Analysis of Useful Energy Demand for Heating Purposes in a Building with a Self-Supporting Polystyrene Structure in a Temperate Climate

Abstract

This article presents an analysis of the useful energy demand for heating purposes in a single-family, single-storey building with a self-supporting polystyrene structure, which is a relatively niche solution, in relation to a traditional masonry structure with similar partition thickness. The structures considered met the requirements for passive buildings. The analysis was performed on three locations in Europe with a temperate climate, i.e., Kołobrzeg in Poland, Vienna in Austria, and Essen in Germany. The research showed significant savings in the energy demand of the polystyrene structure compared to the masonry structure for each location, ranging from 38% to 52%. Similarly, the heating period was 21% to 38% shorter in individual locations. This shows that polystyrene construction allows for a significant reduction in building energy demand, leading to lower operating costs.

1. Introduction

The construction industry is facing a series of challenges, with the primary concern being the reduction in energy demand in response to increasing energy costs. According to the IEA (International Energy Agency), the construction sector is responsible for 30% of global energy consumption [1]. The observed increase in energy prices is associated with economic development, a process that requires substantial energy consumption, as well as with the ongoing energy transition, characterized by a gradual shift away from fossil fuels, whose reserves are constantly diminishing. Consequently, it is necessary to implement solutions that will reduce energy demand across a variety of sectors, including construction. The present age is witnessing an intensive effort to identify novel technologies and materials that exhibit high energy efficiency, a development that is of supreme importance to the field of construction.

Energy-efficient construction focuses on minimizing energy consumption through the implementation of various strategies. These include the utilization of partitions that restrict heat losses, the employment of materials with superior thermal insulation properties, and the incorporation of active systems such as mechanical ventilation with heat recovery. The efficacy of these systems in reducing ventilation loss is substantial. The implementation of renewable energy systems is a common practice in such contexts. An example of energy-efficient construction is the so-called passive house (PH) developed by the Passive House Institute in Darmstadt. The foundation of this approach is rooted in five fundamental principles: high-quality insulation of partitions with a heat transfer coefficient (U-value) below 0.15 W/(m²K), windows with a heat transfer coefficient of less than 0.8 W/(m²K), ventilation with heat recovery values greater than 75%, a building’s air tightness being no greater than 0.6 air changes per hour, and the elimination of thermal bridges [2]. A comprehensive review of the principles and technologies employed in passive construction is provided in [3], while studies delineating energy consumption in this category of buildings are presented in [4,5,6,7].

It is evident that thermal insulation of partitions constitutes a key element in the design and construction of low-energy buildings. An analysis of the insulation properties of inorganic materials, such as concrete and brick, and organic materials, such as wood and straw, is presented in [8]. The available technologies easily enable the achievement of the required heat transfer coefficient values, as stipulated by the passive building standard, in the context of residential construction. Masonry structures, when employed in conjunction with the optimal insulation thickness, have been demonstrated to meet stringent requirements. Analyses of such a structure can be found in [9,10]. However, due to the total thickness of the partition, it may be necessary to abandon ceramic or silicate materials in favor of aerated concrete, which has better insulating properties, or to use insulating materials that have higher parameters yet are more expensive. In the context of single-family houses characterized by elevated energy standards, it is more common to find frame structures that allow for better insulation parameters with a smaller partition thickness, due to the fact that the thermal insulation fills the structural element of the partition. The insulation properties of various types of frame partitions are described in the article by J. Kosny et al. [11]. This research indicates that such structures can achieve U values in the range of 0.30–0.11 W/(m²K). A comprehensive review of the latest technological advancements in wooden partition wall systems, with a focus on enhancing energy efficiency, is presented in [12]. Research on passive buildings with different structures is presented in [13,14,15].

