Active thermal insulation as an element limiting heat loss through external walls

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ACTIVE THERMAL INSULATION AS AN ELEMENT LIMITING HEAT LOSS THROUGH EXTERNAL WALLS Tomasz Kisilewicz , Ma lgorzata Fedorczak-Cisak , Tamas Barkanyi PII: DOI: Reference:

S0378-7788(19)32182-6 https://doi.org/10.1016/j.enbuild.2019.109541 ENB 109541

To appear in:

Energy & Buildings

Received date: Revised date: Accepted date:

14 July 2019 8 October 2019 18 October 2019

Please cite this article as: Tomasz Kisilewicz , Ma lgorzata Fedorczak-Cisak , Tamas Barkanyi , ACTIVE THERMAL INSULATION AS AN ELEMENT LIMITING HEAT LOSS THROUGH EXTERNAL WALLS, Energy & Buildings (2019), doi: https://doi.org/10.1016/j.enbuild.2019.109541

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Highlights     

Active thermal insulation is a system for direct coupling a ground with a wall heat exchanger. Active thermal insulation decreases significantly heat losses through the external wall. In tested building average heat loss reduction was 63% in relation to standard insulation. Minimum heat loss reduction in the cold period was higher than 50%. Automatic smart control system should be applied to minimize space overheating.

ACTIVE THERMAL INSULATION AS AN ELEMENT LIMITING HEAT LOSS THROUGH EXTERNAL WALLS

Tomasz Kisilewicz1*, Małgorzata Fedorczak-Cisak1, Tamas Barkanyi2 1

Cracow University of Technology, Cracow, Poland

2

Nyiregyhaza Templom u. 20, Hungary

* corresponding author: CUT, ul. Warszawska 24, 31-155 Kraków, Poland, e-mail: [email protected]

Abstract The authors present the preliminary results and analyses of research performed in an experimental residential building located in the town of Nyiregyhaza in Hungary. The building is equipped with an innovative system for direct coupling a ground heat exchanger with a wall heat exchanger. In 2012, the creator of the system, Tamas Barkanyi, obtained patent for active thermal insulation of buildings. In this paper, the authors attempt to answer the question of to what extent the active insulation system can replace the commonly used standard passive insulation systems. The initial results of the research lead to the conclusion that active thermal insulation significantly improves the insulation parameters of the external wall. In the analyzed periods, the reduction of the total amount of heat loss through external walls was from 53% in February to 81% in November. The equivalent thermal transmittance Ueq of the analysed wall was dependent upon local climate conditions and amounted to 2

2

0.047 W/(m K) in November and 0.11 W/(m K) in March, while the standard transmittance value was 0.282 W/(m2K).The obtained positive research results should be the basis for the implementation of an innovative system in NZEB buildings.

Keywords: active building thermal insulation, pipe-embedded wall, direct wall and ground thermal coupling, equivalent thermal transmittance, nZEB buildings, building thermal comfort.

Introduction In the face of exhaustion of the natural energy resources of the Earth and the progression of environmental pollution, policy and actions of the majority of world leaders are aimed at reducing the energy demand in sectors with the highest energy-intensity indicators. The residential construction sector is responsible for around 25% of the share of final energy consumption in the EU. In 2010, energy consumption in this sector was the highest in the 1990-2014 period [1]. The necessity to implement the near zero energy demand (NZEB) building standard, which constitutes the implementation of the Directives on Energy Characteristics 2002/91 / EU [2] and 2010/31 / EU [3], influences the development of more and more energy-efficient technologies. An important element, apart from minimising the energy demand in the construction sector, is the shift from exploiting conventional energy carriers to obtaining energy from renewable sources (RES) [4, 5, 6, 7]. Research on the possibility of using energy from unconventional sources for the heating/cooling of buildings in various climate zones has been conducted for years, among others by RopuszynskaSurma et al. [8], Mensah-Darkwa et al. [9] and Ferrucci et al. [10]. Another research problem is the method of storing the obtained energy, Maleki et al. [11] and Wita et al. [12]. When looking for optimal solutions for the use of renewable energy, the aim is to increase the efficiency of systems whilst simultaneously ensuring economic viability and care for the environment. Systems based on solar energy acquire energy from radiation reaching the surface of the earth and convert it into either electricity (photovoltaic systems), Jäger et al. [13], or into thermal energy which covers the heat demand of buildings (solar collectors), Koller et al. [14]. Exploiting the large, but unevenly distributed, amount of solar energy that reaches the Earth's surface during the year, even in high latitudes, remains a challenge as the prospect of storing the periodic excess of energy in the summer and using it in the winter seems very promising. Such possibilities, to a limited extent, are created by heat accumulating in the ground around the building. Strategies extracting heat from the ground are currently very popular; most often, these are heat-pump based systems or simple air exchangers that enable the preheating of ventilation air, Nemś et al. [15]. Teams of scientists and practitioners are conducting increasingly advanced works, the main task of which is to make buildings independent of conventional, non-renewable energy sources. In [16], Pater et al. analysed the structure of energy balance of a residential building and indicated that there were still significant losses through the

standard building envelope. Further thickening of insulation raises economic doubts, other, unconventional methods of reducing heat losses can be used. 1. Active thermal insulation

1.1. Concept of active insulation An interesting technological solution is the introduction of a ‘thermal barrier’, Krecké [17], or an ‘active insulation’ layer into the structure of the external partitions of the building; this would reduce heat loss through external partitions, and at the same time, use energy from unconventional sources. Such a system does not require the operation of a heat pump, which significantly reduces its costs in relation to surface heating systems based on pump operation. Active thermal insulation reduces heat loss through external partitions although it cannot replace the heating system. A thermal barrier or active thermal insulation is a system of pipes placed inside the structure of an external building envelope in which a heating and cooling medium circulates, supplied with low temperature energy from the ground. The operation of the active thermal barrier is not based on the direct transmission of low temperature energy to the room, but is related to the increase (or decrease during the summer) of the temperature inside the external envelope. The basic principle of active insulation is that it uses the energy of the medium at a temperature lower than the temperature of the internal room, but at a higher than that of the outside air. Fig. 1 illustrates the operation of the thermal barrier in the simplest conditions of stationary heat transfer. In the case of active insulation, the density of the thermal flux (qi) lost from the inside of the building is related to the temperature gradient t = ti - tf, qi = Ui ·(ti-tf). In the case of a partition with no thermal barrier, the value of the heat flow from the inside of the building (qo) is related to the temperature gradient t = ti-te, qo = Uo · (ti - te). It is worth noting that in the case of active thermal insulation, when calculating the heat flux density value (qi), only the partial thermal transmittance of the external wall from the interior to the active insulation plane is taken into account.

