Transparent Roofs Research Articles

Radiative cooling and indoor light management enabled by a transparent and self-cleaning polymer-based metamaterial

Transparent roofs and walls offer a compelling solution for harnessing natural light. However, traditional glass roofs and walls face challenges such as glare, privacy concerns, and overheating issues. In this study, we present a polymer-based micro-photonic multi-functional metamaterial. The metamaterial diffuses 73% of incident sunlight, creating a more comfortable and private indoor environment. The visible spectral transmittance of the metamaterial (95%) surpasses that of traditional glass (91%). Furthermore, the metamaterial is estimated to enhance photosynthesis efficiency by ~9% compared to glass roofs. With a high emissivity (~0.98) close to that of a mid-infrared black body, the metamaterial is estimated to have a cooling capacity of ~97 W/m2 at ambient temperature. The metamaterial was about 6 °C cooler than the ambient temperature in humid Karlsruhe. The metamaterial exhibits superhydrophobic performance with a contact angle of 152°, significantly higher than that of glass (26°), thus potentially having excellent self-cleaning properties.

A comprehensive evaluation of water spray system on transparent roof towards optimal operation schedule

Indoor overheating induced by transparent roofs sharply increases the building energy consumption. Water spray offers a potential solution but requiring effective strategy to balance cooling effects and cost-effectiveness. Aiming at a spray system installed on transparent roof (63.2 × 24.6 m) of a mixed-use building in Guangzhou, China, this study provides a comprehensive evaluation of multiple strategies including continuous and intermittent operation with different spray/interval time. In sunny weather, continuous spray reduces the exterior, interior surface temperature, and long-wave radiation by 17.5 °C, 9.6 °C, and 66.3 W/m2, respectively. Besides, the indoor air temperature, globe temperature, and mean radiant temperature are also lowered by 4.4, 5.2, and 5.7 °C, respectively. Comparatively, the intermittent spray produces worse cooling effect, the reduction of exterior, interior surface temperature, and long-wave radiation are 9.4–15.9 °C, 4.1–7.8 °C, and 24.1–47.7 W/m2, respectively. The intermittent operating conditions, sorted according to the exterior surface temperature reduction, are ranked as 30/10 > 20/10 > 10/10 > 10/50 > 10/20 min, with the cooling effect not decreasing linearly with interval time, but increasing monotonically with spray time. The air conditioning electricity saved by continuous spray is higher than that by intermittent spray, but the water pump electricity and water consumptions are higher as well. Technical-economy evaluation indicates that water consumption is primary cost factor in spray systems and intermittent spray with 10/50 min is the optimal scenario. This study provides insights into the economical and efficient operation of transparent roof spray system, and lays a foundation for its smart control.

Spray optimization to enhance the cooling performance of transparent roofs in hot-humid areas

Spray cooling was regarded as an effective technique for outdoor cooling but its application to transparent roofs is still limited, owing to the absence of an explicit system design. In this study, the influence of three spray nozzle types with six modes on the spray cooling performance of glass curtain samples that belong to one transparent roof was first determined by a test device. Thereafter, the spray system, designed based on the selected nozzles, was assembled on the transparent roof inside a laboratory building. The thermal property moderation of the roof and indoor environment and the corresponding cost effectiveness generated by this system were further assessed. The results revealed that the spray system could effectively cool glass curtains. Compared to water-spray, mist-spray can achieve a better cooling and shading effect by shaping more dispersed and smaller droplets that effectively enlarge the contact areas with the targeted surface. The exterior glass surface temperature generated by the mist-spray was 8.0 °C lower than the surrounding air temperature, and the solar transmittance ratio decreases up to 14% compared to dry conditions. Field experiments further revealed that the mist-spray system could noticeably mitigate indoor overheating and further eliminate thermal stratification among different floors. Air temperature 10 cm below the interior roof surface and black-globe temperature of 1.5 m higher on the third floor demonstrated a decrease of up to 10 °C and 8.9 °C, respectively. The air temperature gap between these three floors decreased to approximately 4 °C. Furthermore, owing to the mist-spray system, a total of 24.36 kW∙h of energy saving was realized during the experiment and the general infrastructure investment could be recovered within 6.26 years. This study is of great significance for promoting the scientific practice of the mist-spray technique to enhance the building thermal performance.

