- Email: [email protected]
Influence of different pigments on the facade surface temperatures
Available online at www.sciencedirect.com
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Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available Energy Procedia 00 (2017) 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia
Energy (2017) 000–000 447–453 EnergyProcedia Procedia132 00 (2017) www.elsevier.com/locate/procedia
11th Nordic Symposium on Building Physics, NSB2017, 11-14 June 2017, Trondheim, Norway
Influence of different pigments on the facade surface temperatures The 15th International Symposium on District Heating and Cooling
Ayman Bisharaa,*, Helge Kramberger-Kaplana, Volker Ptatschekb
AssessingDr.the feasibility of using the heat demand-outdoor Robert-Murjahn-Institute,Industriestraße 12, 64372 Ober-Ramstadt, Germany Germany DAW SE, Roßdörferstr. 23, 64372 Ober-Ramstadt, temperature function for a long-term district heat demand forecast a a
b b
Abstract a
I. Andrića,b,c*, A. Pinaa, P. Ferrãoa, J. Fournierb., B. Lacarrièrec, O. Le Correc
IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal
b Veolia & Innovation, 291 thermal Avenue Dreyfous Daniel, 78520 Limay, France insulation composite systems (ETICS) on energy-efficient More intensive shades of color are Recherche being used with external c Systèmes Énergétiques Environnement - IMT Atlantique, Kastler,of44300 Nantes,examinations France facades. TheseDépartement surfaces heat up extremely andetcause damage in ETICS. Based4 rue on Alfred an analysis laboratory and practical measurements (test houses) as well as on computations, this paper analyzes commonly used relative luminance (RL) and if this is of an adequate size for the prediction of the surface temperature. Significant issues are: (a) the deviation of the RL limit, (b) the performance capability and temperature advantages of improved pigmentation concepts (infrared reflecting pigments) on Abstract ETICS. Additionally, the total solar reflectance (TSR) and its influence on the surface temperature are evaluated. © 2017 The Authors. Published by Elsevier Ltd. ©District 2017 The Authors. Published by Elsevier addressed Ltd. heating networks are commonly in the literature as one of the most effective solutions for decreasing the Peer-review under responsibility of the organizing committee of Nordic Symposium on Building Physics. Peer-review responsibility organizing committee of the the 11th 11th Nordic Building Physics. through the heat greenhouse under gas emissions from of thethe building sector. These systems require highSymposium investmentsonwhich are returned sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, Keywords: Relative Luminance, IR-Color, TSR, Cool Façade, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 1.buildings Introduction that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were The trend shades of color energy-efficient also referred to as usingbyETICS, compared withtoward results more from a intensive dynamic heat demand model,on previously developed facades and validated the authors. Exterior Insulation and Finishing Systems (EIFS), cannot be ignored. Customers increasingly want dark shades. The The results showed that when only weather change is considered, the margin of error could be acceptable for some applications Even using improved renovation pigment problem heatlower up more than for light under solar radiation. (the erroris,in these annualsurfaces demand was than 20% all facades weather scenarios considered). However, after introducing mixtures, surface temperature be (depending avoided. Inonaddition, ETICS surfaces heat up more intensively than a scenarios,high the error value increased upcannot to 59.5% the weather and renovation scenarios combination considered). solid of the system. final coating The brick value façade, of slopesocoefficient increased average within the the range of 3.8% upstability to 8% per decade, thatThe corresponds to the that sometimes its on temperature exceeds temperature in therefore the number of heating hourstensions. of 22-139h during heating season (depending on the combination of weatherand and to great The heavythefluctuations in surface temperature can cause cracking ofdecrease plaster is exposed renovation scenarios Onare thealso otheroffered, hand, function intercept increased 7.8-12.7% per decade (depending the deformation. Special considered). facade colors which are equipped with for special infrared-reflecting pigment on (IRcoupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and color) in order to prevent excessive heating of the façade. improve the accuracy of heat 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 author. Tel.: +4961547172075; fax: +4961547170559. Cooling. E-mail address: [email protected]
Keywords: Heat demand; Forecast; Climate change 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.
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.2017.09.662
Ayman et Bishara et al. Procedia / Energy Procedia (2017) 447–453 A. Bishara al. / Energy 00 (2017)132 000–000
2448
To avoid the risk of damaging the ETIC system, a standard limitation for the relative luminance (RL) was defined at not less than 20 in Germany [1]. RL corresponds to the tristimulus value Y of the CIE XYZ color space (RL = 0 yields black and RL = 100 indicates diffuse white [2]). If the RL drops below 20, an expert must be aware that the risk of damaging the ETICS increases significantly (fig. 1 a). Further Standard test methods currently don’t yet exist. 2. Theoretical background 2.1. Heating up and relative luminance Relative luminance (RL) describes in principle the solar reflectivity and the resulting heating up of coating. However is it a sufficient parameter to describe the whole solar reflectivity? In the determination of the RL only the part of the visible radiation between 400 nm and 700 nm is considered. Due to the fact that solar radiation is made up of 42 percent UV-Vis and 58 percent invisible NIR, only a fraction from an energy point of view is considered [3]. The Total Solar Reflectance (TSR) is also a parameter to describe this phenomenon. TSR is the percentage of solar radiation reflected from a coating. The TSR takes into consideration the near infrared radiation (NIR) in addition to the ultraviolet and visible radiation (UV-Vis) and therefore covers the whole solar spectrum from 250 to 2,500 nm (fig. 1 b) [3]. This is confirmed also by the results of practical measurements in section 4.2.
