Energy-Active Shadow Structures in Single-Family Buildings – Application Possibilities and Architectural Conditions

A building is a basic artifact – a utilitarian object that is necessary to satisfy human needs. Providing a comfortable environment inside a building, in an energy-efficient manner, determines its efficient and economical use in aspects of meeting the criteria of health, productivity and leisure. A building that allows maximizing the efficiency of users’ activities and efficient management of energy resources with minimal operating costs is an intelligent building – the definition of the European Intelligent Building Group [16]. To meet these requirements, in the design solutions of temperature stabilization systems, renewable energy sources – RES – and hybrid systems are used, ensuring operational safety while using additional, conventional, but primarily pro-ecological technologies [17]. A building should be treated as a multiparameter and control flow object, operating in variable climate conditions, which exchanges energy, substances and information with its surroundings – Fig. 1 [18]. Changing trajectory of energy development makes it necessary to move from fossil fuels and energy systems and government-corporate energy policy to an economy characterized by efficiency, widespread use of renewable energy sources, smart infrastructure, as well as independent investors and prosumerism. Prosumerism in the energy industry is the consumer's fulfilment of the dual role of a producer and a consumer of electricity. In [19], technical and energy aspects of the application of micro photovoltaic installations in single-family buildings are presented. This increases energy independence, both locally and globally, affects the optimization of demand and generation volume, and reduces losses in electricity transmission [20]. The development of prosumer power supply fosters sustainable energy-environmental development and is the most effective way to achieve the objectives of the European Green Deal policy and the Fit for 55 package, increasing energy efficiency, an increase of renewable energy share and reduction of carbon dioxide emissions, respectively. The use of RES for heating purposes almost always involves the use of electricity. There are over 5 million single-family houses in Poland, and about 80,000 new ones are put into use every year. The Exploitation of buildings influences very significantly their share in general energy consumption and the natural environment. Improved quality of life, manifested by the increase of the area and standard of furnishing of apartments, office and commercial buildings, as well as by the possibility of obtaining optimal microclimate in rooms, results in significant energy consumption. In energy-efficient construction, it is necessary to strictly observe the principle that energy savings cannot deteriorate the quality of the indoor environment [21]. In the design of low-energy building structures, which are the basis of sustainable development, it is necessary to take into consideration the predicted climate change, i.e. the increase in global temperature, preferably for the climate parameters of Design Summer Year. There are four basic principles of low-energy-intensive sustainable development: switching off, spreading out, blowing away and cooling [22]. The presented principles are proposed to be complemented by two additional methods – inscribed in the mentioned principles, i.e. the first one: emphasizing the use of renewable energy sources in heating, ventilation and air conditioning systems, ensuring the optimal use of local resources for building heating, and the second one: active shadow, which supports cooling, with electricity generation – Fig. 2. In the annual heat balance of a residential and commercial building, it can be assumed, as in a residential building [18], that the whole heated space of the building is one temperature zone, in which the temperature of the internal air is constant and is T_i = 20°C. Active shadow structures capture the essence of the statement “the shadow should turn off the sun” [9], enriching its content with energy efficiency, resulting both from the possibility of reducing the indoor air temperature in the building T_iB and from the reduction of electricity consumption.

Figure 1.

Figure 2.

One of the methods to minimize the energy consumption for heating is the optimal use of a passive solar heating system, expressed by the dimensionless factor of useful solar heat gain for space heating SHF, combined with the use of programming and temperature stabilization systems. In the design phase of a building, it is very important to optimize its dimensions and shape, defined by the ratio of the building area A to its volume V, directly affecting heat loss by infiltration into the environment [18]. In the postulated change of the energy development paradigm, technological innovations – pro-efficiency application of RES and intelligent infrastructure [20, 23] are listed in the first place. As a result of the implemented comprehensive measures of rationalization and increase of efficiency, the annual growth of energy consumption is systematically slowing down, and by the year 2040, it is estimated that it will decrease to approximately 1% per year. More than 90% of global electricity demand is consumed in buildings and industry, and only about 2% in transport [24].

