Low Solar Heat Gain Coefficient Research Articles

A review of complex window-glazing systems for building energy saving and daylight comfort: Glazing technologies and their building performance prediction

The increasing energy consumption and detrimental CO2 emissions contributing to global warming underscore the urgent necessity for energy conservation, especially within buildings. Among different building components, fenestration plays a pivotal role as it accounts for the majority of heat transfer across the building envelope. This emphasises the significance of window-glazing technologies in enhancing their thermal performance. Furthermore, window-glazing systems can lead to overheating issues, particularly in summer, and glare issues, especially in winter. These challenges have spurred the development of various advanced glazing systems. This paper provides a comprehensive review of these advanced glazing technologies based on their functionalities and working principles, with a focus on parameters such as U-value, solar heat gain coefficient and visible transmittance. Among these technologies, vacuum and aerogel glazing systems exhibit superior thermal insulation properties, with U-values below 1 W/m2 K, making them suitable for heating-dominated climates. Smart window systems, such as electrochromic windows, are ideal for cooling-dominated climates due to their low solar heat gain coefficient (0.09–0.47) and visible transmittance (0.02–0.62). Photovoltaic window systems not only provide effective thermal insulation and solar shading but also produce additional power for on-site use. Some of these glazing systems feature complex structures, which present challenges when integrating them into existing building simulation software to assess their impact on building performance. Therefore, this paper also examines techniques for conducting energy and daylight performance simulations for buildings that make use of complex window systems. Ultimately, the authors propose an approach to characterise the thermal, optical and electrical properties of a complex photovoltaic window system within existing building simulation software, such as EnergyPlus. This approach facilitates a thorough investigation into the effects of complex window systems on building energy efficiency and indoor comfort.

Thermosensitive Scattering Hydrogels Based on Triblock Poly-Ethers: A Novel Approach to Solar Radiation Regulation.

Energy conservation in buildings is paramount, especially considering that glass accounts for 50% of energy consumption. The solar heat gain coefficient (SHGC) of glass is a critical energy-saving index for transparent structures. However, the fixed SHGC of ordinary glass makes it difficult to provide both summer shading and winter heating. In this study, we synthesized a hydrogel with a thermosensitive scattering (TS) property using triblock polyether and acrylamide. This hydrogel can realize the transition of clearness and atomization based on the temperature. When sealed within a glass cavity, it exhibits a high SHGC of 0.682 in its transparent state and a low SHGC of less than 0.31 when atomized. The lower critical solution temperature (LCST) of the TS glass can be adjusted from 0 to 70 °C to suit different regions. The photothermal properties of the material remained stable after 200 hot and cold cycles and 200 h of ultraviolet irradiation. This glass can prevent solar radiation from entering the room in summer, thereby reducing air conditioning usage and power consumption. In winter, it allows solar heat radiation to enter the room, minimizing the need for artificial heating. Its adaptable temperature design makes it an excellent solution for designers to create energy-efficient building exteriors.

Robust multi-objective building design optimization approach using NSGA-II algorithm considering weather and occupant uncertainties

A novel methodology is presented to evaluate how real-world operational uncertainties impact multi-objective building design optimization process. NSGA-II algorithm is applied across nine distinct operational scenarios, considering diverse weather datasets and energy usage patterns to optimize energy efficiency and thermal comfort in a residential building within India's hot and dry climate. The analysis considers 382,400 possible design options for each scenario. Using (10.5–12.5) % of model evaluations, NSGA-II significantly reduces Annual Cooling Energy Demand (ACED; 46.7%–58.7%) and Cooling Set-point Unmet Hours (CSUH; 70.92%–86.93%) to identify nine Pareto–Optimal solution sets. The final robust optimal design is confirmed by selecting the most repeated parameter settings, representing the highest robustness. Low thermal transmittance walls, double-glazed windows with a 10% window-to-wall ratio (WWR), deep overhangs, and a low solar heat gain coefficient are recognized as robust optimal building components. However, Air Conditioner (AC) sizing lacks robustness in minimizing energy demand across scenarios, requiring case-specific evaluation due to its sensitivity to weather and operational variations. Further, PAWN sensitivity analysis highlighted the substantial impact of WWR (KSWWR ∼ (0.46–0.66)) and wall type (KSWall ∼ (0.31–0.46)) on ACED and CSUH in chosen climate. AC operation is more important for predicting CSUH (KSAC ∼ 0.35) than ACED (KSAC ∼ 0.10).

