Microclimatic Effects of Habitat Reconstruction in Ksour

2012 International Conference on Environmental, Biomedical and Biotechnology
IPCBEE vol.41 (2012) © (2012) IACSIT Press, Singapore
Microclimatic Effects of Habitat Reconstruction in Ksour
Djamel Alkama and Moufida Sebti
Architecture department, Biskra University, Algeria
Abstract. The traditional Saharan habitat, named ksar, was characterized in the past by a favorite
microclimate conditions; however this habitat is transformed with time by reconstruction with modern
materials and techniques which destructed it adaptation with hot climate. The morphologic transformation in
construction procreate an unfavorable conditions of microclimate in the transformed tissue, which are
affected by the warming of the heat transferred from the energy consumed by buildings and the sensible heat
stored in the building materials.
Keywords: Ksar, Saharan habitat, Microclimate adaptation, Morphologic transformation.
1. Introduction
The Saharan ksour meet the weather conditions by adapting the physical environment and protection
against adverse climatic factors. This adaptation involves several levels (in the form of houses, the rail
system, fragmented system, the facade and building materials). The ksar of Ouargla (Algerian Saharan city)
knows recently a various transformations generated by the socio-economic changes of modern life which
alter the microclimatic adaptation getting by its genius design with environment and climate.
In this paper we introduce the results of a comparative study based on an experiment applied to the
case of the Ksar Ouargla between transformed and untransformed urban space.
2. Study Description
2.1. Case Study
This study is applied to the case of the city of Ouargla, chosen for its representativeness of the Saharan
cities with hot, dry climate in Algeria. Ouargla includes a vast area of over 180. 000 square kilometers,
almost in its entirety desert, which stretches between 28 and 32 north latitude and the meridians 4 and 8 East.
It is bounded on the north by the municipality of Touggourt, east by that of El Oued, the south by those of
Ajjer Tidikelt and to the west by those of El Gole and Ghardaia 1
The climate in Ouargla is "one of the hardest of the North Eastern Sahara". The average annual
temperature is 23.4 °C, 35.7 °C for the warmest month (July) and 11.6 °C for the coldest month (January),
this figure masks extreme high, exceeding 50 °C under shelter.
Fig. 1: Location of Ouargla, height: 1630 km. Source: Google earth 2010.
185
2.2. Methodology of This Study
This work is based on a comparative study through an experimental method, the microclimatic factors
measured are: air temperature, radiant temperature, relative humidity and air velocity. The purpose of this
study is to evaluate the negative microclimatic effects in the urban ksouran, caused by the different
morphological changes inadequate and inappropriate to the local context and which have varied levels of
discomfort. The desire to work on urban microclimatic condition necessarily involves recourse to both
measures of its physical parameters (climate). To do this, it was mainly used metrology (measurement
campaign) to identify the different parameters of the thermal environment in order to be able to assess in a
quantitative and objective. This method was elaborated and explored by many authors researches such as A.
Bennadji (1999) [2], F. Ahmed Ouameur (2007) [3] and S.D. Boutabba (2007) [4], etc.
We choose two tissues for this study which make subject of campaigns of microclimatic measurement,
we refer to oppositions showed by the differences existed between the two tissues for selecting areas of
measurement in order to avoid the duplication and to be representative of all the tissue. Among these
oppositions are: Traditional / planned, cement / clay, winding / straight, wide / narrow, open / closed, indoor
/ outdoor, sunny / shaded, compact / loose, etc. The choice of these two trajectories is motivated by:
• The diversity of the urban tissue between the two axes (traditional and modern) and the distinct
characteristics of the physical structure (density built-up factor of the sky seen through the surface,
factor of ground reflectivity, etc ....) of each of the urban tissue.
• The joint ownership of the urban tissues promoting dynamic investigation using a route explored by
the investigator.
2
1
Fig. 2: Situation of two trajectories invested in the Ksar of Ouargla
This experiment was performed on two different tissues inside the Ksar. So we divided the measures to
be implemented on two companions in each set was five points. Measurements of four climatic factors must
have taken parallel to an altitude of: 1.60 m above the ground [5]. The measurement points were chosen so as
to be distributed along the two trajectories which represent transformed and untransformed tissues.
Fig. 3: Identification of measurement points selected
from the trajectory 01.
Fig. 4: Identification of measurement points selected
from the trajectory 02.
