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Daytime relapse of the mean radiant temperature based on the six-directional method under unobstructed solar radiation

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This study contributes to the knowledge about the capabilities of the popular “six-directional method” describing the radiation fields outdoors. In Taiwan, measurements were carried out with three orthogonally placed net radiometers to determine the mean radiant temperature (T mrt). The short- and long-wave radiation flux densities from the six perpendicular directions were recorded in the daylight hours of 12 days. During unobstructed direct irradiation, a specific daytime relapse was found in the temporal course of the T mrt values referring to the reference shapes of a standing man and also of a sphere. This relapse can be related to the short-wave fluxes reaching the body from the lateral directions. Through deeper analysis, an instrumental shortcoming of the six-directional technique was discovered. The pyranometer pairs of the same net radiometer have a 10–15-min long “blind spot” when the sun beams are nearly perpendicular to them. The blind-spot period is supposed to be shorter with steeper solar azimuth curve on the daylight period. This means that the locations with lower geographical latitude, and the summertime measurements, are affected less by this instrumental problem. A methodological shortcoming of the six-directional technique was also demonstrated. Namely, the sum of the short-wave flux densities from the lateral directions is sensitive to the orientation of the radiometers, and therefore by deviating from the original directions, the T mrt decrease on clear sunny days will occur in different times and will be different in extent.
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ORIGINAL PAPER
Daytime relapse of the mean radiant temperature
based on the six-directional method under unobstructed
solar radiation
Noémi Kántor &Tzu-Ping Lin &Andreas Matzarakis
Received: 7 August 2013 /Revised: 6 November 2013/ Accepted: 7 November 2013 /Published online: 27 November 2013
#ISB 2013
Abstract This study contributes to the knowledge about the
capabilities of the popular six-directional methoddescribing
the radiation fields outdoors. In Taiwan, measurements were
carried out with three orthogonally placed net radiometers to
determine the mean radiant temperature (T
mrt
). The short- and
long-wave radiation flux densities from the six perpendicular
directions were recorded in the daylight hours of 12 days.
During unobstructed direct irradiation, a specific daytime re-
lapse was found in the temporal course of the T
mrt
values
referring to the reference shapes of a standing man and also
of a sphere. This relapse can be related to the short-wave fluxes
reaching the body from the lateral directions. Through deeper
analysis, an instrumental shortcoming of the six-directional
technique was discovered. The pyranometer pairs of the same
net radiometer have a 1015-min long blind spotwhen the
sun beams are nearly perpendicular to them. The blind-spot
period is supposed to be shorter with steeper solar azimuth
curve onthe daylight period. This means that the locations with
lower geographical latitude, and the summertime measure-
ments, are affected less by this instrumental problem. A
methodological shortcoming of the six-directional technique
was also demonstrated. Namely, the sum of the short-wave
flux densities from the lateral directions is sensitive to the
orientation of the radiometers, and therefore by deviating from
the original directions, the T
mrt
decrease on clear sunny days
will occur in different times and will be different in extent.
Keywords Mean radiant temperature .Six-directional
technique .Clear sky .Daytime relapse .Lateral directions
Introduction
The mean radiant temperature (T
mrt
) combines the thermal
effect of all short- and long-wave radiation fluxes reaching
the body into one, temperature-unit value (Fanger 1972;VDI
1998). It is defined as the uniform temperature of an imaginary
black-radiant enclosure in which the body would exchange the
same energy via radiation as in the real nonuniform environ-
ment (ASHRAE 2001). In indoor conditions, without greater
radiation asymmetry, its value is close to the air temperature
(VDI 1998). In outdoors, however, the radiation environment
around the body may be complex, and the value of T
mrt
may be
much higher than the air temperature, even up to 30 °C, as
shown by studies conducted in Germany (Mayer and Höppe
1987;Ali-Toudert and Mayer 2007;Matzarakis et al. 1999,
2007,2010), Algeria (Ali-Toudert et al. 2005;Ali-Toudert
2005;Ali-Toudert and Mayer 2006), Hungary (Gulyás et al.
2006), Sri Lanka (Johansson and Emmanuel 2006), Sweden
(Thorsson et al. 2007), and Greece (Shashua-Bar et al. 2012).
In urban areas, very different radiation conditions, and
therefore, very different T
mrt
values may be developed in the
vicinity of each other due to the different shading conditions
(Mayer and Höppe 1987; Gulyás et al. 2006;Lee et al. 2013).
Several researchers have already pointed out that daytime, in
clear sky conditions, the T
mrt
is the primary factor that governs
the course of human-biometeorological indices like
Electronic supplementary material The online version of this article
(doi:10.1007/s00484-013-0765-5) contains supplementary material,
which is available to authorized users.
N. Kántor (*)
Program of Landscape and Recreation, Research Center for the
Humanities and Social Sciences, National Chung Hsing University,
250 Guoguang Road, South Dist, Taichung City 40227, Taiwan,
Republic of China
e-mail: sztyepp@gmail.com
T.<P. Lin
Department of Architecture, National Cheng Kung University, 1
University Road, Tainan 701, Taiwan, Republic of China
e-mail: lin678@gmail.com
A. Matzarakis
Chair of Meteorology and Climatology, Alberts-Ludwigs-University
Freiburg, Hebel Str. 27, D-79104 Freiburg, Germany
e-mail: andreas.matzarakis@meteo.uni-freiburg.de
Int J Biometeorol (2014) 58:16151625
DOI 10.1007/s00484-013-0765-5
physiologically equivalent temperature (Höppe 1999), and
this is the main parameter that results in heat stress on sunny
summer days (Jendritzky and Nübler 1981;Mayer and Höppe
1987;Mayer 1993;Gulyás et al. 2006;Ali-Toudert and
Mayer 2007;Mayer et al. 2008;Holst and Mayer 2010;
Shashua-Bar et al. 2012;Lee et al. 2013).
To calculate T
mrt
accurately, one needs to determine all the
radiation flux densities reaching the body and also the angular
factors of the surrounding radiation surfaces (Fanger 1972).
This task would require too much time and energy in such
complex environments like the urban areas (Höppe 1992;
VDI 1998). Therefore, the researchers either simulate the
radiation conditions by numerical models, like ENVI-met
(Bruse and Fleer 1998), RayMan (Matzarakis et al. 2007,
2010), and SOLWEIG (Lindberg et al. 2008;Lindberg and
Grimmond 2011), or apply field-measurement techniques
with some assumptions and simplifications. The most popular
measurement methods are the six-directional technique sug-
gested by the VDI 3787 (VDI 1998) and the globe thermom-
eter technique described in the ISO 7726 (ISO 1985,1998).
Up today, the six-directional technique, introduced by
Höppe (1992), is considered the most accurate measurement
to obtain outdoor T
mrt
values. Instead of measuring the indi-
vidual radiation flux densities and determining the countless
corresponding angular factors to them, this method simplifies
the surrounding environment into six perpendicular parts: four
lateral directions and the upper- and lower-hemisphere. It
measures the radiation fluxes only from this six directions
and orders simple angular factors to them. The most reliable
way to get the necessary short- and long-wave fluxes is to
measure them simultaneously from the six directions; howev-
er, this requires the usage of six parano- and six pyrgeometers,
or three net radiometers (Ali-Toudert 2005;Ali-Toudert et al.
2005;Ali-Toudert and Mayer 2007;Thorsson et al. 2007),
which makes the measurements very expensive and rather
immobile. Other researchers apply only one rotatable net
radiometer (Streiling and Matzarakis 2003;Kántor et al.
2012a,b) or a rotatable pyranopyrgeometer pair (Höppe
1992;Oliveira and Andrade 2007;Andrade et al. 2011).
Because of the lighter instrumentation, the rotatable version
allows mobile measurements; however, it serves with coarser
temporal resolution of T
mrt
. In frame of the KLIMES project,
researchers used both the three net radiometer version, and
took mobile recordings with a measurement cart equipped
with a rotatable pyranopyrgeometer combination (Holst
and Mayer 2010,2011;Lee et al. 2013).
The six-directional method served also as an essential part
of on-site thermal comfort measurements, which were com-
pared to subjective thermal comfort assessments of visitors on
selected urban public places (Oliveira and Andrade 2007;
Andrade et al. 2011;Kántor et al. 2012a,b). The separate
measurement of the short- and long-wave fluxes make it
possible to take different absorption coefficients into account
in the short- and long-wave domain, similar to the clothed
human body. In addition, because of the directional weighting
factors, this technique allows to represent the shape and pos-
ture of the human body. Therefore, this method is treated as
the most accurate one in the field of outdoor thermal comfort
measurements (Höppe 1992;Thorsson et al. 2007).
In contrast to the models, which work with many assump-
tions, the major advantage of measurements is that they reflect
the actual thermal conditions. Therefore, six-directional field
measurements are often used to validate the results of numer-
ical simulations. For example, T
mrt
values from the RayMan
model have been compared to those derived from six-
directional measurements in Germany (Matzarakis et al.
2007,2010), Sweden (Thorsson et al. 2007), and Portugal
(Andrade and Alcoforado 2008), and the ENVI-met has been
also validated via on-site measurements in Germany (Ali-
Toudert 2005;Ali-Toudert and Mayer 2007). Lindberg et al.
(2008) compared the results of SOLWEIG model with mea-
surements in Sweden, while Lindberg and Grimmond (2011)
used measurement data from Sweden and Germany for the
validation. Moreover, the methodological basics of this simu-
lation tool are the same, i.e., modeling the radiation fluxes from
six orthogonal directions (Lindberg et al. 2008). Not only the
models but also the other popular measurement technique
(using globe thermometer) should be validated with the six-
directional method. Thorsson et al. (2007) validated the globe
technique via six-directional measurements. They used not the
standard black copper sphere (ISO 1985,1998), but a smaller,
gray-painted acrylic globe, more suitable for outdoor
measurements.
