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11th Nordic Nordic Symposium Symposium on on Building Building Physics, Physics, NSB2017, NSB2017, 11-14 11-14 June June 2017, 2017, Trondheim, Trondheim, Norway Norway 11th
Total Solar Transmittance Quantifying of Transparent Insulation Building Materials Based on Real Climate The 15th International Symposium on DistrictOutdoor Heating andMeasurements Cooling Miroslav Čekona,a,*, Richard Slávikaa
Miroslav Čekon *, Richard Assessing the feasibility of using theSlávik heat demand-outdoor Brno University University of of Technology, Technology, Faculty Faculty of of Civil Civil Engineering, Engineering, Centre 602 Brno Centre AdMaS, AdMaS, Veveří Veveří 331/95, 602 00, 00, Brno, Brno, Czech Czech Republic Republic temperature function for a long-term district331/95, heat demand forecast a a
Abstract Abstract
I. Andrića,b,c*, A. Pinaa, P. Ferrãoa, J. Fournierb., B. Lacarrièrec, O. Le Correc
Solar transmittance belongs the properties that frequently field Pais of buildings buildings as those those specifically SolaraIN+ transmittance belongs to to Technology the optical optical and properties that are are more more frequently required in the field of as specifically Center for Innovation, Policy Research - Instituto Superiorrequired Técnico, in Av.the Rovisco 1, 1049-001 Lisbon, Portugal related aspects point of possible method for the Veolia Recherche Innovation, 291A Dreyfous Daniel, Limay, Franceof related to to solar solar energy energy and and bthermal thermal aspects & point of view. view. AAvenue possible method for 78520 the measurement measurement of solar solar transmittance transmittance of of c building’s and introduced and tested. tested. The The method is based based on an anKastler, outdoor climate conditions and two two Département Systèmeswas Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred 44300 Nantes, France and building’s systems systems and materials materials was introduced and method is on outdoor climate conditions pyranometers measurement approach. approach. The The experimental experimental setup setup was was contrasted contrasted by by pyranometers setup setup applying applying of of comparative comparative in-situ in-situ measurement spectrophotometer method and its validity was tested by measurements comparison with different options to obtain the best solar spectrophotometer method and its validity was tested by measurements comparison with different options to obtain the best solar transmittance determination determination in in an an outdoor outdoor uncontrollable uncontrollable condition. condition. Although, transmittance Although, these these measurements measurements are are applicable applicable only only for for the the Abstractmeasurement particular measurement environment, environment, they they can can easily easily provide provide an particular an information information about about studied studied parameters. parameters. A A good good agreement agreement was was found and and the the introduced found introduced method method was was verified verified for for aa typical typical building’s building’s transparent transparent and and translucent translucent systems systems like like simple simple glass glass pane pane District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the and Plexiglas. This was also implemented for the solar transmittance determination of a particular transparent insulation and Plexiglas. This was also implemented for the solar transmittance determination of a particular transparent insulation material material emissions from the Methyl buildingMethacrylate sector. Thesebasis. systems require of high which are through the the heat in the honeycomb on Coupling the two (or photodiodes) with ingreenhouse the form form of ofgas honeycomb on Poly Poly Methyl Methacrylate basis. Coupling of theinvestments two pyranometers pyranometers (orreturned photodiodes) with the sales. Dueof the intensity changed behind climateand conditions building renovation policies, demandenables in the its future could decrease, monitoring in the materials its estimation applicability as monitoring oftosolar solar intensity behind and in front front and the measured measured materials and and its ratio ratioheat estimation enables its applicability as an an prolonging the investment return period. alternative, integrated and less cost consuming method towards the characterization by more sophisticated spectrophotometer alternative, integrated and less cost consuming method towards the characterization by more sophisticated spectrophotometer or or Thesimulator main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand solar method. solar simulator method. district of Alvalade, locatedLtd. in Lisbon (Portugal), was used as a case study. The district is consisted of 665 ©forecast. 2017 The TheThe Authors. Published by Elsevier Elsevier Ltd. © 2017 Authors. Published by ©buildings 2017 Thethat Authors. Published by Elsevier Ltd. committee vary in both construction period and typology. Three scenarios (low, medium,Physics. high) and three district Peer-review under responsibility of the organizing of the 11thweather Nordic Symposium on Peer-review under responsibility of the organizing committee Nordic Symposium on Building Building Physics. Peer-review responsibility of the organizing committee of of the the 11th 11thTo Nordic Symposium Buildingheat Physics. renovation under scenarios were developed (shallow, intermediate, deep). estimate the error,onobtained demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. Keywords: Solar transmittance; Outdoor measurements; TIMs; Spectrophotometry; Transparent; Translucent; Pyranometer Keywords: Solar transmittance; Outdoor measurements; TIMs; Spectrophotometry; Transparent; Translucent; Pyranometer The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). 1. Introduction 1.scenarios, Introduction The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hoursthere of 22-139h during the heating season (depending on the combination of weather and Currently sector, are needs for building physical and Currently in in the the building building sector, there are continuously continuously needs increased for determining determining building physical and optical optical renovationofscenarios considered). On the other hand, Transparent function intercept forbuilding 7.8-12.7% per decade (depending on the properties structures, systems and components. and translucent structures form an important properties of structures, systems and components. Transparent and translucent building structures form an important coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and part of envelopes. Besides thermal part of building building envelopes. thermal quantification quantification of of transparent transparent and and translucent translucent systems, systems, optical optical properties properties improve the accuracy of heat Besides demand estimations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and * Corresponding Corresponding author. author. Tel.: Tel.: +420-541-148-078; +420-541-148-078; fax: fax: +420-541-240-996. +420-541-240-996. * Cooling. E-mail address: address:
