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Building and Environment 39 (2004) 297 – 305
www.elsevier.com/locate/buildenv
Outdoor human comfort in an urban climate
Theodore Stathopoulosa;∗ , Hanqing Wub , John Zachariasc
a Centre for Building Studies, Concordia University, 1455 de Maisonneuve Boulevard West, Montreal, Que., Canada H3G 1M8
b Rowan Williams Davies & Irwin Inc., 650 Woodlawn Road West, Guelph, Ont., Canada
c Department of Geography, Planning and Environment, Concordia University, Montreal, Que., Canada H3G 1M8
Received 18 August 2000; received in revised form 4 April 2003; accepted 3 September 2003
Abstract
Outdoor human comfort in an urban climate may be a2ected by a wide range of weather and human factors. This paper describes a
research program investigating the comprehensive relationship between the comfort level of typical human activities and major weather
parameters through questionnaire surveys, 4eld measurements and statistical analyses. The study reveals the integrated e2ects of wind
speed, air temperature, relative humidity and solar radiation on the human perception, preference and overall comfort in an urban
environment. An equivalent temperature has been de4ned and related to the outdoor human comfort by considering acclimatization and
other bio-meteorological principles.
? 2003 Elsevier Ltd. All rights reserved.
Keywords: Climate; Comfort; Design; Outdoors; Pedestrian; Wind; Urban environment
1. Introduction
Outdoor human comfort in an urban climate may be
a2ected by a wide range of parameters, including wind
speed, air temperature, relative humidity, solar radiation,
air quality, human activity, clothing level, age, etc. Several criteria have been developed in the wind engineering
community for evaluating only the wind-induced mechanical forces on the human body and the resulting pedestrian
comfort and safety [1–3]. Attempts have also been made
to incorporate other outdoor weather parameters with indoor thermal comfort models for the assessment of outdoor
human sensation [4–7].
All existing criteria for wind and thermal comfort are absolute criteria, which specify the threshold values or comfort
ranges for respective weather parameters. A direct adoption
of the indoor criteria for outdoor conditions is not possible
for two reasons: Firstly, under most circumstances, the experienced outdoor conditions lie outside the so-called indoor
comfort zone. Secondly, there exists a consensus among acclimatized residents on local weather conditions that vary
seasonally. Thus, shared expectations of seasonable weather
∗ Corresponding author. Tel.: +1-514-848-2424x3186; fax: +1-514848-7965.
E-mail address: [email protected] (T. Stathopoulos).
0360-1323/$ - see front matter ? 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.buildenv.2003.09.001
conditions among local residents may condition the physiological response to weather.
Di2erent approaches and criteria are necessary for the
evaluation of human subjective response and behavior as a
function of outdoor climatic conditions. The current project
aims at the establishment of comprehensive relationships
between the comfort level for human activities and major
weather parameters in the urban environment. This has been
achieved through a survey of human subjective responses,
4eld measurement of weather parameters and further statistical analyses based on human bio-meteorological principles.
The results from questionnaire surveys and physical measurements are discussed in this paper, concentrating on the
e2ects of four weather parameters (wind speed, air temperature, solar radiation and relative humidity) on human
perception, preference and the overall outdoor comfort. Another important part of the project, which dealt with the human behavior a2ected by the outdoor microclimate in public
space, has been presented elsewhere [8].
2. Field data collection
The 4eld data collection included simultaneous questionnaire surveys on human response and physical measurements of major weather parameters. This was carried out at
298
T. Stathopoulos et al. / Building and Environment 39 (2004) 297 – 305
Please circle one number to indicate the level at which you agree or disagree with the
following statements regarding the present weather conditions at this place.
Considering the time & season
Disagree
Uncertain
Agree
the wind force is strong.
-2
-1
0
1
2
the air temperature is high.
-2
-1
0
1
2
the air is humid.
-2
-1
0
1
2
the solar radiation is warm.
-2
-1
0
1
2
Overall, the weather conditions
Disagree
are acceptable for your activity.