Global electricity demand is projected to grow by 2.1% per year through 2040, twice as fast as primary energy. The share of electricity in total final energy consumption is estimated to increase to 24% in 2040. The Sustainable Development Scenario assumes that the share of electricity in final energy consumption will be 31%. At the same time, the EU package “Ready for 55” increases the share of renewable energy use from 32% to 40%, implementing the program to reduce greenhouse emissions by 55% in 2030 [25]. Renewable energy sources are assumed to provide two-thirds of the world's electricity supply by 2040, that is: solar photovoltaic and wind together about 40%, plus 25% from other renewable sources, including hydropower and bioenergy – biomass and biogas. It is expected that in 2040 the share of cooling in buildings, will reach 17% [24, 25]. In 2019, the share of the residential sector accounted for 26.3% of final energy consumption in EU-28 countries. In 2040, as a result of energy efficiency improvements and an assumed slow increase in the number of apartments, it is planned to reduce the share of households in final energy consumption to 18% [26]. The structure of final energy consumption in the residential sector is: natural gas – 2.13%, electricity – 24.7%, renewable energy sources – 19.5%, oil and petroleum products – 11.6%, delivered heat – 8.7% and solid fuels – 3.4% [27]. Table 1 shows a comparison of final energy consumption in the residential sector in the EU-28 countries and in Poland according to its purpose in 2019 [27].

The analysis of the data presented shows that in Poland and the EU-28, the shares in final energy consumption are similar, with bigger differences in lighting and cooking. Space cooling in Poland in the residential sector until 2019 was relatively insignificant and is not included in Table 1. Table 2 shows the shares of carriers in energy consumption in residential heating in the EU-28 and in Poland in 2019. In Poland, the shares of energy carriers in space heating are essentially different from the average shares in the EU-28 countries, only with regard to the share of renewable energy sources the values differ only by 26.9%.

The analysis of the data in Table 2 shows that in the EU, the main changes were a 5% decrease in the share of gaseous fuel (natural gas) with a 4.5% increase in RES and waste. In relation to Poland, the main differences in energy consumption data – Table 2, included a 4.4% decrease in the share of solid fuel, a 2.4% increase in RES and waste, and a 1.6% increase in gaseous fuel.

Consumption of fuels, especially solid ones, directly affects the condition of the external air quality, which is most often defined by the CAQI index. It is particularly important in Poland, where about 12 million Mg of hard coal is consumed for heating purposes, which together with the emission of pollutants from means of transport accounts for the last place in Europe in the ranking of air cleanliness in relation to concentrations of PM2.5 and PM10. The number of households in Poland is about 6.4% of EU households, with the average number of people per household in Poland being higher, i.e. 2.8, compared to the EU average of 2.3. The energy efficiency index in Poland is 76%, about 5% lower than the EU average of 81%. The emission of carbon dioxide in Poland per household is 2.47 Mg/year, which is 25% higher than the EU average, due to the high share of fossil fuels [28]. Almost 80% of dwellings in Poland are equipped with a central heating system, with the EU average being almost 85% [29]. In Poland, more than 80% of primary energy is consumed in households for space and water heating [30]. Table 3 shows the shares of energy carriers in central heating and hot water installations in single-family buildings [32]. According to the forecasts of the Polish National Energy Conservation Agency, the demand for district heat in Poland is expected to grow until 2025, and then it will start to decrease. Reversal of the trend will be the effect of introduced revitalization programs, thermal modernization and adopted normative rules concerning the construction, especially concerning the partitions – external walls and windows, in new energy-saving buildings.

Equipping residential homes with air conditioning units results in the optimization of indoor environmental quality (IAQ) and largely promotes independence from climatic conditions. It also contributes to the architectural versatility of house designs, which can be implemented in different locations. In many countries of the world, there is a dynamic development in the use of air conditioning. For example, in the USA in 1938 the share of air conditioning in residential buildings was 2.5‰, and in 2019 – already nearly 90% [33]. In 2018, more than 1.6 billion air conditioning units were installed in buildings worldwide [34]. It is estimated that, depending on climatic conditions, between 30 and 50% of the world's electricity production is consumed for air conditioning and refrigeration purposes. According to the 2018 Global Alliance for Buildings and Construction, energy consumption for “space cooling” has already increased by 25% since 2010.

An analysis of the projected 2K increase in Earth's temperature, shows that this will cause, for example:

decrease in heating degree days from 3988 to 3396, i.e. a decrease of 592 HDD will occur,

Thus, although the number of degree-days will decrease by 232 and the demand for heating will be reduced by about 17%, the demand for cooling will increase by about 40%, which results from differences in average efficiency of heat generation η_ogrz =0 ÷ 50.85 (depending on the fuel used) and of cooling generation η_chł = 0 ÷ 250.30. As a consequence of reduced demand, the transmission efficiency of the heating heat will decrease. As a result of climate change forecasts, there will be an increase in the demand for electricity to produce cold, which will necessitate investments to increase the power plant capacity [31, 32, 33].

