Human thermal comfort in summer within an urban street canyon in

Transcription

Meteorologische Zeitschrift, Vol. 17, No. 3, 241-250 (June 2008)
c by Gebrüder Borntraeger 2008
Article
Human thermal comfort in summer within an urban street
canyon in Central Europe
H ELMUT M AYER∗ , J UTTA H OLST, PAUL D OSTAL , F LORIAN I MBERY and D IRK S CHINDLER
Meteorological Institute, Albert-Ludwigs-University of Freiburg, Germany
(Manuscript received October 10, 2007; in revised form January 11, 2008; accepted January 18, 2008)
Abstract
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 Tmrt . 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 Tmrt increased during the day from about 70% in the morning to about 90% in the evening
before sunset.
Zusammenfassung
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 Strahlungsflussdichten 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.
1
Introduction
The thermal climate of cities depends on their location in a specific climate zone as well as topographic
∗ Corresponding
author: Helmut Mayer, Meteorological Institute,
Albert-Ludwigs-University of Freiburg, Werthmannstraße 10, 79085
Freiburg, Germany, e-mail: [email protected]
DOI: 10.1127/0941-2948/2008/0285
and orographic factors. These background conditions
are modified by energetic and dynamic characteristics
of cities, which lead to an elevated thermal level. Compared to the rural surroundings, it is well known as urban heat island UHI. This typical phenomenon of the
urban climate is analysed by numerous investigations
worldwide (e.g. A RNFIELD, 2003; O KE, 2006; E M -
0941-2948/2008/0285 $ 4.50
c Gebrüder Borntraeger, Berlin, Stuttgart 2008
242
H. Mayer et al.: Human thermal comfort in summer
MANUEL and F ERNANDO , 2007). However, there are
only a few studies focussed on the assessment of the
thermal component of the urban climate related to people in cities, i.e. in a human-biometeorologically significant way, although thermal comfort strongly controls their efficiency, well-being and health (M AYER,
1999b; M ERTENS, 1999; H ÖPPE, 2002; T HORSSON
et al., 2004; A LI -T OUDERT et al., 2005; K NEZ and
T HORSSON, 2006; A LI -T OUDERT and M AYER, 2006,
2007a, 2007b). During extreme heat waves like in Central Europe in 2003 (R EBETEZ et al., 2006; S CHINDLER
and M AYER, 2007), thermal comfort of people in cities
is particularly affected by the interaction between extreme weather at a regional scale and the UHI at a local
scale. It induces heat stress for people in cities and the
heat-dependent mortality increases dramatically like in
France in summer 2003 (PASCAL et al., 2006).
Results of regional climate models predict for Central Europe that extreme heat waves will be more frequent and intense as well as will last longer (M EEHL
and T EBALDI, 2004). Against this background, methods
of city planning, which are aimed for the optimisation
of human thermal comfort within cities, become more
and more important (E LIASSON, 2000; S VENSSON and
E LIASSON, 2002; M ILLS, 2006). They have to take into
account the limited area of action due to the existing urban structures in central European cities. One important
requirement for the success of such planning methods
is the close collaboration between the disciplines being
engaged in the maintenance of human thermal comfort
in cities.
The joint research project KLIMES meets this demand. As a detailed website is available (www.klimesbmbf.de), the concept of KLIMES will be introduced in
this article only in form of a brief overview. The main
objective of this study is to explain the experimental approach on human thermal comfort in summer conducted
in KLIMES by a specific case study in an urban quarter
in Freiburg, SW Germany.
