Analyses of the Life Cycles and Social Costs of CO₂ Emissions of Single-Family Residential Buildings: A Case Study in Poland

Abstract

Comprehensive environmental impact assessments of buildings and construction as a whole consider the preparation of construction and finishing materials, their transportation, the process of erecting buildings, long-term operations—including the consumption of electricity, water, and fuels—and the management of the waste generated during the demolition of facilities. In terms of the above-mentioned elements, the most negative environmental impact on a building’s life cycle is in its exploitation stage. In order to reduce this impact, modern sustainable construction uses renewable energy sources. In the area of the Polish building market, analyses of CO₂ emissions, the application of LCAs for building materials, and assessments of the social impacts of modern buildings are still very limited. The aim of this study is to evaluate the environmental life cycles and social costs of the CO₂ emissions of single-family residential buildings, in which four different systems providing energy (heat and electricity) from renewable and nonrenewable sources are used. In this research, it was found that the annual CO₂ emissions per square meter of building surface area in the analyzed objects were in the range of 30 to 176 kg CO₂. The greatest contributor to the environmental effects was energy consumption (58% to 90%). The CO₂ analysis conducted showed that facilities that use a heat pump are characterized by an environmental effect that is six times lower than that of facilities that are powered by coal combustion and electricity from the network. Similarly, the social costs associated with CO₂ emissions were significantly lower in the case of the use of renewable energy sources.

1. Introduction

The construction sector is one of the fastest-growing industries. The Central Statistical Office [1] reported that, in Poland, in 2019, 12% more flats (207,200) were completed than in 2018. In the private building sector, 5.1% more flats were completed (69,600), and in the building sector for sale or rental, 16.6% more flats were completed (130,900). Tatara et al. [2] stated that, over the last few decades, together with newly commissioned buildings, the philosophy of construction has changed. Innovative building materials with low heat-transfer coefficients have come to play an increasingly important role. These measures are particularly important, as construction has a significant anthropogenic environmental impact. The construction process has direct impacts on the atmosphere (transportation of building materials), the biosphere (transformation of biologically active areas), the lithosphere (exploitation of mineral deposits, oil, gas, and metal ores), the hydrosphere, and the troposphere (production of building materials and the building construction process). Comprehensive environmental impact assessments for buildings and construction also consider the long-term use of a building, including its electricity, water, and fuel consumption [3], as well as the management of waste (end-of-life stage) that appears during construction and demolition [4]. The production of building materials and the management of waste from the renovation and demolition of buildings are significant environmental problems. According to Ciura et al. [5], rubble and other construction waste represent more than 50% of all waste that is deposited in wild dumps.

Among the basic elements of a building’s life cycle, the greatest negative environmental impact is caused in the stage of its use, which is mainly due to the consumption of electricity and heat [6,7,8,9]. In the last 20 years, primary energy consumption in Europe has increased by 5%. Households are an important link in the process of improving energy efficiency in the countries of the European Union (EU) [10]. Buildings and construction account for nearly one-third of global energy consumption, and global energy-related CO₂ emissions represent nearly 40% of the total global emissions when indirect building emissions from power generation are considered [3]. According to Sharma et al. [8], 80–85% of the final energy is used to heat buildings, i.e., directly during their use phase. It is, therefore, necessary to invest in new technologies for construction using renewable energy sources that have much fewer negative impacts on the environment [11]. In addition, renewable energy sources (RESs) provide various social and economic benefits, e.g., diversification of energy offerings, new jobs, improvement of regional and local development opportunities, and building solid national industries [12]. The use of RESs in construction must be preceded by careful planning and balancing of the energy gains and losses during construction in order to make it more sustainable, especially in view of the wide range of energy systems that can be used.

The term “sustainable construction” was first proposed by Kibert [13]. Nowadays, sustainable construction is understood as that characterized by the careful planning (design) of a building, the thoughtful use of materials, and the use of RESs [3]. The most important goal of sustainable construction is to care for the needs of future generations [14] so that they can benefit from the same environmental resources that are available today. Therefore, in the EU, the 2020 Climate and Energy Package [15] includes a set of binding laws to ensure that the EU meets the climate and energy targets for 2020, including a 20% decrease in greenhouse-gas emissions (from 1990 levels), a share of 20% of EU energy that comes from renewables, and a 20% improvement in energy efficiency.