Experimental and numerical study of an energy-efficient building fenestration system with seasonal adaptability

Previous building-integrated solar thermal fenestrations were limited to the single function, either air heating or water heating. Thus, they failed to meet the seasonal thermal needs of buildings. To address this limitation, this paper proposed a novel building fenestration-integrated solar collector. This system is designed to harness solar irradiation on the fenestrations for air heating in winter and recover irradiation for water heating in summer, effectively addressing seasonal thermal demands and improving annual solar utilization efficiency. Firstly, the prototype of the proposed system was fabricated, and its thermal performance was tested. The experimental results indicated the thermal efficiency of 40∼50% for air heating and 39% for water heating. Subsequently, a mathematical model of the proposed system was developed and experimentally validated. Based on the validated model, a comparative performance analysis was conducted between the proposed system and double clear glazing. Additionally, the energy-saving potential and economic viability of the proposed system were predicted. Compared to double clear glazing, the proposed system exhibited a higher solar heat gain coefficient (SHGC) in air heating mode, lower SHGC in water heating mode, and lower U value at night. The prediction outcomes underscored the substantial energy-saving advantages conferred by the proposed system across diverse building types. The projected payback periods in subtropical and tropical regions were estimated to be around 2–4 years.

Comparative study on the overall energy performance between photovoltaic and Low-E insulated glass units

A novel semi-transparent building integrated photovoltaic (BIPV) laminate was developed and introduced in this paper. It was produced by cutting standard mono-crystalline silicon solar cells into small strips and then making electrical connections between each strip before laminating the cells between two layers of glass. The overall energy performance and energy saving potential of the BIPV insulated glass unit (IGU) under real world conditions were identified through a side by side comparative study. Compared to the reference IGU, the BIPV IGU had lower solar heat gain coefficient (SHGC) but much higher U-factor. The average HVAC electricity saving of the BIPV IGU was about 10% relative to the reference IGU. Daylighting measurement and analysis were carried out to evaluate the trade-offs associated with the BIPV IGU between daylight, glare, and lighting energy use. The results indicated that the BIPV IGU is better than the reference IGU in reducing discomfort glare. However, if the most conservative viewpoint near the window is used for the assessment, a lower transmittance BIPV IGU is required to bring the overall discomfort levels below the perceptible level. Lastly, the net energy saving potential associated with the novel BIPV IGU was identified based on the power, thermal and daylighting performance. On average, the BIPV IGU saved 16.8% of the total electricity use of the room. Further studies and improvement on the energy conversion efficiency of solar cells, the optimal transmittance as well as the thermal properties would make this technology more energy-efficient and affordable.

Investigation on the thermal performance of a novel vacuum PV glazing in different climates

Abstract With the rapid development of photovoltaic technologies, building-integrated photovoltaic (BIPV) windows could be used to replace traditional glazing, especially semi-transparent amorphous silicon (a-Si) photovoltaic (STPV) windows which can generate electricity in situ and admit daylight into the indoor environment. The utilization of semi-transparent PV modules provides the benefit of low solar heat gain coefficient (SHGC) as a key characteristic of window products. Meanwhile, it also produces a drawback as the remaining solar energy could be converted into heat gain which increases cooling load. Due to the excellent thermal insulation performance of vacuum glazing, the integration of STPV and vacuum glazing provides the potential to achieve the best energy-efficient performance by the low solar heat gain of the PV modules and low heat losses of the vacuum glazing. However, the determination of a suitable glazing of a building in different locations must consider the climate background. In this paper, the thermal performance of the proposed vacuum photovoltaic insulated glass unit (VPV IGU) in different climate zones has been investigated. The simulation work has shown that the vacuum PV glazing can provide a significant energy saving potential in Harbin, Beijing, Wuhan and Hong Kong, which represent the severe cold, cold, hot summer and cold winter, and hot summer and warm winter regions, respectively. However, it is not suitable for the moderate climatic region like Kunming. The results have indicated the advantages of utilizing the vacuum PV glazing in different climates as well as its limitations.

