Evaluation of a sustainable urban redevelopment project in terms of microclimate improvement

Abstract

An urban redevelopment project in Thessaloniki, Greece, aiming on microclimate and pedestrian comfort improvement has been completed and evaluated to ensure achievement of initial goals set at design stage. The project interventions consist of pavement replacement, tree planting, water elements installation and addition of external fans at a dense urban site of approximately 110000m2. Preliminary microclimate simulations anticipated reduction of ambient temperature, surface temperatures and thermal comfort indices PET by 1.9oC, 9.7oC and 7.6oC respectively at summer noon. After construction evaluation, is based on monitoring and simulations of the completed project with ENVI-met v4 considering vegetation at fully grown state. The final simulations resulted in area averaged reductions of ambient and surface temperatures of approximately 2oC and 10oC respectively at summer noon and comfort indices reduction of 6.5oC. Consideration of external fans effect at spotted areas revealed further comfort improvement. Summertime data from two on site meteorological stations show more than 3oC lower air temperatures at afternoon hours. The project presents effective design measures to upgrade microclimate and comfort conditions outdoors, applicable as redevelopment strategies in similar cases and climates.

Full text

Evaluation of a sustainable urban redevelopment project in terms of
microclimate improvement
Angeliki Chatzidimitriou1, Spyros Kanouras2, Lena Topli3 and Michael Bruse4
1 Aristotle University of Thessaloniki, Thessaloniki, Greece, ange1iki@arch.auth,gr
2 Diopsis Consultants, Thessaloniki, Greece, diopsis@diopsis.gr
3 Municipality of Thessaloniki, Thessaloniki, Greece, e.topli@thessaloniki.gr
4 University of Mainz, Institut for Geography, Mainz, Germany, bruse@uni-mainz.de
Abstract: An urban redevelopment project in Thessaloniki, Greece, aiming on microclimate and pedestrian
comfort improvement has been completed and evaluated to ensure achievement of initial goals set at design
stage. The project interventions consist of pavement replacement, tree planting, water elements installation
and addition of external fans at a dense urban site of approximately 110000m2. Preliminary microclimate
simulations anticipated reduction of ambient temperature, surface temperatures and thermal comfort indices
PET by 1.9oC, 9.7oC and 7.6oC respectively at summer noon. After construction evaluation, is based on
monitoring and simulations of the completed project with ENVI-met v4 considering vegetation at fully grown
state. The final simulations resulted in area averaged reductions of ambient and surface temperatures of
approximately 2oC and 10oC respectively at summer noon and comfort indices reduction of 6.5oC. Consideration
of external fans effect at spotted areas revealed further comfort improvement. Summertime data from two on
site meteorological stations show more than 3oC lower air temperatures at afternoon hours. The project
presents effective design measures to upgrade microclimate and comfort conditions outdoors, applicable as
redevelopment strategies in similar cases and climates.
Keywords: Urban redevelopment, open spaces, microclimate, monitoring, simulations
Introduction
The microclimate in dense urban environments often presents elevated air temperature and
uncomfortable outdoor conditions for pedestrians in the summer period along with
increasingly high intensity of the urban heat island effect. The influence of urban design
features such as morphology, materials, vegetation and water elements on the microclimate
conditions that develop in open spaces has been widely documented and many researchers
have reported on improvement potential by urban redevelopment strategies (Akbari et al
2001, Yannas 2001, Nikolopoulou et al 2004, Doulos et al 2004, Alexandri and Jones 2006, Ng
2009, Altinisik et al 2014, Tsitoura et al 2016).
This study presents a redevelopment project for a downgraded area in the centre of
Thessaloniki, in Greece. The project was initiated and constructed by the municipality in the
framework of the “Bioclimatic improvement program for public open spaces”, a national level
program aiming on sustainable refurbishment of open spaces in Greek cities with focus on
microclimate amelioration in summer period. The project goals were substantial reduction of
air and surface temperatures and improvement of pedestrian comfort indices at warm
summer daytime conditions; goals difficult to achieve in the narrow and shaded canyons and