2
Joint research project KLIMES
The joint research project "Development of strategies
to mitigate enhanced heat stress in urban quarters due
to regional climate change in Central Europe", abbreviated by KLIMES, is carried out by four research groups
within the scope of the research initiative “klimazwei”
funded by the German Federal Ministry of Education
and Research (BMBF) from 2006 to 2009. Based on
an overview on the state-of-the-art in the planningrelated urban human-biometeorology and identification
of deficits, working hypotheses were derived, which lead
to the general aims of KLIMES: (i) update of humanbiometeorological methods available to quantify the perception of heat by people in cities (outdoors and indoors) under current and future climate conditions, (ii)
Meteorol. Z., 17, 2008
quantification of the perception of human thermal comfort (discomfort) in different urban quarters (outdoors
and indoors) during extreme summer heat, (iii) development and verification of urbanistic strategies based on
human-biometeorological results to mitigate the negative impacts of climate trends and extreme weather on
people in different urban quarters (optimisation of human thermal comfort under consideration of objectives
of environmental protection, e.g. abandonment of electric air conditioning), and (iv) synthesis of all results in a
guideline for urban planning orientated to the challenges
due to regional climate change in Central Europe.
To achieve the aims, a coordinated combination of
different methods is applied in KLIMES: (i) experimental investigations on the perception of heat by people in different urban quarters in Freiburg (SW Germany), which is the warmest city in Germany, (ii) interviews with people about their current perception of
heat under consideration of their thermal history and
their use of open spaces (see also N IKOLOPOULOU et
al., 2001; K NEZ and T HORSSON, 2006; K ATZSCHNER
et al. 2007; E LIASSON et al., 2007), (iii) model-based
simulations of human thermal comfort in different urban
quarters (outdoors and indoors) under current and future
thermal conditions using the stationary model ENVImet (B RUSE and F LEER, 1998) and the unsteady model
BOTworld (B RUSE, 2007), (iv) development of humanbiometeorologically based strategies for urban planning
to optimise human thermal comfort outdoors and indoors against the background of predictions on heat in
the future, and (v) permanent dialogue with the planning
practice and the public.
3 Methodology
Within KLIMES, experimental investigations on human
thermal comfort are carried out in urban street canyons
within different urban quarters in Freiburg, SW Germany. The experimental design as well as the way of
data processing and analyses is explained exemplarily
for the “Rieselfeld” quarter. They were also applied for
the other 14 quarters in Freiburg investigated in summer
2007 in a sequential order.
The general method to assess the thermal environment in a human-biometeorologically significant way
is described in Fig. 1. In this study, the thermophysiological assessment index PET (physiologically equivalent temperature) is used to quantify the level of thermal comfort. PET is derived from the human energy balance model MEMI (M AYER and H ÖPPE, 1987). In the
meantime, PET has turned out to be a widely used thermal index (Thorsson et al., 2004; J OHANSSON and E M MANUEL , 2006; A LI -T OUDERT and M AYER , 2007b;
E MMANUEL et al., 2007; O LIVEIRA and A NDRADE,
2007). To determine PET, the meteorological variables
243
Figure 1: Scheme for the human-biometeorological assessment of
the thermal environment (according to M AYER, 2006).
air temperature, vapour pressure, wind speed and mean
radiant temperature as a measure of the absorbed radiation heat are necessary, whereas characteristics of human beings are often set constant, if thermal stress level
at different sites should be compared. The procedure
to determine PET as output of the MEMI model is described by M AYER and H ÖPPE (1987) as well as H ÖPPE
(1999) in detail. PET provides a measure for the perception of heat by a collective of city dwellers, which
is represented by standardised standing person. According to human-biometeorological methods, the reference
height for PET is 1.1 m a.g.l. Therefore, the meteorological variables necessary to determine PET should be
measured or simulated in the same height or related to
it, if meteorological variables are available from screen
level in 2 m a.g.l.
Regarding the demands of city planning, the single
KLIMES sites in Freiburg have been carefully selected
by all KLIMES research groups. At each KLIMES
site, a stationary station (Fig. 2) and a mobile humanbiometeorological station were installed to measure the
required meteorological variables. The instrumentation
of both stations is described in Table 1. As the mean
radiant temperature Tmrt was calculated on the basis of
measured short- and longwave radiation flux densities
from the three-dimensional surroundings of a standing
person according to H ÖPPE (1992) and T HORSSON et
al. (2007), both types of human-biometeorological stations include appropriate systems to measure the incoming and outgoing radiation flux densities in vertical direction as well as the radiation flux densities from the
four main horizontal directions.
