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Building and Environment 44 (2009) 18–26

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The influence of wind flows on thermal comfort in the Daechung ofa traditional Korean house

Youngryel Ryua,�, Seogcheol Kimb, Dowon Leea

aDepartment of Environmental Planning, Graduate School of Environmental Studies, Seoul National University, Republic of KoreabBoolt Simulation Technology, Republic of Korea

Received 19 September 2007; received in revised form 5 January 2008; accepted 15 January 2008

Abstract

Daechung, a semi-open space with wooden floor located between the front and backyards of traditional Korean residences, is well

known as a cool space in summer due to cross-ventilation, but it has not yet been scientifically explained thoroughly. The purpose of this

paper is to characterize the wind flow measured at a Daechung to interpret the effects of the wind characteristics on thermal comfort. We

measured 10-Hz turbulence data at the Daechung and partitioned the wind vector into two directions (i.e. backyard to Daechung and

front yard to Daechung). Interestingly, the wind from the cool backyard flowing through the Daechung was of less frequency and shorter

duration but had higher velocity compared to wind from the opposite direction, which can provide thermal comfort to the dwellers. We

suggest that the wind characteristics were determined by various aspects of the house’s design, such as its location and the degree of

enclosure in front and backyards. The results show that traditional Korean house made use of a natural ventilation system during the

summer. The principles of this system could be helpful in constructing environmentally friendly and sustainable residences.

r 2008 Elsevier Ltd. All rights reserved.

Keywords: Wind flow; Natural ventilation; Thermal comfort; Traditional Korean home

1. Introduction

Daechung is a unique space generally located in themiddle of traditional Korean houses (Fig. 1). Koreaexperiences summer monsoon, so it is very hot and humidin the season (Fig. 2). To escape the heat, residents spendmost of the daytime inside during summer, unless theywork outside. In particular, people usually sit near thebackdoors with their arms on the doorsill for exposure tothe cool wind blown from the backyard. Generally, theDaechung is always open to the front yard, while back-doors are open to the backyard only in the summerdaytime (Fig. 1), thereby allowing cross-ventilation toprovide thermal comfort to dwellers. In addition, naturalconvection induces the cool air in the backyard to flow into

e front matter r 2008 Elsevier Ltd. All rights reserved.

ildenv.2008.01.007

ing author at: Department of Environmental Science,

anagement, University of California at Berkeley, 137

3114, Berkeley, CA 94720-3114, USA.

2 9048; fax: +1 510 643 5098.

ess: yryu@nature.berkeley.edu (Y. Ryu).

the Daechung through the backdoors [1–4]. The cross-ventilation system of a Daechung is well known in theacademic world, but it has not yet been characterized indepth.In this study, we analyzed naturally driven turbulence

data measured at the Daechung in a traditional Koreanhouse in order to explain the effects of turbulencecharacteristics on the thermal comfort of dwellers. Naturalventilation systems providing thermal comfort in tradi-tional dwellings have been noted in various researches[1,4–7], but thorough analyses on turbulence measurementwere rare. We characterized the turbulence at the Daechung

by separating the v-axis wind component, the orthogonalvector to the back door of Daechung, into positive (fromfront yard to backyard) and negative (from backyard tofront yard) parts. By analyzing these two wind partsindependently, we successfully characterized the turbulenceand found meaningful phenomena closely linked withthermal comfort.In this research, we conducted three steps: (1) character-

ization of turbulence measured in a Daechung, (2) analysis

ARTICLE IN PRESSY. Ryu et al. / Building and Environment 44 (2009) 18–26 19

of the factors which cause the turbulence characteristics,and (3) analysis of turbulence characteristics’ effects onthermal comfort.

2. Material and methods

2.1. Site description

The old house of Yunjeung (3611605500N, 1271705200E) islocated in Gyochon-li, Nosung-myun, Nonsan City,Chungnam Province in Republic of Korea (Fig. 3(a)).It faces a rice paddy to the south and is backed byMt. Nosung on the north (Fig. 3(b)). The backyard isenclosed by 1-m-high walls and the front yard is enclosedby the main buildings and the front gate (Fig. 3(c)). Thefront part of the Daechung is open to the front yard, and

Fig. 1. Daechung, the wooden-made main floor of traditional Korean

residences (note the three backdoors).

