Field measurements on micro-climate and cooling effect ... - IEEE Xplore

3 downloads 0 Views 679KB Size Report
Abstract----With Yangtze River through the downtown area, large urban river have great influence on urban climate in. Wuhan, which is typical representative of ...
Field measurements on micro-climate and cooling effect of river wind on urban blocks in Wuhan city Ganbo Han a Hong Chen a,b a

Li Yuan a

Ying Caia

Mengtao Han a

School of Architecture and Urban Planning, Huazhong University of Science and Technology

b

State Key Laboratory of Subtropical Building Science South China University of Technology Wuhan, China

[email protected] Abstract----With Yangtze River through the downtown area,

regulation law, micro-climatic conditions of a block alongside

large urban river have great influence on urban climate in

the river are investigated in this research using field

Wuhan, which is typical representative of summer hot and

measurement. Air temperature, surface temperature, relat ive

[1] [2]

conditions of

humid ity, wind direction and velocity, solar radiat ion and so

urban blocks in Wuhan city are of great research value. In order

on are obtained. After a series of data collection and analysis,

to acquire blocks realities to study the large urban river

some advices are given to direct urban planning and

regulation law on micro-climate and to give directions to urban

architecture design.

winter cold area. Therefore, micro-climate

planning and architecture design, a typical block alongside the

II. OUTLINE OF FIELD M EASUREM ENT

Yangtze River in Hankou, Wuhan city, was chosen to perform

2.1 Measurement Object

the field measurement and relevant analysis.

Fig.1 shows the block measured in this study. The site is located between Sanyang Road and Eryao Street. Inside the

Keywords---- Field measu rement; Thermal environment;

block are mostly traditional types of buildings, in other words,

Block micro-climate; Large urban river

Lifen building. And they are all well p lanning. There is a high-rise

I. INTRODUCTION

residential

mu lti-storey

Accompanied by the accelerating process of urbanization,

co mmun ity

commercial

on

buildings

the on

west,

the

east

some and

mu lti-storey buildings on the south.

quantities of immigrants brought in as well as the ongoing large-scale construction, lead to radical changes of urban environment, such as the emerging skyscrapers, chaotic layouts of buildings and continuous anthropogenic heat emissions. The deterioration in urban climate is under way. It is imperative to create sound block environments as the urban heat island effect rages higher. However, there has been little study into urban planning and architecture design based on climate adaptation. So it is of necessity to establish links and

Fig.1 Block Measured

apply urban climate information to urban planning. Wuhan has a dense water network and the water surface

2.2 Schedules and Methods

area in the city center covers more than 200 square km.

This study is carried out fro m a t wo-day (Ju ly 31-August

Nevertheless, with the increasing urban development in recent

1, 2010) field measurement in the summer of 2010. Data of

years, the water-covering area of downtown rapidly declines.

hours from 9:00~17:00 is measured.

Studies show that large urban rivers in the city provide

About 10 fixed points are spread out along streets in the

thermoregulat ion on urban climate [3] [4]. To investigate into

block and Fig.2 shows the sites.

Support projects of National Natural Science Foundation of China: Project No. Support projects of State Key Laboratory of Subtropical Building Science South China University of Technology: Project No..% 978-1-61284-774-0/11/$26.00 ©2011 IEEE

4446

Items such as air temperature, surface temperature,

Maximu m value of wind velocity reached about 8.1 m/s, and

relative hu midity, wind direction and velocity, solar radiat ion

the average was 1.7m/s. The daily average air temperature was 32.65ć while the temperature peak appeared fro m 13:00

are obtained, as Table.1 shows.

to 15:40 over 36.5ć. Changes of humidity and temperature could be seen in Fig.4.