Enabling a Ductile Failure of Laminated Glass Beams with Iron‐Based Shape Memory Alloy (Fe‐SMA) Strips

AbstractLaminated glass beams are used as structural elements to support transparent roofs or to transfer wind loads acting on transparent facades. However, in case of breakage, laminated glass beams only exhibit a low residual load‐carrying capacity provided by the interlayers. A more efficient solution is to add a filigree ductile reinforcement on the tension side of the laminated glass beams, for instance by adhesive bonding. By these means, the post‐cracking behaviour of the beams and their redundancy can be improved and a ductile failure behaviour can be achieved. Moreover, an additional pre‐stressing of this reinforcement allows increasing the initial glass cracking resistance. Despite their obvious potential, an application of pre‐stressed laminated glass beams in real projects is prevented by the rather complicated necessary procedures for pre‐stressing. This contribution discusses first experimental results on a novel concept for pre‐stressed laminated glass beams with adhesively bonded strips made of an iron‐based shape memory alloy (Fe‐SMA). The pre‐stress can be applied in this case by heating up the Fe‐SMA. The feasibility of the concept is analysed based on results from four‐point‐bending tests on medium‐scale simple, reinforced and pre‐stressed laminated glass beams.

Dynamic glazing with switchable solar reflectance for radiative cooling and solar heating

Dynamic control of sunlight entering a building through glazing panels (e.g., windows, curtain walls, and skylights) is essential for reducing building energy consumption. Here, we demonstrate a dual-mode glazing panel with switchable reflectance (89% versus 17%) via reversible electrodeposition of a silver film on a transparent glass of the glazing. In cooling mode, the silver film-coated glazing, functioning as a radiative cooler, achieves net cooling power of 20–60 W/m 2 on a summer day with direct solar irradiance of 560–970 W/m 2 . In heating mode, transparent glazing absorbs only 13% and allows ∼70% of sunlight to shine through, providing a net heating power of around 400 W/m 2 on a winter day with solar irradiance of 540 W/m 2 . Simulations show that employing such dynamic glazing panels in a medium-size office building (∼5,000 m 2 ) could save up to 23% annual heating/cooling energy consumption under the local climates of 15 U.S. cities. • Reflectance-switchable glazing panel via reversible silver electrodeposition • Heating-mode glazing panel allows ∼70% of sunlight transmission in cold weather • Cooling-mode glazing panel achieves a net cooling power of 20–60 W/m 2 in hot weather • Dynamic glazing panel can save up to ∼23% annual HVAC energy consumption By reversibly depositing a silver film on a transparent glass substrate, Zhao et al. demonstrate a reflectance-switchable glazing panel for solar heating and radiative cooling. The dynamic glazing panel can significantly reduce heating/cooling loads of buildings and is promising for applications such as skylight windows, transparent roofs, and ceiling walls.

Improved Pyrolysis Model of Polymer Materials under Windy Conditions

The polymer materials are widely used in various occasions, of which polymethyl methacrylate(PMMA) is used in architectural transparent roofs, telephone booths, stairs, and their fire risk is getting more and more attention. The ignition conditions （critical surface temperatures and critical mass flow rates） of polymer materials have extensively researched, but their internal heat transfer studies have been relatively rare, especially in wind environments. Considering that internal heat transfer research is important for the heat transfer of multi-layer materials, the study of heat transfer inside materials is also worthy of attention. In this work, we found that in-depth absorption theory is more suitable for solid pyrolysis models under wind conditions. An absorption coefficient depends with temperature are assumed, and it fits better than the constant absorption coefficient. In addition, this work made some improvements to the ignition model by employing the theory of in-depth absorption.

CdS/CdTe Heterostructures for Applications in Ultra-Thin Solar Cells.

The preparation of ultra-thin semi-transparent solar cells with potential applications in windows or transparent roofs entails several challenges due to the very small thickness of the layers involved. In particular, problems related to undesired inter-diffusion or inhomogeneities originated by incomplete coverage of the growing surfaces must be prevented. In this paper, undoped SnO2, CdS, and CdTe thin films with thickness suitable for use in ultra-thin solar cells were deposited with a radiofrequency (RF) magnetron sputtering technique onto conductive glass. Preparation conditions were found for depositing the individual layers with good surface coverage, absence of pin holes and with a relatively small growth rate adapted for the control of very small thickness. After a careful growth calibration procedure, heterostructured solar cells devices were fabricated. The influence of an additional undoped SnO2 buffer layer deposited between the conductive glass and the CdS window was studied. The incorporation of this layer led to an enhancement of both short circuit current and open circuit voltage (by 19 and 32%, respectively) without appreciable changes of other parameters. After the analysis of the cell parameters extracted from the current-voltage (I-V) curves, possible origins of these effects were found to be: Passivation effects of the SnO2/CdS interface, blocking of impurities diffusion or improvement of the band alignment.

