Journal of Heat Island Institute International Vol. 9-2 (2014)

Academic Article

Evaluation of the outdoor thermal environment
in redevelopment buildings in front of Osaka Station
based on observations
Kentaro Aoyama*1
Hideki Takebayashi*1

Etsuko Ishii*1*1

Sae Kyogoku*1

Sintaro Nakayama*1

Makiko Kasahara*2

Shingo Tanabe*2

Rieko Yagi*1
Makoto Kouyama*2

Graduate School of Engineering, Kobe University*2
Nikken Sekkei Ltd.

Corresponding author: Kentaro AOYAMA, 144t001t@stu.kobe-u.ac.jp
ABSTRACT
Several technologies used as countermeasures against urban heat islands, such as green cover and watersurfaces, are being applied to redevelopment buildings in front of central Osaka Station. In this study, we evaluatedthe outdoor thermal environment by focusing on the effects of wind velocity and MRT, which is reflective of solar
radiation shielding, in an open plaza with water surfaces, a rooftop garden with plants, and a sunken garden placed
between high-rise buildings. In the open plaza, SET* was high due to high MRT and reduced by slightly strong
wind at some measurement points. In rooftop garden, SET* was high due to high MRT and not reduced so much bywind with a little variation in each measurement point. In the sunken garden, SET* was low due to low MRT,
because solar radiation is shielded by plants and high-rise buildings at most of the measurement points, while windvelocity is low due to wind resistance offered by plants. To conclude, the improvement of MRT is the mostsignificant factor for the improvement of the outdoor thermal environment during the daytime.
Key Words : Outdoor thermal environment, Wind velocity, MRT, SET*, Redevelopment buildings

outdoor thermal environment. In this study, we evaluated the

1. Introduction

outdoor thermal environment by focusing on the effects of wind
Several technologies used as countermeasures against urban heatvelocity and mean radiative temperature, which is reflective ofislands, such as green cover and water surfaces, are being

solar radiation shielding, in an open plaza with water surfaces, aapplied to redevelopment buildings in front of central Osaka

rooftop garden with plants, and a sunken garden placed between

Station. With regards to a previous study, Akagawa et al.(1)high-rise buildings. Mean radiative temperature is transcribedanalyzed the outdoor thermal environment of a rooftop garden

into MRT.

on a large commercial building. In subsequent research,Akagawa et al.(2) also compared standard effective temperature

2. Measurement

at an area shielded by objects, trees, and semi-open spaces in alarge, artificial green space. standard effective temperature is

2.1 Measurement method

transcribed into SET*. SET* was found to be lowest in

The selected measurement period was from July 22 to 26, 2013.

semi-open spaces in the morning and evening, and in spaces

Air temperature, relative humidity, surface temperature, windshielded by trees in the daytime. As well, SET* was highest in

direction and velocity, and thermal images were obtained by aspaces shielded by various objects, due to low wind velocities inthermistor, capacitive humidity sensor, infrared thermometer,

the daytime and high air temperatures at night. The authors

windsock,concluded that ventilation and solar radiation shielding canMeasurements were made at 10:00, 13:00, 17:00, and 20:00 in 5

effectively improve the outdoor thermal environment. However,or 6 measurement points in each of the following areas: open

they did not discuss whether ventilation or solar radiation

plaza, rooftop garden, and sunken garden. We selected these 3

shielding was more important for the improvement of theareas in the redevelopment building complex because several- 86 -

hot-wire

anemometer,

andthermo-camera.

urban heat island countermeasure technologies, such as green

Table 1 Measurement elements, measurements, and analytical

cover and water surfaces, had already been applied at those sites.

methodsThe open plaza is located on the southern tip of theElement

Measureent and analysis method

redevelopment building complex. There are two tall buildings toAir temperature

Measured at 5 sec., averaged in 5 min.

the northeast and south of the open plaza, while the western side

Relative humidity

Measured at 5 sec., averaged in 5 min.

of the plaza is open. There is little vegetation present, and open

Surface temp.

