The energy demand for space heating for each calculation period (month) is computed by:

$Q_{\text{NH}}=Q_{\text{L,H}}-{\eta }_{\text{G,H}}\times Q_{\text{G,H}}$ (1)

where Q_L,H is the total heat losses, η_G,H is the utilization factor of heating gains and Q_G,H is the total heat gains in MJ. Total heat transfer (loss) for each month and each zone is given by the total heat transfer Q_T and the total heat transfer by ventilation Q_V in MJ. The equation is written as:

$Q_{\text{L}}=Q_{\text{T}}+Q_{\text{V}}$ (2)

and the total gains for the building zone are:

$Q_{\text{G}}=Q_{\text{i}}+Q_{\text{s}}$ (3)

where Q_i is the sum of internal heat sources over the given period and Q_s is the sum of solar heat sources in MJ. The total heat transfer by transmission is calculated for each month and each zone by:

$Q_{\text{T}}={\sum }_k\left\{H_{\text{T,}k}\cdot ({\theta }_{\text{i}}-{\theta }_{\text{e,}k})\right\}\times t\times \text{f}$ (4)

where θ_i, θ_e,k are the internal and external temperatures respectively, t is the duration of the calculation period and f is the factor of conversion from Wh to MJ. The heat transfer coefficient H_T,k through the building elements between the heated space and external air is computed by:

$H_{\text{T,}k}={\sum }_i{A}_i{U}_i+{\sum }_k{l}_k{\Psi }_k$ (5)

where A_i is the surface area of the building envelope, U_i is the thermal transmission coefficient, l_k is the length of liner thermal bridge, and Ψ_k is the thermal conductivity. The units for these parameters are shown in the Nomenclature. The heat gains are calculated more specifically including the internal heat production Q_i, the solar heat gain through transparent surfaces Q_sun,t, and solar heat gain through opaque surfaces Q_sun,nt. The equation is as follows:

$Q_{\text{gain}}=Q_{\text{i}}+Q_{\text{sun,t}}+Q_{\text{sun,nt}}$ (6)

The internal gains from internal sources are expressed by the heat production from occupants Q_i,occ, internal heat production from appliances Q_i,app and internal heat production from lighting Q_i,li. The equation is written as:

$Q_{\text{i}}=Q_{\text{i,occ}}+Q_{\text{i,app}}+Q_{\text{i,li}}$ (7)

And lastly, the heat transfer by ventilation for heating mode is calculated by:

$Q_{\text{V-heat}}=H_{\text{V-heat}}({\theta }_{\text{i}}-{\theta }_{\text{e}})\times n\times 0.0864$ (8)

where H_V-heat is the ventilation heat loss coefficient, n is the number of days within a month. The environmental impact, namely the CO₂ emission are calculated for each energy type for different scenarios using the fuel load B_fuel and the specific CO₂ emission of the fuel:

$E{M}_{{\text{CO}}_2}=B_{\text{fuel}}\times {\text{CO}}_2{}_{\text{sp}}$ (9)

The fuel load B_fuel is calculated based on the heat demand Q_N,H and energy source used for each scenario through the LHV lower heating value of fuel and the boiler efficiency, using:

$B_{\text{fuel}}=\frac{Q_{\text{N,H}}}{LHV\times {\eta }_{\text{b}}}$ (10)

According to the annual report of the Kosovo Regulatory Office (ERO) [31], Kosovo’s energy-generating capacities include 1,441.88 MW, including the energy from RES. Whereas the operating capacity only reaches 1,092.38 MW, where coal-based power plants (CPP) account for 87.88% and the rest 12.12% is from RES, namely hydro, wind, and solar systems. The distribution of these generating capacities is presented in Figure 2.

Since the primary electricity providers are two old CPP [21], and because low calorific value lignite is used as fuel, the amount of fossil fuel and consequently, the CO₂ emissions from the energy sector in Kosovo are very high. Thus, using this electricity for direct heating purposes is a misuse of energy and should be avoided. However, due to the dearth of other heating alternatives, this is currently an ongoing concern from the energy and environmental perspective. Furthermore, the limited electricity production sources in Kosovo can barely keep up with the ever-growing electricity demand [32].