The stationary measurements were continuously
conducted on summer days between 9 a.m. and 12 p.m.
CET. They were complemented by mobile measurements carried out in a sequential order at four sites near
the stationary site, but with mainly different orientations
to the sun. One profile route took about 45 minutes, as
all measurements were performed manually.
Figure 2: Stationary human-biometeorological measurement unit
applied in the research project KLIMES.
Figure 3: View from SE to the stationary site in the “Rieselfeld”
quarter in Freiburg.
Both types of sites were well documented by general
photos and fish-eye photos to determine the sky view
factor SVF in five directions (upwards and to the four
horizontal main directions E, S, W and N). To calculate the H/W value, building height H and street width
W were measured for each investigated street canyon.
To link the thermal conditions between outdoors and
indoors, measurements of air temperature and relative
humidity were conducted during the outdoor measurements in selected S oriented rooms adjacent to the stationary sites.
Stationary and mobile human-biometeorological
measurements were carried out at five sites in the “Rieselfeld” quarter showing different aspects. They are located in a neighbourhood planned and built since the
nineties of the last century. It is characterised by mod-
244
Table 1: Instrumentation of the stationary and mobile human-biometeorological measurement units used in KLIMES.
meteorological variable
stationary
air temperature
Humicap HMP45D, Vaisala
Comp., 1.1 m a.g.l.
Pt 100, Friedrichs Comp., 2
m a.g.l.
vapour pressure
Humicap HMP45D, Vaisala
Comp., 1.1. m a.g.l.
via psychrometer principle,
Friedrichs Comp., 2 m a.g.l.
wind speed
3-D sonic anemometer
81000, Fa. Young, 1.2 m
a.g.l.
hot-wire anemeometer,
Dantec Comp., 2 m a.g.l.
short-wave radiation
CM3 (as part of CNR1),
Kipp & Zonen Comp., 1.1 m
a.g.l.
CM21, Kipp & Zonen
Comp., 1.1 m a.g.l.
long-wave radiation
CG3 (as part of CNR1), Kipp CG1, Kipp & Zonen Comp.,
& Zonen Comp., 1.1 m a.g.l. 1.1 m a.g.l.
data recording
CR3000 datalogger +
AM16/32 multiplexer,
Campbell Comp.
scan interval
averaging period
manually
5s
instantaneous
1 min
1 min
Figure 4: Hourly mean values of air temperature Ta , wind speed v,
mean radiant temperature Tmrt and physiologically equivalent temperature PET at the stationary site in the “Rieselfeld” quarter in
Freiburg, SW Germany, on a typical summer day.
ern, three- to four-storeyed block buildings. Some streets
are tree-lined and have small grass-covered front gardens. The stationary measurements were conducted in
the middle of a SW oriented sidewalk within a NW-SE
street canyon (H/W=0.49), which is separated by a 3 m
wide front garden from the house wall (Fig. 3).
4
mobile
Results
For the stationary site in the “Rieselfeld” quarter, the results in Fig. 4 show the thermophysiological conditions
on a hot summer day, which are typical of a SW oriented
sidewalk within a NW-SE urban street canyon in Central
Europe. Based on hourly mean values, the peak value
of air temperature Ta was 30.8 ◦ C, whereas the maximum of the mean radiant temperature Tmrt reached 63.4
◦ C. The relatively low wind speed v had its maximum
with about 1.2 m s−1 in the late afternoon. Values of
the vapour pressure VP were between 14 hPa in the late
afternoon and 18 hPa in the late morning (Fig. 13). As
known from previous investigations at comparative sites
(A LI -T OUDERT and M AYER, 2007a), the behaviour of
PET was similar to Tmrt . Therefore, the peak value of
PET with 44.5 ◦ C occurred at the same time interval
as for Tmrt . Neglecting adaptation and acclimatisation
effects and assuming a PET range between 18 and 22
◦ C for mean thermal comfort under the current climate
conditions in Central Europe, the PET results indicate a
distinct heat stress during the whole afternoon (PET >
40 ◦ C).
