Society for Testing & Materials (ASTM) and the industry to create test procedures, The subcommittee believes that two existing ASTM standards ''E —Test. ASTM E Standard test method for solar absorptance, reflectance, http:// musicmarkup.info Jan 31, accordance with ASTM Standard rI'est Method E — The measurements were performed with a Beckman Spectrophotometer.
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ASTM E Solar Absorptance, Reflectance and Transmittance of Materials Using. Integrating Spheres. This test method covers the measurement of. E - 96 Standard Test Method for Solar Absorptance, Reflectance, and Available on line at musicmarkup.info ASTM E —96 Standard Test Method Solar Absorptance, Reflectance and Transmittance of Materials Using Integrating Spheres (Withdrawn ) (PDF.
More E This test method provides a means for determining these values under fixed conditions that represent an average that would be encountered during use of a system in the temperate zone. This test method also provides a means for determining these values for extraterrestrial conditions. Materials that are textured, inhomogeneous, patterned, or corrugated require special consideration. Measurements are typically made indoors using light sources other than natural sunlight, though it is possible to configure systems using natural sunlight as the illumination source, as in Practice E
In Field Continuous Monitoring Campaign As previously mentioned, two geometrically equivalent dedicated buildings were used for comparing the thermal-energy performance of the cool shutter with respect to the traditional dark shutter.
For this purpose, a continuous monitoring campaign was designed in order to measure the thermal effect of the optimized shutter on external surface shutter temperature Te-s , internal surface shutter temperature Ti-s , air-gap temperature between the shutter and the glass system Tag , indoor air-operative-mean radiant temperature Tair, Top, Tmr.
All these parameters were compared to significant weather variables such as outdoor dry bulb temperature Tout and global solar radiation on a horizontal plan Gh measured on the roof of a building located in close proximity.
The permanent continuous monitoring setup Figure 1 allowed a measurement every 20 s and post-processing of all the microclimate and weather data , while the specific sensors applied on the shutter systems, measuring Te-s, Ti-s, and Tag, consisted of independent temperature probes with incorporated data-loggers dedicated to this campaign.
Figure 1. Continuously monitored buildings. The agenda of the continuous monitoring campaign was designed in order to analyze a Baseline Scenario BS conditions, i.
In particular, the step-by-step layout of the campaign is reported in Table 1. Therefore, the continuous monitoring allowed assessing the thermal-energy effect of the cool shutter in free floating and thermally controlled regimes. The thermal properties of the two test buildings are reported in Table 2, where thermal properties of opaque envelope components of the test-rooms were calculated according to . Energies , 8 Table 1. Agenda of the continuous monitoring campaign. Table 2. Analysis of the Baseline Scenario BS In order to compare the thermal performance of the window system and the indoor environment of the two test-rooms with varying the shutter reflectance, the configuration of the test-room buildings before the implementation of the cool shutter was analyzed and indicated as Baseline Scenario BS.
In particular, the thermal behavior of the shutter system and the indoor thermal behavior of the buildings were compared in order to identify their performance before the modification of solar reflectance capability in only one test-room TR-2, Figure 1b.
Therefore, all the considerations carried out to compare the two scenarios BS and CS , were performed by taking into account the comparative dynamics of the two monitored buildings, before the optimization of the shutter.
Analysis of the Cool Scenario CS The analysis of the cool shutter was performed starting from the results of the BS aimed at defining a sort of reference behavior of the test-rooms. After the implementation of the cool shutter, a comparative analysis of the CS applied in TR-2 compared to the non-cool scenario in TR-1 was carried out, by considering both free-floating and indoor thermal controlled conditions.
In particular, external and internal surface temperature of the shutters and the air temperature measured between the shutter and the glass Tag were registered every 10 min for both the test-rooms in parallel. A comparative assessment has been performed in order to investigate the overheating reduction of the window system and its effect on the indoors.
The CS was also analyzed in terms of energy requirements for cooling, indoor air and mean radiant temperature in the center of the thermal zone, by comparing the cool shutter TR-2 with respect to the non-cool shutter installed in TR Discussion of the Results 3.
Analysis of the Optical Properties The lab measurements Figure 2 indicate a huge increase of solar reflectance of the Cool Shading system, which reported to have a solar reflectance of The thermal emittance of both systems was measured and gave the same value, i.
