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ScienceDirect Procedia Engineering 118 (2015) 268 – 275

International Conference on Sustainable Design, Engineering and Construction

Performance assessment of sustainable composite roofing assemblies using experimentation Vishakha Sakharea, Sanjay Rautb, Rahul Ralegaonkarc* a Research Scholar, Department of Civil Engineering, VNIT, Nagpur 440010, India Assistant Professor, Department of Civil Engineering, YCCE, Nagpur 440010, India c Associate Professor, Department of Civil Engineering, VNIT, Nagpur 440010, India

b

Abstract Over the hot climatic zones where the exposed building roofs impart significant heat gain in the buildings can be protected using reflecting and insulating materials as a retrofitting solution. The present paper elaborates application of sustainable reflectingcum-insulating (R-I) materials over the flat concrete roof surface for reducing the impact of heat gain inside the buildings. The composite R-I assemblies used for thermal performance assessment include aluminum sheet, broken glazed tiles, expanded polystyrene (construction waste), sawdust (industrial waste), mineral fiber board (recycled content 38%) and false ceiling panels (recycled content 90%). These materials were placed in two different combinations as a composite heat barrier assembly for exposed concrete roof of the two model rooms in an educational building over the considered geographic location. In comparison to the untreated concrete slab, the applied composite R-I assemblies resulted in an overall increase in thermal resistance of the first and second assembly by 1.9 and 3.9 times respectively. Over a period of a year under experimentation, the first and second retrofitted assembly resulted in 6% and 19% reduction in surface temperature respectively. The considered R-I materials for the experimentation have proved to be thermally efficient, lighter and cost effective solution for energy conservation inside the buildings. The R-I product can further be applied on larger roof areas by the designers to reduce the cooling load of the built environment as well as to increase the occupants comfort over the local climatic zone. © Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2015 2015The The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing committee of the International Conference on Sustainable Design, Engineering Peer-review under responsibility of organizing committee of the International Conference on Sustainable Design, Engineering and and Construction Construction 2015 2015. Keywords: Sustainable reflecting-cum-insulating (R-I) assembly; concrete roof; temperature; thermal resistance

* Corresponding author. Tel.: +91 712 2801090 E-mail address:[email protected]

1877-7058 © 2015 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 organizing committee of the International Conference on Sustainable Design, Engineering and Construction 2015

doi:10.1016/j.proeng.2015.08.426

Vishakha Sakhare et al. / Procedia Engineering 118 (2015) 268 – 275

1. Introduction Thermal insulation plays significant role in reducing cooling requirement inside a building in hot climate. In a typical commercial establishment, the space conditioning accounts for 50-70% of the total energy used [1]. The construction practices adopted mainly involve concrete as the roofing element which is noted for its high thermal conductivity. The exposed roof surfaces absorb solar heat that will input continuous heat inside the building and will add to the cooling load. Thermal barrier for building roof is generally installed either as over or under deck insulation. Al-Homoud (2005) presented an overview of the basic principles of thermal insulation along with detailed investigations on the most commonly used building insulation materials and their performance characteristics [2]. Alvarado et al. (2009) investigated the thermal effects of newly designed passive cooling systems on concrete roofs in existing buildings. Commercially available materials such as aluminum-1100 and galvanized steel were used as radiation reflectors; and polyurethane, polystyrene, polyethylene, and an air gap was used as insulation [3]. Double envelope roof constructions were investigated either as a preheating system of the external air [4] or as a double shell system in tilted roofs. In this case, ambient air passes through the air gap that incorporates a wet surface into its lower part, becomes cooler through evaporation and thus, lowers the surface temperature of the internal part of the roof [5]. Heat-insulating materials provided an effective means of reducing the apparent density and improving the refractory properties of manufactured components. Materials of natural occurrence viz., vermiculite, diatomite, infusorial earth, perlite, as well as synthetic materials - hollow microspheres obtained by sputtering of high-melting oxides such as Al2O3, mullite, and spinel were used as porous fillers [6-9]. However, the hollow spheres are costly products and are normally used to fabricate special high-temperature heat insulators [10]. Al-Malah et al. (2007) focused on the formulation of polyester–clay composite as an insulating material that gives the best thermal and mechanical properties [11]. Korjenic et al. (2011) developed, optimized, and observed the behavior of thermally insulating materials composed of renewable raw material resources originating from agricultural sources [12]. Hasegawa and Konna (2001) carried out an analysis on the thermal effect of the rooftop spraying system on slant roof [13]. Tanabe et al. (2000) had done a field study on a rooftop spraying system. The effect of roof spraying contributed to room temperature reduction in the summer season [14]. Ishihara et al. (1996) carried out an experimental study on thermal characteristics and water performance of rooftop lawn [15]. Hoyano et al. (2000) clarified the indoor thermal control effect of rooftop lawn planting with thin soil layer on a wooden building [16]. Al-Sanea (2002) evaluated and compared the thermal performance of building roof elements subject to steady periodic changes in ambient temperature, solar radiation and nonlinear radiation exchange. An implicit, control volume finite-difference method was developed and applied for six variants of a typical roof structure used in the construction of buildings in Saudi Arabia [17]. Tsang & Jim (2011) developed a theoretical basis of green roof thermal performance and applied theoretical calculations to estimate the effectiveness of green roof thermal performance and associated energy saving [18]. From the reviewed literature, it is significant that the substantial amount of energy is consumed for the space conditioning. It was also observed that the appropriate design of thermal barrier over the roof surfaces plays a significant role to improve the thermal performance inside the buildings. Application of appropriate, reflecting-cum-insulating material either over or under the roof slab is an effective solution to conserve the energy and the cost of operation (cooling load) as well. A very little research had revealed the application of sustainable materials for the reduction of overheating of the buildings. The present paper focuses on analyzing the behavior of roof surface temperature due to application of sustainable composite roofing assemblies for reducing cooling load of the built environment by experimentation. The techno-economic feasibility of considered composite roofing assemblies is also carried out. 2. Methodology In order to assess the performance of considered sustainable composite roofing assemblies the following stepwise methodology was adopted. x The ambient temperature data over the specific geographic location was collected for the study of temperature variations. x The volume of the built room under the study was estimated. x Locally available low cost, sustainable materials were identified.