Energy Performance Assessment of a 2nd-Generation Vacuum Double Glazing Depending on Vacuum Layer Position and Building Type in South Korea

(1) Background: The application of high insulation to a building envelope helps reduce the heating load, but increases the cooling load. Evaluating the installation of high insulation glazing to buildings in climate zones with four distinct seasons, as in the case of South Korea, is very important; (2) Methods: This study compared the heating energy performance of four types of glazing, inside vacuum double glazing, outside vacuum double glazing, single vacuum glazing, and low-e double glazing, with fixed low-e coating positions on the inside of the room in a mock-up chamber under the same conditions. The annual energy consumption according to the building type was analyzed using a simulation; (3) Results: As the insulation performance of building envelopes has increased, the energy saving rate of inside vacuum double glazing has been increased further in office buildings. In residential buildings, the energy saving rate of inside vacuum double glazing with a low SHGC (solar heat gain coefficient) has become higher than that of outside vacuum double glazing; (4) Conclusions: Since the effects of SHGC on the energy saving rates are greater in high insulation buildings, SHGC should be considered carefully when selecting glazing in climate zones with distinct winter and summer seasons.

Analysis of combinations of glazing properties to improve economic efficiency of buildings

The ideal combination of low solar heat gain coefficient (SHGC) and high visible transmittance (VT) to maximize energy efficiency of buildings is difficult to achieve because the two quantities have a trade-off relationship. This study analyzed the combination to reduce the energy consumption of office and residential buildings, then proposed a guideline to improve the economic efficiency based on energy cost compared with initial investment cost. First, the glazings used in South Korea were investigated and the possible combinations of SHGC and VT were classified. Then the energy consumption of each combination was quantified. As SHGC decreased and VT increased, energy consumption decreased in the office building, but not in the residential building. Next, the economic efficiency was analyzed for each combination. The efficiency of the office building can be improved by weighting to favor energy consumption over investment cost. While due to nonlinear relationship of energy consumption between SHGC and VT in the residential building, the increased investment cost and decreased energy cost should be compared. This study can contribute to decision-making in ambiguous conditions, such as when the energy cost decreases but investment cost increases.

Assessment of window performance in classrooms by long term spatial comfort metrics

Providing good environmental conditions for educational buildings has always been critical because of the negative influence of thermal and visual discomfort on students’ learning and performance. Unsatisfactory conditions mostly caused by overheating and glare due to the presence of direct solar radiation, could be compensated by appropriate window configurations. Since occupants are obligated to sit in defined positions in classrooms, spatial analysis of the thermal and visual field are necessary in addition to temporal evaluations. This paper applies both spatio-temporal thermal and visual comfort metrics, to assess the effect of window design on comfort by dynamic simulations in a south and north faced classroom model in Tehran’s Climatic condition. The SolarCal method, which considers the direct effect of solar radiation on occupants, validated by field measurements, is used to assess local thermal comfort. A solution space, presented in graphs has been defined for each orientation by the defined comfort targets. These graphs could be used to select the optimum glazing properties based on the desired window wall ratio. The defined solution areas are larger in the south orientation and could be extended by considering shadings. Results show that low U-values and low Solar Heat Gain Coefficient (SHGC) are needed in both north and south faced classrooms to decrease the overheating risk. Also the use of double glazing units is not always required or the most favorable option for all window sizes. Based on the results the most effective factors for window design in regard to spatio-temporal thermal comfort are Window Wall Ratio (WWR), glazing SHGC and window shadings, orientation, and window U-value respectively. However, WWR, orientation, and glazing Visual Transmittance (VT) and shadings have almost equal effect on spatio-temporal visual comfort.

