Numerical study: How does a high-rise
building affect the surrounding thermal
environment by its shading?
Hidenori KAWAI, Dr.Eng Takashi ASAWA, Dr. Eng.
[Tokyo Institute of technology] [Tokyo Institute of technology]
Riku Saito Rihito SATO, Dr. Eng.
[Japan Meteorological Agency] [Misawa Homes Instituite of Research and development]
ABSTRACT
In rural Japanese cities, many old and densely populated urban districts have been replaced by high-
rise residential buildings because of urban redevelopment. High-rise building affects the sunshine
conditions and wind environment of the surrounding areas. These problems have been already
discussed; however, it is rarely discussed how high-rise buildings affect the outdoor and indoor thermal
environment of their surroundings. Particularly, shading is a serious problem in winter because it makes
the outdoor environment colder and increases the energy consumption for heating of adjacent buildings
in addition to daylight shortages.
The shading effect of a high-rise building on the outdoor and indoor thermal environment in winter
is simulated by a 3D CAD-based thermal environment simulator. As a result of the simulation, shading
effect by high-rise building at noon extends widely to the area apporoximately 200m away in the north,
but the 7 °C difference in the mean radiant temperature in the shaded area is caused by the surrounding
space geometry and material. Also, in the northern or western street of high-rise building, many shops
exist and their façade with large windows make the shading effect on the building heat load more
remarkable. The building heat loads of these buildings are more than 30% larger than that in the case
when the high-rise part is removed.
INTRODUCTION
In rural Japanese cities, many people used to live in densely populated urban districts near train
stations with many prospering businesses nearby. However, because of decreasing district population
and development of suburban areas, many district buildings were vacated and replaced by high-rise
residential buildings, and many businesses closed.
High-rise buildings cause problems such as preventing access to sunlight, and creating strong wind
conditions, and affect the landscape. When constructing high-rise buildings in Japan, the building height
is regulated by the Building Standards Law. The law has a regulation about indexes such as duration of
solar shading and sky factor from the viewpoint of access to sunlight. Moreover, in several cities,
environmental assessments are required when the height of high-rise buildings is greater than 100 m. For
these assessments, wind conditions are simulated using CFD (RANS).
As previous studies, Saito (2003) researches the effect of high-rise building on the illuminance and
30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad
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sky factor on the surroundings. Also, Curreli (2011) researches solar access in densely built urban
environments. However, it is rarely discussed how high-rise buildings affect the outdoor and indoor
thermal environment of their surroundings. As mentioned above, shading is a serious problem in winter.
In particular, shading by high-rise building makes the neighboring outdoor environment colder, and
increases the energy consumption for heating.
This study reveals the shading effect of a high-rise building on the outdoor and indoor thermal
environment in winter using numerical simulations. The building heat load is calculated considering the
effect of the outdoor thermal environment. An urban district with and without high-rise buildings are
reproduced using the 3D CAD system and then compared.
METHODOLOGY
Target urban district
The target district is in Tsuchiura city, which is approximately 60 km from Tokyo in the north, and
is located in the city center near Tsuchiura Station. The district has high pedestrian traffic and several
shops. Low-rise shops and residential buildings were closely built, and commercial and high-rise
residential buildings were first built in 1997. Furthermore, parking lots have replaced many of the
original houses and shops. The height of the high-rise building in the target district is 109 m, with a
north-facing open space for events. The high-rise building affects the thermal environment of the
surrounding outdoor spaces, particularly the thermal radiation environment of sidewalks and parking lots.
Moreover, it affects the thermal environment of the surrounding buildings, and the shading owing to the
high-rise building increases the energy consumption for heating.
Figure 1 3D CAD model of the target urban district
Simulation method
In order to reveal the effect of shading owing to the high-rise building on the thermal environment
of outdoor and indoor spaces, we analyzed the thermal environment in the target urban district using an
in-house 3D CAD-based thermal environment simulator (Jiang H. et al., 2009; Asawa T. et al., 2008).