Fig. 1. The principle of the operation of a thermal barrier in stationary conditions ti - internal temperature (oC) o te - outdoor temperature ( C) tfo - temperature in the active insulation layer when active insulation is not working [oC] o tf - temperature in the active insulation layer when active insulation [ C]) is running 2 Uo – thermal transmittance across the whole partition [W/(m K)] Ui – partial thermal transmittance from the internal space to the active insulation layer [W/(m2 K)] The effective operation of active thermal insulation is possible due to the energy from the building partitions that is stored in the ground. During the summer, thermal energy received from the partitions is stored in the ground, and during the heating season, it is then returned to the interior of the partitions, creating a layer of elevated temperature, or a ‘thermal barrier’, Krecké [17].

1.2 Review of research on active insulation The concept of active thermal insulation has been used, inter alia, in the ISOMAX system [18] [19] [20]. The system's manufacturers assumed that the temperature obtained in the area of the thermal barrier in Polish climatic conditions should be at a level of +8oC for winter months and +16oC during the transitional period, Leciej-Pirczewska et al. [21]. Website study [20] presents the concept of the first public utility building in Poland with a thermal barrier. The temperature of a thermal barrier of 16oC was adopted for the calculations. The results of calculations of the total heat demand and the heating power demand for this scenario showed that with active insulation, there is a 60% reduction in heat demand, and for seasonal heat demand even above 80%.

Leciej-Pirczewska et al. [21] calculated what the minimum temperature of the liquid flowing in the tubes should be. The authors were also looking for the optimal position of the exchanger within the partition section. The conclusions given by the authors indicate that in the case of an active barrier located in the axis of the partition, in order to fulfil its function, the average temperature in the heating season should be higher than 11.3oC for the first climatic zone in Poland. At the end of the heating season, the barrier temperature should be above 16oC. At another position of the barrier, a fairly obvious relationship should be maintained in which the smaller the relative resistance between the barrier and the heated room is, the higher the barrier temperature should be. In the article [22], Leciej-Pirczewska et al. analysed the effect of the initial temperature and thermal capacity of the heating/cooling medium flowing through the tube exchanger on the heat flow through the partition. The authors also analysed the cost-effectiveness of using a partition with a thermal barrier. According to the authors, the use of a thermal barrier begins to be profitable when the cost of the heat unit for supplying the thermal barrier is at most equal to half the unit cost of the heat used for heating the building. With the reduction of unit heat costs delivered to the barrier, its use is becoming more and more profitable. In another article [23], the same authors presented a barrier model with a thermal barrier taking into account the cooling of the fluid flowing in the core and determined how the temperature of the medium flowing in the core influences the possibilities of limiting heat loss from the rooms of a building. The solutions were compared with a partition with identical layers but with no thermal barrier. The authors concluded that for the assumed calculation conditions, the thermal flux penetrating from the room decreases by around 11% for each 2°C increase in the temperature of the heating medium. Małek et al. [24] calculated the temperature field for the outer partition both with and without a thermal barrier. The temperature on the inner surface of the partition with the barrier was only 0.2°C lower than the internal temperature, while in the case with no thermal barrier, it was 1.5°C. In the article [25], Krecké et al. presented the results of simulations they performed comparing a wall with no thermal barrier and a wall with a thermal barrier with an average assumed temperature of +18°C; they showed that heat loss through the wall was reduced from 21.02 to 3.28 kWh/(m²·year). This corresponds to a reduction in the heat demand for heating purposes by as much as 71%. The authors investigated the heat 2

demand of an 80 m residential building. For the outside walls with no thermal barrier, the energy

demand index was EA = 60.7 kWh/m²a; for the outside walls with a thermal barrier of +18°C, EA = 17.3 kWh/m². A very interesting approach to the evaluation of the active insulation efficiency was presented by Meggers et al. [26]. The authors calculated in two ways a value of the coefficient of performance (COP) of the active insulation system in a small house located in Zurich. Firstly it was a ratio of heat delivered to the wall and energy needed to circulate medium, and secondly it was a ratio of achieved heating savings to energy used to run the pumps. The both calculated values (23 and 15) were several times higher than the values obtained by the heat pump thus confirming the sense of using a low exergy solution. Active thermal insulation, in addition to its function of reducing thermal loss in cool climates, is also considered in hot climate countries as protection against the inflow of heat to the building. Li et al. [27] analysed the thermal efficiency of the thermal barrier for five climate regions in China. The simulations made by the authors show that the potential for savings is the greatest in regions with the hottest climate. Shen et al. [28] proposed a system for the installation of cooling pipes in window blinds in order to lower temperatures during the summer months. The study presents a numerical model verified on the basis of experimental data. The effectiveness of the developed system reduces solar gains causing overheating in all analysed Chinese cities by more than 20%. The largest reduction in radiation has been achieved in the southern cities of China, where the cooling season is long. Shen et al. [29 and 30] analysed system performance throughout the summer season. The numerical model they created was verified on the basis of experimental data and then used in the case study. The authors conducted simulations for three typical cities in China. The cooling system's total reduction rates for electricity consumption were 51.9% in Shanghai and 58.9% in Guangzhou. According to the authors, the thermal barrier is more effective for orientation with greater sunlight, such as the roof and western wall. Many publications are devoted to the validation of models used in dynamic simulations based on the results of experimental research. Zhu et al. [31] presented an experimental validation of a dynamic model of an external wall with a thermal barrier. The semi-dynamic model of a wall, based on the finite-difference method, consisted of nodes with thermal resistance and thermal capacity (RC-model). It was coupled with a NTU model of heat exchange effectiveness in the coil. Experimental tests were performed on samples in environmental chambers. Temperatures and heat fluxes were measured on

both sides of the tested sample, as was the temperature of the medium at the inlet and outlet, and the intensity of its flow. The obtained results proved the accuracy of the RC model and its high computational performance. Xie et al. [32] created the FDFD Model which can directly predict the thermal temperature response of the barrier. The article also presents the experimental validation of the model as a function of time. In the paper [33] Xie at al. presented a comparison of the energy demand for a building both with and without active insulation. This work also presents the effects of the water temperature and the pipe spacing on the heat transfer of this structure. The internal surface heat transfer may reduce by about 2