Electricity production in Poland is expected to increase by 2040. This is due to assumed economic growth and also anticipated increased demand for cooling in residential and office buildings. It is assumed that after 2040 there will be a downward trend in electricity generation. This will be caused by the development of new technologies and greater use of other methods to obtain cooling, e.g. thermal ones. The production of cooling from the district heating network will make it possible to relieve the load on the power grid, increase the electricity production of thermal power plants and increase the security of the national power system [35]. In EU-28, it is assumed that about 10% of the building area is cooled, with their share in energy consumption accounting for 16% [36]. The value of energy consumption for building cooling depends on many factors (parameters), including the design and equipment with control systems for shaping the indoor environment. In [37] energy consumption in office buildings – energy-efficient and traditional, in heating, ventilation and cooling systems is presented. The share of cooling needs in a traditional building is 25.5% of the total consumption in heating and ventilation systems, while in an energy-efficient building the corresponding share is only about 2%. In Poland, practically the entire demand for cooling in the summer period is covered by equipment powered by electricity. High external temperatures, droughts and difficulties with cooling of blocks of flats as well as overhauls of power equipment significantly limit the production of electricity. These constraints can lead to an imbalance between demand and supply. In recent years, there has been a significantly higher demand for electricity in the summer, which manifests itself in a clear tendency to fill the previously existing “summer valley”. The demand for power in the summer period increases every year, which is manifested by the consumption records in consecutive years, i.e. 1.09.2015 – 22 490 MW, 23.06.2016 – 22 630 MW, 1.08.2017 – 23 215 MW, 2.08.2018 – 23 680 MW, and 12.06.2019 – 24 096 MW, 10.12.2020 – 26 839 MW, 12.02.2021 – 27 MW400. In the summer period, the record in power demand occurred on July 15, 2021, and amounted to 24,533 MW. According to forecasts, by 2035, the average annual increase in power demand may be 1.6% in the winter peak and 2.2% in the summer peak. It is expected that the average annual growth of electricity demand will be around 1.7%, but in a situation of rapid economic growth, it may be higher. According to the results of analyses related to 2015, each 1K increase in outdoor air temperature, from 22.5°C, causes an additional increase in power demand of 100 MW to 200 MW from the National Power System. On the warmest days, more than 2 GW of installed energy capacity is used for space conditioning.

In Poland, the area of the residential sector is 951 Mm², which is about 71.2% of the total building area [38, 39]. The share of single-family houses accounts for 45% of the floor area of buildings. Providing a comfortable environment inside the building, in an energy-efficient manner determines its efficient and economic use in aspects of meeting the criteria of health, work efficiency and leisure. Electric energy is consumed primarily in the ventilation and air conditioning systems and in the systems of automatic regulation and control of media streams to ensure optimum quality of the indoor environment, mainly the thermal and humidity parameters of the rooms.

The design of energy-efficient buildings, which is the basis of sustainable development, makes it necessary to minimize energy consumption in heating, ventilation and air conditioning systems [9]. In achieving the desired goals, it is necessary, first of all, to increase the share of electricity from renewable sources, mainly solar. Providing power supply is an indispensable condition in the operation of buildings. The damage resulting from lack of electricity is 20–30 times higher than the cost of providing it [40]. Architectural, structural and aesthetic Building Integrated Photovoltaics (BIPV) systems are an appropriate form of solar energy utilization. BIPV systems are design-incorporated structural elements of buildings that generate electricity, mostly for their own use, but can also transmit energy to the grid. BIPV building photovoltaic systems can have different forms of application depending on where and when they are installed. During the construction phase of a building, systems are installed on the roof or façade of the building and integrated into the façade, such as curtains. It is also possible to install “Shadow-Voltaic” systems during any phase of building construction or operation. These are photovoltaic modules optimally positioned on the south side of the building that are angled – manually or automatically adjustable – to shade the building or increase the electricity and generated. The development of photovoltaic systems is characterized by a systematic increase in efficiency, the emergence of new technologies and manufacturing methods for their optimal use. Thin film cells of the third generation, such as flexible organic OPV photovoltaic cells, offer a wide range of application possibilities. They are manufactured using the “roll-to-roll” (R2R) technique, which enables the cell to cover large substrate areas. Therefore, OPV photo-voltaic cells are particularly desirable for mobile active shadow structures. The flexible R2R printed electronics market is estimated to reach $18.3 billion by 2025, while cell efficiency will increase to 20.25%.