2.3. Instruments and Moments of Measurement
186
In this study the measurements
m
s are taken using two instruments thaat are: An Ennvironment Meter
M
modell
8820 and a Hot Wire Annemometer.
Fig. 4: Hot-w
wire anemometter.
Fig.. 5: Environm
ment meter 882
20.
These devices
d
are used to obbtain direct measuremen
nts of climaatic factors 4. Like any
y measuringg
instrument Multi-Functtion Environnment Meteer model 88
820 and Hott Wire Aneemometer haave its ownn
characteristics relating to the condduct of its opperation and
d harvesting quantities oof which theey is able too
d
to acquire
a
four sizes using different prrobes and byy switching each time a
measure. Thhe first is designed
switch for either:
e
the airr temperaturre, relative huumidity, noise or lighting, the secondd is designed
d to acquire::
the air tempperature andd the air vellocity. Thesee materials are
a the only elsewhere iin the posseession of thee
Departmentt of Architectture at the University
U
of Biskra.
The choosen momentts are relatedd to daily tem
mperature reg
gime [6]:
• Befoore sunrise: first
f
heat gainn.
• Afteer the sunrisee: early gain.
• At noon:
n
when thhe sun is direectly overheaad.
• Befoore the sun: after
a
a maxim
mum accumuulation of heaat.
• Afteer the Sunset: Beginning the return off the stored heat.
h
The mooments choseen for compaarison are thoose extracted
d: 5:00, 9:00, 12:00, 17:000 and 21:00.
3. Comp
parison off Results between
b
t Two Tissues
the
T
mparison off Mean Vallues of Air Temperatu
ure and Raadiant Tem
mperature between
b
3.1. Com
the Two
T Trajecctories
Air tem
mperature trajectorry 1
Air tem
mperature trajectorry 2
Meteo. air temperature
45
43
41
39
37
35
33
31
29
27
Temperature (°C)
Temperature (°C)
The graaphs below show the evoolution of daiily mean valu
ues of air tem
mperature annd radiant tem
mperature inn
the two trajeectories (tradditional tissuue +transform
med tissue) du
uring a summ
mer day.
5
9
Time
T 12
17
radiant temperature trajecctory 1
radiant temperature trajecctory 2
Meteo. Air temperature
45
43
41
39
37
35
33
31
29
27
5
21
Graph 1: Comparisoon of mean values of air
ajectories
tempeerature between the two traj
9
12
Time
17
21
Graph 2: Comparison off mean values of radiant
temperaature between the two trajecctories
187
The graaphs below show
s
the evoolution of daaily mean vallues of gap in
i air and raddiant temperrature of twoo
trajectories (traditional tissue
t
+transformed tissuue) during a summer
s
day..
gap in aiir temperature of trrajectory 1
gapp in radiant temperrature of trajectoryy 1
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
5
9
12
17
gapp in radiant temperrature of trajectoryy 2
Temperature (°C)
Temperature (°C)
gap in aiir temperature of trrajectory 2
21
Time
6
5
4
3
2
1
0
-1
1
2
-2
-3
-4
4
-5
5
-6
6
Graph 3:
3 variation off mean valuess of radiant
temperaturee differences between
b
the tw
wo trajectoriees
5
9
1
12
17
21
Timee
Graph
G
4: variaation of meann values of air temperature
differennces between the two trajecctories
Analysiis of these reesults shows that:
t
• The air temperatture measureed in the twoo paths is slightly above that measurred in the traj
ajectory 1, inn
exceeption of the value measuured at 9 o’cllock which reecorded a gaap of 1.38 ° C
C.
• From
m 9 to 12: thhe mean valuues of air teemperature coincide withh those of thhe radiant tem
mperature inn
eachh trajectory, the values of either thee air or rad
diant temperaature measurred in the trrajectory 022
exceeed those meeasured in thhe trajectory 01, they increase under the effect off beginning of
o heat gain,,
but they
t
are close to the valuue measured by
b the meteo
orological staation.