In the course of a study, which was aimed to validate the
standard black-globe with the six-directional method in
Taiwan, a special midday-relapsewas found in the daily
course of the T
mrt
based on the six-directional technique
during clear sky conditions. The present study objects to:
&Show this special feature of the six-directional measure-
ments in Taiwan
&Compare for examples all over the world
&Identify the source of the relapse including instrumental
and methodological issues
&Discuss the potential effects of the identified shortcomings
in terms of characterizing the short-wave radiation fields.
Materials and methods
Radiation measurements in Taiwan
The six-directional radiation measurements were carried out
in the National Formosan University, Huwei, Taiwan (23.7°
N, 120.43° E, 30 m asl). One-minute averages of the short-
1616 Int J Biometeorol (2014) 58:16151625
and long-wave flux densities [K
i
,L
i
(W/m
2
)] from six per-
pendicular directions (i:E, East; S, South; W, West; N, North:
, upper hemisphere; , lower hemisphere) were measured
separately with three orthogonally arranged net radiometers.
Kipp&Zonen CNR1 net radiometer was used for the two
vertical directions, and Hukseflux NR01 net radiometers were
used for the four lateral directions. In correspondence to the
gravity center of a standing man, the sensors were mounted at
1.1-m height (Mayer and Höppe 1987).
The individual radiation flux densities were weighted and
summed to get the total radiation flux density absorbed by the
human body [S
rad
(W/m
2
)] from which the T
mrt
was
expressed:
Srad ¼X
i¼1
6
WiakKiþalLi
 ð1Þ
Tmrt ¼ffiffiffiffiffiffiffi
Srad
alσ
4
r273:2¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
X
i¼1
6
WiakKiþalLi
ðÞ
alσ
4
v
u
u
u
t273:2ð2Þ
For short- and long-wave absorption coefficients (a
k
and
a
l
), the commonly used 0.7 and 0.97 values were adopted, as
these represent the average absorptive capacity of the clothed
human body (Höppe 1992;VDI 1998). Selecting different
values for the W
i
directional weighting factors allows to
consider different reference shapes, e.g., a standing man and
a sphere. In the latter case, all fluxes were weighted identically
with 0.167, while in the standing mancase, the role of the
lateral fluxes became relatively greater than the vertical ones
according to the W
i
of 0.22 and 0.06, respectively.
The investigations were carried out in the daylight hours of
12 days, mainly on the top of the university without consid-
erable horizon limiting objects, i.e., with a Sky View Factor
(SVF) near to 1. To show the special characteristics in the
temporal course of the T
mrt
and the radiation flux densities
observable during clear sky conditions, this study uses the
data measured on 20110127 between 0644 and 1708 hours
(Chinese Standard Time).
Model calculations
To increase the knowledge about the six-directional technique,
with special emphasis on the probable shortcomings we found
in clear sky conditions, additional short-wave radiation calcu-
lations were made. Without horizon limiting objects and
clouds, the model calculations have the advantage over the
measurements that they offer clear picture about the behavior
of the radiation flux densities reaching the body. The calcula-
tions were completed for the location of the measurements
(Huwei, Taiwan, 23.7° N, 120.43° E, 30 m asl). To simply
represent the annual variability of the radiation conditions, we
choose four specific days: Spring Equinox (20110320),
Summer Solstice (20110621), Autumn Equinox (2011
0923) and Winter Solstice (20111222).
Sun elevation (elev.) and azimuth (azim.) data were obtain-
ed from the RayMan model (Matzarakis et al. 2007,2010)in
1-min resolution together with the data of global (G), diffuse
(D), and direct (I) radiation. The simulated Gvalues corre-
spond to the short-wave radiation flux densities from the
upper hemisphere: K=G. The reflected radiation, i.e., the
short-wave flux densities from the lower hemisphere was
calculated as K=albedo K by assuming a mean surface
albedo of 0.2. The direct radiation flux densities on a perpen-
dicular surface (I
) were calculated according to:
I¼I=sin elev:ðÞ ð3Þ
The lateral short-wave flux densities (K
)fromanarbi-
trary lateral direction were calculated according to the follow-
ing general equations (based on Lindberg et al. 2008;simpli-
fied for SVF=1 condition):
K¼DþIcos elev:ðÞsin azim:
ðÞif 0<azim:<180
ð4Þ
K¼Dif 180<azim:<360ð5Þ
The azim.
means the modified azimuth anglesmodified
according to the specific lateral direction what we are talking
about. In the case of the Eastern direction, there is no need for
modification: azim.E=azim. However, in the case of any other
lateral direction, there is a need for adjustment: azim.S =azim.
90°, azim.W=azim.180°, and azim.N= azim.270° for the
Southern, Western, and Northern directions, respectively.
Theoretically, the six-directional technique should not be
sensitive to the exact orientation of the lateral radiometers as
long as the criterion of perpendicularity satisfies. This means
that the (absorbed) sum of the short-wave flux densities
reaching the body from NESWdirectionsshouldbeequal
to the sum of them from any other four perpendicular lateral
directions. To verify this assumption, we have analyzed these
sums not only for the original NESW orientation (0°
deviation), but for the NNEESESSWWNW (22.5° devia-
tion) and NESESWNW (45° deviation) orientations, too.
Results and discussion
Radiation conditions on a clear day in Taiwan
The 1-min data of 20110127, a clear-weather measurement
day, were used in order to show the temporal characteristics of
the radiation environment influenced by the apparent path of
the sun, i.e., elevation and azimuth angles. The sun elevation
and azimuth angles were calculated with the RayMan model
(Matzarakis et al. 2007,2010).
Int J Biometeorol (2014) 58:16151625 1617
Corresponding to the wintertime measurement on 2011
0127, the daylight period was somewhat shorter than the half
of the day, but because Huwei locates on the Tropic of Cancer,
it is still relatively long, ca. 11 h. The highest daily sun
elevation angle at the solar noon (1211 hours) was 47.8°,
and the corresponding maximal value of the simulated global
radiation (G)was830W/m
2
(Fig. 1a). Despite the totally clear
sky conditions on the sample day, the measured values of the
global radiation (K; measured by the upper pyranometer)
were consistently somewhat lower than the simulated G
values. This can be attributed to that we have not changed
the RayMan's default turbidity value, which depends only on
the date but not on the geographical location. For 201101
27, it was 1.5, which was probably somewhat lower (resulting
higher simulated global radiation values) than the real turbid-
ity in Huwei.
The air temperature ranged from 13 to 20 °C, meaning 7 °C
daily amplitude. The T
mrt
values calculated from the measured
radiation flux densities showed much greater temporal vari-
ability (Fig. 1b). Even though they were around 10 °C at
sunrise, they quickly exceed the 30 °C and remained above
this from ca. 0730 to1650 hours. The highest values occurred
during the midday period and were around 60 °C, which
means that the T
mrt
values were up to 40 °C higher than the
air temperature. This result corresponds to the findings of
other studies conducted in clear weather conditions
(Matzarakis et al. 1999;Ali-Toudert et al. 2005;Gulyás
et al. 2006; Johansson and Emmanuel 2006; Ali-Toudert and
Mayer 2007;Thorsson et al. 2007;Mayer et al. 2008;
Shashua-Bar et al. 2012).
There are some remarkable differences between the T
mrt
values characterizing the radiation load of a spherical body
(T
mrt-sp.
) and a standing man (T
mrt-st.
). The latter was clearly
higher before 1030 and after 1400 hours, while around mid-
day, the spherical shape had greater values (Fig. 1b). This can
be attributed to the different weighting factors: in the case of
the standing shape, the role of the lateral fluxes became
considerably greater than the vertical ones, which results in
T
mrt-st.
values higher than T
mrt-sp.
during the time of lower sun
elevation.
In the cases of both reference shapes, there is a very clear
decrease around 1240 hours; this is however more pro-
nounced in T
mrt-st.
(Fig. 1b). Similar T
mrt
decreases were
found also on other measurement days (6 from the 12 days),
which could be also characterized by free (or relatively free)
horizon and clear sky conditions.
Individual radiation flux densities on a clear day in Taiwan
To reveal the background of this daytime T
mrt
relapse, Fig. 2
illustrates all of the individual short- and long-wave radiation
flux densities on 20110127. Keep in mind, that according to
real orientation of the instrument on this day, the lateral flux
densities indexed with E, S, W, and N are meaning the
radiation flux densities measured by the radiometers facing
to 101.5, 191.5, 281.5, and 11.5°, respectively. This 11.5°
deviation angle explains that the daily maximum of K
s
oc-
curred around 1300 hours, i.e., after the daily maximum of the
global radiation Kat local solar noon (Fig. 2a). It explains
also that the E-facedpyranometer got direct radiation for
longer period than the W-facedone, and measured higher
values. Due to the lower sun elevation angles in winter, the
maximal K
s
values exceeded slightly the maximum of K
(Fig. 2a).
As the measurements were conducted on a roof without
significant horizon limitations, the long-wave flux densities
from the four lateral directions (L
E
,L
S
,L
W
,andL
N
)were
absolutely similar to each other, and did not show remarkable
temporal fluctuations (Fig. 2b). The atmospheric counter ra-
diation L(measured by the upper pyrgeometer) was clearly
lower. As the surface of the roof was warmed up by the
absorbed short-wave radiation during the day, it caused
Fig. 1 a Sun path properties on 20110127 in Huwei together with the simulated (G)andmeasured(K) global radiation values. bThe six-directional
technique-based mean radiant temperature for a spherical shape (T
mrt-sp.