Table 1 Items Measured NO 1 2 3 4

Location

Items

Solar Radiation Top of Air Wuhan Architectur Temperature al Design Relative Institute Humidity Building Wind Direction and

Amounts 1 1 1 1

Apparatus Pyrradiometer Auto Timer Datalogging Humidity/Temperature Meter Auto Timer Datalogging Humidity/Temperature Meter TES 1365 Anemograph

5

Air Temperature

10

Auto Timer Datalogging Humidity/Temperature Meter

6

Relative Humidity

10

Auto Timer Datalogging Humidity/Temperature Meter

8

Hot-wire Anemometer

8

Ribbon, Compass

3

Black Globe Thermometer

10

Thermal Infrared Imager

Block Wind Velocity measured in Hankou Wind 8 Direction black globe 9 temperature Surface 10 Temperature 7

Fig 3 Wind Rose of Reference Point

Fig.4 Comparison of Air Temperature and Humidity on July 31

III. FIELD M EASUREM ENT RESULTS 3.1 Wind Distribution Fig.5 shows the average wind velocity of each field measurement point, the wind average velocity of Po int 1 was higher than other points. It can be seen that Point 2 as well as Point 3 was located in Sanyang Road, but the wind velocity of Point 2 was much faster than Point3; Point 4 and Point 5 were located in the alleyway, and the Point 5 was a little faster; the wind velocity of Po int 7 was much faster than Point8. Fig.2 Distribution of Measured Points

2.3 Local Weather It was sunny, hot and cloudless during the measurement. Radiat ion and winds along the river were strong. All above showed good agreement with the typical summer hot and winter co ld climate. Solar radiat ion started fro m 5:40 and ended at 19:00. The maximu m value was about 1200 W/΃. Wind directions were unstable in the morning but stable in the afternoon. The main Fig.5 Average Wind Velocity of Each Point

direction ranged fro m 22.5°east of south to 45°west of south.

4447

Table 2 is a representation of the highest frequency in

be seen that the variation trend of temperature and hu midity in

July 31 and August 1.The wind direction of Po int1 was SW in

Point 2 and Point 3 were basically the same, which is 2ć

July 1, and SE in August 1.In Point 3, 4, 5, 6, the wind

higher in temperature and lo wer in hu midity than that of Po int

direction was identical in these two days. The wind d irect ions

1 near the rive. Fro m the data we measured for several days, it

of Po int7, 8 were changed regularly in July 1, but it became

is obvious that temperature was going down while getting

disordered in August 1.

close to the riverside.

Table 2 Predominant Wind Direction of Each Point Point

1

2

3

4

5

6

7

8

Dire ction

SSW

SSE

E

SEE

SWW

SEE

SWW

SEE

The wind velocity of Po int 1 located near the river was faster. As Fig.6 shows, the wind direction of Point 1 was disordered to some extend in the morning, and then became stable in the afternoon. Generally the main direction was SSW

Fig.7 Comparison of Air Temperature of Point 1, 2, 3, 9 on July 31

parallel to the river. The wind of point 5 had been very stable 3.3 Mean Radi ati on Temperature

and was basically SWW, the main wind velocity ranged fro m

The mean rad iation temperature (M RT) of Point 3 was

0.5m / s to 0.8m / s. It is because Point 5 was located in the alley way, and the wind direction basically along the alley. We can see that the main wind direct ion of Point 8 was SE, and the wind was not strong. Point 8 was located in the end of the Eryao Street wh ich was closed to the block center, so the wind direction of this point was affected by a variety of factors in the city but not the river wind. Therefore, the wind direction appeared disordered.

Fig.8 Comparison of Relative Humidity of Point 1, 2, 3, 9 on July 31

lower and that of Po int 4 and Point 8 were higher. The hig hest temperature reached almost 60ć fro m 13:00 to 14:00 when the peak appeared. Sites of Point 4 and Point 8 were exposed to thermal rad iation before 14:00. (Fig.9)

Fig.6 Distribution of Wind of Point 1 on July 31

3.2 Air Temperature and Humi di ty Distri bution Fig.9 MRT of Point 3, 4, 8 on July 31

Fig.7 and Fig.8 g ive the comparison of air temperature and relative hu midity of Po int 1 located near the Yangzi River

