Impact of the ambient temperature rise on the energy consumption for heating and cooling in residential buildings of Greece

Abstract

Annual values of heating and cooling degree-days for two typical base temperatures, namely 15 °C for heating and 24 °C for cooling, and for the two main cities of Greece (Athens and Thessaloniki) from 1983 to 2002 are presented in the study, calculated using hourly dry bulb temperature records from the meteorological stations of the National Observatory of Athens and of the Aristotle University of Thessaloniki. The decade average (1983–1992 and 1993–2002) values of the heating and cooling degree-days of the two cities are compared, for various base temperatures. The results show that the average value of heating degree-days of Athens for the decade 1993–2002, depending on the base temperature, is reduced from 8% to 22% as compared to the corresponding value of the decade 1983–1992. Similarly, the reduction in the Thessaloniki case is found in the range 4.5%–9.5%. The difference in the average value of cooling degree-days of the decades is more pronounced, the increase ranging from 25% to 69% for Athens and from 10% to 21% for Thessaloniki. In order to evaluate the effect of these changes on the energy requirements for heating and cooling of a typical residential building, the latter were calculated using the variable base degree-day method and the data sets of the two decades. The results show a reduction of the heating energy demand by 11.5% and 5% and an increase of the cooling energy demand by 26% and 10%, for Athens and Thessaloniki respectively.

Full text

Impact of the ambient temperature rise on the energy consumption for heating
and cooling in residential buildings of Greece
K. Papakostas
a
,
*
, T. Mavromatis
b
, N. Kyriakis
a
a
Aristotle University of Thessaloniki, Faculty of Engineering, Department of Mechanical Engineering, Process Equipment Design Laboratory, 541 24 Thessaloniki, Greece
b
Aristotle University of Thessaloniki, School of Geology, Department of Meteorology-Climatology, 541 24 Thessaloniki, Greece
article info
Article history:
Received 30 May 2009
Accepted 3 August 2009
Available online 25 November 2009
Keywords:
Heating and cooling degree-days
Energy consumption
Climate change
abstract
Annual values of heating and cooling degree-days for two typical base temperatures, namely 15

C for
heating and 24

C for cooling, and for the two main cities of Greece (Athens and Thessaloniki) from 1983
to 2002 are presented in the study, calculated using hourly dry bulb temperature records from the
meteorological stations of the National Observatory of Athens and of the Aristotle University of
Thessaloniki. The decade average (1983–1992 and 1993–2002) values of the heating and cooling degree-
days of the two cities are compared, for various base temperatures. The results show that the average
value of heating degree-days of Athens for the decade 1993–2002, depending on the base temperature, is
reduced from 8% to 22% as compared to the corresponding value of the decade 1983–1992. Similarly, the
reduction in the Thessaloniki case is found in the range 4.5%–9.5%. The difference in the average value of
cooling degree-days of the decades is more pronounced, the increase ranging from 25% to 69% for Athens
and from 10% to 21% for Thessaloniki. In order to evaluate the effect of these changes on the energy
requirements for heating and cooling of a typical residential building, the latter were calculated using the
variable base degree-day method and the data sets of the two decades. The results show a reduction of
the heating energy demand by 11.5% and 5% and an increase of the cooling energy demand by 26% and
10%, for Athens and Thessaloniki respectively.
Ó2009 Elsevier Ltd. All rights reserved.
1. Introduction
The change of climate is already in progress and it will
undoubtedly continue during the following decades, even in case
the efforts made for the moderation of the phenomenon will be
absolutely successful.
In Europe and especially in the southern parts and around the
Mediterranean basin, where Greece belongs geographically, there
has been observed an increase in the average temperature during
the summer as well as during the winter months. This climate
change has direct consequences to the energy consumption for
heating and cooling. In the existing buildings the demand on
heating energy is diminishing whereas the demand of cooling
energy is increasing.
One of the climate indices of an area is the heating and cooling
degree-days. The degree-days are an indirect indication of the
outside air temperature fluctuations and are used for calculating
heating and cooling energy demands of buildings [1–6].
Within the framework of the present study, the total annual
values of the heating and cooling degree-days for the two main
cities in Greece, namely Athens and Thessaloniki, were calculated,
and their time evolution from 1983 until 2002 is presented for
typical base temperatures. The average annual heating and cooling
degree-days of the two above mentioned cities, for the decades
1983–1992 and 1993–2002, are compared for different base
temperatures, and the influence of their changes to the energy
demands of a model-building during the two decades is
investigated.
2. Calculation of the heating and cooling degree-days
The heating and cooling degree-days are calculated either from
the average daily ambient dry bulb temperature or from the
average hourly temperatures or from the average value of the
maximum and minimum daily temperature. The different
calculation methods explain the differences in the values given by
various sources.
In the present study the values of the degree-days were derived
from the statistical processing of the hourly measured ambient dry
bulb temperatures of years 1983–2002. The temperature data were
*Corresponding author. Tel.: þ30 2310 996025; fax: þ30 2310 996087.
E-mail address: dinpap@eng.auth.gr (K. Papakostas).
Contents lists available at ScienceDirect
Renewable Energy
journal homepage: www.elsevier.com/locate/renene
0960-1481/$ – see front matter Ó2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.renene.2009.11.012
Renewable Energy 35 (2010) 1376–1379