0

50

100

150

200

250

300

350

JanMon

Pre

cipi

tatio

n (m

m)

Precipitation

Feb Mar Apr May Jun

Fig. 2. Climate characteristics of the study site from 30-year averaged month

National Weather System (NWS) to Nonsan City.

three rectangular back doors are open to the backyard(Fig. 1). The back doors are apart each other by 1.1m andthe dimension of each back door is 1.1� 1.3m2. The maingate is open in the daytime and closed at night throughoutthe year. The surface ratio of the main gate to the frontwall of residential area is approximately one-eleventh. The30-year averaged monthly precipitation and air tempera-ture at Booyeo, the nearest National Weather System(NWS) site to Nonsan City, is presented in Fig. 2. The 30-year averaged annual precipitation and air temperature are1334mm and 12 1C, respectively.

2.2. Field measurements

Field data were collected depending on the availability ofmonitoring equipment from September 2003 to August2004: air temperature (September 2003–August 2004); windcomponents of u-, v-, and w-axis (August 2004); and windvelocity and direction (January 2004–August 2004). Themost reliable summer data (August 5–August 8, 2004) wereselected by testing data quality and analyzed for this study.Wind components (u-, v-, and w-axis) were measured by

three sonic anemometers at a frequency of 10Hz in thefront yard and backyard at a height of 1.8m (CSAT3,Campbell Sci. accuracy: 0.04m s�1), and adjacent tothe middle backdoor of the Daechung at a height of0.7m (SATI/3Sx, Applied technologies Inc. accuracy:0.03m s�1). To measure the ambient wind flow, anAutomated Weather System (AWS) (HOBO wind velo-city/direction and weather data station logger, Onset comp.accuracy: 74% of wind velocity and 751 of winddirection) was used. The AWS was set up 10m in frontof the house at a height of 1.5m, and data were loggedevery 1min. Air temperature (HOBO Temp, Onset comp.accuracy: 70.4 1C at 25 1C) was measured in the backyard,

th

-5

0

5

10

15

20

25

30

Tem

pera

ture

(°C

)

Temperature

Jul Aug Sep Oct Nov Dec

ly precipitation and air temperature taken at Booyeo, site of the nearest

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Fig. 3. (color online) Study site, the old house of Yunjeung located in Gyochon-li, Nosung-myun, Nonsan City, Chungnam Province, South Korea:

(a) location of Nonsan City, (b) topography around the house, (c) plain figure of the house (redrawn from Kim [21]), and (d) cross-sectional view

and dimension (cm) of the house (reference for cross-section is indicated in (c) by the red arrow line).

Y. Ryu et al. / Building and Environment 44 (2009) 18–2620

front yard, and at the Daechung. Data were measured every10min at a height of 1.5m, except at the Daechung, whereit was measured at a height of 0.5m. The experimentaldesign is illustrated in Fig. 4.

2.3. v-component at the Daechung

The v-component at the Daechung is the componentparallel to the floor and perpendicular to the back door. Ingeneral, it comprised at least 90% of the horizontal windvelocity (

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiu2 þ v2p

) and determined the horizontal winddirection at the backdoor of the Daechung. Therefore, wecan regard this component as the dominant wind flowthrough the Daechung. A positive v-component means thatthe wind flows from the front yard to the backyard, while anegative v-component indicates the opposite direction.Analyzing turbulence characteristics including times, dura-tion, velocity, skewness and kurtosis at the Daechung, weonly dealt with the v-component measured by a sonicanemometer at the Daechung.

2.4. Skewness and kurtosis

Skewness characterizes the degree of asymmetry of adistribution around its mean. If positive extremes dom-inate, the skewness is positive and if negative extremesdominate, the skewness is negative. If the probabilitydensity function is a Gaussian distribution, then theskewness is zero. Skewness can be written as

S ¼1

n

Xn

j¼1

xj � x

s

� �3

, (1)

where n is the number of data, s the standard deviation, xj

the raw data, and x is the mean.Kurtosis is a measure of the extent to which observations

cluster around a central point. A kurtosis is large if thetails of the probability density function are relativelylarge and small if the tails are relatively small. If theprobability density function is Gaussian, the kurtosis valueis three. So, kurtosis 43 indicates a peaked distributionand kurtosis under three shows a flat distribution. Kurtosis

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Fig. 4. Experimental design.