-2
Considering your activity and
clothing, it would be (more)
comfortable, should
Lower
Uncertain
-1
0
Agree
1
Unchanged
2
Higher
the wind force be
-2
-1
0
1
2
the air temperature be
-2
-1
0
1
2
the humidity be
-2
-1
0
1
2
the solar radiation be
-2
-1
0
1
2
Lower
Unchanged
Higher
Fig. 1. First part of the questionnaire for outdoor comfort survey.
seven public open spaces in downtown Montreal under different weather conditions.
Fig. 1 shows the 4rst part of the questionnaire, developed
through a series of pilot investigations at the early stage of
this study. There are three question boxes for
tion on a horizontal surface was detected by a pyranometer.
Its reading was a2ected by the season, cloudiness as well
as shade from surrounding buildings and trees. Unlike wind
speed, the last three parameters remained relatively stable
during the short period of interview.
(1) the perception of individual weather parameters,
(2) the overall comfort (or acceptability), and
(3) the preference for better conditions.
3. Questionnaire correlations
The questionnaire was designed using plain, concise language and a 4ve-point scale was employed for the purpose
of simplicity. Other parts of the questionnaire collected information regarding the human behavior in and opinions on
public spaces, noise and pollution levels, gender, age, clothing and activity of interviewees, which is not discussed in
this paper.
The four major weather parameters were recorded near
interviewee(s) while an interview was taking place. Special
caution was taken to ensure accurate and representative measurements. Using a vane anemometer at 2 m above grade,
wind speeds were measured three times during the period of
an interview with the highest reading recorded as the gust
wind speed, which varied with the measurement location
and time. An outdoor sensor for air temperature and relative
humidity was held at a height about 0.5 –1 m. The sensor
was wrapped with a protective sheet and was not placed in
any direct sunlight during the measurement. The solar radia-
A total of 466 sets of valid records were obtained from
downtown Montreal on 34 days. Data were collected primarily at noontime, when a high concentration of people
could be found in downtown public spaces. The majority
of data came from spring and fall when the air temperature was moderate so that the e2ects of other parameters
might become more evident. Correlations for these data are
discussed in this section. The statistical signi4cance of the
correlations has been provided elsewhere [8].
Fig. 2 shows the distributions of survey responses to the
wind force and the overall comfort. Using these data, perception of and preference for the wind force can be related
to overall comfort. In each diagram, the horizontal axes are
comprised of two responses to the three question boxes, i.e.
the perception (strong wind?), the overall comfort, and the
preference (stronger wind desired?) with “+2 and +1” for
agree, “0” for uncertain, and “−2 and −1” for disagree. The
vertical axis indicates always the number of responses received.
T. Stathopoulos et al. / Building and Environment 39 (2004) 297 – 305
140
100
120
80
299
100
80
Number of
Responses
60
2
0
20
0
2
(a)
0 -1
Strong Wind
2
-2
Overall
Comfort
-2
1
0
-1 -2
High Temperature
(a)
120
Number of
Responses
2
1
0
-1
-2
1
0
-1
Stronger Wind
Desired
Overall
Comfort
60
100
50
80
40
Number of
30
Responses
20
2
0
20
-1
0
-2
1
0
-1
Strong Wind
-2
2
1
0
-1
0
2
(c)
Overall
Comfort
-2
10
Stronger
Wind Desired
-2
0
-1
2 1
0 -1
Higher Temperature
Desired
120
1
2
1
0
(b)
60
80
40
-2
40
(c)
0
160
2
2
0
-1
-2
1
160
140
120
100
Number of
80
Responses
60
40
20
0
Number of
Responses
1
20
Overall
Comfort
-1
2
40
1
40
(b)
60
Number of
Responses
-2
1
0 -1
-2
High Temperature
Higher
Temperature
Desired
Fig. 2. Distribution of responses to questions on wind force and overall
comfort.
Fig. 3. Distribution of responses to questions on air temperature and
overall comfort.
It is noted in Fig. 2 that (a) among a total of 273 responses
with overall comfort=2, 186, or 68%, felt that the wind force
was not strong (strong wind=−2 or −1). In contrast, among
41 responses with overall comfort = −2, 25 responses, or
61%, felt that the wind force was strong (strong wind = 2
or 1); (b) a small portion of people (35 out of 466, or 7.5%)
wanted the wind to be stronger (stronger wind desired = 2
or 1); and (c) weak wind forces were preferred in general (stronger wind desired = −2 or −1), especially for
people who felt the present wind forces were too strong
(strong wind = 2 or 1).