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x The thermal properties of the used reflecting-cum-insulating (R-I) materials were assessed. x Two different combinations from the identified sustainable materials as a composite heat barrier assembly were retrofitted on the exposed concrete roof of the two model rooms. x The composite R-I assemblies retrofitted over the roof of model rooms were analyzed further experimentally and statistically (using the area under the curve approach) to check the performance of thermal barrier at various retrofitted layered assemblies. x The R-I combinations were checked and compared for economic viability. 3. Experimentation

North Fig. 1. Model room 1

Fig. 2. Model room 2

Fig. 3. Temperature gun

Two non air conditioned model rooms of dimension 3.2X3.2X4.0 cum (Fig 1 & Fig 2) were selected for experimentation at Visvesvaraya National Institute of Technology, Nagpur (Latitude: 21°06' N, Longitude: 79°03' E, Elevation: 310 m.), India. The geographic location has varying seasonal conditions as summer (February-May), rainy (June-September), winter (October-January). The monthly average ambient temperature and relative humidity are in the range of 27-41°C and 24-70% respectively [19]. The average wind speed is 44 m/s [20] and the average solar radiation is 18.34 MJ/m2/day [21] over the considered geographic location. The roof of the model rooms which were directly exposed to the sun were made up of conventional concrete slab (0.15 m. Thick). The vertical walls were made up of burnt clay bricks. Model room 1was having a wooden door (0.9X2.1 m.) on North facing wall and a window (1X1.2 m.) on the West and South wall (Fig 1), while model room 2 was having a wooden door (0.9X2.1 m.) on South facing wall and a window (1X1.2 m.) on the West wall (Fig 2).

Fig. 4. Variation of indoor surface temperature without insulation


With the help of temperature gun (Fig 3) the internal (I) exposed surfaces (I-East, I-South, I-West, I-North, Iuntreated concrete roof, I-Floor) temperature data were recorded (Fig 4). The monitoring was done on alternate hourly basis during working hours (8 am to 6 pm) over three months of duration (September–November 2010). The temperature data were recorded on four corners as well as the center of all the surfaces and the average values were used for the analysis. It is evident from Fig 4 that roof surface is the primary concern due to which excess heat in the model room. To reduce the temperature of the untreated roof, it must be protected with appropriate sustainable composite roofing assembly which intern reduces the cooling load. In order to apply sustainable composite roofing materials locally available raw materials were identified. 3.1. Application of sustainable composite roofing materials

Concrete slab (150 mm)

Expanded polystyrene + Saw dust

Plaster (10 mm)

Air gap (1m)

Fig. 5 (a). Assembly 1 composition

Fig. 5 (b). Over deck retrofitting

Fig. 5 (c). Under deck retrofitting

Fig. 5. Assembly 1: Aluminum sheet + expanded polystyrene + saw dust + false ceiling developed from industrial waste

Concrete slab (150 mm)