2.6 W/m when the water temperature reduces by 1°C in the case of a brick wall with pipes embedded inside. When the pipe spacing is reduced by 50 mm, the internal wall surface heat flux can also be reduced by about 2.3 W/m2. In [34] Schon et al. analysed the use of active insulation placed in shaft sets. According to their study, such a system, used in hot-climate countries, can reduce solar energy gains by 60%. With the use of this system in windows and walls, the seasonal cooling energy consumption in the analysed office was reduced by 25%-50%. Xua et al. [35] presented numerous solutions and models of active pipe heat exchangers in the building envelope which allow the use of low temperature energy sources. The authors showed solutions in which heavy, massive building elements were used to store heat or cold, as a result of which, it was possible to use off-peak energy. They also pointed out that thanks to such exchangers, there is even the possibility of completely giving up mechanical cooling. In paper [36] Krzaczek presented the results of simulation calculations of a 3D model of an active thermal barrier with ground heat storage in northern Poland. In this case, the time-varying stream of the medium in the exchanger was analysed, striving to maintain a near-constant barrier temperature of 17oC during the year as well as the constant direction of heat flow from the inside to the outside of the wall. The tested partition consisted of 3 layers: internal thermal insulation, a massive concrete layer with a tube heat exchanger and thermal external insulation. Such a layer system was confirmed during the simulation to be the most advantageous for the thermal balance of the wall throughout the whole year. It was also indicated that it is possible to modernise existing buildings using a thermal barrier and ground heat exchangers. The utilisation of low-grade energy sources can also be achieved in a different way. Zhang et al. [37] developed a simulation model and performed experimental studies of an innovative outer wall with a

closed capillary tube system on the inside and outside. External tubes are laid at the bottom of the wall, and the internal tubes are placed above them. The medium, circulating in this passive system due to phase transformation and gravity, transfers heat to the interior and increases the temperature of the internal surface. As a result of this strategy, heat loss through the wall was reduced by 14.5% across the entire heating season in the climate of Jinan in China. The authors emphasised the high profitability of this solution. In work [38] Ibrahim et al. presented the idea of transferring energy obtained by a south-oriented wall to a north-oriented wall. This is accomplished through a closed system of heat exchangers mounted in both walls. The application of this solution enabled the reduction of heat loss through the northern wall by up to 50% in a moderate climate. This system can be used in both new and existing buildings.

1.3 The aim of the paper In the above-mentioned literature review, most of the authors presented computational models which were partially verified in laboratories. There is little information about the real effect of active insulation at full scale and in normally used facilities. In this article, the authors present and analyse the results of a functioning of a building with active insulation connected directly to a ground heat exchanger. The designer, investor and user of this facility, Hungarian engineer Tamas Barkanyi, in 2012 obtained patent no. P398122: Element of building construction for active insulation of buildings [39, 40]. The authors obtained open access to the results of measurements in this facility. The main goal of this article is the preliminary review of a large amount of measurement data acquired over several years in a building with active insulation and energetic assessment of its effectiveness. The assessment was based on a comparison of a wall with active insulation with a similar wall of a standard structure in the selected environmental conditions. Due to limitations of the data system, related to measurements of air and liquid temperature only, it was necessary to combine measurements with the non-stationary numerical simulations of heat transfer.

2. Description of the experimental facility

2.1. Monitored building and its equipment This experimental installation is realised in a low-energy building located in the city of Nyiregyhaza in Hungary. It is a one-family, three-storey building (cellar, ground floor and usable attic with a total usable area of 357 m 2, built in an open area with good access to solar energy. The building contains a

number of different energy-saving solutions, the result being a very low demand for conventional energy for such an object. The demand of the building for final energy is approximately 12.1 2

kWh/(m ·year). In order to achieve such a low level of energy demand, the building's exterior walls have been insulated with effective thermal insulation; the windows and external doors also meet high standards of thermal insulation. The building is equipped with a mechanical ventilation system with heat recuperation. The recuperator has a capacity of 500 m 3/h. The ventilation system is connected to a ground heat exchanger with a length of 75 m and of 250 mm diameter, placed at a depth of 1.6 m, due to which, the preheating / cooling of the air takes place. The building is also equipped with a heat 2

pump and flat-plate solar collectors of the "Ariston" type – 10 panels with a total area of 20 m ; however, these panels are not connected to the active thermal insulation system. The building has a storage system for acquired solar energy in the form of a thermally insulated concrete energy storage system (35 m3), located beneath the floor. In fact, each of these building elements could be an independent subject for extended energy efficiency computational analysis, confrontation of modelling with real operation, etc.

Fig. 2a. General view of the west façade

Fig. 2b. Arrangement of the heat exchanger in the ground floor wall

2.2. Applied active insulation system The subject of this article is an original active thermal insulation implemented in the presented building. The external wall of the ground floor of the building consists of the following layers (from inside to outside – Fig. 3): - plastered reinforced concrete, 5 cm in total, - thermal insulation (EPS) 12 cm,

- reinforced concrete 7cm, - thermal insulation (EPS) 8 cm, - adhesive layers and thinned external plaster 1 cm in the ETICS system.

Fig. 3.

Cross section of the tested wall

Both of the concrete structural layers of the wall are mechanically connected with each other using diagonally laid steel anchors. In the 7 cm-thick concrete layer, a coil made of PE pipes of 20 mm internal diameter is installed; the average distance between the tubes is 20 cm. The coil is directly connected to a horizontal ground heat exchanger located 1.75 m below ground level. The ground heat 2

exchanger consists of two parts: next to the building (area of 60 m ) and under the building (area of 2

145 m ). The medium (glycol) is circulated through the entire system by a continuously working pump. Coils from all the walls of the ground floor of the building are connected into one circuit. The temperature of the medium is measured and recorded at the entrance to the wall coil and at its outlet. The ground around and under this object is treated as a seasonal heat accumulator of a large capacity, from which energy is drawn in the winter to heat the outer casing of the building, and in the summer, energy from the cooled partitions is accumulated in it, Barkanyi et al. [41] [42].

2.3. Data collection system In situ measurements consisted of the continuous recording of: - external air temperature, - temperature at the inlet to the heating / cooling medium in the coil, - temperature at the outlet of the heating / cooling medium in the coil, - indoor air temperature.

The measurements were performed using digital temperature sensors DS18B20 with a 1-wire interface. The measuring range was from -55°C to 125°C. The voltage supply ranged from 3.0 V to 5.5 0

V. The measuring accuracy was +/- 0.5 C.

3. Energy saving potential As mentioned above, the circulation of the medium in the coils occurs in a continuous manner, regardless of the current temperature of the outdoor air and the temperature in the soil. Despite the fact that it is possible to turn off the coil circuit, the cells that have been used thus far have remained switched on for measurement purposes. Figure 4 shows the average daily values of the outdoor air temperature and the average daily temperature of the refrigerant in the coil of the ground floor walls during a selected long period from 22/02/2011 to 24/12/2013. The average daily temperature of the medium in the coil is equal to the

35 30 25 20 15 10 5 0 -5 -10 -15

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medium in coil

2011-02-22 2011-04-02 2011-04-29 2011-05-26 2011-06-23 2011-07-25 2011-08-22 2011-09-18 2011-10-15 2011-11-11 2011-12-08 2012-01-04 2012-01-31 2012-02-28 2012-03-26 2012-04-22 2012-05-20 2012-06-16 2012-07-15 2012-08-12 2012-09-08 2012-10-06 2012-11-02 2012-11-29 2012-12-27 2013-01-24 2013-02-22 2013-03-25 2013-05-16 2013-06-14 2013-07-11 2013-08-10 2013-09-10 2013-10-07 2013-11-07 2013-12-07

temperature, oC

mathematical mean value of the input and output temperatures.

