Building Energy Optimization: Implementing Green Roof and Rainwater Harvester System for a Residential Building

Document Type: Research Article


Department of Mechanical Engineering, Faculty of Engineering & Technology, Alzahra University, Deh-Vanak, Tehran, Iran.


Both energy and environmental criticisms push a society toward energy-efficient buildings with green technologies. Green roofs are of significant importance due to their remarkable role in decreasing the thermal loads ofbuildings, especially in summer, and also in sound insulation. Here in, the thermal loads of a residential building were calculated, and then, an optimized green roof was designed for it in three different cities of Tehran, Rasht, and Tabriz. The energy saving was analyzed in each case, and proper plants and roof thickness were selected to achieve both comfortable air conditioning and energy optimization. It is also important to use water resources in an optimized manner. Considering the annual mean rain magnitude, here, a suitable system is designed to harvest rainwater for watering the plants. Results indicate that a sedum grass-based green roof with the thickness of 10 cm leads to a 21.3 % reduction in the annual total thermal loads in Tehran; one with thickness of 8 cm in Tabriz will result in a 11.7 % thermal load reduction per year; a green roof with 9 cm thickness in Rasht, Iran shows 13.2 % energy saving per year. Therefore, Tehran is the best option here to integrate the green roof into the structure of the building. The patterns of the obtained data indicate that the reduction of cooling loads is more noticeable when implementing a green roof in comparison with heating loads. Moreover, it has been revealed that harvested rainwater is sufficient to support about 72 % of required water in Tehran, 81 % of it in Tabriz, and 93 % in Rasht.


Main Subjects

1.     Zhang, X., Shen, L., Tam, V.W.Y. and Lee, W.W.Y., "Barriers to implement extensive green roof systems: A Hong Kong study", Renewable and Sustainable Energy Reviews, Vol. 16, (2012), 314-319. (

2.     Chen, C.-F., "Performance evaluation and development strategies for green roofs in Taiwan: A review", Ecological Engineering, Vol. 52, (2013), 51-58. (

3.     Vijayaraghavan, K., "Green roofs: A critical review on the role of components, benefits, limitations and trends", Renewable and Sustainable Energy Reviews, Vol. 57, (2016), 740-752. ( /10.1016/J.RSER.2015.12.119).

4.     Takebayashi, H. and Moriyama, M., "Surface heat budget on green roof and high reflection roof for mitigation of urban heat island", Building and Environment, Vol. 42, (2007), 2971-2979. ( /J.BUILDENV.2006.06.017).

5.     Yang, A.S., Juan, Y.H., Wen, C.Y. and Chang, C.J., "Numerical simulation of cooling effect of vegetation enhancement in a subtropical urban park", Applied Energy, Vol. 192, (2017), 178-200. (

6.     Ouldboukhitine, S.E., Belarbi, R. and Sailor, D.J., "Experimental and numerical investigation of urban street canyons to evaluate the impact of green roof inside and outside buildings", Applied Energy, Vol. 114, (2014), 273-282. ( 2013.09.073).

7.     Speak, A.F., Rothwell, J.J., Lindley, S.J. and Smith, C.L., "Rainwater runoff retention on an aged intensive green roof", Science of the Total Environment, Vol. 461-462, (2013), 28-38. ( J.SCITOTENV.2013.04.085).

8.     Getter, K.L., Rowe, D.B., Robertson, G.P., Cregg, B.M. and Andresen, J.A., "Carbon sequestration potential of extensive green roofs", Environment Science and Technology, Vol. 43, (2009), 7564-7570. (

9.     Chemisana, D. and Lamnatou, C., "Photovoltaic-green roofs: An experimental evaluation of system performance", Applied Energy, Vol. 119, (2014), 246-256. ( 2013.12.027).