Fig. 1. (a) Definition of relative luminance; (b) Chart (not to scale) of the electromagnetic spectrum of solar radiation relevant to heating, wavelength ranges for the determination of the RL value and the TSR value are marked.
2.2. Solar reflection of pigments The use of the TSR-value is closely linked with a new technological solution for reducing the solar heating of facades. The technical principle is that special pigments are used in the color shade formulations of facade paints that better reflect the solar radiation. Since color shades are nothing more than pigment mixtures, it is worth having a look at the individual pigments in table 1. Titanium dioxide is the most important pigment and has the highest TSR-value. As a result, it causes the lowest surface heating. At the other end of the spectrum, carbon black and iron oxide black pigments have the lowest TSR values of about 5 %. These pigments are responsible for intense surface heating. When considering common colored pigments, the TSR-values are considerably higher than those of black pigments, even the special IR-black pigments [4]. Colored pigments, therefore, play a minor role in the heating up, especially in very intensive shades. Table 1: TSR values of different pigments according to ASTM G173 Pigment
TSR [%]
Pigment
TSR [%]
Pigment
TSR [%]
Pigment
TSR [%]
Phthalocyanine blue
31.7
Dioxazine violet
41.1
Bismuth vanadate
71.1
Carbon black
5.4
Phthalocyanine green
29.1
Iron oxide red
36.3
Cobalt blue
50.9
Iron oxide black
5.4
Diketopyrrolopyrrole red
55.1
Iron oxide yellow
Titanium dioxide
83.5
IR-black 1, 2
45
14.4 22.6
AymanetBishara et al.Procedia / Energy00 Procedia (2017) 447–453 A. Bishara al. / Energy (2017) 132 000–000
3449
2.3. Formulations of very intensive color shades If the pigment composition of dark shades is analyzed with RL < 20, it can be seen that black pigments play a crucial role. The darker the shade, the more black pigment is used, because black pigments are coloristically, economically, and technically the pigment of first choice. This causes a dilemma, due to the fact that dark shades heat up more as a result of having a higher amount of black pigment. Experience (section 4) shows that the highest surface temperatures are obtained with dark gray and black shades. As a result, black pigments are the key to dark coatings. If this heating effect should be reduced, then there are two coloristic possibilities: Elimination of carbon black and iron oxide black pigments and use of black pigments with higher NIR reflectance, or total elimination of black pigments. However, the latter alternative demands the use of intensive colored organic pigments. In addition, complementary colors must be mixed to create neutral gray and black shades. This is considered to be a coloristically unsatisfactory method because of undesirable deviations in shade accuracy and color fastness. This increases the risk of having “multi-colored” facades. Moreover, a pure white intermediate coating or plaster must be applied as an NIRreflector in order to take advantage of the higher NIR-transparency of these pigments [4]. 3. Calculation of the surface temperature The surface temperature can be calculated based on the surface energy balance, depending on the following known boundary conditions: Heat transfer coefficient [W/(m²·K)], specific heat capacity [J/(kg·K)], Sun intensity [W/m²] and air temperature[°C], total reflectance coefficient (TSR) /Absorption coefficient [-]. 3.1. Energy balance on the outer surface For the thermal modeling, a wall with ETICS is selected. Fig. 2 shows schematically the energy balance on the outer surface (1). It results from partial heat flows, which flow into and out of the surface. These are: heat flow by absorption in W (Φa), heat flow by convection in W (Φconv), heat flow by conduction in W (Φcon), stored heat flow from the effective storage mass in W (Φst) and heat flow by long-wave emission/absorption in W (Φl) [5]. (1)
a st cond conv l
α
l
a
o
oeo aa
cond
i CCo e
conv
st
Fig. 2. Scheme of the energy balance on the outer surface
Equation (2) describes the absorbed heat flow, aS is the absorption coefficient, which influenced by pigments and is the outcome of the absorbed radiation divided by incident radiation. aS + TSR = 1, TSR is the result of the absorbed radiation divided by reflected radiation. IS = solar radiation intensity in W/m², Ao wall area in m², ϑ incident angle of sun. Equation (3) describes the stored heat flow from the effective storage mass, where Co = co·mo is the heat capacity of the outer storage effective mass in Ws/K. Equation (4) describes the heat exchange between air and surface by convection, is the heat transfer coefficient, it is equal to 10 W/(m²·K) at wind speed up to 1 m/s and to 20 W/(m²·K) at wind speed up to 3 m/s [6]. Equation (5) defines the heat exchange between the surface and substrate (conduction). Heat exchange between the surface and environment by longwave radiation is given in (6-8). a s I s A0 cos(s )
st C0
d 0 dt
(2, 3)
Ayman Bishara et al. / Energy Procedia 132 (2017) 447–453 A. Bishara et al. / Energy Procedia 00 (2017) 000–000
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conv A0 ( air 0 )
A0 ( i 0 ) d 4 e am A0 am
cond
la 0 A0 04
(4, 5) (6, 7)
The energy balance of the long-wave radiation Φl at the surface, when the surface temperature is θo and the ambient temperature is θam, is as follows: 4 l le 0 la A0 ( 0 am am 0 04 )
l 0 A0 ( am
4 am
) 4 0
(8a) (8b)
