An integrative analysis of an extensive green roof system: A case study of the Schleman green roof
Abstract
As city populations continue to rise, so does the stress on stormwater systems as demand increases. In addition to this system stress, increases in runoff from impervious surfaces are also leading to a greater release of pollutants and increased flow into rivers, lakes and natural waterways. Green roofs are one type of management practices that is being discussed as a means to reduce the runoff and stress being put on urban stormwater systems. Additional benefits of installing a green roof include reduction in energy use for the building, reduced greenhouse gas emissions and more. In an effort to quantify and evaluate these potential benefits, a case study was performed for the Schleman extensive green roof at Purdue University. A water balance, water quality evaluation and extended cost-benefit analysis were completed for the 165 m2 roof. The nutrients and water quality tests included Nitrate-Nitrite, Orthophosphate, Ammonia, Sulfate, total suspended solids and pH. The results from the water balance analysis revealed retention rates on average of 58% of precipitation per rain event where retention included soil moisture, ET and detention/depression storage. The pollutant concentration and load results were variable but the pH was raised from a slightly more acidic level to a more basic level after passing through the substrate. The TSS analysis was inconclusive based on a small sample size. The cost benefit analysis primarily demonstrated the need for further research and detailed simulations regarding energy analysis and the valuing of ecosystem services offered by the green roof. Using the TRNSYS 17 energy auditing program to simulate Schleman room energy needs with and without the presence of the green roof, it was found that the green roof resulted in a decrease in energy needed to maintain a near constant temperature in the conference room below the green roof. In accordance with these results, the total costs of the green roof construction were less than the estimated benefits of the roof for the Schleman case, but greater for the expanded 10 building scenario. The State Farm grant awarded in the construction of Schleman is the primary contributor to the high benefits yielded in the result. If similar grants were achieved for the other eligible buildings, then the benefits would exceed the construction costs resulting in a large net present value.
Degree
M.S.E.
Advisors
Bowling, Purdue University.
Subject Area
Environmental management|Water Resources Management|Urban planning
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