10.   Raji, B., Tenpierik, M.J. and van den Dobbel steen, A., "The impact of greening systems on building energy performance: A literature review", Renewable and Sustainable Energy Reviews, Vol. 45, (2015), 610-623. (

11.   Santamouris, M., Pavlou, C., Doukas, P., Mihalakakou, G., Synnefa, A., Hatzibiros, A. and Patargias, P., "Investigating and analyzing the energy and environmental performance of an experimental green roof system installed in a nursery school building in Athens, Greece", Energy, Vol. 32, (2007), 1781-1788. ( J.ENERGY.2006.11.011).

12.   Susca, T., "Green roofs to reduce building energy use? A review on key structural factors of green roofs and their effects on urban climate", Building and Environment, Vol. 162, (2019), 1-15. ( 10.1016/ J.BUILDENV.2019.106273).

13.   Kumar, R. and Kaushik, S.C., "Performance evaluation of green roof and shading for thermal protection of buildings", Building and Environment, Vol. 40, (2005), 1505-1511. ( /J.BUILDENV.2004.11.015).

14.   Feng, C., Meng, Q. and Zhang, Y., "Theoretical and experimental analysis of the energy balance of extensive green roofs", Energy and Buildings, Vol. 42, (2010), 959-965. ( J.ENBUILD.2009.12.014).

15.   Ouldboukhitine, S.E., Belarbi, R., Jaffal, I. and Trabelsi, A., "Assessment of green roof thermal behavior: A coupled heat and mass transfer model", Building and Environment, Vol. 46, (2011), 2624-2631. (

16.   Tabares-Velasco, P.C. and Srebric, J., "A heat transfer model for assessment of plant based roofing systems in summer conditions", Building and Environment, Vol. 49, (2012), 310-323. (https://doi. org/10.1016/J.BUILDENV.2011.07.019).

17.   Sailor, D.J., "A green roof model for building energy simulation programs", Energy and Buildings, Vol. 40, (2008), 1466-1478. (

18.   Ameri, M. and Grami, A., "A multi-scenario zero-energy building techno-economic case study analysis for a renovation of a residential building", Journal of Renewable Energy and Environment (JREE), Vol. 5, No. 3, (2018), 10-26.

19.   Niachou, A., Papakonstantinou, K., Santamouris, M., Tsangrassoulis, A. and Mihalakakou, G., "Analysis of the green roof thermal properties and investigation of its energy performance", Energy and Buildings, Vol. 33, (2001), 719-729. (

20.   Onmura, S., Matsumoto, M., Hokoi, S., "Study on evaporative cooling effect of roof lawn gardens", Energy and Buildings, Vol. 33, (2001), 653-666. ( 00134-1).

21.   Eumorfopoulou, E. and Aravantinos, D., "The contribution of a planted roof to the thermal protection of buildings in Greece", Energy and Buildings, Vol. 27, (1998), 29-36. (

22.   Moody, S.S. and Sailor, D.J., "Development and application of a building energy performance metric for green roof systems", Energy and Buildings, Vol. 60, (2013), 262-269. ( J.ENBUILD.2013.02.002).

23.   Chan, A.L.S. and Chow, T.T., "Evaluation of Overall Thermal Transfer Value (OTTV) for commercial buildings constructed with green roof", Applied Energy, Vol. 107, (2013), 10-24. ( J.APENERGY.2013.02.010).

24.   Takakura, T., Kitade, S. and Goto, E., "Cooling effect of greenery cover over a building", Energy and Buildings, Vol. 31, (2000), 1-6. (

25.   Yang, Z., Xiong, K. and Tang, M., "Influence of indoor temperature on equivalent thermal resistance of green roof", Journal of Civil Engineering, Environment and Architecture, Vol. 2, (2015), 109-114.

26.   Jiang, L. and Tang, M., "Thermal analysis of extensive green roofs combined with night ventilation for space cooling", Energy and Buildings, Vol. 156, (2017), 238-249. ( J.ENBUILD.2017.09.080).

27.   Tian, Y., Bai, X., Qi, B. and Sun, L., "Study on heat fluxes of green roofs based on an improved heat and mass transfer model", Energy and Buildings, Vol. 152, (2017), 175-184. ( J.ENBUILD.2017. 07.021).