Plaster (10 mm)

Air gap (1m)

Expanded polystyrene + Saw dust

Fig. 6 (a). Assembly 2 composition Fig. 6 (b). Over deck retrofitting Fig. 6 (c). Under deck retrofitting Fig. 6. Assembly 2: Broken glazed tiles +expanded polystyrene + saw dust + false ceiling of mineral fiber board For the R-I composite assembly identified locally available sustainable materials were used. The composite assembly (Fig 5a) of expanded polystyrene, mortar, saw dust and reflectors with aluminum foil (reflectivity (r) 0.80, [22]) were applied over the RCC roof surface of model room 1. The commercially available aluminum was retrofitted with expanded polystyrene and sawdust as the over deck solution (Fig 5b). The false ceiling material (12 mm thick, 90% recycled paper mill waste) with thermal conductivity (k) as 0.3 W/m K [23] was applied as under deck solution (Fig 5c). The composite assembly (Fig 6a) of broken glazed tiles (reflectivity (r) 0.35, [22]), expanded polystyrene, sawdust and the commercially available mineral fiber board (false ceiling material, R=0. 25 m² K/W, 14 mm thick, 38% recycled content) was applied over the RCC roof surface of the model room 2. The broken glazed tiles were retrofitted as over deck solution (Fig 6b). The commercially available mineral fiber board was retrofitted with expanded polystyrene and sawdust composite as under deck solution (Fig 6c). A non-ventilated air cavity of 1 m. (Thermal conductance (Ca) as 6.22 W/m²K, [22]) was maintained between concrete roof slab and the false ceiling of both the assemblies (Fig 5a & Fig 6a). Experimental temperature log for various surfaces of the designed composite roof were recorded with the help of contact type temperature sensors & a data logger.

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4. Results and Discussion 4.1 Performance assessment of sustainable composite roofing assemblies The thermal properties (thermal conductivity, density, and specific heat) of various materials used for the development of composite roof slab (Fig 5a & Fig 6a) were studied further (Table 1) [22]. The overall thermal resistance of untreated concrete roof slab in combination with the external and internal plaster, including film coefficients was estimated as 0.28 m2 K/W. In order to evaluate the effectiveness, the overall thermal resistance for the applied sustainable R-I combination was estimated using equation 1. Total thermal resistance for assembly 1 and assembly 2 was estimated as 0.55 m² K/W and 1.093 m² K/W respectively. Thus, in comparison to the untreated concrete slab, the applied composite roofing materials resulted in an overall increase in thermal resistance of the first and second assembly by 1.9 and 3.9 times respectively. Table 1. Thermal properties of the materials used for retrofitting Sr No Materials with thickness (L) in m.

Thermal conductivity, k (W/mK)

Density (kg/m3)

Specific heat (J/kgK)

Position in assembly

1

Aluminum (0.02005)

0.268

1900

800

Reflecting material - Over deck

2 3

Glazed tiles (0.006) Industrial waste panels (0.012)

1.500 0.300

1900 670

800 904.41

False ceiling material - Under deck

4

Mineral fiber board (0.014)

0.057

-

-

5

Expanded polystyrene + sawdust (0.015) 0.038 Mortar (0.005) Air gap (1)

0.719 Ca=6. 22 W/m²K

1340 1000 920 -

Over deck or Under deck

6 7

16 188 1648 -

8

External plaster (0.010)

0.721

1762

840

-

9

Concrete slab (0.150)

1.580

2300

1000

-

10

Internal plaster (0.010)

0.721

1762

840

-

Over deck Between concrete slab and false ceiling

Total thermal resistance (RT) of overall R-I composite assembly ୐

ଵ

୏ ୧

େ౗

୘ ൌ ቂσ଻୧ୀଵ ቀ ቁ ቃ ൅

ଵ

ଵ

୤౟

୤౥

൅ ൅

(1)

Where; Inside film coefficient; fi= 9.36 W/m2K; Outside film coefficient; fo=19. 86 W/m2K [22] Ambient temperature

Below untreated concrete slab

36 33 30 27

Age (Days)

Fig. 7. Temperature variations below untreated concrete slab

30-Nov

25-Nov

20-Nov

15-Nov

10-Nov

5-Nov

31-Oct

26-Oct

21-Oct

16-Oct

11-Oct

6-Oct

1-Oct

26-Sep

21-Sep

16-Sep

11-Sep

6-Sep

24

1-Sep

Temperature (oC)

39

273


Ambient temperature

False ceiling (assembly 1)

False ceiling (assebmly 2)

39

Temperature (oC)