Moreover, the recently approved European Green Deal [16] boosts the efficient use of resources for a clean and circular economy. In the building sector, this objective simultaneously reduces the life-cycle impact and provides healthy and comfortable spaces [17] by reducing whole-life carbon consumption, increasing reused and recycled content, and offering the sustainable management of construction and demolition waste, leading to what is referred to as circular buildings. This term is used to define a building that is designed, planned, built, operated, maintained, and deconstructed in a manner that is consistent with the principles of a circular economy [17,18]. One of the tools for assessing the circular economy is a life-cycle assessment (LCA).

An LCA is the collection and assessment of the inputs, outputs, and potential environmental impacts of a product during its life cycle. It is a tool used to quantify the material used, energy flows, and environmental impacts of products; it systematically evaluates the impact of each material and process. LCA is a technique for assessing various aspects related to a product’s development and its potential impact throughout its life (i.e., from cradle to grave)—from raw material extraction to processing, production, use, and, ultimately, disposal. The use of LCA facilitates decision-making and the selection of a product or process that has the least impact on the environment [18,19]. Ideas of life-cycle thinking from LCAs are being extended to other pillars, such as the economic pillar (life-cycle costing; LCC), the social pillar (social life-cycle assessment; S-LCA), and sustainability as an entire concept (life-cycle sustainability assessment; LCSA) [19].

An analysis of the environmental impact of the entire life cycle of a building comprises the following stages: construction, operation, maintenance, demolition and dismantling, consumption of energy resources, and production of byproducts (such as CO₂); such an analysis requires special tools. An example of a method for comprehensively measuring resource and energy consumption and environmental byproduct emissions during the life cycle of a building is LCA [20]. LCA is a method for determining the environmental impacts of products or services [21,22,23,24], and it is widely used in various sectors of the economy [25,26,27]. As a result of the application of an LCA, company managers identify areas that are particularly burdensome for the environment or human health [7,8,28,29]. This method is not free from drawbacks, can limit the use of the above-mentioned analysis by some manufacturers. It is a time-consuming and costly technique. The complexity of the analysis and the need for very detailed data on the process under study are also disadvantages [30].

The life cycles of buildings have been studied by various institutions and scientific bodies. LCA has become a tool for supporting the process of designing and modernizing buildings. From the point of view of energy, Lis et al. [31], Hossain and Marsik [32], Moňoková et al. [33], and Srinivasan et al. [34] estimated life-cycle energy use in example buildings (single-family). Abejón et al. [35] and Ylmén et al. [36] analyzed the energy impacts and material resources used (water and other consumable items (paper)) in the operation phase of a building. Asif et al. [37] assessed the use of energy and environmental impacts in the production of five construction materials: wood, aluminum, glass, concrete, and ceramics. Wu et al. [38] analyzed the environmental impacts of different types of concrete and steel used in the construction industry in China. For Polish conditions, there is research on the energy performance of multifamily buildings [39] and the use of gas-powered boilers to heat residential houses in northern Poland [40], as well as the use of hybrid central-heating systems that use REs in southern Poland [41]. Moreover, Adamczyk et al. [42] used the LCA methodology to determine the ecological benefits resulting from thermal insulation and heat-source replacement.

Many LCA studies on buildings consider only their environmental impacts without the LCC or S-LCA of CO₂ emissions. The common goal of LCC studies is to inform stakeholders of the best design options. LCC is a method that summarizes all costs in the life cycle of a product that are directly assumed by one or more participants in the product’s system [43]. The studies usually only investigate the energy-efficiency performance of their designs. Some studies estimated the costs of all life-cycle phases, except for disposal or maintenance costs [44]. In this article, we assess the social costs of the CO₂ emissions of the analyzed buildings.

Relatively fewer studies [45,46] integrated both LCA and LCC in their analyses, but these analyses often concern only some parts of the buildings or materials. There are not many published studies that used LCAs and social costs together to identify optimal variants of energy use in buildings [47,48].