Figure 2. Spectrophotometer measurement results of solar reflectance of Cool Shading vs. Dark Shading. Energies , 8 3. Analysis of the Baseline Scenario The baseline analysis was carried out in order to monitor and to study the thermal-energy behavior of the continuously monitored prototype buildings before the implementation of the Cool Shading system in one of the buildings TR2—Test-Room 2, Figure 1b. Figure 3 reports the thermal profiles of the air-gap temperature and internal surface temperature of the shading systems in both the test-rooms.
It shows how the two buildings could be approximated to have equivalent thermal behavior for the purpose of this work, since the average difference during the monitoring period 10 February—10 April was 0.
The differences between thermal maximum and minimum peaks were 0. Therefore, the following analysis of the shading system will take into account these few differences. The all data of the monitored period are reported in Figure 4, where a negligible difference was confirmed between the two test-rooms. Figure 3. Thermal profiles of the monitored test-rooms during the baseline characterization.
Figure 4. Shutter external surface temperature a and airgap temperature b of the two test-rooms vs. Figure 5 reports the main indoor thermal parameters affecting indoor thermal comfort conditions in buildings: air temperature of each test-room a and mean radiant temperature b. These thermal parameters showed a non-negligible difference between the two buildings, which have been taken into account in further analyses.
While the average difference in terms of air temperature was lower than 0. This finding guided the choice of the test-room where the Cool-Shading should be installed. In fact, the Cool-Shading has been installed in the hotter test-room TR-2 in order to making safe the results of this experiment, and to Energies , 8 underestimate the effect of the cool shutter. These peculiarities could be motivated by the fact that the test-rooms were designed in order to have the same stationary properties Table 2 but they are characterized by different dynamically variable properties, such as roof solar reflectance, for instance.
These properties mainly affect the surface temperature of the opaque envelope systems, detected by mean of global thermometer measuring mean radiant temperature within each test-room. Figure 5.
Indoor thermal behavior of the test-rooms before the implementation of the Cool Shading systems in TR2. Indoor air temperature trends a , and mean radiant temperature trends b.
Thermal Behavior of the Shading System The analysis of the thermal behavior of the monitored shading system was carried out in order to highlight its effect in terms of passive cooling for the prototype buildings.
Now the air and surface temperature of the shading system is analyzed vs. The main data collected in summer 12 June—27 August in free floating conditions showed that there was an important correlation between external thermal conditions and the thermal behavior of shading air gap, while this correlation was weaker with respect to the radiative conditions of the site.
Energies , 8 Figure 6. Figure 7. Air gap and surface temperature of the shutters vs. Thermal Behavior of the Indoors The indoor thermal comparative analysis is carried out by considering both the free floating conditions and the operative-HVAC conditions. Figure 8 shows the indoor mean radiant temperature and air temperature values vs. Even larger effects were found in terms of mean radiant temperature, as expected.
Additionally, these differences were in the opposite direction with respect to the baseline analysis where the TR-2 Cool Shading scenario was the hottest one. Therefore, the effects of the installed cool shutter have to be considered even larger than the ones plotted in Figure 8, by taking into account the observations reported in Section 3. Figure 8.
Indoor thermal comparative assessment of the two configurations in terms of a mean radiant temperature and b air temperature, when the HVAC system is operative.
The comparative thermal analysis of the two scenarios is then performed in free floating conditions, in summer period 12 June—27 August. Figure 9. Indoor thermal comparative assessment of the two configurations in terms of a air temperature and b mean radiant temperature, in free floating conditions.
Energy Analysis The analysis of the energy performance of the prototype buildings showed that the Cool Shutter produced an important reduction in the cooling energy requirements as reported in Figure CS registered much lower energy needs than DS with varying weather conditions, as described by the two lines representing the daily maximum peaks of global solar radiation and outdoor dry bulb temperature.
In particular, the correlation coefficient between the energy saving varying from Therefore, the main experimental findings demonstrated how the more is the outdoor thermal peak, the more is the shutter effect in reducing cooling energy consumption, with no evident correlation with daily global solar radiation peaks.
Figure Daily energy requirement for cooling of CS and DS with varying daily weather parameters, i. Conclusions Starting from previous studies about the effect of cool roof systems and cool coatings for reducing building energy consumption in summer, this study aimed at experimentally assessing the in-field behavior of cool shutters vs.
To this end, a dedicated continuously monitored experimental apparatus was used in order to monitor these two shading systems in parallel, with varying weather conditions and operative conditions, i. The experimental apparatus consisted of two full-scale prototype buildings representing typical residential construction where two microclimate stations and one weather outdoor station are installed and used for the purpose of the work.