According to Kirchhoff's law, the emission coefficient and the absorption coefficient are the same for a certain wavelength range. So the surface absorbs in the longwave field a proportion εo from the longwave irradiation. The ambient, radiating on the walls has in general the air temperature, therefore the ambient temperature can be used with the air temperature. Thus, the surface temperature can be calculated from the energy balance equation (1). 4. Laboratory and in-situ analysis A series of laboratory tests and outdoor measurements on real facades were carried out to examine the heating up of a facade as well as the depending parameters and coefficients (RL, TSR, etc.). In addition, the lab test results are compared with the result of the real scale and the calculated one, so that finally a meaningful result can be obtained. 4.1. Laboratory plate test An insulation board (80 cm x 40 cm) is irradiated in the laboratory with artificial infrared radiation (radiation intensity 400 W/m², wave length 780 nm - 2500 nm). The board is made of 120 mm expanded polystyrene (EPS), adhesive and reinforcement compound with fabric; white scraped plaster (K20) and two final coats of paint with eight differently pigmented colours. A temperature sensor was placed in the centre of each pigmented colour area in order to measure the surface temperature. Fig. 3 (a) shows the measured temperature of each different pigmented surface. In order to determine the influence of the distance between radiation sources and the test board as well as of the incidence angle of the radiation the board was rotated by 30° so that the side A-B is farther away and the side G-H is closer to the emitter. In this case, the surface temperatures change decisively. The temperature of the D - Granit 5 (Caparol fan deck) decreases from 86°C to 67°C and that of the G - Malachit 5 (IR-color, Caparol fan deck) rises from 63°C to 85°C. The same test is repeated with a smaller distance between the plate and the radiation source, resulting in higher measured temperature values. After a rotation of 10°, so that H-G side is now further toward the emitter, it can be seen that the sensors, which are near the emitter (A, B, C, D), show again an increase of temperature values (fig.3 b).
Ayman Bishara et al. / Energy Procedia 132 (2017) 447–453 A. Bishara et al. / Energy Procedia 00 (2017) 000–000
451 5
4.2. Outdoor test of stand structure
83,0
surface temperature [°C][°C] Surface temperature
Coating 2
Coating 1
81,0 81
carbon black Carbon black
79,0
IR-black IR-black 1 1
77,0 77
Coating 4
Coating 3
Surface temperature [°C] Max. surface temperature [°C]
On an ETIC system (120 mm board of expanded polystyrene (EPS)), the surface temperatures of four coatings with identical color but different TSR values were measured (fig. 4, table 2). TSR measured over white background surface; 200μm dry film thickness according to [3]. Despite identical RL surface, temperatures from 71°C to 81°C are measured. Coatings with low TSR values create the highest temperatures. Coatings with high TSR values generate the lowest temperatures. The TSR-value is the suitable variable for predicting the surface temperatures.
IR-black 2 2 IR-black
75,0 73,0 73
organic pigments Organic
90 81 80 75
70 eight pigmented surfaces, test 2 Fig. 3. (a) Measured temperature of the eight71,0pigmented surfaces, test 1; (b) measuredpigment temperature of the 69 69,0 67,0
65 65,0 13:50 13:50
14:00 14:00
Local13:55 time local time
65 60
5.4
14.5 22.6 28.7 TSR-Value TSR-Value[%] [%]
Fig. 4. (a) ETICS test board with 4 different coatings; (b) measured surface temperatures on August 18 of four coatings; (c) maximum Surface temperatures on August 18 of the four coatings (with about 90° sun incidence angle) Table 2: Surface temperatures of four coatings with identical color but different TSR values on an ETIC system TSR [%]
[22.6] Coating 3
[28.7] Coating 4
RL [-]
[5.4] Coating 1 6.8
[14.5] Coating 2 6.8
6.8
6.8
θmax [°C]
81
77
73
71
4.3. Test house in Ober-Ramstadt, Germany At the façade of a test house in Germany, the outdoor climate, additional to the outer surface temperature has been measured. For the calculation of the surface temperature we have used the calculation method mentioned above, which is based on energy balance. The approx. 80 m² of south-south-west oriented facade was divided into two equal parts and provided with the following structure: EPS insulation, adhesive and reinforcement compound with fabric. On the left side mineral plaster and silicon based-white-paint is used, and on the right side organic plaster. The whole area was divided again into four equal-width, vertical strips. The two outer strips were coated in Granit 5 formulated with IR-black 1, and the two inner ones in the same shade formulated with IR-black 2. Nine temperature sensors were installed systematically on the façade as seen in fig. 5 (a). The measurement of surface temperature was started in 2011 and is still running. Temperature stability of EPS
A. Bishara et al. / Energy Procedia 00 (2017) 000–000
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Ayman Bishara et al. / Energy Procedia 132 (2017) 447–453
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Fig. 5 (a) Test house, location of the sensors, measured max. surface temperature in 2011; (b) measured temperature (29.08- 10.10. 2011)