the two small confined squares of the densely-built site. Cooling degree hours reduction for
building energy savings was also expected as a consequence of microclimate improvement.
Design strategies, proposed and implemented at the site, included pavement
replacement, additional trees and vegetation, installation of water elements and external
fans at specific spots. The project interventions were evaluated, both at design stage and after
construction considering initial and future stages of the redeveloped area. Evaluation was
attempted through monitored data from meteorological stations within the site compared to
the airport station outside the city and through microclimate simulations with the analytic
software ENVI-met v4 (Huttner and Bruse 2009). The final assessment highlights the
effectiveness of the applied design measures to improve microclimate and comfort in
summer conditions and their potential applicability to similar cases and climates.
Urban redevelopment project
The project site is a dense urban area in the city centre of Thessaloniki (Lat. 40.5N, Long. 23E)
covering approximately 110000m2 which include several building blocks, various open spaces,
relatively deep street canyons and two small squares. The temperate climate of the city is
characterised by cold winter periods with high humidity and strong winds and warm summer
periods with intense insolation and frequent heat waves. Studies have reported a heat island
in the city centre (Stathopoulou et al 2004) around the project site which has been considered
a downgraded area regarding the built environment and the microclimate conditions.
Microclimate improvement strategy included cool materials on streets and pavements,
new trees, fountains, sprinklers, and water curtains as well as installation of external fans. A
preliminary evaluation of the project has been made at design stage, through simulations, to
estimate the extent of expected improvement by the proposed interventions (Chatzidimitriou
et al 2013). Initial simulation results revealed microclimate amelioration in terms of air and
surface temperatures, comfort indices and cooling degree hours and set the goals to be
achieved after construction; potential improvement was 1.9oC or 5% lower ambient
temperature, 9.7oC or 17.5% lower surface temperature and 7.6oC or 15.3% lower comfort
indices PET, in terms of area averaged values at very hot midsummer noon conditions.
Simulation results also revealed 30.9% lower cooling degree hours (26oC base temperature
set by project specifications) in terms of area averaged mean daily values in typically warm
summer conditions.
The proposed interventions were implemented as planned in the final construction
stage except for a few minor changes due to technical impediments and complications.
Figures 1 and 2 present photos of the area at initial state and after the project construction.
a b c
Figure 1: Site images in square A before (a) and after (b,c) the project implementation.

a b c
Figure 2: Site images in square B before (a) and after (b,c) the project implementation.
Monitoring and simulations
Spot measurements
Twelve spots evenly distributed in the site were selected for monitoring to include the entire
project area (Figure 3) and monitoring took place during construction and after the project
completion, in winter period. Air temperature, relative humidity and wind velocity and
direction were measured at 1.80m above ground level. Surface temperatures were measured
at the street surfaces and the side pavements. Air temperature and relative humidity were
measured with HOBO Pro v2 U23-002 thermistor and capacitance sensors, placed within a
solar radiation shield RS3 of 102mm diameter. A portable Kestrel 4600 anemometer with
25mm impeller and internal compass, mounted on a vane was used for wind velocity and
direction readings. Surface temperature readings were taken with an Extech 42530 IR
thermometer. Data at the 12 monitoring points were tested against simulations results and
revealed good agreement for ambient and surface temperatures with mean daily differences
up to 1oC for most cases.
On site meteorological stations
Two meteorological stations were set in the small squares, after the project completion in
early spring, recording continuously air temperature, relative humidity, and barometric
pressure at 1.8m height and wind velocity and direction at 6m height above ground level.
Summer period monitoring data from the meteorological stations are used for a preliminary
evaluation of the project regarding microclimate improvement.
Figure 3: Site plan with indication of the spot measurements points and meteorological stations location.