Fig. 5. The numbers of negative and positive v-components from 09:00 to

17:00 (August 5–8, 2004) from raw 10-Hz data.

Y. Ryu et al. / Building and Environment 44 (2009) 18–26 21

can be indicated by

S ¼1

n

Xn

j¼1

xj � x

s

� �4

. (2)

3. Results

3.1. Wind characteristics at the Daechung

3.1.1. Frequencies

The numbers of negative and positive v-componentsfrom 9:00 to 17:00 during 4 days were analyzed from 10-Hzraw data (Fig. 5). The number of the positive v-componentwas approximately twice as much as that of the negativecomponent throughout the 4 days. This indicates that thedominant wind blew from the front yard to the backyard.

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Fig. 7. (a) The wind velocities of negative and positive v-components from

09:00 to 17:00 (August 5–8, 2004) from the raw data measured over 10Hz,

and (b) time series of 10-min average wind velocity of negative and

positive v-components from 09:00 to 17:00 on August 7, 2004.

Y. Ryu et al. / Building and Environment 44 (2009) 18–2622

3.1.2. Duration

The duration of directional wind (i.e. positive or negativev-component) is shown in Fig. 6. A duration below 1 scontributed to around 60% of all durations in thepositive and negative v-components. The duration from 0to 10 s was higher for the negative v-component than forpositive v-component, while the trend was reversed fordurations over 10 s. This shows that most wind changeddirection transiently, and the direction of continuous windfor longer periods of time was mainly southerly (i.e. fromthe front yard to the Daechung).

3.1.3. Velocity

The velocities of positive and negative v-componentsranged from 0.22 to 0.28m s�1 and from 0.42 to 0.48m s�1,respectively, indicating that wind velocity of the negativev-component is twice that of the positive v-component(Fig. 7(a)). Time series of 10-min-average wind velocityrevealed that the negative v-component had both highermean wind velocity and higher fluctuation (Fig. 7(b)).Standard deviations of positive and negative v-componentvelocities were 0.05 and 0.17m s�1, respectively.

3.1.4. Skewness and kurtosis

The skewness and kurtosis of the v-component of windare shown in Table 1. Throughout the 4 days (09:00–17:00),skewness was always negative, indicating that the mode ofv-component velocity is greater than the median values.Kurtosis values were nearly higher than three, which meansthat the kurtosis of v-components was higher than is seenin a Gaussian distribution.

3.2. Wind velocity at the front yard and backyard

The 30-min-average wind velocity at the front yardand backyard is presented in Fig. 8. The figure indicatesthat the wind at the front yard was very calm, o0.5m s�1.

Fig. 6. The durations of negative and positive v-components from 09:00 to

17:00 (August 5–8, 2004) from the raw data measured over 10Hz.

Table 1

Skewness and kurtosis of v-component wind at the Daechung from 09:00

to 17:00 (August 5–8)

August 5 August 6 August 7 August 8

Sa Kb S K S K S K

Average �1.29 5.98 �1.06 3.90 �1.29 5.34 �1.23 5.23

Stdevc 0.74 4.63 0.39 1.57 0.56 2.87 0.49 1.92

Note: Skewness and kurtosis were calculated over a 10-min interval.aS ¼ skewness.bK ¼ kurtosis.cStdev ¼ standard deviation.

The average wind velocities at the front yard and backyardfrom 09:00 to 17:00 during 4 days were 0.36 and 0.62m s�1,respectively; the wind velocity of backyard was, therefore,almost twice that of front yard.

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Fig. 8. Time series of 30-min average wind velocity at the front yard and

the backyard from August 5 to 8. Some data in former 2 days were missed

due to the lack of power supply in the sonic anemometer.

Fig. 9. Time series of 30-min average air temperature in the front yard, at

the Daechung and backyard from August 5 to 8.

Fig. 10. Time series of 10-min average wind velocity and direction at 10m

in front of the house from August 5 to 8. Wind velocity of 0m s�1 data

were skulled.