Another technology that can be used in the construction of low-energy buildings is Insulated Concrete Forms (ICFs), where polystyrene forms serve both as an insulating layer and as a framework for the reinforced concrete layer, which is the load-bearing element of the structure. Such structures are distinguished by their enhanced thermal capacity in comparison to frame structures. Research on insulated concrete form (ICF) partitions in two variants—with solid concrete filling and with a frame structure, as described in publication [16]—demonstrated a minor difference with regard to thermal insulation properties. At the same time, the superior capacity of solid partitions to stabilize internal conditions was highlighted. An analysis of the use of this type of wall for energy storage is presented in [17,18], while the use of ICF foundations for energy storage is described in [19]. An analysis of different types of ICF partition cores and their impact on energy consumption reduction and strength is described in [20].

Another significant aspect pertains to the comparison of diverse technologies for the construction of energy-efficient buildings. In [21], a multi-criteria comparison of technologies was carried out. As demonstrated in [22], a comparison of energy consumption in ICF and timber frame buildings reveals that ICF buildings exhibit a reduced energy demand. However, it is imperative to note that the utilization of materials characterized by specific thermal parameters exerts a substantial influence on this outcome. In turn, Ref. [15] underscores the significance of environmental impacts in addition to the insulation parameters of a given technology. A comprehensive comparison of timber and concrete technologies, with consideration for the building lifecycle, is presented in [23].

Another type of construction that can use polystyrene in partition design is a Structural Insulated Panel (SIP) system. A comprehensive overview of this technology is provided in [24], while its utilization in the construction of nZEB (nearly zero energy building) and buildings of PH standard is elaborated in [25].

The technologies described above enable the construction of buildings that are highly energy-efficient. However, there is a clear gap in research on the subject of self-supporting polystyrene structures. Despite the growing interest in technologies that improve energy efficiency of buildings through the use of new materials or alternative uses of existing materials, there is currently a lack of systematic analyses of the energy requirements of this niche structure. Hence, the authors proposed to conduct such analyses in order to initiate a broader discussion covering other aspects related to microclimate, comfort, and durability prospectively. The ultimate aim of this discussion is to highlight the possibilities and limitations of polystyrene structures.

Contemporary analyses of the energy demand of buildings are based on various computer tools that have been validated to enable effective simulations of heat and moisture transport in both building envelopes and entire buildings. One such software product is WUFI^®Plus 3.5, developed by the Fraunhofer Institute for Building Physics [26]. The tool’s validation is documented in the following publications: [27,28,29]. The WUFI^®Plus tool has been employed in a variety of residential, agricultural and historical building types [30,31,32,33,34].

2. Materials and Methods

2.1. Research Object

The aim of the research is to analyze useful energy demand for heating in a single-family, single-storey building with a polystyrene structure, which is a relatively niche construction solution. The building’s partitioning is composed of self-supporting blocks of compressed polystyrene, which adopt an arch shape, seamlessly integrating with the external walls and the roof surface. The constituent modules are interconnected, as illustrated in Figure 1. This cross-section is notable for the absence of a wooden or steel frame, a feature common to frame structures, and the lack of a concrete layer, which is characteristic of ICF technology. Consequently, the polystyrene foam functions both as a structural and insulating layer. This innovative solution facilitates the comprehensive utilization of the partition cross-section for the purpose of enhancing the thermal insulation of the building. It also eliminates the occurrence of thermal bridges, which are characteristic of other structural types, due to the seamless integration of external walls with the roof slope.

In the technology under discussion, masonry structures are utilized exclusively in the construction of gable walls, with the primary function of these walls being to enhance the structural integrity and rigidity of the building as a whole. Furthermore, masonry walls have been shown to possess an accumulative function, thereby buffering thermal energy within themselves. This property stands in contrast to that of polystyrene walls, which have been demonstrated to possess low thermal capacity. As a result, such a structure is being considered a hybrid structure. The diagram is shown in the graphic (Figure 2).