Figure 4: Portable on site monitoring equipment and meteorological stations in squares A and B.
Microclimate simulations
Both the initial and the final evaluation of the project were based on microclimate simulations
of the area before and after implementation of proposed interventions. Microclimate
simulations were performed with Envimet v4 software specially edited to include the water
droplets evaporation effects. The simulation model contained the entire project site and the
surrounding streets, and included buildings, vegetation, pavement materials and water
elements. The size of model area was 460m X 460m and 75m high with 3m grid resolution.
Simulations were performed in daily cycles using, according to the project requirements,
climate data of a typically warm summer day and of the hottest day of the year. Figure 5
presents the area models at the two different simulation stages.
a b
Figure 5 Models of the site (a) at the original state and (b) after full implementation of the project
interventions including full growth of vegetation for the microclimate improvement evaluation with ENVI-met
simulations
Table 1. Simulation input data for a typical warm summer day (21 July) and the hottest day of the year (25 July)
Simulation input parameters project evaluation cases
Simulation dates 21 July 25 July
Start time and duration 06:00 | 6h 06:00 | 14h
Initial wind velocity and direction (10m) 3.30 m/s, 225ο (NW) 2.30 m/s, 225ο (NW)
Roughness length 0.1 0.1
Air temperature range 24.98οC- 29.30οC 33.20οC- 42.60οC
Relative humidity range 33% - 73% 30% - 60%
Specific humidity (gwater /kgair) 11.5 15.0
Soil temperature & humidity (depth 0-20cm,
20-50cm, 50-200cm)
31.75
ο
C,20%, 30.07
ο
C,30%,
27.11οC,30%
31.75
ο
C,20%,30.07
ο
C,30%,
27.11οC,30%
Building surface albedo 0.3 0.3
Cool pavements albedo (asphalt | concrete) 0.37 | 0.67 0.37 | 0.67
Solar adjustment factor 1.0 1.0
Cloud cover 0/8 0/8

Results and project evaluation
Project evaluation is presented in two stages. An initial evaluation, in summer conditions after
the construction completion, is based on monitored climate data by two meteorological
stations located in the site, at the two redeveloped squares compared to data from the airport
meteorological station located outside the city. A further evaluation of the future stage of the
project is attempted through simulations of the site taking into account the effects of
vegetation in fully grown state, which is considered of major significance for the microclimate
improvement.
After construction evaluation
Monitored data by meteorological stations located at the two squares of the refurbished area
indicate the improvement in terms of air temperature reduction due to the redevelopment,
in the summer period right after the project completion. The data in the two squares are
compared with measurements at the airport meteorological station
(https://www.wunderground.com/gr/thessaloniki). Air temperature improvement is
observed during daytime and mainly from midday to evening hours. Readings from the three
stations during a week in July 2016 are presented in Figure 6 and indicate lower midday air
temperatures at the two squares and higher night time temperatures compared to the airport
station outside the city, except for two cloudy days (26th - 27th) in which a storm and showers
occurred briefly. In general, from midday to evening hours during a week, the two squares
were cooler that the suburban airport area with maximum daily differences between 1.8oC
and 4.3oC in the first square (A) and between 2.3oC and 3.4oC in the second (B). In particular,
on the 25th of July from 13:00 to 19:00, air temperature at the first square (A) was between
0.2oC and 2.5oC lower and at the second square (B) it was between 1.3oC and 3.3oC lower
compared to the airport station while at night air temperature was higher up to 2.7oC and
2.6oC respectively.
The recently planted new trees were not yet sufficiently large to provide the expected
improvement. Street and sidewalks pavement replacement with cool materials and traffic
load decrease are significant cooling factors, however, the highest influence in air
temperature reduction is attributed to the water elements introduced in the two squares, i.e.
the water curtains in the first square and the large number of fountains in the second. The
extensive effect of water evaporation, on air temperature drop, compared to other
interventions, was confirmed in previous project stages (Chatzidimitriou et al 2013).
Figure 6: Air temperature data for July 2016 from meteorological stations in the two squares of the
project area and from the airport station outside the city.

