Scholarly article on topic 'Scale Study of Traditional Shophouse Street in South of China Based on Outdoor Thermal Comfort'

Scale Study of Traditional Shophouse Street in South of China Based on Outdoor Thermal Comfort Academic research paper on "Economics and business"

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{"Wet and hot climate zone" / microclimate / scale / "traditional shophouse street"}

Abstract of research paper on Economics and business, author of scientific article — Shi Yin, Yiqiang Xiao

Abstract As a colonial style urban space, the shophouse became one of the most important urban spatial types in the south of china, such as Canton city. The article attempts to re-introduce the mechanism, through researching the contribution of scale on the microclimate of shophouse streets via simulation software (ENVI-Met). Two groups of experiments were conducted by varying only the width of road and verandah, according to a certain scale range. After comparing the PET of monitoring points in different streets, conclusions on range of scale can be obtained, which will contribute to better microclimate in the shophouse street.

Academic research paper on topic "Scale Study of Traditional Shophouse Street in South of China Based on Outdoor Thermal Comfort"

Procedia Engineering

www.elsevier.com/locate/procedia

4th International Conference on Countermeasures to Urban Heat Island (UHI) 2016

Scale Study of Traditional Shophouse Street in South of China Based on Outdoor Thermal Comfort

Shi Yina, Yiqiang Xiaoa*

a School of Architecture, South China University of Technology,Guangzhou,510640,China

Abstract

As a colonial style urban space, the shophouse became one of the most important urban spatial types in the south of china, such as Canton city. The article attempts to re-introduce the mechanism, through researching the contribution of scale on the microclimate of shophouse streets via simulation software (ENVI-Met). Two groups of experiments were conducted by varying only the width of road and verandah, according to a certain scale range. After comparing the PET of monitoring points in different streets, conclusions on range of scale can be obtained, which will contribute to better microclimate in the shophouse street.

© 2016 The Authors.PublishedbyElsevierLtd. Thisis an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of the 4th IC2UHI2016 Keywords: Wet and hot climate zone; microclimate; scale; traditional shophouse street

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Available online at www.sciencedirect.com

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Procedia Engineering 169 (2016) 232 - 239

* Corresponding author. Tel.: +086-139-2604-1501; fax: +86-20-85287629. E-mail address: easefore@163.com

1877-7058 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of the 4th IC2UHI2016 doi: 10.1016/j.proeng.2016.10.028

1. Introduction

Fig. 1. The traditional shophouse street in Enning Road, Canton

The traditional shophouse is a typical vernacular architecture type widely spread in the south of China as well as southeastern Asian cities. Born and evolved with modern urbanization, the shophouse represents a unique cultural bond among these regions [1]. Usually, the shophouse is regarded to be originated from arcade, which can be found in Mid-Age European cities. The first floor of arcade is built on stilts and stretches to the main streets, thus forming the verandah. Undivided verandahs constitute the shaded pedestrian street while the second floor seems to ride over this layer. That's why shophouse is literally translated to "Qilou" in Cantonese and Mandarin. In southern China, where typical sub-tropical climate prevails, air temperature and humidity are both very high due to the rising radiation level and heavy precipitation rate. Typhoon and heavy rains are also very frequent in these areas. The Shophouse streets can not only provide comfortable walking areas for pedestrians regardless of the weather, but also create amiable business areas for those commercial shops on the first floor [2]. Therefore, the shophouse streets are well-adapted to local daily life and commercial activities.

1.1. Scale survey

2220181614-

£ 12-

g 1086420

■ -......................... .....-...............-..... -..................-...... ■ Road Verandah

.........-.....f........... -.................-.......

.........-.....1............

............■ ............. -...................-......

-.................-......

■ ............■ ............. ■ ■

• ■ 1 a

.! * ..............b........

-................ -..................- •

.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Aspect Ratio (-)

Fig. 2. The distribution of scale

The scale for shophouse streets is usually pre-determined by government regulations. However, most of the existing shophouse streets bear the slightly inconsistence with the scale requirements in the regulation. The widths of both the streets and the verandah are below the standard. According to the database (Fig. 2), the width of streets ranges from 7 m to 21 m while the buildings on both sides are usually two to four stories with the height from 7 m to 18 m. The height-width ratio thus varies from 0.7 to 1.7, with the majority falls to around 1. As for the scale of verandah, the width is usually 3 m to 6 m, since the wider, the more expensive while the narrower, the more difficult for business operation and passengers' transit. Usually, the first floor will be 4.5 m or 5 m high. So the aspect ratio for verandah varies from 0.7 to 1.3.