Fig. 5 (a) shows the location of the temperature sensors as well as the maximum (T8) and minimum (T5) temperature measured during the testing period. Fig 5 (b) gives the results of surface temperature measured between August and October 2011, where the highest temperatures were recorded. Table 3 shows the calculated and measured max. temperatures of the IR-black1 and IR-black 2 pigments on both mineral and organic plaster from 2011 until 2015 in comparison. The calculated and measured values of the surface temperature correspond well. It is especially striking that the annual maximum surface temperatures are decreasing with time, despite the same sun radiation intensity. The max temperature was recorded on October 1, 2011 at sensor 8, which is located at the edge of the façade (IR-black 1 on organic plaster). The average of maximum temperatures is approx. 77°C occurred independently of the binder of the plaster layer on the surfaces painted with IR-black 1(TSR 14,5%). The temperatures on the surfaces painted with IR-black 2 (TSR 22.6%) averaged about 6°C under the temperatures of the surfaces IRblack 1; this temperature difference corresponds to the TSR-values difference between both pigments. Using this IRcolor the surface temperature remains under temperature stability of ETICS. Also the ETICS test after 4 years of outdoor weather is fulfilled according to ETAG 004, section 6.1.4.1. Visible damage to the surfaces or in the insulation layer is also not present after 4 years of outdoor weather exposure. Table 3. Maximum surface temperatures measured and calculated (2011 - 2015) Max. θo [°C]
2011
calculated 2012
calculated 2013
calculated 2014
calculated 2015
calculated
Area1 (mineral pla., IR1)
76.5
78.6
75
76.4
74
75.7
74
76.3
74
75
Area2 (mineral pla., IR2)
72
71.8
70
69.4
69
72.1
68
69.6
68
70.2
Area3 (organic pla., IR2)
74
71.8
70
69.4
71
72.1
70
69.6
70
70.2
Area4 (organic pla., IR1)
80
78.6
76
76.4
75
75.7
75
76.3
75
75
5. Results The outdoor tests confirm that carbon black and iron oxide pigments lead to the highest surface temperatures (fig. 4). Temperatures higher than 80°C are often reached in this area. By using IR-black pigments or organic pigment mixtures, the surface temperatures can be reduced by up to 10 K. This reduction in temperature has a technical advantage for temperature-dependent degradation processes of facade coatings. So the exceeding of temperature stability of ETICS can be avoided. On the other hand, temperatures over 70°C were also measured on surfaces with optimized IR reflection color (fig. 5). The temperature advantages of up to 20 K that are advertised in the brochures were never achieved in the practice test [7]. The reason for this discrepancy is the result of using artificial radiation sources in laboratory tests. For Halogen lamps, about 80% of the emitted energy lies in the IR and NIR parts of the spectrum. Only about 20 percent falls into the UV-Vis part [4]. These radiation sources cannot fully imitate the solar radiation and, therefore, leads to different results. Radiation sources that simulate solar radiation are essential for obtaining comparable results. This is confirmed by the results of practical measurements and of calculation. 6. Conclusions Coating structures on single insulation boards as well as complete facades were tested. The surface temperatures were measured over a long period, and calculated according to a calculation method based on surface energy balance. The total solar reflectance value (TSR) can be used to describe and forecast the heating up of facade. Depending on the TSR-value of a pigment the surface temperatures can be accurately calculated, so that they correspond well with the measurements. By using suitable optimized infrared radiation (NIR)-reflectance pigments, the surface temperatures can be reduced by up to 10 K. Yet, temperatures above 70°C still cannot be avoided in practice. Carbon black and iron oxide black
Ayman Bishara et al. / Energy Procedia 132 (2017) 447–453 A. Bishara et al. / Energy Procedia 00 (2017) 000–000
453 7
pigments are mainly responsible for heating up and should be avoided. Inorganic black pigments with increased NIRreflectance give coatings the following advantages: optimized TSR values, reduced heating, and weathering fastness for all silicate, silicone resin, and dispersion based facade paints. References [1] DIN 55699. Processing of thermal insulation composite system, Germany; 2005 [2] Manfred R. Introduction in colorimetry. Berlin New York; 1976 [3] ASTM G173- 03. Standard Tables for Reference Solar Spectral Irradiances; 2012. [4] Ptatschek V. Coloristic Ways to a Cool Façade. Sunspots; 2014. [5] Bishara, A. Bauklimatische Simulationsverfahren zur Lösung von Entwurfs-, Planungs- und Sanierungsaufgaben, Dissertation, TUD; 2011 [6] DIN 4108-3. Thermal protection and energy economy in buildings, NABau, 2013 [7] SolReflex with TSR formula for limitless dark shades on ETICS (http://www.baulinks.de/webplugin/2012/0627.php4)
ScienceDirect
Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available Energy Procedia 00 (2017) 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia
Energy (2017) 000–000 447–453 EnergyProcedia Procedia132 00 (2017) www.elsevier.com/locate/procedia
11th Nordic Symposium on Building Physics, NSB2017, 11-14 June 2017, Trondheim, Norway
Influence of different pigments on the facade surface temperatures The 15th International Symposium on District Heating and Cooling
Ayman Bisharaa,*, Helge Kramberger-Kaplana, Volker Ptatschekb
AssessingDr.the feasibility of using the heat demand-outdoor Robert-Murjahn-Institute,Industriestraße 12, 64372 Ober-Ramstadt, Germany Germany DAW SE, Roßdörferstr. 23, 64372 Ober-Ramstadt, temperature function for a long-term district heat demand forecast a a