Current Case Removed Case
High-risebuilding:Height=109m
Parking lot
Parking lot(p1)
N
N
235m
Eaves
Windows
Balcony Fence
Tree
CAD Model detail of each building
High-rise part:Removed
Parking lot (p2)
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We collected spatial geometry and material data for 2009 and constructed 3D CAD models of the site at
a scale of 1:500 (Sato R., et al., 2009). Two models were constructed; the first (current case) reproduces
the current state, whereas the second (removed case) reproduces the state when the high-rise part is
removed from the high-rise building.
Next, we calculated the outdoor surface temperature distribution in the target district under clear
sky conditions in winter using the 3D CAD-based thermal environment simulator (Weather condition:
Fig. 2). First, the 3D spatial forms of buildings, trees, and other structures and the 2D ground surfaces
are divided into voxel mesh grids (mesh size: 400 mm). Then, the outdoor surface temperature for each
grid was determined by solving the unsteady-state 1D heat balance equation in the vertical direction of
the surface. The terms of the heat balance equation are direct solar radiation, sky solar radiation,
reflected solar radiation, atmospheric radiation, longwave radiation exchange with surroundings,
convective heat transfer, latent heat transfer, and conductive heat transfer. Each radiation is calculated by
the ray tracing method, and the convective heat transfer is calculated assuming outdoor uniform
distribution for the outdoor air temperature and wind velocity.
Figure 2 Weather conditions (December 21, a clear sky winter day)
The thermal radiant field in the urban district is evaluated using mean radiant temperature (MRT) at
a height of 1.5 m. The MRT is calculated using the following equation, as the shortwave and longwave
radiation absorbed by humans. Rhuman is the solar radiation and longwave radiation absorbed on the
human surface, calculated from equation (2).
√ ⁄ (1)
{
∑ ( )
} ∑ (
)
(2)
Furthermore, the building heating loads, which consider the effect of surrounding buildings and
trees, are calculated using the calculated total radiation and surface temperature distribution on the
building’s external surfaces. To evaluate the effect of the outdoor thermal environment on the building’s
indoor thermal environment, each building floor is assumed to be a single room. We further assume that
the air-conditioning system is set at 20 °C all day in winter, and the internal heat gains’ schedule is based
on the standard model of the Architectural Institute of Japan (Architectural Institute of Japan, 1985).
Normal directsolar radiation
0
20
40
60
80
100
-5
0
5
10
15
0 3 6 9 12 15 18 21
Rel
ativ
e h
um
idit
y[%
]
Ou
tdo
or
air
tem
p.[°C
]
Time
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0
200
400
600
800
1000
1200
0 3 6 9 12 15 18 21
Win
d v
elo
city
[m/s
]
Sola
r ra
dia
tio
n[W
/m2]
Time
Horizontal sky solar radiation
Wind velocity
Outdoor air temp.
Relative humidity
30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad
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RESULTS AND DISCUSSIONS
Effect on the thermal radiation environment of the outdoor space
Surface temperature distribution
Figure 3 shows the surface temperature distribution in the two cases at 12:15. In the current case,
where the high-rise building shades the surrounding urban area, its shade extends 200 m toward the
north. Because of the shade, the sidewalk (s1) surface temperature at 12:15 (Fig. 3) is 5 °C, which is
10 °C less than that of the removed case.
On the ground of the parking lot, the surface temperature is different at each spot that is shaded by
the high-rise building. Such differences depend on the duration of the shading of the high-rise building.
In the current case, the surface temperature of the east side of the parking lot (p1) is 5 °C lower than the
rest. On the other hand, the surface temperature of the west side of the parking lot (p2) is greater than
10 °C because the asphalt pavement accumulates heat by solar radiation in the morning.
In some parking lot which is not shaded at 12:15, the cold accumulation owing to the morning solar
shading remains on the ground. As a result, the surface temperature at 12:15 in the parking lot (p1)
adjacent to the shaded area decreases by 5 °C compared with the removed case. The area where the
surface temperature decreases owing to cold accumulation occupies approximately 25% of the parking
lot (p1) area.