Future stage expectations
The microclimate improvement expected after vegetation has reached fully grown state is
examined through simulation results by ENVI-met model, in summer daytime conditions
which is the focus of the project strategy. The simulations of the area before the project
initiation and after the full implementation of the all interventions including water
evaporation elements and full growth of the newly planted trees are compared to examine
future stage development of the microclimate and comfort conditions. Figure 7 presents
simulation results of air temperature, surface temperatures and PET comfort indices in very
warm midsummer noon conditions at the site, before and after implementation of the project.
Taking into account area average results, calculated from 60 spots evenly distributed
in the site, microclimate amelioration was observed with air temperature reduction by 2oC or
5.1%, surface temperature reduction by 9.4oC or 18.8% and comfort indices PET reduction by
6.5oC or 15.3% at summer noon conditions. In terms of mean daytime PET values, between
10:00 and 18:00, the results show a reduction by 5.8oC or 15% in a typical summer day. In
terms of cooling degree hours (CDH with base temperature 26oC) calculated by air
temperatures between 06:00 and 20:00 on a typically warm summer day, the reduction was
estimated at 43.9%.
More specifically in the two small squares of the site, expected mean reduction of air
and surface temperatures at summer noon is 2.5oC and 22.3oC respectively in the first square
(A) and 4.3oC and 11.8oC respectively in the second (B). Regarding comfort indices PET in
spotted areas within the squares, when the effect of the external fans is taken into account,
as wind velocity increase by 1m/s in calculations by RayMan software (Matzarakis et al 2010),
the expected spot reduction of PET indices at noon is 7.3oC or 19.8% in the first square and
15.2oC or 32.6% in the second while the respective daily average reduction is 7.9oC or 18.7%
in the first square and 13.1oC or 27% in the second (Table 2).
It should be noted that air temperature and cooling degree hours reduction were used
to examine cooling loads and energy savings for two typical buildings at the project site, a
residential and a commercial building. According to the specific program requirements the
buildings’ thermal performance was simulated using two different climate data sets; the
original local climate data file and a modified data set featuring the air temperature reduction
caused by the project interventions. Thermal simulation results indicated cooling energy
savings of 7.2% for the two buildings and approximately 99tn reduction of CO2 emissions for
the entire project area in the summer period.
Table 2. Microclimate simulation results before and after implementation of the interventions
Microclimate parameter | date | time Final evaluation | before
project implementation
Final evaluation | after
project implementation
Air Temperature (oC) 25 July 1200 38.7 36.7
Surface Temperature (oC) 25 July 1200 46.3 36.9
PET (oC) 21 July 1200 39.5 33.0
PET (oC) 21 July daily average 37.5 31.8
PET in square A (oC) 21 July 1200 (+fans) 36.8 29.5
PET in square B (oC) 21 July 1200 (+fans) 46.6 31.4
PET in square A (
o
C) 21 July daily average (+fans) 38.3 30.4
PET in square B (oC) 21 July daily average (+fans) 43.3 30.4