All-solid-state electrochromic device integrated with near-IR blocking layer for image sensor and energy-saving glass application

The all-solid-state electrochromic device (ECD) integrated with near-IR (NIR) blocking layer fabricated by reactive DC magnetron sputtering technique has been developed for image sensor and energy-saving glass applications. The all-solid-state ECD with the single-substrate structure of glass/NIR-blocking transparent conductive oxide (TCO)/NiO/Ta2O5/WO3/ITO could potentially modulate the optical transmittance between 81.9% and 17.5% at 550 nm in the visible region and between 38.0% and 9.5% at the NIR wavelength larger than 1100 nm. The better energy-saving and light blocking performance, including the larger optical density difference (ΔOD) and lower solar heat-gain coefficient (SHGC) could be achieved in the NIR-blocking ECD structure, even with the general criteria SHGC(bleach)/SHGC(colored) < 3. With the application of ECDs, it is possible to directly apply the device onto an image sensor and energy-saving glass with the NIR rejection function even in the bleached state. Furthermore, the NIR-blocking TCO with the low sheet resistance and high transparency characteristics also provides the lower power consumption in the switching cycle at voltages as low as 5 V, and makes ECDs the ideal components for applications of large area and battery powered devices.

Heat transmission through a glass window with a curved venetian blind installed

This article reports a study on the effect of installing a curved venetian blind to a glass window on the solar heat transmission into the space. The mathematical model of the combined glass window and venetian blind is developed. Predicted results from the developed mathematical model are compared with the previous experimental ones to verify their accuracy. The variation of the solar heat gain coefficient (SHGC) with the related blind parameters (optical properties of venetian blind, slat spacing, distance between the blind and glass window, slat angle and solar profile angle) are studied. The variation of the SHGC in the shortwave part (ShW SHGC) and in the longwave part (LoW SHGC) with the related blind parameters are also studied. The understanding of their variation will provide the important information for the study of the thermal comfort for a person who stays near the glass window with blind. The SHGC can be further classified as the SHGC for direct solar radiation (SHGCD) and the SHGC for diffuse solar radiation (SHGCd). From the study it is found that installing a curved venetian blind to the glass window causes a significant reduction in solar heat gain compared to the plain glass window. The SHGCD, ShW SHGCD and LoW SHGCD are all dependent on the slat angle and solar profile angle. The slat reflectance of the venetian blind has direct effect on the ShW SHGCD. The slat absorptance of the venetian blind has direct effect on the LoW SHGCD. The glass window and blind with high slat reflectance gives a lower value of SHGCD compared to the glass window and blind with low slat reflectance. The slat curvature also affects the SHGCD of the fenestration system (glass window with blind installed). The slat with more curvature (lower value of slat radius of curvature) causes more reduction in the value of SHGCD compared to the slat with less curvature. The blind with lower slat spacing yields a lower value of SHGCD compared to the blind with higher slat spacing. The effects of slat emittance and distance between the blind and the glass window on the SHGC D of the fenestration system are only appeared on the LoW SHGCD and such effects are quite small.

Inside air and surface temperature characteristics of window systems depending on low-E coating and blind location during cooling period

Windows have significant effects on heating and cooling energy in buildings due to the fact that windows are the thermally weak parts among the building constructions and that they can directly transmit the solar radiation into the room space. Therefore, proper selection of window materials and blind operation type is an essential factor for energy saving. One of the advanced window systems that has been actively applied these days is low-E windows, whose thermal efficiencies are improved compared to the conventional clear windows by applying the low emissivity coating, resulting in lower solar heat gain coefficient and U-value. In addition, proper operation of blinds can also significantly reduce the thermal load and energy consumption in buildings. In this study, experimental research was performed to evaluate the inside air and surface temperature characteristics of six small-scale test chambers during cooling period, since those temperatures can be good indicators for the indirect assessment of the cooling effects of different window types and blind locations.

