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Present Environment and Sustainable Development
Volume 18, number 2, 2024
DOI: https://doi.org/10.47743/pesd2024182018
PESD 2024, 18, 2; DOI: https://doi.org/10.47743/pesd2024182020 www.pesd.ro
The economic impact of minimum air-
temperatures on energy consumption.
Case Study: Bucharest - Băneasa
Raul-Gabriel ILEA1,2, Nicoleta IONAC1, Laura-Elena PETRESCU1,2 , Alexandru
DUMITRESCU2, Giorgiana LÜFTNER1,2
1University of Bucharest, Faculty of Geography, Bucharest, Romania
2National Meteorological Administration, Bucharest, Romania
*Correspondence: raul11_bv@yahoo.com (R.G.I.), nicoleta.ionac@geo.unibuc.ro (N.I)
Keywords: economic impact; minimum air-temperatures; energy consumption; Bucharest-
Băneasa
Abstract: The energy consumption has become a real concern in choosing the most cost-
effective way and resources for indoor-heating. This experimental study tried to estimate both
the energy amounts needed to heat up the residential indoor spaces and the resulting average
costs that people living in the Bucharest Metropolitan Area might have to pay for heating during
the winter months. The daily minimum air-temperatures, incoming solar radiation and wind-
speed values provided by the Bucharest-Băneasa weather station were used to calculate the
corresponding mean monthly values of an expressive compound index for December, January
and February, over the 1980-2015 period. In this respect, the Cooling Energy Consumption (CEC)
index has been calculated. Then, its values were related to two different types of individual
heating systems (CT): a conventional CT produced by Ariston (net efficiency of 93%) and a
gaseous condensation CT produced by Viessmann (net efficiency of 108%). Finally, the results
were multiplied by the actual unit cost of energy in Romania (1.3 lei/kWh), provided that the
total monthly consumption of electricity per household keeps less than 300 kWh/month, so that
some interesting and realistic estimates of heating expenditures could be obtained for either each
or all winter months in Bucharest – Romania’s capital city. This method might be useful both to
local authorities and inhabitants to estimate and plan in advance their public or domestic budget
to more economically sustain their energy resources and expenditures.
1. Introduction
Bucharest is the capital city of Romania and the largest city in the country (Ielenicz,
2005). It is located in Muntenia, the central part of the Romanian Plain, at an average
altitude of 85 m (Figure 1) (Enciclopedia României, 2023). The lowest area of this city is
around 57 m (Cățelu area, in the South-East) and the highest altitude is above 95 m
(Bucureștii Noi area, in the North-West) (Dumitrescu, 2007). This city is constantly
expanding and the surrounding settlements are continually growing (Posea, 2006)
(Otopeni, Chitila, Afumați and Berceni), thus gradually turning it into a metropolitan area
(Ghid turistic România, 2023).
The town area is drained by the Dâmbovița and Colentina rivers, both belonging to
the Argeș River basin (Pișota, 2005).
Lying at the intersection of the 44˚30’N latitude and 26˚04’E longitude coordinates,
Bucharest is characterized by a mid-latitude climate of transition between the eastern
and north-eastern cold and dry continental air-masses and the western humid ones
(Ciulache and Ionac, 1995; Ionac and Matei, 2014).
PESD 2024, 18, 2 332
Figure 1. Geographical position of Bucharest city in the southern part of Romania
(Source: Spatial data – LAKI II MNT, belonging to ANCPI)
The morphological limits of the country`s area have a large influence on both the
air-circulation patterns and the climate of the city. For instance, the Carpathian
Mountains act as an important climatic barrier, often blocking the transport of moist air
from Transylvania, on one hand, but, on the other hand, by changing the general wind
direction towards the city (Ion-Bordei, 2008). In winter, the wind from North-East (called
Crivăț) gets very strong, thus amplifying the cold sensations (Bogdan, 2009). On its
turn, the Romanian Plain, extending at the feet of the Southern Carpathians and the
Getic Tableland area, between the Dobrudjan Plateau, the Black Sea and the Danube
River, acts like a large natural depression (Ion-Bordei, 1983), so, in case of an easterly
circulation pattern, a lot of moisture is brought in from the Black Sea, and if there is any
thermal inversion produced at that time (caused by an anticyclone conditions), fog may
persist for many days on end (Ciulache and Ionac, 2007).
