Numerical study: How does a high-rise building …...residential buildings, and many businesses closed. High-rise buildings cause problems such as preventing access to sunlight, and

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In rural Japanese cities, many old and densely populated urban districts have been replaced by high-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

1

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)


2

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


3

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


4

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


5

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


6

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


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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)


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Numerical study: How does a high-rise building …...residential buildings, and many businesses closed. High-rise buildings cause problems such as preventing access to sunlight, and