b b
Abstract a
I. Andrića,b,c*, A. Pinaa, P. Ferrãoa, J. Fournierb., B. Lacarrièrec, O. Le Correc
IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal
b Veolia & Innovation, 291 thermal Avenue Dreyfous Daniel, 78520 Limay, France insulation composite systems (ETICS) on energy-efficient More intensive shades of color are Recherche being used with external c Systèmes Énergétiques Environnement - IMT Atlantique, Kastler,of44300 Nantes,examinations France facades. TheseDépartement surfaces heat up extremely andetcause damage in ETICS. Based4 rue on Alfred an analysis laboratory and practical measurements (test houses) as well as on computations, this paper analyzes commonly used relative luminance (RL) and if this is of an adequate size for the prediction of the surface temperature. Significant issues are: (a) the deviation of the RL limit, (b) the performance capability and temperature advantages of improved pigmentation concepts (infrared reflecting pigments) on Abstract ETICS. Additionally, the total solar reflectance (TSR) and its influence on the surface temperature are evaluated. © 2017 The Authors. Published by Elsevier Ltd. ©District 2017 The Authors. Published by Elsevier addressed Ltd. heating networks are commonly in the literature as one of the most effective solutions for decreasing the Peer-review under responsibility of the organizing committee of Nordic Symposium on Building Physics. Peer-review responsibility organizing committee of the the 11th 11th Nordic Building Physics. through the heat greenhouse under gas emissions from of thethe building sector. These systems require highSymposium investmentsonwhich are returned sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, Keywords: Relative Luminance, IR-Color, TSR, Cool Façade, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 1.buildings Introduction that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were The trend shades of color energy-efficient also referred to as usingbyETICS, compared withtoward results more from a intensive dynamic heat demand model,on previously developed facades and validated the authors. Exterior Insulation and Finishing Systems (EIFS), cannot be ignored. Customers increasingly want dark shades. The The results showed that when only weather change is considered, the margin of error could be acceptable for some applications Even using improved renovation pigment problem heatlower up more than for light under solar radiation. (the erroris,in these annualsurfaces demand was than 20% all facades weather scenarios considered). However, after introducing mixtures, surface temperature be (depending avoided. Inonaddition, ETICS surfaces heat up more intensively than a scenarios,high the error value increased upcannot to 59.5% the weather and renovation scenarios combination considered). solid of the system. final coating The brick value façade, of slopesocoefficient increased average within the the range of 3.8% upstability to 8% per decade, thatThe corresponds to the that sometimes its on temperature exceeds temperature in therefore the number of heating hourstensions. of 22-139h during heating season (depending on the combination of weatherand and to great The heavythefluctuations in surface temperature can cause cracking ofdecrease plaster is exposed renovation scenarios Onare thealso otheroffered, hand, function intercept increased 7.8-12.7% per decade (depending the deformation. Special considered). facade colors which are equipped with for special infrared-reflecting pigment on (IRcoupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and color) in order to prevent excessive heating of the façade. improve the accuracy of heat 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 author. Tel.: +4961547172075; fax: +4961547170559. Cooling. E-mail address: [email protected]
Keywords: Heat demand; Forecast; Climate change 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.
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.2017.09.662
Ayman et Bishara et al. Procedia / Energy Procedia (2017) 447–453 A. Bishara al. / Energy 00 (2017)132 000–000
2448
To avoid the risk of damaging the ETIC system, a standard limitation for the relative luminance (RL) was defined at not less than 20 in Germany [1]. RL corresponds to the tristimulus value Y of the CIE XYZ color space (RL = 0 yields black and RL = 100 indicates diffuse white [2]). If the RL drops below 20, an expert must be aware that the risk of damaging the ETICS increases significantly (fig. 1 a). Further Standard test methods currently don’t yet exist. 2. Theoretical background 2.1. Heating up and relative luminance Relative luminance (RL) describes in principle the solar reflectivity and the resulting heating up of coating. However is it a sufficient parameter to describe the whole solar reflectivity? In the determination of the RL only the part of the visible radiation between 400 nm and 700 nm is considered. Due to the fact that solar radiation is made up of 42 percent UV-Vis and 58 percent invisible NIR, only a fraction from an energy point of view is considered [3]. The Total Solar Reflectance (TSR) is also a parameter to describe this phenomenon. TSR is the percentage of solar radiation reflected from a coating. The TSR takes into consideration the near infrared radiation (NIR) in addition to the ultraviolet and visible radiation (UV-Vis) and therefore covers the whole solar spectrum from 250 to 2,500 nm (fig. 1 b) [3]. This is confirmed also by the results of practical measurements in section 4.2.
