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Sustainable Benefits of Green Roofs

Sustainable Benefits of Green Roofs. William Retzlaff , Ph.D. SIUE Department of Biological Sciences Susan Morgan, Ph.D., P.E. SIUE Department of Civil Engineering Serdar Celik , Ph.D. SIUE Department of Mechanical Engineering ISTC 2009 – 2010 Seminar Series on Sustainability

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Sustainable Benefits of Green Roofs

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  1. Sustainable Benefits of Green Roofs William Retzlaff, Ph.D. SIUE Department of Biological Sciences Susan Morgan, Ph.D., P.E. SIUE Department of Civil Engineering SerdarCelik, Ph.D. SIUE Department of Mechanical Engineering ISTC 2009 – 2010 Seminar Series on Sustainability “The Path to Curbing Global Warming: Becoming Carbon Neutral” March 18, 2010

  2. Outline • Introduction • Results • Runoff quantity • Runoff quality • Thermal • Summary

  3. Introduction: What are they?

  4. Why consider them?

  5. Results: Runoff Quantity

  6. Mean storm water retention (%) for study period 09/05-04/07 for green roof systems with 5, 10, 15, and 20 cm planted medium depths. (C=Control, P=Planted. Bars with same letter not significantly different at the p<0.05 level. Error bars + 1se) (Forrester 2008).

  7. Mean storm water retention (%) for study period 04/07-11/07 for green roof systems with 5, 10, 15, and 20 cm planted medium depths. (C=Control, P=Planted. Bars with same letter not significantly different at the p<0.05 level. Error bars + 1se) (Woods 2009).

  8. Results: Runoff Quality – Metals April 11, 2008 collection event. Effect of media treatments on zinc concentration (bars denote mean [zinc] and standard error, n=3-4) measured from leachate collected from empty built-in-place control roofs and from each planted media placed in 10 cm Green Roof Blocks; bars with same letter not significantly different at the p<0.05 level. F = 74.48; p < 0.0001.

  9. Results: Runoff Quality – Solids

  10. Growing Media

  11. Vegetation

  12. Vegetated Media TSS 120 mg/L 20 mg/L

  13. Vegetated Media Turbidity 280 NTU

  14. Non-Vegetated Media Turbidity 280 NTU

  15. Effect of Vegetation – Haydite 280 NTU

  16. Effect of Vegetation – Bottom Ash 120 mg/L 20 mg/L

  17. Results: Thermal Coupled green roof model

  18. Theory Reflected irradiation Diffuse irradiation Normal direct irradiation Unit thermal resistance through all layers

  19. Theory • Adiabatic side walls • 1-D heat transfer Heat flux through a selected combination

  20. Vegetation

  21. Growing Media

  22. August 2007 Data for All Combinations

  23. Peak Hours on August 12, 2007

  24. Heat Flux on August 12, 2007

  25. Energy Cost of a 50,000 m2 Roof during Peak Hours

  26. Summary: Runoff Quantity • Green roof systems reduce storm water runoff in the Midwest. • When saturated, stormwater retention of green roof systems is approximately 40 - 50%. • At 10-14 day intervals between rainfall events, green roofs can retain as much as 0.75 - 1.0 inch of stormwater (no through-flow). • During a “normal” St. Louis growing season, stormwater retention of green roof systems can reach 80%.

  27. Summary: Runoff Quality • There has been no heavy metal contamination in runoff. • TSS and turbidity of the growing media and the vegetated media decrease over time. • TSS and turbidity vary between media. • Vegetation provides a reduction in TSS and turbidity only during the first flush.

  28. Summary: Thermal • The color of the growth media and the vegetation affects the thermal radiation to/from the green roof blocks significantly. • The more condensed the leaves are, the better shading effect occurs, resulting in better insulation in air-conditioning seasons. • Fully covered blocks act as better insulators compared to partially covered ones, due to having a higher reflectivity and a better shading effect.

  29. Questions? www.green-siue.com

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