Geoscience Reference
In-Depth Information
here. The results are being used to prescribe climate guidelines for urban design and
planning at the microscale.
5.8.1.
Spatial variation of physiologically equivalent temperature
In order to prepare climate guidelines for urban planning the thermal comfort
had to be assessed. The main objective was to make detailed maps and to assess how
individuals would feel in the different parts of this neighborhood. The
Physiologically Equivalent Temperature (PET) was chosen as an index for thermal
bioclimate [HOP 99]. The discussion of the index and its application to Lisbon was
performed in detail by Andrade [AND 03; AND 08]. PET has the advantage of
being expressed in ºC. It allows assessing the thermophysiologic combined influence
of atmospheric parameters important for the energy balance of the human being
[MAT 99]: air temperature (Ta), mean radiant temperature (MRT), vapor pressure
(Pa), wind speed (v). The following parameters were considered constant: the
production of internal heat (80 W/m
2
) and the clothing insulation (0.9 Clo). For a set
of actual atmospheric conditions, PET is equivalent to the air temperature in a room
with a standard environment (Ta=MRT; v=0.1 m/s; Pa=12 hPa) that requires the
same thermophysiologic response as an actual environment. For example, the
combination of Ta=30ºC, MRT=45ºC, Pa=22 hPa, and v=2 m/s corresponds to a
PET value of 34.1ºC. This means that the actual thermal environment requires the
same thermophysiologic response as a standard environment with Ta=34.1ºC,
MRT=34.1ºC, v=0.1 m/s, and Pa=12 hPa.
The first step was the measurement of meteorological parameters performed by
means of the “microclimatic network” (Figure 5.4c), devices and shelters similar to
the ones used for the abovementioned mesoclimatic experiment (Figure 5.3d-e) and
also some itinerary campaigns within the city district [AND 03; AND 08]. The sites
where the sensors were placed ensured they represented the various micro-
environments in the neighborhood.
The SVF of each site was calculated using the
RayMan
program [MAT 07] as an
alternative to the use of fish-eye lenses. In the program, one can represent both the
celestial hemisphere and horizon obstructions (trees and buildings) as well as sun
trajectories at any specific date at a specific site. Figure 5.12 shows four different
types of measuring sites in Telheiras. The calculation of SVFs by
RayMan
was
verified by comparison with photographs with fish-eye lenses for 23 sites. The
values of SVFs measured by both methods were not statistically different using
analysis of variance (ANOVA; F=0.006, with a critical value of 4.05 for 0.95
probability) [AND 08]. There are clear differences between site 10 with a SVF of
0.74 in an open area and site 3 in a residential street with a SVF of 0.29. The solar
paths at the solstices and equinoxes are shown in Figure 5.12. It is clear that site 3
stays in the shade during a great part of the year due to E-W orientation and low
SVF. Site 2 in a N-S street with a 0.5 SVF, is in the sun during a large part of the
day (with the exception of early morning and late afternoon) all the year round.
