Lee S.I., Nguyen H.D., Lee K., Hong S., Han C., Cho M., Choi H., Kwak K.

Automatically controlling the optical transmittance of solar light provides an energy-saving strategy for designing energy-efficient buildings. Ideally, the smart windows should be able to show homogeneous and large-scale color-switching performance while modulating the intensity of daylight. Among the suitable candidates for smart windows, the photochromic device has a great potential for homogenous and large-scale color-switching material. In a photochromic device, the intercalation/deintercalation of Li-ions is a key step determining the kinetics and efficiencies of the coloring/bleaching process. Herein, we exploit operando Raman spectroscopy to investigate the photochromic mechanism, which reveals the movement of Li ions into specific sites within the tunnels that exist in hexagonal tungsten oxide (WO3). These spectroscopic results demonstrate that the intercalation/deintercalation of the Li ions is related to specific sites in the WO3 lattice which stabilizes the energy of the intermediate state during the coloring/self-bleaching process. Additionally, theoretical simulation supports that electrons, as well as Li ions, participate in the color-switching performance. This study improves our understanding of the photochromic performance of this special device and opens up a research field toward the development of smart windows applications.

Ávila-Delgado J., Robador M.D., Barrera-Vera J.A., Marrero M.

In building retrofitting works, window openings are generally the first thermal envelope’s element to be assessed, both technically and economically. This is of special interest in office buildings characterized by a high glazed area, energy consumption, and the potential use of natural light. This paper explores the criteria for window selection where glazing parameters are selected independently, and in the market, where glass is defined by the number of glass panels or its emissivity. A glazing selection procedure, based on both the parameter’s direction and order of influence, has been proposed by combining the thermal transmittance, the solar heat gain coefficient and the visible transmittance parameters in the Mediterranean climate in Spain (Barcelona, Seville, and Malaga). It was used a methodology not considered before which also let designers know the thermal behavior of each office room throw glazing. The binomial and visible transmittance procedure of selection generated the highest number of office room orientations and configurations low CO2 emissions. The difference between placing all low emission glazing and the best option in each room does not significantly reduce emissions in both building configurations (N–S and W-E). Finally, the building configuration does not alter the selection pattern. However, corner offices with windows in two directions have a high significance in the building emissions, so they are singularly considered in each Mediterranean climate studied.

Cannavale A.

Chromogenic materials and devices include a wide range of technologies that are capable of changing their spectral properties according to specific external stimuli. Several studies have shown that chromogenics can be conveniently used in building façades in order to reduce energy consumption, with other significant effects. First of all, chromogenics influence the annual energy balance of a building, achieving significant reductions in consumption for HVAC and artificial lighting. In addition, these technologies potentially improve the indoor level of visual comfort, reducing the risks of glare and excessive lighting. This brief review points to a systematic discussion—although not exhaustive and mainly limited to recent results and investigations—of the main studies that deal with building-integrated chromogenics that have appeared, so far, in the scientific literature.

Saha S., Bonda S., Tripathi S.N., Shukla D.K., Srivastava V.K., Srinivasa Rao G.S., Jasra R.V.

Bourdin M., Salek G., Fargues A., Messaddeq S., Messaddeq Y., Cardinal T., Gaudon M.

WO3−x (oxygen deficient tungsten oxide) thin films and WO3−x/Ta2O5 (tantalum oxide) composite films exhibit a huge photochromic effect with 60% near-infrared transmission modulation.

Teixeira H., Rodrigues A.M., Aelenei D., Gomes M.G.

Tahmasbi F., Khdair A.I., Aburumman G.A., Tahmasebi M., Thi N.H., Afrand M.

Huang Y., He Z., Qin Y., Lu Y., Chen K.

Khaled K., Berardi U.

Teixeira H., Moret Rodrigues A., Aelenei D., Ferreira I., Gomes M.G.