Y. Ryu et al. / Building and Environment 44 (2009) 18–26 23

3.3. Air temperature in the front yard, Daechung and

backyard

The time series of air temperature at the front yard, theDaechung and backyard are shown in Fig. 9. The standarddeviations are 3.61, 1.76 and 3.47 1C, respectively. Thetemperature at the Daechung fluctuated the least, andmaintained a relatively cool temperature in the daytimeand a relatively warm temperature at night. Air tempera-ture appeared to be 1–1.5 1C higher in the front yard thanin the backyard during the daytime due to different landcovers—bare soil in the front yard while full of grass andshrubs in the backyard—and the adjacency of the backyardto the forest in mountainous area.

3.4. Wind velocity/direction at 10 m in front of the house

The diurnal patterns of wind velocity and direction at thelocal scale are given in Fig. 10. In the daytime, wind blew

from the south and southwest around 1m s�1, while anearly dead wind blew from the north at night. Thesediurnal patterns are consistent with valley wind in thedaytime and mountain wind at night [9].

4. Discussion

Traditionally, the Daechung has been used as the place toescape the hot summer in Korea [1]. Actual field dataindeed showed that the Daechung was the coolest sitecompared with the front yard and the backyard during thedaytime (Fig. 9). The main reason for this can be attributedto the roof protecting from solar radiation and providing ashaded area. In another aspect, we focused on the effects ofthe turbulence characteristics at the Daechung on thermalcomfort.As a first step, a thorough analysis of wind character-

istics at a Daechung was conducted. The field datademonstrated that positive and negative v-components ofwind at the Daechung were different in number, durationand velocity. The number of the positive component wasnearly twice as much as that of the negative component(Fig. 5) and durations over 10 s mainly occurred in thepositive component (Fig. 6). These phenomena can beascribed to the southerly wind (from the rice paddy tothe mountain) that consistently blew around 1m s�1 in thedaytime (Fig. 10). Wind velocity of the negative componentwas almost twice that of the positive component (Fig. 7(a))and showed a more fluctuating pattern compared to thepositive component (Fig. 7(b)).Skewness and kurtosis analysis of the v-components

support the characteristics of each component mentionedabove. Skewness values consistently showed negativevalues in the daytime, indicating that the probabilitydensity function is biased to the right. This means that thenumber of the positive component consistently exceeds thatof the negative component in the daytime (Fig. 5). Most ofkurtosis values of 4-day data exceeded 3.00, indicating that(1) the probability density function has a pronounced

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Fig. 11. Comparison of different time-scale average v-components at the Daechung. (a) 10-m average from August 5 to 8, (b) 1-min average during August

7, (c) 10-s average from 09:00 to 15:00, August 7 and (d) raw data measured over 10Hz from 13:00 to 13:30, August 7. Shaded area indicates the same

period from 13:00 to 13:30, August 7.

Y. Ryu et al. / Building and Environment 44 (2009) 18–2624

peaked distribution, and (2) the tails of the probabilitydensity function are large [10]. High kurtosis valuesexplain that consistent wind blew dominantly fromthe front yard to the backyard (Fig. 5), and the windvelocity of the positive component was relatively constantaround 0.3m s�1 (Fig. 7(b)). Second, the large tails in theprobability density function mean that the v-component issubject to very extreme events, influenced by strongnegative v-component winds of short number and duration(Fig. 11(d)).

The factors that caused these turbulence characteristicscan be attributed to the location and aspect of the homeand the degree of enclosure in the front yard and backyard.Constructing residences on the south-facing foot of a

mountain exposes them to naturally induced wind flows [8].In the hot summer, the tree canopies on the south face ofthe back mountain are heated more than the rice paddybecause the incident angle of solar radiation on themountain is nearly perpendicular, and the energy parti-tioning into latent heat flux is dominant in the rice paddy.So the wind blows from the rice paddy (south) to themountain (north) to achieve mass conservation in thedaytime. The naturally driven wind flow at the localscale passed through the entrance gate of the house andwould influence the turbulence at the entrance of theDaechung. Next, the degree of enclosure in the frontyard and the backyard can be considered as a factorimpacting the turbulence at the Daechung. The wind

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velocity at front yard is quite calm and less fluctuated(Fig. 8), presumably due to the enclosing buildings (3–5mheight), and these characteristics are quite similar with thepositive v-component (Fig. 7(b)). The backyard open to theenvironment with low walls (1-m height) showed higherwind velocity with more fluctuations (Fig. 8), which issimilar with negative v-component.