The polystyrene partitions of the building are reinforced on both sides with fiberglass mesh. Aluminum profiles are utilized internally for the purpose of securing plasterboard panels. Externally, the roof surface is reinforced with waterproof plywood strips to support the installation of steel sheet roofing. The building is founded on a conventional foundation slab, where a layer of lean concrete is initially applied, followed by a layer of thermal insulation composed of compacted polystyrene, construction foil, and subsequently, a reinforced concrete slab and a leveling layer are poured. The entire building is founded on this prepared base Figure 3. Due to its construction, the floor on the ground performs an accumulation function, similar to the gable walls. The construction of the building on a foundation slab insulated from below and the continuity of insulation serve to eliminate the formation of typical thermal bridges at partition joints.

2.2. Assumptions for Calculations

The calculations are based on a generic single-storey detached house with a usable area of 106 m² (Figure 4). The floor plan of the building (Figure 5) is based on the letter ‘L’. The total dimensions of the building are 12.96 m × 12.96 m, and its height is 4.5 m. The net volume of the building is 177 m³. The total window area measures 21.61 m². The roof pitch measures 27°. The building partitions and window frames included in the analysis meet the requirements for passive buildings; i.e., the heat transfer coefficient for walls is U < 0.15 W/m²K, and that for windows is U < 0.8 W/m²K.

The calculations of the useful energy demand for heating purposes were performed using the WUFI^®Plus 3.5 calculation platform based on a coupled heat and moisture exchange model for non-stationary building analyses. The simulations were conducted on an annual basis, with a 1-h time step. In order to facilitate the process of simulation and comparison with traditional masonry partition walls, the arched shape of the partitions was simplified to a flat form. The thickness of the polystyrene structure ranges from 0.30 to 0.85 m, and thus its cross-section was divided into a total of 180 segments. The mean thickness of the polystyrene cross-section employed for subsequent calculations was determined to be 0.48 m. A schematic representation of the simplified arched cross-section is presented in Figure 6. Simulations frequently require simplification of the building geometry due to limitations of the calculation tool or the requirement to combine different structures. It has been demonstrated that this may result in disparities in the outcomes when compared to the original geometry. Consequently, prior to conducting additional simulations, it is imperative to estimate the potential impact of the simplifications employed on the calculations. In this analysis, the arched polystyrene wall was simplified to a flat form, characteristic of most buildings. The non-uniform thickness of the material may result in the formation of local thermal bridges in cross-section constructions when compared to the average variant. In order to estimate potential discrepancies in the relevant simulations, both variants were analyzed. It was demonstrated that the simplification of the cross-section generates an error of 2.45%, thereby limiting heat exchange in comparison to the original partition. This low discrepancy confirmed the high consistency between the analyzed cross-sections and allowed for effective simulations to be carried out.

The analysis incorporated a total of six calculation variants. A comparative study was conducted for two structures: polystyrene and masonry structure. The study was conducted for three locations characterized by a temperate climate.

In order to compare the construction variants analyzed, the thickness of the external walls and roof slopes was set at 0.5 m. The layers of individual partitions are presented in the tables below. The layer arrangement for the polystyrene wall is shown in

Table 1. Polystyrene wall—layers.

Layers	Thickness [m]	Thermal Conductivity [W/m·K]
Plasterboard	0.0125	0.2
Fibreglass mesh	0.0005	0.035
Compacted polystyrene	0.48	0.036
Fibreglass mesh	0.0005	0.035
External plaster	0.01	0.87

, while the heat transfer coefficient U for this structure is 0.073 W/m²K. The layers of the masonry structure are shown in

Table 2. Masonry wall—layers.

Layers	Thickness [m]	Thermal Conductivity [W/m·K]
Interior plaster	0.01	0.2
Aerated concrete	0.25	0.14
Compacted polystyrene	0.23	0.036
External plaster	0.01	0.87

, and the heat transfer coefficient was 0.12 W/m²K.

With regards to roof construction, the layer arrangement for a polystyrene building is presented in

Table 3. Roof of polystyrene structure—layers.