Due to the dominating influence of Tmrt on PET during hot summer days, detailed analyses of the radiation flux densities significant for Tmrt were performed.
The values of the short-wave radiation flux densities K
(Fig. 5) reflect the influence of the street canyon geometry, particularly those for the main horizontal directions.
While K coming from E reached its peak value about
10 a.m., K coming from W has a higher maximum at
about 5 p.m. The pattern of incoming K and K from S
were similar, but the incoming K showed values, which
characterises a typical summer day.
In contrast, the dependence of the long-wave radiation flux densities L (Fig. 6) on street geometry was less
pronounced. Outgoing L emitted from the horizontal
surface dominated throughout the whole day, whereas
the lowest values were measured for the atmospheric
245
Figure 5: Hourly mean values of short-wave radiation flux densities
K reaching a standing person from the three-dimensional environment at the stationary site in the “Rieselfeld” quarter in Freiburg,
SW Germany, on a typical summer day.
Figure 6: Hourly mean values of long-wave radiation flux densities
L reaching a standing person from the three-dimensional environment at the stationary site in the “Rieselfeld” quarter in Freiburg,
SW Germany, on a typical summer day.
counter radiation. L values from the four main horizontal directions differed slightly in the morning and
evening. Caused by the street geometry, these differences were more distinct in the afternoon.
As already mentioned, the human-biometeorological
assessment of the thermal environment within cities is
most frequently related to a standardised standing person, which represents mean properties of a collective of
people. Due to its position and the assumption that it is
rotationally symmetric, its projection fractions are 0.06
for vertical incoming and outgoing radiation flux densities as well as 0.22 for horizontal radiation flux densities
from the four main directions, respectively. As a consequence, both the horizontal short- and long-wave radiation flux densities absorbed by a standing person became
more important than the vertical ones (Figs. 7 and 8). For
Kabsorbed , the dependence on the horizontal directions is
maintained. The slight influences of the horizontal directions observed for L, however, are hardly identifiable
for Labsorbed . On average, the Labsorbed values from the
Figure 7: Hourly mean values of short-wave radiation flux densities
K from the three-dimensional environment absorbed by a standardised standing person at the stationary site in the “Rieselfeld” quarter
in Freiburg, SW Germany, on a typical summer day.
Figure 8: Hourly mean values of long-wave radiation flux densities
L from the three-dimensional environment absorbed by a standardised standing person at the stationary site in the “Rieselfeld” quarter
in Freiburg, SW Germany, on a typical summer day.
main horizontal directions were about 60 W m−2 higher
than those from vertical directions.
The question, whether the absorbed short- or longwave radiation flux densities are more significant all in
all for Tmrt , can be responded by adding all absorbed
short-wave and long-wave radiation flux densities from
the six directions considered to K* and L*, respectively:
6
K∗ =
∑ Kabsorbed,i
(4.1)
i=1
6
L∗ =
∑ Labsorbed,i
(4.2)
i=1
As expected from Figs. 7 and 8, the results in Fig. 9
show that the largest contribution to Tmrt came from L*,
whereas the portion of K* was clearly lower. For the
specific site conditions (NW-SE oriented urban street
canyon, H/W = 0.49, SVF = 0.51, SW oriented sidewalk), the contribution of the totally absorbed long-wave
radiation flux density L* to Tmrt increased during the
246
Figure 9: Hourly mean values of total short-wave radiation flux density K* and total long-wave radiation flux density L* from the threedimensional environment absorbed by a standardised standing person at the stationary site in the “Rieselfeld” quarter in Freiburg, SW
Germany, on a typical summer day.
Figure 11: Mean radiant temperature Tmrt determined for stationary
and mobile (measurement points MP1 to MP4) measurements in the
“Rieselfeld” quarter in Freiburg, SW Germany, on a typical summer
day.
Figure 10: Air temperature Ta recorded during stationary and mobile (measurement points MP1 to MP4) measurements in the “Rieselfeld” quarter in Freiburg, SW Germany, on a typical summer day.
