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Specific heating consumption in the residential sector of Serbia—Example of the city of Kragujevac
Energy and Buildings 107 (2015) 163–171
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Specific heating consumption in the residential sector of Serbia—Example of the city of Kragujevac ´ N. Nikolic´ ∗ , D. Gordic´ N. Lukic´ ∗ , N. Juriˇsevic, Faculty of Engineering, University of Kragujevac, Sestre Janji´c 6, 34000 Kragujevac, Serbia
a r t i c l e
i n f o
Article history: Received 17 June 2015 Received in revised form 4 August 2015 Accepted 5 August 2015 Available online 7 August 2015 Keywords: Specific energy consumption District heating Gas heating Electric heating Tariffs
a b s t r a c t In this paper, the specific consumption of the heat energy supplied by three most utilized heating systems (district heating, gas and electricity system) in the residential sector of the city of Kragujevac (Serbia) is analysed. Required data are provided by combining data from local utility companies with national census results. Comparison of present tariff systems shows that consumers in the residential buildings are the most motivated for energy savings if they use electricity or gas as energy source. The specific energy consumption in district heating system shows relatively high quantities, primarily as a consequence of dominant unmotivating tariff payment system. The average heat consumption from gas and electricity sources relatively fits to EU average, but the electricity consumption of the electric heaters is not acceptable in long term. Low electricity price in Serbia and high price of unit of energy from district heating system of the city of Kragujevac (and Serbia) will lead to an increase of electric energy consumption which will cause additional problems related to covering of that consumption from domestic energy sources. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Scientific and technological development has contrived to modern society high level of thermal comfort that requires high energy consumption. In the year 1995 each of 6 billion people on the planet Earth consumed 2 kW, while the resident of USA consumed 13 kW of energy consumption [1]. Although in 2009 developed countries reduced their energy consumption per capita (US 10.3 kW, EU 4.8 kW) global energy consumption per capita has grown up to 2.37 kW [2]. These are a very high quantities considering that the physiological functioning of human requires only 120 W [1]. Parallel to the increasing need for the energy consumption the awareness of the need for more efficient use of energy was increasing too, especially in developed countries. More efficient use of energy is encouraged by states that impose law restrictions and subsidies. However, the strongest influence on increasing energy efficiency has a market and rising prices of practically all energy sources. To form a strategy to reduce specific energy consumption it is necessary to analyze the final energy consumption by sector. It is common that these sectors be divided into industry, transportation and buildings. Furthermore, the energy consumption in buildings is divided into residential and non-residential sector (commercial and
∗ Corresponding authors. Tel.: +381 34357884. ´ [email protected] (N. Nikolic). ´ E-mail addresses: [email protected] (N. Lukic), http://dx.doi.org/10.1016/j.enbuild.2015.08.012 0378-7788/© 2015 Elsevier B.V. All rights reserved.
public buildings). In the EU these shares (2009) has been as following: 41% for the building sector, 32% for the transportation sector, 25% for the industry sector (and 2% for the agriculture) [3]. In 1990, energy consumption in the EU industry had a share of 34% and in the building sector 36%. These data confirm the trend in developed countries that energy consumption moves from the building to the industry sector [1]. With the exception of the southernmost states of the EU, all the other consumes significant amounts of final energy in the building sector for space heating (60–80%) (the average for the EU is 67%) [3]. This share decreases slightly (in 1997 it was 71%) on account of increase of energy consumption of lighting and electrical appliances. The average specific consumption of final energy in the residential sector of the EU was 200 kW h/m2 a, while the nonresidential sector consumed significantly more 300 kW h/m2 a [3]. Although new buildings in the EU consume considerably less energy for heating, the average consumption of the existing residential sector according to the mentioned data was 134 kW h/m2 a (data for 2009). Within the total energy consumption in the residential sector (2009), the most consumed is gas (39%) and electricity (25%), while coal as an energy source is almost completely eliminated (3%). The share of district heating in the EU is relatively low (7%), and it is still pronounced in the Baltic and East European countries, although even there this share decreases. Serbia, as a potential member of the EU is burdened with very unfavorable indicators in the energy sector. In comparison with the 1989 in 2000 Serbia had 2.5 times lower gross domestic product
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(GDP) and the highest consumption of energy in Europe per unit of GDP [4]. In Serbia, shares in final energy consumption by sector (2008) amounted to: industry 34%, transportation 28% and buildings 38% (27% residential, non-residential 11%) [5]. Averagely 65% of final energy consumption in Serbia is consumed for heating, which is close to the European average [6]. In Serbia, after the Second World War the urban environments were intensively built, so that the share of apartments of 27% (1961) was changed to 56% (2008) [5]. Unfortunately, the most of these apartments were built until 1980 as a part of the building within the urban areas. These buildings are characterized by oversized heating systems, lack of insulation and high specific heating consumption [7,8]. According to the scarce information about the specific heating consumption in the residential sector in Serbia, for space heating and heating of a domestic hot water in apartments in Serbia an average of 220 kW h/m2 a is consumed, which is far more than the average in the EU [9]. In literature it can be found data that this consumption in Serbia is significantly higher [4]. According to [10] the share of certain energy sources used for heating of the residential buildings in Serbia is as follows: wood 43%, district heating 22%, electricity 15.5%, gas 10%, coal 9% (and all other fuels 0.5%). Although the state of Serbia stimulated different measures to increase energy efficiency and reduce energy consumption in the residential sector by adopting laws and regulations, supporting and funding various projects (NEEP [4], NEAP [5], Energetic lows 2004, 2014, the Law on Efficient Use of Energy 2013) significant advances in this area have not been made [11]. We believe that the main cause of poor energy indicators in the Republic of Serbia is the significant absence of market incentive of citizens to save energy. First of all, this relates to low cost of electricity, market price of the mainly imported oil and gas, as well as tariff payment system for district heating defined per m2 of the residential area and independent of the consumed heat energy. In the case of the city of Kragujevac and achieved consumption of energy sources (electricity, gas and district heating) in the residential sector for heating seasons 2009–2013, the achieved specific consumptions as well as relations between consumption, tariff payment system and weather conditions will be shown.
2. The tariff systems and ratios of heating prices for household for the city of Kragujevac 2.1. Current prices for electricity, gas and district heating The Serbian energy sector pulls longstanding problems of the socialist economy with controlled policy of low prices of energy sources, with low energy efficiency in all sectors, with high debts for imported energy sources which were uneconomically consumed. One of the most significant structural problems is extremely low price of electricity (the lowest in Europe), which is mainly produced in thermal power plants, which burn domestic low-calorie coal (lignite) [12]. It has led to that the currently 1 kW h of thermal energy of the supplied gas (0.05 D ) costs approximately as 1 kW h of electricity (approximately D 0.06), although the conversion factor of converting thermal energy into electrical is 2.5–3.5. In Serbia, the buildings within the urban areas are heated by district heating, electricity and gas. The prices of gas and electricity are virtually the same for the entire state, while the prices for the district heating vary from city to city. The tariff payment system for consumed electricity in Serbia is shown in Table 1. The tariff system is defined so that the price of electricity for small and medium consumers is very favorable, especially during night. To avoid excessive consumption of electricity, this non-market tariff system has disincentive price of electricity for consumers who consume more than 1600 kW h per month
(red zone). The official mean price of electricity in Serbia is 7.32 RSD/kW h (RSD/EUR = 120). The price of natural gas supplied by the main distributor of this energy source in Serbia currently amounts to 55.33 RSD/N m3 (adopting the lower heating value (LHV) for gas of 34,000 kJ/N m3 and the price of 13.56 D /GJ). The tariff system and the price of district heating in Serbia is formed at the city level and currently the double tariff system is in effect: for most consumers the tariff is fixed and defined per m2 of the residential area of the apartment and for the smaller number of consumers it is variable defined per consumption with a significant fixed part. Specifically, in the city of Kragujevac district heating defined per consumption currently pay about 20% of connected consumers in the residential sector. The double tariff payment system of district heating in the city of Kragujevac for residential sector is given in Table 2. 2.2. Comparison of the heating prices for households in the city of Kragujevac For a comparison of the heating costs for various energy sources used in Kragujevac the following data were adopted: -
household of 100 m2 of useful living space is considered, heating season lasts 6 months (180 days), ratio of daily and nightly electricity tariff is 70/30, electricity consumption unrelated to the heating is 500 kW h per month, engaged electrical power of a household is 10 kW, efficiency of a gas boiler is g = 0.9, adopted LHV of natural gas is 34,000 kJ/N m3 , four specific heating consumptions are analyzed: 50, 100, 150 and 200 kW h/m2 a, four options of the heating in the city of Kragujevac are analyzed: electricity (heaters), gas (boiler), district heating – fixed charge and district heating – charge per consumption.