Layers	Thickness [m]	Thermal Conductivity [W/m·K]
Sheet metal	0.0005	60
Fibreglass mesh	0.001	0.035
Compacted polystyrene	0.48	0.036
Fibreglass mesh	0.001	0.035
Plasterboard	0.0125	0.2

, where the thermal conductivity coefficient U was 0.074 W/m²K. In the case of the masonry structure, a rafter roof construction was adopted (

Table 4. Rafter roof structure—layers.

Layers	Thickness [m]	Thermal Conductivity [W/m·K]
Sheet metal	0.0005	60
Air layer	0.12	0.035
Vapour barrier foil	0.001	2.3
Mineral wool/rafter	0.16	0.036
Mineral wool	0.2	0.036
Vapour barrier foil	0.001	2.3
Plasterboard	0.0125	0.2

), where U was 0.095 W/m²K.

The foundation slab on which the building was constructed was the same for both structures. The layers are delineated in

Table 5. Foundation slab—layers.

Layers	Thickness [m]	Thermal Conductivity [W/m·K]
Concrete screed	0.0005	1.6
Reinforced concrete slab	0.2	1.6
Compacted polystyrene	0.4	0.036
Construction film	0.0001	2.3
Lean concrete	0.1	1.6

, and the heat transfer coefficient U for this partition was determined to be 0.087 W/m²K.

2.3. Indoor Climate

In the course of the simulations, the internal temperature was assumed to be 20 °C. This value denotes the minimum temperature for rooms. Once exceeded, the instantaneous demand necessary to achieve the above-mentioned value within a given time step is calculated. It was further hypothesized that the building is inhabited by a family of four. On this basis, a scenario of internal heat gains was adopted according to the WUFI^®Plus database for a typical weekday for a family (two adults + two children) including gains from people and appliances. The daily pattern that has been assumed in the calculations is demonstrated in Figure 7. Furthermore, solar radiation gains are calculated on an hourly basis. This calculation is based on the shading of partitions, which takes into account climate data. The ventilation flow in the building was assumed in the calculations at a level of 1 air change per hour.

2.4. Outdoor Climate

The calculations were performed for a period of one year in three locations with a temperate climate: Kołobrzeg in Poland, Vienna in Austria and Essen in Germany. The assumed locations are illustrated in Figure 8. The climate data employed in the simulations is drawn from the WUFI^® Plus database, comprising long-term data that has undergone statistical processing. This data set has been used to derive a reference year for each location, thereby ensuring the consistency and reliability of the data.

2.5. Kołobrzeg

The climate of Kołobrzeg is classified as temperate maritime. The range of temperatures is from −9.8 to 29.7 °C, with an average temperature of 8.6 °C, which is also the lowest among the locations analyzed. The mean relative humidity is 81.3%. The total radiation is 2253.2 kWh/m²a. The annual precipitation is 560.9 mm/a and the prevailing winds are south-westerly winds, with an average speed of 2.3 m/s. The fundamental climate parameters are illustrated in Figure 9 and Figure 10.

2.6. Vienna

The climate of Vienna is characterized as temperate transitional with continental influences. The annual temperature range extends from −10.9 to 32.4 °C, with an average temperature of 10.4 °C, representing the highest of the locations analyzed. The mean relative humidity is 73.0%. The total radiation is 2317.2 kWh/m²a. The annual precipitation is 625.1 mm/a. Vienna is subject to westerly and south-easterly winds, with an average speed of 3.6 m/s. The fundamental climate parameters for Vienna are illustrated in Figure 11 and Figure 12.

2.7. Essen

The climate in Essen is described as temperate. The annual temperature range is from −9.7 to 30.2 °C, with an average temperature of 9.5 °C. The mean relative humidity is 78.1%. The total radiation is 2434 kWh/m²a. The annual precipitation is 1094.6 mm. Essen is subject to westerly and south-westerly winds, with an average speed of 2.74 m/s. The fundamental climate parameters for Essen are demonstrated in Figure 13 and Figure 14.