The aim of this work is the environmental and economic assessment of the life cycles of detached, single-family residential buildings for which different energy-supply systems (including renewables) were selected with the aim of identifying the stages in the life cycles of buildings that cause the most CO₂ emissions. The four variants of the energy supply applied to the buildings are among the most popular solutions that are currently used in Poland. Moreover, the aim of this research was to conduct a social life-cycle analysis of the variants (costs of CO₂ emissions). A measurable effect of the LCCO₂ and social cost analyses conducted for different variants of energy supplies in buildings is the determination of equivalent CO₂ emissions per square meter of building area per year of their use.

2. Materials and Methods

2.1. Characteristics of the Buildings’ Construction and the Energy Systems in the Analyzed Variants

Single-family residential buildings with an area of approximately 120 m² and a population of four people were analyzed. These objects were chosen for research because, in Poland, more than 55% of the population lives in such buildings [42]. The buildings were built in the third climatic sphere of Poland, where the average annual temperature is 7.6 °C (Poland’s climatic zones are described in [49]). The distribution of rooms on the ground floor and first floor of the buildings is shown in Figure 1. Information on the facilities and construction materials was taken from the construction design.

The analyzed buildings were free-standing houses with gable roofs. The walls were constructed with YTONG PP2/0.4 cellular concrete blocks (λ = 0.11 W/mK). The roofs were wooden, but were covered with roof tiles. All of the analyzed buildings had 10 cm of polystyrene insulation on the external walls and polyvinyl chloride (PVC) windows and doors. The roofs were insulated with 10 cm of mineral wool, and the roof pitch was 40 degrees. The calculated internal temperature was 20 °C. The buildings did not have a usable attic or garage. The ventilation was natural, without a cooling system. The planned service life of the buildings was 99 years.

2.2. LCCO₂ and Social Cost Assessment of CO₂ Emissions of Variants

In the 21st century, many new computer programs, models, and guidelines have been developed to assess the environmental impacts of buildings. This was described in detail by Anand and Amor [51]. Such software makes it possible to assess the life cycles of existing or planned buildings by using sustainable construction criteria, but there are only a few programs that allow LCA in terms of the social costs of CO₂ emissions. The LCA technique was applied according to the recommendations provided by the ISO 14040 and 14044 standards [52,53].

2.2.1. Goal and Scope of the LCA

The goal of the present research is to compare four variants of energy supply systems (heat and electricity) in buildings with the same structure in terms of the life-cycle CO₂ emissions and the social costs of these emissions. The scope of the LCA framework is defined by the system boundary, which includes the entire life cycle from cradle to grave (Figure 2):

• Extraction and production of raw materials and semi-finished products, as well as their transportation to the places of preparation of the building and construction materials in specific masses and volumes (A1–A3);
• Transportation of materials to the construction site (A4);
• Construction processes (A5);
• Building use, maintenance, replacement, and renovation (e.g., wall coverings, floors, water and sewage equipment, and building equipment), heat, electricity, and water consumption, and sewage production (B1–B7);
• End-of-life management and transportation of waste generated during the demolition of a facility (C1–C4).

The scope of data collected for the environmental analysis included detailed information on the materials (including their weight or volume) that were used for the construction of the houses and the distances from the building depots from which the materials were brought to the construction sites. The construction process and equipment elements were also considered, with particular emphasis on the heating- and electricity-supply options, as well as the water, fuel, and energy consumption. The analysis also assumed that construction waste, such as rubble, concrete, or concrete blocks, was stored after the dismantling of a facility, while wooden and metal elements were recycled.

The studied objects were divided into four variants that differed in terms of the in-stalled energy supply systems (the values given in

Table 1. Energy supply systems used for the analysis.

System Type (Variant)	Type of Energy Supply	Boiler Power Output (kW)	Annual Coal Consumption(kg)	Annual Electricity Consumption 4(kWh)	Annual Electricity Sales to the Grid (kWh)
1	coal + electricity from the grid	20	6008	1932	0
2	coal + solar collectors (area 4 m2) + electricity from the grid	20	3016	1904	0
3	coal + photovoltaic panels (power, 4.46 kWp)	20	1498	0	831
4	heat pump type: air-to-water, 6 kW power) + electricity from the grid	20	0	2860	0

The functional unit enabling comparison of the analyzed variants was 1 m² of the floor area per year.

are the averages of the data calculated per year of the object’s use).