Fig. 4. The temperature of the external air and the average temperature of the medium in the coil

The temperature of the medium circulating in the coil was high not only in relation to the external air temperature, but also in relation to the normal temperature in the ground at this depth. The average temperature of the medium in the analysed period was 17.91oC, and it varied by around 12 to 23oC. During this time, the average daily temperature of the external air was 11.87oC. The observed difference between the average temperature of the medium and the average external air temperature is the effect of intensive recharging of the ground with energy received from the walls of the building

during the summer. Figure 5 presents a graph of the average daily values of the temperature difference of the medium in the coil and the outside air temperature. A significant advantage of the positive temperature difference values (5843 degree days) above the negative values (-493 degree days) could be treated as the heating potential of this system. 30.00 25.00

15.00 10.00 5.00 0.00 -5.00

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2011-02-22 2011-04-05 2011-05-05 2011-06-05 2011-07-07 2011-08-09 2011-09-09 2011-10-09 2011-11-08 2011-12-08 2012-01-07 2012-02-06 2012-03-08 2012-04-07 2012-05-08 2012-06-07 2012-07-09 2012-08-09 2012-09-08 2012-10-09 2012-11-08 2012-12-08 2013-01-09 2013-02-09 2013-03-15 2013-04-21 2013-06-11 2013-07-11 2013-08-13 2013-09-16 2013-10-16 2013-11-20 2013-12-24

temperauture difference, K

20.00

Fig. 5. Temperature difference between fluid in coil and external air

The location of the coil in the wall is important for the thermal efficiency of the entire system under examination. It cannot be too close to the interior so as not to take up the energy conducted through the wall materials in the heating season, and it must simultaneously be well protected from the external environment so as not to diffuse too much energy from the ground to the environment. In the analysed building, the decision regarding the location of the coil was made by the designer; an assessment of whether this was the best possible solution will be considered in another article on this topic.

4. Dynamic simulation model The measuring system was designed and implemented by the building investor. At present, only the indoor and outdoor air temperature and the refrigerant temperature in the heat exchanger is measured in the analyzed building.The data collected by this system do not allow a full analysis of temperature distribution or heat transfer, hence the need to use a numerical model of a wall to analyse its response to boundary conditions. A finite differences method and an electric network analogue were used to

create a simple dynamic RC simulation model. The derivatives used in the basic differential heat transfer equation are replaced here with differences of the respective quantities in the defined time steps. Wall materials are replaced with a discrete network consisting of nodes both without thermal capacity (surface nodes) and with thermal capacity (internal nodes) [31]. Heat exchange between the nodes occurs via the material or surface resistances. Nodal temperature is a result of the balance between incoming and outgoing heat fluxes, i.e. heat exchange between the neighbouring nodes without thermal capacity and accumulated heat flux in the case of nodes with thermal capacity. Because the initial temperatures of the nodes are not usually known, calculations are repeated long enough to achieve fully repeatable cycles that are independent of the initial values. The temperature of node i that belongs to a one-dimensional network and at the moment p+1 may be derived from general equation {1}:

Ti , p 1 

t   qi  Ci 

 j

T j , p  Ti , p    Ti , p Ri , j 

{1}

where: Δt - time step Ci - i-node thermal capacity, equal to the product of density, specific heat and volume qi - heat flux density (e.g. solar radiation) Tj,p - j-node temperature at the moment p, node j is in thermal contact with node i Ri.j - thermal resistance between nodes i and j A convergent solution in an explicit computational diagram is found when the time step meets the following condition:

t  min[Ci  ( j

1 1 ) ] Ri , j

{2}

Figure 6 shows the analysed wall divided into the following five layers: thin external plaster (1 cm), thermal insulation (8 cm), reinforced concrete (7 cm), thermal insulation (12 cm), reinforced concrete combined with internal plaster (5 cm). In this simplified approach, capacitance node 4 represents a layer with an embedded coil. The temperature of this node is equal to the mean value of the measured inlet and outlet temperature of the medium circulating in the system. One coil covers the entire wall area of the ground-floor.

Boundary conditions of the simulation period were adopted from experimental data sets. The node temperature is therefore a result of non-stationary simulation of temperature field in the wall, resulting from the measured boundary conditions (air temperature of both environments, inlet and

outlet refrigerant temperature). Fig. 6. Simulation model of external wall As previously mentioned, in order to avoid the influence of unknown initial temperature distribution and to obtain results that are fully repeatable and independent of the initial values, the first 24 hours of data has been discarded and is not presented below.

5. Results of experimental measurements and simulations 5.1. Initial assumptions The effects of the functioning of the innovative wall equipped with a heat exchanger and supplied with energy from the ground in several different periods of climatic conditions are presented below. The analysis of the results consists of the comparison of thermal losses through the wall with coil and through a wall with an identical structural layer but without the support of energy stored in the ground. The graphs presented below were obtained by subjecting the above described calculation model to the operation of boundary conditions obtained from experimental measurements. The internal and external air temperature measured with a 10-minute step for a period of 3 days was introduced to the

computational algorithm. However, as mentioned above, in order to avoid the influence of initial conditions, the results of calculations for the first day were discarded and only two days are considered within the analyses. The values of heat transfer coefficients on both wall surfaces were adopted in accordance with standard 6946 [37] as for standard conditions. In the case of the wall connected to the ground heat exchanger, not were only the temperature values of both environments introduced to the calculation algorithm but also the boundary condition in the form of the mean temperature of the medium circulating in the coil constituting the heat exchanger.

5.2. Cold period – February 25 20

internal air

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temperature, oC

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time, h Fig. 7. Temperature distribution on 27th and 28th February 2018 in a wall with no heat exchanger Figure 7 shows the temperature conditions on both sides of the standard wall and in its individual calculation nodes during the cold winter period. The average outside air temperature during this period was -8.42o C. The temperature of the thin layer of external plaster (node 2) closely follows the temperature of the outside air. Temperature changes in the node of the outer thermal insulation layer (node 3) are still not suppressed and the effects of the outside temperature fluctuations remain clearly visible here. However, in the massive reinforced concrete layer (node 4), the temperature changes no longer occur, yet a clear downward trend is visible here and it is associated with the continuous lowering of the outside temperature. The average temperature in this layer during the entire 48-hour analysis period

was 6.110C. The total amount of energy flowing through the internal surface during this 2-day period 2

