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A numerical model of solar transmittance for isolated trees in an urban area
○Eiko Kumakura, Tokyo Institute of TechnologyKazuaki Nakaohkubo, Saga UniversityAkira Hoyano, The Open University of Japan
Direct solar radiation
Sky solar radiation
Reflected solar radiation
Sun burnHeat attack
2
Solar radiation environmentin urban areas
Background
Requirement to calculate of solar transmittance for tree crown
‐ Various incident angle‐ Various tree species, density, crown shape
Based on numerical analysis results, a new formula of solar transmittance was proposed.
Ray‐tracing method
Tree geometries
Solar transmittance
Analyze
5mm
3
LBBLLRL G
PEATBAG
PEATLA
expexp
Solar transmittance of leaf Solar transmittance of branch
・Leaf density・Branch density・Leaf angle
Solar transmittance
・Branch angle
・Overlapping coefficient function
・New clumping index
New added parameters
Development of new numerical tree model to calculate solar transmittance
Leaf Area Index [m2/m2] 3.3 ‐ 5.4 9.5 ‐ 13.2 3.2 ‐ 8.52.7 ‐ 5.42.5 ‐ 5.0
tree species
crown shape
D) Platanusorientails
A) Ginkgo biloba
B) Zelkovaserrata
C) Liquidambar styraciflua
E) Prunusyedoensis
Proposed solar transmittance formula clearly shows the difference among tree species, seasonal change and leaf density.
00,020,040,060,080,10,12
RMSE value
□■■■ exp ⁄ · θ · · · · exp ⁄ · θ ·
exp ⁄ · θ · · exp ⁄ · θexp ⁄ · θ · · exp ⁄
exp ⁄ · θ · · · exp ⁄ · θ ·
Formula by G. Talbot et al.
Proposed functions
Added functions
D) Platanusorientails
A) Ginkgo biloba B) Zelkovaserrata
C) Liquidambar styraciflua
E) Prunusyedoensis
Accuracy validation of new formula 4
As shown in the accuracy validation of calculation results, a comparison was made between the ray tracing method and the new formula. The result was 0.02 to 0.05 of RMSE
Sky SR
Reflected SR
Reflected SRDirect SR
Diffe
rent in
incide
nt solar
radiation at sitting po
sition
with
and
with
out trees [W/m
2 ]
winter
summer
A) B) C) D) E)
0
400
1200
400
800
Area of Simulation
N
50m
SR : Solar Radiation
Comparison the solar shading effects of 5 trees at an actual open space 5
At 12:00
Summer 12:00, 8/5 Tokyo
Winter 12:00, 1/23 Tokyo
D) PlatanusorientailsA) Ginkgo biloba B) Zelkova serrata
C) Liquidambar styraciflua
E) Prunusyedoensis
Thermal environment at sitting position at 12:00
Mean RadiationTemperature[ ]5 20 35
Mean Radiation Temperature[ ]32 42 6052
Reducing effects of solar radiation in summerReceiving effects of solar radiation in winter
Prunus yedoensisThin branch, flat leaf, and widely spread crown form
6
Conclusion
Thank you for your attention.
‐ A new numerical tree model that uses overlapping coefficient and improved clumping index functions is developed.
‐ The calculated quantitative visualization results help landscape designers when they select tree species, tree shape and communicating witharchitectures and urban planners.
‐ Using 3D CAD compatible thermal simulation tool, solar shading effects of five isolated deciduous tree species were calculated in summer and winter.
7
‐ This tree model can simulate the effects of tree species and leaf status on solar shading in both summer and winter.