2.2.2. Life-Cycle Inventory and Impact Assessment (LCIA)

This research was based on an analysis of the life cycles of buildings through LCAs (focused on CO₂ emissions) by using OneClickLCA. This software was developed by Bionova Ltd. (Helsinki, Finland), and it complies with the EN 15978 standard. It is a standardized platform for LCC and holistic environmental impact analysis. This software allows for the calculation of the impact of the life cycle by using data obtained from all stages of the building’s life. In its database, OneClickLCA uses the European Product Declaration (EPD) based on the ISO 14044 and EN 15804 standards. The EPD is an externally verified, standardized, and detailed description of the environmental profile of each product. It contains transparent information about the environmental impact of a product throughout its use. The OneClickLCA software also allows for the analysis of the environmental impacts of objects and processes in the fields of global warming, acidification, eutrophication, ozone formation and depletion, and total use of primary energy. In this article, we focused on global warming to indicate the benefits of using RESs in buildings in terms of performance to meet the Polish climatic and energy targets. OneClickLCA provides access to international data on the development of building materials after the demolition of an object and information on the cost of pollutant emissions for various variants of the LCA analysis. The assumptions of the program are based on EUROSTAT data and data from the manufacturers of building materials in order to calculate the carbon footprints of their products. The software was selected due to its availability to authors, ease of use and simplicity of result presentation, which makes it desirable for the general public or practitioners.

The applied LCIA method combines the results of a classical LCA analysis and the results of economic analyses that are specific to future climatic conditions [55,56,57]. The assumptions of the conducted analysis are based on the guidelines of the European framework for sustainable buildings, which is called Level(s). It is a new tool that is used to verify indicators that contribute to achieving EU and national environmental policy goals. A developed standard is not yet fully available in all European countries (including Poland). Level(s) uses sustainability indicators that have been validated by the construction sector and that measure carbon emissions and the impacts of materials on the environment, water, health and comfort, and climate change, including life-cycle cost and value assessments. Building on the objectives of the European Green Deal and the EU’s Circular Economy Action Plan, Level(s) supports the construction sector’s efforts to improve energy and material efficiency, thereby reducing overall carbon dioxide emissions. To apply the EU guidelines, which are aimed at adjusting the standards of construction evaluations, it was decided to use tools that are specific to the analysis of the social costs of environmental exploitation. To assess the total costs of the buildings for society, a calculation was used based on the unit CO₂ emissions per square meter of an object per year at the average annual price of 1000 kg of CO₂ that is applicable in the EU (the cost was assumed to be 50 EUR) [58,59].

3. Results and Discussion

In the first and second phases of the construction process, the building materials with the most significant impacts on the environment are concrete blocks and their production. Their impacts are mainly visible in Stages A1–A3 (raw material extraction and production process), as well as in the supply of raw materials and transportation to the construction site, as a result of which 25,000 kg CO₂ is emitted into the environment from the concrete blocks, and 14,000 kg CO₂ is emitted during concrete production. The reason for these high CO₂ emissions is mainly the production process. CO₂ is the main gas (next to water vapor) generated by the clinker-firing process. This results in the decarbonization of calcium carbonate into calcium oxide. The byproduct is carbon dioxide in amounts of 510 to 610 kg per 1000 kg of cement. Apart from the firing process, CO₂ emissions also result from transportation and electricity consumption during the construction process of a facility [60].

Figure 3 illustrates an environmental assessment of the contributions of individual elements of a building to the CO₂ emissions. The impacts of energy consumption (B6) at the use phase include exhaust emissions due to energy production for the building, as well as the environmental impacts of the production processes of fuel and externally produced energy. Energy transmission losses are also taken into account. Energy consumption definitely dominates and represents 58–90% of the total CO₂ emissions. The raw material acquisition and renovation phases have similar CO₂ factors of less than 20%. Sharma et al. [8] concluded that, as in the present study, the primary energy systems in the operational phase alone contribute more than 50% to greenhouse gas emissions and are the highest energy consumers (80–85%), which is a matter of concern that cannot be ignored.