36 33 30 27 24 5-Dec

30-Nov

25-Nov

20-Nov

15-Nov

10-Nov

5-Nov

31-Oct

26-Oct

21-Oct

16-Oct

11-Oct

6-Oct

1-Oct

26-Sep

21-Sep

16-Sep

11-Sep

6-Sep

1-Sep

21

Age (Days)

Fig. 8. Temperature variations below false ceiling of both the assemblies In order to analyze the temperature variations of the assembly below the concrete slab (untreated & treated) and at the false ceiling bottom surface with respect to ambient temperature, hourly temperature data were recorded over the period of September–November (Fig 7 and Fig 8). Using area under the curve approach, the estimated areas under untreated concrete slab and false ceiling (bottom) of assembly 1 and assembly 2 were estimated as 2783 sq. units, 2506.9 sq. units and 2427 sq. units respectively. Thus, when compared with internal untreated concrete roof slab, the average temperature reduction at the bottom surface of false ceiling is 11% and 13% for assembly 1 and assembly 2 respectively. 45.0

Below Aluminum assembly False ceiling (top)

Below concrete slab False ceiling (bottom)

42.0 39.0

33.0 30.0 27.0 24.0 21.0 18.0 20-Jul 1-Aug 13-Aug 25-Aug 6-Sep 18-Sep 30-Sep 12-Oct 24-Oct 5-Nov 17-Nov 29-Nov 11-Dec 23-Dec 4-Jan 16-Jan 28-Jan 9-Feb 21-Feb 4-Mar 16-Mar 28-Mar 9-Apr 21-Apr 3-May 15-May 27-May 8-Jun 20-Jun 2-Jul 14-Jul 26-Jul

Temperature (oC)

36.0

Age (Days)

Fig. 9. Overall temperature variations of assembly 1


54.0 51.0 48.0 45.0 42.0 39.0 36.0 33.0 30.0 27.0 24.0 21.0 18.0

Below glazing tiles False ceiling (bottom)

Below concrete slab Ambient temperature

False ceiling (top)

20-Jul 1-Aug 13-Aug 25-Aug 6-Sep 18-Sep 30-Sep 12-Oct 24-Oct 5-Nov 17-Nov 29-Nov 11-Dec 23-Dec 4-Jan 16-Jan 28-Jan 9-Feb 21-Feb 4-Mar 16-Mar 28-Mar 9-Apr 21-Apr 3-May 15-May 27-May 8-Jun 20-Jun 2-Jul 14-Jul 26-Jul

Temperature (oC)

274

Age (Days)

Fig. 10. Overall temperature variations of assembly 2 Further, for the retrofitted R-I assembly the temperature log was recorded for a year (July 2011- July 2012) over the various salient composite roof surfaces (Fig 5a & Fig 6a) and resulted in further temperature control in the built environment of model rooms (Fig 9 & Fig 10). For assembly 1, using the area under the curve approach the area under the internal treated concrete slab is 12056 sq. units and internal exposed false ceiling bottom surface was found to be 11355 sq. units. Thus, there is 709 sq. units (6%) reduction in surface temperature as compared to treated concrete slab. Using the similar (area under the curve) approach for assembly 2, the area under the internal exposed composite false ceiling (saw dust, expanded polystyrene and mineral fiber board) bottom surface was found to be 10919 sq. units and of treated concrete slab below glazing tiles is 13524 sq. units. Thus, there is 2605 sq. units (19%) reduction in surface temperature as compared to concrete slab. In turn, it will help to reduce the cooling load of the built environment. 4.2 Economic feasibility of considered composite roofing materials The developed R-I product from aluminum sheet, expanded polystyrene, saw dust were locally available materials and false ceiling panels were made up of industrial waste material. The R-I composite was cost effective (INR 900 per sq. m) and having a dead load (less than 50 kg/m²). Assembly 2 (broken glazed tiles, saw dust, expanded polystyrene and mineral fiber board false ceiling) was having the cost INR 1250 per sq. m and lesser dead load (less than 30 kg/m²). 5. Conclusion In order to reduce the impact of heat gain inside the buildings, sustainable reflecting-cum-insulating assemblies were effectively applied over concrete slab. The applied two compositions have significantly higher thermal resistance over conventional concrete slab. The computed thermal resistance values for sustainable composite roofing assemblies have shown correlation with the experimentally recorded and analyzed temperature values. The retrofitted assemblies resulted in 6% and 19% surface temperature reduction when the thermal resistance of the roof slab is increased by 1.9 and 3.9 times respectively with the use of sustainable materials. The applied R-I materials found to be thermally efficient, lighter in weight and cost effective for energy conservation in the buildings. The experimental investigations helped to conclude that retrofitting R-I solutions over the concrete slab found to be effective in decreasing the indoor temperature. The elaborated methodology is helpful in the application of sustainable composite material assembly as per the geographic location and local climatic condition. As the


retrofitting R-I assembly is lighter in weight and cost effective it can be effectively applied to the larger areas for reducing cooling load of the built environment. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]

