Energetic and Environmental Aspects of Individual Heat Generation for Sustainable Development at a Local Scale—A Case Study from Poland

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Article Energetic and Environmental Aspects of Individual Heat Generation for Sustainable Development at a Local Scale—A Case Study from Poland

Michał Kaczmarczyk * , Anna Sowi˙zd˙zał and Barbara Tomaszewska

Faculty of Geology, Geophysics and Environmental Protection, Department of Fossil Fuels, AGH University of Science and Technology, 30-059 Kraków, Poland; [email protected] (A.S.); [email protected] (B.T.) * Correspondence: [email protected]

Received: 18 December 2019; Accepted: 12 January 2020; Published: 17 January 2020

Abstract: The housing sector, especially with respect to energy generation to provide heating and domestic hot water, has been identified, after transport, as contributing the most to air pollution and the occurrence of low emissions in Poland. In particular, this applies to areas where there is a lack of heating and gas networks. This paper presents the results of calculations relating to the emission of atmospheric pollutants (TSP—total suspended particles as particulate matter PM10 and PM2.5, SOx—sulphur dioxide, NOx—nitrogen dioxide, CO—carbon monoxide) from individual sources of heat. The fact that a commune that does not have the network infrastructure, noted above, was taken into consideration, and the structure of heat generation was estimated on the basis of coal, fuel oil and biomass. The analysis was carried out taking into account the variable heat generation structure in households depending on the fuels used, including the heating values of fuels and the efficiency of heating devices. Based on the calculations carried out, an ecological effect was obtained by assuming the replacement of heat sources by devices with higher efficiency and also by considering the possibility of using heat pumps as a zero-emission solution in the households. This article attempts to answer the question posed by municipal authorities on how to limit the negative impact on the environment of individual heating devices in order to achieve sustainable development, including the specific conditions resulting from limited infrastructural opportunities.

Keywords: sustainable development; heat generation; low emissions; earth and environmental science

1. Introduction Energetic and environmental aspects of heat generation play an important role in the context of the sustainable development of each country. In the energy context, access to the energy carriers used for heat generation (heating of buildings and production of domestic hot water) and electricity production is crucial. In the ecological context, it becomes important to maximise the reduction of pollutant emissions into the atmosphere arising from the use of renewable energy sources. The consequences of energy pollution are increasingly felt in the modern world. Poland is a country that has struggled with the problem of high concentrations of pollutants in the air for many years. In the heating season, high concentrations of suspended particulate matter—PM10 (with a diameter of no more than 10 µm) and PM2.5 (with a diameter of no more than 2.5 µm) and benzo(a)pyrene (organic highly carcinogenic compound), which are highly carcinogenic compounds, SOx (sulphur dioxide—inorganic compound, a heavy, colourless, poisonous gas), NOx (nitrogen dioxide—inorganic compound, at room temperature it is a brown, highly toxic gas with a pungent odour reminiscent of chlorine gas) and CO (carbon monoxide—inorganic compound with strong toxic properties)—are recorded in the air. The reason for this is primarily the energy sector (based on coal), as well as transport and industrial

Energies 2020, 13, 454; doi:10.3390/en13020454 www.mdpi.com/journal/energies Energies 2020, 13, 454 2 of 16 emissions. Solutions currently implemented in these sectors result in the phenomenon of so-called low emissions—emissions of the products of combustion of solid, liquid and gaseous fuels into the atmosphere from emission sources (emitters) located at a height of not more than 40 m [1]. This issue is widely discussed at the national level [2,3] and at the global level [4–7], and the authors of the publications cited raise two main issues that should be agreed. First of all, it is widely recognised that the main reason for the problem of low emissions is the combustion of solid fuels for space heating and the production of domestic hot water. Secondly, the health, social and environmental consequences of heat generation based on conventional fuels prevent sustainable development both locally and globally. The health consequences resulting from the above-mentioned impacts are of particular importance for the functioning of society [8–12], which can mainly be overcome by changing the structure of heat generation in the municipal sector through increasing the use of renewable energy sources [13–17]. Increasing energy efficiency and reducing emissions is a key issue for many economies worldwide [18–20]. An important factor in improving air quality is increasing the use of distributed renewable energy sources, especially on a local scale [21]. A multitude of environmental, economic, political and social challenges demonstrate that current practices of natural resource management are unsustainable. Effective management of natural resources builds on political processes and governance structures [22]. The European Union (EU) strategies for a low-carbon built environment include the modernisation of heating systems in buildings by increasing the use of renewable energy sources. For example, heat pumps currently account for 5% of sales for the heating requirement and provide 3% of the energy for heating in the EU. However, in the International Energy Agency scenarios towards a sustainable future, heat pumps make up from 10% to 30% of the heating equipment stock [23]. About 79% of the energy used in EU households is for space heating and the production of domestic hot water [24]. In Poland, solid fuels, mainly hard coal (an exception at the scale of the European Union) and firewood [25], form the most important elements in the structure of energy consumption in households. The use of renewable energy is still at a very low level. In 2018, the share of energy from renewable sources in gross final energy consumption was 11.6%. Over 70% of energy obtained from renewable sources in Poland comes from biomass [26]. An increase in the importance of heat pumps has been observed in recent years, although in 2018, heat pumps were only used in one household in 200. Responsibility for actions to improve air quality at the local scale lies with the executive bodies of local government units. Thanks to the so-called anti-smog resolutions, provincial assemblies in Poland have been given the power to introduce restrictions or a ban on the operation of installations which burn solid fuels if that prevents negative effects on human health or the environment. This article attempts to answer the question of how to reduce the negative impact of individual heat generation on the environment in a rural area. The results obtained are to be a universal solution, and therefore the calculations were carried out for a commune typical of those located in Poland, and which does not have the infrastructure of district heating and gas networks, which, in consequence, requires the use of individual heat sources. In practice, it mainly results in the use of coal. There are 1555 rural communes in Poland, and in most of them, there is a need to exchange individual heat sources for more ecological solutions.

