Acta Polytechnica https://doi.org/10.14311/AP.2022.62.0459 Acta Polytechnica 62(4):459–472, 2022 © 2022 The Author(s). Licensed under a CC-BY 4.0 licence Published by the Czech Technical University in Prague FUNCTIONAL AERODYNAMICS AND ITS INFLUENCE ON THE ENERGY AND THERMAL MODE OF A NATURALLY VENTILATED DOUBLE-SKIN TRANSPARENT FAÇADE Michal Franeka,∗, Boris Bieleka, Marek Macákb, Josip Klema a Slovak University of Technology in Bratislava, Faculty of Civil Engineering, Department of Building Structures, Radlinského 2766/11, 810 05 Bratislava, Slovakia b Slovak University of Technology in Bratislava, Faculty of Civil Engineering, Department of Mathematics and Descriptive Geometry, Radlinského 2766/11, 810 05 Bratislava, Slovakia ∗ corresponding author: michal.franek@stuba.sk Abstract. This article deals with the dynamics of airflow through a cavity. In windless conditions, where a natural flow causes the flow of air in the cavity, the overall aerodynamic resistance of the cavity is the important aerodynamic parameter, which is the sum of the local resistances alongside the air movement trajectory through the cavity. The total aerodynamic resistance of the cavity must be lesses than the force of the convective buoyancy of the air in the cavity. The following conclusions were found experimentally. The convection occurs in the cavity at every time step with a velocity range from 0.05 ≤ v [m/s] ≤ 0.2 to 0.3. The energy regime in the cavity is characterised by inhomogeneity. In the cavity, there are zones of increasing temperatures along the height of the cavity at the inlet. A large area with increased temperatures at the air outlet and a small area with particularly high temperatures in the upper part of the inlet were found. Keywords: double-skin transparent façade, energy and thermal mode, aerodynamic resistance of the cavity, total pressure coefficient. 1. List of Acronyms BLWT Boundary Layer Wind Tunnel CFD Computational Fluid Dynamics DNS Direct Numerical Simulation DSTF Double-Skin Transparent Façade LES Large Eddy Simulation N-S Navier-Stokes RANS Reynolds Averaged Navier-Stokes Equations SRS Scale-Resolving Simulation NBS National Bank of Slovakia 2. Introduction There are many factors that affect the technology of construction of façades, such as architectural trends, technology itself, and public requests. Today, the im- portance of environment specific contexts is as impor- tant as public requests for the quality of work. Current modern trends, such as ecology, energy-saving, auto- matic control systems, have not been addressed by façade technology, which also uses ecological renewable energy sources, which follow the concept of ecological improvement in the European construction industry. One of the most environmentally friendly alternative sources of solar energy is the double-skinned transpar- ent façade (DSTF), the concept of which is not new, but the trend of constructing buildings with DSTF has only recently been growing, mostly in Europe because of high energy costs and ecological awareness. The originality in the creation of a new façade technology is characterised by four aspects: • theory of the creation of new façade technology is designated for intelligent buildings, • façade elements have the character of items of cir- cuits of automated systems of building control, • façade elements or systems have the ability to utilise natural physical phenomena, • façade elements or systems have the ability to dy- namically reduce the required volume of the envi- ronment technology of the building [1]. Considering the technical aspect, the development of a double-skin transparent façade has its foundations in the physical theory of cavities, which allows various adjustments, e.g., in the geometry of the cavity or in the type of glazing used. The theory of natural physi- cal cavities has its roots in the development of recent technical disciplines, which are solar heat technology and aerodynamics of buildings with their substantial activity in the field of the physics of buildings and constructions. Cavity theory quantifies their physical behaviour, called multi-skin structures, and has been a topic discussed by many authors. There are many 459 https://doi.org/10.14311/AP.2022.62.0459 https://creativecommons.org/licenses/by/4.0/ https://www.cvut.cz/en M. Franek, B. Bielek, M. Macák, J. Klem Acta Polytechnica ways to design DSTF and predict its behaviour, such as models for predicting the airflow or temperature inside a cavity. Underestimating the systems and com- ponents of the DSTF as a whole can result in major errors that significantly affect its operation. We can find proof of this in existing buildings, which have these problems [2], [3]. Todorovic et al. [2] developed a computational model usable in the climatic environment of Central Europe that approximates the temperature of the air and the heating (cooling) load in the DSTF cavity every hour. Arons [3] used a numerical model for a cal- culation of energy performance of a typical DSTF. In 2001, Gan [4] used a model for calculating the thermal transmittance of multiple glazing based on computa- tional