Measured on ground and wall surface

spaces and water surfaces are dominant. The rooftop garden (GLWind direction

Recored most frequent wind direction+ 45 m) is on the roof of the southernmost building in theWind velocity

Measured at 1 sec., averaged in 30 sec.

redevelopment building complex. The sunken garden, whereView factor

Calculated by fisheye photo at 1.5m

plants are prevalent, is located between the northernmost andThermal image

Taken to capture panoramic view

southernmost high-rise buildings.
The measured variables and the measurement and analyticalmethod are shown in Table 1. We carried out the measurements
by moving between the measurement points. Figure 1 shows themeasurement points and photos taken via fisheye lens in eacharea. The measurement points were selected with considerationof surface cover, ventilation, and solar radiation shielding. Six
measurement points in the open plaza were numbered from “1”
to “6,” five measurement points in the rooftop garden werelabeled “A” to “E,” and six measurement points in the rooftop
garden were labeled “a” to “f’’.

(a) Air temperature(b) Relative humidity(a) Open plaza(c) Ground surface temperature(b) Rooftop garden(d) Wind velocity(c) Sunken garden

Fig. 2 Air temperature, relative humidity, ground surface

Fig. 1 Location of the measurement points and photos taken via

temperature, and wind velocity at 13:00 on July 25, 2013

fisheye lens

- 87 -2.2 Measurement results

minimum MRT, and about 8oC due to the differences between

In the daytime, the air temperature increased in the following

measured maximum and minimum wind velocity. The effect oforder: open plaza, rooftop garden, and sunken garden. At night,

wind velocity on SET* was found to be greater than that of

the temperature was lowest in the rooftop garden. Differences inMRT.

relative humidity were small; however, relative humidity values

MRT components at each measurement point are shown inwere greatest at the measurement points located near water

Figure 4. MRT was primarily affected by ground surface

surfaces in the open plaza and sunken garden. The wind velocity

temperature, wall surface temperature, and direct solar radiation.

was high during the daytime at several measurement points in

In particular, the ground surface temperature dominated MRT.

the rooftop garden. In the daytime, the artificial ground surface

The ground surface temperature was low at measurement points

temperature in the open plaza and rooftop garden was high due“1” and “3,” where solar radiation was shielded in the morning.

to solar radiation absorption. Air temperature, relative humidity,

The wind vectors are shown in Figure 5. Wind directions varied

ground surface temperature, and wind velocity in eachdepending on the obstacles present around the measurement

measurement point at 13:00 on July 25, 2013, is shown in Figure

points.

2.

The characteristics of the thermal environment at each

3. Calculation of SET*
Measuredvaluesoffourenvironmentalelements;

airtemperature, surface temperature, relative humidity, and windvelocity, were used for calculating SET*. SET* is commonlyused as an indicator of the outdoor thermal environment,
particularly in Japan. Therefore, we have focused on SET* inthis study. We set a metabolic rate of 2.0 Mets, with theassumption of a certain walking pace, and we set the amount ofclothing at 0.6 clo, assuming the use of summer clothes.
Through the sensitivity analysis of SET* for changes in fourFig. 3 Effects of MRT and wind velocity on SET* in all areas atenvironmental elements, it was observed that MRT and wind

13:00 on July 25, 2013velocity are the dominant factors in SET*.
Therefore, we evaluated the outdoor thermal environment byfocusing on the effects of wind velocity and MRT. MRT wascalculated with surface temperature, view factor, direct solar
radiation, and diffuse solar radiation. We divided the measured
global solar radiation into direct and diffuse solar radiation forthis purpose.
MRT was an instantaneous value and wind velocity wasaveraged over 30-seconds, based on measurements taken at
one-second intervals. The effects of MRT and wind velocity on
SET* in all areas at 13:00 during July 25 is shown in Figure 3.

Fig. 4 Components of MRT in the open plaza at 13:00 on July 25,

The thermal comfort of SET* is shown in accordance with the2013

study results of Ishii et al.(3). In the open plaza, MRT was highand the variation in wind velocity was large. In the rooftopgarden, MRT was also high, while the wind velocity wasgenerally high. In the sunken garden, the variation in MRT waslarge as well, but the wind velocity was low.
4. Discussion of SET*
4.1 Open plaza
The variation in SET* in the measurement points was about
4.5oC due to the differences between measured maximum and- 88 -Fig. 5 Wind vectors in the open plaza at 13:00 on July 25, 2013

measurement point were as follows:- At measurement point “2,” SET* was low because the windvelocity was high due to the wind passage in high-rise buildings.
- At measurement point “3,” SET* was high because the windvelocity was low, due to shielding by trees.
- At measurement point “4,” SET* was low because the windvelocity was high, due to a lack of obstructions in the center ofthe open plaza.
- At measurement points “5” and “6,” SET* was high because