Mean radiant temperature distribution
Figure 4 shows the mean radiant temperature distribution and surface temperature distribution in
the outdoor space shaded by the high-rise building. At the sidewalk (s1), the mean radiant temperature
for the current case decreases by more than 15 °C compared with the removed case owing to shading and
decrease in surface temperature. In the parking lots shaded by the high-rise building, the mean radiant
temperature in the current case also decreases compared with the removed case. However, the mean
radiant temperatures of the parking lots differ in the shaded area of current case and the difference is
7 °C. At point X, the mean radiant temperature is 0 °C, which is 7 °C lower than the air temperature.
Figure 3 Surface temperature distributions at 12:15
Shade of high-rise building
Cool accumulation remaining due to shading in the morning Sidewalk (s1)
Parking lot (p2)
Parking lot (p1)
Current Case Removed Case
0 5 10 15 20 25[°C]
Air temp. 7.9°CN
30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad
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Figure 4 Mean radiant temperature distribution at 12:15 and at a height of 1.5 m, and surface
temperature distribution at 12:15 in the outdoor space shaded by the high-rise building.
This is attributed to the ground that is shaded by the high-rise building and the surrounding buildings,
and the building wall with low surface temperature (see View K in Fig. 4). On the other hand, at point Y,
the ground surface temperature is more than 10 °C higher than that at point X, and the surrounding
building wall keeps the surface temperature high owing to heat accumulation (see View M in Fig. 4). As
a result, the mean radiant temperature at point Y of the current case is 7 °C higher than that at point X.
Effect on the building heat load
The relation between the daily solar radiation, which is received by the windows, and the heat load
of each building is examined to demonstrate the effect of shading by the high-rise building. We focus on
the building that is shaded by the high-rise building for more than 1 h and calculate the building heat
load. Figure 5 shows the daily solar radiation distribution in each case and the increasing rate map of the
building heat load. Figure 6 shows the diurnal change in the solar heat gain and heat load in the buildings.
In this district, many buildings have large windows in the southern or eastern facades, which face the
street in the north or west of the high-rise building. As shown in Fig. 5, in the building shaded by the
high-rise building for more than 2 h, the daily solar radiation on the building southern facade is 5 MJ/day
lower in the current case than in the removed case. Hence, these buildings with large windows increases
by more than 30% in the heat load.
The shading effect on the building heat load depends on not only the distance from the high-rise
building and but also the window location and site conditions. When the building is close to and has no
windows facing the high-rise building, such as building (a), the rate of increase in the building heat load
is within 5% despite being shaded by the high-rise building for more than 2 h.
Current Case: MRT
0 5 10 15[°C]
Air temp.7.9°C
MRTN 0 5 10 15 20 25[°C]
Air temp. 7.9°C
N
N N
N
Current Case: Surface temperature
Removed Case: Surface temperatureRemoved Case: MRT
View K View M
View K View M
PointX View K
High-risebuilding
ViewM PointX ViewK
PointY
PointX
PointX
PointY
PointY
Sidewalk(s1)
Sidewalk(s1) ViewM
PointY
30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad
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Figure 5 Increasing rate map of building heat load and daily solar radiation distribution
in each case
Figure 6 Diurnal change in the solar heat gain and building heat load in buildings (b),(c)
Increasing rate of building heat load in the current case compared with the removed case
Shaded by high-rise building during 1h
0 50 100[m]
N
Current Case in View N
Removed Case in View N
30
25
20
15
10
5
0
[%]30
View N
N
0 5 10 15 20 [MJ/m2·day]
Daily solar radiation distribution
Building (a)
2.5h
2h
3hBuilding (b)
Building (c)
0
5
10
15
0 3 6 9 12 15 18 210
5
10
15
20
25
30
35
40
45
0 3 6 9 12 15 18 21
0
5
10
0 3 6 9 12 15 18 21
0
5
10
15
20
0 3 6 9 12 15 18 21
Sola
r h
eat
gain
[kW
]So
lar
hea
t ga
in[k
W]
Bu
ildin
g H
eat
load
[kW
]B
uild
ing
Hea
t lo
ad[k
W]
Difference=Current-Remove
Current
Current
Difference=Current-Remove
Current
Current
Remove
Remove
Direction for high-rise building
Building(b):Wooden house
Building(c):Shop(Construction: Reinforced Concrete)
N
N
Direction for high-rise building
Time Time
TimeTime
30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad
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On the other hand, although building (b) is 170 m away from the high-rise building, the rate of
increase in the building heat load is 10%. This is because building (b) has windows facing the high-rise
building and the adjacent parking lot has no buildings or external objects as shown in Fig. 6.