Fig. 1 shows the unit price of energy (kW h) which pays the owner of the household of 100 m2 for heating expressed in D /kW h for four defined options of heating and for different specific consumptions. From Fig. 1 it can be seen that the price of energy from gas is fixed, irrespective of consumption which maximally simplifies the calculation of a household to save energy or to invest in insulation of an object. The price of heating by conventional electric heaters for low specific consumptions is more cost effective than district heating. Although it is not shown in the diagram the heating by electricity as a part of a system with heat pump (estimated heating factor of 2–5) would be undoubtedly the cheapest heating option under this ratio of prices in Kragujevac (Serbia). District heating system has been built in a time of urbanization of Serbia and cheap energy. Long-time charging system fixed per unit of residential area of the residential building discouraged the investment in increasing the efficiency of production and transport of heat energy. For a long time the price for heating based on square meter of heating area is built in that manner that now it is the most expensive heating option for well insulated buildings (consumption less than 100 kW h/m2 a). The charging system based on consumption, which will soon become the only tariff system within the district heating makes this system slightly competitive especially for consumptions to 100 kW h/m2 a. It is clear that in these circumstances and with fixed tariff thinking of a family in the residential apartment connected to the district heating system about investment in insulation of the object is excluded without any economic sense.
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Table 1 Tariff payment system for consumed electricity in Serbia (for two tariff electricity meter). Households
Higher (daily) tariff (RSD/kW h)
Lower (nightly) tariff (RSD/kW h)
Capacity charge (RSD/kW)
Green zone 0–350 kW h Blue zone 350–1600 kW h Red zone over 1600 kW h
6.49 9.79 19.48
1.62 2.44 4.87
51.41
Ratio RSD/EUR = 120. Table 2 Double tariff payment system of district heating for residential sector in the city of Kragujevac. Fixed per residential area (RSD/m2 )
Type of consumer
Residential sector
Per consumption
92.55
Fixed part (RSD/m2 )
Variable part (RSD/MW h)
29.2
5430
Ratio RSD/EUR = 120.
Price of consumed energy (€/kWh)
0.2 0.18
Gas
0.16
District heang (fixed charge) District heang (variable charge)
0.14
Electricity
0.12 0.1 0.08 0.06 0.04 0.02 0 0
50 100 150 200 Yearly consumpon per m² of residenal area (kWh/m² )
250
Fig. 1. Price of kW h of heating energy for the household of 100 m2 in the city of Kragujevac for different options of heating.
2500
Total heang costs (€/a)
2000
Gas District heang (fixed charge) District heang (variable charge) Electricity
1500
1000
500
0 0
50
100 150 Specific heang consumpon (kWh/m²)
200
250
Fig. 2. The total yearly heating cost for the household of 100 m2 of residential area for different heating options in the city of Kragujevac.
Fig. 2 shows the total yearly heating cost for the household of 100 m2 of residential area in the city of Kragujevac. Analyzing Fig. 2 it is clear that increasing the slope of the line means the higher incentive of consumer for reducing heating consumption. This means that in Kragujevac (Serbia) consumers in residential buildings have the most economic incentive to save
energy if they are heated by electricity or gas. The tariff system defined per consumption for district heating is lagging behind electricity and gas. The tariff system with fixed charge for district heating which uses 80% of connected residential consumers in Kragujevac is virtually fatal to any idea of increasing the energy efficiency of residential buildings.
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Table 3 Climatic characteristics of Kragujevac for the heating months from 1981 to 2010 [13].
Temperature (◦ C) Max average Min average Normal Max absolute Min absolute
Jan.
Feb.
Mar.
5.2 −2.9 0.9 20.6 −27.4
7.3 −1.9 2.3 24.2 −23.8
12.5 1.8 6.6 29.4 −18.3
Apr. 17.8 5.9 11.7 31.4 −5.8
Table 4 The values of heating degree days for the city of Kragujevac for the period 2009–2013. Year
2009
2010
2011
2012
2013
Heating degree day (◦ C day)
2461.2
2522.3
2918.9
2695.3
2359
3. Energy consumption in the district heating system, electricity and gas consumption for heating residential buildings in the city of Kragujevac in the period 2009–2013 According to the census of 2011 [10] Kragujevac with 179,417 inhabitants is the fourth most populated city in Serbia. It is located in the central part of Serbia. The city area extends over 835 km2 and the altitude ranges from 185 to 220 m. Basic microclimate temperature characteristics of the city with a temperate continental climate are shown in Table 3. According to the census of 2011 [10] the share of certain types of heating systems is slightly different in Kragujevac in relation to Serbia: district heating 31% (Serbia 22%), wood 42% (43%), electricity 9.5% (15.5%), gas 13.5% (10%), coal 3.5% (9%). As an urban environment Kragujevac has a higher share of users of district heating and gas, and a smaller share of users of electricity and coal for heating purposes in relation to Serbia. Traditionally Serbia consumes large amounts of wood for heating especially on the outskirts of cities and in rural areas. Consumption of thermal energy for heating in Kragujevac is analyzed for the period 2009–2013. The needs for heating, caused by weather conditions during the specified period are presented by heating degree days determined for ambient temperature of 20 ◦ C and heating temperature threshold of 12 ◦ C. Mean outdoor temperatures were retrieved from the database of the local utility company, responsible for district heating. The values of heating degree days for the city of Kragujevac for the period from 2009 to 2013 are shown in Table 4. 3.1. Consumption of heat energy in the district heating system The district heating company in the city of Kragujevac is a former industrial power plant of the company Zastava cars. Within this power plant for the purposes of technological steam as well as independent electricity production the steam coal-fired boilers which today can produce 240 MW of thermal power were built. At the same location besides the steam coal-fired boilers there are gasfired boilers (total power of 63 MW). In addition to the central boiler plant at the city there are dislocated boiler plants with hot water boilers fueled by oil and gas. Due to the structure of boiler plants of district heating system in Kragujevac and lower coal price, reduced to heating value, coal is energy source that is mostly used for heating. In the analyzed period 2009–2013 the share of coal in the total production of heat energy in the district heating system in Kragujevac amounted to 76% (see Table 5). Use of coal as an energy source caused a slightly lower price of district heating in Kragujevac in relation to other major cities in Serbia (Belgrade, Novi Sad, Niˇs). Although the Law on Efficient Use of Energy (Official Gazette 25/13) provides that from the beginning of the heating season of
Oct. 18.5 7.1 11.9 32.6 −6.6
Nov.
Dec.