Using a similar format, Fig. 3 presents the air temperature
and overall comfort data, demonstrating a clear preference
for higher temperatures by people in Montreal. Note that out
of 41 responses with overall comfort = −2, (a) 31, or 76%,
felt the air temperature was too low (high temperature =
−2); and (b) 34, or 83%, thought the air temperature should
be higher (higher temperature desired = 2 or 1). Overall,
only 23 out of 466 answers, or 5%, suggested that the air
temperature should be lower (higher temperature desired =
−2 or −1).
Higher solar radiation and lower relative humidity were
also desired. This tendency can be corroborated with the
cross-correlation coeNcients between responses for all four
weather parameters, as listed in Table 1.
Among these four parameters, the air temperature played
an important role in determining the overall comfort, as
demonstrated by the highest cross-correlation coeNcient
300
T. Stathopoulos et al. / Building and Environment 39 (2004) 297 – 305
Table 1
Cross-correlation coeNcients between responses to perception (x), overall
comfort (y) and preference (z)
Wind force
Air temperature
Relative humidity
Solar radiation
Rxy
Ryz
Rzx
−0.23
0.29
−0.19
0.20
0.26
−0.28
0.05
−0.18
−0.38
−0.20
−0.37
−0.34
60
50
40
Number of
30
Responses
20
2
1
0
10
-1
0
2
between responses to the perception and the overall comfort
(Rxy ). The wind force and relative humidity were found
to have negative impacts on the overall human comfort in
most cases (Rxy ¡ 0). The sign of Ryz is always opposite
to that of the respective Rxy due to the opposite inclination
of perception and preference when dealing with the overall
comfort.
Values of Rzx are all negative, indicating that if x is low
(high), then z is preferred to be higher (lower). It was
less likely that in Montreal the relative humidity would
be blamed for discomfort, or credited for comfort, as
shown by the lowest values of Rxy and Ryz among the four
parameters. The Rzx value for air temperature is clearly
lower than that for other factors, that is again caused by
the demand for higher air temperatures, i.e. “although the
temperature is high (positive x), I would prefer an even
higher temperature (positive z)”.
Although much lower than unity for a perfect correlation,
these coeNcients are comparable with, or higher than, typical survey statistics for human comfort [9–11]. Considering
the diverse settings and other uncertainties associated with
the outdoor survey using questionnaires, it is felt that the
results obtained from this study are reliable and indicative.
To reveal the integrated impact of these weather parameters on human comfort, conditional response distributions
were also examined. For instance, Fig. 4 shows the distributions of responses to the wind force and overall comfort
questions only from those who considered the air temperature was not high (high temperature = −2 or −1). As a
result, the sample size dropped from 466 to 220. Although
the distribution patterns in Figs. 2 and 4 seem very similar,
some noticeable changes do exist. The number of people responding with overall comfort = −2 changed from 41 (9%)
in Fig. 2 for all air temperatures to 34 (15%) in Fig. 4 for
low temperatures. The number of people asking for stronger
winds (stronger wind desired = 2 or 1) dropped from 35
(8%) in Fig. 2 to 11 (5%) in Fig. 4. The e2ect of air temperature on people’s perception of and preference for the wind
force is evident.
In addition, under the low-temperature conditions, the
three cross-correlation coeNcients for the wind force in
Table 1 became −0:28, 0.34 and −0:33, respectively. The
4rst two values increased in magnitude, when compared with
the numbers for all temperatures in Table 1, due to an increased sensitivity to wind forces under cold conditions. The
(a)
Overall
Comfort
-2
1
0
-1
Strong Wind
-2
60
50
40
Number of
30
Responses
20
2
1
0
10
-1
0
2
-2
1
0
-1
Stronger Wind
Desired
(b)
Overall
Comfort
-2
50
40
30
Number of
Responses 20
2
1
0
10
-1
0
2
(c)
-2
1
0 -1
Strong Wind
Stronger
Wind Desired
-2
Fig. 4. Distribution of responses to questions on wind force and overall
comfort when air temperature was felt low.
last one (Rzx ), on the other hand, became lower since a higher
percentage of people asked for lower winds (negative z)
even though wind forces were already low (negative x).