Fig. 6 Relationship between the distance from the water surface

the wind velocity was low, due to the presence of a glass fence

boundary and MRT, at 0.88 m (child) and 1.5 m (adult) height

between the ground and water surfaces.
At measurement point “5” or “6,” any improvement of MRT
derived from water surfaces was not observed. Therefore, weanalyzed the relationship between the distance from the water
surface boundary and MRT, using a view factor as an indicator.
The relationship between the distance from the water surface
boundary and MRT is shown in Figure 6. We calculated the view
factor by the water surface by changing the distance from thewater surface boundary, with a height of 0.88 m assuming achild’s stature, and a height of 1.5 m assuming an adult’s stature.
If the distance was closer than 2 m and 3.5 m to the water

Fig. 7 Components of MRT in the rooftop garden at 13:00 on

surface boundary, the improvement of MRT by the water surface

July 25, 2013

was confirmed at both 0.88 m and 1.5 m heights.
4.2 Rooftop garden
The variation in SET* in the measurement points was about 3oC,
due to differences between the measured maximum andminimum MRT, and about 2.5oC due to differences between themeasured maximum and minimum wind velocity. The effect ofMRT on SET* was found to be more significant than that ofwind velocity.
The MRT components at each measurement point are shown inFig. 8 Wind vectors in the rooftop garden at 13:00 on July 25,Figure 7. The MRT was primarily affected by plant surface

2013

temperature, ground surface temperature, and direct solar
radiation. The ground surface temperature dominated MRT,
similar to the results obtained from the open plaza.
Wind vectors are shown in Figure 8. The primary wind direction
on the rooftop garden was from the southwest. The windvelocity was high at measurement points “A” and “B” on thewindward side, and slightly lower at measurement points “C,”
“D,” and “E” on the leeward side, due to the wind resistanceoffered by plants and obstacles.
The characteristics of the thermal environment on eachFig. 9 Components of MRT in the sunken garden at 13:00 on

measurement point were as follows:

July 25, 2013

- At measurement points “A” and “C,” SET* was low because
the MRTs were low, due to low ground surface temperatures onbrick and stone.

was high, due to high ground surface temperatures on the wood

- At measurement point “B,” SET* was low because the MRTdeck.

was low, due to the large view factor of plants.

- At measurement point “E,” SET* was high because MRT was- At measurement point “D,” SET* was high because the MRT

high, due to high ground surface temperatures on stone.

- 89 -4.3 Sunken garden
The variation in SET* in the measurement points was about
9.5oC due to the differences between the measured maximum
and minimum MRT, and about 3oC due to the differences
between the measured maximum and minimum wind velocity.
The effect of MRT on SET* was dominant, as compared to windvelocity.
The components of MRT at each measurement point are shownin Figure 9. There were few plants at measurement point “a,”and more plants present at measurement point “f’. Solar orbital
diagrams corresponding to the date of July 25 are shown inFigure 10. At the majority of the measurement points, the solar
radiation was shielded by high-rise buildings and plants

Fig. 10 Solar orbital diagrams from the sunken garden on July25, 2013

throughout the day.
MRT was primarily affected by plant surface temperatures,
direct solar radiation, and ground surface temperatures. MRT

Table 2 Averaged values of SET*, MRT, and wind velocity atwas low at most of the measurement points because of the large

13:00 on July 25, 2013

view factor of plants, while MRT was high at measurement

SET*

MRT

points “a” and “d,” due to the incidence of direct solar radiation.

Open plazao

38.9 Co

50.0 C

2.2 m/s

The wind velocity at each measurement point was low, due toRooftop garden

38.6 oC

50.3 oC

2.1 m/sthe wind resistance offered by plants.