) and for a standing man (T
mrt-st.
), as well as their differences (delta T
mrt
=T
mrt-sp.
T
mrt-st.
)
1618 Int J Biometeorol (2014) 58:16151625
gradually higher amount of emitted long-wave radiation L
(measured by the lower pyrgeometer). Contrary to the short-
wave flux densities, which were quite different and could be
characterized with spectacular temporal patterns (Fig. 2a), the
long-wave flux densities showed relatively constant values
during the day, as well as they were more similar to each other
(Fig. 2b).
In the course of the T
mrt
calculation, using different ab-
sorption coefficients (0.7 for the short- and 0.97 for the long-
wave domain), the role of the long-wave flux densities be-
came relatively greater than the short-wave flux densities.
Additionally, due to the directional weighting factors (W
i
)
all flux densities became lower in magnitude. There are,
however, remarkable differences between the two reference
shapes. Using the W
i
=0.167 for all directions in the spherical
reference shape, the resulted absorbed radiation flux densities
showed similar temporal tendencies as the originally mea-
sured ones. However, by representing a standing person the
relative importance of the lateral flux densities grows signif-
icantly to the detriment of the vertical ones.
Combined radiation flux densities on a clear day in Taiwan
To clearly illustrate the overall effect of the different W
i
factors on the resulted T
mrt
values, Fig. 3displays the total
absorbed short- and long-wave flux densities separated ac-
cording the vertical and lateral directions. The sum of the
absorbed flux densities from the four lateral directions is
higher than the sum of them from the two vertical directions
in every cases of wavelength or reference shape. Additionally,
the order of importance is also the same in the short- (Fig. 3a)
and long-wave (Fig. 3b) domain; in ascending importance:
vertical standing, vertical spherical, lateral spherical, and
lateral standing. That is, the sums of the absorbed radiation
flux densities from vertical and lateral directions are
closer to each other in the cases of a spherical reference
shape, while in the standing man casethe sum of the
lateral fluxes is more important.
There are two other interesting characteristics on this fig-
ure. Firstly, the magnitude of the absorbed long-wave flux
densities (Fig. 3b) overcomes to the corresponding absorbed
short-wave flux densities (Fig. 3a) in every case. Secondly,
while the former (Fig. 3b) are more stable with time, the latter
(Fig. 3a) showed clear time dependence during the day. The
most interesting temporal variability can be seen in the cases
of the lateral short-wave sums (K
lat
*
): a clear decrease around
1240 hours (Fig. 3a), which coincides exactly the time of the
formerly discovered T
mrt
relapse (Fig. 1b), and as the T
mrt-st.
relapse was more pronounced than the T
mrt-sp.
(Fig. 1b), the
K
lat
*
decrease is also more obvious in the case of the standing
shape (Fig. 3a).
Through the analysis of the total absorbed short- (K*) and
long-wave (L*) flux densities (Fig. 4a), we can realize that, in
the long-wave domain, there is a slight and almost constant
difference between the two shapes. Delta L*isaround5W/
m
2
, indicating that the standing human body absorbs all day
long higher amount of long-wave radiation than the spherical
shape (Fig. 4b). On the contrary, the difference between the
two shapes from the point of view of K*ismuchbiggerin
absolute values, and it shows remarkable time dependence;
delta K*rangesbetween17.3 and 22.6 W/m
2
(Fig. 4b). This
is because the standing shape absorbs more short-wave radi-
ation during lower sun elevations and less during higher sun
elevations. In our sample day, the change points (delta K*=0)
occurred at 1001 hours (elevation= 37.2°) and at 1426 hours
(elevation=36.5°). The greatest negative differences (delta
K*≤−16.5 W/m
2
; standing shape absorbed more radiation)
were found between 0752 and 0826 hours and between 1559
and 1628 hours. The greatest positive differences (delta K*
22 W/m
2
; spherical shape absorbed more radiation) occurred
around 12341244 hours, after the local solar noon.
The difference between the total absorbed all-wave radia-
tion flux densities (delta S
rad
) shows similar temporal patterns
Fig. 2 The measured original ashort- and blong-wave flux densities on 20110127 in Huwei
Int J Biometeorol (2014) 58:16151625 1619
than the delta K*, with the same time intervals of the positive
and negative extremes (Fig. 4b). However, because of the
nearly constant negative delta L* values, the time period when
the spherical shape absorbed more all-wave radiation (positive
delta S
rad
) is shorter than the corresponding time interval for
the positive delta K*.
As a consequence of the former findings, despite the fact
that the long-wave flux densities are primarily responsible for
the magnitude of the daytime T
mrt
values, the specific tempo-
ral characteristics of T
mrt
are governed by the short-wave flux
densities (see also by Holst and Mayer 2010), and these are
responsible mainly for the differences between the T
mrt-st.
and
T
mrt.sp.
(Fig. 1b). The interesting T
mrt
relapse around 1240
hours (Fig. 1b) can be explained by the decrease of the
absorbed short-wave radiation (K*) at that time (Fig. 4a),
which in turn is attributable to the local minimum of the
short-wave flux densities absorbed from the lateral directions
(K
lat
*
;Fig.3a). More specifically, this special shape can be
traced to the short-wave flux densities measured by the East-
and West-faced pyranometers (K
E
and K
W
; Fig. 2a).
T
mrt
relapse in other studies
Besides 20110127, T
mrt
relapses were found on every
measurement days, which could be characterized with free
(or relatively free) horizon and clear sky conditions (Table 1).
By reviewing the literature, similar T
mrt
decreases were found
in Swedish (Thorsson et al. 2007) and German (Ali-Toudert
and Mayer 2007;Mayer et al. 2008) studies, which were
based also on six-directional measurements during clear-
weather conditions (Table 1). The T
mrt
relapses in the
Swedish study (Thorsson et al. 2007) are as obvious as the
presented one in Taiwan because both analyzes were based on
1-min data. However, due to the hourly mean values, the
midday T
mrt
relapses are not so clear in the German studies
Fig. 3 Sum of the absorbed ashort-wave (K
*) and blong-wave (L
*) radiation flux densities from vertical (vert) and lateral (lat) directions for a
spherical shape (sp.) and a standing man (st.) on 20110127 in Huwei
Fig. 4 a Sum of the totally absorbed short- (K*) and long-wave (L*)
radiation flux densities for a spherical shape (sp.) and a standing man (st.).
bThe differences between the reference shapes (delta=sp.st.) in terms
of the totally absorbed short-wave (delta K*), long-wave (delta L*), and
all-wave (delta S
rad
) radiation on 20110127 in Huwei
1620 Int J Biometeorol (2014) 58:16151625
and look more like break points in the temporal courses of the
T
mrt
(Ali-Toudert and Mayer 2007; Mayer et al. 2008).
Based on our findings, the T
mrt
relapse can be connected to
the absorbed short-wave flux densities (K*), which have a
daytime local minimum at the same time (Fig. 4a). A study
from Germany explained this midday minimum in K*with
the smaller irradiated body surface at the time of the highest
sun elevation (Ali-Toudert 2005;Ali-Toudert and Mayer
2007). However, if this explanation would be absolutely suf-
ficient, then the daytime relapse would be occurred only in the
case of the standing manreference shape and not in the case
of the spherical. On the other hand, according to this explana-
tion, the T
mrt
relapses (or breakpoints) should have occurred
only at the time of the local solar noon.
In fact, the T
mrt
relapses occurred sometimes before the
solar noon and sometimes after that, in relation to the devia-
tion angles of the instruments compared to the original NE
SWdirections(Table1). When the instruments' deviation
angle was positive (eastwards compared to N), then the
breakpoints occurred after the solar noon; in the other case,
before that. It should be noted that this pattern is not so
unequivocal in the case of the German studies with 1-h reso-
lution and without information about the orientation.
Moreover, on two of the summertime measurements (2006
0726, Sweden; 20070619, Germany), additional
breakpoints have been found in the daytime courses of the
T
mrt
(Table 1).
Instrumental explanation of the relapse
According to Thorsson et al. (2007), these T
mrt
patterns on
clear days are attributable to the orthogonal instrument setup,
i.e., the increased mean instrumental error with high angles of
incidence. This explanation seems to be closer to the reality,
but it requires further clarification. Therefore, we investigated
the short-wave fluxes more closely, taking special care on the
instrumentations physical characteristics. So far, based on the
time course of the T
mrt
on clear days, we can find the
following:
&The interesting T
mrt
relapses/breakpoints are attributable
to the local minimum of the short-wave flux densities
absorbed from the lateral directions (K
lat
*
; Fig. 3a). More
specifically, they seem to be connected with the short-
wave flux densities measured by the East- and West-
faced pyranometers (K
E
and K
W
;Fig.2a).
&The time of T
mrt
decreases appear to be connected to the
exact orientation of the instruments, i.e., the deviation
angles from the original NESW directions (Table 1).
Tabl e 1 List of six-directional
measurementdayswithobserv-
able daytime T
mrt
relapse: present
study in Taiwan and earlier stud-
ies in Sweden and Germany
a
Based on Figs. 4 and 10 of
Thorsson et al. 2007
b
BasedonFig.10ofAli-Toudert
and Mayer 2007
c
Based on Fig. 4 of Mayer et al.