• A 177 o’clock: thhe mean air temperature is confused
d with the vaalue measureed by the staation in eachh
trajeectory with a very smalll gap, whille the valuee of the radiiant temperaature exceed
ds the valuee
measured by thee station. Raddiant temperrature in the trajectory 2 takes its maaximum valu
ue of 44 ° C,,
exceeeding the vaalue measureed by the stattion with a gap
g of 3 ° C,, while the raadiant tempeerature in thee
trajeectory 1 slighhtly exceeds that of a stattion with a diifference 0.5° C.
mparison off Mean Vallues of Relaative Humiidity betweeen the Twoo Trajectorries
3.2. Com
relative humidity of trajecto
ory 1
relative hu
umidity of trajectory 2
relative hu
umidity of meteo station
s
Relative Humidity (%)
Relative Humidity (%)
40
35
30
25
20
15
10
5
5
9
12
Time
17
18
16
14
12
10
8
6
4
2
0
-2
-4
21
Graph 5: Comparison of
o mean valuees of relative
midity betweenn the two trajeectories
hum
Gap in relative humidity of trajecctory 1
Gap in relative humidity of trajecctory 2
5
9
1
12
Timee
17
21
Graph
G
6: variattion of mean vvalues of relattive humidity
differennces between the two trajecctories
Comparrison of meaan values of relative
r
humiidity shows:
• The decrease in mean valuess of relative humidity fro
om the station throughouut the day in each course,,
aparrt from the vaalue measureed at 9 o’clocck.
188
• The average relaative humidity measuredd in the trajecctory 2 exceeds those meeasured in th
he course byy
bringging one of the
t values measured
m
by thhe station in most of the time.
• The value of relaative humidiity measuredd in the courrse a slightly above the vvalue of HR measured inn
the trajectory
t
02
mparison off Mean Vallues of Relaative Air Velocity
V
betw
ween the T
Trajectoriess
3.3. Com
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
G in air velocity in trajectory 2
Gap
air veloccity of meteo statio
on
air veloccity in trajectory 2
5
9
12
Time
17
7
air velocity (m/s)
air velocity (m/s)
G in air velocity in trajectory 1
Gap
air veloccity in trajectory 1
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
21
5
Graph 7: variation of mean
m
values of air velocity
differences betweeen the two trajjectories
9
12
Time
17
21
Graph 8: Com
mparison of m
mean values off air velocity
between the tw
wo trajectories
Comparrison of meaan values of air
a velocity shows:
s
• The significant decrease
d
in the
t values off air velocity
y in the two courses from
m the value measured
m
byy
the station
s
througghout the dayy.
• The values of thhe air velociity measuredd in the cou
urse an overllap with thoose measured
d in the twoo
courrses, registeriing a significcant departurre from the station.
• The maximum air
a velocity iss recorded inn a course at noon, when we recordedd a minimum
m value in thee
two courses at thhis time.
• Minimum valuess are recordeed in the two paths after sunset,
s
obserrved with a m
maximum vaalue recordedd
by thhe station.
3.4. Syntthesis
This invvestigation allowed
a
us to
t make a coomparison between
b
the processed annd unprocesssed ksourann
tissue in terrms of the urrban microcllimate condiitions. The teemperature is
i mainly afffected by sun
nlight, wind,,
and altitudee and soil tyype. The ratte of heatingg and coolin
ng of the earrth's surfacee is the main
n factor thatt
determines the air tempperature whicch is in contaact [7]. In thee transformedd tissue, we identify a th
hermal effectt
characterizeed especiallyy the period of
o the afternooon, which iss manifested in the increaase of the av
verage valuess
of air tempeeratures closse to those of the meteorrological stattion with a slight differennce of 0.34 ° C (at noonn
and before sunset), whiile the averaage values off the radiantt temperaturees exceed thhose of the resort
r
with a
significant difference
d
off 2.98 ° C (beefore sunset)).
4. Referrences
[1] M. Cotee. The city andd the desert, down
d
the Algeerian Sahara. Edit:
E
Ireman-kkarthala. 20055.
[2] A. Bennnadji. Adaptattion or culturaal climate in arid
a zones. Casse in south-eaastern Algeria. Ph.D. thesis,, University
of Aix-M
Marseille I, University
U
of Provence,
P
UFR
R of Geograph
hical Sciencess and Planningg, France, 199
99.
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med Ouameur. Urban morphhology and theermal comfortt in public spaaces: Comparaative study of three urban
fabric of
o Quebec Cityy. Submissionn under the maaster's program
m in science of
o architecture, School of Arrchitecture
Facultyy of Planning, Architecture and
a Visual Arrts, University
y Laval Quebeec. 2007.
[4] S.D. Booutabba. Urbaan thermal com
mfort betweenn measurement and perceptiion. Case Studdy in Sidi-Okb
ba.
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matology: meaasurements, modeling and validation
v
of
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Strasbourg, Ph.D. thesis, University Louis Pasteur Strasbourg 1, 2004.
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190