Depending on the use of coal, grid electricity, or RESs in the analyzed variants, the share of energy changes the structure of the effect of the facility and its life cycle with respect to the environment. The smallest share of energy was observed in Variant 4, in which a heat pump was used to generate heat energy. Secret [61] carried out an analysis of the environmental impact of building heat supply systems by using an LCA methodology. In his analyses, the environmental impacts were similar to the results of the analyses in this work in terms of the so-called environmental damage, i.e., a building’s impact on human health, ecosystems, and resources. On the basis of the conducted analyses, he concluded that the most important role in a building’s heat supply system is played by installations that use heat pumps and waste heat. According to [62], only systems that use recuperation and heat pumps can balance their costs and the environmental impacts of such installations. However, similarly to the analyses in this work, it was found that systems based on coal had by far the most negative impacts on the environment. A comparative environmental analysis of the use of RESs and conventional energy was also conducted by [63]. Their research allowed them to conclude that, in the face of constantly rising prices of conventional fuels (coal, gas, oil), heat pumps—ecological sources of renewable energy—are also a beneficial investment in the long term from a financial point of view.

The largest share of energy in the structure of the environmental effects of the life cycles of the buildings was in Variant 1 (hard coal and grid electricity). With a decreasing share of energy, the share of waste management increases after the demolition of the facility and the performance of repairs and maintenance in the structure of a building’s life cycle.

The impact of energy consumption throughout a building’s life cycle is shown in Figure 4. The energy system in the building that used hard coal and electricity from the grid (Variant 1) was the option with the highest CO₂ emissions, with emissions of 1,760,000 kg CO₂/m²/year, which resulted mainly from the combustion of solid fuel. The results showed that the life-cycle CO₂ savings were in accordance with the reduction in operating energy, which, in turn, was proportional to the passive and active energy savings in the building. This indicates that changes in traditional building energy systems (Variant 1) could reduce energy use in building operations in order to produce low-energy buildings. Reductions can be achieved by increasing the use of energy-saving devices; in Variant 4, fossil-fuel demand could be reduced to zero. A building without fossil-fuel devices requires electricity for its operation.

Such elements of the system as foundations, walls, and ceilings in each variant were characterized by similar environmental impacts (the objects were not significantly different). Differences in terms of the environmental effects appeared in the scope of building equipment (which resulted from the installed energy systems) and in terms of fuel and energy consumption. The embodied energy of Variant 4 was greater than the highest energy usage of the other variants. This limit varied depending on the type and mix of active and passive energy systems installed in the building, climatic conditions, and the construction materials used. The results proved to be the most sensitive (an effect of over 50% in the results) to changes in electricity consumption.

The energy system using photovoltaic panels and hard coal (Variant 3) did not show CO₂ emissions due to grid electricity consumption (Figure 3). The environmental effect for the electricity category, in this case, was zero because surplus energy was fed into the grid. When using an energy system consisting of a heat pump and electricity from the grid (Variant 4), users do not need to use hard coal at all to heat the building. This system emits only 358,000 kg of CO₂ (

Table 2. Carbon dioxide emissions.

System Type (Variant)	Total Carbon Dioxide Equivalent Emissions	Total Carbon Dioxide Equivalent Emissions Divided by Assessment Period and Gross Inland Floor Area	Cost of CO2 Emissions
	1000 kg CO2	kg CO2/m2/Year	EUR
1	2093	176	104,661
2	1643	138	82,168
3	590	50	29,487
4	358	30	17,917

), which is six times more than that of the system of coal and electricity from the grid (Variant 1).

Mendecka et al. [63], who carried out an analysis of the environmental effects of the substitution of nonrenewable fuel (reference fuel) with selected renewable energy sources, used the concept of an indicator of efficiency and thermoecological cost and concluded that, in environmental terms, renewable energy sources show positive effects that are directly due to lower environmental pollution and exergy consumption compared to nonrenewable sources. In this work, the cost related to CO₂ emissions was also proved to be lower by up to 83% when using RES substitutions for coal and electricity from the grid. An interesting analysis would be the environmental assessment of the life cycle of a building equipped with a heat pump and photovoltaic panels, but due to financial reasons, the number of such buildings in Poland is small. However, there is a Polish subsidy system that is implemented on the local (municipalities) and central government levels for replacing boilers with ecological ones [42].