2. Air Quality in Poland The main source of low emissions is found in the heat generation processes needed for space heating and domestic hot water [27,28]. This is evidenced by the data presented in Figure1 regarding the percentage share of individual heating devices in the emissions of PM10, PM2.5 and benzo(a)pyrene. It should be emphasised that for both PM10 and PM2.5, almost 50% of emissions are covered by so-called non-industrial combustion processes, respectively 48.5% (PM10) and 49.7% (PM2.5). In the case of benzo(a)pyrene, this value reaches 86%, which is of particular importance. With the problem deﬁned in this manner, it is necessary to look for solutions in the ﬁeld of the modernisation of heat Energies 2020, 13, x FOR PEER REVIEW 3 of 16 Energies 2020, 13, 454 3 of 16 modernisation of heat sources, especially in areas where there is no district heating or gas network infrastructure. The natural direction seems to be to increase the use of renewable energy sources, sources, especially in areas where there is no district heating or gas network infrastructure. The natural whose resources in many regions of Poland are adequate, although their level of use is still low [29– direction seems to be to increase the use of renewable energy sources, whose resources in many regions 31]. of Poland are adequate, although their level of use is still low [29–31].

Figure 1. Sectors responsible for particulate matter (PM)10, PM2.5 and benzo(a)pyrene emissions in FigurePoland 1. (based Sectors on responsible Reference [for27]). particulate matter (PM)10, PM2.5 and benzo(a)pyrene emissions in Poland (based on Reference [27]). Air quality control in Poland has been carried out for several decades, and since 2004 it has beenAir adapted quality to control European in Poland Union has regulations been carried and out requirements. for several decades, The air qualityand since monitoring 2004 it has system been adaptedconsists to of European various types Union of suitablyregulations equipped and requirements. measuring stations. The air quality Research monitoring is also conducted system basedconsists on ofother various monitoring types of techniques,suitably equipped such as measuring modelling, stations. passive methodsResearch and is also additional conducted tests based [31]. Testson other and monitoringassessment techniques, of air quality such in Poland,as modelling, in accordance passive withmethods the Actand on additional Environmental tests [31]. Protection Tests and [32], assessmentare carried of out air by quality the Inspectorates in Poland, in of accordance Environmental with the Protection Act on Environmental as part of the State Protection Environmental [32], are carriedMonitoring out by (SEM) the system.Inspectorates The average of Environmental annual norms Protection for individual as part pollutants of the State are, respectively:Environmental for 3 3 3 3 MonitoringPM10—40 µ(SEM)g/m , system. for PM2.5—25 The averageµg/m annual, for benzo(a)pyrene—1 norms for individual ng/m pollutants, for SO2 are,and respectively: NOx—20 µg for/m 3 3 3 3 2 x 33 PM10—40(applicable μg/m acceptable, for PM2.5—25 levels for μ plantg/m , protection),for benzo(a)pyrene—1 for NO2—40 ng/mµg/m, forand SO for and CO—10,000 NO —20 μµg/mg/m (applicable(concentration acceptable averaging levels period, for plant 8 h). protection), for NO2—40 μg/m3 and for CO—10,000 μg/m3 (concentrationThe results averaging of the annual period, air 8 quality h). assessment for 2017 in Poland do not signiﬁcantly diﬀer from the resultsThe results obtained of the in 2016annual and air in quality previous assessment years. There for is2017 a slight in Poland increase do (compared not significantly to 2016) differ in the fromnumber the results of exceedances obtained setin 2016 for PM2.5 and in and previous PM10 ye forars. the There criterion is a slight on average increase annual (compared concentrations to 2016) inand the an number improvement of exceedances of these parameters set for PM2.5 compared and to PM10 2015. Forfor benzo(a)pyrene,the criterion on the average highest averageannual concentrationsannual values wereand an obtained improvement as a result of ofthese measurements parameters carriedcompared out into 20172015. in For the benzo(a)pyrene, following provinces: the highestMałopolska average (22.7, annual 14.6 and values 10.0 were ng/m 3obtained), Silesia (16.0,as a re 14.5sult and of measurements 12.3 ng/m3) and carried Lower Silesiaout in (15.92017 ngin /them3). followingIn the case provinces: of PM10 Ma dust,łopolska the highest (22.7, average14.6 and annual 10.0 ng/m concentration3), Silesia (16.0, in 2017 14.5 was and recorded 12.3 ng/m at3) urban and Lowerbackground Silesia stations(15.9 ng/m in the3). In Małopolska the case of (64.3PM10µ dust,g/m3 )the and highest Silesia average (55.6 µg annual/m3) zones. concentration In previous in years,2017 wasthe valuerecorded of this at urban parameter background was the higheststations at in the the communication Małopolska (64.3 station μg/m in the3) and Krak Silesiaów Agglomeration (55.6 μg/m3) zones.(56.7 µ Ing/ mprevious3 in 2016 years, and 67.8the valueµg/m 3ofin this 2015) parameter [27]. was the highest at the communication station in the KrakówThese dataAgglomeration prove that (56.7 the airμg/m quality3 in 2016 standards and 67.8 in μ Polandg/m3 in are2015) permanently [27]. exceeded. This is alsoThese demonstrated data prove in that data the published air quality by standards the European in Poland Environment are permanently Agency exceeded. [28]. The This problem is also of demonstratedexceeding the permissiblein data published standards by applies the Europe mainlyan to PM10,Environment PM2.5 and Agency benzo(a)pyrene, [28]. The andproblem to a lesser of exceedingextent SO xthe, NO permissiblex and CO. Figuresstandards2 and applies3 show mainly data on to the PM10, concentration PM2.5 and of benzo(a)pyrene, PM10 and PM2.5 and in 2016 to a lesser(annual extent limit SO value)x, NO inx and Europe CO. [ 28Figures], where 2 and Poland 3 show is characterised data on the byconcentration one of the highest of PM10 exceedances and PM2.5 of inpermissible 2016 (annual PM10 limit standards value) (locallyin Europe above [28], 50 wherµg/me3 )Poland and PM2.5 is characterised (locally exceeding by one 30 ofµ gthe/m 3highest). exceedances of permissible PM10 standards (locally above 50 μg/m3) and PM2.5 (locally exceeding 30 μg/m3).

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FigureFigure 2. 2. ConcentrationConcentration of of PM10 PM10 in in Poland Poland and and Europe Europe in in 2016 2016 (based on Reference [28]). [28]). Figure 2. Concentration of PM10 in Poland and Europe in 2016 (based on Reference [28]).