Season
11.6 2.5 6.4 27.6 −11.8
6.2 −1.1 2.1 21.0 −20.6
11.3 1.63 5.98 32.6 −27.4
2014/2015 all central heating systems in Serbia should switch to the tariff system based on consumption, it did not happen and the tariff system based on fixed charge is still the dominant system of charging. From heating season 2011/2012 the district heating company in Kragujevac offers residential customers to switch to the tariff system based on consumption (presented in Section 2.1). So far this tariff system accepted 20% of residential units that are surely newer and insulated buildings in the city. Unfortunately, the remaining 80% of residential consumers pay fixed tariff which excludes interest in reducing energy consumption. Total energy consumption for the analyzed period 2009–2013 is calculated according to the available data on the total consumed energy sources in the district heating system. These data are given in Table 5 as well as the data on the heated areas and shares of energy consumed for industrial purposes. All these data were taken from the company responsible for the operation of the district heating system in the city of Kragujevac. In order to calculate the consumed energy in residential buildings of consumers of district heating system the following data were adopted: LHV for heavy oil is 42,000 kJ/kg, for gas 34,000 kJ/N m3 , the efficiency of coal-fired boilers is 0.8, the efficiency of heavy oil-fired boilers and gas-fired boilers is 0.9 and the average transportation losses are 7% (calculated in [14]). Data on the average efficiency of boilers were adopted from [14]. As the total consumption of energy sources in the district heating system covered all consumers it was necessary to separate the consumption of industry according to the given shares as well as the consumption of commercial and public buildings from the consumption of the residential buildings. Specific data on measured consumption were not available, so for this separation the data from the literature was used. It is known that commercial and public buildings consume significantly more energy than residential buildings. In the EU (2009) non-residential buildings were consuming an average of 295 kW h/m2 a of total final energy while residential buildings were consuming 200 kW h/m2 a. Certainly in Serbia non-residential buildings consume significantly more energy than residential buildings which is particularly evident in public buildings (schools, hospitals, administrative buildings, etc). In Serbia, in the period 2010–2012 in the framework of Serbia Energy Efficiency Project (SEEP), 62 public buildings were reconstructed and for which the heating consumption before and after the reconstruction were measured [15]. Before the reconstruction (2011) it was found that these buildings consumed an average of 301.5 kW h/m2 a for heating. As it has been already mentioned that in Serbia residential buildings consume an average of 220 kW h/m2 a for heating and domestic hot water. According to this it was adopted that the ratio of heating consumption for non-residential and residential buildings in Kragujevac is 3:2. By adopting this ratio and knowing the total consumption and area of non-residential and residential buildings of consumers of district heating, it was possible to calculate the average consumption for residential buildings in Kragujevac, as shown in Fig. 3. Otherwise, the standard heating season of the district heating system is defined for the period from 15.10 to 15.04 of the next year. Fig. 3 shows that the specific heating consumption is very high (an average of 173 kW h/m2 a) and practically very close to the
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Table 5 Consumption of energy sources and heated areas of consumers of a district heating system. Year
2009
2010
2011
2012
2013
Coal (t) Oil fuel (t) Gas (N m3 ) Average LHV of coal (kJ/kg) Heat energy for industry (%) Total heated area (m2 ) Residential heated area (m2 )
106,559 10,014 5932,000 14,142 0.14 1457,826 960,633
82,014 7945 3156,000 14,156 0.11 1457,825 957,048
106,559 6410 6932,000 12,676 0.11 1479,406 967,140
105,956 6437 12,060,000 13,246 0.06 1561,969 1036,429
74,423 3920 6245,000 12,489 0.07 1518,281 1010,408
250.00
Average consumpon 172,8 kWh/m2a
3000 District heating Degree day
200.00 2600 2400
150.00
2200 100.00
2000
Degree day (oCday)
Specific yearly consumption (kWh/m2a )
2800
1800 50.00 1600 0.00
1400 2009
2010
2011
2012
2013
Fig. 3. Specific heating consumption for residential buildings, consumers of district heating system in Kragujevac and heating degree days for the period 2009–2013.
Table 6 Specific heating consumption for residential buildings, consumers of district heating system in Kragujevac and deviation of the specific consumption per heating degree days in relation to the specific consumption in 2013. Year
2009
2010
2011
2012
2013
Specific consumption (kW h/m2 a) Specific consumption per heating degree day (kW h/m2 a ◦ C day) Deviation of the specific consumption per heating degree day in relation to the consumption in 2013 (%)
200.41 0.081 49.3
156.32 0.062 13.6
176.80 0.061 11.0
201.84 0.075 37.3
128.68 0.055 0
fact that the residential buildings in Serbia consume an average of 220 kW h/m2 a for heating and domestic hot water [9]. The structure of a residential buildings connected to the district heating system in Kragujevac is very diverse. The non-insulated buildings from the period of 70s and 80s of the last century prevail, then insulated buildings and a significant number of insulated and noninsulated family houses. In [14] it can be found information on the measurement of the heating consumption (2004/2005) of the noninsulated residential building with heated area of 4047 m2 , with an extensive problem of overheating. Consumption reduced to the heating degree days from 2011 would amount to 187 kW h/m2 a. Also, Fig. 3 shows a stable relation between energy consumption and needs (heating degree-days). However, there are some deviations for 2009 and 2012. Standard daily period of operation of the district heating system in Kragujevac is from 6:00 am to 9:00 pm. If the average night temperatures are very low the heating lasts 24 h. For the analyzed period there were not significant number of those days except for heating season 2012 (the end of January and the first half of February) when consumers were continuously heated about 20 days. This operation of the district heating system has led to increased energy consumption in 2012, although the number of heating degree days was lower than for the coldest
season 2011 (see Table 4). Specific heating consumption for residential buildings, consumers of district heating system in Kragujevac and deviation of the specific consumption per heating degree days in relation to the specific consumption in 2013 are given in Table 6. The deviation of the specific consumption per heating degree days was highest in 2009. It can be explained by the effects of the economic crisis during 2008 which with certain inertia (since 2010) affected the decrease of purchasing energy sources of the local utility company. Heat energy production is mainly based (Table 5) on a cheaper coal and the general characteristic of the consumption was overheating of the most buildings and lack of interest for energy savings. 3.2. Heating consumption for gas consumers In Kragujevac for the analyzed period (2009–2013) only one (state) company delivered natural gas to consumers. Using data obtained from the same company the specific heating consumption of residential buildings in Kragujevac, connected to the gas installations, is calculated. Table 7 presents the consumption of gas for heating and area of the residential buildings (consumers) for the analyzed period.
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Table 7 Consumption of the natural gas for heating and residential area of the consumers for Kragujevac. Year
2009
2010
2011
Consumption (N m3 ) Area of the consumers (m2 )
7785,028 500,573
6940,865 550,562
7813,121 577,323
7887,203 589,005
Average consumpon 112,1 kWh/m2a
2013 6574,173 606,121
3000 Natural gas Degree day
130.00
2800 2600
110.00 2400 90.00
2200
70.00
2000 1800
50.00
Degree day (oCday)
Specific yearly consumption (kWh/m2a )
150.00
2012
1600 30.00 1400 10.00 -10.00
1200 2009
2010
2011
2012
2013
1000
Fig. 4. Specific heating consumption for residential buildings, gas consumers in Kragujevac and heating degree days for the period 2009–2013.
The amount of consumption of gas consumed for heating is calculated as follows. Consumption in the heating season for each year is obtained as the sum of consumptions in the period JanuaryMarch and November-December plus half the consumption for April and October. The difference between the total annual gas consumption and gas consumption in the heating season (180 days) gives the (summer) gas consumption for other purposes (domestic hot water, cooking, . . .). Subtracting the summer gas consumption from the winter gas consumption the amount of gas used for heating is obtained. For this simple calculation it was assumed that the consumption of gas for other purposes is the same in winter and summer. In order to calculate the specific heating consumption data about the LHV for gas of 34,000 kJ/N m3 and the average efficiency of gas boilers of 0.9 was adopted. Fig. 4 shows the specific heating consumption for residential buildings, gas consumers in Kragujevac and heating degree days for the period 2009–2013. From Fig. 4 it can be seen even better agreement between the energy consumption and values of heating degree days in relation to the energy consumption for the district heating system. The first observation relates to a significantly smaller amounts of energy consumed for heating per unit of heated area, an average of 112 kW h/m2 a, which represents only 65% of the average consumption for the district heating system. These values fairly good correspond to the average value of the heating consumption in the EU. Regarding the specifics of consumption in some years, consumption in 2012 does not well correspond to the decreasing of the value of the heating degree days, because of the very cold February 2012 and probably prolonged period of heating of individual consumers. Similarly to the energy consumption for the district heating system, the maximum deviation in relation to the value of the heating degree days is for 2009 which can be reliably explained by the relatively lower cost of gas in relation to the consumer incomes and the lagged effects of the economic crisis. Market incentive of consumers to save energy in the gas system is clearly expressed and gives good effects, notwithstanding the absence of government incentive measures.
3.3. Heating consumption for electricity consumers In Kragujevac for the analyzed period (2009–2013) only one (state) company delivered electricity to consumers. Using data obtained from the same company the specific consumption of electricity used for heating of the residential buildings in Kragujevac is calculated. In this case the most complicated thing was to obtain reliable data on the specific heating consumption. On the one hand it was necessary to separate the electrical energy used for heating from the total consumed electrical energy, and on the other hand to define a total area of the residential buildings in Kragujevac which was heated by electricity. When it says heating by electricity in Serbia it means heating by using the electric heater, and in a very small percentage using the heat pump. According to the available data it was not possible to separate these two groups of consumers. A particular problem is represented by the fact that the consumers of the district heating system in the transition periods of the heating season (October and April) often reheat by using electric heaters. In general, the average electricity consumption in Serbia during the winter is greater, without the amount that is used for heating. The reason lies in the increased consumption of electricity for lighting, cooking and electrical appliances, since the population spends more time in their homes, in relation to the summer period. Fig. 5 shows the electricity consumption per month, in the city of Kragujevac for 2010. It can be noticed that the electricity consumption during the winter is significantly higher. Also, Fig. 5 shows the average monthly electricity consumption for the month of April and September (30,804 MW h). For the average monthly electricity consumption during the year, and without the amount of electricity used for heating, exactly this value was adopted. The annual consumption of electricity used for heating the households was calculated as the difference between the total energy consumption in the heating season (month I–III and XI–XII plus half of the consumption for month IV and X) and the six-month consumption, averaged as described above. On the other hand data on the total heated area of the households heated by electricity was not available. Data on the total
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45,000 Consumpon April, September (average consumpon) 40,000
Electricity consumpon (MWh)
35,000 30,000 25,000 20,000 15,000 10,000 5,000 0 I
II
III
IV
V
VI
VII
VIII
IX
X
XI
XII
Fig. 5. Monthly electricity consumption (2010) for the city of Kragujevac.