fluid dynamics (CFD), and in experimental cases, Saelens et al. [5] introduced a numerical model for calculating the thermal power of active envelopes. Later, Hensen et al. [6] used a network to calculate the characteristics of the air inside the DSTF cavity and included it in the thermal and energy model of the building. A model for single-storey buildings was presented by Saelens [7], he created a computational algorithm for two dimensional double-skin façades with both mechanical and natural ventilation. In Bel- gium, Gratia et al. [8] developed a model for thermal efficiency and cooling (heating) load according to the season. Grabe [9] developed a practice for modelling the temperature and air behaviour in DSTF. More modern works include computational fluid dynamics models, which can calculate airflow in DSTF cavity more accurately as compared to abovementioned mod- els [10], [11], [12]. Manz et al. [13] used an algorithm to calculate the heat transfer from a natural convec- tion in DSTF. The CFD method can offer much more detailed results especially for airflow through shading devices, recirculation zones or when the wind profile is irregular [13], [14], [15]. A brief document was issued in 2007 by the Commission of the European Coun- cil [16] with guiding principles for the construction of DSTF. In the case of double-skin transparent façades using an alternative source of solar energy, the transforma- tion of short-wave solar radiation into long-wave heat radiation is a natural physical phenomenon [17], [18]. The exploitation of this physical phenomenon with contribution of quantified dynamics of air flows is con- ditioned by the development of the theory of physical cavities. The double-skin transparent façade participates in energy conservation of buildings in winter periods by its energy, which is gained from renewable energy sources – solar radiation and also by the transfor- mation of solar radiation into heat radiation in the cavity of the façade. Well-designed aerodynamics of cavity can also meaningfully decrease the heat load of a building in summer seasons [19]. The double-skin transparent façade offers the possibility of natural ventilation, which is directly connected to the outside climate. At the same time, it delivers a new quality of psycho-physiological comfort in the working space. It is characterised by a better connection of an artificial architectural environment with nature. The main objective of this article is the new façade technology for buildings, that is the double-skin trans- parent façade in Figure 1. The methodology of the paper is a theoretical anal- ysis based on scientific disciplines and in-situ measure- ment: • building solar thermal technology in a more complex perception, including the input of solar radiance, • aerodynamics of buildings in „a more complex per- ception than that represented by a rigid model“ with an external pressure coefficient cpe (-), quantified by an aerodynamic coefficient of overall pressure cp = cpe − cpi (-), in which the knowledge of the aerodynamic coefficient of internal pressure cpi (-) substitutes for the imperfection of a rigid model, • aerodynamics of a cavity, quantified by the overall aerodynamic resistance of the cavity Z, which is the sum of the friction resistances and local resistances lengthways to the flow trajectory in the cavity. 3. Theoretical background The physical theory of cavities is the base idea of the double-skin transparent façade. The paper deals with a naturally ventilated double-skin transparent façade with a corridor-type cavity (cavity width 0.5 ≤ b ≤ 1.5 m) and open circuit (the whole volume of air entering the cavity is air flowing from the out- door climate, also, the entire volume of air through the cavity is conducted to the outdoor climate) in Figure 2. A general correlation of the temperature in the cavity (Figure 2) is visible if the external air enters the cavity: θa,OUT LET − θa,INLET = θa,OUT LET − θae = τg · Im mean Um (1 − e− mean Um·L qm·c H), (1) where θa,OUT LET is the air temperature from the out- let of the cavity [°C], θa,INLET is the air temperature from the inlet of the cavity [°C], τg is the the overall transmission coefficient of the glazed system of the front – outer transparent wall [-], Im is the mean in- tensity of global solar irradiation on the outer vertical transparent wall [W/m2], mean Um is the mean heat transfer coefficient of the bounding structures of the cavity [W/(m2 · K)], L is the length (horizontal) of the cavity division [m], qm is the mass air flow rate through the cavity [kg/s], H is the height of the cavity [m], c is the mass heat capacity of the air [J/(kg · K)]. The energy regime of these cavities depends on the air flow rate qm [kg/s], qV [m3/s], which is determined by the dynamics of the air flowing through the cavity 460 vol. 62 no. 4/2022 Functional aerodynamics of a naturally ventilated double-skin façade Figure 1. Illustration of classic transparent façade and double-skin transparent façade, a) classic transparent façade, b) double-skin transparent façade: 1A global solar radiation transmitted into the building, 1B – global solar radiation transmitted to the cavity, 2 – heat flux by transfer to the exterior, 3 – heat consumed to heat the air and conducted to the outside climate, 4A – heat load of the building in summer, 4B – heat flux through the transfer to the building – heat load of the building core during the summer. Figure 2. Quantification of aerodynamic and energy regimes of DSTF with open circuit. Width of cavity is 0.5 ≤ b ≤ 1.5 m (corridor type cavity). Height of the cavity H [m] is identical to floor height. 