Figure 3. Concentration of PM2.5 in Poland and Europe in 2016 (based on Reference [28]). Figure 3. Concentration of PM2.5 in Poland and Europe in 2016 (based on Reference [28]). Figure 3. Concentration of PM2.5 in Poland and Europe in 2016 (based on Reference [28]). Access to the infrastructure of heating and gas networks is also a problem. Statistical data on the populationAccess to the using infrastructure gas from the of networkheating and gas networks consumption is also per a capitaproblem. indicate Statistical that 52.1%data on of the Access to the infrastructure of heating and gas networks is also a problem. Statistical data on the population usedusing gas gas in from Poland the innetwork 2017 (Figure and 4gas). Thisconsumption value should per becapita considered indicate as that low. 52.1% In addition, of the population using gas from the network and gas consumption per capita indicate that 52.1% of the populationtaking into used account gas thein Poland fact that in it 2017 was (Figure 71.2% in4). urban This value areas should and only be 23.3%considered in rural as low. areas, In there addition, is an population used gas in Poland in 2017 (Figure 4). This value should be considered as low. In addition, takingobvious into conclusion account ofthe a linkfact that to limited it was access 71.2% to in the urban gas networkareas and [25 only]. The 23.3% lack in of rural local heatingareas, there networks is an obvioustaking into conclusion account theof facta link that to it limited was 71.2% access in urtoban the areas gas networkand only [25].23.3% The in rurallack areas,of local there heating is an obvious conclusion of a link to limited access to the gas network [25]. The lack of local heating

Energies 2020, 13, x FOR PEER REVIEW 5 of 16 Energies 2020, 13, x FOR PEER REVIEW 5 of 16 Energiesnetworks2020 ,was13, 454 recognised as the second element excluding municipalities from the possibility5 of 16of networkssustainable was development recognised andas theimprovem second entelement in air exquality.cluding Statistical municipalities data on from the densitythe possibility of heating of 2 wassustainablenetworks recognised in development 2017 as in the Poland second and indicate improvem element an excluding averageent in air length municipalitiesquality. of 8.1Statistical km from per data 100 the on possibilitykm the. The density most of sustainable ofimportant heating 2 developmentnetworksissue, however, in 2017 and is in improvementthat Poland 98.3% indicate of the in airheating an quality. average networks Statistical length occur of data 8.1 in onkmurban the per areas density 100 km(Figure of. heatingThe 5). most Unfortunately, networks important in 2017issue,the fuel in however, Poland used in indicate isexisting that 98.3% an heating average of the plants lengthheating is usually of networks 8.1 km solid per occur fuel, 100 km inat urban266.2%. The areas[25]. most (Figure important 5). issue,Unfortunately, however, isthe that fuel 98.3% used ofin theexisting heating heating networks plants occur is usually in urban solid areas fuel, (Figure at 66.2%5). [25]. Unfortunately, the fuel used in existing heating plants is usually solid fuel, at 66.2% [25].

Figure 4. Population using gas from the network and gas consumption per capita in 2017 Figure(based 4.on Population Reference [25]).using using gas gas from from the the network network an andd gas gas consumption consumption per per capita capita in in 2017 2017 (based on Reference(based on [Reference25]). [25]).

FigureFigure 5.5. Heat network density inin 20172017 (based(based onon ReferenceReference [[25]).25]). Figure 5. Heat network density in 2017 (based on Reference [25]). There are 1555 rural communes in Poland, which in relation to the above data shows the scale of There are 1555 rural communes in Poland, which in relation to the above data shows the scale the problem. Lack of access to the network infrastructure necessitates the use of other energy carriers. of theThere problem. are 1555 Lack rural of accesscommunes to the in networkPoland, whichinfrastructure in relation necessitates to the above the datause showsof other the energy scale Additionally, statistical data published by the Central Office of Building Control [33] indicate that the ofcarriers. the problem. Additionally, Lack ofstatistical access todata the published network byinfrastructure the Central Office necessitates of Building the useControl of other [33] indicateenergy number of building permits issued in Poland in 2018 was 196,322 (226,469 facilities) and these should carriers.that the numberAdditionally, of building statistical permits data issued published in Poland by the in Central 2018 was Office 196,322 of Building (226,469 Control facilities) [33] and indicate these be taken into account. In this overall figure, residential buildings accounted for 98,915, of which, 94.7% thatshould the numberbe taken of into building account. permits In this issued overall in Poland figure, in residential 2018 was 196,322 buildings (226,469 accounted facilities) for and98,915, these of were single-family houses. Unfortunately, 65% of newly built houses are equipped with solid fuel shouldwhich, 94.7%be taken were into single-family account. In ho thisuses. overall Unfortunately, figure, residential 65% of newl buildingsy built housesaccounted are equipped for 98,915, with of boilers [34]. The above statement is confirmed by data on fuels used to generate energy for space which,solid fuel 94.7% boilers were [34]. single-family The above ho statementuses. Unfortunately, is confirmed 65% by data of newl on fuelsy built used houses to generate are equipped energy with for heating and domestic hot water purposes, as presented in Figure6. solidspace fuel heating boilers and [34]. domestic The above hot waterstatement purposes, is confirmed as presented by data in onFigure fuels 6. used to generate energy for space heating and domestic hot water purposes, as presented in Figure 6.