2008
Location Measurement place Date Solar
noon
hours
Instrument's
deviation (°)
Time of the
daytime T
mrt
relapse (hours)
Taiwan, Huwei
(23.7 °N)
Roof 20101207 1151 16 1250
20101229 1201 3 1145
20110127 1211 11.5 1240
20110209 1213 9.5 1235
20110303 1211 20 1235
Open space 20110409 1200 0 1200
Sweden, Göteborg
(57.7 °N)
largeopensquare
a
20051011 1158 20 0900
20060726 1218 20 1130 (1620)
Germany, Freiburg
(48 °N)
E-W oriented street,
S-oriented sidewalk
b
20030714 1234 0 (?) 1300
20030715 1234 0 (?) 1300
NW-SE oriented street,
SW-oriented sidewalk
c
20070619 1230 0 (?) 1300 (1700)
Fig. 5 Explanatory figure for the daytime minimum of the sum of the
lateral short-wave fluxes from E (K
E
)andW(K
W
):Thereareacoupleof
minutes when neither of the pyranometersfacing away from each
othergets direct solar radiation. The exact time interval of this
pyranometer blind spotcorresponds to the time when the corrected
azimuth angle is 180°±2.5°, i.e., when the sun shines from the direction
of the axis of the net radiometer
Int J Biometeorol (2014) 58:16151625 1621
We try to find a possible instrumental explanation for these
results, taking the 20110127 measurement day as an exam-
ple. The Fig. 5illustrates in detail the time period of the day
when the T
mrt
relapse occurred. There are a couple of minutes
around 1240 hours when both of the K
E
and K
W
curves are
quite flat, meaning that neither of the E- nor the W-facing
pyranometers got direct solar radiation that time. The figure
displays also the original azimuth angles and the so-called
corrected azimuth angles. The latter were calculated by
subtracting the instrument's deviation angle from the original
azimuth angles.
The specific time interval, when both K
E
and K
W
were
without direct radiation, can be concluded based on the time
when the corrected azimuth angle was between 177.5 and
182.5° (Fig. 5). That is, instead of the 2×180° angular view
of the pyranometers facing in opposite directions, there is a 5°-
wide blind-spot. By analyzing the other clear-sky measure-
ment days, the findings verified this explanation. The time of
the day when the critical time interval(both K
E
and K
W
are
without direct radiation) occurred is affected by the instru-
ment's actual orientation: at positive (Eastwards) deviation
angle, this interval occurred after the solar noon, and at neg-
ative deviation, before noon. Moreover, in the cases when the
(corrected) azimuth curve was steeper around 180°, the critical
time interval was shorter, as the sun went through quickly on
the pyranometer blind spot. This finding means that because
of this instrumental shortcoming, the winter-time measure-
ments have bigger failure than the summer-time measure-
ments, as the winter-time azimuth curves are flatter during
the day (Appendix 1(a) series). Moreover, in the cases of
geographical locations closer to the Poles like Göteborg, with
flatter daytime azimuth curves (Appendix 2(a) series), the
problem of the equipment may be more serious all year long.
It should be noted that these results were found in the case
of Hukseflux net radiometers. It would be worthwhile to
examine the existence and measure of these pyranometer
blind spotsin the cases of other constructions, e.g.,
Kipp&Zonen CNR-1 and CNR-2 net radiometers, as well as
single rotatable pyranometerpyrgeometer pairs.
The illustrated instrumental problemmay occur not only in
the cases of K
E
K
W
, but K
S
K
N
pairs, too. Assuming 0°
instrumental deviation, the latter situation is possible only in
the summer half of the year, i.e., when the sun rises Northeast
and sets Northwest, and therefore the North-facing
pyranometer also get some direct radiation. This offers an
explanation also for the finding that in the German and
Swedish studies there was another, second T
mrt
breakpoint
on the summertime measurement days (Table 1).
Methodological explanation of the relapse
In spite of that the pyranometer-related instrumental short-
coming of the six-directional technique seems to elucidate
well the daytime T
mrt
relapse on clear days, it is not a
completely satisfactory explanation. Namely, if problems
would exist only from instrumental point of view, than the
model simulations based on the six-directional philosophy
would be free from that. Indeed, by reviewing the literature,
we can discover the daytime T
mrt
decrease also on the figures
of Swedish researchers (Lindberg et al. 2008;Thorsson et al.
2007), who modeled the radiation conditions by SOLWEIG.
The model simulates the radiation flux densities on the theo-
retical basis of Höppe 1992, i.e., from six perpendicular
directions. In spite of that the equations for short-wave flux
densities are not affected by the pyranometer problem, the
T
mrt
relapses are clearly noticeable, and the time of those are
related to the orientation of the simulations. Therefore, we can
conclude that the problem is rather methodologically and may
be associated with the restricted number of sides from which
the radiation components are considered (measured or
modeled).
To verify the former assumption, radiation calculations
were carried out for four special days of a year (Spring
Equinox, Summer Solstice, Autumn Equinox, and Winter
Solstice) with three different orientations. The aim was to
identify the differences between the absorbed short-wave flux
densities (K*) modeled in the case of the original NESW
orientation (0° deviation) and in the cases of the lateral direc-
tions, which deviate with 22.5 and 45° from that (Fig. 6). In all
three cases, the vertical flux densities were the same. The
calculations were performed not only for Huwei (23.7° N)
but also for the location of Göteborg (57.7° N), in order to
ensure the representativeness in spatial manner, and taking
into account quite different sun path and radiation conditions
(Appendices 1and 2).
As the hourly temporal resolution of the SOLWEIG model
is too rough, we performed the 1-min short-wave radiation
calculations manually according to the published equations of
Lindberg et al. (2008). The necessary data of sun elevation
and azimuth,as well as global, diffuse, and direct radiation for
the selected four days and two geographical locations were
obtained from the RayMan model. Figure 6illustrates
the final results in terms of the short-wave flux densities
absorbed by a standing man (K
st.
*
) on the four special
days in Huwei, while Appendix 1displays the details
(vertical and lateral sums) also for the standing human
and for the spherical shape. Appendix 2illustrates the
same series for Göteborg.
The different orientation have resulted in dissimilar time
courses of K
st.
*
(Fig. 6), and even K
sp.
*
, which in turn are
derived from the absorbed lateral short-wave flux densities
(K
lat
*
;Appendices1and 2). The maximal values of K
st.
*
may be
similar sometimes (Table 2); nevertheless, the most obvious
differences are between the shapes of the K
st.
*
curves, namely,
the number and timing of daytime minimums or breakpoints
(Fig. 6, Appendices 1and 2). In absolute values, the greatest
1622 Int J Biometeorol (2014) 58:16151625
discrepancies were found between the 0 and 45° K
st.
*
,
exceeding even 50 W/m
2
during the Winter Solstice in
Huwei and during the Spring Equinox in Göteborg
(Table 2). However, if we analyze the delta K
st.
*
values relative
to the actual values of the 0° K
st.
*
, we can notice the greatest
differences at the Equinox days in the cases of both cities;
meaning more than 40 % differences between the 0 and 45°
cases (Table 2).
Tabl e 2 Differences between the short-wave radiationflux densitiesabsorbed by a standing man (K
st.
*
) in the cases of different orientation (NEWS:
0° deviation, NNEESESSWWNW: 22.5° deviation, NESESWNW: 45° deviation) at different days of the year in Huwei and Göteborg
Location Day Maximal K
st.
*
(W/m
2
) Maximal delta K
st.
*
(W/m
2
) Maximal delta K
st.
*
(%)
deviation
22.5°
deviation
45°
deviation
022.5°
deviation
045°
deviation
022.5°
deviation
045°
deviation
Taiwan, Huwei (23.7° N) Spring Eq. 211 231 226 26; 36 30; 36 31; 17 42; 21
Summer St. 213 231 231 19; 13 20; 0 9; 23 10; 4
Autumn Eq. 223 234 227 20; 30 24; 31 32; 13 43; 15
Winter St. 238 227 211 30; 41 53; 59 25; 21 33; 25
Sweden, Göteborg (57.7° N) Spring Eq. 229 232 231 38; 38 51; 50 38; 18 40; 22
Summer St. 230 233 228 25; 26 34; 33 14; 13 19; 30
Autumn Eq. 221 229 231 30; 30 41; 38 31; 14 41; 18
Winter St. 149 172 179 33; 30 45; 14 25; 21 31; 25
Fig. 6 Absorbed short-wave flux densities by a standing man (K
st.
*
)inthe
cases of three orientations (NEWS: 0° deviation, NNEESESSW
WNW: 22.5° deviation, NESESWNW: 45° deviation), as well as the
delta K
st.
*
between the 0 and 22.5° and the 0 and 45° cases. The calcula-
tions were carried out for aSpring Equinox, bSummer Solstice, c
Autumn Equinox, and dWinter Solstice
Int J Biometeorol (2014) 58:16151625 1623
Based on our recent findings, in contrast to the previous
assumptions, the six-directional technique (measurements and
modeling too) is quite sensitive to the lateral orientation; i.e.,
we get different results when we taking the investigations with
different orientations. This is because the standing man
reference shape is in fact a rectangular column and not a
rotationally symmetric cylinder. As well as, the spherical
reference shape is actually a cube, according to the six-
directional technique. Because of the edges of the reference
shapes, we cannot expect identical results in the cases of
different orientations.
There is a theoretical solution for the discovered problem,
which could be useful in the cases of the model simulations.
By solving the equations for the lateral flux densities consid-
ering 90 different orientation cases (089° deviation) and by
averaging the resulted K* values, we could achieve the values
represent really a rotationally symmetric cylinder, which is a
closer approximation to the standing human body.
Conclusions
In the frame of a survey series in Huwei (Taiwan), radiation
measurements were carried out from the six perpendicular
directions of a space to determine the T
mrt
. A specific relapse
was found in the temporal course of the T
mrt
values around
midday, but not exactly at the time of the local solar noon.
This decrease was noticeably both in the cases of a standing
man (T
mrt-st.
)andaspherical(T
mrt-sp.
