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Energy Procedia 158 Energy Procedia 00(2019) (2017)3191–3195 000–000 www.elsevier.com/locate/procedia
10th International Conference on Applied Energy (ICAE2018), 22-25 August 2018, Hong Kong, 10th International Conference on Applied Energy China(ICAE2018), 22-25 August 2018, Hong Kong, China
Numerical investigations on the thermal performance of adaptive NumericalThe investigations the thermal performance of adaptive 15th Internationalon Symposium on District Heating and Cooling ETFE foil cushions ETFE foil cushions Assessing the feasibility ofFlor, using theSun heat Haomin Wang, Jan-Frederik Yanyi anddemand-outdoor Yupeng Wu* Haomin Wang, Jan-Frederik Flor, Yanyi Sun and Yupeng Wu* forecast temperature function for a long-term district heat demand Department of Architecture and Built Environment, The University of Nottingham, University Park, Nottingham, NG7 2RD, UK Department of Architecture and Built Environment, The University of Nottingham, University Park, Nottingham, NG7 2RD, UK
I. Andrića,b,c*, A. Pinaa, P. Ferrãoa, J. Fournierb., B. Lacarrièrec, O. Le Correc
a
IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal
b Abstract Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France Abstract It has become increasingly popular among designers and engineers to use ETFE pneumatic foil constructions as an alternative to glass state of the art building envelopes, due to the weight,tohigh transparency, mechanical resistanceasand self-cleaning It has in become increasingly popular among designers andlow engineers use ETFE pneumatic foil constructions an alternative to features of ETFE. However, is still unclear theweight, thermalhigh performance of mechanical the ETFE resistance cushions and can self-cleaning be assessed glass in state of the art buildingitenvelopes, due to how the low transparency, Abstractof ETFE. comprehensively andHowever, what are the buildinghow thermal This studyofinvestigated thermal can performance of a features it effects is stillonunclear the performance. thermal performance the ETFEthe cushions be assessed developed prototype cushion through experimental measurementThis and study numerical simulation. numerical model of hasa comprehensively andETFE what are the effects onboth building thermal performance. investigated the The thermal performance District heating areexperimental commonly literature oneand of numerical the most effective solutions decreasing the been validated by networks results from tests experimental usingina the large climaticas chamber. The thermal resistance of numerical the for developed ETFE developed prototype ETFE cushion throughaddressed both measurement simulation. The model has greenhouse gas from the buildingtests sector. These systems require high investments which are also returned through the heat cushion at various environmental conditions (different indoor and outdoor temperature conditions) and different inclination been validated byemissions results from experimental using a large climatic chamber. The thermal resistance of the developed ETFE sales. were Due to theenvironmental changed conditions and based building renovation policies, heat demand in the could decrease, angles studied. Empiricalclimate correlations generated onand simulations be used for future building energy simulation. cushion at various conditions (different indoor outdoor could temperature conditions) and alsofuture different inclination prolonging the investment return period. angles were studied. Empirical correlations generated based on simulations could be used for future building energy simulation. The main©scope this paper to assess the feasibility of using the heat demand – outdoor temperature function for heat demand Copyright 2018ofElsevier Ltd.isAll rights reserved. ©forecast. 2019 The Authors. Published by responsibility Elsevier Ltd. The district of Alvalade, located in Lisbon (Portugal),committee was used of as the a case The district is consisted of 665 International Conference on Applied Selection and peer-review under of the scientific 10th study. Copyright © 2018 Elsevier Ltd. All rights reserved. This is an open access article under the CC period BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) th (low, medium, high) and three district buildings that vary in both construction and typology. Three weather scenarios Energy (ICAE2018). Selection and peer-review under responsibility of the scientific committee of the 10 International Conference on Applied Peer-review under responsibility of the scientific of ICAE2018 The 10th the International Conference on Applied Energy. renovation scenarios were developed (shallow,committee intermediate, deep). To– estimate error, obtained heat demand values were Energy (ICAE2018). comparedETFE; with Thermal results from a dynamic heat demand model, previously developed and validated by the authors. Keywords: Performance; Numerical simulation. The results showed thatPerformance; when only Numerical weather change is considered, the margin of error could be acceptable for some applications Keywords: ETFE; Thermal simulation. (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.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 1. Introduction decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and The pneumatic ethylene tetrafluoroethylene (ETFE) foil cushion has been widely applied into building facades renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the The pneumatic tetrafluoroethylene (ETFE) foil cushion mechanical has been widely applied into building facades and atrium in recentethylene years, due to its lightweight, hightotransparency, resistance, properties, coupled scenarios). The values suggested could be used modify the function parameters for theself-cleaning scenarios considered, and and atrium in recent years, due to its lightweight, high transparency, mechanical resistance, self-cleaning properties, etc.. Many landmark buildings adopted the ETFE cushion as their façade such as National Aquatics Center and improve the accuracy of heat demand estimations.
etc.. Many landmark buildings adopted the ETFE cushion as their façade such as National Aquatics Center and © 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. * Corresponding author. Tel.: +44 115 74 84011; fax: +44 115 95 13159.