[email protected],
[email protected],
[email protected] [email protected] E-mail
Keywords: Heat demand; Forecast; Climate change 1876-6102 © © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. 1876-6102 Peer-review Peer-review under under responsibility responsibility of of the the organizing organizing committee committee of of the the 11th 11th Nordic Nordic Symposium Symposium on on Building Building Physics. Physics. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the organizing committee of the 11th Nordic Symposium on Building Physics 10.1016/j.egypro.2017.09.694
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are equally important parameters, particularly optical properties such as solar transmittance etc. There are several ways for measuring solar transmittance, such as laboratory spectrophotometric or indoor solar simulator methods applying of a spectrophotometer or solar simulator for determining the optical properties respectively. For this purpose, various types of devices are developed, e.g. UV/VIS/NIR spectrophotometers or specific solar simulators, whose acquisition costs have a higher requirements and less available character in this sense. The possible limitation of spectrophotometer method is that it can measure obviously certain materials of limited homogenous structure and maximum thicknesses. More thicker materials or specific types of texture based are very difficult to measure or finally it cannot be done at all, thus special prototypes usually need to be used. Another way concerns on solar simulator utilizing, where uniformed, controlled and standardized solar distribution can be exposed to the measured sample and finally determines the solar transmittance as ratio of monitored solar intensities behind and in front of measured sample. The initial idea of this purpose was to obtain solar transmittance parameters of various transparent insulation systems whose internal structures, dimensions and overall thicknesses are specific to measure by available methods, such as spectrophotometry [1]. Several studies aimed to measure the directional-hemispherical (also sometimes called direct-diffuse) solar transmittance for several different honeycomb-type structures with an indoor solar simulator and a 40 cm diameter integrating sphere for incidence angles up to 70° [2, 3]. In this relation, outdoor measurements using the sun as the source might be the option. Platzer [2] point out that it is not an option for Central European climate. Although there are many specific issues to take into account, such as inclined angular dependence, fluctuations of solar irradiation and overall solar distribution as well as cardinal point aspect, we tried to test and verify the using of solar transmittance estimating by real outdoor measurements. This is already implemented in standard test method for solar transmittance of sheet materials using sunlight with detailed specification and procedures according to ASTM E1084-86(2015) [4]. Overall, there is lack information regarding real outdoor measurements in literature as typically used for solar transmittance measurements. This may represent very simple and well available way of measuring the total solar transmittance parameter. 2. Objective and method The object of this study demonstrates an availability and simple use of two pyranometers setup and/or alternatively two small photodiodes [4] as a solar detector for possible substitution of measuring a total solar transmittance using the sun as the source. During measurements were obtained data with aim to develop and optimize final experimental setup as contrasted with spectrophotometry results. Own measurement apparatus was proposed taken fundamental specification of ASTM E1084-86(2015) into account. Finally, two pyranometers implemented in square boxes and third additionally opened to the outdoor conditions were applied in order to determine the total solar transmittance of typical building transparent and translucent materials, such as transparent insulation material etc. All results were taken during measurements where maximum sun height above horizon has been achieved during midday at 60° conducted at the research center AdMaS of Brno University of Technology (longitude 16°34´, latitude 49°14´, altitude 297.23 m). Two different methods were contrasted. First based on laboratory spectrophotometer measurements, a Perkin Lambda 1050 UV/VIS/NIR spectrophotometer with a 150mm Spectralon integrating sphere was used to measure solar spectral transmittance. This apparatus can register spectral properties ranging from 200 nm to 3300 nm. Spectral curves and integrated Total Solar Transmittance (TST) values from 280 to 2 500 nanometers are obtained. Second method is based on proposed outdoor experimentation applying of comparative in-situ measurements approach using the sun as the source. 3. Presented concept and procedure of test setup development As aforementioned, the initial idea of this research was to obtain solar transmittance parameters of transparent insulation material in the form of honeycomb on Poly Methyl Methacrylate basis as well as Polycarbonate systems that are strongly specific to measure by available methods, such as spectrophotometry. The first concept of measuring was simply based on two pyranometer sensors, one implemented into square cardboard box covered by white office paper including measured sample to obtain required data. Overall, we integrate three pyranometer sensors for this study, whose mutual accuracy were contrasted. Only at their maximum peaks, some deviations were measured,
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however at the low and acceptable level. In general, the error of pyranometer is according to producer lower than 7% of measured value. Results presented in Fig. 1 demonstrate an initial measurement taken horizontally for almost sunny and in Fig. 2 partly cloudy weather conditions respectively. Test setup can be seen on right of both figures. For the midday time, we can see solar transmittance of transparent insulation combined with glass pane varying between values 0.6 and 0.7, particularly somewhere around 0.65. This value was also measured and corresponded by spectrophotometry (see Table 1). Results obtained after 15:00 are not representative due to sunset and decreasing solar intensities up to zero.
