Critical Review of Thermal and Energy Performance of Tropical Green Roofs
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Transcript of Critical Review of Thermal and Energy Performance of Tropical Green Roofs
KXGM 6102 Applied Heat Transfer
Critical review of thermal and energy performance of tropical
green roof Lecturer: Assc.Prof. Ir. Dr. YauYHProject Member: 1.WongKH (Leader)2.Mohd.Hafiz3.Mohd.Shazwan4.Krishan5.SimSY
Content 1 Introduction2 Thermal Conductivity3 Mathematical modelling of an green
roof4 Thermal performance5 Energy efficiency and saving
Green roof
Advantages Disadvantages
Additional insulation to the roof structure
Increase building cost & maintenance cost
Reduce the building temperature
Provide habitat and biodiversity
Reduce building noise
Minimize the energy consumption
Reduce the long wave radiation emitted by the building surface
Green roof structure and thermal conductivity
Structure & Layer
Green roof & other Bare roof
Green roof
White roof
Green roof performance & other
Roof type Conductance Thermal
Capacity Solar
Absorptance
(W/m2 oC) kJ/oC Common flat roof (BFR) 0.59 479 0.8
White roof (BWR) 0.59 479 0.4
Green roof(BGR) 0.42 519 0.37
Table 2 : Thermal and optical properties of the roof materials under dry conditions
Net RadiationI = Ki + Kr + Li + Lr
Earth’s Solar Energy Balance
Ki = incident shortwave radiationKr= reflected shortwave radiationLi = incident longwave radiationLr= reflected longwave radiation
I net
Ki &Li
Mathematical modeling of green roofs
Total Solar Radiation
Re-emitted Energy
Convection
Evapotranspiration
Reflected Radiation
ShadingThermal Mass (Varies with Material Properties)
Ki+Kr+Li+Lr = QE+QH+QS
QE, latent heat loss due to soil surface and vegetation evapotranspiration.Influencing factors are soil water content, LAI and relative humidity,
QH, sensible heat loss due energy difference btw the soil surface and atmosphere.(excess heat loss by convection)
QH= hc (Ts –Ta)hc = 12Wm-2 K-1
QS,heat absorbed in building materals, likely to be reliesed at night (contribute to urban island effect).
QS= ρIρ ratio of heat storage to the net radiation
Thermal performanceComparison of green roof to bare roof (Heat
Flux)
Comparison of green roof to bare roof (Temperature)
Insulated and un-insulated green roof
Energy efficiency and saving
Green Roof
Green Roof
Conventional Roof
Conventional Roof
ConclusionGreen roof shows a significant effect on the
building’s temperature It show a small temperature fluctuations of indoor
and outdoor temperature differentIt plays role as insulation and cool building by
direct shading , evapo-transpiration and photosynthesis of plant.
Higher leaf area index provide better reduction of temperature fluctuation.
High humidity of the soil will lower surface temperature of the green roof
In tropical region, solar radiation and building heat gain are high ,therefore green roof is highly recommended
Thank you
Q & A