[15] [16] [17] [18] [19] [20] [21] [22] [23]

M. Iosifides, Experience, problems and suggestions for building, In: Proceedings of the National Conference on the Implementation of Renewable Energy Sources, NTUA-RENES Network, Athens (1998) 18–26. S. Al-Homoud, Performance characteristics and practical applications of common building thermal insulation materials, Building and Environment 40 (3) (2005) 353-366. J. Alvarado, W. Terrell, and M. Johnson, Passive cooling systems for cement-based roofs, Building and Environment 44 (9) (2009) 18691875. S. Serres, A. Trombe, and J. Conilh, Study of coupled energy saving systems sensitivity factor analysis, Building and Environment (1997) 137–148. M. Manzan, and O. Saro, Numerical analysis of heat and mass transfer in a Passive Building Component Cooled by Water Evaporation, Energy and Building 34 (2000) 369–375. A. Suvorov, and V. Skurikhin, Vermiculite — a promising material for high-temperature heat insulators, Refractories and Industrial Ceramics 44 (3) (2003) 44-52. I. Abramova, Y. Grinberg, and V. Zhebrunov, Heat insulators based on expanded perlite for steel teeming technology, Ogneupory 12 (1990) 11–14. T. Stelmah, Perlite in the production of lightweight bricks, Tile and Brick International 6 (1990) 6-10. K. Jungk, H. Halceband, K. Elett, and W. Kremar, ,Porosities for the production of lightweight brick, Tile and Brick International 13 (1) (1997) 7 – 12. M. Permikina, and U. Evdokimova, Heat insulating refractories based on spherical corundum for the lining of high temperature furnaces, In: Refractories-91: Technology and Applications, All-Russia Research Workshop, VostIO, Chelyabinsk (1991). K. Al-Malaha, and B. Abu-Jdayilb, Clay-based heat insulator composites: Thermal and water retention properties, Journal of Applied Clay Science 37 (1-2) (2007) 90-96. A. Korjenic, V. Petránek, J. Zach, and J. Hroudova, Development and performance evaluation of natural thermal-insulation materials composed of renewable resources, Energy and Buildings 43 (9) 2518-2523 (2011). T. Hasegawa, and Y. Konna, A study on improvement of the thermal environment in a large building with folded roof deck plate, In: Summaries of Technical Papers of Annual Meeting Architectural Institute of Japan (2001) 473–474. T. Tanabe, R. Sayama, and H. Saito, Measurement of the effect of a change in slate-roofing from single to double with water spraying on lowering the ceiling surface temperature, In: Summaries of Technical Papers of Annual Meeting Architectural Institute of Japan (2000) 507–508. O. Ishihara, Q. Zhang, and K. Shimoyama, Experimental study on thermal characteristics and water performance of rooftop lawn, Journal of Architectural Planning and Environmental Engineering 484 (1996) 17-22. A. Hoyano, K. Shirai, N. Otsuka, and K. Iwamura, Indoor thermal control effect of rooftop lawn-planting with thin soil layer on a wooden building, Journal of Architectural Planning and Environmental Engineering 527 (2000) 15-19. A. Al-Sanea, Thermal performance of building roof elements, Building and Environment 37 (7) (2002) 665-675. S. Tsang, and Y. Jim, Theoretical evaluation of thermal and energy performance of tropical green roofs, Journal of Energy 36 (5) (2011) 3590-359. A. Krishan, N. Baker, S. Yannas, and S. Szokolay, Climate responsive architecture: a design handbook for energy efficient buildings, Tata McGraw-Hill Publishing Company Limited, New Delhi (2007). IS 875: Part III. (1987). Wind loads on buildings and structures. Solar radiation handbook, A joint project by Solar Energy Centre, MNRE & Indian Meteorological Department (2008). SP: 41, Part 1-4. Handbook on Functional Requirements of Buildings (Other than Industrial Buildings), New Delhi: Bureau of Indian Standards, (1987). S. Raut, R. Sedmake, S. Dhunde, R. Ralegaonkar, and S. Mandavgane, Reuse of recycle paper mill waste in energy absorbing light weight bricks, International Journal of Construction & Building Materials 27 (2012) 247-251.

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