3. Results

3.1. Energy Demand—Kołobrzeg

In the first of the analyzed locations, the annual energy demand for heating in the polystyrene building was 1173.7 kWh, while in the masonry structure, the demand was 1851.1 kWh. Hourly data for heating power is presented in Figure 15.

The heating season in Kołobrzeg was found to be the longest among the locations analyzed. For the polystyrene structure, the mean duration of heating season was 128 days, and for the masonry structure, it was 169 days. The heating season values presented for Kołobrzeg were calculated based on the hourly energy demand when the temperature inside the building falls below the set limit of 20 °C. It was determined that, in the event of inadequate energy from external sources and internal heat gains, the heating system should be activated in order to supply the building with the requisite heat flow to achieve the set temperature. This approach was replicated in the case of the other locations. Figure 16 illustrates a monthly summary of the useful energy demand for heating purposes for both structures.

3.2. Energy Demand—Vienna

In the second location analyzed, Vienna, the annual energy demand for heating in the polystyrene building was 803.3 kWh, while in the masonry structure it was 1681.1 kWh. Hourly data for heating power is presented in Figure 17.

For Vienna, the heating season lasted 117 days for the polystyrene construction and 149 days for the masonry construction. Figure 18 illustrates the monthly summaries for both constructions.

3.3. Energy Demand—Essen

In the third location analyzed, in Essen, the annual energy demand for heating in the polystyrene building was 854.9 kWh, while in the masonry structure the demand was 1622.3 kWh. Figure 19 illustrates hourly data for heating power.

In Essen, the heating season for the polystyrene structure lasted 103 days, whereas for the masonry structure it lasted 166 days. Figure 20 illustrates a monthly summary for both structures.

4. Discussion

The study compared the annual energy demand for heating for two types of buildings meeting passive building standards: polystyrene and masonry, in three locations with a temperate climate: Kołobrzeg in Poland, Vienna in Austria and Essen in Germany. The two structures possessed comparable thicknesses in their external walls and roof surfaces. Both the floor on the ground and the window and door frames exhibited identical characteristics. The polystyrene structure was found to exhibit a substantially lower energy demand across all calculation variants. The most significant disparity in energy consumption was observed in Vienna, with a recorded difference of 878 kWh per year, representing a 52% saving in energy consumption. In Essen, the discrepancy was 767 kWh, which corresponds to a 47% variance. The lowest recorded difference was observed in Kołobrzeg, with a total of 683 kWh, representing an energy saving of 37%.

With regard to the duration of the heating season, the highest advantage of polystyrene construction was observed in Essen. In this case, the heating season was shorter by 63 days, which represents a 38% reduction compared to masonry construction. In Kołobrzeg, the season was shorter by 41 days, which corresponds to a 24% difference. The discrepancy in the length of the heating season was smallest in Vienna, where the recorded value was less than 32 days, representing a 21% difference.

The disparity in useful energy demand in the studied structures is predominantly ascribed to the marked difference in their heat transfer coefficient: with polystyrene insulation exhibiting a coefficient of 0.073 W/m²K, in comparison to masonry coefficient of 0.12 W/m²K. This represents a 31.2% difference.

Another factor that significantly affects energy efficiency and differences in useful energy demand is thermal capacity of the building. In the case of low thermal mass of a building, full utilisation of heat gains is not possible. This is a characteristic feature of lightweight structures. In order to confirm this, additional calculations were made for one of the locations (Essen). In the simulation of energy demand for a polystyrene structure, the reinforced concrete slab and thermal insulation of the floor on the ground were switched. As a result, thermal mass of the concrete slab was excluded outside the building’s insulation shell. Consequently, the annual energy demand of the building grew from 854.9 kWh to 918 kWh, representing an increase of 6.9%. Analogous calculations were conducted for the masonry version. In this case, upon excluding the reinforced concrete slab situated outside the thermal envelope of the building, the energy demand exhibited a comparatively minor increase, from 1622 kWh to 1659 kWh, representing an increment of 2.2%. The lower increase in energy demand can be attributed to the fact that the reinforced concrete slab, excluded from the insulation, constitutes a smaller proportion of the total storage mass of the masonry building.