E-mail address:author.
[email protected]. * Corresponding Tel.: +44 115 74 84011; fax: +44 115 95 13159. Keywords: Heat demand; Forecast; Climate change E-mail address:
[email protected]. 1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. th Selection peer-review under responsibility the scientific 1876-6102and Copyright © 2018 Elsevier Ltd. All of rights reserved. committee of the 10 International Conference on Applied Energy (ICAE2018). Selection and peer-review under responsibility of the scientific committee of the 10th International Conference on Applied Energy (ICAE2018). 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 © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of ICAE2018 – The 10th International Conference on Applied Energy. 10.1016/j.egypro.2019.01.1012
Haomin Wang et al. / Energy Procedia 158 (2019) 3191–3195 Author name / Energy Procedia 00 (2018) 000–000
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Changzhou Flora Expo in China[1]. In addition, ETFE cushion has great potential to contribute to building energy saving by actively managing the solar irradiation entering the room. However, there is limited amount of available information about ETFE cushion in terms of thermal performance, which is required by architects and engineers for building energy performance analysis. Consequently, there are issues arising in practice with the use of ETFE cushion where the simulated energy consumption data deviates significantly from real operational data. The main difference between the ETFE cushion and traditional double glazing is that the ETFE cushion has curved surface, which means the surface temperature distribution and air movement in the gas space is different from those for traditional double glazed window. So that the trend of U-value is different between the ETFE cushion and glazing. Therefore, a deep understanding of ETFE thermal property with different conditions is necessary instead of assuming it as glazing. This paper aims to investigate the thermal performance of a double layer ETFE cushion mock-up (clear foil, 200 µm), with the dimension of 1.2m in height and 1.2m in width, through experimental measurements using a large size climatic chamber and numerical simulations using CFD (Computational Fluid Dynamics). 2. Methodologies 2.1 Experimental measurement The thermal performance of the ETFE units was measured in a TAS series 2 LTCL600 climatic chamber as shown in Figure 1. The climate chamber comprises two insulated walk-in rooms (both are 4 m × 3.5 m × 2.6 m) providing a controlled temperature in the range from −25 °C to +60 °C and the relative humidity between 10% and 95%. Each enclosure can be individually controlled and thus it is possible to simulate external climate conditions in one, whilst the other mimics internal conditions. The apparatus setup was informed by International Standard ISO 12567-1:2012 for the determination of window and door thermal transmittance using the hot-box method, where the ETFE was placed between the two rooms at the centre of a developed insulated partition wall. The measurement method followed International Standard ISO 9869-1:2014 for in-situ thermal resistance measurements using heat flow meters. Surface temperature, air temperature and heat flux of the ETFE were obtained during operation [2-3].
(a) (b) Fig. 1: (a) External view of the climatic chamber, (b) position of the ETFE with sensors 2.2 Numerical calculations A relative simple and accurate method is going to be developed to evaluate the thermal resistance of the prototype ETFE cushion. Three methodologies are proposed for analysing the ETFE cushion, including standard calculation method based on EN673-1998 and computational fluid dynamics (CFD) simulations under varying boundary conditions. In detail, for method 1, the thermal resistance of the ETFE was obtained using the equations
Haomin Wang et al. / Energy Procedia 158 (2019) 3191–3195 Author name / Energy Procedia 00 (2018) 000–000
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mentioned in EN673-1998, which provides the empirical calculation procedures for multiple-layer glazing systems. As the ETFE cushion has curved boundary, the aspect ratio of the model might not be defined accurately. The compromise is using the integrated left and right surface distance as gas space distance. In addition, the other drawback is that the surface temperature profile cannot be presented in this model. The ANSYS FLUENT is used for simulating the steady state ETFE cushion under specified conditions. In the second method, fixed surface temperatures for the external and internal surface of the ETFE were used to simulate the ETFE cushion. In this way, the aspect ratio of the ETFE model is relatively accurate as the model is plotted into the ANSYS FLUENT. Also, it would be easy to adjust the mean cushion temperature and internal/external surface temperature difference therefore to obtain the thermal resistance at different environmental conditions. The method 3 is similar to the method 2 but adopts convective and radiative boundary conditions for the ETFE cushions rather than the fixed temperature. The benefit of this method is more realistic boundary conditions and possibly more accurate result. However, this method is time consuming as the mean cushion temperature and internal/external temperature difference cannot be changed directly, the target surface temperature value can be achieved only after several times of modifying the free stream temperature. In both methods 2 and 3, the simulation boundary conditions were obtained from the experimental tests for the initial mode validation. 3. Results and discussion Following EN673-1998, a standard condition, which is normally used for glazing and door U-value evaluation, was proposed for the experiment to achieve a temperature difference of 15℃ between the internal and external surface of the ETFE and average temperature of 10℃. Therefore, it is 2.5℃ for the left surface and 17.5℃ for the right surface of ETFE respectively for the experimental test. After a few attempts, it is obtained a condition close to the proposed standard condition where the ETFE surface temperature is 4.1 ℃ for the left surface and 17℃ for the right surface. The experimental measurement and also results obtained from the proposed 3 numerical methods are shown in Table 1. The obtained thermal resistance and also U-value of the cushion are shown in Table 2. It can be seen from the results that all three simulation methods achieve values of surface temperature and heat flux in close proximity to the experimental measurements. However the simplified method 1 and the method 3 seem to deliver the best results in comparison to the method 2. The deviation of the average R value is approximately 6% for Method 1 compared to the experimental measurement, and it is 7% for method 3. Experiments with other boundary conditions have also been evaluated, the Method 3 is generally more accurate than the other methods, therefore is preferred for further works. In addition, Method 3 with the more realistic boundary conditions enables to evaluate the temperature distribution and heat flux at various points on the sample surface, delivering very accurate results, but to the cost of a more complex model set-up and longer calculation times. Table 1: Measured and predicted surface temperatures and heat flux for the prototype ETFE.