a b
c d
e f
Figure 7: Summer noon simulation results of the area before and after implementation of the project
interventions (a,b) air temperature, (c,d) surface temperature, (e,f) thermal comfort indices PET.
Conclusions
A redevelopment project for a downgraded urban area in Thessaloniki has been completed
and evaluated based on microclimate amelioration criteria. Evaluation by means of on site
monitoring by meteorological stations in the summer period revealed 2-4oC lower daytime
ambient temperatures in two small squares of the site compared to the airport station data,
but higher nighttime temperatures. Further evaluation of the future state of the project by
means of microclimate simulations, considering the new trees fully grown, present area
averaged improvement of approximately 2oC for air temperature, 10oC for surface
temperatures and 6.5oC for comfort indices PET at very warm summer midday conditions.
These results indicate that the project interventions which include pavement replacement
with cool materials, increase of trees and vegetation canopies and addition of multiple water
41.0
42.0
40.0
41.5
41.0
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41.0
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38.5
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32.5
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xrmt_bef 12:00 25.07
Air Temperatu re
below 33.0 °C
33.0 to 34.0 °C
34.0 to 35.0 °C
35.0 to 36.0 °C
36.0 to 37.0 °C
37.0 to 38.0 °C
38.0 to 39.0 °C
39.0 to 40.0 °C
40.0 to 41.0 °C
above 41.0 °C
Min: 37.2 °C
Max: 42.8 °C
Objects
Buildings
Vegetation: LAD lower 0.5
Vegetation: LAD 0.5 - 1.0
Vegetation: LAD 1.0 - 1.5
Vegetation: LAD 1.5 - 2.0
Vegetation: LAD above 2.0
42.0
40.0
42.0
40.5
41.0
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40.0
36.0
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40.0
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35.0
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34.5
38.0
35.0
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37.5
36.0
37.5
40.0
38.5
35.0
37.0
40.0
35.5
39.5
40.0
40.0
40.0
40.0
40.0
34.0
37.5
36.5
32.0
36.0
38.0
37.0
36.0
32.5
17.5
35.0
27.5
37.5
30.0
41.0
32.5
37.0
23.5
39.0
25.0
35.0
31.0
39.0
36.5
32.0
36.0
36.5
36.5
37.0
37.5
39.5
37.5
38.0
38.0
37.0
37.5
39.0
40.0
40.0
41.0
41.0
40.0
40.0
39.0
40.0
40.0
40.0
40.0
40.5
40.0
40.0
41.5
42.0
42.5
41.0
41.0
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xrmt_aft 12:00 25.07
Air Temperatu re
below 33.0 °C
33.0 to 34.0 °C
34.0 to 35.0 °C
35.0 to 36.0 °C
36.0 to 37.0 °C
37.0 to 38.0 °C
38.0 to 39.0 °C
39.0 to 40.0 °C
40.0 to 41.0 °C
above 41.0 °C
Min: 30.4 °C
Max: 42.6 °C
Objects
Buildings
Vegetation: LAD lower 0.5
Vegetation: LAD 0.5 - 1.0
Vegetation: LAD 1.0 - 1.5
Vegetation: LAD 1.5 - 2.0
Vegetation: LAD above 2.0
48
56
52
52
52
52
52
52
44
52
52
40
36
40
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52
40
36
56
52
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36
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48
36
36
52
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40
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36
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48
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36
40
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40
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40
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36
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36
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40
48
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36
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36
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40
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36
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36
40
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36
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48
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xrmt_bef 12:00 25.07
T Surface
below 32.0 °C
32.0 to 34.0 °C
34.0 to 36.0 °C
36.0 to 38.0 °C
38.0 to 40.0 °C
40.0 to 42.0 °C
42.0 to 44.0 °C
44.0 to 46.0 °C
46.0 to 48.0 °C
above 48.0 °C
Min: 33.9 °C
Max: 61.2 °C
Objects
Buildings
Vegetation: LAD lower 0.5
Vegetation: LAD 0.5 - 1.0
Vegetation: LAD 1.0 - 1.5
Vegetation: LAD 1.5 - 2.0
Vegetation: LAD above 2.0
40
44
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48
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36
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36