Fig. 1. (a) Definition of relative luminance; (b) Chart (not to scale) of the electromagnetic spectrum of solar radiation relevant to heating, wavelength ranges for the determination of the RL value and the TSR value are marked.
2.2. Solar reflection of pigments The use of the TSR-value is closely linked with a new technological solution for reducing the solar heating of facades. The technical principle is that special pigments are used in the color shade formulations of facade paints that better reflect the solar radiation. Since color shades are nothing more than pigment mixtures, it is worth having a look at the individual pigments in table 1. Titanium dioxide is the most important pigment and has the highest TSR-value. As a result, it causes the lowest surface heating. At the other end of the spectrum, carbon black and iron oxide black pigments have the lowest TSR values of about 5 %. These pigments are responsible for intense surface heating. When considering common colored pigments, the TSR-values are considerably higher than those of black pigments, even the special IR-black pigments [4]. Colored pigments, therefore, play a minor role in the heating up, especially in very intensive shades. Table 1: TSR values of different pigments according to ASTM G173 Pigment
TSR [%]
Pigment
TSR [%]
Pigment
TSR [%]
Pigment
TSR [%]
Phthalocyanine blue
31.7
Dioxazine violet
41.1
Bismuth vanadate
71.1
Carbon black
5.4
Phthalocyanine green
29.1
Iron oxide red
36.3
Cobalt blue
50.9
Iron oxide black
5.4
Diketopyrrolopyrrole red
55.1
Iron oxide yellow
Titanium dioxide
83.5
IR-black 1, 2
45
14.4 22.6
AymanetBishara et al.Procedia / Energy00 Procedia (2017) 447–453 A. Bishara al. / Energy (2017) 132 000–000
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2.3. Formulations of very intensive color shades If the pigment composition of dark shades is analyzed with RL < 20, it can be seen that black pigments play a crucial role. The darker the shade, the more black pigment is used, because black pigments are coloristically, economically, and technically the pigment of first choice. This causes a dilemma, due to the fact that dark shades heat up more as a result of having a higher amount of black pigment. Experience (section 4) shows that the highest surface temperatures are obtained with dark gray and black shades. As a result, black pigments are the key to dark coatings. If this heating effect should be reduced, then there are two coloristic possibilities: Elimination of carbon black and iron oxide black pigments and use of black pigments with higher NIR reflectance, or total elimination of black pigments. However, the latter alternative demands the use of intensive colored organic pigments. In addition, complementary colors must be mixed to create neutral gray and black shades. This is considered to be a coloristically unsatisfactory method because of undesirable deviations in shade accuracy and color fastness. This increases the risk of having “multi-colored” facades. Moreover, a pure white intermediate coating or plaster must be applied as an NIRreflector in order to take advantage of the higher NIR-transparency of these pigments [4]. 3. Calculation of the surface temperature The surface temperature can be calculated based on the surface energy balance, depending on the following known boundary conditions: Heat transfer coefficient [W/(m²·K)], specific heat capacity [J/(kg·K)], Sun intensity [W/m²] and air temperature[°C], total reflectance coefficient (TSR) /Absorption coefficient [-]. 3.1. Energy balance on the outer surface For the thermal modeling, a wall with ETICS is selected. Fig. 2 shows schematically the energy balance on the outer surface (1). It results from partial heat flows, which flow into and out of the surface. These are: heat flow by absorption in W (Φa), heat flow by convection in W (Φconv), heat flow by conduction in W (Φcon), stored heat flow from the effective storage mass in W (Φst) and heat flow by long-wave emission/absorption in W (Φl) [5]. (1)
a st cond conv l
α
l
a
o
oeo aa
cond
i CCo e
conv
st
Fig. 2. Scheme of the energy balance on the outer surface