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FigureFigure 6. Types 6. Types of offuels fuels used used to togenerate generate heat heat for for heatin heatingg purposes purposes in in2017 2017 (based (based on on Reference Reference [25]). [25]). 3. Materials and Methods 3. Materials and Methods Analytical work was carried out for a theoretical rural commune with a population of 8000. Analytical work was carried out for a theoretical rural commune with a population of 8000. Taking into account the statistical data [35,36], the density of population in rural communes in Taking into account the statistical data [35,36], the density of population in rural communes in Poland Poland is from 100 to 149 people per square kilometre (78.4% of all rural communes.) In addition, is from 100 to 149 people per square kilometre (78.4% of all rural communes.) In addition, the average the average area of a rural commune in Poland is 126 km2. Multiplying these values gives a range of area of a rural commune in Poland is 126 km2. Multiplying these values gives a range of 12,600–18,774 12,600–18,774 inhabitants. Considering the data on access to the gas network in Poland (52.1%) and inhabitants. Considering the data on access to the gas network in Poland (52.1%) and assuming an assuming an uneven distribution of the size of municipalities in terms of population, it was decided to uneven distribution of the size of municipalities in terms of population, it was decided to adopt the adopt the value of 8000 inhabitants as representative. value of 8000 inhabitants as representative. The average number of people in a household was adopted as 3.4 [25], which allowed us to The average number of people in a household was adopted as 3.4 [25], which allowed us to calculate the total number of households in the commune as being 2353. According to data published by calculate the total number of households in the commune as being 2353. According to data published the Central Statistical Office [25], the average area of a household in Poland in a rural region is 108.3 m2. by the Central Statistical Office [25], the average area of a household in Poland in a rural region is The average energy demand is 216 kWh/m2year [37]. This information allowed for the calculation 108.3 m2. The average energy demand is 216 kWh/m2year [37]. This information allowed for the of the total heat demand of a commune for space heating and domestic hot water production, at calculation of the total heat demand of a commune for space heating and domestic hot water 198,150.776 GJ. The first stage was to determine the structure of the energy carriers and heating devices production, at 198,150.776 GJ. The first stage was to determine the structure of the energy carriers used. As a baseline, it was assumed that 70% of the inhabitants of the commune use coal to produce and heating devices used. As a baseline, it was assumed that 70% of the inhabitants of the commune heat, 25% use biomass and 5% use fuel oil (Model 1). Simulations of the potential ecological effect use coal to produce heat, 25% use biomass and 5% use fuel oil (Model 1). Simulations of the potential resulting from the exchange of the energy source were carried out in six variants (Model 2–7), assuming ecological effect resulting from the exchange of the energy source were carried out in six variants different shares of energy carriers in the energy balance of the commune. (Model 2–7), assuming different shares of energy carriers in the energy balance of the commune. The analysis was carried out for six models: The analysis was carried out for six models: Model 2 (biomass dominance): 70% biomass, 25% coal, 5% fuel oil. • • Model 2 (biomass dominance): 70% biomass, 25% coal, 5% fuel oil. Model 3 (balanced): 47.5% coal, 47.5% biomass, 5% fuel oil. • • Model 3 (balanced): 47.5% coal, 47.5% biomass, 5% fuel oil. Model 4 (balanced with increased efficiency): 47.5% coal, 47.5% biomass, 5% fuel oil, 5% increase • • Model 4 (balanced with increased efficiency): 47.5% coal, 47.5% biomass, 5% fuel oil, 5% increase inin nominal nominal heating heating device device efficiency. efficiency. Model 5 (share of heat pumps): 40% coal, 40% biomass, 5% fuel oil, 15% heat pump. • • Model 5 (share of heat pumps): 40% coal, 40% biomass, 5% fuel oil, 15% heat pump. • ModelModel 6 6(share (share of of heat heat pumps pumps and and increase inin eefffificiency):ciency): 40%40% coal, coal, 40% 40% biomass, biomass, 5% 5% fuel fuel oil, oil, 15% • 15%heat heat pump, pump, 5% 5% increase increase in nominalin nominal effi efficiencyciency of heatingof heating devices. devices. • ModelModel 7 (100% 7 (100% from from renewable renewable energy): energy): 50% 50% biomass, biomass, 50% 50% heat heat pump. pump. • ModelModel 2 is 2 isincluded included in inthe the models models calculated calculated ab aboveove due due to toa desire a desire to tocompare compare the the base base state state pollutantpollutant emissions emissions with with other other models, models, assuming assuming that that renewable renewable energy energy provision provision is ispredominantly predominantly providedprovided by by solid solid fuel fuel boilers boilers fired fired with with biomass. biomass. The The assumptions assumptions for for models models 4–6 4–6 result result from from the the technicaltechnical and and financial financial possibilities possibilities of ofa total a total de departureparture from from solid solid fuels fuels towards towards renewable renewable energy energy sources, hence a balanced share of solid fuel boilers fired with coal and biomass was assumed, with a constant share of fuel oil, however with the assumption of an increase in the share of heat pumps,

Energies 2020, 13, 454 7 of 16 sources, hence a balanced share of solid fuel boilers fired with coal and biomass was assumed, with a constant share of fuel oil, however with the assumption of an increase in the share of heat pumps, as well as an increase in the nominal efficiency of heating devices resulting from the modernisation of the heat source. Model 7, based on the use of biomass and heat pumps, was adopted as the most ecological solution because of the need to strive to increase the share of renewable energy sources when generating heat for space heating and domestic hot water. Each of the energy carriers analysed was assigned lower heating values (LHW) and the nominal efficiency of heating devices (in the case of oil boilers, including traditional and condensing boilers) on the basis of the catalogues of heating equipment manufacturers and the typical lower heating values (LHW) of conventional fuels and the efficiency factor of the heat pump in Polish conditions (Table1)[38]. In total, six types of biomass were analysed (pellets, dry wood, straw briquettes, wood briquettes, rape straw, corn straw), three types of coal (eco-pea coal, nut coriander, culm), two types of fuel oil (light and heavy) and three types of heat pumps (air/water, brine/water with vertical heat exchanger, brine/water with horizontal heat exchanger).

Table 1. Type of fuels, nominal eﬃciency and lower heating value (LHW) used in calculations [38].

Nominal Lower Heating Value Type of Fuel Eﬃciency (–) (LHW) (MJ/Unit) Pellet 0.80–0.88 17.0–21.0 Dry wood 0.80–0.88 16.0–19.0 Straw briquette 0.80–0.88 16.9–17.1 Biomass Wood briquette 0.80–0.88 16.1–20.4 Rape straw 0.80 15.0 Corn straw 0.80 16.8 Ekogroszek 0.75 24.0–28.0 Coal Nut-type coal 0.75 24.0–28.0 Culm 0.75 18.0–26.0 Coke Coke 0.75 27.0 Condensing boiler 0.99 36.12 Light fuel oil Traditional boiler 0.88 36.12 Condensing boiler 0.99 39.7 Heavy fuel oil Traditional boiler 0.88 39.7 Brine/water with vertical heat exchanger 3.5–4.0 3.6 Heat pump Brine/water with horizontal heat exchanger 3.5–4.0 3.6 Air/water 3.5 3.6