Figure 12: Physiologically equivalent temperature PET calculated
for stationary and mobile (measurement points MP1 to MP4) measurements in the “Rieselfeld” quarter in Freiburg, SW Germany, on
a typical summer day.
day from about 70% in the morning to about 90% in
the evening before sunset.
To analyse the effect of street geometry on Ta , Fig. 10
additionally contains Ta values from mobile measurements conducted at sites with varying street geometry parameters. Neglecting the different temporal scales
(stationary site: hourly mean values, mobile measurement points MP: instantaneous values) and taking into
account the different heights of the Ta probes, the results did not show remarkable Ta differences between
the sites. In contrast to Ta , the temporal behaviour of Tmrt
was characterised by stronger variations between the
measurement sites, which were caused by the distinct influence of street geometry parameters on the radiant heat
absorbed by a standing person (Fig. 11). Due to the pronounced control of PET by the radiant heat and Tmrt , respectively, on typical summer days, PET also varied significantly between the measurement sites (Fig. 12). Particularly noticeable are the different results in the afternoon between opposite measurement sites (SW and NE
exposed) in the NW-SE street canyon. Mainly due to the
shaded direct solar radiation and its consequences for
the local radiation and heat flux densities (O KE, 1988),
a distinct heat stress was perceived by people at the SW
exposed sidewalk, whereas the PET values for the NE
exposed sidewalk indicated only a slight level of thermal discomfort.
As indoor conditions should be included in investigations on human thermal comfort, the magnitude of Ta
and VP differences between outdoor and indoor conditions can be exemplarily estimated from Fig. 13. Indoor
values of Ta and VP were measured in a SW exposed
room in the third floor with ajar windows during the
whole day. Ta and VP indoors were influenced by the
building design at the investigation site. It can be characterised by five year old, three-storeyed modern block
buildings. During the day, Ta values indoors were up to
4 ◦ C lower than outdoors, but during the night Ta seemed
to be higher indoors due to the heat storage within build-
Figure 13: Hourly mean values of air temperature Ta and vapour
pressure VP determined for outdoor and indoor conditions at the stationary site in the “Rieselfeld” quarter in Freiburg, SW Germany, on
a typical summer day.
ings. VP revealed a contrasting behaviour with higher
indoor values (up to 3.5 hPa) during the day.
5
Discussion
The joint research project KLIMES combines different subprojects conducted by urban climatology, environmental meteorology, geomatics and urban development. The main objective is the synthesis of all results in a guideline for urban planning in Central Europe, which is orientated to the challenges for people in
cities due to more frequent, extreme heat periods predicted by regional climate models. This heat is locally
strengthened by characteristics of complete cities and
urban quarters, respectively. Therefore, methods from
urban human-biometeorology (M AYER, 1993) are used
to obtain data on human thermal comfort in urban quarters, which have the potential for the implementation of
human-biometeorologically based strategies for urban
planning to optimise human thermal comfort against the
background of stronger and longer lasting regional heat
periods.
This study exemplifies the concept and data analyses of experimental investigations carried out on typical summer days in 2007 in different urban quarters in
Freiburg. Due to its location at the eastern border of the
N-S oriented upper Rhine plain, the climatic background
conditions of Freiburg are characterised by heat in summer. Therefore, Freiburg is identified as the warmest city
in Germany.
To quantify the perception of thermal comfort by
people in cities, the well-known physiologically equivalent temperature PET is applied in KLIMES as thermal
index. The procedure to analyse PET was exemplarily
explained for the “Rieselfeld” quarter in Freiburg, where
stationary and mobile measurements of relevant meteorological input variables were conducted on a typical
247
summer day by specific human-biometeorological measuring units. Though a general grading scale for PET,
which considers effects of adaptation and acclimatisation of city dwellers to the thermal environment, is not
available up to now, PET values above 40 ◦ C, which occurred during the whole afternoon, can be interpreted
as distinct heat stress. This behaviour is typical of comparable sites in urban street canyons in Central Europe
on cloudless summer days (A LI -T OUDERT and M AYER,
2007a). Among the meteorological variables necessary
to calculate PET, the strongest influence on PET was
exerted by the mean radiant temperature Tmrt . Under the
assumption, that the linear regression
PET = a0 + a1 · Tmrt
(5.1)
can be used to describe the relationship between PET
and Tmrt on cloudless summer days, the relatively high
values of the coefficient of determination R2 obtained in
this and similar studies (Table 2) indicate the clear dependence of PET on Tmrt for this specific weather conditions. The values for the regression coefficient a1 , which
varies between 0.5 and 0.6, show, that a Tmrt drop of 2 ◦ C
is necessary at least to achieve a reduction of PET in the
range of 1 ◦ C.