Table 8 Consumption of electricity for heating, for the city of Kragujevac. Year
2009
2010
2011
2012
2013
Consumption (MW h)
40,567
40,905
49,570
46,436
32,903
number of the households heated by electricity were taken from [10] and their number is 5485. From the same source the average residential area in the city of Kragujevac was calculated and it amounts 67.92 m2 . Table 8 shows the separated consumption of electricity for heating during the heating season, in the analyzed period, described above. Fig. 6 shows the specific consumption of electricity for heating the residential buildings in Kragujevac and heating degree days for the period 2009–2013. From the analysis of the shown diagram it can be seen almost complete dependence of the specific consumption from the variation of the heating degree days. It was mentioned earlier (Fig. 2) that the tariff system for electricity charging most stimulates energy savings (the steepest curve of costs), so the mentioned reason influenced relatively low mean energy consumption, virtually identical to the gas consumption (112 kW h/m2 a). Commonly tenants use electricity for heating by using devices for local space heating. Although many of these residential buildings are not insulated the high costs of increased electricity consumption (red zone) encourage the tenants to minimize the number of heated zones as well as thermal comfort. 3.4. Analysis of the results for all three considered options for heating in the city of Kragujevac Section 2 presents the ratios of the prices of thermal energy in the city of Kragujevac for the three selected and the most common urban heating systems. From the analysis of the price, it was concluded that the district heating system has an extremely unmotivating tariff system of charging and the highest unit price of energy for properly insulated buildings. On the other hand regardless of the great disparity in the prices of electricity and natural gas (unit price of energy is almost identical), the existing tariff systems stimulate savings because although Serbia has a low electricity price it has a very low average incomes of citizens. In Fig. 7, the achieved specific heating consumptions in the city of Kragujevac are presented. Long-held, non-stimulating tariff
system for district heating (fixed tariff per unit of fixed area), has led to the fact that consumers of this heating system are not interested in energy savings, there is no throttling of the consumption and it is considerably higher than for the other two heating systems (electricity and gas). For wealthier citizens who have insulated their households the unit price of energy for the district heating system is very expensive and they will in the future probably choose another option for heating, if the ratios of prices and the tariff systems do not significantly change. On the other hand their possible determination for electricity as an alternative will cause an increased consumption which domestic production will not be able to cover, and the import of electricity is at much higher prices. Poorer citizens with its non-insulated households connected to the district heating system consume high amounts of energy which is lower per unit price (fixed tariff system) but the heating costs for their small budgets remain high. When upcoming tariff system for the district heating system based on consumption replaces the existing tariff system based on fixed charge the amounts of the heating costs for this segment of the consumers will be simply unbearable. Their expected reaction will be disconnection from the district heating system and the transition to the local heating by electricity which would also have the effect of inability to cover electricity consumption from domestic sources. A particular problem is that it is very difficult to disconnect the individual consumers from the district heating system within the buildings as they will be still heated by the same system through the uninsulated walls of their neighbours. Regarding the consumption of gas and electricity for heating they are in a relatively satisfactory level which can be primarily explained by the stimulating tariff systems. These heating systems have a clear and expected relation with the change of the heating degree days. The diagram clearly shows that if in the next few years in Kragujevac (Serbia) a significant reorganization of the district heating system does not implement, with its high prices of unit of energy (fixed or variable) it will be extremely unfavorable as an heating option. A massive disconnection from this heating system is likely if unit prices of heating do not balance. A particular problem is the non-insulated buildings where it is necessary to harmonize the large number of tenants to invest funds for the insulation of the building. The encouraging is the fact that although they have averagely low-income the citizens of Kragujevac (Serbia) who use gas
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140.00
Average consumpon 112,2 kWh/m2a Electricity Degree day
3000 2800 2600
100.00
2400 2200
80.00
2000 60.00
1800
Degree day (oCday)
Specific yearly consumption (kWh/m2a)
120.00
1600
40.00
1400 20.00 1200 0.00
1000 2009
2010
2011
2012
2013
Fig. 6. Specific consumption of electricity for heating the residential buildings in Kragujevac and heating degree days for the period 2009–2013.
District heating
Natural gas
Electricity
Degree day
3500
200.00
3000
150.00
2500
100.00
2000
50.00
1500
0.00
Degree day (oCday)
Specific yearly consumption (kWh/m2a)
250.00
1000 2009
2010
2011
2012
2013
Fig. 7. Achieved specific heating consumptions in the city of Kragujevac and heating degree days for the analyzed period.
for heating generate heating consumption that is in the average level of the EU. Although the consumers who use electricity for heating generate the same consumption, it cannot be justified because the used devices are usually electric heaters, which will be unsustainable when electricity price reach its real level in relation to the prices of heat energy. 4. Conclusions The largest part of the final energy consumption in the residential sector in the EU and Serbia is consumed for heating. The heating systems in Serbia in urban entities are mainly district heating, gas and electricity. In the city of Kragujevac, the fourth-largest city in Serbia, the situation is similar. The current tariff systems show that consumers have the highest interest in energy savings if they use gas or electricity for heating. Also, this shows the results of specific heating consumption for these heating systems. The district heating system is burdened by still market incomprehensible tariff system based on fixed tariff per heated area and totally unmotivated for energy savings. Also, it shows the results of specific consumption. The tariff system that will replace tariff system
based on fixed charge stimulates energy savings and insulation of buildings but is still significantly more expensive for well insulated buildings in relation to gas and electricity heating options. There is no doubt that according to the present structure and the amounts of energy consumption for heating in Serbia, the strategic moves of the local government in Kragujevac (in Serbia) should be connecting more consumers to gas installations and stimulation for using the heat pump as a heating system. The district heating system will certainly remain an heating option but reduced and relieved of unnecessary losses and expenses, limited to the city core and building blocks with the local power plants. By analyzing the specific heating consumptions it was clearly demonstrated that stimulating tariff systems significantly reduce energy consumption regardless of the absence of incentives and subsidies from the state. Acknowledgements This investigation is a part of the project TR 33015 of the Technological Development of the Republic of Serbia and project III 42013 of Integral and Interdisciplinary investigations of the Republic of
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Serbia. We would like to thank the Ministry of Education, Science and Technological Development of the Republic of Serbia for their financial support during this investigation. References [1] A. Fay James, S. Golomb Dan, Energy and the Environment, Oxford University Press, New York, NY, 2002. [2] U.S. Energy Information Administration: International Energy Statistics (http://www.eia.gov/cfapps/ipdbproject/IEDIndex3.cfm) (accessed 11.03.15). [3] Intelligent Energy Europe Programme, Energy Efficiency Trends in Buildings in the EU, ODYSSEE MURE project, Intelligent Energy Europe Programme, 2012, http://www.odyssee-mure.eu/./Buildings-brochure-20. ´ ´ Energy efficiency in Serbia—research [4] S. Oka, A. Sedmak, M. Ðurovic-Petrovi c, and development activity, Therm. Sci. 10 (2) (2006) 5–32. [5] Ministry of Energy, Development and Environmental Protection of the Republic of Serbia, The First Energy Efficiency Plan of the Republic of Serbia for the Period from 2010 to 2012, July 2010 (https://www.energy-community.org/pls/portal/docs/986181.PDF) (accessed 16.03.15). [6] V. Jovanovic, K. Stieldorf, Influence of energy prices and income inequalities on retrofit strategies in developing countries: comparative analysis of cost-efficiency of retrofits on case studies in Belgrade, Nis and Vienna, in: Proceedings—8. Internationale Energiewirtschaftstagung (IEWT), TU Wien, January 2013. ´ Jaume Roset Calzada, Miloˇs Eric, ´ Mihajlo Babin, Economically [7] Dubravka Matic, feasible energy refurbishment of prefabricated buildingin Belgrade, Serbia, Energy Build. (2014), http://dx.doi.org/10.1016/j.enbuild.2014.10.041.