IV. DISCUSS ION

and Point 2 as well as Point 3 located on Sanyang Road. It can

4.1 Wind Velocity and Direction

4448

environment. All above say that large urban rivers have great

During the field measurements, the wind directions of the basic point are basically SW and SE. Higher wind velocity

influence on urban micro-climate.

during the day, and weaker at night. The data collected shows

3) Urban streets beneficial to the blowing of river wind have

good agreement with the typical climate in Wuhan.

better thermal environ ment than obstructive streets. As

Point 1, Point 2 & Point 3 were sited along the Sanyang

Sanyang Road is spacious and has good natural ventilation

Road in a line. The wind velocity of these points reduced

while Eryao Street is very narrow and has too many cars to

successively. That is to say, corresponding to our expectations,

remove heat, resulting in poor natural ventilation. The thermal

the more extending into the inner city, the weaker the wind

comfo rt on Sanyang Road is better than that on Eryao Street.

velocity. Po int 4 and Po int 5 are sited in the alley and the wind

Through proper adjustment of planning, guiding river wind

direction parallels the alley. Sited on the Eryao Street, Point 7

into urban blocks will p lay an active role in the improvement

& Po int 8 differ in wind velocity and direction. There would

of urban thermal environment.

be some impact on wind velocity and direction of point 7 beside Ergang Hotel when river wind blo ws to the building

Note˖ ˖

forming lower punch air. In contrast, the wind direction of

1)

Point 8 is in disorder and low velocity, due to the narrow

Fig.1 fro m GOOGLE EA RTH, other figures and tables are the author's own drawings.

Eryao Street and too much parking there. 4.2 Air Temperature and Rel ati ve Humi di ty

Acknowledgement

The air temperature of Po int 1 & Point 9 is lower than

This paper supported by projects of National Natural

Point 2 & Point 3 for t ranspiration effect and high speed of

Science Foundation of China: Pro ject No. 50978110,projects

river wind.

of State Key Laboratory of Subtropical Build ing Science

The air temperature in the alley is 2-3 ć higher than

South

Zhongshan Road and Sanyang Road. Due to the narrow alley,

China

Un iversity

of Technology: Pro ject

No.

2009KB16.

high build ing density and low green space, heat gathers in the alley and cannot go out. Moreover, there is little ventilat ion

References

channels formed between the alley and the river bank, so the [1]

air temperature in the alley is much higher. The air temperature of Point 7 rose faster than point 8 for

[2]

the continuous heat emission fro m s mall restaurants and retail stores nearby. Due to messy arrangement and parking cars

[3]

around, the wind of Point 8 is weak. On the contrary, the wind velocity of Point 7 is quite h igh because of the canyon wind

[4]

formed by existence of Ergang Hotel.

[5]

V. CONCLUS ION 1) The average wind velocity of most sites in the block is below 1m/s. The maximu m air temperature is above 37ć, and the average is about 35.5ć. All indicate the deterioration of urban thermal environ ment and seriousness of urban heat island phenomenon. 2) The air temperature near Yangtze River is 2ć lo wer and the wind velocity is higher than that inside the urban block. Areas close to Yangtze River bank provide more co mfortable

4449

Norman J. Rosenberg, Blaine L. Blad, Shashi B. Verma. Microclimate: The Biological Environment. (Second Edition). New York: A Wiley-Interscience Publication: 1983. Bonan, Gordon B. Microclimates of a suburban Colorado (USA) landscape and implications for planning and design. Landscape and UrbanPlanning (Amsterdam), 2000, v49: 97-114. Li Shuyan, Xuan Chunyi. Analysis of Microclimate Effects of Water Body in a City. Chinese Journal of Atmospheric Sciences, March. 2008: 53-560 (In Chinese). Song Xiaocheng, Liu Jing, Guo Liang. Field Measurement of the Large Urban River Effect on Urban Thermal Climate. Proceedings 2011 International Conference on Computer Distributed Control and Intelligent Environmental Monitoring, Feb. 2011: 19-20 (In Chinese). Liu Nianxiong, Qin Youguo. Building Thermal Environment. Beijing: T singhua Publishing House, 2005 (In Chinese).