A comparison between Tmrt , which indicates the radiation heat absorbed by a standardised standing person,
and Ta , which informs about the level of sensible heat,
shows the dominating significance of the radiation heat
during the daylight hours on PET. The highest difference between Tmrt and Ta obtained in this study at the
stationary site with 32.9 ◦ C (between 2 and 3 p.m.) is in
the range between 32 and 34 ◦ C, which is known from
a few similar experimental investigations in Central Europe (A LI -T OUDERT and M AYER, 2007a).
Due to the explicit importance of Tmrt for PET on
typical summer days, the measured radiation flux densities from the three-dimensional surroundings receiving
the stationary site within the urban street canyon were
analysed in detail. They revealed patterns, which reflect
site characteristics like orientation of the street canyon,
orientation of the local measurement site to the sun or
H/W ratio. Despite their supposed simple form, real urban street canyons have a certain complexity, which is
caused by small-scale factors like extent and configuration of front gardens, street trees (M AYER, 1999b),
parked cars or design and colour of facades. Therefore,
the simulation of the three dimensional radiation flux
densities within urban street canyons in an adequate spatial and temporal resolution is not simple (A RNFIELD,
1990, 2003; K ANDA, 2006). An interesting approach to
simulate the radiation flux densities within regular building arrays has been proposed by K ANDA et al. (2005),
whereas the radiation scheme in the widely used RayMan model (M ATZARAKIS et al., 2007) does not meet
the demands up to now (T HORSSON et al., 2007), which
248
Table 2: Coefficients a0 and a1 from the linear regression (5.1) between PET and Tmrt (both in ◦ C) for typical summer days, R2 : coefficient
of determination.
site
Freiburg, NW-SE street
canyon, H/W = 0.49, SVF
= 0.51, SW oriented
sidewalk
Freiburg, E-W street
canyon, H/W = 1.0, SVF =
0.26, S oriented sidewalk
Freiburg, northern
downtown, measurement
points with different
orientations
Munich, NNE-SSW street
canyon,WNW oriented
sidewalk
Munich, northern
downtown, measurement
points with different
orientations
Munich, downtown,
measurement points with
different orientations
a0
9.6
a1
0.536
R2
0.868
reference
this study
7.3
0.614
0.919
7.0
0.585
0.893
ALI-TOUDERT
and MAYER
(2007a)
MAYER (1999b)
11.1
0.504
0.870
MAYER (1993)
9.0
0.561
0.958
MAYER (1996)
12.9
0.493
0.904
MAYER (1996)
follow from the influence of three-dimensional urban
structures on the radiation pattern within urban street
canyons.
In human-biometeorology, the use of Tmrt is related
to thermal indices describing the perception of heat by
a collective of people, which is represented by a standardised standing person, i.e. the absorbed short- and
long-wave radiation flux densities mainly determine the
human thermal comfort within urban structures on typical summer days. Due to the position of the standardised person, the absorbed long-wave radiation flux densities from the four horizontal directions dominated at
the stationary site in the “Rieselfeld” quarter in Freiburg
during the whole day. With respect to the site-specific,
absorbed short-wave radiation flux densities, only those
from E and W temporarily reached values in the magnitude of the absorbed long-wave radiation flux densities.