Fig. 1. Measurement taken at initial stage based on higher solar intensities (a) Total solar intensity course and calculated total solar transmittance curve; (b) Initial simplified test setup (TIM – transparent insulation material, G – glass pane, PYR –pyranometer, T – solar transmittance)
Fig. 2. Measurement taken at initial stage based on lower solar intensities; (a) Total solar intensity course and calculated total solar transmittance curve; (b) Initial simplified test setup (TIM – transparent insulation material, G – glass pane, PYR –pyranometer, T – solar transmittance)
Further steps led us to propose a more sophisticated form of final test setup. Again, the idea was based on two pyranometers implementation into two square boxes to have reference value, that is principally guarded by background diffuse irradiation and third pyranometer typically opened above whole hemisphere to contrast with global solar radiation. In terms of integrating sphere principles, white round bowl was tested for circular collecting of solar irradiation penetrated throughout the measured sample. Results presented in Fig. 3 and 4 demonstrate a preliminary test stage of measurement taken horizontally for totally sunny and partly cloudy weather conditions respectively. Test setup can be seen on right side of both figures. For the midday time, we can see solar transmittance of transparent insulation combined with plexiglass at value around 0.8 and both transparent insulation and Plexiglas respectively at more than 0.9 level, which was not expected. The reason of those high values measured is in high reflective properties of all internal collecting parts, exactly the place where solar radiation sensor is located. Overall, the pyranometer application in white round bowl highly overestimates measured data. This is also principally specified in standard test method for total solar transmittance measurement using the sunlight, that the inside of the box shall be blackened so that its solar reflectance should be less than 0.10.
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Fig. 3. Measurement taken at preliminary test stage, clear sunny day (a) Obtained results, (b) Pyranometers implemented in white reflective round bowl of whole guarded box concept (TIM – transparent insulation material, PG – plexiglass pane, PYR –pyranometer, T – solar transmittance)
Fig. 4. Measurement taken at preliminary test stage, cloudy day (a) Obtained results; (b) Pyranometers implemented in white reflective round bowl of whole guarded box concept (TIM – transparent insulation material, PG – plexiglass pane, PYR –pyranometer, T – solar transmittance)
Based on all obtained findings of testing phases, a final test setup was proposed respecting the fundamental principles given in standard test method. All surfaces inside the boxes were blackened. In terms of comparative approach, test setup is based on reference and test box. Solar intensity sensor is implemented in the middle of round black bowl. For that purpose, a pyranometer or silicon PIN photodiode [5] can be used. For our case, both boxes are covered by transparent glass material at the top due to weather protection, if the long-term measurements are provided. Solar transmittance of transparent and translucent materials is then the ratio of the flux measured between test and reference box. 5. Optical properties investigation Finally, a combination of two separate methods of spectral and total solar transmittance quantification were contrasted with each other due to a specific property of applied transparent insulation, where an aspect of structured and diffuse solar radiation transfer appears to have a significant role. The first method takes the form of laboratory testing based on spectrophotometer measurements. A Perkin Lambda 1050 UV/VIS/NIR spectrophotometer was used. The spectrally obtained results are presented in Fig. 5, where the measurement data for the analyzed TIM is supplemented with other transparent materials used in tests. The second method is based on outdoor experiments applying the comparative in-situ measurement approach as was demonstrated during test setup development and its final optimization into functional type. The authors proposed their own test setup for this task. Two pyranometers were mounted in square boxes and a third additional device was left exposed to outdoor conditions. The equipment was used to determine the total solar transmittance of the TIM and other materials tested. The experimental setup is illustrated on right side of result presentations.
