International Journal of Scientific & Engineering Research, Volume 3, Issue 7, July-2012 1 ISSN 2229-5518 IJSER © 2012 http://www.ijser.org The Energy Consumption Performance of Roof Garden Shailendra Kasera, Ashish Nayyar, Dr. Dilip Sharma Abstract—Green roofs are a passive cooling technique that stops incoming solar radiation from reaching the building structure below. Many studies have been conducted over the past 10 years to consider the potential building energy benefits of green roofs and shown that they can offer benefits in winter heating reduction as well as summer cooling. Statistics have confirmed that a lawn placed on a roof top can reduce the cooling load. In this study, the eQUEST energy simulation program was used to determine the effects of roof gardens on the annual energy required for cooling, and annual electrical us age in a computer based model. In this case study two different cases were considered first one of only roof garden, later with 2inch XPS (Extended Polystyrene). It has been found that 3.79% of cooling load can be reduced by best case. Index Terms—Green Roof, Building Energy Simulation, eQUEST, Energy Saving ——————————  —————————— 1 INTRODUCTION A green roof is a roof that contains a soil (growing media) and vegetation layer as its outermost surface. Green roofs have been recognized as a great means of removing heat from the air through evapotranspiration of the plants, which leads to a reduction of the temperatures of the roof surface and the surrounding air.[1] The roof of a building can be fully or part covered with a layer of vegetation known as a green roof. A green roof is a layered system comprising of a waterproofing membrane, growing medium and the vegetation layer itself. Green roofs often also include a root barrier layer, drainage layer and, where the climate necessitates, an irrigation system.[2] Environmental problems, especially in urban areas, have become a serious issue. The increasing numbers of buildings in cities causes a loss of green areas, resulting in the Urban Heat Island effect (UHI), which makes temperatures increase and causes uncomfortable conditions for human living. The reduction of heat coming into buildings is very important with respect to thermal comfort and saving energy. Thus the need for vegetation in urban areas is increasing.[3] 2 BUILDING ENERGY BENEFITS Buildings account for around half of primary energy consumption, hence CO2 emissions. A large proportion of this energy is used to maintain internal building temperatures through heating and cooling systems. This section of the report will therefore address the potential building energy reduction benefits arising from the enhanced thermal properties of a green roof.[4] 2.1 Reduction of Heat Flux and Solar Reflectivity In summer the exposed area of a black roof can reach 70-80 ◦C when the equivalent area beneath a green roof is only 27 -30◦C. Green roofs cool through latent heat loss and improved reflectivity of incident solar radiation. The ratio of total reflected to incident electromagnetic radiation is defined as albedo. Green roofs cool as effectively as the brightest possible white roofs, with an equivalent albedo of 0.7–0.85, compared with the typical 0.1–0.2.[4,5] The hard ground reradiated the stored heat, increasing the ambient air temperature. However, planted roofs suffered less heat gain during the day. By measuring the air temperature at various heights above the green roof it was found that after sunset the ambient air temperature above the vegetation was reduced significantly and continued to cool the ambient air throughout the night. ———————————————— Mr. Shailendra Kasera is Research Scholar, Dept. of Mech. Engg at Poornima College of Engineering Jaipur, India Mr. Ashish Nayyar is Associate Professor, Dept. of Mech. Engg at Swami Keshvanand Institute of Engineering, Technology, Management & Gramothan, Jaipur, India Dr. Dilip Sharma is Associate Professor, Dept. of Mech. Engg at Malviya National Institute of Technology Jaipur, India