Användning tak för att minska risken för översvämning orsakade av skyfall Kaj R. Pettersson PhD student Department of Civil and Environmental Engineering Chalmers tekniska högskola November 25, 2016 Kaj R. Pettersson 1/20
Agenda Introduction Green roof placement Green roof performance Research products Introduction Kaj R. Pettersson 2/20
A few examples of green roofs Left: Rommen, Skole, 2009. Corner: Limhamn, Garage, 2008. Below: Finspång, Siemens, 2012. Photos credit of Veg Tech AB [1]. Introduction Kaj R. Pettersson 3/20
General structure of green roofing Growth substrate and drainage element. Vegetation. Green roof schematic [2]. Introduction Kaj R. Pettersson 4/20
Current issues driving green roof research Flooding/overflow risks Building façade and structural damage Limited space for alternatives Projections of increased rainfall Improved urban ecosystem/welfare Major points for research: How can green roofs be used to mitigate stormwater contributions to water management problems? 1. How can we maximize the efficiency of green roofs by placement? 2. How can we maximize the efficiency of green roofs by design? Introduction Kaj R. Pettersson 5/20
What is Computational Fluid Dynamics (CFD)? Numerical solutions to fluid flows One or more fluids (liquid/gas) Well defined boundary conditions Appropriate computational grid Reduce time and cost in the development of new materials, designs, etc. Alternative to pure experimental data Introduction Kaj R. Pettersson 6/20
Improvement by placement How can green roofs be used to mitigate stormwater contributions to water management problems? 1. How can we maximize the efficiency of green roofs by placement? 2. How can we maximize the efficiency of green roofs by design? Green roof placement Kaj R. Pettersson 7/20
What is wind-driven rain (WDR)? Damage related to WDR Salt, frost, vegetation Cosmetic Structural Rainfall exhibiting a horizontal velocity component. Green roof placement Kaj R. Pettersson 8/20
How can calculating incident WDR help us? Identify areas of heavy exposure. Evaluate requisite rainwater management. Identify effect of different atmospheric conditions. Provide more accurate boundary conditions. Green roof placement Kaj R. Pettersson 9/20
Case 1 Rainfall trajectories d = 1.2 mm. Rainfall distribution η. Green roof placement Kaj R. Pettersson 10/20
Case 2: wind Velocity profile (y = 18.0). Velocity contour (y = 18.0). Velocity profile (z = 5.4). Velocity contour (z = 5.4). Green roof placement Kaj R. Pettersson 11/20
Case 2: results η global (east view) Results are taken at t = 50 sec (not fully converged). η global (north view) η global (west view) Green roof placement Kaj R. Pettersson 12/20
Improvement by performance How can green roofs be used to mitigate stormwater contributions to water management problems? 1. How can we maximize the efficiency of green roofs by placement? 2. How can we maximize the efficiency of green roofs by design? Green roof performance Kaj R. Pettersson 13/20
Key factors in simulating green roofs Porous media treatment 1. Continuous solid or channel structure 2. Pore size 3. Homogeneity and thermal properties 4. Cavities Air and water present Temperature (freezing/thawing) 1. Ice formation Runoff and drainage treatment Effect of vegetation (absorption/evaporation) Green roof performance Kaj R. Pettersson 14/20
Methods for calculating moisture transport Heat air moisture (HAM) model Solve for temperature and water content. No treatment of continuous water (drainage). Diusion dominant. Limited to non negative temperatures. CFD model Solve for temperature, velocity, saturation, etc. Two phase system of liquid gas. Convection and diusion considered. Negative temperatures possible.* Green roof performance Kaj R. Pettersson 15/20
Experimental data Performance data for field test roofs 1. Atmospheric conditions 2. Runoff, water content, etc. Lab experiment data 1. Material properties incl. hydraulic conductivity, temperature, permeability, porosity, etc. 2. Controlled environment validation Green roof performance Kaj R. Pettersson 16/20
What do we hope to provide? Identify best locations for green roofs. Provide information on performance of various materials. Determine runoff predictions for various rainfall quantities. Examine effects from roof geometry on performance. Research products Kaj R. Pettersson 17/20
Financing partners Research products Kaj R. Pettersson 18/20
Questions and comments Questions and comments Questions Kaj R. Pettersson 19/20
References [1] Veg Tech AB. Sedumtak fotogalleri. http://www.vegtech. se/grona tak gardar/sedumtak/fotogalleri/. Accessed: 2016 11 25. [2] K. Vijayaraghavan. Green roofs: A critical review on the role of components, benets, limitations and trends. Renewable and Sustainable Energy Reviews, 57:740752, 5 2016. Questions Kaj R. Pettersson 20/20