Thermal comfort is defined as the condition of mindwhich expresses satisfaction with the thermal environment[11], related to air temperature, humidity and wind speed[12]. We believe that the wind characteristics at theDaechung are very effective in providing thermal comfortto dwellers. Traditionally, dwellers would sit near backdoorswith their arms on the doorsill to escape the heat in summer(note the position of matting and the height of the doorsill inFig. 1. Numerical and laboratory studies have reported thatthe airflow through windows drops to and then flows alongthe floor [13,14]. This phenomenon explains why dwellersfeel the most thermal comfort sitting at that site. Further,the unique characteristics of the negative v-component—lessnumbers and short duration but strong velocity—canprovide thermal comfort to dwellers. Considering that theair temperature in the backyard is around 1 1C lower than inthe front yard in the daytime (Fig. 9), the intermittent strongcool wind from the backyard could cool the dwellers. Inaddition, the Venturi effect at the backdoors can contributeto strengthening the negative v-component. Many studieshave also reported that window opening can effectivelyregulate indoor airflow strength by the Venturi effect[15–18]. Our findings support the importance of turbulenceon thermal sensation [12,19,20].

We additionally suggest the importance of time-averagedwind velocity for considering the effect of turbulence onthermal comfort. We measured 10-Hz turbulence data andaveraged them over 10 s, 1 and 10min (Fig. 11). Note thechange in minimum wind velocity depending on the scale ofaverage time during the daytime. During the shaded period(13:00–13:30, Aug. 7), average minimum wind velocities for10 and 1min, and 10 s and raw 10-Hz data are�0.05,�0.76,�1.8 and �2.4m s�1, respectively, indicating that the windvelocity is highly sensitive to the averaging time. Withrespect to thermal comfort, we should consider how long ahuman can sense wind in any given environment.

If 1 s is the threshold to sense wind, for example,averages longer than 1 s can underestimate the effect ofturbulence on thermal comfort. These characteristicscannot be considered in the previous indices of thermalcomfort (e.g., percentage dissatisfied [19], draught index(DR) [11]). These indices use wind speed as an inputvariable, because it is related to cooling effect of the airflow on the skin. Two issues should be stressed out. First,wind speed is always higher than wind velocity due to thefact that the former is always positive and the latter hasboth signs (i.e., plus and minus. Fig. 11). As describedearlier, wind direction is an important component forthermal comfort in Daechung, so wind velocity needs to beconsidered rather than wind speed. Second, there is no

explicit reference of average time interval for analysis. Anobjectively oriented average time scale should be carefullyselected to effectively explain thermal comfort.

5. Summary and conclusions

Our main findings are as follows: (1) less frequent, shortduration but strong wind blew from the cool backyard tothe Daechung, (2) the home received naturally driven localwind and (3) the degree of enclosure in the front yard andbackyard caused different wind characteristics between twoyards, and consequently affected v-components at theDaechung. From these findings, we conclude that theintermittent strong cool wind blown from the backyardprovided the thermal comfort to the dwellers at Daechung,and a natural ventilation system for thermal comfort wasused in a traditional Korean home during the summer. Theprinciples on which this system relies could be helpful inconstructing environment-friendly, sustainable residences.Further, we pointed out the sensitivity of wind velocitymeasures to the time over which they are averaged,indicating that the selection of that time in a givenenvironment should be carefully considered for under-standing the effect of turbulence on thermal comfort.

Acknowledgments

We thank Insu Koh, Seung Kim and Youngil Kim fortheir assistance of our field experiments. We greatlyappreciate the members of ‘Research for TraditionalEcology’ about their continued participation and discus-sion on this paper. Especially, we are grateful to Drs. Jin IlYun, Dong-Hwan Sung, and Sinkyu Kang for theirconstructive advices and comments on our ideas, experi-mental skills, data processes, and manuscript. Specialthanks should go to the family of ‘the old house ofYunjeung’ for providing us with lots of accommodationduring field works. This research was supported by NCIRFand NICEM at the Seoul National University, and fundedby a Grant no. 03-03-211-39 from the Institute of KoreanStudies, Seoul National University, Republic of Korea.

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