was 216 Wh/m . The temperature distribution in individual nodes of the wall equipped with a heat exchanger and supplied with energy from the ground is shown in Fig. 8. At first glance, the diagrams are very similar to those shown earlier. The main difference between them, however, is the introduction of temperature forced by the heat exchanger in node 4. Due to the energy accumulated in the ground, and despite the low temperature of the outside air, the temperature of the medium in the coil was practically constant at ca. 14oC during the period shown. In comparison to the wall with no exchanger, the temperature in this calculation node was nearly 8 K higher. This entails raising the temperature in other parts of the wall, including its inner surface. As a result of these changes, the amount of heat lost from the interior through the analysed wall decreased to a value of 101.32 Wh/m 2, which is 46.7% of the thermal loss occurring through the wall with no exchanger. To facilitate the interpretation of the obtained effects, the value of the equivalent thermal transmittance Ueq of such a partition in the average measurement 2

conditions adopted here has been calculated at 0.072 W/m . The term ‘equivalent thermal transmittance’ used above is the value of the thermal transmittance which would have a hypothetical component with standard (passive) thermal insulation transmitting in stationary conditions, the same energy as the wall with active insulation. It should be noted that the savings calculated here and resulting from the use of a ground heat exchanger can be strongly dependent on climatic conditions and should not be transferred a priori to any other period. It is necessary to also analyse thermal streams in other climatic conditions.

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time, h Fig. 8. Temperature distribution on 27th and 28th February 2018 in the wall with the ground heat exchanger

5.3. Cool period – January Figure 9 shows the temperature values in individual wall nodes with no heat exchanger for two chosen cool winter days with an average temperature in this period of -2.24oC and a minimum outside temperature of -7.83oC. As before, external temperature fluctuations are clear in the external thermal insulation layer and were effectively suppressed in the massive concrete layer. The average temperature of this layer in the analysed period was 7.59oC, with a slight downward trend. In the nodes closer to the interior, the temperature value results from the overall insulation of the partition and only undergoes very small changes in this short period of time. The total heat flux flowing into the internal surface of the partition in the analysed 48-hour period was 191.31 Wh/m 2.

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time, h Fig. 9. Temperature distribution on 20th and 21st January 2018 in the wall with no heat exchanger

Figure 10 shows the temperature values in individual planes of the wall with the ground exchanger. The ‘ground-coil’ diagram in Fig. 10 corresponds to the values in node No. 4, Fig. 9. The very clear change between the graphs in Figs. 9 and 10 results from the forced raising of the temperature in the concrete layer from an average value of 7.59°C up to a value of 15.3°C; this is due to the action of the ground heat exchanger. As a result of this, the temperature distributions in the other planes have also shifted up. Under these conditions, the total heat flow into the internal surface of the partition in the analysed period was 82.75 Wh/m 2, which is only 42.6% of the value in the case of a wall with no heat exchanger. The average equivalent thermal transmittance Ueq of a wall with a coil would therefore be 0.070 W / m2K in the analysed period.

25 20 internal air

15 temperature, oC

node 6

10

node 5 ground coil

5

node 3

0

node 2 external air

-5

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46

-10 time, h Fig. 10. Temperature distribution on 20th and 21st January 2018 in the wall with the ground heat exchanger. 5.4. Spring period – March Fig. 11 shows temperature distributions in individual computational nodes of the wall with no coil during the spring period of 29-30 March 2018. The average temperature of the outside air in the o

o

analysed period of 48 hours was equal to 8.94 C, and the minimum temperature was 3.5 C. 25

20

temperature, oC

internal air node 6

15

node 5 node 4

10

node 3 node 2

5

external air 46

44

42

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time, h Fig. 11. Temperature distribution on 29th and 30th March 2018 in the wall with no heat exchanger

Significant daily fluctuations of the outside temperature during this time (over 10 K) cause that the thermal flux in the outer part of the wall is periodically reversed, the wall in these conditions acquires

heat from the external environment. For several hours during the day the temperature in node 4 is lower than the temperature of the outer wall layer. Changing external conditions means that the temperature in node 4 and node 5 increases significantly. The average temperature in node 4 is o

10.81 C. The total amount of heat lost by the internal surface of a standard wall is under these conditions equal to 153.91 Wh/m 2. Figure 12 shows the temperature values in the nodes of the wall containing the coil connected to the ground heat exchanger. The average temperature of the medium in the coil during the analysed 2-day period was as high as 16.59oC and during the day changed only by a small extent, with no connection with the external conditions. This made the temperature in the whole partition much higher than in the above-described variant without a coil, and practically no reverse thermal flow was present. A significant increase of the temperature in the wall cross section obviously had a clear effect on the reduction of thermal loss through this partition. Total thermal loss over a period of 48 hours was 62.23 2

Wh/m and constitutes 40.4% of the losses through a wall with no heat exchanger. The average 2

equivalent thermal transmittance Ueq of a wall with a coil is therefore 0.110 W/m K in this warmer period of the year. 25

20

temperature, oC

internal air node 6

15

node 5 ground coil

10

node 3 node 2

5

external air

46

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time, h Fig. 12. Temperature distribution on 29th and 30th March 2018 in the wall with the ground heat exchanger

5.5. Warm period – November

The first days of November in 2018 were extremely warm for this time of the year. Therefore, the conditions prevailing in this period were used for thermal analysis of the wall during the warm period. Figure 13 shows the boundary conditions and temperature distribution in the wall on 2nd and 3rd o

November. To improve the readability of the graph, the vertical axis starts from 10 C. 26 24

internal air

temperature, oC

22

node 6 20

node 5 18

node 4 16

node 3

14

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time, h Fig. 13. Boundary conditions and temperature distribution on 2nd and 3rd November 2018 in the wall with no heat exchanger The average temperature of the outside air in this period was 16.35oC, and the maximum temperature o

even reached 23.5 C, exceeding the value of the air temperature inside the building. Strong daily fluctuations in the outside temperature during this period (over 12 K) cause significant fluctuations in the external thermal insulation layer. As usual, however, the temperature of the massive construction layer (node 4) changes only slightly, in reaction to a slight upward trend of the external boundary condition. The average temperature in the massive reinforced concrete layer (node 4) is 17.15oC. The air temperature inside the building fluctuates slightly below 21oC, and the 48-hour energy balance on 2

the inner wall surface is 55.20 Wh/m . Providing the wall interior with the heat accumulated in the ground around the building caused the temperature in the middle of the partition to be almost aligned with the internal conditions, Fig. 14. The average temperature of the ground coil is 20.05oC. In such conditions, the heat flux on the inner 2

surface of the wall often changes its direction, and its heat balance approaches zero (10.28 Wh/m K). Under the analysed conditions, the average value of the equivalent thermal transmittance Ueq resulting from the balance is 0.047 W / m 2K.