1.2. Overviews

In the field of urban climatology and environmental science study, the shophouse street belongs to the realm of urban street canyon [3], which firstly suggested by Sharon E Nicholson [4], in order to study the pollution within street. Through investigating the energy exchanges occurring within a street canyon, a way of energy balance were founded [5]. After that, plenty of researchers paid attention to this orientation. Especially with the development of computer-assisted technology, some simulation softwares were adopted in many studies gradually [6]. There was a serious studies conducted in Israel, which optimized microclimate in street and also improved thermal environment of pedestrian using field measurement and simulation [7-9]. Similar researches conducted in Algeria as well. With the simulation of Envi-met and assessment of microclimate, the impact of street orientation and plants on street were discussed [10,11].Recently, some researchers concentrated on urban street canyon in wet and hot zone, discussing the different contributions of orientation, plants, and aspect ratio on street canyon [12], and impact of vehicles [13]. According to these researches, the aspect ratio of street is the most significant factor of microclimate.

However, only few studies dealt directly with the microclimate of the shophouse or similar space in city. Some researchers have investigated the microclimate in arcade [14] or such semi-enclosed spaces [15] with field measurement and compared these data with those on the road, postulating that the thermal comfort in arcade is better than that without cover place. In China, the impact of orientation on shophouse street has been studied in Quanzhou with field measurement and the result pointed out that the thermal environment of North -South orientation street is better than that in West-East orientation [16]. In general, a systematic research on microclimate of shophouse streets is insufficient.

2. Method

2.1. Simulation tool and evaluation indicators

The research has adopted Envi-Met as the simulation software. Envi-Met, designed by Bruse, Fleer, et al. in University of Bochum in German back to 1998, can simulate different micro-climate and recode down the climate information at different time spots [17]. The model will be built by mesh, with the smallest one of 0.5 m.

In order to compare the result of thermal comfort environment, the Physiological Equivalent Temperature (hereafter referred as PET) is introduced in this article as an evaluation indicator to comprehensively analyse the wind speed, air temperature and relative humidity in different groups of micro-climate. PET, raised by Hoppe [18,19], is defined as the air temperature at which in a typical indoor setting (without wind and solar radiation) the heat budget of the human body is balanced with the same core and skin temperature as under the complex outdoor or indoor conditions. The premise for the PET calculation in this article is set to be a 35-year-old male with a height of 1.75 m and a weight of 75 kg. Considered that the streets are usually regarded as public space with traversal purpose, the human activity level is adjusted to normal walking speed at 1.21 m/s. Since the study is focus on hot-wet areas in the south of China, and the thermal comfort issue is relevant in summer, the clothing level for heat resistance is adjusted to 0.4 clo as short-sleeve T-shirt and trousers.

2.2. Validation

The simulation data for micro-climate can be more accurate by comparing with actual field measurement data to identify the simulation boundary condition. The field measurement was conducted in the mid-piece of Northwest Enning Road, Canton City. Enning Road is north-south orientation with a width of 10.8 m, and the verandah is 4-meter-wide. On both sides, there are 3-story-high buildings with a height of11.6 m including the parapet and pediment. Therefore, the H/W ratio is 1.09 in this case. During the field measurements, there are three successive monitoring points (Pm1, Pm2 and Pm3) on the transverse cross section --- two at the middle of the verandah on both sides (Pm1, Pm2) and one in the middle of the road (Pm3). All of these three monitoring points are placed at a height of 1.5 m, to record down the air temperature, relatively humidity, surface temperature, black ball temperature, wind speed and direction. Between the time span from 9:00 to 18:00, the data will be abstracted on an hourly basis and such data can be used to calculate the PET at each time spot.

The mesh size is settled as 0.5 m to simulate the scale of Enning Street to build the modeling in ENVI-Met. Given the length of the street is 40 m, generally the same as the tradition blocks in the adjacent areas, the spatial mesh will be 100*100*30 in the ENVI-Met for this case. Based on the weather information of the field measuring day, the simulation condition can be decided as follow (Parameters refer to Table 1).

Table 1. General conditions for the simulations

Location

Climate type

Simulation day

Simulation duration

Initial Temperature Atmosphere

Spatial resolution

Wind speed Wind direction

Specific Humidity in 2500 m Relative Humidity in 2m Initial Temperature Layer 0-20 cm, 20-50 cm, below 50 cm Relative Humidity Layer 0-20 cm, 20-50 cm, below 50 cm Heat transmission

Indoor temperature Albedo

Canton City

23°7'12.00"N 113°15'0.00"E Humid and Hot Typical summer day, 30th July From 8:00 to 20:00 (12 h) 301.95K (28.8°C)

5.0 m horizontally, 2.0 m vertically(Block) 0.5 m horizontally, 2.0 m vertically(Street) 1.5 m/s at 10 ma.g., constant Regional prevailing wind (Block) Parallel to street axis (Street) 20.62g Water/kg air 81%, constant K=301,300,301