taken from the records of National Observatory of Athens [7] and of
the Aristotle University of Thessaloniki meteorological stations.
The total degree-days of the winter period (October–April) were
calculated for base temperatures ranging from 10 to 20

C, and the
total degree-days of the summer period (June–September) were
calculated for base temperatures ranging from 20 to 28

C.
Due to the large bandwidth of the results, the annual heating
degree-days for the period 1983–2002 and for base temperature of
15

C(Figs. 1 and 2 for Athens and Thessaloniki respectively) as well
as the annual cooling degree-days for base temperature of 24

C
(Figs. 3 and 4 for Athens and Thessaloniki respectively) are indic-
atively presented. These temperatures are the most common
balance temperatures of normally insulated buildings without
especially large heat gains from internal heat sources and solar
radiation.
Diagrams on Figs. 1–4 indicate a constant decreasing trend of
the heating degree-days and an increasing trend of the cooling
degree-days for both cities, especially from year 1996. After this
year, the heating degree-days are lower and the cooling degree-
days are higher than the twenty-year average value for both cities.
This is an indication of the climate change that can be attributed to
the increase of ambient temperature, with milder winters and
hotter summers [8].
A uniformity to the increase or decrease of degree-days for the
same year and for both cities is also observed. This means that the
change in climate conditions for both cities is similar.
The comparison of heating degree-days, for various base
temperatures, between the decades 1983–1992 and 1993–2002 is
presented in Figs. 5 and 6 and the comparison of cooling degree-
days in Figs. 7 and 8 for Athens and Thessaloniki respectively.
The results in Figs. 5–8 clearly show the decrease of degree-days
during the heating period and the increase of degree-days during
the cooling period during the decade 1993–2002 as compared to
the 1983–1992 decade. Similar results were concluded in recent
studies in other countries [9].
The average value of annual heating degree-days in Athens
during the decade 1993–2002 was reduced by 8%–22%, depending
on the base temperature, in relation to the 1983–1992 decade. The
corresponding reduction in Thessaloniki ranges between 4.5% and
9.5%. The average value of annual cooling degree-days is increased
by 25%–69% for Athens and by 10%–21% for Thessaloniki, depending
on the base temperature.
During the heating period, the change of the degree-days’ values
is almost double in Athens as compared to that of Thessaloniki
while during the cooling period it is almost triple. Therefore, the
change in temperature is more intense in Athens than in Thessa-
loniki. This can probably be attributed to the heat island effect,
which is more intense in Athens than in Thessaloniki.
Additionally, during the summer period, a higher percentage of
variation of degree-days is observed compared to the winter
period, which means that the temperatures increased more during
the summers than during the winters. Specifically, during the
0
100
200
300
400
500
600
700
800
900
1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
Year
Degree-days (Kdays)
Base temperature 15°C
Average value
Fig. 1. Annual heating degree-days (October–April) of the period 1983–2002, for
Athens - Greece. Base temperature: 15 C.
0
200
400
600
800
1000
1200
1400
1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
Year
Degree-days (Kdays)
Base temperature 15°C
Average value
Fig. 2. Annual heating degree-days (October–April) of the period 1983–2002, for
Thessaloniki - Greece. Base temperature: 15 C.
0
100
200
300
400
500
600
1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
Year
Degree-days (Kdays)
Base temperature 24°C
Average value
Fig. 3. Annual cooling degree-days (June–September) of the period 1983–2002, for
Athens - Greece. Base temperature: 24 C.
0
50
100
150
200
250
300
350
400
1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
Year
Degree-days (Kdays)
Base temperature 24°C
Average value
Fig. 4. Annual cooling degree-days (June–September) of the period 1983–2002, for
Thessaloniki - Greece. Base temperature: 24 C.
K. Papakostas et al. / Renewable Energy 35 (2010) 1376–1379 1377

heating period, as the base temperature increases from the low
(10

C) to the high (20

C), there is a progressive reduction of the
degree-days’ percentage of variation. The opposite happens during
the cooling period. This shows that the greater changes are
observed during extreme climate conditions. That is, during the
decade 1993–2002, the greatest reduction percentages during the
heating period are for base temperatures of 10