28.   Squier, M. and Davidson, C.I., "Heat flux and seasonal thermal performance of an extensive green roof", Building and Environment, Vol. 107, (2016), 235-244. ( 2016.07.025).

29.   Del Barrio, E.P., "Analysis of the green roofs cooling potential in buildings", Energy and Buildings, Vol. 27, (1998), 179-193. (10.1016/j.enbuild.2010.05.004).

30.   Feng, D., Meng, Q. and Zhang, Y., "Theoretical and experimental analysis of the energy balance of extensive green roofs", Energy and Buildings, Vol. 42, (2010), 959-965. (10.1016/j.enbuild.2009.12.014).

31.   Jim, C.Y. and Tsang, S.W., "Biophysical properties and thermal performance of an intensive green roof", Building and Environment, Vol. 46, (2011), 1263-1274. (10.1016/j.buildenv.2010.12.013).

32.   Lin, B.S., Chin-Chung, Y., Ai-Tsen, S. and Yann-Jou, L., "Impact of climatic conditions on the thermal effectiveness of an extensive green roof", Building and Environment, Vol. 67, (2013), 26-33. (

33.   Zhao, M., Tabares-Velasco, P.C., Srebric, J., Komarneni, S. and Berghage, R., "Effects of plant and substrate selection on thermal performance of green roofs during the summer", Building and Environment, Vol. 78, (2014), 199-211. ( j.buildenv.2014.02.011).

34.   Rumble, H., Fincha, P. and Gangea, A.C., "Green roof soil organisms: Anthropogenic assemblages or natural communities", Applied Soil Ecology, Vol. 126, (2018), 11-20. ( j.apsoil.2018.01.010).

35.   Porcaro, M., Ruiz de Adana, M., Comino, F., Pena, A., Martín-Consuegra, E. and Vanwalleghem, T., "Long term experimental analysis of thermal performance of extensive green roofs with different substrates in Mediterranean climate", Energy and Buildings, Vol. 197, (2019), 18-33. (

36.   Schindler, B.Y., Blaustein, L., Vasl, A., Kadas, G.J. and Seifanc, M., "Cooling effect of Sedum sediforme and annual plants on green roofs in a Mediterranean climate", Urban Forestry & Urban Greening, Vol. 38, (2019), 392-396. (

37.   Abdelkader, A., Elshorbagya, A., Tuninetti, M., Laioc, F. and Hoekstra, A.Y., "National water, food, and trade modeling framework", Science of The Total Environment, Vol. 639, (2018), 485-496. (

38.   Musayeva, S., Burgessb, E. and Mellor, J., "A global performance assessment of rainwater harvesting under climate", Change, Resources, Conservation & Recycling, Vol. 132, (2018), 62-70. (

39.   19th Section of National Building Lows, 3rd Edition, Research Center of Building, (2001).



42.   Design builder data library.

43.   He, Y., Yu, H., Ozaki, A., Dong, N. and Zheng, Sh., "Influence of plant and soil layer on energy balance and thermal performance of green roof system", Energy, Vol. 141, (2017), 1285-1299. ( 10.1016/S0378-7788(98)00063-2.


45.   Iran Metrological Organization statistics,

46.   Sepehri, M., Malekinezhad, H., Ilderomi, A.R., Talebi, A. and Hosseini, S.Z., "Studying the effect of rain water harvesting from roof surfaces on runoff and household consumption reduction", Sustainable Cities and Society, Vol. 43, (2018), 317-324. ( j01.sace.23.2.21606).

47.   Lazzarin, R.M., Castellotti, F. and Busato, F., "Experimental measurements and numerical modelling of a green roof", Energy and Buildings, Vol. 37, (2005), 1260-1267. ( J. ENBUILD.2005.02.001).

48.   Coma, J., Perez, G., Sole, C., Castell, A. and Cabeza, L.F., "Thermal assessment of extensive green roofs as passive tool for energy savings in buildings", Renewable Energy, Vol. 85, (2016), 1106-1115. (