Figure 2.

Participation in electricity generation in Kosovo 2020

Compared to other Western Balkan countries, Kosovo is among the countries with low electricity costs, as shown in Figure 3. The prices were retrieved from the electricity costs for the Winter season 2021/2022, for Kosovo [33], Albania [34], Serbia [35], Montenegro [36], North Macedonia [37], and Bosnia and Herzegovina [38]. Considering that other neighboring countries apply different taxes to the end price of electricity; it is beneficial to illustrate the electricity price of Kosovo by comparing the same electricity demand in different countries for high and low tariffs. Therefore, a simple analysis was conducted as an example for illustration purposes to visualize the differences on the energy costs by assuming four scenarios (EC-01 up to 04) on different electricity demand depending on the high and low electricity tariffs. Table 4 shows the assumed scenarios, and the visualizations are depicted in Figure 4.

Figure 3.

Electricity costs calculated by adding the VAT for high and low tariffs (HT and LT) and value-added tax (VAT) for Western Balkan countries for the Winter season 2021/2022

Figure 4 presents the depiction of the four assumed scenarios, and it shows that Kosovo had lower mean electricity costs when considering low and high tariffs and VAT, compared to the mean value of the electricity costs of five other Western Balkan Countries. The first scenario EC-01 has lower electricity costs for 32.28%, scenario EC-02 for 37.29%, scenario EC-03 for 36.08% and lastly scenario EC-04 for 37.90% compared to the mean value of the other 5 countries. These results are presented to visualize the differences in energy prices for the neighboring Balkan countries.

Figure 4.

Electricity costs for neighbouring Western Balkan countries

The electricity demand during the heating season (15October-15April) increases due to higher demand for heating in the domestic sector that uses electricity as the primary heating source. Figure 5 shows the comparison of electricity consumption between the domestic and commercial sectors in 2020 [32]. As a comparison, Figure 6 presents the electricity consumption for 2018, 2019 and 2020, where a drop of around 2% each year in electricity consumption is noted in the winter season due to the increasing distribution of district heating with cogeneration from CPP Kosova B power-plant.

Figure 5.

Energy consumption for domestic and commercial use Electricity in 2020

Figure 6.

Comparison of the yearly domestic electricity consumption

The electricity consumption in Prishtina municipality (Figure 7) which also presents the city with the highest concentration of buildings, accounts for 31.33% of the national energy consumption for domestic use [32]. Figure 8 compares the annual energy consumption based on the season and it shows that there is a significant increase in electricity consumption compared to 2017, by 4.16% and 10.20% in 2018 and 2019, respectively [32]. Additionally, the mean value of the monthly electricity consumption for these three years during the winter season shows that there is a 30.55% increase in the mean electricity consumption per month, which is mainly attributed to the use of electric boilers for heating purposes, but it also is affected by the domestic hot water demand, lighting, and other purposes.

Figure 7.

Electricity consumption through the years of Prishtina district for domestic use

Figure 8.

Monthly mean electricity consumption for Prishtina district

Another heating alternative that is highly used in Prishtina is district heating from cogeneration from the CPP Kosova B, which provides affordable prices compared to other heating solutions and has satisfactory services. Figure 9 presents the thermal energy consumption from Termokos [39] in Prishtina in 2020 [32], where it shows that the domestic and commercial thermal energy demand is very similar. Although the energy from the district heating is coal-based, in the future it can transition to more sustainable solutions to comply with the Zero carbon aim by 2050 for South East Europe as stated in [40].

Figure 9.

Thermal energy consumption from Termokos in Prishtina in 2020

Although in Europe a substantial share of building stock is older than 50 years [1], in Kosovo the building stock is relatively new and the construction development is divided into four periods, namely 1960-1969, 1970-1979, 1980-1999 and 2000-2017 [26]. The number of buildings before 1960 was not considered in the statistics. A major surge in construction is evident in the years with turning historical points of Kosovo such as in the post-war period after 1999, as presented in Figure 10. This comes in contrast to Western countries where only a low rate of 1% growth of construction in the residential sector is reported in [41]. The statistics presented in [26] show that from 1960 up to 2017, the total number of registered buildings in Kosovo has been 247,680 units, the number of residential units is 412,883 and the gross total building area is 32,298,776 m².