Fig. 5 shows the distribution of responses to the wind force
and overall comfort questions only from those who felt the
air temperature was high (high temperature = 2 or 1). For
this set of samples, the three cross-correlation coeNcients
for the wind force in Table 1 became −0:13, 0.04 and −0:40.
Values of the 4rst two numbers are signi4cantly lower than
those in previous cases, indicating lesser importance of wind
forces for overall comfort under warm weather conditions.
The cross-correlation coeNcients for these three temperature
cases are summarized in Table 2 for comparison purposes.
T. Stathopoulos et al. / Building and Environment 39 (2004) 297 – 305
tions were carried out for other pairs of weather parameters.
These relationships, together with further statistical analyses such as those reported in [8], demonstrate the statistical
signi4cance of the 4eld data, and are substantial elements
of the database for the development of outdoor comfort
criteria.
70
60
50
Number of 40
Responses 30
2
1
20
0
10
-1
0
2
(a)
Overall
Comfort
-2
1
0
-1
Strong Wind
4.1. Air temperature
Three air temperatures were used in the analysis of the
relation between air temperature and human perception and
preference:
80
60
2
40
1
0
20
-1
0
2
-2
1
0
-1
Stronger Wind
Desired
(b)
Overall
Comfort
-2
60
50
40
Number of
30
Responses
20
2
1
0
10
-1
0
2
(c)
-2
1
0 -1
Strong Wind
Stronger
Wind Desired
-2
Fig. 5. Distribution of responses to questions on wind force and overall
comfort when air temperature was felt high.
Table 2
Cross-correlation coeNcients between responses to wind perception (x),
overall comfort (y) and wind preference (z) for all, cool and warm
temperatures
All temperature
Cool temperature
Warm temperature
4. Physical measurements
This section discusses physical measurements in association with the questionnaire responses, starting with air
temperature.
-2
100
Number of
Responses
301
Rxy
Ryz
Rzx
−0.23
−0.28
−0.13
0.26
0.34
0.04
−0.38
−0.33
−0.40
These comparisons indicate that wind force and air
temperature are dependent parameters and should be treated
together in determining the overall comfort. Similar calcula-
Ta : on-site measurements during questionnaire survey
Tn : daily maximum, derived from the monthly norm of
long-term records at the Dorval International Airport
in Montreal; and
Tf : forecast daily high temperature, taken from a local
newspaper on the morning of 4eld survey.
It is assumed that people’s perception of and preference for
the air temperature can be related to the absolute values of
these temperatures as well as deviations of the measured
temperature from the seasonal norm and/or the weather forecast. Table 3 lists the cross-correlation coeNcients between
various air temperatures (t) and the perception (x) and the
preference (z) based on all individual records and daily averages. The calculation of daily average and its applications
will be explained later in this section.
Note that 22:5◦ C is the so-called universal indoor comfort
temperature with other conditions assumed to be moderate.
Ta and Ta − 22:5 should have the same correlation with x
or z. The weather norm based on long-term meteorological
records (Tn ) reQects the experience and expectation of acclimatized residents and could be used as another reference
value. It is also expected that residents, who have access to
a weather forecast will adjust their clothing and activities
according to the forecast temperature (Tf ). However, unawareness and errors in forecasting may reduce such a correlation. The daily high temperature was used in the analysis, since our survey was taken around noon when the air
temperature typically reaches its daily maximum.
When all 466 records were calculated individually, the
cross-correlation coeNcients were found to be generally low.