20%, 30%, 40%

Wall: Uvalue = 1.7 W/m2K , Roof: Uvalue = 2.2 W/m2K 303K (29.85°C), constant Asphalt road = 0.1 Brick walls = 0.3 Roof = 0.15

By comparing the PET data from field measurement and software simulation, the validity of ENVI-Met can be verified. Three sample-testing points (Ps1, Ps2, Ps3) can be identified in the simulation model at the same position where field measurement data are collected. The results prove that the trend for PET is generally the same in both database, while in the simulation data, PET has a 1-2°C higher peak value and a larger variation. Notably, the rest PET data are much the same in both data base, with less than 1°C sample error. Therefore, it can be concluded that ENVI-Met is validated with simulation results that can truly reflect the real situation.

2.3. Simulation models

The paper discusses the impact from scale on thermal environment on the streets (Fig. 3). The aspect ratio is the chief influence factor regarding scale and thus, in this scale survey, the width of road (Wr) and the width of verandah (wv) would be considered as variables while the other factors are parameters. The height of the building (Hr) would be set as 15 m for 4-story-high. The height of verandah (hv) would be fixed at 5 m. The length of the road would be

40 m, referring to common practice in traditional local communities. The roads will be orientated to the south, since those S-N orientated roads are of most importance in Canton. Located around the tropic of area, the solar altitude can reach almost 90 degrees in summer. West-East orientated roads will be always under the sunshine while the north-south orientated ones enjoys the shades from trees or buildings on both sides. Such simulation boundary conditions are derived and aligned with above software validation.

2.4. Simulation experiment design

The simulation experiments are designed to observe the thermal environment under different aspect ratios. The variables will be the width of the road (Wr) and of the verandah (wv), which lead to the changes of aspect ratio. Meanwhile, the result can be measured and compared via PET evaluation. Based on previous field measurements, the width of the road (Wr) ranges from 7 m to 21 m, given that the width for each traffic lane is set as 3 m. The experiment would be conducted by two groups, with each five samples. Wr in each sample accrues by 3 m from 9 m to 21 m, while the width of verandah (wv) increased from 3 m to 7 m.

Afterwards, ENVI-Met is used to simulate the wind distribution at the height of 1.5 m. Data are collected to form the spatial and temporal variation of the PET (8:00 - 20:00) to compare PET values in different streets, as well as PET under both sides' verandah ( Pri, Pr3/Pvi,Pv3 ) and mid-point of the street (PR2/PV2) and to calculate the average value of above three points. These observation and analysis lead to the conclusion and recommended scale for the best thermal environment for the shophouse streets.

3. Result

3.1. The effect of the width of road

3.1.1. The distribution of wind

According to the simulation, the sample with Wr as 9 m (H/W=1.67), maintains a significantly worse wind environment. The wind speed is below 0.5 m/s in most areas. Meanwhile, benign wind environment can be found in roads with Wr up to 12 m. The wind distribution is also similar in those roads.

Such analysis on wind environment leads to the proposition that the colonnade in those shophouses will impede the wind adoption, thus forming a weak wind field where wind speed fluctuates around 1-1.5 m/s and radiation scope

Fig. 3. The parameters and variables in the simulation model

ranges from 3 m to 4 m. The wind speed in verandah is significantly slower than that in the middle of the road. However, in those much narrower roads (WR= 9 m), the colonnade will further prevent the wind from street canyon, and thus circumventing over the top of buildings. That's the reason why the wind speed is slower in narrow roads. In contrast, when the WR is above 12 m, there is enough space for the wind to traverse though. Furthermore, the weak wind field demolishes the room for street canyon, accelerating the wind speed in the street.

3.1.2. The PET of measuring point from 8:00 to 20:00

Q. 35-

Time (h)

A: PET of Pr1 (In west verandah)

-rn- H/W=1.67 -•- H/W=1.25 H/W=1

-»- H/W=0 83 -*- H/W=0 67

10 12 14 16 1

Time (h)

C: PET of PR3 (In east verandah)

40.0 39.5 39.0 38.5 38.0 37.5 37.0 36.5 "3 36.0 ¿35.5 W 35.0 P34.5 34.0 33.5 33.0 32.5 32.0 31.5

1 H/W=1.67 H/W=1.25 ' H/W=1 _ H/W=0.83

10 12 14 16 1

Time (h)

B: PET of Pr2 (In middle road)

H/W=1.67 H/W=1.25 H/W=1 H/W=0.83 H/W=0.67 Aspect Radio D: The Average PET of each point

Fig. 4. The PET of different measuring point (PR)