C and lower,
therefore winters are milder, while during the cooling period the
greatest increase percentages are for base temperatures of 28

C
and over, therefore summers are hotter.
3. Impact of the temperature change on the energy
consumption for heating and cooling in a residential building
In order to reach conclusions regarding the effect of tempera-
ture changes on the energy consumption of buildings, the energy
demands of a typical residential building-model were estimated for
heating and cooling. The method used was that of degree-days with
variable base every 4 h. The advantage of this method, as compared
to the classical variable base degree-day method, is the higher time
analysis of the energy calculations. This method has the ability of
varying the indoor temperature of the building and the air change
rate at 4 h interval. It also allows to define the internal heating
sources as well as to account for heat gains from solar radiation
with higher accuracy (4-h rather than 24-h average). This way, the
balance temperature of the building and its energy demands can be
determined for 6 daily shifts and thus with increased accuracy.
Heating and cooling degree-days in 4 h-shifts as well as data for
interior heat sources, solar radiation, etc. are given in [10].
The building is a three-story apartment building, in a continuous
building system, with flat roof, pilotis and two 100 m
2
apartments
per floor. Every apartment has floor dimensions 8.8 12.5 m and
3 m height. The openings are distributed on the northern and
southern sides of the building and represent approximately 30% of
the exterior surface. The building sides facing east and west touch
adjacent buildings and thus do not have any openings.
The building insulation is of typical insulating materials avail-
able to the Greek market, and the heat transfer coefficients of the
building elements are as close to the Greek Insulation Code as
possible. The total heat transfer coefficient of the building K
m
is
0.787 W/m
2
K and is common for the 2 thermal zones where Athens
and Thessaloniki belong.
The interior temperature of the building was considered
constant from 08:00 until 24:00 and equal to 20

C for the winter
period and 26

C for the summer period. For the remaining hours it
was considered that the temperature is lower by 3K and higher by
21.7
19.3
17.3
15.6
14.0
12.7
11.5
10.5
9.6
8.0
8.8
0
200
400
600
800
1000
1200
1400
1600
1800
10 11 12 13 14 15 16 17 18 19 20
Base tem
p
erature
[
°C
]
Degree-days (Kdays)
0
5
10
15
20
25
Percenta
g
e of variation [ΔDD%]
Period: 1983-1992
Period: 1993-2002
ΔDD%
Fig. 5. Average annual heating degree-days (October–April) of the 1983–1992 and
1993–2002 decades for various base temperatures and percentage of variation. Athens -
Greece.
4.5
4.9
5.3
5.7
6.1
6.4
7.0
7.4
8.0
8.7
9.6
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
10 11 12 13 14 15 16 17 18 19 20
Base temperature [°C]
Degree-days (Kdays )
0
2
4
6
8
10
12
Percentage of variation [ DD%]
Period: 1983-1992
Period: 1993-2002
DD%
Fig. 6. Average annual heating degree-days (October–April) of the 1983–1992 and
1993–2002 decades for various base temperatures and percentage of variation. The-
ssaloniki - Greece.
68.8
24.7
60.2
28.2
32.1
36.6
41.5
47.1
53.1
0
100
200
300
400
500
600
700
800
900
28 27 26 25 24 23 22 21 20
Base tem
p
erature
[
°C
]
Degree-days (Kdays)
0
10
20
30
40
50
60
70
80
Percenta
g
e of variation
[
DD%
]
Period: 1983-1992
Period: 1993-2002
DD%
Fig. 7. Average annual cooling degree-days (June–September) of the 1983–1992 and
1993–2002 decades for various base temperatures andpercentage of variation. Athens -
Greece.
9.8
11.0
12.2
13.3
14.5
15.8
17.6
19.5
20.9
0
100
200
300
400
500
600
700
28 27 26 25 24 23 22 21 20
Base temperature [°C]
Degree-days (Kdays)
0
5
10
15
20
25
Percenta
g
e of variation [ DD%]
Period: 1983-1992
Period: 1993-2002
DD%
Fig. 8. Average annual cooling degree-days (June–September) of the 1983–1992 and
1993–2002 decades for various base temperatures and percentage of variation. The-
ssaloniki - Greece.
K. Papakostas et al. / Renewable Energy 35 (2010) 1376–13791378