Responses of seedling performance to altered seasonal precipitation in a secondary tropical forest, southern China

Abstract Given the intensified global climate change, understanding the responses of seedlings in tropical forests to changing precipitation patterns is critical for predicting plant community regeneration. In a field study, we investigated the potential effects of changes in seasonal precipitation on seedling establishment and growth of Cinnamomum burmanni, a dominant tree species in a secondary tropical forest, southern China. The field precipitation treatments included ambient rainfall (CT), increased precipitation (IP) in the wet season, and extended dry (ED) season without change in annual rainfall. For the IP treatment, 25% of the mean annual precipitation was added in the wet season using pumps and sprinklers. For the ED treatment, 60% of incoming throughfall was removed in March and April to extend dry season for two months using transparent roofs, and re-added back in October and November with the total annual rainfall amount not changed. The results showed that the IP treatment increased seedling height growth in June and August when extra water was applied. By the end of experiment, stem biomass was significantly greater in IP plots than in ED plots. Precipitation treatments also affected biomass allocation. Seedlings in ED plots had a lower root/shoot ratio and root mass to total mass ratio. Compared to the control, the IP treatment significantly increased leaf and stem nitrogen concentrations of the seedlings. Nitrogen and phosphorus contents in stems and roots were much higher in IP plots than in ED plots, which might be explained by the increased NO3−-N and available phosphorus concentrations in soil. Our findings indicate that extended dry season without change in annual rainfall or increased precipitation in the wet season induced by climate change, is likely to affect soil nutrients, seedling biomass accumulation and partitioning, and nutrient uptake, and thereby impact regeneration dynamics and future community structure in tropical forests.

Extreme effects of drought on composition of the soil bacterial community and decomposition of plant tissue

SummaryThe decomposition of soil organic matter, as an essential part of nutrient cycling, has a crucial role in maintaining soil fertility and the regulation of climate. This function of the soil is likely to be affected by extreme weather events that are expected to be more frequent and severe in the future. We conducted an experiment fromMarch 2014 toMarch 2015 to test the effects of extreme drought on composition of the bacterial community and decomposition of plant tissue with soil microclimate variables such as soil temperature and moisture. Precipitation was excluded for a 5‐month period by transparent roofs. To follow organic matter decomposition, we used the tea bag method. Soil samples were taken to determine the effects of extreme drought on the bacterial community 6 months after the dry period (mid‐term). Drought plots were drier (P < 0.001) and warmer (P < 0.001) than control plots as a consequence of the extreme drought treatment. Thepermanovatest showed that the dry period altered soil bacterial communities accordingly (Fpermanova = 10.36,P = 0.002). However, there was no significant difference between the control and drought‐treated plots 6 months after the dry period in terms of bacterial alpha diversity. Furthermore, rates of organic matter decomposition in the control plots were significantly larger by an average of 93.7% than in the drought plots. The results also indicated that soil temperature and moisture had significant effects on decomposition. Overall, the findings demonstrate clearly the response of soil bacteria and soil function to experimental drought. The strong effect of changes in precipitation and increasing temperature on mass loss suggests that extreme weather events, such as extreme droughts, can markedly change the composition of soil bacterial communities and processes of decomposition. This effect is expected to be more pronounced during dry periods of increasing severity and frequency.HighlightsWe studied the effects of extreme drought on plant tissue decay and soil bacterial diversity.Microbial degradation of organic matter was followed by the novel tea bag method.Changes in soil microclimate altered bacterial community structure and decomposition.Microbiota and soil function were markedly affected by extreme weather events like droughts.

A Robust Gradient Based Method for Building Extraction from LiDAR and Photogrammetric Imagery.