Sunken garden

5. Discussion and Summaryowind velocityo

33.1 C

38.0 C

0.9 m/s

Table 3 Variations in SET* due to differences in MRT and windvelocity at 13:00 on July 25, 2013

The averaged value of SET*, MRT, and wind velocity in eachdue to difference

due to difference inarea at 13:00 on July 25, 2013, is shown in Table 2. The

in MRTwind velocityOpen plaza

4.5 oC

8.0 oCin each area at 13:00 on July 25, 2013, is shown in Table 3.

Rooftop garden

3.0 oC

2.5 oCThe averaged value of SET* in the sunken garden was theSunken garden

9.5 oC

3.0 oCvariation in SET* due to differences in MRT and wind velocity

lowest out of the three measurement areas because the lowest
MRT was present at this location, despite the fact that the windvelocity was also the lowest at the same site. The improvement

Table 4 Averaged values of SET*, MRT, and wind velocity at
10:00, 17:00 and 20:00 on July 25, 2013

in MRT due to solar radiation shielding by plants and high-riseSET*buildings is more effective for the improvement of the outdoor
thermalenvironment,

ratherthanthroughThe averaged value of SET*, MRT, and wind velocity in eachOpen plaza
10:00

study area for other measurement times and days, i.e., underalternative weather conditions, are shown in Tables 4 and 5. The
tendency for SET* to be lower in the sunken garden during these

17:00

17:00 and 20:00 is low due to the low MRT derived fromradiative cooling and a slightly stronger wind.
To conclude, the improvement of MRT is the most significant
factor for the improvement of the outdoor thermal environment
during the daytime, although ventilation enhancements are also
important for the improvement of the outdoor thermal
environment during the evening.

- 90 -o41.9 oCo

1.7 m/s

31.3 C

41.1 C

2.6 m/sSunken garden

30.8 oC

37.2 oC

0.8 m/so

38.9 Coo

0.7 m/so

45.4 C

Rooftop garden

31.3 C38.5 C

2.1 m/sSunken garden

30.6 oC

36.3 oC

1.4 m/s

Open plaza
20:00

32.7 oC

Rooftop garden
Open plaza

measurement times and days is similar to the observations taken
at 13:00 on July 25. However, the SET* in the rooftop garden atwindvelocity

ventilation

enhancements.

MRTo26.0 Coo

0.4 m/so30.0 C

Rooftop garden

24.2 C

27.5 C

1.3 m/sSunken garden

25.3 oC

29.3 oC

0.8 m/sTable 5 Averaged values of SET*, MRT, and wind velocity at
13:00 on July 22, 23, 24 and 26, 2013

July
22
July
23
July
24
July
26

Open plaza
Rooftop garden
Sunken garden
Open plazaMoriyama, Study on thermal environment and behavior ofvelocity

visitors at a large rooftop garden on a commercial building in

2.6 m/ssummer, Journal of Environmental Engineering (Transactions ofo

3.4 m/s

AIJ) 611, 67-74 (2007)o

2.0 m/s(2) H. Akagawa and H. Sugimoto, Environmental evaluation ato

1.7 m/slarge-scale greening area in urban canyon: Part 2 Investigation

oMRT

35.3 oC

46.8 oC

34.8 Co

29.7 Co

30.4 C(1) H. Akagawa, K. Fukumi, T. Kubota, H. Takebayashi and M.
windSET*oReferences

48.1 C37.1 C38.5 C

Rooftop garden

30.8 C39.2 C

1.7 m/sof thermal environment in the district, Summaries of technicalSunken garden

28.7 oC

36.3 oC

1.9 m/s

papers of annual meeting of AIJ D-1, 793-794 (2011)

oOpen plaza-40.8 C

2.3 m/s(3) A. Ishii, T. Katayama, Y. Shiotsuki, H. Yoshimizu and Y. Abe,

Rooftop garden

35.7 oC

47.6 oC

2.3 m/sExperimental study on comfort sensation of people in theSunken garden

26.4 oC

32.9 oC

1.2 m/s

Open plaza

34.6 oC

43.6 oC

2.4 m/sRooftop garden

34.6 oC

45.4 oC

3.0 m/s

38.0 oC

0.9 m/sSunken gardenoo31.8 C

outdoor environment, Journal of Architecture and Planning(Transactions of AIJ) 386, 28-37 (1988)(Received Nov. 20, 2014, Accepted Dec. 27, 2014)- 91 -