In the case of heat pumps, it was decided to consider three variants because of their widespread use in Polish conditions. The temperature stability of the ground as a heat source is important from the point of view of using a heat pump for heating and domestic hot water preparation, hence it was decided to consider devices with vertical and horizontal heat exchangers. However, taking into account the changing standards for new buildings (decreasing demand for heat), an air/water heat pump for central heating and domestic hot water preparation has also been taken into account. This type of device is increasingly used due to the investment costs, which are lower because of the lack of the need to carry out work related to the implementation of the heat source. Arithmetic means were calculated for individual groups (biomass, coal, fuel oil and heat pumps) and then the percentage share of the model analysed was assigned. In addition, an increase in nominal eﬃciency has been assumed for solid-fuel boilers (coal and biomass). For biomass boilers, the eﬃciency increase was assumed to be from 80%–88% to 90%, while for coal boilers from 75% to 80%. The emission of pollutants into the atmosphere was calculated on the basis of the National Centre for Emissions Management (KOBIZE) guidelines, on emission factors for Energies 2020, 13, 454 8 of 16

fuel combustion in boilers with a nominal thermal capacity of 5 MW [39]. Calculations were made according to the equations: Q A B = · (1) η W · O Energieswhere: 2020, 13, x FOR PEER REVIEW 8 of 16 where:B—amount of fuel (m3) or (Mg), Q—amountB—amount of energy of fuel produced (m3) or (Mg), (MJ/ m2rok), assuming 1 MJ/m2year, 2 2 A—heatedQ—amount area (m of2 energy), assumed produced 1 m2, (MJ/m rok), assuming 1 MJ/m year, 2 2 η—boilerA—heated eﬃciency area (–),(m ), assumed 1 m , η—boiler efficiency (–), 3 WO—lower heating value (LHW) of fuel, (MJ/m ) or (MJ/Mg). WO—lower heating value (LHW) of fuel, (MJ/m3) or (MJ/Mg). E = B W (2) 𝐸=𝐵·· 𝑊 (2) where: where: E—emissionE—emission of pollutants of pollutants (g/MJ), (g/MJ), 3 B—amountB—amount of fuel, of fuel, (m3) (m or (Mg),) or (Mg), W—emissionW—emission factor factor (Mg). (Mg).

4.4. Results Results TheThe results of thethe calculationscalculations are are shown shown in in Figures Figures7– 137–13.. Model Model 1, with1, with a 70% a 70% share share of coal, of coal, a 25% a 25%share share of biomass of biomass and aand 5% sharea 5% share of fuel of oil, fuel was oil, adopted was adopted as the baseline,as the baseline, against against which further which variantsfurther variantsof the calculations of the calculations were compared. were compared. The results The obtained results obtained (Figure7) (Figure showed 7) the showed quantities the ofquantities pollutants of pollutants emitted into the atmosphere during the year to be: SOx—35,191 kg, NOx—11,394 kg, CO— emitted into the atmosphere during the year to be: SOx—35,191 kg, NOx—11,394 kg, CO—234,280 kg 234,280and TSP kg (particulate and TSP (particulate matter PM10 ma andtter PM10 PM2.5)—55,639 and PM2.5)—55,639 kg. kg.

Figure 7. Annual emissions of pollutants in the baseline scenario (Model 1): 70% coal, 25% biomass, Figure 7. Annual emissions of pollutants in the baseline scenario (Model 1): 70% coal, 25% biomass, 5% fuel oil. 5% fuel oil. The results obtained in Model 2 (Figure8), assuming the opposite situation in relation to the baseThe state—70% results obtained share of biomass,in Model 25% 2 (Figure share of8), coalassuming and 5% the share opposite of fuel situation oil—indicate in relation a signiﬁcant to the basereduction state—70% in emissions, share of depending biomass, 25% on the share pollutant of coal concerned, and 5% share ranging of fuel from oil—indicate 11.23% to 59.45%. a significant By far reduction in emissions, depending on the pollutant concerned, ranging from 11.23% to 59.45%. By the largest emissions reduction concerns SOx (59.45%) and TSP (24.23%). The smallest reduction is CO, farat 11.23%.the largest In Model emissions 3 (Figure reduction9), an equalconcerns share SO ofx (59.45%) coal and and biomass TSP utilisation(24.23%). The was smallest assumed reduction at 47.5%, iswith CO, a at 5% 11.23%. share of In fuel Model oil. The3 (Figure results 9), obtained an equal indicate share of about coal half and of biomass the reductions utilisation seen was in the assumed case of atModel 47.5%, 2, with that is,a 5% in theshare range of fuel 5.62%–29.72%. oil. The results obtained indicate about half of the reductions seen in the case of Model 2, that is, in the range 5.62%–29.72%.

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Figure 8. Annual emissions of pollutants in Model 2: 25% coal, 70% biomass, 5% fuel oil.

Figure 8. Annual emissions of pollutants in Model 2: 25% coal, 70% biomass, 5% fuel oil. Figure 8. Annual emissions of pollutants in Model 2: 25% coal, 70% biomass, 5% fuel oil.

Figure 9. Annual emissions of pollutants in Model 3: 47.5% coal, 47.5% biomass, 5% fuel oil. Figure 9. Annual emissions of pollutants in Model 3: 47.5% coal, 47.5% biomass, 5% fuel oil. The last model, which does not take into account the share of heat pumps using renewable energy sources,TheFigure waslast Modelmodel, 9. Annual 4 which (Figure emissions does 10), of basednot pollutants take on theinto in same Modelaccount assumptions 3: 47.5%the share coal, as 47.5%of Model heat biomass, 3,pumps but 5% with using fuel the oil. renewable additional energycondition sources, that the was effi Modelciency 4 of(Figure heating 10), devices based on would the same increase assumptions by 5%. The as Model assumed 3, but value with of the additionalincreaseThe inlast condition effi model,ciency isthatwhich relatively the does efficiency low, not buttake of this heatin into is becauseaccountg devices the the would increase share increase of in theheat eby ffipumps ciency5%. The ofusing assumed the entirerenewable value space energyofheating the increase sources, and domestic inwas efficiency Model hot water 4is (Figure relatively installation 10), low, based (transmission, but on this the is same because regulation assumptions the increase and accumulation as inModel the efficiency 3, but effi ciency)with of thethe is additionalentiretaken intospace condition account, heating andandthat notdomesticthe justefficiency the hot effi waterofciency heatin instal ofg heatdeviceslation generation. (transmission, would increase Nevertheless, regulation by 5%. theThe and resultsassumed accumulation obtained value ofefficiency)show the increase that theis taken in replacement efficiency into account, is of relatively solid and fuel not low, boilers just but th withthise efficiency is class-5 because boilersof theheat increase thatgeneration. meet in the the Nevertheless, efficiency requirements of thethe of entireresultsEcoDesign, space obtained evenheating withoutshow and that domestic a comprehensive the replacement hot water modernisation instal of solilationd fuel (transmission, of boilers the installation, with regulationclass-5 brings boilers and the desiredaccumulationthat meet results. the efficiency)requirementsCompared is to taken Modelof EcoDesign, into 4, the account, reduction even withoutand in not SO axjust comprehensiveincreased the efficiency from 29.72%modernisation of heat to 33.80%,generation. of the for NOinstallation,Nevertheless,x from 8.69% brings the to results obtained show that the replacement of solid fuel boilers with class-5 boilers that meet the the14.19%, desired for COresults. from Compared 5.62% to 11.87% to Model and 4, for the TSP reduction from 12.12% in SO tox increased 18.71%. It from is worth 29.72% noting to 33.80%, that in thefor requirements of EcoDesign, even without a comprehensive modernisation of the installation, brings NOcasex offrom the 8.69% reduction to 14.19%, of CO emissions,for CO from the 5.62% value ofto 11.87%11.87% obtainedand for TSP in Model from 312.12% is slightly to 18.71%. higher thanIt is theworthin thedesired casenoting ofresults. that Model in Compared the 1, where case of itto the was Model reduction 11.23%. 4, the of reduction CO emissions, in SO xthe increased value of from 11.87% 29.72% obtained to 33.80%, in Model for NO3 isx slightly from 8.69% higher to than14.19%, in the for case CO offrom Model 5.62% 1, where to 11.87% it was and 11.23%. for TSP from 12.12% to 18.71%. It is worth noting that in the case of the reduction of CO emissions, the value of 11.87% obtained in Model 3 is slightly higher than in the case of Model 1, where it was 11.23%.