A preliminary experimental analysis of the coating was operated. Solar reflectance and thermal emittance was measured.
Also the indoors were cooled by the passive system, showing a lower temperature by about 1. The energy analysis showed that the cool shutter was able to largely reduce the energy requirement for cooling of the Cool Scenario, in hotter days in particular.
The author thanks the PhD student Gloria Pignatta for carrying out the spectrophotometer measurements. Conflicts of Interest The author declares no conflict of interest.
References 1. Salata, F. A case study of technical and economic comparison among energy production systems in a complex of historic buildings in Rome. Energy Procedia , 45, — Nearly zero-energy buildings of the Lombardy region Italy , a case study of high-energy performance buildings. Energies , 6, — Thermal comfort: Design and assessment for energy saving. Energy Build. Thiel, C. A materials life cycle assessment of a net-zero energy building.
Peng, L. Regarding the building's performance, lower surface temperatures decrease the heat penetrating into the building and, therefore, decrease the cooling loads in case of air-conditioned buildings, or create more comfortable thermal conditions in case of non-air-conditioned buildings.
In an urban environment, it contributes to decrease in the ambient air temperature, mitigating the heat island effect [ 2 , 4 , 8 , 9 ]. The intensive research that has been carried out in recent years has led to the development of new-generation materials and techniques that present advanced thermal characteristics, dynamic optical properties, increased thermal capacitance and a much higher heat island mitigation potential [ 6 ].
One main requirement of an innovative material is the ability to be more reflective and present lower surface temperatures during the cooling period, while being more absorptive and taking advantage of the solar gains during the heating period [ 10 ].
This property can be described and analyzed by thermochromism. The thermochromic effect can be defined as a change in the spectral properties of an organic or inorganic substance caused by heating or cooling. In intrinsically reversible organic thermochromic systems, heating above a defined temperature causes a change in color from darker to lighter tones.
This transition is achieved by a thermally reversible transformation of the molecular structure of the pigments that produces a spectral change of visible color. When temperature decreases below the color-changing point, the system returns to its thermally stable state [ 11—16 ].
Toward this direction, thermochromic color-changing coatings have been developed and tested. Thermochromic pigments have been developed as three-component organic mixtures, and they were incorporated into common white coating [ 13 , 14 ]. Karlessi et al. These results reveal the potential of thermochromic materials to avoid overheating in summertime and absorb heat in wintertime when it is necessary. However, photodegradation is a major problem for thermochromic materials when exposed to an outdoor environment.
During a day experimental period in outdoor conditions of eleven thermochromic coatings, the colored phase faded and solar reflectance was increased, while the tone of the colorless phase became darker and solar reflectance was decreased [ 10 ]. Ma et al.
Various techniques have been tested to decrease the degradation of the thermochromic coatings and improve their outdoor performance. Experiments proved that when UV absorbers are incorporated in the thermochromic coatings, the optical efficiency does not improve and the aging problems remain.
Efficiency is improved when the UV protectors are applied on the surface of the coatings but still the problem of degradation is important. UV filters with a transmittance at the UV part of the solar radiation close to zero have also been used for the photostabilization of the thermochromic coatings [ 6 , 19—21 ].
Results, however, showed that although the optical performance improves considerably the problem remains. This indicates that not only the ultraviolet but also other parts of the solar radiation interact with the molecular bonds, having a negative effect on thermochromism. The advantages that can be derived from their color-changing properties concerning energy efficiency in buildings, indoor air environment and urban microclimate encourage further investigation [ 10 ] and have inspired this work.
The following study aims to investigate the optical performance of a thermochromic coating under accelerated aging conditions, using combinations of UV and optical filters to isolate the influence of different parts of the solar radiation. Microencapsulation serves as a barrier between the thermochromic system and the chemicals around it, such as the paint base, protecting the system from weather conditions, oxidation, etc. An appropriate binder system that should not itself absorb infrared radiation was produced for the development of the thermochromic coatings.
In Figure 1 , the thermochromic sample in three different thermal phases before the exposure to accelerated aging conditions is presented.
An intermediate phase is presented in Figure 1 b. Figure 1. Figure 2.
View large Download slide a Transmittance of the filters at a range of — nm. The appropriate selection of the filters was based on their transmittance range and the aim was to cover partially the whole wavelength range, providing thus the ability to isolate the influence of the aging conditions in each part of the spectrum and for each filter.