26 24 internal air

22

node 6

temperature, oC

20 node 5

18

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node 3 node 2

14 external air

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internal heat flux

46

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time, h Fig. 14. Boundary conditions and temperature distribution in the wall with the heat exchanger on 2nd and 3rd November 2018

5.6. Hot period - August 35

temperature, oC

30

25

20

15 external air

from ground

to ground

internal air

2018-07-10 00:00 2018-07-10 21:20 2018-07-12 10:40 2018-07-13 10:20 2018-07-14 07:40 2018-07-15 05:10 2018-07-16 02:30 2018-07-16 23:50 2018-07-17 21:20 2018-07-18 18:40 2018-07-19 16:00 2018-07-20 13:20 2018-07-21 10:40 2018-07-22 08:10 2018-07-23 05:30 2018-07-24 02:50 2018-07-25 00:10 2018-07-25 21:30 2018-07-26 18:50 2018-07-27 16:10 2018-07-28 13:30 2018-07-29 10:50 2018-07-30 08:20 2018-07-31 05:40 2018-08-01 03:00 2018-08-02 00:20 2018-08-02 21:40 2018-08-03 19:40 2018-08-04 17:30 2018-08-05 14:50 2018-08-06 12:30 2018-08-07 10:10 2018-08-08 10:30 2018-08-09 08:40 2018-08-10 06:10

10

10.07 - 10.08.2018 Fig. 15. The temperature of the outdoor air, internal air, coil supply and outflow from July 10th to August 10th 2018 Fig. 15 shows the conditions that prevailed in and around the building during the period from 10th July to 10th August 2018. For a detailed analysis of the summer conditions, a hot 3-day period at the very

end of the graph was selected (August 8th to August 10th) with the maximum temperature during the day exceeding 34°C. Due to effective thermal insulation of the external partitions, consistent shading of the windows against direct solar radiation and high thermal capacity of the object, the air o

o

temperature on the ground floor varies from 21 C to 24 C, providing thermal comfort to the users. In the analysed period, a ceiling cooling system in the building was not running. The long period of high ambient temperature and intense solar radiation caused the temperature of the ground around the exchanger to increase to around 24oC. However, the process of ground heat loading continues as the temperature of the medium flowing into the wall exchanger (from the ground) is lower than the return temperature (to the ground). The analysis of the partition in summer conditions was carried out in a similar way as before. In the first step, the measured values of the exterior and interior air temperature were used to calculate the temperature distribution in the wall with no heat exchanger. Figure 16 presents the values of temperature in individual computational nodes of the wall without a coil during the hot days of 9th-10th August 2018. The average temperature of the outside air in the analysed period of 48 hours was 25.65°C, the minimum temperature was 18.0°C, and the maximum was 34.17°C. The average indoor o

air temperature on the ground floor of the building was 22.95 C. 40 35

internal air 30

temperature, oC

node 5 25

node 4

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time, h Fig. 16. Temperature and heat flux distribution on 9th and 10th August 2018 in the wall without a heat exchanger

The daytime fluctuations of the outside temperature were very high during this period and resulted in significant temperature changes in the interior of the external walls. As before, in node 3, the

temperature changed in a way similar to the external conditions but with a clear suppression of the amplitude of fluctuations and a very small time shift. The lowest temperature values in this period can be observed inside the massive reinforced concrete layer and the adjacent insulation layer (node 4 and node 5), as a result of this, they are thermally protected against external influences. The average temperature in layer 4 was 22.84°C, which is slightly lower than the internal air temperature. In relation to the previously shown diagrams, a change has been introduced in Fig. 16. This shows the values of the heat flux density on the inner surface of the partition. A positive value of heat flux indicates a flow of heat from the interior to the partition. The graph depicts the outflow of heat from the interior to the external wall. However, it can be noted that in the early morning, there is an inflow of accumulated heat to the interior of the building. The heat flux balance during the 48-hour hot period, in the case of a standard wall, remains positive and is 17.22 Wh/m2. Figure 17 shows the temperature values in the nodes of the wall containing the coil connected to the ground heat exchanger. The temperatures of both environments and the coil were obtained from measurements. The average temperature of the medium in the coil during the 2-day period was as high as 24.96°C and was changing only slightly during this period. This caused the temperature in the whole wall to be much higher than in the previously described variant without a coil. A significant increase in the temperature in the cross section of the wall obviously affects the thermal balance of the partition. The internal heat flux diagram in Fig. 17 suggests that the negative values prevail, and thus the partition provides heat to the interior of the building; the total balance for this period is negative and equal to -19.17 Wh/m2. This result is not a surprise if one considers that the temperature of the medium supplying the exchanger in the wall is higher than the room temperature. According to this observation, it should be stated that the system controlling the installation should automatically turn off the circulation of the medium in the circuit during the analysed period. The natural temperature distribution in the wall, shown in Fig. 16, would be more advantageous for the interior than that which was forced by the continuously operating circulating pump.

40

temperature, oC

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time, h Fig. 17. Distribution of temperature and heat flux on 9th and 10th August 2018 in the wall with the heat exchanger

6. Discussion In this article, the authors performed an energy analysis of the external wall in terms of the effectiveness of active thermal insulation. However, the impact of this solution on the energy and economic efficiency of the entire building was not analysed; this will be the subject of further research by the authors. Table 1 presents results for all analysed periods.

6.11 7.59 10.81 17.15 22.84

13.98 15.37 16.59 20.05 24.96

216.00 191.31 153.91 55.20 17.22

101.32 82.75 62.23 10.28 -19.17

Reduction of thermal loss [%]

-8.42 -2.24 8.94 16.35 25.65

Energy loss with active thermal insulation [Wh/m2]

27-28.02.2018 20-21.01.2018 29-30.03.2018 2-3.11.2018 9-10.08.2018

Average temperature of the concrete core layer without thermal insulation o [ C] Average temperature of the concrete core layer with active thermal insulation [0C] Energy loss without active thermal insulation [Wh / m2]

Average external temp. [0C]

1 2 3 4 5

Analysed period

Table 1. Summary results of research.

53 57 60 81 -

Table 2 presents the values of thermal transmittance based on "in situ" tests in the analysed periods. The obtained results of the experimental studies should be considered to be very promising. The

tested system, in the form of a wall heat exchanger connected to a ground heat exchanger, enables significant (more than 50% in average climatic conditions) limitation of thermal loss.