) reference shape. We
find instrumental and methodological shortcomings.
The detailed analysis for 20110127 corresponded with
already existing studies about the daytime T
mrt
relapse and
that it can be related to the short-wave radiation fluxes
reaching the body from the lateral directions. The time period
about the occurrence of the T
mrt
decrease can be partly ex-
plained by an instrumental shortcoming of the six-directional
technique (pyranometer blind spot).When the sun shines from
the direction which is nearly perpendicular for both
pyranometers of the same net radiometer, there are a couple
of minutes (515 min) when neither of the pyranometers gets
direct radiation. Assuming 0° deviation angle form North (i.e.,
NESWfacing lateral pyranometers) and free horizon (at
least free Southern hemisphere), the problem will occur every
clear-sky time in the case of the EW facing pyranometer
pairs. In summer time, the relapse will occur also in the caseof
the NS facing pyranometer pairs, provided the direct sun
beams are not obstructed by the surrounding objects. The time
of the pyranometer blind spotperiod is supposed to be
shorter when the solar azimuth curve is steeper during the
daylight period. In the case of Huwei, this means that the
summertime measurements are more accurate. On the other
hand, the problem gets bigger in wintertime and in the case of
locations with higher geographical latitude.
In addition, a methodological problem of the six-
directional technique was also discovered, which explains
the patterns that have been seen also in earlier studies.
Namely, the (absorbed) sum of the short-wave flux densities
from the four lateral directions (K
lat
*
) is very sensitive to the
orientation of the radiometers, and therefore, by deviating
from the original four cardinal directions, the K* and the
T
mrt
relapse on clear sunny days will occur in different times
and will be different in extent. In terms of absorbed short-
wave flux densities (K*), the biggest differences were found
between the original instrument orientation and the case when
the instruments deviate 45° from that. On the days of the
Equinoxes, the K* difference may be up to 40 %.
Both the instrumental and the methodological shortcom-
ings of the six-directional technique need further and deeper
research (measurements and simulations, too) in order to
quantify the magnitude of the effects of these specific prob-
lems on the resulted T
mrt
. The importance of this research
topic can be confirmed by that the six-directional technique is
treated as the most accurate outdoor method to determine the
T
mrt
, and it is used to validate the other measurement tech-
niques (e.g., with globe thermometers) and the outcomes of
model simulations. The validation is necessary as, during clear
weather conditions, the T
mrt
is the main influencing factor of
state-of-the-art thermal indices for the quantification of ther-
mal comfort and heat stress issues.
Acknowledgments The authors would express a special thank for the
sponsorship of the Research Center for the Humanities and Social Sci-
ences at the National Chung Hsing University.
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... Finally, wind speeds ranged between an average minimum (maximum) of 0.11 ms −1 (4.9 ms −1 ). MRT IRM values in Fig. 2f show a small dip, or relapse, in MRT at solar noon, which has occurred in numerous studies of clear-sky day MRT using the 3D set up (Ali-Toudert and Mayer 2007;Mayer et al. 2008;Kántor et al. 2014;Holmer et al. 2015). This dip is attributable to the local minimum of the short-wave flux densities from the lateral (left, right) sensors at noon (Fig. 2d), similarly demonstrated by Kántor et al. (2014). ...
... MRT IRM values in Fig. 2f show a small dip, or relapse, in MRT at solar noon, which has occurred in numerous studies of clear-sky day MRT using the 3D set up (Ali-Toudert and Mayer 2007;Mayer et al. 2008;Kántor et al. 2014;Holmer et al. 2015). This dip is attributable to the local minimum of the short-wave flux densities from the lateral (left, right) sensors at noon (Fig. 2d), similarly demonstrated by Kántor et al. (2014). ...
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... When L is higher than 15,000 lx, SW is set to 600 W m −2 . Because the MoBiMets IR and L measurements are only performed in one direction-up-the six-directional method for mean radiant flux density (Sstr) used in previous human biometeorology studies [46][47][48] was modified to calculate an approximation of Tmrt (°C) (2): ...
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Full-text available
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... This feature is also observed on the other days (not shown) but not simulated by SOLWEIG_O (Figure 4), as discussed above. In addition, SOLWEIG_O simulates a local minimum at 1100 UTC, which follows from the fact that around noon a smaller fraction of the human body is exposed to direct sunlight, resulting in a reduced amount of absorbed shortwave radiation (Kántor et al., 2014;Thorsson et al., 2007). ...
Thesis
In dieser Arbeit wird die Entwicklung eines Gebäudeenergiemodells (BEM) und eines Schemas für die mittlere Strahlungstemperatur ($T_mrt$) vorgestellt, das in das Doppel-Canyon basierte städtische Bestandsschichtsschema (DCEP) integriert ist. Das erweiterte DCEP-BEM Modell zielt darauf ab, eine Verbindung zwischen anthropogener Wärme und dem Stadtklima herzustellen, indem Gebäude in Straßenschluchten einbezogen werden, um die Energieflüsse auf städtischen Oberflächen, die Auswirkungen der anthropogenen Wärme auf die Atmosphäre, die Innenraumlufttemperatur und die Abwärme von Klimaanlagen zu untersuchen. Das DCEP-BEM wird mit dem mesoskaligen Klimamodell COSMO-CLM (COnsortium for Small-scale MOdelling in CLimate Mode, im Folgenden CCLM) gekoppelt und zur Simulation des Winters und Sommers 2018 in Berlin. Die Auswertung der Wintersimulationen zeigt, dass CCLM/DCEP-BEM den mittleren Tagesverlauf der gemessenen turbulenten Wärmeströme gut reproduziert und die simulierte 2-m-Lufttemperatur und den städtischen Wärmeinseleffekt (UHI) verbessert. Im Sommer bildet das CCLM/DCEP-BEM die Innenraumlufttemperatur richtig ab und verbessert die Ergebnisse für die 2-m-Lufttemperatur und die UHI leicht. Außerdem wird das CCLM/DCEP-BEM angewendet, um die Abwärmeemissionen von Klimaanlagen im Sommer zu untersuchen. Die Abwärmeemissionen der Klimaanlagen erhöhen die Lufttemperatur in Oberflächennähe erheblich. Der Anstieg ist in der Nacht und in hochurbanisierten Gebieten stärker ausgeprägt. Es werden zwei Standorte für die AC-Außengeräte betrachtet: entweder an der Wand eines Gebäudes (VerAC) oder auf dem Dach eines Gebäudes (HorAC). Die Auswirkung von HorAC ist im Vergleich zu VerAC insgesamt geringer, was darauf hindeutet, dass HorAC einen kleineren Einfluss auf die oberflächennahe Lufttemperatur und den UHI hat. Ein Schema für $T_mrt$ wird für das CCLM/DCEP-BEM entwickelt und umfassend validiert. Es wird gezeigt, dass dieses Schema eine zuverlässige Darstellung von $T_mrt$ bietet.
... En ambos casos la curva con datos monitoreados cuenta con mayor delta T: en el 1° nivel dicha diferencia (ΔT) es de 1.5°C con datos monitoreados y de 1.1°C con datos de ENVI-met; mientras que en el 5° nivel las diferencias son de 2.9°C con datos monitoreados, de 2.5°C de acuerdo al archivo climático con datos de ENVI-met y de 1.9°C con la opción del día de diseño. El aplanamiento de la curva de temperatura calculada con ENVI-met ocurre con mayor intensidad en las simulaciones de estaciones intermedias (otoño-primavera) e invierno, debido a que el ángulo solar es menor (Kántor et al., 2014). ...
Conference Paper
El microclima alrededor de un edificio, establecido por la interacción con su entorno, es uno de los factores determinantes en el comportamiento termo-energético edilicio. La presente investigación propone desarrollar un método de integración de dos programas de simulación, uno a escala edilicia-EnergyPlus-y otro a escala urbana-ENVI-met-, con el objetivo de determinar la potencialidad predictiva del modelo de simulación urbano para crear datos microclimáticos fiables para conformar las bases climáticas del software EnergyPlus. El análisis se llevó a cabo en la zona con mayor concentración de densidad del área metropolitana de la ciudad de Mendoza y se tomó como caso de estudio un edificio másico de altura media. La investigación se divide en las siguientes etapas: (i) descripción de área urbana; (ii) diseño y validación del modelo numérico urbano (ENVI-met) y edilicio (EnergyPlus); (iii) ingreso de variables climáticas-monitoreadas versus calculadas-para un día de diseño en el programa EnergyPlus y según nivel de altura de departamento; (iv) contrastación de los resultados termo-energéticos interiores. Los resultados de la presente investigación revelan las capacidades y ventajas de trabajar con ENVI-met como herramienta para la generación de datos climáticos. El alto grado de ajuste-R 2 superiores a 0.94-de la temperatura del aire interior monitoreada y ajustada con EnergyPlus versus la utilizada con los datos microclimáticos calculados con el simulador urbano ENVI-met, apoya la fiabilidad de los resultados predictivos del método de integración de ambos softwares. Abstract The microclimate around a building, established by the interaction with its environment, is one of the determining factors in the building thermo-energetic behavior of a building. The present investigation proposes to develop a method of integration of two simulation programs, one at building scale-EnergyPlus-and another at urban scale-ENVI-met. The objective consists in determining the predictive potential of the urban model to create reliable microclimatic data to conform the climatic bases of the EnergyPlus software. The analysis was carried out in the area with the highest concentration of density in the metropolitan area of Mendoza city and a medium-height mass building was taken as case studied. The investigation is divided into the following stages: (i) description of urban area; (ii) design and validation of the urban numerical model (ENVI-met) and building (EnergyPlus); (iii) input of climatic variables-monitored versus calculated-for a design day in the EnergyPlus program and according to department height level; (iv) comparison of the interior thermo-energetic results. The results of this research reveal the capabilities and advantages of working with ENVI-met as a tool for the generation of climate data. The high degree of adjustment-R2 above 0.94-of the indoor air temperature monitored and adjusted with EnergyPlus versus that used with the microclimatic data calculated with the urban simulator ENVI-met, supports the reliability of the predictive results of the integration method of both softwares.
