The Thermal and Rainwater Runoff Performance of an Extensive ...

More documents

Recommendations

Info

• Urban greenhouse effect – increase of long-wave radiation reflected from thepolluted, warmer urban atmosphere• Reduced turbulent heat transfer – transfer of heat to the air is reduced due to lessair turbulence in streetsOne solution for reducing the effect of the urban heat island effect is to introduce morevegetation into the urban environment to provide shading and cooling throughevapotranspiration. Another solution is to increase the reflectiveness (or albedo) of roofs andother exposed surfaces. This will reflect a higher proportion of the received solar radiationback to the sky; producing less sensible heat.Green roofs combine both of these solutions and are increasingly being proposed asmitigation for the urban heat island effect. Green roofs have a high equivalent albedo ofbetween 0.7 and 0.85, depending upon the availability of water for evapotranspiration [20].Evaporative cooling on green roofs works by increasing humidity and reducing the amount ofenergy available for conversion into sensible heat. During warmer, drier months the reducedmoisture content of a green roof reduces the real evapotranspiration rate compared with thetheoretical potential evapotranspiration rate, thus reducing the cooling effect. Therefore, inwarmer, drier months irrigation may be required to maintain the evapotranspiration benefitsof green roofs.4.5 Sound InsulationThe combination of soil, plants and trapped layers of air within green roof systems can act asa sound insulation barrier. Sound waves are absorbed, reflected or deflected. The substratetends to block lower sound frequencies and the vegetation blocks higher frequencies. Theamount of sound insulation a green roof provides mainly depends on the depth of substrateused.Research has shown that a depth of growing medium of 20-100 mm can achieve an extrasound pressure level attenuation of 10-40 dB, depending on frequency [15]. This compareswith a typical reduction of 43 dB for a 100 mm concrete wall. Compared with a conventionalroof, green roofs can reduce sound within a building by 8 dB or more [21].Niall Carroll Page 34The Thermal and Rainwater Runoff Performance of an Extensive Green Roof System
4.6 Building FabricWhen vegetation is introduced to roofs, the underlying materials of the structure areeffectively given a blanket of protection. This blanket prolongs the roofs lifespan and reducesthe stress applied to the roofing materials [6].The key benefits for protecting the building fabric for green roofs are [8]:• Protecting the roof from ultra violet radiation.• Reducing diurnal/seasonal temperatures changes in the roof.Ultra violet light can have a damaging effect on roofing materials when high levels ofexposure occur. The ultra-violet radiation causes roofing materials to lose their inherentstrength which can result in substantial maintenance costs. Likewise, large fluctuations inannual and diurnal temperatures cause roofing materials to expand and contract [8]. Thestress incurred by these fluctuations can be sufficient to cause the eventual failure of the roof.The layer of vegetation acts as a buffering system to the physical impact imposed by ultravioletradiation and temperature variations within the roof. The inclusion of a barrier system,against root penetration, is essential when providing protection to the waterproof membrane.4.7 Green Roofs and Solar PanelsNiall Carroll Page 35The Thermal and Rainwater Runoff Performance of an Extensive Green Roof System
Page 1 and 2: Department of Mechanical Engineerin
Page 3 and 4: AbstractThis project addresses the
Page 5 and 6: Table of Contents1 Introduction…
Page 7 and 8: 6.2.1 Rainfall Runoff Relationship
Page 9 and 10: List of FiguresFigure 1: Traditiona
Page 11 and 12: Figure 32: Humidity Sensor Located
Page 13 and 14: 1 Introduction1.1 Green Roof Defini
Page 15 and 16: incorporate green roofs into their
Page 17 and 18: 2.3 ExtensiveFigure 5: Extensive Gr
Page 19 and 20: 2.33 Green/Brown Roofs for Biodiver
Page 21 and 22: 3 Construction of Green RoofsThe co
Page 23 and 24: 3.2 Inverted Warm Green Roof Constr
Page 25 and 26: Although less versatile than intens
Page 27 and 28: There are four main methods of esta
Page 29 and 30: • extension of park system• pro
Page 31 and 32: In summer, green roofs can retain 7
Page 33: The urban heat island effect descri
Page 37 and 38: 5 UK Policy on Green RoofsThere are
Page 39 and 40: Figure 16: Summer Temperatures of R
Page 41 and 42: However, the previous study mention
Page 43 and 44: Similarly, Simmons et al. [41] foun
Page 45 and 46: Figure 20: Green Roof Test Rig for
Page 47 and 48: The mineral content of the substrat
Page 49 and 50: Figure 25: NI USB-9211 Thermocouple
Page 51 and 52: It was used to acquire the relative
Page 53 and 54: Figure 33: NI USB-6008 Terminal Ass
Page 55 and 56: Figure 35: Labview Signal Express T
Page 57 and 58: 7.2 Green Roof Energy BalanceThe gr
Page 59 and 60: (4)Where,α s = Shortwave Absorptiv
Page 61 and 62: A green roof test rig was set up to
Page 63 and 64: Figure 40: Green Roof Test Rig for
Page 65 and 66: second day of the experiment. The l
Page 67 and 68: with the artificial rain event. Whe
Page 69 and 70: References1. Sailor D.J. ‘A Green
Page 71 and 72: 31. Mellor, R.S. Salisbury, F.B. Ra
Page 73 and 74: Appendix 1Niall Carroll Page 73The

The Thermal and Rainwater Runoff Performance of an Extensive ...

Create successful ePaper yourself

Delete template?

Save as template?