Table 2. Thermal transmittance based on "in situ" tests in the analysed periods. Analysed period

1 2 3 4

27–28.02 2018 r. 20-21.01.2018 29-30.03.2018 2-3.11.2018

Uo value for the variant without active thermal insulation [W/m2K]

0. 2817

Ueq value for the variant with active thermal insulation [W/m 2K] 0.072 0.07 0.11 0.047

However, on the basis of the only analysis of the hot period, it should be stated that it is not effective to use this installation for protection against overheating. In the hot days of August, the continuous forced circulation of the medium in the exchangers increased the thermal flux delivered to the interior of the building. It can be expected that in the transitional periods, receiving heat absorbed by the walls will be more effective in protecting the interior. This analysis also showed that it is necessary to modify the way in which the system is controlled. The intelligent system of control of the medium flow, suggested by the authors of the cited publications, should enable improvement of the obtained results, especially in summer conditions. It should be emphasised that obtaining profits from the active insulation system in addition to the initial material investment requires only a small amount of energy to force the circulation of the medium throughout the system. As a result of this, it is possible to use efficiently low-grade energy and to reduce building carbon footprint. The results of numerical analyses performed on the basis of input data from experimental studies, are also confirmed by the conclusions of other authors analysing active thermal insulation. This temperature-active layer, located inside the structure of the external walls, significantly reduces the flow of the heat flux through the partition and shortens the heating period. In the analysed case, active thermal insulation, supplied with heat accumulated in the ground, reached a temperature in the range of around 14oC to 25oC. In the temperate climate zone, the standard ground temperature at a depth of about 2 m is approximately 8-11oC. This is the temperature in natural conditions when the ground is not additionally supplied and energy is not received. Higher temperature, obtained in active insulation, is the result of charging a ‘battery’, which is the mass of the

ground, during the summer by the heat gained from the building envelope. The results of active insulation temperature analysis are similar to those given in the available literature [21], [22], [23], [24], [25]. In work [21], the minimum temperature of active insulation at which the system is profitable was determined. This minimum is a temperature of around 11 degrees in the heating season, and 16 degrees at the end of the heating season. Higher temperature values were obtained in the tested object, which means that using active insulation in such conditions would be profitable. The creators of the Isomax system [23] assumed that the temperature of active insulation should be at the level of +8oC for winter months and +16oC during the transitional period. The research presented in this article shows much higher temperatures in the active insulation layer. This may be due to the warmer climate in Hungary, where research was conducted, as well as to a different wall construction with active insulation than in the Isomax system [20]. Article [25] specifies the optimal temperature of active insulation at the level of + 16oC to + 18oC, which is similar to the result obtained from the presented research. As shown in Table 1, in the winter period, the 53-60% reduction of heat loss can be clearly seen in relation to the system with no active thermal insulation, and in the transition period, heat loss reduction is up to even 80%. In [25], the authors showed that a wall with a thermal barrier (assuming an active barrier temperature of +18 °C) allowed a reduction of transmission heat loss through the wall from 21.02 to 3.28 kWh/m²year. This result corresponds to a reduction of the heat loss by 71 % and is close to the results obtained in the Hungarian building for the more favourable weather conditions.

7. Conclusions  In this paper, the authors analysed a building solution called ‘active thermal insulation’. This is a specific concrete layer in the external wall of the building, which contains a coil connected directly to a ground heat exchanger. The refrigerant circulating in this system has a lower temperature than the internal air and a higher temperature than the external air temperature in winter season. As a result of this, it is possible to reduce the thermal flux that penetrates this wall during the cold season. The energy efficiency of active thermal insulation and the possibility of improving thermal comfort in both winter and summer depends on the extent to which it is possible to raise or lower the temperature in the active insulation layer in relation to the standard partition.



Measurements in the tested building have been conducted in a continuous manner for several years, but the preliminary results presented in the article only concern selected short periods. The test results were also the basis for the dynamic simulation analyses of the standard component.



Conclusions from the performed tests and simulations show that the reduction of heat loss through the building envelope can be reduced by an average of 63% in relation to standard insulation, while the minimum reduction in the cold period was higher than 50% and the maximum temporary reduction was even 81%.



In the analysed hot summer period, no positive effects of wall cooling were obtained. Under these conditions, the refrigerant circulation in the active insulation system should be turned off to enable the natural cooling of the wall.



The authors predict that the directions of further broad research will concern:

- the continuous analysis of results over a long period of time, - optimisation of the layer arrangement and location of active insulation in the external wall, - a control strategy for summer cooling and effective energy storage in ground, - the impact of the active thermal insulation method on the total long-term energy balance of the building, - developing a methodology for calculating the energy performance of a building with active thermal insulation, - the evaluation of economic aspects related to the replacement of traditional passive insulation with the analysed solution of ‘active thermal insulation’. - optimisation of the operation of the automation system that controls the analysed system.

Declarations of interest: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Literature

[1] Sustainable construction in the EU. Information of the Institute of Building Technology LXVI 3/2016 file:///C:/Users/MFC/Downloads/Informator%20ZB%20w%20UE%20nr%20LXVI_Zu%C5%BCycie%20 energii%20w%20budynkach%20mieszkalnych%20w%20UE%20w%20latach%202000-2014.pdf (accessed in February 2019) [2] DIRECTIVE 2002/91/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 16 December 2002 on the energy performance of buildings [3] DIRECTIVE 2010/31/EU OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 19 May 2010 on the energy performance of buildings (recast) [4] Florescu, A.; Barabas, S.; Dobrescu, T. Research on Increasing the Performance of Wind Power Plants for Sustainable Development. Sustainability 2019, 11, 1266. https://doi.org/10.3390/su11051266 (accessed in July 2019) [5] Photovoltaic Design and Installation For Dummies (1st Edition) by Ryan Mayfield, published by Wiley 2010-09-07, ISBN 9780470598931 [6] The Solar Revolution by Steve McKevitt, Tony Ryan, published by Icon Books Ltd ISBN 9781848317871 https://www.amazon.com/Solar-Revolution-Solution-ProvidingBillion/dp/1848316550 (accessed in July 2019) [7] Tolmie, R.; Rosen, M.A. A Dual Function Energy Store. Sustainability 2014, 6, p. 8297-8309. [8] Ropuszyńska-Surma, E.; Węglarz, M. Profiling End User of Renewable Energy Sources among Residential Consumers in Poland. Sustainability 2018, 10, p. 4452. [9] Mensah-Darkwa, K.; Zequine, C.; Kahol, P.K.; Gupta, R.K. Supercapacitor Energy Storage Device Using Biowastes: A Sustainable Approach to Green Energy. Sustainability 2019, 11, p. 414 https://www.mdpi.com/2071-1050/10/12/4452 (accessed in July 2019) [10] Ferrucci, M.; Peron, F. Ancient Use of Natural Geothermal Resources: Analysis of Natural Cooling of 16th Century Villas in Costozza (Italy) as a Reference for Modern Buildings. Sustainability 2018, 10, 4340. https://www.mdpi.com/2071-1050/10/12/4340/htm (accessed in July 2019) [11] Maleki, A.; Rosen, M.A.; Pourfayaz, F. Optimal Operation of a Grid-Connected Hybrid Renewable Energy System for Residential Applications. Sustainability 2017, 9, 1314.