... For comparison of radiative flux according to insolation, a sunny day and a cloudy day were selected (Yi et al., 2018a(Yi et al., , 2018b. A comparison of the radiant flux based on the direction of the long wave and the short wave during one day was also done by Kántor et al. (2014). The analysis of more cases (hourly, monthly, general summer days, and precipitation days) is presented by Lee et al. (2018), but it was not analysed alongside spatial characteristics data of an urban environment. ...
Article
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This study analysed the spatial temperature differences among urban structural environments with different meteorological elements, and radiant fluxes in the energy balance system using surface characteristics. A simulation was performed by evaluating the radiant flux, using the SOlar and LongWave Environmental Irradiance Geometry (SOLWEIG) model. The simulation reading of upward longwave radiant flux, which shows the surface effect in an urban landscape, showed a slightly higher daily maximum than actual value for man-made structures but it was very accurate for natural areas. Most of the R² values were 0.8–0.9 or higher, and the RMSE was 19–60 w/m². The net radiant fluxes of the ten study sites were similar. According to the local climate zone (LCZ) classification, even in areas with artificial structures, the highest and mean radiant temperatures were observed in LCZ 2 and 3. In Seoul metropolitan area, the residential areas of LCZ 2 and 3, which were built 30 to 40 years ago, have very high heat stress. They have recently been changed to LCZ 4 and 6 through urban redevelopment and regeneration. Through such urban surface management, it is expected that high heat stress in Seoul will be relieved by 1–3 °C.
... Around noon, T mrt_SM clearly showed lower values than those of T mrt_TM . This phenomenon was already mentioned as a shortcoming of T mrt_SM by Kántor et al. (2014) and Vanos et al. (2021). The reason is that the amounts of K b coming from the cardinal (east and west) directions will be minimum around noon (Fig. 4a). ...
Article
The mean radiant temperature (Tmrt) is the most important meteorological factor influencing human thermal comfort in urban areas. Numerous methods have been implemented for estimating Tmrt using measured radiometer or thermometer data, and exhibit different levels of accuracy. This study presents a simple technique based on the traditional method (Tmrt_TM) to estimate Tmrt by utilizing measured radiation data from the radiometers. The estimated Tmrt values from the six-directional method (Tmrt_SM) and two black globe thermometer methods (Tmrt_BG and Tmrt_BGv) at two stations (sky view factor 0.69 and 0.94) in Jeju, Republic of Korea, for 8 days (5 sunny days, 3 (semi-) cloudy days) in spring and summer were used to validate the Tmrt_TM. The results showed that the mean differences between Tmrt_TM and Tmrt_SM were within the required accuracy for comfort in ISO 7726 (± 2 ℃) on sunny days and were reduced to 0.1-0.3 ℃ in high Tmrt conditions such as clear summer days. The Tmrt_BG in most sunny and semi-cloudy days and Tmrt_BGv on all days resulted in large mean differences from the Tmrt_TM that exceeded the required accuracy for thermal stress in ISO 7726 (± 5 ℃). Therefore, both black globe thermometer methods should be used carefully when estimating Tmrt, especially during sunny days. The correlations between Tmrt_TM and Tmrt_SM were highly significant, 0.93 on all days (p = 0.01). The newly developed regression equations between Tmrt_TM and Tmrt_SM could reduce mean differences within 0.5 ℃ for all days, and their r2 values exceeded 0.87. Therefore, the simple Tmrt_TM technique can be used for Tmrt estimation in human thermal comfort studies.
... In the past several decades, the influence of solar irradiance on human outdoor thermal comfort has been explored from various perspectives. Models have been developed to predict the MRT and human outdoor thermal comfort levels, including measurement-based methods such as the six-directional method and simulation-based methods like SOLWEIG, RayMan, and the 3D numerical process [17][18][19][20][21]. The factors influencing outdoor thermal comfort, such as clouds, trees, and building morphologies, have also been explored based on these models [22][23][24]. ...
Article
The effects of solar radiation play an important role in human thermal comfort. When predicting the shortwave solar thermal effect through windows on indoor occupants, the spectra of solar irradiance, window transmittance, and skin absorptance must be considered. This work proposes a spectrally-resolved method for predicting this effect on occupants facing windows in the near-window zone. The vertical and horizontal penetration of direct solar irradiance is also characterized. In this work, we quantify the differences in resultant thermal comfort estimations between the spectrally-resolved and conventional constant-value methods through a series of simulated conditions on different days of the year and at different times of day, as well as with various window orientations and sky conditions. Through numerical analysis, we investigate the effects of and interactions among the various parameters and demonstrate situations in which the spectrally-resolved method is necessary. By understanding the necessity of the spectrally-resolved method and the influence of variations in spectral and energy intensities, we are able to make preliminary judgments regarding when the spectrally-resolved method is essential to making relatively accurate predictions of indoor thermal comfort in the near-window zone. This research provides a new and fundamental numerical method that can be used to take the spectral characteristics of solar energy, windows, and human skin into account for more accurate user thermal comfort analyses in the near-window zone.
... Radiation is a decisive parameter in the study of outdoor thermal comfort (Brown and Gillespie 1995;Thorsson et al. 2007;Kántor et al. 2014;Lee et al. 2014;Manavvi and Rajasekar 2020); however, it remains the most elusive element of the landscape (Brown and Gillespie 1995). ...
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Sensing and measuring meteorological and physiological parameters of humans, animals, and plants are necessary to understand the complex interactions that occur between atmospheric processes and the health of the living organisms. Advanced sensing technologies have provided both meteorological and biological data across increasingly vast spatial, spectral, temporal, and thematic scales. Information and communication technologies have reduced barriers to data dissemination, enabling the circulation of information across different jurisdictions and disciplines. Due to the advancement and rapid dissemination of these technologies, a review of the opportunities for sensing the health effects of weather and climate change is necessary. This paper provides such an overview by focusing on existing and emerging technologies and their opportunities and challenges for studying the health effects of weather and climate change on humans, animals, and plants.
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During daylight hours, the mean radiant temperature Tmrt$T_{\text{mrt}}$ is one of the most important meteorological parameters to analyse heat stress for humans. This study conducts a spatio-temporal analysis of Tmrt$T_{\text{mrt}}$ for a summer period in 2018 for the city of Berlin, Germany. To this end, the mesoscale climate model COSMO-CLM (CCLM) is coupled with the urban Double Canyon Effect Parameterization scheme with a building energy model (DCEP–BEM) to derive Tmrt$T_{\text{mrt}}$. This coupled model system CCLM/DCEP–BEM enables a dynamic calculation of Tmrt$T_{\text{mrt}}$ for the microscale urban street canyons using a mesoscale model. To bring a more accurate comparison, a two-step approach is applied to assess the radiative fluxes and Tmrt$T_{\text{mrt}}$ from CCLM/DCEP–BEM. The radiation model SOLWEIG is first validated against measurement and then used to evaluate the DCEP–BEM model. Overall good agreement in Tmrt$T_{\text{mrt}}$ is found between CCLM/DCEP–BEM and SOLWEIG (R2=0.96$\text{R}^2 =\nobreak 0.96$). Nighttime Tmrt$T_{\text{mrt}}$ simulated with CCLM/DCEP–BEM is higher than that with SOLWEIG (MBE=2.9K$\text{MBE}=\nobreak 2.9\,\text{K}$), yet closer to measurements. Tmrt$T_{\text{mrt}}$ during the afternoon hours modeled with CCLM/DCEP–BEM is underestimated compared to SOLWEIG (MBE=-3.1K$\text{MBE}=\nobreak -3.1\,\text{K}$). Further, excluding vegetation, higher values for nighttime Tmrt$T_{\text{mrt}}$ are found in the densely built-up city center than in the suburbs with more open structures, while the city center has lower values for Tmrt$T_{\text{mrt}}$ during midday. This study provides a reliable representation of Tmrt$T_{\text{mrt}}$ in a mesoscale model and would be beneficial for future implementation of human-biometeorological variables such as the Universal Thermal Climate Index or Physiological Equivalent Temperature. These quantities are calculated using Tmrt$T_{\text{mrt}}$.
Article
Mean Radiant Temperature (Tmrt) is a crucial indicator to assess urban radiant and thermal environments. In this study, Tmrt derived from the globe thermometer method and three simulation models (SOLWEIG, RayMan, and ENVI-met) were analyzed and modified based on the standard six-directional method (Tmrt(six)). Performances of the techniques were compared for two contrasting seasons, summer and winter, and at sites with different degrees of openness. The accuracies of each method were assessed via patterns in time series, coefficient of determination, root mean square error, and Willmott index of agreement. Results showed that globe thermometer method was more suitable for estimating Tmrt in summer than winter, and it showed better performance in more open spaces. The simulation inaccuracies were mainly reflected in winter. Comparatively, SOLWEIG exhibited the best performance in correlation and discrepancy; RayMan presented an advantage in describing the trend consistency of Tmrt than ENVI-met; ENVI-met simulated Tmrt closer to Tmrt(six) than RayMan. Principle-based causes of the techniques’ inaccuracies were analyzed. Correlation and cluster analyses were applied for the globe thermometer method, and global radiation showed the strongest correlation and nearest distance with globe temperature, followed by air temperature. Sensitivity and components analyses were utilized for the simulation models involving isotropic and anisotropic issues considering direct and diffuse radiation, solar position, and surrounding environment. Based on the characteristics of different techniques, multiple nonlinear (introducing equivalent globe temperature) and unary linear regressions were utilized to modify globe thermometer and simulation results, respectively. Both modifications significantly improved Tmrt determination accuracies.