The highest Rtx was obtained with t = Ta − Tn . The temperature norm (Tn ) represents the common expectation of acclimatized residents whose perception of the air temperature
depends primarily upon the di2erence between the actual
temperature and such a norm. Unlike the indoor situation,
302
T. Stathopoulos et al. / Building and Environment 39 (2004) 297 – 305
Table 3
Cross-correlation between temperatures (t) and perception (x) and preference (z) for air temperatures
Daily average
Rtx
Rtz
Rtx
Rtz
0.23
0.02
0.14
0.31
0.22
−0.30
−0.18
−0.25
−0.20
−0.17
0.51
0.18
0.36
0.58
0.42
−0.78
−0.58
−0.71
−0.46
−0.40
people’s perception of air temperature is not solely based on
the absolute value Ta or its di2erence from 22:5◦ C, which
had a lower correlation coeNcient, but similar to that for
Ta − Tf .
On the other hand, the highest cross-correlation coeNcient between the air temperature and the preference (Rtz )
was obtained by the absolute value of air temperature Ta or
Ta −22:5. There is a clear di2erence between perception and
preference; the latter reQects the desire for an ideal condition by local residents. For example, 10◦ C in January might
be perceived by people in Montreal as a high air temperature compared to the temperature norm, but an even higher
temperature would be preferred for more comfortable conditions.
As mentioned previously, the 466 sets of records were
collected over 34 days. To reduce the uncertainty with the
individual records, daily averages of all questionnaire responses and physical measurements were calculated. Then
higher cross-correlation coeNcients were obtained, as shown
in Table 3. In the column of daily average in Table 3, the
highest correlation was also obtained by Ta − Tn for Rtx , and
by Ta for Rtz . The cross-correlation coeNcients increased to
0.58 and −0:78, respectively.
These increases assist in the presentation for the relations
between air temperatures and human perception/preference,
as shown in Fig. 6. Note that in Fig. 6(a), the daily averaged
perception could be directly related to the daily averaged
temperature di2erence (Ta −Tn ), but the regression line does
not go through the point (0; 0). In fact, when perception = 0,
Ta − Tn is at about 3:4◦ C. This may be caused by the
di2erences in temperature measurements. The temperature
norm (Tn ) was recorded at a weather station in the Dorval
Airport, about 20 km from Montreal downtown, while the
on-site temperature (Ta ) might be raised by the heat generated and/or reQected by the immediate surroundings in an
urban environment. More importantly, this may be related
to the preference of local residents for higher temperatures.
In Fig. 6(b), there is no record for preference ¡ 0 based
on the daily averages. The rationale behind this is believed
to be the generally cold climate in Montreal. If the same
questionnaire were to be applied to hot areas such as Las
Vegas and Hong Kong, the preference between −2 to 0
would likely be obtained. As a result, the regression line of
preference would be moved vertically down in Fig. 6(b).
2
Perception (x)
Ta or Ta − 22:5
Tn
Tf
Ta − Tn
Ta − Tf
Individual records
1
0
x = 0.1(Ta - Tn) - 0.5
R = 0.58
-1
-2
-5
0
5
10
15
Ta-Tn (ooC)
(a)
2
Preference (z)
Temperature t (◦ C)
1
0
z = - 0.05Ta + 1.7
R = - 0.78
-1
-2
0
(b)
5
10
15
Ta (oC)
20
25
30
Fig. 6. Dependence of (a) perception on Ta − Tn and (b) preference on
Ta , based on daily averages.
4.2. Wind, humidity and solar radiation
A similar approach can be applied to other weather
parameters such as wind speed, relative humidity and solar
radiation. Figs. 7 and 8 show the perception and preference
for the daily averaged data of wind speed, relative humidity
and solar radiation.
In general, perceptions reQected the actual conditions
of the wind speed, relative humidity and solar radiation
as shown in Fig. 7, although the survey data were found
to be widely dispersed. The averaged gust wind speed encountered was below 4 m=s. Around or above such a value,
the wind force would be perceived as strong due to the
mechanical e2ect alone. When the wind speed was lower
than 2 m=s, the wind force would more likely be perceived
as not strong or uncertain. The relative humidity and solar
radiation covered relatively large ranges. The perception
of solar radiation was more accurate than that of other climate factors. People in Montreal would generally regard a
2
2
1
1
Preference
Perception
T. Stathopoulos et al. / Building and Environment 39 (2004) 297 – 305
0
-2
-2
0
1
2
3
4
0
1
(a)
Wind Speed (m/s)
2
1
1
0
-1
-2
2
3
4
60
80
Wind Speed (m/s)
2
Preference
Perception
(a)
0
-1
-2
0
20
(b)
40
60
80
0
20
(b)
Relative Humidity (%)
2
1
1
0
-1
40
Relative Humidity (%)
2
Preference
Perception
0
-1
-1
0
-1
-2
-2
0
(c)
303
200
400
600
800
0
1000
Solar Radiation (W/m2 )
Fig. 7. Relations of physical measurements with preference, based on
daily averages.