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Energies 2020, 13, 454 10 of 16 Energies 2020, 13, x FOR PEER REVIEW 10 of 16

Figure 10. Annual emission of pollutants in Model 4: 47.5% coal, 47.5% biomass, 5% fuel oil and 5%

improvementFigure 10. Annual in the emission efficiency of of pollutants the devices. in Model 4: 47.5% coal, 47.5% biomass, 5% fuel oil and 5% improvementFigure 10. Annual in the emission efficiency of ofpollutants the devices. in Model 4: 47.5% coal, 47.5% biomass, 5% fuel oil and 5% Modelsimprovement 5 and in 6 the contain efficiency a 15% of the share devices. of heat pumps. This is an optimistic and cautious option, whichModels results 5 from and 6the contain development a 15% share of the of heat pu pumps.mp market This isin an Poland optimistic and andthe decreasing cautious option, price differencewhichModels results between 5 fromand 6 theclass-5 contain development solid a 15% fuel share ofboilers the of heatheat and pumppumps. air/water market This heat is in anpumps. Poland optimistic On and theand the other decreasingcautious hand, option, priceit is difficultdiwhichfference results to betweenforesee from a class-5 heatthe development pump solid fuelin buildings boilers of the and with heat air high/puwatermp heat heatmarket demand pumps. in Polandand On possessing the and other the hand, adecreasing heating it is disystem ffipricecult operatingtodifference foresee aatbetween heat high pump supply class-5 in temperatures. buildings solid fuel with boilers This high is heat anddue demand toair/water the need and heat possessingto modernise pumps. a On heating the the installation other system hand, operating to work it is atdifficult highthe lower supplyto foresee temperatures temperatures. a heat pump required Thisin buildings is dueby heat to with the pumps high need heat tofor modernise demandefficient and operation. the possessing installation The a heating toresults work systemof at the calculationsloweroperating temperatures at forhigh models supply required 5 (Figuretemperatures. by heat 11) and pumps This 6 (Figure foris due effi 12) cientto theshow operation. need a higher to modernise The level results of thepollution of installation the calculations reduction to work for for at the lower temperatures required by heat pumps for efficient operation. The results of the NOmodelsx, CO 5 and (Figure TSP 11 than) and in 6all (Figure the other 12) showmodels a higherinvestigated. level of Only pollution in the reduction case of SO forx are NO thex, CO values and calculations for models 5 (Figure 11) and 6 (Figure 12) show a higher level of pollution reduction for betterTSP than than in those all the in other Model models 2. Emissions investigated. of pollutants Only in are the reduced case of by: SO x39.99%–43.43%are the values betterfor SO thanx, 21.88%– those NOx, CO and TSP than in all the other models investigated. Only in the case of SOx are the values 26.5%in Model for 2.NO Emissionsx, 20.51%–25.77% of pollutants for CO are and reduced 25.93%–31.49% by: 39.99%–43.43% for TSP. for SOx, 21.88%–26.5% for NOx, 20.51%–25.77%better than those for in COModel and 2. 25.93%–31.49% Emissions of pollutants for TSP. are reduced by: 39.99%–43.43% for SOx, 21.88%– 26.5% for NOx, 20.51%–25.77% for CO and 25.93%–31.49% for TSP.

Figure 11. Annual emissions of pollutants in Model 5: 40% coal, 40% biomass, 5% fuel oil, 15% Figureheat pumps. 11. Annual emissions of pollutants in Model 5: 40% coal, 40% biomass, 5% fuel oil, 15% heat

pumps. Figure 11. Annual emissions of pollutants in Model 5: 40% coal, 40% biomass, 5% fuel oil, 15% heat pumps.

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Figure 12. Annual emissions of pollutants in Model 6: 40% coal, 40% biomass, 5% fuel oil, 15% heat

Figurepumps 12.andAnnual 5% growth emissions of the ofefficiency pollutants of devices. in Model 6: 40% coal, 40% biomass, 5% fuel oil, 15% heat pumpsFigure 12. and Annual 5% growth emissions of the eofﬃ pollutantsciency of devices. in Model 6: 40% coal, 40% biomass, 5% fuel oil, 15% heat pumpsThe conclusions and 5% growth drawn of thefrom efficiency the analysis of devices. of the results obtained in models 2–6 indicate that the optimalThe solution conclusions would drawn be the from replacement the analysis of coal-fired of the results solid-fuel obtained boilers in models with solutions 2–6 indicate based that on the optimaluse ofThe renewable solutionconclusions wouldenergy drawn besources. the from replacement theFor analysis this reason, of of coal-ﬁred the a modelresults solid-fuel inobtained which boilers inonly models biomass with 2–6 solutions boilersindicate basedand that heat the on theoptimalpumps use are ofsolution renewable used would(each energy technologybe the sources. replacement providing For thisof coal-fired50%), reason, was asolid-fuel modelalso investigated. in boilers which with only When solutions biomass compared based boilers onto and the heatusebaseline, of pumps renewable Model are used7, energy to (eachwhich sources. technology these For assumptions this providing reason, refer, 50%),a model indicates was in also which the investigated. highestonly biomass reduction When boilers comparedof pollutantand heat to the baseline, Model 7, to which these assumptions refer, indicates the highest reduction of pollutant pumpsemissions are to used the atmosphere,(each technology as shown providing in Figure 50%), 13. was In thealso case investigated. of SOx, it isWhen a reduction compared of 403 to thekg, emissions to the atmosphere, as shown in Figure 13. In the case of SO , it is a reduction of 403 kg, baseline,which is 87.32%Model less7, to than which in the these base assumptions state. For NO refer,x, it is indicates 3636 kg (68.09%), the highestx for CO,reduction 94,439 ofkg pollutant (59.69%) whichemissionsand for is suspended 87.32% to the lessatmosphere, dust than TS inP, the 16,344 as base shown kg state. (70.63%). in ForFigure NO x13., it In is 3636the case kg (68.09%), of SOx, it for is CO,a reduction 94,439 kg of (59.69%) 403 kg, andwhich for is suspended 87.32% less dust than TSP, in the 16,344 base kg state. (70.63%). For NOx, it is 3636 kg (68.09%), for CO, 94,439 kg (59.69%) and for suspended dust TSP, 16,344 kg (70.63%).