In [41, 42, 43] heating systems in single-family houses are presented as an instrument of prosumer energy. Some of the proposed solutions have been considered in the developed scheme of control and interrelation of the complex systems of thermal and electric energy generation in a single-family house – Fig. 3. These systems use mainly solar energy, intercepted and converted by a set of hybrid collectors, additionally supported by rollable solar panels (RSP). The principle of operation is illustrated in Fig. 3. In case of insufficient sunshine, a heat pump is used to generate heat, and at the lowest outside temperatures a pulse gas boiler is also activated. During the summer, the production of cooling – the operation of the air conditioning – is supported by a system of vertical and horizontal rollable solar panels (RSP) – which act as an active shadow – while generating electricity. The RSP controller rolls out the PV panels at certain times of day with the right conditions for their use. Processed data on current weather conditions (T_zewn.) are fed into the central heating and hot water controller from the weather station processor. Indoor air quality data is sent from temperature, humidity and ventilation airflow sensors. Energy obtained from the RSP panels, as in the case of the PVT hybrid panel array, flows into the charge controller unit and is then routed to battery energy storage or via an inverter to 230/400 V AC domestic consumers. In the ON GRID system, the electricity is discharged into the power grid in the event of overproduction. The system of connections of an exemplary system of production of heat and electricity in a single-family house, using some of the renewable and pro-ecological energy sources, e.g. natural gas, is presented in Fig. 4. Bold lines indicate energy connections, and thinner ones – control and data buses. The main source of electricity is a set of hybrid solar panels. The controller for the rollable solar panels exchanges data with the charge controller, the controller for central heating and hot water production and the weather station.

Figure 3.

Figure 4.

An example of a process diagram for the production of electricity, heat and cooling using a dual-circuit heat pump and PVT-HP hybrid photovoltaic collectors, using a ground exchanger, a recuperator and rollable solar panels is shown in Fig. 5. The presented original generation system solutions are mainly characterized by the use of heating/cooling of the supply air of the residential building and its static heating with the use of heat storage – a hot/hot water reservoir for the production of central heating and hot water. The system additionally generates electricity from rollable solar panels. In summer, electricity consumption is reduced by the active shadow effect – supporting the energy-intensive forced air cooling system. A dual-circuit heat pump directly extracts heat from a set of PVT-HP panels, which, when concentrated, is returned to an air heater or heat storage as needed. Excess heat during the summer can be returned to the swimming pool.

Figure 5.

The use of two types of rolled solar panels is shown in Fig. 6. The system, depending on the time of day and year, actively adjusts its active area, capturing heat, relative to the illuminated surface of the vertical south and west walls of the building. The area, slope and distance of the rollable solar panels from the insolated walls are mainly determined by the geometrical dimensions of the building and the plot area. Increasing the distance of the installation from the building walls makes it possible to increase the maximum area of the rollable solar panels.

Figure 6.

The inclination of the active surface of PV panels is a function of latitude and time of year. The optimum inclination of the flat surface absorbing solar radiation with respect to the horizontal plane for the latitude of 52° for southern exposure is 35° for the hottest months of June, 36° for July and 44° for August, respectively. As a guide, it can be assumed that their inclination, similarly to that of the solar collectors in the so-called warm period, should be α = 42.5° depending on the season of the year and should range from 30° to 45° [44].

For fixing the horizontal, rollable solar panel, it is proposed to use the so-called “soffit” fixing of the roof truss and the upper part of the frame fixing the lower photovoltaic blind. Optimal use of the building requires the installation of a comprehensive control system for utilities, energy production using RES and optional shaping of the parameters of the internal environment of the building, depending on the preferences of its users.

A comprehensive system of control of access, utilities, electricity production and equipment of a smart residential house, supplemented by the use of mobile active energy shadow structures is shown in Fig. 7 [45]. Operation of active shadow structures, i.e. switching on and off – is controlled by sensors using collected data of sunlight, rain and wind.

Figure 7.

Single-family housing is characterized by tremendous diversity. Nowadays, the most important issue in design is the creation of energy-efficient buildings, in which all heating, cooling and ventilation systems are integrated with each other [21] in order to optimize their performance. Creating sustainable architecture, however, is not a new concept, but has been known since the beginning of human settlements [47]. Nowadays, for creating the best possible energy-efficient building design, in addition to the aforementioned A (ground contact area) to V (volume) ratio, other parameters will also be important. The leading ones are: the form of the building (solid or compact), the height of the building, the type of roof, the angle of inclination of the roof slopes, the number of openings in the building, its exposure to the directions of the world as well as the materials and colours [48]. The building body is by far the most important issue for cooling demand, but façade colour also matters [49, 50]. A naturally shading building, with far-reaching eaves, and a body designed in such a manner that parts of the building shadow other parts of the building at appropriate times of the day and year, will undoubtedly result in less energy demand for air conditioning and cooling. The study of the degree of solar penetration for architecture is performed in two stages. 3D simulations are conducted by determining the latitude for a given location and choosing a date, but in parallel it is advisable to verify the degree of solar penetration inside the building on a real model [51], as illustrated in Fig. 8.