Figure 10.

The share of residential units in the construction period 1960-2017 (the total number of buildings divided per the number of AB for each period)

According to the same report [26], the built environment in Kosovo is characterized by four classes of buildings, namely: Type A: individual homes, Type B: terraced houses, Type C: low-rise block apartments, and Type D: high-rise block apartments (used as reference model in this study). The AB stock has had significant growth during the past few decades, especially during 1980-1999 and 2000-2017, as presented in Figure 11. Along these lines, in the first period, the constructed building area had an increase of 79.21%, as depicted in Figure 12. The AB presents a multi-story building with a large floor area consisting of three or more residential units. The AB account for a high share in the building stocks in Kosovo [26], specifically, 1.13% of the total number of buildings are AB, 28.32% of the total number of residential units, and 31.93% of the total gross building area. Therefore, they have high heating demand, but the actual main heating solution is electric boilers. The issue with heating supply in Kosovo is also asserted in the WBIF report [42], where the EU allocated additional grants to add central heating solutions in municipalities in Kosovo, as the existing central district heating in Kosovo (in Prishtina 140 MW, Gjakova 11 MW and Mitrovica 38MW) only cover 3-5% of heating demand on the national level [42].

Figure 11.

The number of AB for 1960-2017

Figure 12.

The amount of AB area for 1960-2017

According to the Kosovo Agency of Statistics [43], the population number in Kosovo in 2011 was 1,739,825 residents, whereas the mean used area per capita is 13.3 m². This means that Kosovo had 23,139,672 m² of residential area in 2011. On the other hand, according to the growth estimation statistics from [44] and [45], Kosovo in 2020 had 1,783,531 residents and according to [26] it has 32,298,777 m² residential area, meaning that the growth in the residential area from 2011-2017 can be inferred to an estimate of 9,159,105 m². Additionally, the mean of used area per capita has increased to 18,11m². This shows that a continuous increase in electricity and heating demand is inevitable.

The impact of the proposed EEM in different scenarios fuel cost and savings are presented in Figure 16, compared to the current state of the reference building.

The results show that the heating cost in scenario S-01/NE-EB presenting the existing state that has no EEM and uses electric boilers is 20,548 Euro/year, when adding EEM to the building with the same heating system (S-02/EE-EB) the cost drops to 10,013 Euro/year resulting in monetary savings of 10,535 Euro/year. Furthermore, if the heating system is substituted with heat pumps (S-03/EE-HP), the cost savings reach a maximum of 17,750 Euro/year compared to the cost savings using district heating (S-04/EE-DH) which is 13,681 Euro/year.

Figure 16.

Total fuel cost and fuel savings for the reference AB building model

When comparing the electricity, thermal and fuel costs on one side, and the carbon emissions on the other, also by estimating the cost of an electric boiler with a capacity of 12-24 kW by 750 Euro/unit and the cost of a 13.7 kW heat pump by 7,200 Euro/unit, two conclusions can be drawn: 1) The specific cost per kWh for heating from electric energy is 0.073 €c/kWh, which is 209% higher than heating with wood as fuel, and 143% higher than the pellet as presented in Figure 17. The capacities of the electric boiler and heat pumps have been evaluated according to the heating demand. However, since in most AB there are no storage areas for fuel, as well as the high price of wood or pellet boilers, it makes the electricity a more convenient solution for heating although for a higher cost. 2) When considering heat pumps as a HVAC solution, their initial price is 960% higher than electric boilers, but the energy saving per residential unit is 171.78 Euro/year, meaning that the payback period is 37.68 years. This payback is attributed to the high initial investment but it goes in line with the range reported in an economic analysis for heat pumps in research [46] which starts from 28 years and can go up to 34 years depending on other factors as well such as climate conditions [47], energy prices and energy use, etc.

Figure 17.

Comparison of the impact of fuel type on environmental impact and costs