Under the circumstances, mean air temperatures may often go to extremes in this
city, also having a great variability in time. For example, all through the 1981-2020
period, the lowest monthly (in January) mean value of daily air-temperatures recorded
at Bucharest-Băneasa weather station (located in the northern part of the town area)
was -9.3°C and the highest one (in July) is +32.9°C, resulting into a relative (mean)
annual amplitude of 42.2°C (Ionac et al., 2023).
In the context of the ongoing climate changes, the energy consumption has become
a topic of utmost concern, especially that the inhabitants of big cities are trying to find
more cost-effective ways and resources for economical indoor-heating (Gabril, 2014;
Ionac et al., 2012) provided that the frequency and intensity of climatic extremes and
hazards are increasing (Ionac et al., 2023; Ilea and Ionac, 2022).
Consequently, the main purpose of this experimental study is to prospect for a
simple and efficient way to estimate the energy amounts required to heat up the
residential indoor spaces in the Băneasa district of the Bucharest town area and the
associated resulting costs, for better budget planning solutions during the winter
months. So, the practical importance of this study relates to the fact that specific
quantitative indices, derived from certain meteorological parameters, may prove to be
efficient tools in estimating the energy demands and expenditures needed for different
heating systems that are currently being used to heat indoor spaces.
PESD 2024, 18, 2 333
2. Materials and Methods
The weather station that was taken into consideration for this experimental study is
Bucharest-Băneasa, being located in the northern part of the city, at 44°30’N latitude
and 26°04’E longitude, at an altitude of 90 m. This automatic weather station is part of
the national network of meteorological stations (WMO index: 15420), being operated by
the National Meteorological Administration (NMA) since 1929 (Figure 2).
(a) (b)
Figure 2. Bucharest – Băneasa weather-station (a) and its location within Bucharest
town-area (b) (Sources: personal image (a) and data processed in QGis with
OpenStreetMap (b))
In order to highlight some of Bucharest`s extreme climatic features, a number of 8
out of the 27 existing WMO’s Expert Team on Climate Change Detection and Indices
(ETCCDI) indices were used in this study. Designed to reflect some of the most relevant
aspects of extreme weather and climatic events (Zhang et al., 2011), they have been
selected and calculated according to RClimDex or FClimDex methods (CLIMDEX –
Datasets for Indices of Climate Extremes, 2022), over the 1980-2015 period, as follows:
• Mean of daily average temperature (TG) is the average value of all the mean
air-temperatures recorded in a certain period of time. Let TGij be the mean air-
temperature at day i of period j, then the average values in period j are given by
the next formula:
(1)
• Mean of daily minimum temperature (TN) is the average value of all the
minimum air-temperatures recorded in a certain period of time. Let TNij be the
minimum air-temperature at day i of period j, then mean values in period j are given
by the next formula:
(2)
• Monthly minimum value of daily minimum temperature (TNn) is the lowest
daily minimum air-temperature value in a month. Let TNij be the daily minimum air-
temperature at day i of period j, then the minimum daily minimum air-temperature
for period j is given by the formula:
(3)
PESD 2024, 18, 2 334
• Monthly maximum value of daily minimum temperature (TNx) is the highest
daily minimum air-temperature value in a month. Let TNij be the daily minimum air-
temperature at day i of period j, then the maximum daily minimum air-temperature
for period j is given by the formula:
(4)
• Frost days (FD) express the total number of days in a period (usually one year)
when the daily minimum air temperature gets lower than 0°C (TN<0°C). Let TNij be
the daily minimum air-temperature at day i of period j, then FD index is given by
the next formula:
(5)
• Maximum number of consecutive frost days (CFD) points to the longest period
with consecutive frost days in which minimum air temperature keeps lower than 0°C
(TN<0°C). Let TNij be the daily minimum air-temperature at day i of period j, then
CFD index is given by the next formula:
(6)
• Cold spell duration index (CSDI) represents the total number of intervals
(number / count of days) comprising at least six consecutive days in which daily
minimum air temperature (TN) is less than 10 percentiles (TN< 10 percentiles). Let
TNij be the daily minimum air-temperature at day i of period j and let TNin10 be the
calendar day 10th percentile calculated for a 5-day window centred on each calendar
day in the 1980-2015 period, then CSDI index is given by the next formula:
(7)
• Heating degree-days (HDDn18) is the sum of all the differences between the
daily minimum air temperatures and the value of +18°C for all days within a period
of reference. Let TNij be the daily minimum air-temperature at day i of period j, then
the heating degree-days is given by the next formula:
(8)
Moreover, additional daily meteorological data were obtained from Bucharest-
Băneasa weather station, such as the incoming solar radiation (RADaw), the average
minimum air-temperatures (Ta min) and wind-speed values (Wspaw), which were used
to calculate the corresponding mean monthly values of HDDs for December, January and
February over the entire 1980-2015 period.