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´ ´ Marina Jovanovic, ´ Naim Afgan, Valentina Turanjanin, [8] Biljana Vuˇcicevi c, Assessing the sustainability of the energy use of residential buildings in Belgrade through multi-criteria analysis, Energy Build. 69 (2014) 51–61. ´ First NEEAP/BS national energy efficiency action plan/building [9] M. Todorovic, sector 2009–2018, in: Study Report and NEEAP-BS for the Republic of Serbia Ministry of Mining and Energy, IRG, Washington, DC, June 2010. [10] Statistical Office of the Republic of Serbia, Census 2011 (http://popis2011.stat.rs/?page id=2162&lang=en) (accessed 03.03.15). [11] Ministry of Energy, Development and Environmental Protection of the Republic of Serbia, Report on Implementation of the First National Energy Efficiency Action Plan in the Period 2010-2011, June 2012, (https://www.energy-community.org/ portal/page/portal/ENC HOME/DOCS/1750177/UPDATE Preliminary Report on Serbian NEEAP implementation 12-06-2012 - W2003.pdf) (accessed 18.03.15). ´ Miloˇs Tanasijevic, ´ Dejan Ivezic, ´ Serbian energy development [12] Predrag Jovanˇcic, based on lignite production, Energy Policy 39 (2011) 1191–1199. [13] Republic Hydrometeorological Service of Serbia (in Serbian) (http://www. hidmet.gov.rs/eng/meteorologija/stanica sr.php?moss id=13278) (accessed 02.03.15). [14] The Ministry of Science, Technology and Development of the Republic of Serbia, National Energy Efficiency Program (NEEP), The project NPEE403-109A, The program of implementation and monitoring of the effects of using the heat meters within the central heating system in Kragujevac, Final Report, (2002-2004) (in Serbian). ´ ´ Mileva Vasic, ´ Methodology and results of Serbian c, [15] Sanja Petrovic´ Becirovi energy-efficiency refurbishment project, Energy Build. 62 (2013) 258–267.
Contents lists available at ScienceDirect
Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild
Specific heating consumption in the residential sector of Serbia—Example of the city of Kragujevac ´ N. Nikolic´ ∗ , D. Gordic´ N. Lukic´ ∗ , N. Juriˇsevic, Faculty of Engineering, University of Kragujevac, Sestre Janji´c 6, 34000 Kragujevac, Serbia
a r t i c l e
i n f o
Article history: Received 17 June 2015 Received in revised form 4 August 2015 Accepted 5 August 2015 Available online 7 August 2015 Keywords: Specific energy consumption District heating Gas heating Electric heating Tariffs
a b s t r a c t In this paper, the specific consumption of the heat energy supplied by three most utilized heating systems (district heating, gas and electricity system) in the residential sector of the city of Kragujevac (Serbia) is analysed. Required data are provided by combining data from local utility companies with national census results. Comparison of present tariff systems shows that consumers in the residential buildings are the most motivated for energy savings if they use electricity or gas as energy source. The specific energy consumption in district heating system shows relatively high quantities, primarily as a consequence of dominant unmotivating tariff payment system. The average heat consumption from gas and electricity sources relatively fits to EU average, but the electricity consumption of the electric heaters is not acceptable in long term. Low electricity price in Serbia and high price of unit of energy from district heating system of the city of Kragujevac (and Serbia) will lead to an increase of electric energy consumption which will cause additional problems related to covering of that consumption from domestic energy sources. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Scientific and technological development has contrived to modern society high level of thermal comfort that requires high energy consumption. In the year 1995 each of 6 billion people on the planet Earth consumed 2 kW, while the resident of USA consumed 13 kW of energy consumption [1]. Although in 2009 developed countries reduced their energy consumption per capita (US 10.3 kW, EU 4.8 kW) global energy consumption per capita has grown up to 2.37 kW [2]. These are a very high quantities considering that the physiological functioning of human requires only 120 W [1]. Parallel to the increasing need for the energy consumption the awareness of the need for more efficient use of energy was increasing too, especially in developed countries. More efficient use of energy is encouraged by states that impose law restrictions and subsidies. However, the strongest influence on increasing energy efficiency has a market and rising prices of practically all energy sources. To form a strategy to reduce specific energy consumption it is necessary to analyze the final energy consumption by sector. It is common that these sectors be divided into industry, transportation and buildings. Furthermore, the energy consumption in buildings is divided into residential and non-residential sector (commercial and
∗ Corresponding authors. Tel.: +381 34357884. ´ [email protected] (N. Nikolic). ´ E-mail addresses: [email protected] (N. Lukic), http://dx.doi.org/10.1016/j.enbuild.2015.08.012 0378-7788/© 2015 Elsevier B.V. All rights reserved.
public buildings). In the EU these shares (2009) has been as following: 41% for the building sector, 32% for the transportation sector, 25% for the industry sector (and 2% for the agriculture) [3]. In 1990, energy consumption in the EU industry had a share of 34% and in the building sector 36%. These data confirm the trend in developed countries that energy consumption moves from the building to the industry sector [1]. With the exception of the southernmost states of the EU, all the other consumes significant amounts of final energy in the building sector for space heating (60–80%) (the average for the EU is 67%) [3]. This share decreases slightly (in 1997 it was 71%) on account of increase of energy consumption of lighting and electrical appliances. The average specific consumption of final energy in the residential sector of the EU was 200 kW h/m2 a, while the nonresidential sector consumed significantly more 300 kW h/m2 a [3]. Although new buildings in the EU consume considerably less energy for heating, the average consumption of the existing residential sector according to the mentioned data was 134 kW h/m2 a (data for 2009). Within the total energy consumption in the residential sector (2009), the most consumed is gas (39%) and electricity (25%), while coal as an energy source is almost completely eliminated (3%). The share of district heating in the EU is relatively low (7%), and it is still pronounced in the Baltic and East European countries, although even there this share decreases. Serbia, as a potential member of the EU is burdened with very unfavorable indicators in the energy sector. In comparison with the 1989 in 2000 Serbia had 2.5 times lower gross domestic product
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(GDP) and the highest consumption of energy in Europe per unit of GDP [4]. In Serbia, shares in final energy consumption by sector (2008) amounted to: industry 34%, transportation 28% and buildings 38% (27% residential, non-residential 11%) [5]. Averagely 65% of final energy consumption in Serbia is consumed for heating, which is close to the European average [6]. In Serbia, after the Second World War the urban environments were intensively built, so that the share of apartments of 27% (1961) was changed to 56% (2008) [5]. Unfortunately, the most of these apartments were built until 1980 as a part of the building within the urban areas. These buildings are characterized by oversized heating systems, lack of insulation and high specific heating consumption [7,8]. According to the scarce information about the specific heating consumption in the residential sector in Serbia, for space heating and heating of a domestic hot water in apartments in Serbia an average of 220 kW h/m2 a is consumed, which is far more than the average in the EU [9]. In literature it can be found data that this consumption in Serbia is significantly higher [4]. According to [10] the share of certain energy sources used for heating of the residential buildings in Serbia is as follows: wood 43%, district heating 22%, electricity 15.5%, gas 10%, coal 9% (and all other fuels 0.5%). Although the state of Serbia stimulated different measures to increase energy efficiency and reduce energy consumption in the residential sector by adopting laws and regulations, supporting and funding various projects (NEEP [4], NEAP [5], Energetic lows 2004, 2014, the Law on Efficient Use of Energy 2013) significant advances in this area have not been made [11]. We believe that the main cause of poor energy indicators in the Republic of Serbia is the significant absence of market incentive of citizens to save energy. First of all, this relates to low cost of electricity, market price of the mainly imported oil and gas, as well as tariff payment system for district heating defined per m2 of the residential area and independent of the consumed heat energy. In the case of the city of Kragujevac and achieved consumption of energy sources (electricity, gas and district heating) in the residential sector for heating seasons 2009–2013, the achieved specific consumptions as well as relations between consumption, tariff payment system and weather conditions will be shown.
