Assessment of green roof performance for sustainable buildings under winter weather conditions

Abstract

A green roof is a specialized roof system that supports vegetation growth on rooftops. This technology is rapidly gaining popularity as a sustainable design option for buildings. In order to contribute to an understanding of green roof in regions with cold winters and snow, an on-site experimental investigation was present with a focus on the assessment of green roof performance during the winter. This field experiment took place on a six small buildings during the winter of 2010–2011. The work monitored three buildings with green roofs, two buildings with reference roofs and one building with a bare soil coverage for the roof. These six buildings were identically constructed and instrumented with sensor networks to provide heat flux data through the roofs. The 15 min averaged data were statistically analyzed for a week under the two separate periods, first without a snow cover and second with a snow cover. The results show that the roof type is a significant factor in affecting the thermal performance of these buildings. Most importantly, green roofs reduce heat flow through the roof and thus reduce the heating energy demand during the winter. However, the energy savings for buildings with the green roofs are reduced under snow conditions because the snow diminishes thermal resistance of the roof and increases the heat transfer process through the roofs.

Keywords

green roof / energy savings / building envelop / sustainable buildings

References

[1] SailorD. J.. Thermal property measurements for ecoroof soils common in the western US [J]. Energy and Buildings, 2008, 40(7): 1246-1251

[2] TABARES-VELASCO P C, SREBRIC J. The role of plants in the reduction of heat flux through green roofs: Laboratory experiments [C]// ASHRAE Transactions, 2009: 1–8.

[3] LIU K K Y, BASKARAN B A. Thermal performance of extensive green roofs in cold climates [C]// 2005 World Sustainable Building Conference. Tokyo, Japan, 2005: 1–8.

[4] WilmersF.. Effects of vegetation on urban climate and buildings [J]. Energy and Buildings, 1990, 15(3/4): 507-514

[5] LIU K K Y, BASKARAN B A. Green roof infrastructure-technology demonstration, monitoring and market expansion project [R]. Institute for Research in Construction, B1054.1, 2004.

[6] WongN.. Investigation of thermal benefits of rooftop garden in the tropical environment [J]. Building and Environment, 2003, 38(2): 261-270

[7] MILLER C, NAREJO D. State of the green roof industry in the united states [M]. Geo-Frontiers, 2005: 4057–4064.

[8] PITA.Air conditioning principles and systems [M], 2002, Upper Saddle River, New Jersey, Pearson Education, Inc.: 47-55

[9] KaempferT. U.. Phase-field modeling of dry snow metamorphism [J]. Physical Review E, Statistical, Nonlinear, and Soft Matter Physics, 2009, 79(3): 031502-031502

[10] GoldL. W.. Influence of the snow cover on the average annual ground temperature at Ottawa, Canada [J]. International Association of Scientific Hydrology, 1963, 61: 82-91

[11] GoodrichL. E.. Influence of snow cover on the ground thermal regime [J]. Canadian Geotechnical Journal, 1982, 19(4): 421-432

[12] LiuK. K. Y.Energy efficiency and environmental benefits of rooftop gardens [R], 2002, Ottawa, National Council of Canada

[13] ZhangT.. Influence of the seasonal snow cover on the ground thermal regime: An overview [J]. Reviews of Geophysics, 2005, 43(4): 23-23

[14] Tabares-VelascoP. C., SrebricJ.. Experimental quantification of heat and mass transfer process through vegetated roof samples in a new laboratory setup [J]. International Journal of Heat and Mass Transfer, 2011, 54(25/26): 5149-5162

[15] SantamourisM.. Investigating and analyzing the energy and environmental performance of an experimental green roof system installed in a nursery school building in Athens, Greece [J]. Energy, 2007, 32(9): 1781-1788