solar heat below 200 W=m2 as low and above 500 W=m2
as high.
Similar to that for air temperature, preferences for wind
speed, relative humidity and solar radiation were also
biased (Fig. 8), as shown by the daily average data. Very
few people preferred a higher wind speed, a higher relative
humidity or a lower solar radiation, regardless of the actual weather conditions. However, preference could still be
correlated with the weather readings, as shown in Fig. 8.
For instance, highest preference for solar radiation occurred
when the actual solar radiation is at the lowest. Again, these
preferences reQected the general demand for ideal weather
conditions by the acclimatized residents, and they are likely
to vary with climatic conditions.
It should be kept in mind that all physical parameters
are interrelated when the perception, preference and overall
comfort are considered. Therefore, correlations between
physical conditions and human responses as shown in
Figs. 6–8 are signi4cant.
(c)
200
400
600
800
1000
Solar Radiation (W/m2)
Fig. 8. Relations of physical measurements with perception, based on
daily averages.
5. Towards an overall comfort index
The main objective of this research program was to
develop a climatic index and a relative comfort criterion,
accounting for the combined thermal and mechanical impact, residents’ acclimatization and subjective perception in
the urban environment. Acclimatization includes not only
adaptation to the local climate through changes in activities and clothing, but also increased tolerance to climatic
extremes. As discussed previously, air temperature is the
dominant factor while others may also contribute to the
overall comfort. A straightforward approach would be to
add the wind speed, relative humidity and solar radiation
into the two-node transient energy balance model [6]. However, the indoor comfort criteria may not be appropriate
for outdoor conditions due to acclimatization and di2erent
environmental factors.
Multiple regression was considered for the overall
comfort against all four weather elements. Mathematical
T. Stathopoulos et al. / Building and Environment 39 (2004) 297 – 305
functions for the regression, that typically are not linear,
however, must be pre-determined to reQect the interactive
nature of the subject under investigation. The sample size
and climate range of the current data are other limits to a
straight multiple regression approach.
The present approach attempts a provisional expression of
an overall index by combining the energy balance concept
with human responses from the survey. The criteria to be
established are relative to local climate, or to the expectation
of local residents. An equivalent temperature (Te ) is de4ned
as an index integrating the e2ects of wind speed (Sw ), air
temperature (Ta ), relative humidity (RH) and solar radiation
(Rs ) on human outdoor comfort.
Wind Qow brings heat away from human body by heat
convection. Most expressions in [12] suggest that the convective heat transfer coeNcient is proportional to a power
function of Sw . Solar radiation does the opposite; the radiant
heat Qux can be directly related to the di2erence between the
mean radiant temperature and the air temperature. Assuming
a linear relationship between subjective response and temperature, the temperature felt by the human body becomes
t = Ta − c1 Sw + c2 Rs :
(1)
The e2ect of relative humidity is more complex. For the
indoor comfort, the e2ective temperature (ET∗ ) is used to
combine the humidity and temperature [12]. Two environments with the same ET∗ should evoke the same thermal
response. For low temperatures, the e2ect of humidity becomes insigni4cant. Again, the calculation is very tedious
and diNcult. A simple regression was carried out for the
charts for the e2ective temperature in [12] for typical outdoor conditions, yielding a modi4cation function of the type
1 + 0:03e0:07Ta (RH − 50%):
The modi4cation function equals to one when the relative
humidity RH = 50%. Relative humidity has a more signi4cant impact on comfort perception when the air temperature
(Ta ) is high, as indicated by the exponential function. The
4nal equation of the equivalent temperature can then be expressed by applying this modi4cation function on Eq. (1):
Te = (Ta − c1 Sw + c2 Rs )
×[1 + 0:03e0:07Ta (RH − 50%)]:
(2)
Two equivalent temperatures have to be calculated; one
based on the weather norm (Te; n ), and the other based on
the actual outdoor conditions (Te; a ). Di2erences in the air
temperature and relative humidity may exist between the
two locations where data were recorded. The norm for urban wind speed at ground level, say 2 m above grade, can
be estimated by using the power laws for typical open and
urban terrain and the wind data from a nearby airport, measured normally at a height of 10 m. The actual wind speed
around buildings in a public space can only be determined
by wind-tunnel or full-scale testing. The solar radiation can
be calculated from the local data of solar time, solar angle
2.0
Overall Comfort
304
1.5
1.0
0.5
0.0
-15
-10
-5
0
5
10
15
Te,a - Te,n
Fig. 9. Example of the overall comfort a2ected by the di2erence of
e2ective temperatures, based on daily averages.