Existing automatic building extraction methods are not effective in extracting buildings which are small in size and have transparent roofs. The application of large area threshold prohibits detection of small buildings and the use of ground points in generating the building mask prevents detection of transparent buildings. In addition, the existing methods use numerous parameters to extract buildings in complex environments, e.g., hilly area and high vegetation. However, the empirical tuning of large number of parameters reduces the robustness of building extraction methods. This paper proposes a novel Gradient-based Building Extraction (GBE) method to address these limitations. The proposed method transforms the Light Detection And Ranging (LiDAR) height information into intensity image without interpolation of point heights and then analyses the gradient information in the image. Generally, building roof planes have a constant height change along the slope of a roof plane whereas trees have a random height change. With such an analysis, buildings of a greater range of sizes with a transparent or opaque roof can be extracted. In addition, a local colour matching approach is introduced as a post-processing stage to eliminate trees. This stage of our proposed method does not require any manual setting and all parameters are set automatically from the data. The other post processing stages including variance, point density and shadow elimination are also applied to verify the extracted buildings, where comparatively fewer empirically set parameters are used. The performance of the proposed GBE method is evaluated on two benchmark data sets by using the object and pixel based metrics (completeness, correctness and quality). Our experimental results show the effectiveness of the proposed method in eliminating trees, extracting buildings of all sizes, and extracting buildings with and without transparent roof. When compared with current state-of-the-art building extraction methods, the proposed method outperforms the existing methods in various evaluation metrics.

Separating drought effects from roof artifacts on ecosystem processes in a grassland drought experiment.

1Given the predictions of increased drought probabilities under various climate change scenarios, there have been numerous experimental field studies simulating drought using transparent roofs in different ecosystems and regions. Such roofs may, however, have unknown side effects, called artifacts, on the measured variables potentially confounding the experimental results. A roofed control allows the quantification of potential artifacts, which is lacking in most experiments.2We conducted a drought experiment in experimental grasslands to study artifacts of transparent roofs and the resulting effects of artifacts on ecosystems relative to drought on three response variables (aboveground biomass, litter decomposition and plant metabolite profiles). We established three drought treatments, using (1) transparent roofs to exclude rainfall, (2) an unroofed control treatment receiving natural rainfall and (3) a roofed control, nested in the drought treatment but with rain water reapplied according to ambient conditions.3Roofs had a slight impact on air (+0.14°C during night) and soil temperatures (−0.45°C on warm days, +0.25°C on cold nights), while photosynthetically active radiation was decreased significantly (−16%). Aboveground plant community biomass was reduced in the drought treatment (−41%), but there was no significant difference between the roofed and unroofed control, i.e., there were no measurable roof artifact effects.4Compared to the unroofed control, litter decomposition was decreased significantly both in the drought treatment (−26%) and in the roofed control treatment (−18%), suggesting artifact effects of the transparent roofs. Moreover, aboveground metabolite profiles in the model plant species Medicago x varia were different from the unroofed control in both the drought and roofed control treatments, and roof artifact effects were of comparable magnitude as drought effects.5Our results stress the need for roofed control treatments when using transparent roofs for studying drought effects, because roofs can cause significant side effects.

Microclimate monitoring of Ariadne’s house (Pompeii, Italy) for preventive conservation of fresco paintings

BackgroundAriadne’s house, located at the city center of ancient Pompeii, is of great archaeological value due to the fresco paintings decorating several rooms. In order to assess the risks for long-term conservation affecting the valuable mural paintings, 26 temperature data-loggers and 26 relative humidity data-loggers were located in four rooms of the house for the monitoring of ambient conditions.ResultsData recorded during 372 days were analyzed by means of graphical descriptive methods and analysis of variance (ANOVA). Results revealed an effect of the roof type and number of walls of the room. Excessive temperatures were observed during the summer in rooms covered with transparent roofs, and corrective actions were taken. Moreover, higher humidity values were recorded by sensors on the floor level.ConclusionsThe present work provides guidelines about the type, number, calibration and position of thermohygrometric sensors recommended for the microclimate monitoring of mural paintings in outdoor or semi-confined environments.

The ARoS Rainbow Panorama – Curved Glass as a Load Bearing Element

The application of glazing allows the construction of very transparent roofs. To determine a transparent structure the lightness is a measurable factor within the subjective experience of transparency. At the example of transparent space grid structures with axial load-bearing glazing the interaction between measureable transparency, percept transparency and constructive criteria is analyzed. The constructive criteria include different parameters as pre-assembling, stability, member length, knot geometry and joint sealing. The measureable transparency criteria include lightness and transparency values due to contrast investigation and the percept transparency bases on a psychological study of 325 people assessing film sequences of 3D environments.