Thesis
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The present work addresses the contribution of street design toward the development of a comfortable microclimate at street level for pedestrians. The work is design-oriented and seeks to provide a quantitative knowledge readily interpretable from the perspective of urban designers. Street geometries are investigated, including various aspect ratios, i.e. height-to-width ratio H/W, solar orientations and a number of design details. First, symmetrical urban canyons with H/W equal to 0.5, 1, 2 and 4 and for different solar orientations (i.e. E-W, N-S, NE-SW and NW-SE) are studied. Secondly, asymmetrical profiles with different openness to the sky are investigated together with the role of ar-chitectural details such as galleries, horizontal overhangs on façades and rows of trees, considered as possible ways to improve the outdoor thermal comfort further in the summertime. Moreover, the analysis focuses on the local differences in the thermal sen-sation across the street, i.e. street centre vs. street sides, which influence the frequenta-tion of the street. A special emphasis is placed on a human bio-meteorological assess-ment of these microclimates by using the thermal index PET, Physiologically Equiva-lent Temperature. The investigation is carried out by using the three-dimensional numerical model ENVI-met 3.0, which simulates the microclimatic changes within urban environments in a high spatial and temporal resolution. Model calculations are run for typical summer conditions in Ghardaia, Algeria (32.40° N, 3.80° E), a subtropical region characterized by a hot and dry climate. Additionally, short-term field measurements are carried out in Freiburg, Germany, and in Ghardaia (Beni-Isguen), Algeria, during the summer 2003. In the former site, the microclimate changes due to geometry and the effects of the street irradiation patterns on the heat gained by a human body are dealt with in detail. In the latter site, a quantitative evaluation of the thermal effectiveness of existing architectures in a hot-dry climate is the focus. The simulations show that the thermal comfort is difficult to reach passively in such an extreme climate but improvements are possible by means of appropriate geometrical forms. All investigated urban describers are found to influence the final thermal sensa-tion. Contrasting patterns in the comfort situation are found between shallow and deep urban streets as well as between the various orientations studied. Wide streets (H/W  0.5) are highly uncomfortable for both orientations. Yet, N-S ori-entation shows some advantage over E-W orientation, and this benefit increases as the aspect ratio increases. Explicitly, this is expressed by a shorter period of heat stress and lower PET maxima. Moreover, heat stress can effectively be mitigated if galleries, trees or textured façades are appropriately combined with the aspect ratio and solar orientation. A comparison of all case studies reveals that the duration, the period of day of extreme heat stress, as well as the spatial distribution of PET across the canyon depend strongly on aspect ratio and on street orientation. This is crucial since this will directly influence the design choices in relation to street usage, e.g. streets exclusively planned for pedes-trian use or including motor traffic, and also the time of frequentation of urban spaces. The simulations as well as the on-site measurements also confirmed the dominant role of the radiation fluxes expressed by the mean radiant temperature Tmrt for summer con-ditions. The human body absorbs energy from the irradiated surrounding surfaces and from a direct exposure of his body. This fact points out the necessity of shading as a main strategy for keeping the street area in comfort range. Air temperature and wind speed are secondary factors with respect to comfort as these vary less with urban ge-ometry changes in comparison to Tmrt. The issue of solar access indoors has been briefly discussed as an additional criterion in designing the street by including winter needs and draw attention on the double role of the street, i.e. as interface of urban and architectural scales. Design recommendations are also outlined for designing a comfortable urban street. Methodologically, ENVI-met revealed to be a good tool for the prognosis of the urban microclimate changes within urban areas, and also in the assessment of outdoor comfort through a satisfactory estimation of the mean radiant temperature. A number of eventual refinements of the model are mentioned to improve its accuracy. The work also highlights the necessity of more on-site measurements and more subjec-tive votes of people for validating the simulations results and in order to strengthen a practice-oriented knowledge about comfort in urban areas.
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Increasing heat will be a significant problem for Central European cities in the future. Shading devices are discussed as a method to mitigate heat stress on citizens. To analyze the physical processes, which are characteristic of shading in terms of urban human-biometeorology, experimental investigations on the thermal effects of shading by a building and shading by tree canopies were conducted in Freiburg (Southwest Germany) during typical Central European summer weather. Urban human-biometeorology stands for the variables air temperature T a, mean radiant temperature T mrt, and physiologically equivalent temperature PET, that is the human-biometeorological concept to assess the thermal environment which was applied. The measuring setup consists of specific human-biometeorological stations, which enable the direct or indirect determination of T a, T mrt, and PET. With respect to both shading devices, the T a reduction did not exceed 2°C, while PET as a measure for human heat stress was lowered by two thermal sensation steps according to the ASHRAE scale. As T mrt has the role of a key variable for outdoor thermal comfort during Central European summer weather, all radiant flux densities relevant to the determination of T mrt were directly measured and analyzed in detail. The results show the crucial significance of the horizontal radiant flux densities for T mrt and consequently PET.
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This study examines the effects of single trees and small clusters of trees on the bioclimate of a city. Investigations of the thermal environment and air quality of the urban climate were carried out on September 19 and September 29,2000, at Fahnenbergplatz, in the northem city center of Freiburg in southwest Germany. The study area, approximately 1,700 m2 , contains 12 horsechestnut trees (Aesculus hippocastanum) of different ages and sizes. The positive effect of trees on the thermal environment and air quality component was confirmed by the study. In particular, the mean radiation temperature Tmn , and the human biometeorological thermal index known as the physiological equivalent temperature (PET) showed distinct differences between areas with trees and areas without trees, despite the small size of the investigation area. A high reduction potential for nitrogen oxides and ozone was found inside the tree crowns, but outside the crowns there was no measurable reduction. The most important result regarding volatile organic compounds (VOCs) was the absence of terpene emissions [rom the horsechestnuts. Similarly, no isoprene emissions from horsechestnuts were found. Therefore, horsechestnut trees have a very small ozoneforming potential.
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Regional climate models predict an intensification of extreme heat waves in Central Europe. Against this background, the significance of human-biometeorologically orientated urban planning strategies is increasing by which the impairment of thermal comfort for people in cities in the future can be minimised. Such strategies require quantitative information on factors determining human thermal comfort within different urban quarters. With respect to these problems, the joint research project KLIMES funded by the German Federal Ministry of Education and Research was initiated. Its methodical approaches and objectives are presented in this article. One part of KLIMES are experimental investigations on human thermal comfort within different urban street canyons, whose variable arrangement generally characterises urban quarters. The investigations are conducted in Freiburg (SW Germany). The experimental design and the concept to analyse the measured data related to the objectives of KLIMES are exemplarily explained based on investigations in the "Rieselfeld" quarter on a typical summer day in 2007. The internationally well-known physiologically equivalent temperature PET is used as thermal index to quantify the perception of the thermal conditions by a collective of people within cities. During typical summer weather in Central Europe, PET is strongly influenced by the radiation heat, which is parameterised by the mean radiant temperature . Therefore, the short- and long-wave radiation flux densities from the three-dimensional surroundings of a standardised standing person representing mean properties of a collective of people in cities are analysed in detail. For the specific conditions at the stationary site "Rieselfeld" (NW-SE oriented urban street canyon, H/W = 0.49, SVF = 0.51, SW oriented sidewalk), the contribution of the total long-wave radiation flux density absorbed by a standing person to increased during the day from about 70% in the morning to about 90% in the evening before sunset. German Regionale Klimamodelle prognostizieren für Mitteleuropa eine Intensivierung von extremen Hitzeperioden im Sommer. Vor diesem Hintergrund steigt die Bedeutung von human-biometeorologisch orientierten Strategien in der Stadtplanung deutlich an, mit denen die zukünftige Beeinträchtigung des thermischen Komforts für Menschen in der Stadt möglichst gering gehalten werden kann. Solche Strategien erfordern quantitative Angaben zu den Einflussfaktoren auf den thermischen Komfort in unterschiedlichen Stadtquartieren. Hier setzt das BMBF Verbundprojekt KLIMES an, dessen methodisches Konzept und Zielsetzungen vorgestellt werden. Teil von KLIMES sind experimentelle Untersuchungen zum thermischen Komfort in verschiedenen Straßenschluchten, deren variable Anordnung generell Stadtquartiere charakterisiert. Diese Untersuchungen werden in Freiburg (SW Deutschland) durchgeführt. Das messtechnische Versuchsdesign und die Ansätze zur problemspezifischen Datenanalyse werden exemplarisch anhand von experimentellen Untersuchungen im Stadtteil "Rieselfeld" an einem typischen Sommertag im Jahr 2007 erklärt. Dabei wird für die Quantifizierung der Wahrnehmung der thermischen Umgebungsbedingungen durch ein Kollektiv von Stadtbewohnern die international häufig eingesetzte physiologisch äquivalente Temperatur PET als thermischer Bewertungsindex verwendet. Sie wird bei typischem Sommerwetter in Mitteleuropa maßgeblich von der Strahlungswärme beeinflusst, die sich über die mittlere Strahlungstemperatur Tmrt parametrisieren lässt. Aufgrund ihrer besonderen Bedeutung werden die kurz- und langwelligen Strahlungs-flussdichten aus der dreidimensionalen Umgebung eines standardisierten stehenden Menschen detailliert analysiert. Er repräsentiert mittlere Eigenschaften eines Kollektivs von Stadtbewohnern. Für die spezifischen Bedingungen am stationären Standort "Rieselfeld" (NW-SE orientierte Straßenschlucht, H/W = 0.49, SVF 0.51, nach SW orientierter Bürgersteig) stieg am typischen Sommertag der Anteil der gesamten, vom stehenden Menschen absorbierten langwelligen Strahlungsflussdichte an Tmrt von ca. 70% am Vormittag auf ca. 90% am Abend vor Sonnenuntergang an.