Then, a compound quantitative index, named the Cooling Energy Consumption –
CEC (Reus-Netto et al., 2019), has been calculated by a formula based on both the
monthly and seasonal mean values of the three above-mentioned weather elements plus
the Heating Degree Days (HDDs) totals, representing the monthly/seasonal sum of all
differences between daily minimum air-temperatures and the base temperature of
+18.33°C, as recommended by ISO 7730:2005 thermal standards as the temperature
of optimal bioclimatic comfort.
The formula for the CEC index is:
CEC = 394.912 + (0.164 Ta min) + 3.233Wspaw (9)
The measuring units for the indices are as follows: kWh/m2/month for CEC, °C for
Ta min and HDDn18, kW/m2 for RADaw and km/h for Wspaw.
As the period of reference (1980-2015) included homogenous data series, each of
the above-mentioned indices could be calculated on Excel table sheets, also providing
adequate graphs to analyze their time evolution throughout the year or over the three
winter months in the entire period of reference.
Then, two different types of individual heating systems (CT) were taken into
consideration: a conventional CT produced by Ariston, with a net efficiency of 93%, and
a gaseous condensation CT produced by Viessmann, with a net efficiency of 108%; their
PESD 2024, 18, 2 335
energetic efficiency being used to calculate the corresponding actual energy consumption
for each of the heating systems of reference (Eurostat, 2022).
Finally, the results being obtained were multiplied by the actual unit cost of energy
in Romania (1.3 lei/KWh), provided that the total monthly consumption keeps less than
300 kWh/month, according to OUG 27/2022, thus obtaining the final costs of energy
being consumed for heating either on each winter month (D, J, F) or for the entire cold
season.
3. Results and discussions
The lowest minimum air-temperatures in Bucharest are usually recorded due to the
persistence of an extensive anticyclone area. The intense radiative cooling of the ground,
the resulting thermal inversions and the high humidity loads brought by the eastern air
circulation currents from the Black Sea (Sfîcă et al., 2019), may all produce heavy fogs
and dense low clouds, representing the ideal synoptic pattern leading to very low
minimum air temperatures. The lowest minimum air temperature that has ever been
recorded (absolute minimum temperature) over the entire 1980-2015 period in Băneasa
was -25.6°C (26th December 2002), while the average of the lowest annual values over
the entire period was -18.5°C (Table 1).
The most extreme values ranged from -25.6°C in 2002 (on 26th December) as the
absolute lowest minimum value, to -11.2°C in 1984 (on 14th November), as the highest
minimum value recorded in the analyzed period. An interesting fact is that, out of all the
36 years taken into consideration, 11 absolute annual minimum air temperatures
occurred in each winter month (December, January and February) and three in
November (-11.2°C: 14th November 1984; -18.8°C: 30th November 1989; -19.4°C:
26th November 1993). There were also many years when the minimum air temperature
was below -20°C (1980, 1985, 1987, 1997, 1998, 2002-2005, 2010, 2012 and 2015),
showing that there may often be extreme cold conditions during winter months in
Bucharest, especially due to persistent thermal inversions.