https://www.researchgate.net/publication/318740672_Optimal_Operation_of_a_GridConnected_Hybrid_Renewable_Energy_System_for_Residential_Applications (accessed in July 2019) [12] A. Wita, A. Balcerzak, D. Mirosław-Świątek. Heating system with a ground thermal energy accumulator - results of experiments, XIV Scientific Conference - Korbielów 2002 - Computer Methods in Designing and Analysis of Hydrotechnical Constructions [13] Jäger-Waldau, A. Snapshot of Photovoltaics—March 2017. Sustainability 2017, 9, 783. https://www.mdpi.com/2071-1050/9/5/783 (accessed in July 2019) [14] Koller, C.; Talmon-Gros, M.J.; Junge, R.; Schuetze, T. Energy Toolbox—Framework for the Development of a Tool for the Primary Design of Zero Emission Buildings in European and Asian Cities. Sustainability 2017, 9, 2244.

https://www.researchgate.net/publication/321825772_Energy_ToolboxFramework_for_the_Development_of_a_Tool_for_the_Primary_Design_of_Zero_Emission_Buildings _in_European_and_Asian_Cities (accessed in July 2019) [15] Nemś, A.; Nemś, M.; Świder, K. Analysis of the Possibilities of Using a Heat Pump for Greenhouse Heating in Polish Climatic Conditions—A Case Study. Sustainability 2018, 10, 3483. https://www.mdpi.com/2071-1050/10/10/3483 (accessed in July 2019) [16] S. Pater, J.Magiera. Assessment of the energy demand of a residential building using two independent computer programs, Technical Transactions of Chemistry. Krakow University of Technology Publishing Office, 2-Ch/2011 Issue 10, Year 108. [17] Edmond D. Krecké, Passive House Building Technology ISOMAX, https://www.yumpu.com/en/document/read/23550241/temperature-barriers-isomax-terrasol (accessed in February 2019) [18] https://informatorbudownictwa.pl/domy-i-konstrukcje/isomax (accessed in February 2019) [19] http://www.odnowawsi.eu/serwis/index.php?id=433 (accessed in February 2019) [20] http://www.isomax-terrasol.eu/fileadmin/_migrated/content_uploads/streszczenie.pdf (accessed in February 2019) [21] Dorota Leciej-Pirczewska, Władysław Szaflik. The use of low temperature factor in wall heating, Heat engineering, heating, ventilation 41/5 (2010) p. 168-172 [22] D. Leciej-Pirczewska, W. Szaflik "The use of low temperature factor in wall heating Part II". Heat engineering, heating, ventilation 41/12 (2010) p. 455-459

[23] D. Leciej-Pirczewska, W. Szaflik. Influence of temperature of thermal barrier in the building's wall on heat loss, X Forum Cieplowników Polskich, Międzyzdroje, 2006. [24] M. T. Małek, H. Koczyk "The influence of the external wall solution on the temperature distribution in the partition". Journal of Civil Engineering, Environment and Architecture, XXXIII, 63 (3/16), July September 2016, p. 247-254. [25] Edmond Krecke, Roman Ulbrich, Grzegorz Radlak. Connection of solar and near-surface geothermal energy in Isomax technology, Proceedings of CESB 07 PRAGUE Conference, 2007, p. 622-628 [26] Meggers F., Baldini L., Leibundgut H.: An Innovative Use of Renewable Ground Heat for Insulation in Low Exergy Building Systems, Energies 2012, 5, p. 3149-3166; doi:10.3390/en5083149. [27] Anbang Li, Xinhua Xu, Yongjun Sun. A study on pipe-embedded wall integrated with ground source-coupled heat exchanger for enhanced building energy efficiency in diverse climate regions, Energy and Buildings, Volume 121, 1 June 2016, p.139-151. [28] Chong Shen, Xianting Li. Thermal performance of double skin façade with built-in pipes utilizing evaporative cooling water in cooling season, Solar Energy, Volume 137, 1 November 2016, p. 55-65. [29] Chong Shen, Xianting Li. Dynamic thermal performance of pipe-embedded building envelope utilizing evaporative cooling water in the cooling season, Applied Thermal Engineering, Volume 106, 5 August 2016, p. 1103-1113 [30] Chong Shen, Xianting Li. Energy saving potential of pipe-embedded building envelope utilizing low-temperature hot water in the heating season, Energy and Buildings, Volume 138, 1 March 2017, p. 318-331 [31] Qiuyuan Zhu, Anbang Li, Junlong Xie, Weiguang Li, Xinhua Xu. Experimental validation of a semi-dynamic simplified model of active pipe-embedded building envelope, International Journal of Thermal Sciences, Volume 108, October 2016, p. 70-80 [32] Junlong Xie, Xinhua Xu, Anbang Li, Qiuyuan Zhu. Experimental validation of frequency-domain finite-difference model of active pipe-embedded building envelope in time domain by using Fourier series analysis. Energy and Buildings, Volume 99, 15 July 2015, p. 177-188 [33] Xie Jun-long ZHU Qiu-yuan XU Xin-hua. An active pipe-embedded building envelope for utilizing low-grade energy sources, June 2012 Journal of Central South University 19(6) DOI: 10.1007/s11771-012-1190-3 [34] Chong Shen Xianting Li. Potential of Utilizing Different Natural Cooling Sources to Reduce the Building Cooling Load and Cooling Energy Consumption: A Case Study in Urumqi, Energies 2017, 10(3), p. 366-376. [35] Xua X., Wang S., Wang J., Xiao F., Active pipe-embedded structures in buildings for utilizing lowgrade energy sources: A review, Energy and Buildings, 42 (2010), p. 1567-1581. [36] Krzaczek M., Kowalczuk Z., Thermal barrier as a technique of indirect heating and cooling for residential buildings, Energy and Buildings (2011), doi:10.1016/j.enbuild.2010.12.002 [37] Zhang Z., Sun Z., Duan C. A new type of passive solar energy utilization technology – The wall implanted with heat pipes, Energy and Buildings 84 (2014), p. 111-116. [38] Ibrahim M., Wurtz E., Biwole P.H., Achard P., Transferring the south solar energy to the north facade through embedded water pipes, Energy 78 (2014), p.834-845. [39] Tamas Barkanyi - Patent Nr: P398122 Element of building construction for active insulation of buildings, 2012. [40] Barkanyi T, Nagylucskay L.: Building Structure with Active Heat, 11.06.2009. PCT WO 2009/071958 A1, Espacenet Bibliographic data: EP 2231952 [41] Barkanyi T, Nagylucskay L. : Let's Use Earth Energy for Insulation Instead of Heating, Magyar Installateur (2009/2-3.) p.44-47 [42] Barkanyi T., Barkanyi A. : Active Thermal insulation - A Paradigm Shift in Low-temperature Soil Energy Utilization, Magyar Installateur (2013/1). p.44-46

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Graphical abstract