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36
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40
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36
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48
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56
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48
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40
40
36
36
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36
36
36
40
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36
32
44
44
52
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36
36
40
44
36
36
36
36
48
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36
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40
36
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48
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36
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X (m)
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xrmt_aft 12:00 25.07
T Surface
below 32.0 °C
32.0 to 34.0 °C
34.0 to 36.0 °C
36.0 to 38.0 °C
38.0 to 40.0 °C
40.0 to 42.0 °C
42.0 to 44.0 °C
44.0 to 46.0 °C
46.0 to 48.0 °C
above 48.0 °C
Min: 28.2 °C
Max: 60.8 °C
Objects
Buildings
Vegetation: LAD lower 0.5
Vegetation: LAD 0.5 - 1.0
Vegetation: LAD 1.0 - 1.5
Vegetation: LAD 1.5 - 2.0
Vegetation: LAD above 2.0
38
44
44
41
44
35
35
35
35
38
38
32
32
32
35
41
44
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44
41
44
35
38
38
47
35
44
38
44
35
35
50
41
41
50
35
50
44
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44
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35
41
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35
50
41
38
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38
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41
38
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32
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35
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41
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35
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50
35
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38
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47
35
35
50
41
44
26
44
38
44
32
38
41
35
50
44
38
44
35
35
38
44
44
44
35
41
38
32
35
38
50
50
35
38
44
38
44
35
35
41
50
41
32
35
32
38
38
32
38
38
32
38
38
35
32
32
38
32
35
35
38
44
41
X (m)
0.00 30.00 60.00 90.00 120.00150.00180.00210.00240.00270.00300.00330.00360.00390.00420.00450.00480.00
Y (m)
0.00
30.00
60.00
90.00
120.00
150.00
180.00
210.00
240.00
270.00
300.00
330.00
360.00
390.00
420.00
450.00
480.00
N
xrmt_bef 12:00 21.07
PET
below 26.0 °C
26.0 to 29.0 °C
29.0 to 32.0 °C
32.0 to 35.0 °C
35.0 to 38.0 °C
38.0 to 41.0 °C
41.0 to 44.0 °C
44.0 to 47.0 °C
47.0 to 50.0 °C
above 50.0 °C
Min: 26.8 °C
Max: 53.0 °C
38
38
38
44
44
35
35
35
38
38
38
35
38
32
44
44
44
35
41
35
32
38
32
38
38
35
32
29
38
32
44
35
35
35
32
38
41
38
35
44
32
35
41
44
35
38
41
38
38
41
35
38
41
38
35
38
41
32
32
29
38
32
35
35
26
38
44
38
38
44
38
44
44
44
38
32
38
32
47
35
38
32
32
32
32
35
41
26
38
38
38
38
32
44
35
35
38
41
32
35
29
38
41
32
35
35
44
44
38
35
41
41
32
32
32
35
32
32
35
35
35
35
32
35
35
41
44
38
32
38
32
38
38
38
35
38
38
38
38
38
X (m)
0.00 30.00 60.00 90.00 120.00150.00180.00210.00240.00270.00300.00330.00360.00390.00420.00450.00480.00
Y (m)
0.00
30.00
60.00
90.00
120.00
150.00
180.00
210.00
240.00
270.00
300.00
330.00
360.00
390.00
420.00
450.00
480.00
N
xrmt_aft 12:00 21.07
PET
below 26.0 °C
26.0 to 29.0 °C
29.0 to 32.0 °C
32.0 to 35.0 °C
35.0 to 38.0 °C
38.0 to 41.0 °C
41.0 to 44.0 °C
44.0 to 47.0 °C
47.0 to 50.0 °C
above 50.0 °C
Min: 25.6 °C
Max: 50.8 °C

elements such as fountains and sprinklers can sufficiently improve summertime microclimate
conditions in the open spaces of a dense urban area. Moreover, the installation of external
fans at specific parts of the area assist in airflow increase and pedestrian comfort
improvement. Besides the outdoor thermal comfort benefits, the microclimate amelioration
also enhances energy savings by reducing building cooling loads and presents an overall
upgrading effect of the project in terms sustainable urban development.
References
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improve air quality in urban areas. Solar Energy Journal, 70(3) pp 295-310.
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technique for urban spaces. 23rd PLEA Conf., Geneva, Switzerland, September 2006.
Altinisik, L., W. Klemm, G. Peretti and M. Bruse (2014). Integration of Microclimate-Responsive design in
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