2. The tariff systems and ratios of heating prices for household for the city of Kragujevac 2.1. Current prices for electricity, gas and district heating The Serbian energy sector pulls longstanding problems of the socialist economy with controlled policy of low prices of energy sources, with low energy efficiency in all sectors, with high debts for imported energy sources which were uneconomically consumed. One of the most significant structural problems is extremely low price of electricity (the lowest in Europe), which is mainly produced in thermal power plants, which burn domestic low-calorie coal (lignite) [12]. It has led to that the currently 1 kW h of thermal energy of the supplied gas (0.05 D ) costs approximately as 1 kW h of electricity (approximately D 0.06), although the conversion factor of converting thermal energy into electrical is 2.5–3.5. In Serbia, the buildings within the urban areas are heated by district heating, electricity and gas. The prices of gas and electricity are virtually the same for the entire state, while the prices for the district heating vary from city to city. The tariff payment system for consumed electricity in Serbia is shown in Table 1. The tariff system is defined so that the price of electricity for small and medium consumers is very favorable, especially during night. To avoid excessive consumption of electricity, this non-market tariff system has disincentive price of electricity for consumers who consume more than 1600 kW h per month
(red zone). The official mean price of electricity in Serbia is 7.32 RSD/kW h (RSD/EUR = 120). The price of natural gas supplied by the main distributor of this energy source in Serbia currently amounts to 55.33 RSD/N m3 (adopting the lower heating value (LHV) for gas of 34,000 kJ/N m3 and the price of 13.56 D /GJ). The tariff system and the price of district heating in Serbia is formed at the city level and currently the double tariff system is in effect: for most consumers the tariff is fixed and defined per m2 of the residential area of the apartment and for the smaller number of consumers it is variable defined per consumption with a significant fixed part. Specifically, in the city of Kragujevac district heating defined per consumption currently pay about 20% of connected consumers in the residential sector. The double tariff payment system of district heating in the city of Kragujevac for residential sector is given in Table 2. 2.2. Comparison of the heating prices for households in the city of Kragujevac For a comparison of the heating costs for various energy sources used in Kragujevac the following data were adopted: -
household of 100 m2 of useful living space is considered, heating season lasts 6 months (180 days), ratio of daily and nightly electricity tariff is 70/30, electricity consumption unrelated to the heating is 500 kW h per month, engaged electrical power of a household is 10 kW, efficiency of a gas boiler is g = 0.9, adopted LHV of natural gas is 34,000 kJ/N m3 , four specific heating consumptions are analyzed: 50, 100, 150 and 200 kW h/m2 a, four options of the heating in the city of Kragujevac are analyzed: electricity (heaters), gas (boiler), district heating – fixed charge and district heating – charge per consumption.
Fig. 1 shows the unit price of energy (kW h) which pays the owner of the household of 100 m2 for heating expressed in D /kW h for four defined options of heating and for different specific consumptions. From Fig. 1 it can be seen that the price of energy from gas is fixed, irrespective of consumption which maximally simplifies the calculation of a household to save energy or to invest in insulation of an object. The price of heating by conventional electric heaters for low specific consumptions is more cost effective than district heating. Although it is not shown in the diagram the heating by electricity as a part of a system with heat pump (estimated heating factor of 2–5) would be undoubtedly the cheapest heating option under this ratio of prices in Kragujevac (Serbia). District heating system has been built in a time of urbanization of Serbia and cheap energy. Long-time charging system fixed per unit of residential area of the residential building discouraged the investment in increasing the efficiency of production and transport of heat energy. For a long time the price for heating based on square meter of heating area is built in that manner that now it is the most expensive heating option for well insulated buildings (consumption less than 100 kW h/m2 a). The charging system based on consumption, which will soon become the only tariff system within the district heating makes this system slightly competitive especially for consumptions to 100 kW h/m2 a. It is clear that in these circumstances and with fixed tariff thinking of a family in the residential apartment connected to the district heating system about investment in insulation of the object is excluded without any economic sense.
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Table 1 Tariff payment system for consumed electricity in Serbia (for two tariff electricity meter). Households
Higher (daily) tariff (RSD/kW h)
Lower (nightly) tariff (RSD/kW h)
Capacity charge (RSD/kW)
Green zone 0–350 kW h Blue zone 350–1600 kW h Red zone over 1600 kW h
6.49 9.79 19.48
1.62 2.44 4.87
51.41
Ratio RSD/EUR = 120. Table 2 Double tariff payment system of district heating for residential sector in the city of Kragujevac. Fixed per residential area (RSD/m2 )
Type of consumer
Residential sector
Per consumption
92.55
Fixed part (RSD/m2 )
Variable part (RSD/MW h)
29.2
5430
Ratio RSD/EUR = 120.
Price of consumed energy (€/kWh)
0.2 0.18
Gas
0.16
District heang (fixed charge) District heang (variable charge)
0.14
Electricity
0.12 0.1 0.08 0.06 0.04 0.02 0 0
50 100 150 200 Yearly consumpon per m² of residenal area (kWh/m² )
250
Fig. 1. Price of kW h of heating energy for the household of 100 m2 in the city of Kragujevac for different options of heating.
2500
Total heang costs (€/a)
2000
Gas District heang (fixed charge) District heang (variable charge) Electricity
1500
1000
500
0 0
50
100 150 Specific heang consumpon (kWh/m²)
200
250
Fig. 2. The total yearly heating cost for the household of 100 m2 of residential area for different heating options in the city of Kragujevac.
Fig. 2 shows the total yearly heating cost for the household of 100 m2 of residential area in the city of Kragujevac. Analyzing Fig. 2 it is clear that increasing the slope of the line means the higher incentive of consumer for reducing heating consumption. This means that in Kragujevac (Serbia) consumers in residential buildings have the most economic incentive to save
energy if they are heated by electricity or gas. The tariff system defined per consumption for district heating is lagging behind electricity and gas. The tariff system with fixed charge for district heating which uses 80% of connected residential consumers in Kragujevac is virtually fatal to any idea of increasing the energy efficiency of residential buildings.
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Table 3 Climatic characteristics of Kragujevac for the heating months from 1981 to 2010 [13].
Temperature (◦ C) Max average Min average Normal Max absolute Min absolute
Jan.
Feb.
Mar.
5.2 −2.9 0.9 20.6 −27.4
7.3 −1.9 2.3 24.2 −23.8
12.5 1.8 6.6 29.4 −18.3
Apr. 17.8 5.9 11.7 31.4 −5.8
Table 4 The values of heating degree days for the city of Kragujevac for the period 2009–2013. Year
2009
2010
2011
2012
2013
Heating degree day (◦ C day)
2461.2
2522.3
2918.9
2695.3
2359
3. Energy consumption in the district heating system, electricity and gas consumption for heating residential buildings in the city of Kragujevac in the period 2009–2013 According to the census of 2011 [10] Kragujevac with 179,417 inhabitants is the fourth most populated city in Serbia. It is located in the central part of Serbia. The city area extends over 835 km2 and the altitude ranges from 185 to 220 m. Basic microclimate temperature characteristics of the city with a temperate continental climate are shown in Table 3. According to the census of 2011 [10] the share of certain types of heating systems is slightly different in Kragujevac in relation to Serbia: district heating 31% (Serbia 22%), wood 42% (43%), electricity 9.5% (15.5%), gas 13.5% (10%), coal 3.5% (9%). As an urban environment Kragujevac has a higher share of users of district heating and gas, and a smaller share of users of electricity and coal for heating purposes in relation to Serbia. Traditionally Serbia consumes large amounts of wood for heating especially on the outskirts of cities and in rural areas. Consumption of thermal energy for heating in Kragujevac is analyzed for the period 2009–2013. The needs for heating, caused by weather conditions during the specified period are presented by heating degree days determined for ambient temperature of 20 ◦ C and heating temperature threshold of 12 ◦ C. Mean outdoor temperatures were retrieved from the database of the local utility company, responsible for district heating. The values of heating degree days for the city of Kragujevac for the period from 2009 to 2013 are shown in Table 4. 3.1. Consumption of heat energy in the district heating system The district heating company in the city of Kragujevac is a former industrial power plant of the company Zastava cars. Within this power plant for the purposes of technological steam as well as independent electricity production the steam coal-fired boilers which today can produce 240 MW of thermal power were built. At the same location besides the steam coal-fired boilers there are gasfired boilers (total power of 63 MW). In addition to the central boiler plant at the city there are dislocated boiler plants with hot water boilers fueled by oil and gas. Due to the structure of boiler plants of district heating system in Kragujevac and lower coal price, reduced to heating value, coal is energy source that is mostly used for heating. In the analyzed period 2009–2013 the share of coal in the total production of heat energy in the district heating system in Kragujevac amounted to 76% (see Table 5). Use of coal as an energy source caused a slightly lower price of district heating in Kragujevac in relation to other major cities in Serbia (Belgrade, Novi Sad, Niˇs). Although the Law on Efficient Use of Energy (Official Gazette 25/13) provides that from the beginning of the heating season of
Oct. 18.5 7.1 11.9 32.6 −6.6
Nov.
Dec.