Article
This work investigates how to reduce, by appropriate urban design, air temperature at the street level and to improve pedestrian thermal conditions in summer. The case study is a street in Athens with low aspect ratio H/W (H: building height; W: street width), low trees canopy coverage level, and high traffic. Urban variables for design are trees canopy coverage area ratio, traffic load, walls surfaces albedo, and H/W. Their thermal effect is separately and altogether estimated by applying the microclimatic Green-CTTC model whereas thermal stress is assessed using the Physiological Equivalent Temperature (PET) index. The studied day is relatively hot (36.5 °C at midday) with eight hours of heat stress (two and six hours of extreme and strong heat stress, respectively) at street level. Acceptable near-to-discomfort limits for local pedestrians are considered whereas PET classification heat stress levels are adjusted to local conditions by applying a correction equation to obtained PET values. Results show that the examined scenarios are associated with air temperature decrease and improvement of thermal comfort in the shade, especially during the day's hottest hours. The trees thermal effect is the dominant factor followed by the increase of H/W and of the walls surfaces albedo. All the studied design scenarios are found able to reduce the number of heat stress hours but the trees canopy coverage area ratio increase scenario was found by itself able to be associated only with moderate heat stress for local pedestrians. Alternative local smart controls for thermal comfort (SCAT) options are also discussed.
Data
Increasing heat will be a significant problem for Central European cities in the future. Shading devices are discussed as a method to mitigate heat stress on citizens. To analyze the physical processes, which are characteristic of shading in terms of urban human-biometeorology, experimental investigations on the thermal effects of shading by a building and shading by tree canopies were conducted in Freiburg (Southwest Germany) during typical Central European summer weather. Urban human-biometeorology stands for the variables air temperature íµí±‡ íµí±Ž , mean radiant temperature íµí±‡ mrt , and physiologically equivalent temperature PET, that is the human-biometeorological concept to assess the thermal environment which was applied. The measuring setup consists of specific human-biometeorological stations, which enable the direct or indirect determination of íµí±‡ íµí±Ž , íµí±‡ mrt , and PET. With respect to both shading devices, the íµí±‡ íµí±Ž reduction did not exceed 2 ∘ C, while PET as a measure for human heat stress was lowered by two thermal sensation steps according to the ASHRAE scale. As íµí±‡ mrt has the role of a key variable for outdoor thermal comfort during Central European summer weather, all radiant flux densities relevant to the determination of íµí±‡ mrt were directly measured and analyzed in detail. The results show the crucial significance of the horizontal radiant flux densities for íµí±‡ mrt and consequently PET.
Article
The present study addresses the issue of outdoor thermal comfort in a hot and dry climate in relation to urban geometry. This experimental work, conducted in an old desert city, aims to provide some quantitative knowledge on the effectiveness of traditional design forms in ensuring a comfortable thermal environment outdoors under extreme summer conditions. The study focused on the role of the geometry of urban canyons. Air temperature, air humidity and wind speed were measured during summer 2003 in various urban streets in the old Saharan city of Beni-Isguen, Algeria (32.40 degrees N). The short-wave and long-wave radiation fluxes received by a human body from the 3D surroundings were also measured in order to allow an accurate calculation of the heat gained by a pedestrian. Bio-meteorological methodology was used and thermal comfort was expressed by means of the physiologically equivalent temperature (PET) index. The results show that the heat stress in a hot-dry climate is very high in unobstructed locations in contrast to sheltered urban sites. The vertical street profile is of prime importance in the resulting thermal sensation. Building materials were also found to play a decisive role. Deep streets together with high thermal capacity materials mitigate the heat stress in the daytime. The high and heavy walls provide more shading and more heat storage, leading to lower surfaces temperatures. Hence, a human body absorbs less short-wave radiation owing to reduced direct exposure, and also less radiant heat from the surrounding environment is absorbed by the body. In contrast, air temperature and air humidity show little dependence on the urban geometry. Therefore, these factors are less relevant indicators for outdoor thermal comfort in the summertime.
Article
This study deals with a current problem of urban human-biometeorology on the micro-scale, which becomes more important due to the future increase of severe summer heat in Central Europe. The impact of street design parameters on the thermal comfort of citizens is analysed in an experimental way for typical summer conditions in Central Europe. The investigation is focused on the behaviour of mean radiant temperature and physiologically equivalent temperature PET as the most important human-biometeorological variables for thermal comfort during these atmospheric conditions. To get quantitative results on how they depend on small-scale characteristics of urban street canyons, an investigation design is applied which is based on measurements of relevant meteorological variables – like air temperature – by specific humanbiometeorological measuring systems. They were conducted in selected street canyons within different urban quarters of Freiburg, the warmest city in Germany, from 2007–2009. and PET were calculated from the measured meteorological variables by well-tested approaches. The geometry of urban street canyons is characterised by (i) the sky view factor SVF determined from fish-eye photos, (ii) the ratio of building height to street width , (iii) the orientation to the sun, and (iv) the fraction of ctc (coverage by the street tree canopy). To eliminate the influence of slightly different weather conditions even on typical summer days, the results are not presented in form of absolute values for the human-biometeorological variables, but in form of ratios for the measured radiative flux densities and in form of differences for the measured and calculated temperatures. As the results for and PET should primarily quantify universal patterns of the impact of street design parameters on human thermal comfort, they are only presented as mean values for the period 10–16 CET. The main results obtained from different analyses are: (i) SVF for the southern half of the upper hemisphere (SVF) is more suitable to characterise the sites with respect to the thermal perception of citizens than SVF for the whole upper hemisphere (SVF), (ii) in contrast to wide E-W oriented street canyons, narrow E-W oriented street canyons have larger spatial differences in , and PET, (iii) with respect to the orientation, these differences are larger in E-W than in N-S oriented street canyons, and (iv) an increase of ctc by 10 % leads to a decrease of by only 0.2 °C, but to a reduction of by 3.6 °C and of PET by 1.4 °C. German Diese Studie beschäftigt sich mit einer aktuellen Fragestellung aus der urbanen Human-Biometeorologie auf der Mikroskala, die durch die zukünftige Intensivierung von extremer Sommerhitze in Mitteleuropa an Bedeutung gewinnt. Über einen experimentellen Ansatz werden die Einflüsse des Straßendesigns auf den thermischen Komfort von Stadtbewohnern für typische Sommerbedingungen in Mitteleuropa analysiert. Die Untersuchung bezieht sich auf das Verhalten von mittlerer Strahlungstemperatur T mrt und physiologisch äquivalenter Temperatur PET als diejenigen human-biometeorologischen Variablen, die während dieser atmosphärischen Bedingungen die größte Bedeutung in Bezug auf den thermischen Komfort haben. Um quantitative Ergebnisse über ihre Abhängigkeit von Kennzeichen von Straßenschluchten zu erzielen, wird ein Untersuchungsdesign angewendet, das auf Messungen von relevanten meteorologischen Parametern wie die Lufttemperatur T a beruht. Dafür wurden spezielle human-biometeorologische Messsysteme eingesetzt. Die Messungen erfolgten in ausgewählten Straßenschluchten innerhalb von bestimmten Stadtquartieren in Freiburg, der wärmsten Stadt Deutschlands, im Zeitraum 2007 bis 2009. T mrt und PET wurden aus den gemessenen meteorologischen Parametern über erprobte Verfahren berechnet. Als kleinräumige Kennzeichen von Straßenschluchten werden verwendet: (i) Sky View Factor SVF, abgeleitet aus Fish-eye Fotos, (ii) Verhältnis von Höhe H der Randbebauung zur Straßenbreite W, (iii) Orientierung zur Sonne und (iv) Anteil von ctc (der Abschattung durch den Kronenschirm von Straßenbäumen). Um den Einfluss der Variabilität von leicht unterschiedlichen Wetterbedingungen auch an typischen sommerlichen Strahlungstagen zu eliminieren, werden die Resultate für die human-biometeorologischen Variablen nicht in Form von Absolutwerten, sondern bei den Strahlungsflussdichten als Quotienten und bei den gemessenen sowie berechneten Temperaturen als Differenzen präasentiert. Da die Ergebnisse für T mrt und PET primär die universellen Muster quantifizieren sollen, die die Einflüsse von kleinräumigem Straßendesign auf den thermischen Komfort kennzeichnen, werden sie als Mittelwerte für den Zeitraum 10 bis 16 Uhr MEZ präsentiert. Die wesentlichen Resultate aus den verschiedenen Analysen sind: (i) im Hinblick auf das thermische Empfinden von Stadtbewohnern ist SVF für die südliche Hälfte der oberen Hemisphäre (SVF90–270) besser geeignet als SVF bezogen auf die gesamte obere Hemisphäre (SVF1–360), (ii) im Gegensatz zu breiten E-W orientierten Straßenschluchten weisen enge E-W orientierte Straßenschluchten ausgeprägtere räumliche Differenzen von Ta, T mrt und PET auf, (iii) diese Differenzen treten bei E-W orientierten Straßenschluchten deutlicher als bei N-S orientierten Straßenschluchten hervor, und (iv) eine Zunahme von ctc um 10 % hat bei T a eine Abnahme von nur um 0.2 C zur Folge, während sie bei T mrt 3.6 °C und bei PET 1.4 °C beträgt.