To get an idea about the intensity of cold-spells, suffice to say that the highest
monthly mean of daily minimum air temperatures (TN) occurring in July reaches
+15.5°C, and the lowest, in January, goes down to -4.9°C; with an annual mean of
minimum air-temperatures of +5.5°C.
Table 1. The annual absolute minimum air temperatures (°C) and date of occurrence at
the Bucharest-Băneasa weather-station (1980-2015) (Data source: NMA, 2021)
Year
1980
Day
1981
Day
1982
Day
1983
Day
1984
Day
T
(°C)
-22.4
15-Jan
-16.6
22-Dec
-13.4
11-Jan
-17
18-Feb
-11.2
14-Nov
Year
1985
Day
1986
Day
1987
Day
1988
Day
1989
Day
T
(°C)
-23.9
14-Feb
-18.6
29-Dec
-22
31-Jan
-15.5
3-Feb
-18.8
30-Nov
Year
1990
Day
1991
Day
1992
Day
1993
Day
1994
Day
T
(°C)
-19.8
7-Jan
-19
3-Feb
-14.8
25-Dec
-19.4
26-Nov
-14.4
13-Feb
Year
1995
Day
1996
Day
1997
Day
1998
Day
1999
Day
T
(°C)
-16
19-Jan
-17
30-Dec
-20.1
18-Dec
-20.6
25-Dec
-17
1-Feb
Year
2000
Day
2001
Day
2002
Day
2003
Day
2004
Day
T
(°C)
-18.5
26-Jan
-16.6
18-Dec
-25.6
26-Dec
-20
14-Feb
-20.7
13-Feb
Year
2005
Day
2006
Day
2007
Day
2008
Day
2009
Day
T
(°C)
-23.2
8-Feb
-18.8
24-Jan
-12.4
23-Dec
-15.4
5-Jan
-15.6
22-Dec
Year
2010
Day
2011
Day
2012
Day
2013
Day
2014
Day
2015
Day
T
(°C)
-24.8
26-Jan
-17.1
1-Feb
-24.2
9-Feb
-15.9
10-Jan
-19.4
31-Dec
-20.4
8-Jan
Over the entire analyzed period, the highest annual mean of daily minimum air-
temperatures reached +6.5°C (in 2014) and the lowest value went down to +4°C (in
1993), so the trend of this index is not very statistically significant, but has been
decreasing in the first decade (with 0.5°C on average) and then increasing after the
PESD 2024, 18, 2 336
1990`s (from a value of 5°C up to more than 6°C), as shown in Figure 3b. As for the
monthly mean values of daily minimum air-temperatures (Fig. 3a), they range
from -4.9°C on January, to +15.5°C on July, with a mean annual value of +5.3°C over
the entire analyzed period.
(a) (b)
Figure 3. The annual (a) and inter-annual variation (b) of monthly and annual TNs at
Bucharest-Băneasa meteorological station (1980-2015) (Data source: NMA, 2021)
The lowest of the monthly minimum values of daily minimum air
temperatures (TNn) for the 1980-2015 period was recorded on 26th December 2002
(-25.6°C). This ETCCDI index has positive values only from April tolate September,
reaching as high as +7.4°Con July; with an annual average value of -9.2°C (Fig. 4a).
This is not an extreme value for Romania, but it points to the importance of being aware
of the economic impact of energy consumption, in order to find a more cost-effective
way for indoor-heating in Bucharest town-area. The inter-annual variability of annual
minimum values of TNn’s is very large, even if the time trend is slowly decreasing.
The highest TNn value was recorded on 14th of November 1984 (-11.2°C) and the lowest
value on 26th December 2002 (-25.6°C), followed by a value of -12.4°C, occurring on
23th December 2007, as shown in Figure 4b.