Season
11.6 2.5 6.4 27.6 −11.8
6.2 −1.1 2.1 21.0 −20.6
11.3 1.63 5.98 32.6 −27.4
2014/2015 all central heating systems in Serbia should switch to the tariff system based on consumption, it did not happen and the tariff system based on fixed charge is still the dominant system of charging. From heating season 2011/2012 the district heating company in Kragujevac offers residential customers to switch to the tariff system based on consumption (presented in Section 2.1). So far this tariff system accepted 20% of residential units that are surely newer and insulated buildings in the city. Unfortunately, the remaining 80% of residential consumers pay fixed tariff which excludes interest in reducing energy consumption. Total energy consumption for the analyzed period 2009–2013 is calculated according to the available data on the total consumed energy sources in the district heating system. These data are given in Table 5 as well as the data on the heated areas and shares of energy consumed for industrial purposes. All these data were taken from the company responsible for the operation of the district heating system in the city of Kragujevac. In order to calculate the consumed energy in residential buildings of consumers of district heating system the following data were adopted: LHV for heavy oil is 42,000 kJ/kg, for gas 34,000 kJ/N m3 , the efficiency of coal-fired boilers is 0.8, the efficiency of heavy oil-fired boilers and gas-fired boilers is 0.9 and the average transportation losses are 7% (calculated in [14]). Data on the average efficiency of boilers were adopted from [14]. As the total consumption of energy sources in the district heating system covered all consumers it was necessary to separate the consumption of industry according to the given shares as well as the consumption of commercial and public buildings from the consumption of the residential buildings. Specific data on measured consumption were not available, so for this separation the data from the literature was used. It is known that commercial and public buildings consume significantly more energy than residential buildings. In the EU (2009) non-residential buildings were consuming an average of 295 kW h/m2 a of total final energy while residential buildings were consuming 200 kW h/m2 a. Certainly in Serbia non-residential buildings consume significantly more energy than residential buildings which is particularly evident in public buildings (schools, hospitals, administrative buildings, etc). In Serbia, in the period 2010–2012 in the framework of Serbia Energy Efficiency Project (SEEP), 62 public buildings were reconstructed and for which the heating consumption before and after the reconstruction were measured [15]. Before the reconstruction (2011) it was found that these buildings consumed an average of 301.5 kW h/m2 a for heating. As it has been already mentioned that in Serbia residential buildings consume an average of 220 kW h/m2 a for heating and domestic hot water. According to this it was adopted that the ratio of heating consumption for non-residential and residential buildings in Kragujevac is 3:2. By adopting this ratio and knowing the total consumption and area of non-residential and residential buildings of consumers of district heating, it was possible to calculate the average consumption for residential buildings in Kragujevac, as shown in Fig. 3. Otherwise, the standard heating season of the district heating system is defined for the period from 15.10 to 15.04 of the next year. Fig. 3 shows that the specific heating consumption is very high (an average of 173 kW h/m2 a) and practically very close to the
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Table 5 Consumption of energy sources and heated areas of consumers of a district heating system. Year
2009
2010
2011
2012
2013
Coal (t) Oil fuel (t) Gas (N m3 ) Average LHV of coal (kJ/kg) Heat energy for industry (%) Total heated area (m2 ) Residential heated area (m2 )
106,559 10,014 5932,000 14,142 0.14 1457,826 960,633
82,014 7945 3156,000 14,156 0.11 1457,825 957,048
106,559 6410 6932,000 12,676 0.11 1479,406 967,140
105,956 6437 12,060,000 13,246 0.06 1561,969 1036,429
74,423 3920 6245,000 12,489 0.07 1518,281 1010,408
250.00
Average consumpon 172,8 kWh/m2a
3000 District heating Degree day
200.00 2600 2400
150.00
2200 100.00
2000
Degree day (oCday)
Specific yearly consumption (kWh/m2a )
2800
1800 50.00 1600 0.00
1400 2009
2010
2011
2012
2013
Fig. 3. Specific heating consumption for residential buildings, consumers of district heating system in Kragujevac and heating degree days for the period 2009–2013.
Table 6 Specific heating consumption for residential buildings, consumers of district heating system in Kragujevac and deviation of the specific consumption per heating degree days in relation to the specific consumption in 2013. Year
2009
2010
2011
2012
2013
Specific consumption (kW h/m2 a) Specific consumption per heating degree day (kW h/m2 a ◦ C day) Deviation of the specific consumption per heating degree day in relation to the consumption in 2013 (%)
200.41 0.081 49.3
156.32 0.062 13.6
176.80 0.061 11.0
201.84 0.075 37.3
128.68 0.055 0
fact that the residential buildings in Serbia consume an average of 220 kW h/m2 a for heating and domestic hot water [9]. The structure of a residential buildings connected to the district heating system in Kragujevac is very diverse. The non-insulated buildings from the period of 70s and 80s of the last century prevail, then insulated buildings and a significant number of insulated and noninsulated family houses. In [14] it can be found information on the measurement of the heating consumption (2004/2005) of the noninsulated residential building with heated area of 4047 m2 , with an extensive problem of overheating. Consumption reduced to the heating degree days from 2011 would amount to 187 kW h/m2 a. Also, Fig. 3 shows a stable relation between energy consumption and needs (heating degree-days). However, there are some deviations for 2009 and 2012. Standard daily period of operation of the district heating system in Kragujevac is from 6:00 am to 9:00 pm. If the average night temperatures are very low the heating lasts 24 h. For the analyzed period there were not significant number of those days except for heating season 2012 (the end of January and the first half of February) when consumers were continuously heated about 20 days. This operation of the district heating system has led to increased energy consumption in 2012, although the number of heating degree days was lower than for the coldest
season 2011 (see Table 4). Specific heating consumption for residential buildings, consumers of district heating system in Kragujevac and deviation of the specific consumption per heating degree days in relation to the specific consumption in 2013 are given in Table 6. The deviation of the specific consumption per heating degree days was highest in 2009. It can be explained by the effects of the economic crisis during 2008 which with certain inertia (since 2010) affected the decrease of purchasing energy sources of the local utility company. Heat energy production is mainly based (Table 5) on a cheaper coal and the general characteristic of the consumption was overheating of the most buildings and lack of interest for energy savings. 3.2. Heating consumption for gas consumers In Kragujevac for the analyzed period (2009–2013) only one (state) company delivered natural gas to consumers. Using data obtained from the same company the specific heating consumption of residential buildings in Kragujevac, connected to the gas installations, is calculated. Table 7 presents the consumption of gas for heating and area of the residential buildings (consumers) for the analyzed period.
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Table 7 Consumption of the natural gas for heating and residential area of the consumers for Kragujevac. Year
2009
2010
2011
Consumption (N m3 ) Area of the consumers (m2 )
7785,028 500,573
6940,865 550,562
7813,121 577,323
7887,203 589,005
Average consumpon 112,1 kWh/m2a
2013 6574,173 606,121
3000 Natural gas Degree day
130.00
2800 2600
110.00 2400 90.00
2200
70.00
2000 1800
50.00
Degree day (oCday)
Specific yearly consumption (kWh/m2a )
150.00
2012
1600 30.00 1400 10.00 -10.00
1200 2009
2010
2011
2012
2013
1000
Fig. 4. Specific heating consumption for residential buildings, gas consumers in Kragujevac and heating degree days for the period 2009–2013.
The amount of consumption of gas consumed for heating is calculated as follows. Consumption in the heating season for each year is obtained as the sum of consumptions in the period JanuaryMarch and November-December plus half the consumption for April and October. The difference between the total annual gas consumption and gas consumption in the heating season (180 days) gives the (summer) gas consumption for other purposes (domestic hot water, cooking, . . .). Subtracting the summer gas consumption from the winter gas consumption the amount of gas used for heating is obtained. For this simple calculation it was assumed that the consumption of gas for other purposes is the same in winter and summer. In order to calculate the specific heating consumption data about the LHV for gas of 34,000 kJ/N m3 and the average efficiency of gas boilers of 0.9 was adopted. Fig. 4 shows the specific heating consumption for residential buildings, gas consumers in Kragujevac and heating degree days for the period 2009–2013. From Fig. 4 it can be seen even better agreement between the energy consumption and values of heating degree days in relation to the energy consumption for the district heating system. The first observation relates to a significantly smaller amounts of energy consumed for heating per unit of heated area, an average of 112 kW h/m2 a, which represents only 65% of the average consumption for the district heating system. These values fairly good correspond to the average value of the heating consumption in the EU. Regarding the specifics of consumption in some years, consumption in 2012 does not well correspond to the decreasing of the value of the heating degree days, because of the very cold February 2012 and probably prolonged period of heating of individual consumers. Similarly to the energy consumption for the district heating system, the maximum deviation in relation to the value of the heating degree days is for 2009 which can be reliably explained by the relatively lower cost of gas in relation to the consumer incomes and the lagged effects of the economic crisis. Market incentive of consumers to save energy in the gas system is clearly expressed and gives good effects, notwithstanding the absence of government incentive measures.