Adding the single absorbed short- and long-wave radiation flux densities to K* and L*, respectively, it becomes
obvious that the portion of L* to Tmrt is distinctly higher
(at least 70%) than that of K*. However, the interpretation of this result must include principles of radiation
and heat balances of differently exposed urban surfaces
(O KE, 1988; A RNFIELD, 1990, 2003), which refer to relationships between short- and long-wave radiation flux
densities.
The pronounced importance of absorbed radiation
flux densities from horizontal directions on the ther-
mal index PET represents the basis for the development
of planning concepts to mitigate the effects of extreme
heat given by the regional weather conditions on city
dwellers at the local scale of urban street canyons or
urban quarters (S AD DE A SSIS and BARROS F ROTA,
1999; S PAGNOLO and DE D EAR, 2003; S TATHOPOU LOS et al., 2004; J OHANSSON and E MMANUEL , 2006).
Approaches of human-biometeorologically orientated
strategies to maintain human thermal comfort under extreme heat were analysed in form of numerical simulations for urban street canyons in the subtropical climate
zone by A LI -T OUDERT et al., 2005 and A LI -T OUDERT
and M AYER (2006, 2007b). It must be discussed, how
their results are suitable for the application to urban
structures and climate conditions in Central Europe. A
further extension of simulation models on human thermal comfort should include indoor conditions besides
outdoors situations. Comparative experimental investigations outdoors and indoors, as exemplarily conducted
in the “Rieselfeld” quarter, provide results, which are
suited for model validation.
6 Conclusions
This study reports on experimental investigations on
human thermal comfort conducted on a typical summer day in 2007 within the framework of the joint research project KLIMES. The experimental investiga-
tions exemplarily explained for the “Rieselfeld” quarter in Freiburg have the character of point analyses. The
spatio-temporal distribution of different levels of thermal comfort within a planning area can be obtained by
the application of suited simulation models like ENVImet or BOTworld, which are used in KLIMES. A major
advantage of experimental point analyses is that they reflect the real environmental conditions without any assumptions. Therefore, they can be applied to validate
results from simulation models and enable a realityoriented model initialisation.
Besides the spatio-temporal resolution of information on human thermal comfort required for the application in city planning, the use of simulation models enables the investigation of consequences on human thermal comfort caused by regional climate change. According to predictions of regional climate models, thermal
background conditions in summer will be characterised
by a distinctly higher heat stress level in the future,
which increases the significance of planning concepts to
maintain thermal comfort for people within cities as far
as possible.
Taking into account similar results from other investigations, which are often limited in relation to urban
space and time, and experiences from regions suffering
under thermal stress in summer by now (S AD DE A SSIS
and BARROS F ROTA, 1999; A LI -T OUDERT et al., 2005;
J OHANSSON and E MMANUEL, 2006; E MMANUEL and
F ERNANDO, 2007), the synthesis of results on human
thermal comfort obtained by experimental investigations
and numerical simulations represents the basis for the
development of human-biometeorologically orientated
planning strategies to mitigate heat stress in different
urban quarters in summer. However, focussing on the
maintaining of thermal comfort for people within cities
one should also keep clearly in mind aspects of solar
access in winter, air pollution control, noise control, unpleasant odour, wind discomfort and objectives of environmental protection (M AYER, 1999a; S TONE, 2005)
Acknowledgements
KLIMES partners are (i) Meteorological Institute (Helmut M AYER), Albert-Ludwigs-University of Freiburg,
which also coordinates KLIMES, (ii) Department of
Environmental Meteorology (Lutz K ATZSCHNER), University of Kassel, (iii) Environmental Modelling Group
(Michael B RUSE) of the Institute for Geography, University of Mainz, and (iv) Department of Urban Development (Christl D REY), University of Kassel. The
authors wish to thank the German Federal Ministry
of Education and Research (BMBF) for funding the
project KLIMES ALUF (FKZ: 01LS05020) within the
scope of the research initiative “klimazwei”. Thanks
249
also to Eberhard M ACH from our institute for processing fish-eye photos. Students of the Albert-LudwigsUniversity of Freiburg participated in mobile humanbiometeorological measurements.
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Human thermal comfort in summer within an urban street canyon in

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