Equation (2) describes the absorbed heat flow, aS is the absorption coefficient, which influenced by pigments and is the outcome of the absorbed radiation divided by incident radiation. aS + TSR = 1, TSR is the result of the absorbed radiation divided by reflected radiation. IS = solar radiation intensity in W/m², Ao wall area in m², ϑ incident angle of sun. Equation (3) describes the stored heat flow from the effective storage mass, where Co = co·mo is the heat capacity of the outer storage effective mass in Ws/K. Equation (4) describes the heat exchange between air and surface by convection, is the heat transfer coefficient, it is equal to 10 W/(m²·K) at wind speed up to 1 m/s and to 20 W/(m²·K) at wind speed up to 3 m/s [6]. Equation (5) defines the heat exchange between the surface and substrate (conduction). Heat exchange between the surface and environment by longwave radiation is given in (6-8). a s I s A0 cos(s )
st C0
d 0 dt
(2, 3)
Ayman Bishara et al. / Energy Procedia 132 (2017) 447–453 A. Bishara et al. / Energy Procedia 00 (2017) 000–000
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conv A0 ( air 0 )
A0 ( i 0 ) d 4 e am A0 am
cond
la 0 A0 04
(4, 5) (6, 7)
The energy balance of the long-wave radiation Φl at the surface, when the surface temperature is θo and the ambient temperature is θam, is as follows: 4 l le 0 la A0 ( 0 am am 0 04 )
l 0 A0 ( am
4 am
) 4 0
(8a) (8b)
According to Kirchhoff's law, the emission coefficient and the absorption coefficient are the same for a certain wavelength range. So the surface absorbs in the longwave field a proportion εo from the longwave irradiation. The ambient, radiating on the walls has in general the air temperature, therefore the ambient temperature can be used with the air temperature. Thus, the surface temperature can be calculated from the energy balance equation (1). 4. Laboratory and in-situ analysis A series of laboratory tests and outdoor measurements on real facades were carried out to examine the heating up of a facade as well as the depending parameters and coefficients (RL, TSR, etc.). In addition, the lab test results are compared with the result of the real scale and the calculated one, so that finally a meaningful result can be obtained. 4.1. Laboratory plate test An insulation board (80 cm x 40 cm) is irradiated in the laboratory with artificial infrared radiation (radiation intensity 400 W/m², wave length 780 nm - 2500 nm). The board is made of 120 mm expanded polystyrene (EPS), adhesive and reinforcement compound with fabric; white scraped plaster (K20) and two final coats of paint with eight differently pigmented colours. A temperature sensor was placed in the centre of each pigmented colour area in order to measure the surface temperature. Fig. 3 (a) shows the measured temperature of each different pigmented surface. In order to determine the influence of the distance between radiation sources and the test board as well as of the incidence angle of the radiation the board was rotated by 30° so that the side A-B is farther away and the side G-H is closer to the emitter. In this case, the surface temperatures change decisively. The temperature of the D - Granit 5 (Caparol fan deck) decreases from 86°C to 67°C and that of the G - Malachit 5 (IR-color, Caparol fan deck) rises from 63°C to 85°C. The same test is repeated with a smaller distance between the plate and the radiation source, resulting in higher measured temperature values. After a rotation of 10°, so that H-G side is now further toward the emitter, it can be seen that the sensors, which are near the emitter (A, B, C, D), show again an increase of temperature values (fig.3 b).
Ayman Bishara et al. / Energy Procedia 132 (2017) 447–453 A. Bishara et al. / Energy Procedia 00 (2017) 000–000
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4.2. Outdoor test of stand structure
83,0
surface temperature [°C][°C] Surface temperature
Coating 2
Coating 1
81,0 81
carbon black Carbon black
79,0
IR-black IR-black 1 1
77,0 77
Coating 4
Coating 3
Surface temperature [°C] Max. surface temperature [°C]
On an ETIC system (120 mm board of expanded polystyrene (EPS)), the surface temperatures of four coatings with identical color but different TSR values were measured (fig. 4, table 2). TSR measured over white background surface; 200μm dry film thickness according to [3]. Despite identical RL surface, temperatures from 71°C to 81°C are measured. Coatings with low TSR values create the highest temperatures. Coatings with high TSR values generate the lowest temperatures. The TSR-value is the suitable variable for predicting the surface temperatures.