In their work, Sandanayake et al. [64] described the results of greenhouse gas emissions from buildings located in Australia. A comparison of carbon oxide emissions shows that their results were similar to the results presented here, but in Poland, lower CO₂ emissions could be observed during the foundation stage. The comparison of obtained results also shows the different legal approaches to greenhouse gas emissions in different countries. The calculations show that for the same construction materials, the differences in CO₂ emission factors could be in the range of a few percentage points. A direct comparison of the results obtained with those of Mao et al. [65] shows comparable results for CO₂ emissions during the building of an object and its exploitation. In their work, the authors also present emission values for objects constructed from semi-prefabricated materials. This showed that the assumptions used for the LCCO₂ calculation were made correctly and that the CO₂ emissions for typical construction materials were comparable in Poland and China. The same conclusions were presented by Hong et al. [66]. In their work, the most important CO₂ emissions were those calculated for grid electricity consumption. In the present study, the authors also obtained the highest LCCO₂ values for grid electricity usage in Variants 1 and 2 (Table 2). In Variant 3, a very high energy consumption (73.06% of total CO₂ emissions) was also present, but in this object, the authors used energy that was produced from photovoltaic panels for the calculations.

Weerasinghe et al. [67] described an LCC analysis of traditional and ecological objects built in Sri Lanka. Their analysis found that ecological buildings can save from 17 to 30% of costs, depending on the operation method. The present calculations also show that the usage of renewable energy sources for energy production can reduce standard exploitation costs by up to 80% (Variant 4). This proposition is very important for citizens with respect to the EU Green Deal Directive, and it confirms the results described by Ji et al. [68], Lu et al. [69], and Nematchoua et al. [70].

4. Conclusions

Analyzing buildings using an LCA is one of its most complex applications. In this research, an LCA was used for an environmental analysis of single-family residential buildings with four options for thermal and electrical power supplies (inter alia, using RESs), which showed that:

• The building that used a heat pump had the lowest CO₂ emissions; the emissions of a system based on coal and electricity from the grid were almost six times higher.
• The element of the life cycle that had the greatest impact on the environment was the stage of facility operation, depending on the variant, and the share of electricity consumption in the environmental impact was between 58% and 90%.

In Poland, the cheapest heat sources are coal-fired boilers. The choice of the type of energy source used to heat a building and to supply electricity is most often aimed at reducing operating costs. The largest problem is the lack of access to gas pipelines in the whole territory of Poland (which is why gas energy was not used in our research). On the other hand, this is a chance for the implementation of new RES solutions, which will have the fewest negative impacts on the environment (in terms of CO₂ emissions).

The calculations of CO₂ emissions presented here are very innovative for Poland. The authors presented the possibilities of using different life-cycle sustainability assessments, such as life-cycle assessment (environmental), life-cycle costing (LCC; economic), and social life-cycle assessment (SLCA; social). These results show the cost of carbon dioxide emissions as a universal factor of global warming and as the social cost of environmental exploitation. The implications of the results obtained here may apply to many governments’ agendas and architectural planners, as well as those who are responsible for the sustainable development of the world.

The presented results of the analysis of the case study on Single-family residential buildings showed the significant importance of the impact of various energy production methods on heating purposes. The research also confirmed the advisability of limiting the anthropogenic impact on the environment, necessary to meet the global goals of sustainable development. Changing the traditional energy supply system to RES is beneficial during operation and the associated environmental impact. Further research in the field of the energy transformation of buildings using LCA methods should aim at creating databases in the field of energy characteristics of energy sources. The refinement of the existing LCA analyses can also be used to create new guidelines and recommendations for the use of RES in residential buildings. An additional effect of future works will be the determination of the scope of individual components of the SLCA balance in Central European countries. The developed guidelines may be useful for determining the boundary conditions of LCA analyses, improving and reducing the sensitivity of the analysis to the omission of energy components during the operation of the building, and being an indication of limitations and benefits resulting from the wide use of renewable energy sources as the optimal combination of renewable energy sources for different types of buildings and regions. Further directions for the use of the presented calculations may include the supplementation of the lack of data in the case of using LCAs for complex multi-material systems, such as those described by, e.g., Goh and Sun [71], Heralova [72], and Ilg et al. [73].