(a) (b)
Figure 4. The annual (a) and inter-annual variation (b) of monthly and annual TNn’s at
Bucharest-Băneasa meteorological station (1980-2015) (Data source: NMA, 2021)
The monthly maximum value of daily minimum air temperature (TNx) for the
analyzed period has been recorded on 8th August 2012 (+25.2°C), while the lowest TNx
value occurred on January (+6.4°C); the annual average value of this index being
+16.5°C (Fig. 5a). In this case, the highest value of each month was chosen out of all
the minimum air-temperatures recorded in each of the 30/31 days of the months. The
inter-annual variability of annual maximum values of the TNx’s is moderate (not as
-4.9
0.1
4.9
9.7
13.7
15.5 15.0
10.7
5.5
0.8
5.3
-10
-5
0
5
10
15
20
III III IV VVI VII VIII IX XXI XII
Month
TN Average
5.5
5.1
5.6
4.2
5.5
5.1
6.1
4.0
6.4
4.6
6.2
4.6
5.0
6.1
4.8
6.5
y = 0.0018x2- 0.0496x + 5.4046
R² = 0.182
3
5
7
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
2014
Year
TN Tendency
-24.8 -24.2
-19.9
-4.8
4.8
7.4
5.2
0.4
-8
-19.4
-25.6
-9.2
-30
-20
-10
0
10
III III IV VVI VII VIII IX XXI XII
Month
TNn Average
-22.4
-13.4
-17
-11.2
-23.9
-18.6
-22
-15.5
-19.8
-14.8
-19.4
-14.4
-20.6
-17 -16.6
-25.6
-23.2
-12.4
-24.8
-17.1
-24.2
-15.9
-20.4
y = -0.0564x + 94.226
R² = 0.0291
-30
-20
-10
1980 1987 1994 2001 2008 2015
℃
Year
TNn Tendency
PESD 2024, 18, 2 337
great as shown for the TNn index) and its time trend is slowly increasing. The highest
value has obviously been recorded on 8th August 2012 (+25.2°C), as already stated
above, but many other values exceeding the threshold of +20°C are also specific for
summertime (Petrescu et al., 2024), as observed in Figure 5b, thus showing that there
may occur many tropical nights in Bucharest-Băneasa. The lowest value has occurred on
28th July 2004 (18.1°C).
(a) (b)
Figure 5. The annual (a) and inter-annual variation (b) of monthly and annual TNx’s at
Bucharest-Băneasa meteorological station (1980-2015) (Data source: NMA, 2021)
The highest number of frost days (FD) has been recorded in January (26 days
over the entire analyzed period), followed by December, with 23 frost days, and by
February, with 22 frost days. An interesting fact is that the average FD index value is
zero from May to September (Fig. 6a), meaning that all minimum air-temperatures
occurring these months were positive. The highest FD value was calculated for 2003
(137 days) and the lowest for 2014 (72 days), with the annual FD counts generally
decreasing slowly (Figure 6b), which means that in Bucharest-Băneasa area, the need
for thermal energy still keeps high and that the latest warming trends are not significant.
(a) (b)
Figure 6. The annual (a) and inter-annual variation (b) of frost days (FD) atBucharest-
Băneasa meteorological station (1980-2015) (Data source: NMA, 2021)
The highest number of consecutive frost days (CFD) was reached in 1985, with
76 consecutive days when daily minimum air-temperature values dropped below 0°C
(from 1th of January to 17th of March). The lowest CFD index value was calculated for
1994 and 1999, with only 15 consecutive days, followed by 1984, with 16 consecutive
days. The trend of this index shows a slight decrease over the 1980-2015 period, from
a value of 40 consecutive frost days to almost 20 days; yet this decreasing trend is not
very statistically significant (Fig. 7a).