Effects of reduced N deposition on litter decomposition and N cycling in two N saturated forests in The Netherlands

Chronic atmospheric N input may alter the rate of decomposition and N cycling during needle litter decomposition. Fresh needle litter from Douglas fir ( Pseudotsuga menziesii (Mirb.) Franco.) and Scots pine ( Pinus sylvestris L.) was exposed to high (>37 kg N ha −1 yr −1) and strongly attenuated rates of natural N deposition (4–6 kg N ha −1 yr −1), achieved by means of transparent roofs in the field. Needle litter was exposed in polyethylene litterbags for 2 yr in the field. The isotope 15N was added as a tracer with throughfall to study the fate of throughfall-N in the decomposing litter. The rate of decomposition was not affected by the amount of N deposition in the Douglas fir stand. In the Scots pine stand the rate of decomposition was temporarily reduced at the low-N input rates. Three years of reduced N input did not alter litter decomposition or N dynamics through a change in litter substrate quality (e.g. N concentration). However, effects of the amount of N deposition on litter substrate quality are likely to become evident after several more years of reduced N input. In both litter species total lignin increased initially (within 4 mo) to 50% of the total dry weight and remained at this level while the loss of mass continued. The amount of N deposition affected the N concentration during the first months of decomposition as characterized by a net N immobilization. Retention of the annual throughfall-NH 4 input by the annual litterfall was 0.3 kg N ha −1 yr −1 at strongly attenuated N input rates (9% of throughfall-NH 4 input) and 1.6–2.2 kg N ha −1 yr −1 at natural high rates (4–7% of throughfall-NH 4 input). The 15N tracer results indicate that throughfall-N was retained mainly in easily-decomposable fractions that rapidly decomposed again after the 15N addition stopped. The results suggest a different critical C-to-N ratio in litter exposed to high and strongly reduced N input rates. This may result from a shift in decomposer communities or a change in the C and N metabolism of micro-organisms.

The fate of15N enriched throughfall in two coniferous forest stands at different nitrogen deposition levels

The stable isotope15N was added as (15NH4)2SO4 to throughfall water for one year, to study the fate of the deposited nitrogen at different levels of N deposition in two “N saturated” coniferous forests ecosystems in the Netherlands. The fate of the15N was followed at high-N (44–55 kg N ha−1 yr−1) 1) and low-N (4–6 kg N ha−1 yr−1) deposition in plots established under transparent roofs build under the canopy in a Douglas fir (Pseudotsuga menziesii (Mirb.) Franco.) and Scots pine (Pinus sylvestris L.) forest.

Effects of three rates of atmospheric nitrogen deposition enriched with 15N on litter decomposition in a heathland

The decomposition and nitrogen dynamics of litter were investigated at three rates of N deposition, using 15N enriched (NH4)2SO4 applied in artificial rain (0.5, 2.0 and 8.0 g N m−2 in 11 months). The experiment was done in the field under transparent roofs, on leaf litter from Calluna vulgaris (L.) Hull, Molinia caerulea (L.) Moench and Deschampsia flexuosa (L.) Trin. These leaf litters differed in their contents of nitrogen, carbon and recalcitrant carbon compounds.All the litters increased in their δ 15N value markedly, the increases being greater as the rate of N deposition increased. However, the rates at which Molinia or Calluna leaves decomposed remained unaffected. The decomposition rate of Deschampsia leaved increased only temporarily at the highest rate of N deposition. Deschampsia leaves decomposed fastest; this suggests that the amount of carbon usuable by micro-organisms determines whether an additional amount of N will accelerate the decomposition process.The changes in the δ 15N values and total N contents of the litter indicated that Calluna and Deschampsia litter simultaneously retain and release N. The N released originated at least partly from the initial litter. In contrast, all the N (including the N that was retained from the rain) seemed to remain bound in the litter-microbial biomass complex of Molinia.

A general theory of the light transmittance of complex structures

An hypothesis is stated that allows the transmittance of any array of transparent roofs to be calculated from the transmittance of each measured independently. This hypothesis is shown by analytical argument to be valid to first order in reflection and absorption coefficient, and this is true for absorption by the cladding material or by structural members. Comparison with a computer simulation confirms the hypothesis for non-absorbing roofs. A corollary similarly shows that the mean light transmittance of an infinite multispan house can be determined to first order from measurements made on a single span. The hypothesis and corollary are of value to greenhouse designers as they allow the transmittance of a complex structure to be found from experimental measurements made on individual components. For normal houses, and for realistic sky radiance distributions, errors in transmittance are less than 1 or 2%, and even for a double-glazed vertical south roof house the maximum error was only 3%.

The transmission of diffuse light by a sloping roof

A method of calculating the diffuse light transmission of sloping transparent roofs is given and the results of such calculations are compared with experimental measurements on acrylic sheet. The need to recognize the non-uniform luminance distribution of the light from an overcast sky is demonstrated; it is also shown that light reflected from the underside of a pitched roof makes a significant contribution to the total illumination.