An experimental study of the thermal performance of a novel photovoltaic double-skin facade in Hong Kong

Ventilated building-integrated photovoltaic (BIPV) facades can not only generate electricity at the locations of buildings themselves but if designed optimally, such facades can also reduce the respective heat gains and heat losses in summer and winter via the building envelope. The development of a novel ventilated BIPV double-skin facade (DSF), constituted by a see-through amorphous silicon (a-Si) PV module and an inward opening window, is reported in this paper. In order to enhance ventilation, an air-flow duct, 400mm in depth is situated between the outside PV module and the inside window. This ventilation design can remove much of the waste heat generated by the PV module energy conversion processes, and thus bring down the operating temperature of the solar cells. Infrared thermal imaging was adopted in relation to the ventilated PV-DSF to visually demonstrate this ventilating effect. It was found that the air temperature at the outlet louver is higher than that at the inlet louver by 2.2–2.3°C. The thermal performance of PV-DSFs operating in different modes was studied and compared. The results showed that the ventilated PV-DSF provides the lowest solar heat gain coefficient (SHGC), while the non-ventilated PV-DSF better reduces heat loss. Based on the experimental results, the optimum operation strategy for the PV-DSF under different weather conditions has been determined and proposed. This novel PV-DSF is more suitable for sub-tropical climates because it results in a much lower SHGC than that of a low-e coating DSF.

An experimental study on the annual surface temperature characteristics of amorphous silicon BIPV window

In this study, a mock-up facility equipped with both BIPV windows and normal clear windows was installed to carry out the actual measurement of long-term surface temperature characteristics as the preliminary step for analyzing the impact of the surface temperature rise of thin film BIPV modules on the PV performance. The measurement was carried out for clear double windows and BIPV double windows simultaneously for each inclined angle (0°, 30°, and 90°) for one year, and various statistical analyses were carried out for the collected annual surface temperature data to investigate the surface temperature characteristics of BIPV windows. The analysis result shows that the temperature of windows applied on the vertical plane rises significantly during the winter season, and the temperature of windows applied on the horizontal plane and the inclined plane rises significantly during the summer season with high solar altitude. Regarding indoor surface temperature of windows which is closely related with the thermal comfort of indoor occupants, the surface temperature of BIPV windows with low solar heat gain coefficient was 1°C lower than that of normal windows during the day time in summer season and was approximately 2°C higher during the night time in winter season due to the thermal insulation effect.

Solar heat gain coefficient measurement of semi-transparent photovoltaic modules with indoor calorimetric hot box and solar simulator

In tropical Singapore, buildings receive a high amount of solar radiation. Windows should therefore consist of solar control glazing with a low solar heat gain coefficient (SHGC) and high visible light transmittance to reduce the energy consumption for air-conditioning and electrical lighting respectively. Due to the rising demand for on-site electricity generation, photovoltaic modules are increasingly used in buildings, initially as roof-top systems, but in recent years there are also semi-transparent photovoltaic (STPV) being integrated into the façade or overhead glazing. However, their SHGC is usually not reported, potentially preventing STPV from widespread adoption. The paper presents measurements and novel presentations of SHGC for selected thin-film STPV glazing. It introduces SERIS’ indoor calorimetric hot box and solar simulator including a documentation of environmental conditions and calibrations. A sensitivity analysis concluded that the SHGC measurement is mainly sensitive to the spectrum of the solar simulator and reflection properties of the absorber plate. A correction factor was introduced and the measured results compare well with simulations. In addition, SHGC values for selected STPV are presented as (a) angular dependent and (b) load dependent. The results show that the SHGC is sensitive to the incident angle of solar radiation. Particularly for incident angles above 45°, which would be typical for facades in the tropics, the SHGC reduces significantly, compared to the default at 0°. The SHGC reduces only marginally when an electrical load is connected. Higher PV efficiencies would result in more energy being converted into electricity and not into re-radiating heat and therefore producing a lower SHGC.

Impact of window selection on the energy performance of residential buildings in South Korea

With rapidly increasing energy consumption attributed to residential buildings in South Korea, there is a need to update requirements of the building energy code in order to improve the energy performance of buildings. This paper provides some guidelines to improve the building energy code to better select glazing types that minimize total energy use of residential buildings in Korea. In particular, detailed energy simulation analyses coupled with economical and environmental assessments are carried out to assess the thermal, economical, and environmental impacts of glazing thermal characteristics as well as window sizes associated with housing units in various representative climates within South Korea. The results of the analyses have clearly indicated that selecting glazing with low solar heat gain coefficient is highly beneficial especially for large windows and for mild climates. In particular, it is found that using any double-pane low-e glazing would provide better performance for windows in residential buildings than the clear double-pane glazing, currently required by the Korean building energy code.