3.3. Heating consumption for electricity consumers In Kragujevac for the analyzed period (2009–2013) only one (state) company delivered electricity to consumers. Using data obtained from the same company the specific consumption of electricity used for heating of the residential buildings in Kragujevac is calculated. In this case the most complicated thing was to obtain reliable data on the specific heating consumption. On the one hand it was necessary to separate the electrical energy used for heating from the total consumed electrical energy, and on the other hand to define a total area of the residential buildings in Kragujevac which was heated by electricity. When it says heating by electricity in Serbia it means heating by using the electric heater, and in a very small percentage using the heat pump. According to the available data it was not possible to separate these two groups of consumers. A particular problem is represented by the fact that the consumers of the district heating system in the transition periods of the heating season (October and April) often reheat by using electric heaters. In general, the average electricity consumption in Serbia during the winter is greater, without the amount that is used for heating. The reason lies in the increased consumption of electricity for lighting, cooking and electrical appliances, since the population spends more time in their homes, in relation to the summer period. Fig. 5 shows the electricity consumption per month, in the city of Kragujevac for 2010. It can be noticed that the electricity consumption during the winter is significantly higher. Also, Fig. 5 shows the average monthly electricity consumption for the month of April and September (30,804 MW h). For the average monthly electricity consumption during the year, and without the amount of electricity used for heating, exactly this value was adopted. The annual consumption of electricity used for heating the households was calculated as the difference between the total energy consumption in the heating season (month I–III and XI–XII plus half of the consumption for month IV and X) and the six-month consumption, averaged as described above. On the other hand data on the total heated area of the households heated by electricity was not available. Data on the total
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169
45,000 Consumpon April, September (average consumpon) 40,000
Electricity consumpon (MWh)
35,000 30,000 25,000 20,000 15,000 10,000 5,000 0 I
II
III
IV
V
VI
VII
VIII
IX
X
XI
XII
Fig. 5. Monthly electricity consumption (2010) for the city of Kragujevac.
Table 8 Consumption of electricity for heating, for the city of Kragujevac. Year
2009
2010
2011
2012
2013
Consumption (MW h)
40,567
40,905
49,570
46,436
32,903
number of the households heated by electricity were taken from [10] and their number is 5485. From the same source the average residential area in the city of Kragujevac was calculated and it amounts 67.92 m2 . Table 8 shows the separated consumption of electricity for heating during the heating season, in the analyzed period, described above. Fig. 6 shows the specific consumption of electricity for heating the residential buildings in Kragujevac and heating degree days for the period 2009–2013. From the analysis of the shown diagram it can be seen almost complete dependence of the specific consumption from the variation of the heating degree days. It was mentioned earlier (Fig. 2) that the tariff system for electricity charging most stimulates energy savings (the steepest curve of costs), so the mentioned reason influenced relatively low mean energy consumption, virtually identical to the gas consumption (112 kW h/m2 a). Commonly tenants use electricity for heating by using devices for local space heating. Although many of these residential buildings are not insulated the high costs of increased electricity consumption (red zone) encourage the tenants to minimize the number of heated zones as well as thermal comfort. 3.4. Analysis of the results for all three considered options for heating in the city of Kragujevac Section 2 presents the ratios of the prices of thermal energy in the city of Kragujevac for the three selected and the most common urban heating systems. From the analysis of the price, it was concluded that the district heating system has an extremely unmotivating tariff system of charging and the highest unit price of energy for properly insulated buildings. On the other hand regardless of the great disparity in the prices of electricity and natural gas (unit price of energy is almost identical), the existing tariff systems stimulate savings because although Serbia has a low electricity price it has a very low average incomes of citizens. In Fig. 7, the achieved specific heating consumptions in the city of Kragujevac are presented. Long-held, non-stimulating tariff
system for district heating (fixed tariff per unit of fixed area), has led to the fact that consumers of this heating system are not interested in energy savings, there is no throttling of the consumption and it is considerably higher than for the other two heating systems (electricity and gas). For wealthier citizens who have insulated their households the unit price of energy for the district heating system is very expensive and they will in the future probably choose another option for heating, if the ratios of prices and the tariff systems do not significantly change. On the other hand their possible determination for electricity as an alternative will cause an increased consumption which domestic production will not be able to cover, and the import of electricity is at much higher prices. Poorer citizens with its non-insulated households connected to the district heating system consume high amounts of energy which is lower per unit price (fixed tariff system) but the heating costs for their small budgets remain high. When upcoming tariff system for the district heating system based on consumption replaces the existing tariff system based on fixed charge the amounts of the heating costs for this segment of the consumers will be simply unbearable. Their expected reaction will be disconnection from the district heating system and the transition to the local heating by electricity which would also have the effect of inability to cover electricity consumption from domestic sources. A particular problem is that it is very difficult to disconnect the individual consumers from the district heating system within the buildings as they will be still heated by the same system through the uninsulated walls of their neighbours. Regarding the consumption of gas and electricity for heating they are in a relatively satisfactory level which can be primarily explained by the stimulating tariff systems. These heating systems have a clear and expected relation with the change of the heating degree days. The diagram clearly shows that if in the next few years in Kragujevac (Serbia) a significant reorganization of the district heating system does not implement, with its high prices of unit of energy (fixed or variable) it will be extremely unfavorable as an heating option. A massive disconnection from this heating system is likely if unit prices of heating do not balance. A particular problem is the non-insulated buildings where it is necessary to harmonize the large number of tenants to invest funds for the insulation of the building. The encouraging is the fact that although they have averagely low-income the citizens of Kragujevac (Serbia) who use gas
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140.00
Average consumpon 112,2 kWh/m2a Electricity Degree day
3000 2800 2600
100.00
2400 2200
80.00
2000 60.00
1800
Degree day (oCday)
Specific yearly consumption (kWh/m2a)
120.00
1600
40.00
1400 20.00 1200 0.00
1000 2009
2010
2011
2012
2013
Fig. 6. Specific consumption of electricity for heating the residential buildings in Kragujevac and heating degree days for the period 2009–2013.
District heating
Natural gas
Electricity
Degree day
3500
200.00
3000
150.00
2500
100.00
2000
50.00
1500
0.00
Degree day (oCday)
Specific yearly consumption (kWh/m2a)
250.00
1000 2009
2010
2011
2012
2013
Fig. 7. Achieved specific heating consumptions in the city of Kragujevac and heating degree days for the analyzed period.
for heating generate heating consumption that is in the average level of the EU. Although the consumers who use electricity for heating generate the same consumption, it cannot be justified because the used devices are usually electric heaters, which will be unsustainable when electricity price reach its real level in relation to the prices of heat energy. 4. Conclusions The largest part of the final energy consumption in the residential sector in the EU and Serbia is consumed for heating. The heating systems in Serbia in urban entities are mainly district heating, gas and electricity. In the city of Kragujevac, the fourth-largest city in Serbia, the situation is similar. The current tariff systems show that consumers have the highest interest in energy savings if they use gas or electricity for heating. Also, this shows the results of specific heating consumption for these heating systems. The district heating system is burdened by still market incomprehensible tariff system based on fixed tariff per heated area and totally unmotivated for energy savings. Also, it shows the results of specific consumption. The tariff system that will replace tariff system
based on fixed charge stimulates energy savings and insulation of buildings but is still significantly more expensive for well insulated buildings in relation to gas and electricity heating options. There is no doubt that according to the present structure and the amounts of energy consumption for heating in Serbia, the strategic moves of the local government in Kragujevac (in Serbia) should be connecting more consumers to gas installations and stimulation for using the heat pump as a heating system. The district heating system will certainly remain an heating option but reduced and relieved of unnecessary losses and expenses, limited to the city core and building blocks with the local power plants. By analyzing the specific heating consumptions it was clearly demonstrated that stimulating tariff systems significantly reduce energy consumption regardless of the absence of incentives and subsidies from the state. Acknowledgements This investigation is a part of the project TR 33015 of the Technological Development of the Republic of Serbia and project III 42013 of Integral and Interdisciplinary investigations of the Republic of
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