Standard Testing condition
2
Left Convection Coefficient [W/m K] Right Convection Coefficient [W/m2K] Left Free Stream Temperature[K] Right Free Stream Temperature[K] Left surface 0.25 temperature [K] 0.50 0.75 Right surface 0.25 temperature [K] 0.50 0.75 Right Surface Heat 0.25 Flux [W/m2] 0.50 0.75
Experiment measurement 265.6 300.9 279.2 277.1 275.6 290.9 290.0 288.5 76.5 82.1 84.6
Method 1
Method 2
-
-
277.1
277.1
290
290
83.2
56.7 61.8 71.8
Method 3 8 8 265.6 300.9 276.6 275.9 274.8 291.9 291.0 290.1 71.9 78.4 85.8
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Table 2: Measured and predicted R value for the ETFE. Standard Testing Experiment Method 1 condition measurement R value (m K/W) 0.184957 0.180289 U value (W/m2K) 2.30 2.36
Method 2
Method 3
0.236593 2.21
0.193139 2.23
For a thorough understanding of the thermal performance of the ETFE in more realistic environmental conditions further simulations were conducted. Based on method 3, the simulated thermal resistance of the ETFE cushion at various surface temperature differences and different mean temperatures are shown in Fig. 2. From the graph it can be seen that at a steady average surface temperature difference of 15°C, the thermal resistance reduces by over 30% when the mean temperature drops from 35°C to -15°C. In contrast, at a constant mean average temperature of 10°C, the thermal resistance of the ETFE cushion, reduces only by approximately 10% when the surface temperature difference increases from -15°C to 35°C.
Fig. 2: The predicted thermal resistance of the ETFE under various temperature boundary conditions. Further investigation on the effects of the inclination angles on the thermal performance of the ETFE has also been conducted, the thermal resistance and U value of the ETFE at inclination angles of 90° (vertical position), 45° and 0° (horizontal position) are shown in Table 3. From Table 3, it can be seen that there is no significant difference for the thermal resistance and also U value of the ETFE at different angles. The U value of the ETFE decreases slightly from 2.60 to 2.52 W/m2K, with the inclination changes from 90 to 45°. Table 3: The thermal resistance and U value of ETFE under various inclination angles. Inclination External Surface Internal Surface R-Value angles Total Heat Transfer Total Heat Transfer (m K/W) (°) Coefficient (W/m2K) Coefficient (W/m2K) 90 23.00 6.9147 0.196 45 21.09 6.7928 0.201 0 20.29 7.6676 0.210
U-Value (W/m2K) 2.60 2.52 2.56
4. Conclusions A comprehensive investigation of the thermal performance of a prototype ETFE cushion was conducted using experiments and various numerical methods. Experimental results and CFD simulation results agree well with each other. The effects of various temperature conditions and also the inclination angles on the thermal resistance of ETFE have also been evaluated. It can be concluded that temperature difference across the internal and external
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layers of the ETFE cushion, and also the ETFE cushion average temperature have significant effects on the thermal resistance, it can affect the thermal resistance by over 10% in the temperature range commonly encounter in buildings. There is no significant difference for U value, when inclining the cushion at angles of 90 and 45°, respectively. This work might provide advices for the architects and also engineers applying ETFE for future building applications. References [1] Hu, J., et al., Buildings with ETFE foils: A review on material properties, architectural performance and structural behavior. Construction and Building Materials, 2017. 131: p. 411-422. [2] Sun, Y., et al., Experimental and numerical study of the thermal properties of a glazing system with an interstitial Venetian blind. Building and Environment, 2016. 103, 111-122. [3] Sun, Y., et al., Thermal evaluation of a double glazing façade system with integrated Parallel Slat Transparent Insulation Material (PS-TIM. Building and Environment, 2016. 105, 69-81.