IR-black 2 2 IR-black
75,0 73,0 73
organic pigments Organic
90 81 80 75
70 eight pigmented surfaces, test 2 Fig. 3. (a) Measured temperature of the eight71,0pigmented surfaces, test 1; (b) measuredpigment temperature of the 69 69,0 67,0
65 65,0 13:50 13:50
14:00 14:00
Local13:55 time local time
65 60
5.4
14.5 22.6 28.7 TSR-Value TSR-Value[%] [%]
Fig. 4. (a) ETICS test board with 4 different coatings; (b) measured surface temperatures on August 18 of four coatings; (c) maximum Surface temperatures on August 18 of the four coatings (with about 90° sun incidence angle) Table 2: Surface temperatures of four coatings with identical color but different TSR values on an ETIC system TSR [%]
[22.6] Coating 3
[28.7] Coating 4
RL [-]
[5.4] Coating 1 6.8
[14.5] Coating 2 6.8
6.8
6.8
θmax [°C]
81
77
73
71
4.3. Test house in Ober-Ramstadt, Germany At the façade of a test house in Germany, the outdoor climate, additional to the outer surface temperature has been measured. For the calculation of the surface temperature we have used the calculation method mentioned above, which is based on energy balance. The approx. 80 m² of south-south-west oriented facade was divided into two equal parts and provided with the following structure: EPS insulation, adhesive and reinforcement compound with fabric. On the left side mineral plaster and silicon based-white-paint is used, and on the right side organic plaster. The whole area was divided again into four equal-width, vertical strips. The two outer strips were coated in Granit 5 formulated with IR-black 1, and the two inner ones in the same shade formulated with IR-black 2. Nine temperature sensors were installed systematically on the façade as seen in fig. 5 (a). The measurement of surface temperature was started in 2011 and is still running. Temperature stability of EPS
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Fig. 5 (a) Test house, location of the sensors, measured max. surface temperature in 2011; (b) measured temperature (29.08- 10.10. 2011)
Fig. 5 (a) shows the location of the temperature sensors as well as the maximum (T8) and minimum (T5) temperature measured during the testing period. Fig 5 (b) gives the results of surface temperature measured between August and October 2011, where the highest temperatures were recorded. Table 3 shows the calculated and measured max. temperatures of the IR-black1 and IR-black 2 pigments on both mineral and organic plaster from 2011 until 2015 in comparison. The calculated and measured values of the surface temperature correspond well. It is especially striking that the annual maximum surface temperatures are decreasing with time, despite the same sun radiation intensity. The max temperature was recorded on October 1, 2011 at sensor 8, which is located at the edge of the façade (IR-black 1 on organic plaster). The average of maximum temperatures is approx. 77°C occurred independently of the binder of the plaster layer on the surfaces painted with IR-black 1(TSR 14,5%). The temperatures on the surfaces painted with IR-black 2 (TSR 22.6%) averaged about 6°C under the temperatures of the surfaces IRblack 1; this temperature difference corresponds to the TSR-values difference between both pigments. Using this IRcolor the surface temperature remains under temperature stability of ETICS. Also the ETICS test after 4 years of outdoor weather is fulfilled according to ETAG 004, section 6.1.4.1. Visible damage to the surfaces or in the insulation layer is also not present after 4 years of outdoor weather exposure. Table 3. Maximum surface temperatures measured and calculated (2011 - 2015) Max. θo [°C]
2011
calculated 2012
calculated 2013
calculated 2014
calculated 2015
calculated
Area1 (mineral pla., IR1)
76.5
78.6
75
76.4
74
75.7
74
76.3
74
75
Area2 (mineral pla., IR2)
72
71.8
70
69.4
69
72.1
68
69.6
68
70.2
Area3 (organic pla., IR2)
74
71.8
70
69.4
71
72.1
70
69.6
70
70.2
Area4 (organic pla., IR1)
80
78.6
76
76.4
75
75.7
75
76.3
75
75
5. Results The outdoor tests confirm that carbon black and iron oxide pigments lead to the highest surface temperatures (fig. 4). Temperatures higher than 80°C are often reached in this area. By using IR-black pigments or organic pigment mixtures, the surface temperatures can be reduced by up to 10 K. This reduction in temperature has a technical advantage for temperature-dependent degradation processes of facade coatings. So the exceeding of temperature stability of ETICS can be avoided. On the other hand, temperatures over 70°C were also measured on surfaces with optimized IR reflection color (fig. 5). The temperature advantages of up to 20 K that are advertised in the brochures were never achieved in the practice test [7]. The reason for this discrepancy is the result of using artificial radiation sources in laboratory tests. For Halogen lamps, about 80% of the emitted energy lies in the IR and NIR parts of the spectrum. Only about 20 percent falls into the UV-Vis part [4]. These radiation sources cannot fully imitate the solar radiation and, therefore, leads to different results. Radiation sources that simulate solar radiation are essential for obtaining comparable results. This is confirmed by the results of practical measurements and of calculation. 6. Conclusions Coating structures on single insulation boards as well as complete facades were tested. The surface temperatures were measured over a long period, and calculated according to a calculation method based on surface energy balance. The total solar reflectance value (TSR) can be used to describe and forecast the heating up of facade. Depending on the TSR-value of a pigment the surface temperatures can be accurately calculated, so that they correspond well with the measurements. By using suitable optimized infrared radiation (NIR)-reflectance pigments, the surface temperatures can be reduced by up to 10 K. Yet, temperatures above 70°C still cannot be avoided in practice. Carbon black and iron oxide black
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pigments are mainly responsible for heating up and should be avoided. Inorganic black pigments with increased NIRreflectance give coatings the following advantages: optimized TSR values, reduced heating, and weathering fastness for all silicate, silicone resin, and dispersion based facade paints. References [1] DIN 55699. Processing of thermal insulation composite system, Germany; 2005 [2] Manfred R. Introduction in colorimetry. Berlin New York; 1976 [3] ASTM G173- 03. Standard Tables for Reference Solar Spectral Irradiances; 2012. [4] Ptatschek V. Coloristic Ways to a Cool Façade. Sunspots; 2014. [5] Bishara, A. Bauklimatische Simulationsverfahren zur Lösung von Entwurfs-, Planungs- und Sanierungsaufgaben, Dissertation, TUD; 2011 [6] DIN 4108-3. Thermal protection and energy economy in buildings, NABau, 2013 [7] SolReflex with TSR formula for limitless dark shades on ETICS (http://www.baulinks.de/webplugin/2012/0627.php4)