Figure 8.

The methods of obtaining energy can be various. The passive method of solar energy production, from a technical and physical point of view, seems to be the most obvious [52]. Greenhouses and winter gardens have become popular element of single-family buildings. They are a natural extension and combination of the interior space of the house and the exterior space – terrace and garden. The phenomenon of obtaining heat from solar energy, beneficial in the winter period, is in the summer period quite a problem, causing overheating of the building [53]. To avoid this phenomenon, it is necessary to use movable shadows. Appropriately selected shading coefficient (f_c) achieved by using shadows that do not allow the radiation to the glass, which is also a photovoltaic coating, allows to reduce the heating of the room realistically [54] while obtaining energy [55]. However, external shadows can be a dominant element, often unacceptable for investors, changing both the body of the building and the appearance of its individual facades. Therefore, it is advisable to use movable and controllable elements [56]. Moving shading can be achieved in several ways. Vertically mounted elements can be shells or light breakers (French. Brise soleil). This type of movable sunshade to protect windows from intense sunlight can be covered with thin-film Perovski photovoltaic modules. There are several commercial ones on the Polish market offering such solutions, the leading distributor being Salue Technologies). Energy gains, as in the case of rolled coatings, depend on the number of modules used. Compared to shells, however, it is not possible to fold them completely, which can be easily achieved in the R2R shading system. It can be mounted, as mentioned before, to the roof soffit or to the terrace frame with a slope of 30° to 45°, which is consistent with the slope of most pitched roofs designed in our latitude. Therefore, it will be a natural extension of the roof slope, without the need to introduce an additional slope. In this case, the use of energy active shadow is a solution being a continuation of the roof slope (Fig. 9a), however, often even with such a shape of the body, the investors consciously decide to change the angle of inclination of the shadow plane (Fig. 9b).

Figure 9.

However, the contemporary building form often forces the coatings to be shaped differently than the roof in the slope range mentioned above. Between 2018 and 2021, in the author's designs of single-family houses, 50% of the houses had a flat roof, and even those that had pitched roofs were usually equipped with flat roofing of the terrace, which nowadays serves increasingly as a summer living room. For this purpose, a roll-up panel can be used (basic modules are offered by commercial companies, e.g. Wise Energy or Power Film), which also offer a wide range of customization services. The analysis of several author's designs (Fig. 10) allowed to conclude that the traditional form of shading coatings in R2R technology is feasible and optimal in terms of energy gain in these cases, but it does not always meet aesthetic expectations (Fig. 10a, b, c). Therefore, it becomes necessary to use also coatings in the form of rigid movable panels (moved along rails manually or by means of an electric motor) filled with energy-active coatings (Fig. 10d, e, f). In the case of vertical installation, the optimal technology will be the microgrooves panel (offered, e.g., by the commercial company Power Roll), which provides the maximum surface area for solar energy absorption. A wide range of assembly results in great material possibilities. However, thin-film structures seem to be the best, being a photovoltaic composite containing at least one flexible photovoltaic panel and at least one textile panel, with the foils not having a width of more than 8 cm so as to eliminate the formation of folds when rolled up or in the unfolded position [57].

Figure 10.

They may be slidable to allow more radiation and reduce energy production or extendable so that shading is maximized while shading and enclosing the space.

The loss of efficiency of shading coatings is similar to that of solar panels [58].

As Manbir S. Sodhi, Lennart Banaszek, Chris Magee and Mercedes Rivero-Hudec write, the annual degradation of a panel is between 0.5% and 3%. In the case of rolled panels, this ratio increases from 1% to even 4% [59]. In the case of rolled panels, frequent shape changes can cause delamination of the film from the base material, as well as delamination between the anti-reflective layer and the electrode [48] and degradation of the ETFE (ethylene) polymer covering the modules. However, it should be remembered that the energy-active shading coating should be treated as an additional support of energy production from RES, and not as its main source for a single-family house. Therefore, considering aesthetic issues, it is necessary to use other types of shading than those within the range of the optimal angle, despite the reduced efficiency of the active energy coatings. Calculations for the carbon footprint generated by the rollable photovoltaic coatings over the entire life cycle should be carried out in its entirety together with other photovoltaic solutions used in the building [60]. Rules according to which the carbon footprint is calculated is a complex issue that requires specialist knowledge. For this purpose, research should be carried out, which should be devoted to a separate study.