4K for the winter and summer period respectively. The rate of
ventilation was considered equal to 0.8 air changes per hour for the
period 08:00–24:00. For the rest of the hours 0.5 air changes per
hour for the winter and 10 air changes per hour for the summer
period (due to the opening of windows) was considered. The heat
gains from people, lights and appliances as well as the solar heat
gains were calculated in 4-h shifts. The efficiency of the heating
system (diesel oil or gas boiler) was considered equal to 0.85 and the
performance factor of the cooling system (A/C units) equal to 2.5.
The energy calculations were performed for all the winter and
summer period months for the two cities, and the specific energy
requirements of the building were calculated for heating and
cooling in kWh/m
2
of residential surface, with temperature data of
the decade 1983–1992 as well as of the decade 1993–2002. The
total results for both cities and the energy requirements compar-
ison are presented in Figs. 9 and 10.
For the heating period, during the 1993–2002 decade,
a decrease of the energy requirements is observed for both cities as
compared to the 1983–1992 decade (Fig. 9). The percent reduction
of energy requirements is 11.5% for Athens and 4.9% for Thessalo-
niki. Conversely, for the cooling period during the 1993–2002
decade, an increase of the energy demands for both cities is
observed compared to the 1983–1992 decade (Fig. 10). For Athens
the increase is 26.1% and for Thessaloniki 10.2%. The percent change
of the building energy requirements for both cities is larger for the
cooling period than for the heating period.
4. Conclusions
The change of ambient temperatures is evident from the
evolution of heating and cooling degree-days during the years from
1983 until 2002 for the two largest cities of Greece, Athens and
Thessaloniki, and from the comparison of their values during the
1983–1992 and 1993–2002 decades for different base tempera-
tures. The average annual heating degree-days in Athens during the
1993–2002 decade were reduced by 8%–22%, depending on base
temperatures, compared to the 1983–1992 decade. The corre-
sponding reduction in Thessaloniki ranges from 4.5% to 9.5%. Also,
the average annual cooling degree-days increased by 25%–69% for
Athens and by 10%–21% for Thessaloniki, depending on base
temperatures. The energy calculations for a typical residential
building indicated that the change of temperature affects the
energy consumption of buildings for heating and cooling. From
these results it is concluded that a reduction of energy require-
ments for heating by 11.5% for Athens and by 4.9% for Thessaloniki
and a corresponding increase for cooling by 26.1% for Athens and by
10.2% for Thessaloniki is observed. The differences between the two
cities can probably be attributed to the heat island effect which is
more intense in Athens than in Thessaloniki.
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study of variable-base degree-day heating calculations. ASHRAE Trans
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[6] Papakostas K.T. Contribution to the assessment of energy consumption on
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atmospheric environment, Climatological Bulletin; 1983-2002.
[8] Founda D, Papadopoulos KH, Petrakis M, Giannakopoulos C, Good P. Analysis
of mean, maximum, and minimum temperature in Athens from 1897 to 2001
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48.6
71.7
43.0
68.2
-11,5%
-4,9%
0
10
20
30
40
50
60
70
80
ATHENS THESSALONIKI
Locations
stnemeriuqerygrenegnitaeH
m/hWK[ 2]
-14
-12
-10
-8
-6
-4
-2
0
]%[noitairavfoe
g
atnecreP
Period: 1983-1992
Period: 1993-2002
Percentage of variation
Fig. 9. Specific heating energy requirements (kWh/m
2
) of the model residential
building for Athens and Thessaloniki and percentage of variation between the
1983–1992 and 1993–20 02 decades.
8.4
6.9
10.6
7.6
10,2%
26,1%
0
2
4
6
8
10
12
ATHENS THESSALONIKI
Location
Cooling energy requirements
[KWh/m
2
]
0
5
10
15
20
25
30
Percentage of variation [%]
Period: 1983-1992
Period: 1993-2002
Percentage of variation
Fig. 10. Specific cooling energy requirements (kWh/m
2
) of the model residential
building for Athens and Thessaloniki and percentage of variation between the 1983–
1992 and 1993–2002 decades.
K. Papakostas et al. / Renewable Energy 35 (2010) 1376–1379 1379