Well-insulated buildings with a lightweight structure and low mass are characterised by rapid thermal response, in contrast to heavy masonry structures, which in turn enable effective suppression of short-term temperature fluctuations and better storage of heat gains. The polystyrene structure analysed can be regarded as a hybrid solution, combining the advantages of both light and heavy structures. The employment of lightweight external walls and roofing materials has been demonstrated to facilitate superior thermal insulation properties. In contrast, the integration of brick gable walls and a reinforced concrete floor, insulated from below, has been shown to enable enhanced temperature stabilisation when compared to conventional lightweight structures.

Such a solution allows for increased utilisation of internal gains and solar radiation gains. As a result, the energy demand for heating the building is reduced. Therefore, it is believed that the savings generated in the building in question, compared to the masonry structure, result mainly from the insulation parameters of the polystyrene partitions and the possibility of heat buffering in the building’s capacitive elements.

The simplification of the polystyrene wall cross-section used in the simulations resulted in a 2.45% reduction in heat exchange in this element. For a more accurate analysis, it is necessary to conduct experimental tests to validate and refine the calculation model.

The findings of the analyses evidently demonstrate a substantial discrepancy in energy demand between polystyrene and masonry structures, while the equivalent thickness of the analyzed partitions is maintained. The polystyrene structure is composed predominantly of insulating material, which also functions as a load-bearing element. In contrast, the secondary structure incorporates a load-bearing layer characterized by reduced thermal parameters. A similar situation will occur when we compare, for example, frame structures with masonry structures or even ICF structures with similar partition thicknesses. A review of construction practice indicates that there are a number of objective reasons why the thickness of external partitions or the thermal insulation layer itself is limited. These limitations are the result of technical, aesthetic and economic considerations. This is confirmed, among others, by publication [35], where the use of thermal insulation above 0.24 m on a masonry wall made of aerated concrete is rarely economically justified. Similar conclusions can be drawn from article [36], where a layer of 0.18 m to 0.24 m is indicated as the optimal thermal insulation layer for a masonry structure. Therefore, further increasing the thickness of the partitions is not justified. Hence the attempts at using increasingly better materials or optimizing of the structure of the partitions themselves by making full use of their cross-sections. This is exemplified by the analyzed polystyrene structure. The structure described creates a specific margin, limiting the energy demand compared to a masonry structure, which may allow for greater freedom in the selection of a heat source and internal installations. This leads to measurable savings related to the operation of the building. Therefore, further research on this type of structure is important in order to learn about other aspects such as such as detailed microclimate analysis and the thermal comfort of residents, which the authors intend to undertake in the future. Nevertheless, further studies are required in the domain of structural strength, fire resistance and sound insulation. This approach will facilitate an objective evaluation of the technology’s potential and constraints.

5. Conclusions

The analyses conducted clearly demonstrated that, while maintaining a comparable thickness of external partitions, the polystyrene structure exhibits a substantially diminished annual energy demand for heating in comparison to masonry structures across all studied locations with a temperate climate. The key factor contributing to this advantage is the significantly lower heat transfer coefficient and the favourable combination of light and heavy construction properties, allowing both heat loss to be reduced and internal gains and solar radiation gains to be used effectively. Conventional increases in insulation thickness in masonry structures are limited by technological, economic and functional considerations, reinforcing the rationale for seeking alternative material and structural solutions. The polystyrene structure analysed may provide a solution to these challenges, offering significant potential for reducing energy demand. In view of the findings, further research is required. This should include experimental measurements in real conditions. Such measurements will allow the calculation model to be validated. They will also allow the analysis to be extended to include aspects such as internal microclimate and thermal comfort of users. A comprehensive verification of these and other parameters is an essential step towards a complete and objective assessment of the applicability of polystyrene structures in modern buildings with high energy standards.