6.4
13.2
12.5
14.8
20
22.1
24 25.2
19
15.4
16.2
9.5
16.5
5
10
15
20
25
30
III III IV VVI VII VIII IX XXI XII
Month
TNx Average
20.4
19.5
23.2
19.8
23.4
19 19
20.4
19.6
22
20.8
22.1
18.1
22.2
20.5 19.9
25.2
20.6
22.9
y = 0.0287x + 20.335
R² = 0.0451
17
22
27
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
2014
Year
TNx Tendency
26
22
15
3
00 0 00
3
13
23
0
10
20
30
III III IV VVI VII VIII IX XXI XII
Nr. of days
Month
FD
99
116
85
113
101
110
86
125
90
121
91
102
137
95
121
105
87
126
72
93
y = -0.0934x + 105.62
R² = 0.0052
60
80
100
120
140
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
2014
Nr. of days
Year
FD Tendency
PESD 2024, 18, 2 338
The annual values of the cold-spell duration index (CSDI) were highest in 1986,
when four cold waves occurred (Figure 7b). This index represents the number of intervals
in each year when, for at least six consecutive days, the daily minimum air temperatures
were lower than the calendar 10th percentile calculated for a 5-day window centered on
each calendar day over the 1980-2015 period (Ciulache and Ionac, 2005). It is
noteworthy that there were years with no cold waves (1988, 1997 and 2013) too.
(a) (b)
Figure 7. The inter-annual variation of CFD’s (a) and the maximum values of CSDI’s (b)
at Bucharest-Băneasa meteorological station (1980-2015) (Data source: NMA, 2021)
A specific version of the degree-days (DDs) index (Figure 8), namely the heating
degree-days (HDDs) wasalso needed to calculate the CEC index and ultimately, the
amount of energy required to heat indoor spaces and the energy costs for winter months.
Obviously, the highest heating degree-days (HDDs) sums are specific of the cold
season and the lowest values are commonin summer. In July, for example, the HDDn18
index reached a value of 76.9°C, which means that quite a few of the minimum air
temperature values were greater than +18°C, while in winter, the HDD sums may go up
to 709.3°C (Fig. 8a).The inter-annual variation of heating degree days (HDDs) shows
that 1993 was the coldest year in the 1980-2015 period (5,081°C), followed by 1985,
with a total of 5,024.4°C. The warmest years were both 1994 and 2014 (with 4,223.6°C,
respectively 4,183.3°C).In this case, a slight increase of this index was specific for the
first decade of the analyzed period, but the trend decreases after the 1990`s, by an
average of 350°C (from almost 4750°C to only 4400°C) (Fig. 8b). The main cause of
this trend is most probably the general ongoing climate warming process, more evident
in the evolution trend of minimum air-temperatures.
(a) (b)
Figure 8. The annual (a)and inter-annual variation (b) of the HDDn18 index at
Bucharest-Băneasa meteorological station (1980-2015) (Data source: NMA, 2021)
In this experimental study, only the winter months (D, J, F) were taken into
consideration, both separately and for the entire cold season. First of all, all parameters
31
59
16
76
31
43
22
39
51
15
45
15
41
28
60
17
45
19 20
57
19
21
y = -0.2654x + 39.687
R² = 0.0335
0
20
40
60
80
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
2014
Nr. of days
Year
CFD Tendency
1
2
1
4
1
3
1
2
1
2
3
1
3
1
2
1
y = -0.0117x + 1.7444
R² = 0.0198
0
1
2
3
4
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
2014
Cold waves
Year
CSDI Tendency
709.3
637.6
553.5
392.0
256.0
129.4 76.9 94.3
220.5
388.4
514.9
658.4
0
200
400
600
800
III III IV VVI VII VIII IX XXI XII
Month
HDDn18
4545.6
5024.4
4736.9
4343.1
5081
4223.6
4881.4
4323.3
4891.1
4338.4
4789.8
4183.3
y = -0.6736x2+ 18.397x + 4591.4
R² = 0.1825
4000
4500
5000
5500
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
2014
℃
Year
HDDn18 Tendency
PESD 2024, 18, 2 339
(HDDn18, RADaw, Ta min and Wspaw) that were necessary for the calculation of the
CEC index were selected and introduced in Table 2.