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Fig. 5. Spectral analysis; (a) Measurement apparatus spectrophotometer, (b) Spectral transmittance for solar region UV/VIS/NIR; PG – Plexiglass, TIM – transparent insulation material, SRS – solar radiation spectrum, G4 – clear glass pane 4mm, G6 – clear glass pane 6mm)
The results presented in Figs. 6 to 8 are from three different measurement days representing three different sky conditions: overcast (Fig. 6), occasional clouds (Fig. 7), and almost clear (Fig. 8). All the obtained results were finally evaluated as tabular values (Table 1). As can be seen, good agreement was achieved between both applied methods. A spectral transmittance of around 0.75 was obtained for pure transparent insulation in the laboratory, whilst its total outdoor value reached up to 0.80. This deviation can be caused by final test setup positioning. There is another scope for further improvements, however already obtained results can demonstrate an applicable and adequately relevant level. This test method also allows measurement of solar transmittance at angles other than normal incidence. In addition, it is particularly applicable to the measurement of transmittance of inhomogeneous, fiber reinforced, patterned, or corrugated materials since the transmittance is averaged over a large area.
Fig. 6. Final test stage, overcast; (a) Obtained results; (b) Pyranometers implemented in black non-reflective round bowl in box concept (TIM – transparent insulation material, G – glass pane, PYR –pyranometer, T – total solar transmittance)
Fig. 7. Final test stage, occasional clouds; (a) Obtained results; (b) Pyranometers implemented in black non-reflective round bowl in box concept (TIM – transparent insulation material, G – glass pane, PYR –pyranometer, T – total solar transmittance)
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Fig. 8. Final test stage, almost clear sky; (a) Obtained results; (b) Pyranometers implemented in black non-reflective round bowl in box concept (TIM – transparent insulation material, G – glass pane, PYR –pyranometer, T – total solar transmittance) Table 1. Total solar transmittance values λ λ SRSUV λ SRS VIS λ SRS NIR λ insitu´ ASTM G 0.2 – 0.3 0.3 – 0.8 0.8 – 2.5 0.3 – 3.0 173 μm μm μm μm G4 0.86 0.81 0.90 0.83 0.83 G6 0.81 0.69 0.88 0.76 PG 0.82 0.53 0.88 0.80 TIM 0.75 0.66 0.76 0.75 0.78 TIM+G4 0.65 0.53 0.68 0.62 0.65 ´ - overcast, ´´ - occasional clouds, ´´´ - almost clear sky character:
ρλ
λ
insitu´´ 0.3 – 3.0 μm 0.82 0.80 0.66
λ
insitu´´´ 0.3 – 3.0 μm 0.82 0.80 0.66
Conclusion The presented concept of total solar transmittance quantifying based on real climate outdoor conditions may have a possible utilization in the field of building applications concerning the solar transmittance determining. Presented data confront measurements, both at laboratory and real outdoor level. A good agreement was found and the tested method was applied for typical building’s transparent and translucent systems such as simple glass pane and Plexiglas, in addition material based on diffuse radiation transfer was measured, particularly transparent honeycomb insulation material. Regarding the real outdoor in-situ measurements using the sun as the source, this study aimed to introduce this specific methodical approach. For the future steps, angular dependence and testing in different year periods are planned to be analyzed, however as comparative method is applied, this aspect could be principally eliminated. Next material analyzing is focused on polycarbonate systems of various thickness, multi-wall structure and geometry. Acknowledgements This research was supported by the project GJ 16-02430Y "Contemporary concepts of climatically active solar façades integrating advanced material solutions" supported by Czech Science Foundation and under the project No. LO1408 "AdMaS UP – Advanced Materials. Structures and Technologies", supported by Ministry of Education. Youth and Sports under the "National Sustainability Programme I". References [1] C. Buratti, E. Moretti, Transparent insulating materials for buildings energy savings: experimental results and performance evaluation. Proceedings of third international conference on applied energy. Perugia, Italy. 2011. [2] W.J. Platzer, Directional-hemispherical solar transmittance data for plastic honeycomb-type structures, Solar Energy, Vol. 49, No. 5, 1992, pp. 359-369 [3] W.J. Platzer, Solar transmission of transparent insulation material, Solar Energy Materials, Vol. 16, 1987, pp. 275-287 [4] ASTM E1084-86(2015), Standard Test Method for Solar Transmittance (Terrestrial) of Sheet Materials Using Sunlight, ASTM International, West Conshohocken, PA, 2015 [5] M. Čekon, R. Slávik and P. Juráš, Obtainable Method of Measuring the Solar Radiant Flux Based on Silicone Photodiode Element. Applied Mechanics and Materials, Vol. 824, 2016, pp. 477-484.