Figure 13. Annual emissions of pollutants in Model 7: 50% biomass, 50% heat pumps. Figure 13. Annual emissions of pollutants in Model 7: 50% biomass, 50% heat pumps. In addition, the possibilities of achieving the proposed changes over a 10-year period were also analysed.In addition, TheFigure calculation the 13. possibilitiesAnnual was emissions based of achieving of on pollutants the abovethe inpr Modeoposed models,l 7: changes50% where biomass, theover baseline 50% a 10-year heatwas pumps. period dominated were also by coalanalysed. in addition The calculation to models was which based make on usethe above of heat models, pumps where and the the increase baseline in was efficiency dominated of solid-fuel by coal boilersin additionIn (Figureaddition, to models14 the), as possibilities wellwhich as amake model of achievinguse which of heat onlythe pumps pr usesoposed renewable and changes the increase energy over a sources—biomassin 10-year efficiency period of weresolid-fuel boilers also andanalysed.boilers heat (Figure pumpsThe calculation 14), (Figure as well 15 was as). Theabased model analysis on which the wasabove only conducted models, uses renewable where for the the periodenergy baseline 2019–2029. sources—biomass was dominated The values byboilers coal for individualinand addition heat pumps years to models were(Figure calculatedwhich 15). Themake basedanalysis use onof thewasheat assumption conducted pumps and for of the athe regular increase period change 2019–2029.in efficiency in the The proportions of valuessolid-fuel for in theboilersindividual structure (Figure years of 14), devices were as wellcalculated and as fuels a model based used. which on The the dionly assumptionfference uses inrenewable theof a percentage regular energy change ofsources—biomass the in baseline the proportions and boilers target in stateandthe structureheat was dividedpumps of devices (Figure by the and value15). fuelsThe of ten analysisused. years, The was which differe conducted fornce each in groupthefor percentagethe of period devices 2019–2029.of and the fuels baseline gaveThe andvalues an annual target for change.individualstate was The divided years results were by obtained the calculated value clearly of tenbased show years, on that thewhich movingassumption for each away group of from a regular of hard devices coalchange combustionand infuels the gave proportions to renewablean annual in energythe structure sources of results devices in aand significantly fuels used. faster The meansdiffere ofnce achieving in the percentage reduced emissions of the baseline and achieving and target the state was divided by the value of ten years, which for each group of devices and fuels gave an annual

Energies 2020, 13, x FOR PEER REVIEW 12 of 16 change.Energies 2020 The, 13 results, x FOR obtainedPEER REVIEW clearly show that moving away from hard coal combustion to renewable12 of 16 energy sources results in a significantly faster means of achieving reduced emissions and achieving Energiesthechange. target2020 The ,thresholds.13 results, 454 obtained This is clearly evidenced show by that achiev movinging awaybetter from values hard than coal the combustion target threshold to renewable12 from of 16 Modelenergy 6 sources for the resultsvariant inwith a significantly 100% share fasterof renewable means ofenergy achieving sources reduced in 2024, emissions i.e., five andyears achieving earlier. the target thresholds. This is evidenced by achieving better values than the target threshold from target thresholds. This is evidenced by achieving better values than the target threshold from Model 6 Model 6 for the variant with 100% share of renewable energy sources in 2024, i.e., five years earlier. for the variant with 100% share of renewable energy sources in 2024, i.e., ﬁve years earlier.

Figure 14. Change in pollutant emissions to the environment in the period 2019–2029, including the change in efficiency resulting from the implementation of Model 6. Figure 14. Change in pollutant emissions to the environment in the period 2019–2029, including the changeFigure in14. e ﬃChangeciency in resulting pollutant from emissions the implementation to the environment of Model in 6.the period 2019–2029, including the change in efficiency resulting from the implementation of Model 6.

Figure 15. Change in pollutant emissions to the environment in the period 2019–2029, including the changeFigure in15. e Changefficiency in resulting pollutant from emissions the implementation to the environment of Model in 7.the period 2019–2029, including the change in efficiency resulting from the implementation of Model 7. 5. DiscussionFigure 15. Change in pollutant emissions to the environment in the period 2019–2029, including the 5. Discussion Inchange the contextin efficiency of the resulting results from obtained, the implementation it is important of Model to plan 7. specific actions to improve the qualityIn ofthe the context environment of the results and increase obtained, energy it is important efficiency into theplan region. specific In actions the context to improve of energy the 5. Discussion planning,quality of the the methodology environmen presentedt and increase in this energy article efficiency and the results in the obtained region. canIn the certainly context complement of energy activitiesplanning,In the at the thecontext regionalmethodology of the level. results Thispresented obtained, is particularly in itthis is important importantarticle and to in planthe order resultsspecific to understand obtained actions theto can improve potential certainly the of renewablecomplementquality of energythe activities environmen sources at the tot improveregionaland increase thelevel. quality energy This is of efficiencyparticularly the environment, in importantthe region. primarily in In order the by usingtocontext understand heat of pumpsenergy the aspotentialplanning, a zero-emission of the renewable methodology technology energy sourcespresented in the households. to improvein this tharticle Thee quality results and of obtained the environmresults during obtainedent, the primarily research can bycertainly clearly using indicateheatcomplement pumps that theactivitiesas a optimal zero-emission at the model regional of technology those level. proposed This in isth particularlye is households. the one based important The on results the in use order obtained of biomassto understand during and heat the pumpresearchpotential technology. clearlyof renewable indicate By analysing energy that thesources the optimal dynamics to improve model of change, ofth ethose quality it proposed can of bethe seen environm is the that one theent, based rate primarily of on reduction the by use using ofof pollutantbiomassheat pumps and emissions, heatas a pump zero-emission when technology. compared technology By to theanalysing other in models,th thee households.dynamics is at least of change,The twice results as it high.can obtained be seen thatduring the ratethe ofresearch reductionHowever, clearly of itpollutant indicate should emissions, bethat noted the optimal that when the comparedmodel barrier ofto thosetoachieving the proposedother models, the is assumed the is atone least goalsbased twice may on as the be high. socialuse of acceptancebiomass and of heat the proposedpump technology. solutions By resulting analysing from, the amongdynamics other of change, influences, it can the be wealth seen that of society.the rate Inof areduction similar context, of pollutant namely emissions, the essence when of social compared acceptance to the ofother renewable models, energy, is at least Schumacher, twice as high. Krones,