Table 2. The prerequisite values for CEC index for each and all winter months (D, J, F),
at Bucharest-Băneasa meteorological (1980-2015) (Data source: NMA, 2021)
December
January
HDD
RADaw
Ta min
Wspaw
HDD
RADaw
Ta min
Wspaw
°C
kW/m2
°C
km/h
°C
kW/m2
°C
km/h
658.4
0.04549
-3.2
7.4
709.3
0.057373
-4.9
7.4
February
Winter season (D + J +F)
HDD
RADaw
Ta min
Wspaw
HDD
RADaw
Ta min
Wspaw
°C
kW/m2
°C
km/h
°C
kW/m2
°C
km/h
621.9
0.096528
-4.0
8.3
1989.6
0.0665
-4.0
7.7
Based on the above-mentioned pre-requisite data, then the CEC index could easily
be calculated both for each winter month and for the entire cold season (Gabril N., 2014).
Table 3 shows that the highest CEC value occurred on January (547.6 kWh/m2), followed
by December, with 528.7 kWh/m2 and the lowest value occurred in February (491
kWh/m2). The CEC index value calculated for the entire cold season amounts to 739.9
kWh/m2.
Table 3. The CEC index values (kWh/m2) for each and all winter months (D, J, F), at
Bucharest-Băneasa meteorological (1980-2015) (Data source: NMA, 2021)
Month
December
January
February
Winter
CEC
528.7
547.6
491.0
739.9
However, in the latter case referring to the entire cold season, it is very important
to mention that the CEC value represents neither the average nor the sum value of the
three winter months, but their interpolated values, due to the calculation formula.
Next, the net efficiency of two different heating systems had to be taken into
consideration: 93% for an Ariston CT (Fig. 9a) and 108% for a Viessmann one (Figure
9b). This aspect is important for the calculation of the corresponding energy consumption
for each of the two CT`s.
(a) (b)
Figure 9. A conventional individual heating system produced by Ariston (a) and a
gaseous condensation system produced by Viessmann (b) (Sources: Ariston, 2023 and
Viessmann, 2023)
The Energy Consumption(C) is then obtained by dividing the value of the CEC
index by the net efficiency (η) of each individual heating system: C = CEC/η (Table 4).
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It becomes obvious that the actual energy consumption is higher for conventional
heating energy systems (Ariston) than for the gaseous condensation systems
(Viessmann) (ASHRAE, 2009). For example, in January, the actual energy consumption
value is 588.8kWh/m2 for Ariston systems and only 507.1 kWh/m2 for Viessmann
systems.Over the entire winter season, the energy consumption reaches as high as
795.6 kWh/m2 for Ariston and 685.1 kWh/m2 for Viessmann. The difference between the
two heating system types is pretty large, not only for each month analyzed, but also for
the entire cold season (Table 4).
Table 4. The actual energy consumption (kWh/m2) for two selected heating systems,
for each and all winter months (D, J, F) at Bucharest-Băneasa meteorological station
(1980-2015) (Data source: NMA, 2021)
Month
December
January
February
Winter
Ariston
568.5
588.8
527.9
795.6
Viessmann
489.5
507.1
454.6
685.1
The final step of our experiment was to multiply the energy consumption rates
resulted for each month by 1.3 lei/kWh (the actual cost of energy in Romania, according
to OUG 27/2022), in order to find out the total costs of energy consumption, both for
each month of reference and the entire winter season.
The results obtained are interesting and useful (Table 5), with the highest cost of
energy calculated for January, around a value of 765.5 lei for Ariston heating systems,
that is with 100 lei more expensive than for the Viessmann heating systems (659.2 lei).
In December, the difference between the two heating systems types was also higher
than 100 lei (739 lei for Ariston and 636.4 lei for Viessmann), while in February, it was
less than 100 lei (686.3 lei for Ariston and 591 lei for Viessmann). For the entire winter
season, the difference between the costs of the heating energy provided by the two
heating systems was 143.7 lei, with more than 1,000 lei for Ariston individual energy
systems.