In the western side of verandah (Fig. 4), there are two peak values for PET of Pr1. In streets with aspect ratio less than 1.67, all peak value appears after 10:00 with a same value (50°C) and the tendency are nearly the same. While the narrowest street (H/W = 1.67) are obviously different with others, which highest PET appears on 13:00 about 46°C. Pertaining to the PET at the middle of the road (Pr2), the peak value appears from 13:00 to 14:00. Larger aspect ratio leads to earlier and smaller peak value except the sample with aspect ratio at 1.67, which has a constantly high PET peaking at 60.2°C. The lowest PET can always be found in the street with aspect ratio at 1.25. As for the PET at east verandah (Pr3), the peak value can be observed from 15:00 to 17:00 with the same pattern that the larger the aspect ratio is, the earlier and the lower the peak PET will be, except that one with aspect ratio at 1.67. The largest peak value is 54.8°C in the street with aspect ratio of 0.67 while the smallest PET — 47.2°C occurs to streets of ratio at 1.67 and 1.25. If comparing three observation points on the same street, PET in the middle of the street (Pr2) is always higher than those of both sides' verandah and all of them are found the lowest PET in H/W = 1.25 and the highest in H/W = 1.67.

In conclusion, in the south of China, thermal comfort will be damaged if the shophouse streets are too narrow. However, broaden streets will also enhance the PET with higher radiation level. According to the scale study, a better thermal comfort can be achieved in streets with aspect ratio at 1.25 to 1, namely road width at 12 m-15 m.

3.2. The effect of the width of verandah

3.2.1. The distribution of wind

According to the simulation, if the streets are too narrow (i.e. wv = 3 m), the wind speed will slow down proportionally. When the Wv is larger than 4m, the wind distribution become very similar with average speed rises up alongside with the width. Since colonnade in those verandahs will impede the wind adoption and slow down the wind, the wind speed deceases to less than 1m/s in shophouses and average speed is 1.5 m/s in the road with wv = 3 m. However, when the verandah width is larger than 4 m, the impact of impeding the wind will be restraint to limited areas. Wind distributions in those streets are similar, up to around 2.4 m/s. When the Wv is larger than 6m, the wind distribution in the verandah becomes the same as that in the road, with very limit weak wind field effect.

3.2.2. The PET of measuring point from 8:00 to 20:00

Time (h)

A: PET of PVi (In west verandah)

Time (h)

10 12 14 16 1!

Time (h)

B: PET of Pv2 (In middle road)

1 ! -■— h/w=1.67 —•- h/w=1.25 h/w=1 h/w=0.83 -

C: PET of PV3 (In east verandah)

H/W=1.67 H/W=1.25 H/W=1 H/W=0.83 H/W=0.67 Aspect Radio

D: The Average PET of each point

°„34

Fig. 5. The PET of different measuring point (PV)

In the west verandah (Fig. 5), both the peak PET value and the average value are lower in streets with smaller aspect ratio. The smaller the aspect value is, the earlier and smaller it comes the peak value. The highest peak value

is 53.6°C in the street with largest aspect ratio. As for the observation point in the middle of the road (Pv2), there isn't much variation in PET with peak value coming around 14:00. It's still valid here as the larger aspect ratio, the higher PET at Pv2 with the highest value at 53.6°C and the lowest at 51.4°C. It can be indicated that the aspect ratio for verandah has limited impact on PET in the road. Pertaining to the observation point in the middle of eastern verandah (Pv3), the peak values vary in its time. The data prove that an earlier and larger PET will occur in streets with bigger aspect ratio. Vice versa. The peak value of 59.3°C appears at 15:00 in the street of aspect ratio at 1.67 while in streets with aspect ratio smaller than 1, the peak value come at 16:00 at 49°C. The average PET of all observation points increases with a decreasing aspect ratio, namely a negative correlation. In the west verandah, the PET decreasing rate slows down with the increasing road width while in the east side, average PET decreases faster in the roads whose width range from 3 m to 4 m, and the decreasing rate slows down afterwards. When the road is 5m or 6m, the PET on both sides draw near and the changing rate is retarded. When the road width is larger than 5m, the impact from width on PET is demolished. In conclusion, it's considered to be good thermal environment in shophouse streets with aspect ratio smaller than 1.

4. Conclusions

According to above researches, the microclimate of traditional shophouse street will be influenced by both the width and the aspect ratio of the road and the verandah. Generally speaking, a narrower road can lead to better thermal environment, but it will deteriorate the wind environment in street when the width of road is less than 9 m. To be specific, when the height of the beside building is 15 m, the road with 12 m-to-15 m's width (or the aspect ratio at 1 to 1.25) will conduct a comfortable microclimate. Furthermore, a wider verandah will form a more comfortable microclimate. To be precise, when the height of first story is 5 m, a better microclimate will be conducted with the width of verandah more than 5 m (or the aspect ratio at less than 1). In conclusion, traditional shophouse streets in Canton are offering a comfortable microclimate for residents in urban public space.

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