McKenna and Schultmann [40] made the following comments. They note that this is largely dependent on a given technology and the researcher’s overall experience in renewable energy, as well as the level

Energies 2020, 13, 454 13 of 16 of experience in the field of energy autonomy. The last of the terms, i.e., energy autonomy, may be important in the future because the interesting vision is the role of rural areas as renewable energy exporters to cities in order to meet their growing energy demand [41]. Although the purpose of this study was to address individual heat sources and focus on the thermal management of buildings, it is worth bearing in mind that in an energy planning situation, decision makers should be aware of the potential consequences for public acceptance when setting framework conditions to support specific technologies or projects. In addition, one should agree with the statement [40] that opinion polls at the national level cannot be used as a basis for decisions for local projects in the field of renewable energy sources and sustainable development, because the subject of acceptance is simply different and the approval for specific projects associated with renewable energy sources must be assessed on a case-by-case basis. Returning to the results obtained during the research, the need to decarbonise energy systems in both rural and urban areas is unambiguous. Kostevsek, Petek, Cucek, Kleme and Varbanov [42], as well as Benedek, Tihamér-Tibor and Bartók [43], agree that one of the most important issues relating to the current energy policy is the need to focus on local energy systems and the role of renewable energy in these systems. In the context of this article, it should be stated that this is the right approach, and therefore one should strive to do this, mainly in rural areas characterised by a lack of district heating systems or access to natural gas as a more ecological energy carrier than hard coal or heating oil. An additional advantage of this approach to energy systems, among other approaches proposed in rural areas, is that it is possible to use them as a tool to improve energy security and support economic development [43]. The calculations carried out showed large ecological benefits resulting from the use of renewable energy sources, although the use of only renewable sources in households in the coming years seems unrealistic in Poland. Systems based on renewable energy sources such as sun or wind, which are characterised by unpredictability, require the use of peak sources (e.g., gas or electric) or adequate energy storage technologies; therefore, real energy models are those that take into account both renewable and conventional sources. It should be added that the production of energy from renewable sources is likely to be more decentralised in the future, which may lead to potentially significant changes in the regional economy. Undoubtedly, one should agree with the statement that in the context of the region and its energy transformation, reference should be made to such aspects as employment rates, supply chain analyses, input-output models or economic losses in conventional energy generation sectors due to the growing share of energy production from sources of renewable energy in the structure of local energy production [44]. Renewable energy systems are becoming a strong element of local sustainable development strategies. The answer to the question remains whether direct financial support for renewable energy systems has an impact on the increase in the use of renewable energy [45]. It seems that in Polish conditions, with a less prosperous society and a not very well-developed renewable energy sector, direct support may, however, be the main incentive to invest in renewable energy.

6. Conclusions The occurrence of low-level emissions in Poland is a common phenomenon, which is confirmed annually by reports of the Chief Inspectorate for Environmental Protection in Poland and the European Environment Agency. The main reason for this is the individual combustion of solid fuels to provide space heating and domestic hot water. In the case of rural communes, the reasons for such a situation should be seen, first of all, in the lack of a heating and gas network infrastructure, and secondly, in the wealth of society. The calculation results presented in this article clearly showed that the current structure of heat generation based on fossil fuels is unfavourable from the point of view of environmental protection. One cannot indicate one utilitarian model of conduct for each rural commune in Poland, because each of them has different geographical, topographic, spatial and economic conditions. However, it is Energies 2020, 13, 454 14 of 16 possible to analyse the situation in municipalities using the calculation model presented in the article to indicate specific actions to improve air quality through a planned change in the heat generation structure. It should be clearly stated that the results obtained in individual models indicate the legitimacy of increasing the proportion of renewable energy sources used. In addition, building a sustainable energy mix on a local scale, at the same time as reducing the share of carbon, undoubtedly contributes to reducing emissions of pollutants into the environment. The models presented in this paper show that, although there are already municipalities in Poland that prohibit the burning of fossil fuels (excluding natural gas), the most advantageous solution there is Model 7. The first results of these activities will be known after the end of the heating season, 2019/2020. Model 7 is characterised by the largest decrease in pollutant emissions compared to the basic model, which undoubtedly proves the need to take action to replace old boilers with new equipment and promoting solutions based on renewable energy sources. Key Conclusions:

The problem of low emissions in rural areas is primarily due to individual heat sources, • which results from, among other reasons, a lack of infrastructure for district heating networks and gas networks. The classification of the individual heat sources analysed in this article on the basis of the emissions • they produce, from the most to the least, is as follows: coal, biomass, heating oil, heat pumps. It should be noted that the heat pump in fact does not emit any pollution in the place of heat • delivery, and the resulting emissions derive from the structure of electricity generation in Poland (majorly based on coal), which is necessarily used to drive the compressor and circulation pumps. Although heat pumps are a renewable energy solution to reduce heat emissions due to air • pollution, it should be noted that from the socioeconomic aspect, the procurement of these devices is expensive for rural communities. The results obtained indicate that the structure of the energy sources used is the main problem. • The effectiveness of the devices used does not significantly affect the results.

Author Contributions: Conceptualization: M.K., A.S. and B.T.; Formal analysis: A.S. and B.T.; Methodology: M.K.; Resources, M.K., A.S. and B.T.; Supervision: A.S. and B.T.; Visualization: M.K.; Writing—review & editing, M.K., A.S. and B.T. All authors have read and agreed to the published version of the manuscript. Funding: The research was funded under the AGH-UST statutory research grant No. 16.16.140.315/05. Conﬂicts of Interest: The authors declare no conﬂict of interest

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