Table 5. The final costs (lei) of energy consumption (according to OUG 27/2022) for
each and all winter months (D, J, F) at Bucharest-Băneasa meteorological station
(1980-2015)
Month
December
January
February
Winter
Ariston
739.0
765.5
686.3
1034.3
Viessmann
636.4
659.2
591.0
890.6
Difference
102.6
106.3
95.3
143.7
5. Conclusions
All the minimum air-temperature values that were recorded in the northern part of
Bucharest city had a high range from 1980 to 2015, meaning that the general climatic conditions
have changed a lot over the analyzed period and the variability of all specific meteorological
parameters was pretty large. This fact has been confirmed by all the respective ETCCDI indices
calculated in this study, from one month to another and from one year to another.
The mean monthly value of daily minimum air-temperatures (TN’s) reached
a maximum in July (+15.5°C) and a minimum in January (-4.9°C). The trend of this
index is not very statistically significant, but it showed a slight increase after the 1990`s.
The monthly minimum value of daily minimum air-temperatures (TNn’s) has
positive values from April to late September, reaching as high as +7.4°C, in July. The
value of -25.6°C, recorded on 26th December 2002, was the lowest one over the entire
analyzed period. This index is relevant because it draws attention on the amount of
energy consumption in the Băneasa area of Bucharest city.
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The monthly maximum value of daily minimum air-temperatures (TNx’s)
reached its highest ever recorded limit on 8th August 2012 (+25.2°C), while its annual
average maintained around +16.5°C. For both TNn and TNx indices, there are no statistically
significant changes over time, but there is a high variability from one year to another.
The frost days (FD) evolution trend decreases slowly over time, which is somewhat
good for investing in more cost-efficient heating systems. The highest value of this index
was recorded in January, with 26 days on average. The highest FD value was calculated
for 2003 (137 days) and the lowest in 2014 (72 days).
The maximum number of consecutive frost days (CFD) was reached in 1985, with
76 consecutive days when daily minimum air-temperatures kept below 0°C. The trend of this
index is not very statistically significant, but it shows a decrease over the 1980-2015 period.
The cold spell duration index (CSDI) ranged from zero to four cold waves per
year (the maximum value being reached in 1986). There were years with no cold waves,
such as 1988, 1997 and 2013.The coldest year form the analyzed period was 1993, when
the sum of all daily minimum air temperatures lower than 18°C (HDDn18 index)
reached 5,081°C, resulting in high energy consumption. In contrast, the lowest value of
this index was 4,183.3°C, calculated for 2014, which was a warm year.
The Cooling Energy Consumption (CEC index) reached a maximum value of 547.6
kWh/m2 in January, and a lowest value in February (491 kWh/m2). Over the entire winter
season, the value of the CEC index reached 739.9 kWh/m2. Consequently, the highest energy
cost was calculatedfor January, with a value of 765.5 lei for Ariston heating systems and
659.2 lei for Viessmann heating systems. The difference of more than 100 lei between the
two heating systems types is also valid for December and for the entire winter period as well.
To conclude, it is important to say that this experimental study tried to demonstrate
how relatively simple, fast and precise the energy consumed for indoor heating may be
calculated and how the improved energetic performance of heating systems may actually
help people to save up more money for other living costs. Moreover, this study also proves
how some climatic factors of influence may be used both to forecast, plan and manage
energy consumptions over any period of time and to estimate their respective economic
impact on each household, depending on the climatic region they are located in.
Acknowledgements: All authors have read and agreed to the published version of the
manuscript. The completion of this research paper was possible with the support of Romania’s
National Meteorological Administration, which provided the daily datasets of interest.
Author contributions: Original idea and design: N.I.; methodology: N.I.; data acquisition: A.D.,
G.L., L.E.P., R.G.I.; data processing: R.G.I.; tables and graphs: R.G.I.; formal analysis: R.G.I.,
N.I.; original draft preparation: R.G.I.; writing-editing: R.G.I.; reviewing: N.I.
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nd/4.0).