and cloudiness at an open location for Te; n and based on
the geometry and orientation of surrounding buildings and
structures at the place of interest for Te; a .
More studies should be carried out in di2erent climates
with various human activities, clothing and local settings
in order to establish a comprehensive relationship between
the urban climatic conditions and human sensation and to,
eventually, establish a criterion for human outdoor comfort.
It is worth mentioning that a working group of the International Society of Biometeorology is currently developing
a new standardized universal thermal climate index (UTCI),
which can also be used in the establishment of a criterion
for human outdoor comfort [13].
An example of application of the above-discussed approach is shown in Fig. 9. The dependence of the overall
comfort is expressed by the survey respondents on the proposed equivalent temperature di2erence, based on the daily
average data. It should be noted that (Te; a − Te; n ) is the
most inQuential factor on the overall comfort of the respondents. The constants in Eqs. (1) and (2) are c1 = 4, = 0:5,
and c2 = 0:028, based on a regression of data in [6]. It is
interesting to note that on all 34 survey days the daily averaged overall comfort was always above zero. This is due
to the following facts: (1) more responses were received
under comfortable conditions; (2) it is likely that surveys
took place only on days with weather conditions feasible, or
comfortable, for the interviewers; and (3) residents were
capable of adjusting their clothing and activity levels according to the outdoor conditions in order to make themselves
comfortable.
Notwithstanding the above comments, it is still considered premature to draw a curve for a de4nite mathematical
relationship of overall comfort and equivalent temperature
di2erence. However, it can be observed from Fig. 9 that (1)
most comfortable conditions occur when the equivalent temperature di2erence is about 5◦ C, which may be attributed
to the preference of local residents for higher air temperature as well as the temperature di2erence between Montreal
downtown and the Airport; (2) lower comfort occurs with a
negative temperature di2erence, or when the actual equivalent temperature is lower than the norm; and (3) if the
temperature di2erence is beyond a certain limit, say greater
T. Stathopoulos et al. / Building and Environment 39 (2004) 297 – 305
than 10◦ C, less comfortable (overall comfort ¡ 1) outdoor
conditions may be perceived, although more 4eld data are
needed to con4rm this observation.
6. Concluding remarks
The paper presents results of a research project pioneering the development of relative criteria for human outdoor
comfort based on 4eld survey and physical measurements.
The e2ects of wind speed, air temperature, relative humidity and solar radiation on human perception and preference
for outdoor conditions along with evaluation of overall comfort have been considered. On these grounds, an equivalent
temperature has been de4ned and related to the overall outdoor comfort. Using the approach developed in this study,
it is possible to establish a new criterion for outdoor human
comfort at least for weather conditions similar to those in
Montreal. Naturally, more data for a wider range of weather
conditions and from di2erent climates are needed in order
to generalize the new outdoor human comfort criteria.
Acknowledgements
The authors would like to thank the students from the
Centre for Building Studies and Urban Studies of Concordia University for their assistance in data collection. The
4nancial support provided by the Seagram Fund for Academic Innovation at Concordia University is also gratefully
acknowledged. In addition, the reviewers’ comments were
valuable to the authors.
305
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