In addition, different building materials are not affected in the same manner by shading. In
reinforced concrete buildings, with large heat capacity, increasing building heat load is observed when
shaded by the high-rise building as well as at other times. In building (c), the building heat load is larger
than that in the removed case after the building is shaded. The building heat load of buiding (c) in each
time from 1 p.m. to 8 p.m. is approximately 30% higher than that at 11 a.m., which is the time when the
building is shaded.
CONCLUSION
The shading effect of a high-rise building on the thermal radiation environment in the outdoor space
around it and the neighboring buildings heat load in winter is discussed and the following conclusions
are reached.
・ Shading effect by high-rise building at noon extends widely to the area apporoximately 200m away
in the north and the lowest mean radinant temperature in the shaded area decreases 7 °C lower than
air temperature. However, in the some space, the shading negative effect on the thermal radiation
environment is mitigated by the surrounding space geometry and material. In particular, in the
space close to the building wall and ground, which is heated because of solar heat accumulation in
the morning, the mean radiant temperature keeps equal to the air temperature.
・ In the target district, the northern and western street of high-rise building have many shops with
southern or eastern façade with large windows, and these shops are affected more remarkably by
high-rise building. The heat loads of these buildings are more than 30% larger than that in the
removed case.
・ Even for buildings 170 m away from the high-rise building, shading effect on the building heat load
is not so little when the building is adjacent to the parking lot and has large window. In this
condition, the building heat load increased by 10% compared with the removed case.
The following will be considered for our future work.
・ Combine simulation with CFD simulation and study the wind and cold air distribution around the
high-rise building.
・ Perform simulations of the thermal environment in summer.
REFERENCES
Saito K., Shinozaki M. & Kuwata H.(2003), Illuminance, sky factor and relative solar energy around
high-rise buildings: Design control method considering the quality of daylight in urban open space
(3), J. Archit. Plann. Environ. Eng., AIJ, No.565, 201-208(In Japanese)
Curreli A. & Roura .H.C.(2011), Solar access in densely built urban environments:Formal parameters
and comparative methodology in the case of Barcelona, Spain, Proceedings of PLEA2011, 235-240
Jiang H., Hoyano A. & Asawa T. (2009). A numerical simulation tool for predicting the impact of
outdoor thermal environment on building energy performance, Applied Energy, 86: p. 1596–1605
(in Japanese)
Asawa T. Hoyano A. & Nakaohkubo K. (2008). Thermal design tool for outdoor spaces based on heat
balance simulation using a 3D CAD system, Building and Environment, 43: p. 2112–2123
Sato R., Hoyano A., & Asawa T. (2009) Modeling method of substantial urban area using 3D-CAD and
its application to thermal environment simulation in rural cities, ICUC-7 proceedings, P1-30
Architectural Institute of Japan, (1985). The present situation and the problems of the heat-transfer analysis, The text of the 15th AIJ symposium on heat, 23–33 (in Japanese)
Underwood C.R. & Ward E.J. (1966). The solar radiation area of man, Ergonomics, 9, 155–168
30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad
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NOMENCLATURE
= Direct solar radiation on surface i [W/m2]
= Sky solar radiation on surface i [W/m2]
= Reflective solar radiation on surface i [W/m2]
= Longwave radiation on surface i [W/m2]
= Atmospheric radiation on surface i [W/m
2]
= Surface area of the human body [m2]
= Effective radiation area (Underwood C. R. & Ward E. J., 1966) [m2]
= Solar absorption of the human body [-]
= Emissivity of the human body [-]
= Weighting factor [-]
= Stefan–Boltzmann coefficient [-]
Subscript
= microcube surface (assuming human body)
30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad
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