461 M. Franek, B. Bielek, M. Macák, J. Klem Acta Polytechnica based on natural convection, wind, and their combi- nation. 3.1. Aerodynamic quantification of the cavity It is necessary to know the total aerodynamic resis- tance of the cavity for the quantification of the air flow rate qm [kg/s] under the windless conditions: Z = 1 + ∑ Zl + ∑ Zm = 1 + ∑ λ̄ · (H + b) Dh + 10∑ x=1 ξx, (2) where ∑ Zl is the sum of the frictional resistance along the entire height of the cavity [-], ∑ Zm is the sum of the local aerodynamic resistance [-], H is the cavity height [m], b is the cavity width [m], λ̄ is the coefficient of the friction along the entire height of the cavity [-], λ̄ = f(Re), Re [-] is Reynolds number, as mentioned in Figure 3, ξx is the aerodynamic coeffi- cients of local resistance along the airflow trajectory through the cavity [-] as explained in Figure 4, Dh is the aerodynamic cavity diameter [m]. The resistances are longitudinally directly propor- tional to the length of the trajectory of the movement of the airflow in the cavity H + b (Eq. 2), as shown in Figure 2, and which is in contrast to the diameter of the cavity Dh [m]. Local resistances are connected to the exact space of the airflow movement inside the cavity and are made of parts where the speed or path of the airflow differs (Fig. 2). It is essential that the total aerodynamic resistance Z must be lesser than the convective air buoyancy power of the air in the cavity, if we want to achieve the required airflow through the cavity in all climatic situations (including the windless situation): max Z = 1 + ∑ λ. (H + b) Dh + n∑ x=1 ξx < 18 , (3) Two local resistances are vital in order to calculate Z (Eq. 3): (1.) the local aerodynamic resistance at the inlet of the channel ξ1 with rain protective louvers A ξ2, which characterizes the turbulence at the outlet of the channel B (Fig. 4), (2.) the local aerodynamic resistance at the outlet channel from the cavity ξ10 with a rain louver A ξ9, which is responsible for the turbulence of the air flow from the output channel G (Fig. 4). The rain louvers at the inlet and outlet have a role to prevent the penetration of rainwater from wind-driven rain into the cavity. The aerodynamic coefficients of the local resistances are determined in accordance with the aerodynamic theory shown in Figures 5 and 6. The slats of louvres can be designed as classical rain screens or aerodynamic slats. Their local aerodynamic resistances at the inlet of a distribution channel are shown in Figure 7, and the outlet of the distribution channel is shown in Figure 8. From the analysis of drag coefficients, conventional rain louvers on an inlet of DSTF are not optimal. It can be summarized as follows: (1.) The optimal ratio to the total area with conven- tional rain louvers cannot be ensured (Eq. 4): a A .100 ∼= 80 % , (4) where a is a net area of openings for the air flow, and A is the total inlet area of the air, including the louvers. (2.) Typical rain louvers lead to a high local drag coefficient at the inlet (ξ1), and especially at the outlet (ξ10). These facts affect the overall aerodynamic drag of the cavity to such a large extent, that it is not possible to ensure the requirement given by Eq. 5: opt.Z = 1 + ∑ λ. (H + b) Dh + n=10∑ x=1 ξx = 18 , (5) The convective buoyancy of air is still higher than the overall aerodynamic resistance of the cavity Eq. 5. It means that the convective movement of the air flow is ensured in the cavity naturally without any wind. But the application of conventional louvers leads to the large drag coefficient, which blocks the naturally con- vective flow. Therefore, it is recommended to use the aerodynamic louvers with local resistances of ξ1 ≤ 1.0 and ξ10 ≤ 3.0 at the inlet and outlet. For the calcula- tion and verification, a numerical approach it can be used. To ensure a simulation with accurate boundary conditions, the Computational Fluid Dynamics (CFD) can be used as one possible method. Figure 9 shows the simulation performed in FLOTRAN. The total drag of the cavity of the convective air flow is shown in Eq. 6: vam = √ g.H.∆θam Z.θam,T , (6) where ∆θam is the increase in temperature in the cav- ity [K], g is the gravitational acceleration [9.81 m/s2], ∆θam = θa,OUT LET − θae, (7) where ∆θam,T is the temperature at the point in the centre of mass A = f(H, ∆θam) [°C]: θam,T = θae + θa,OUT LET − θae 3 . (8) From the velocity of the convective air flow vam [m/s] and cross-section of the cavity of the double- skin façade A = L.b [m2], the flow rate in the cavity 462 vol. 62 no. 4/2022 Functional aerodynamics of a naturally ventilated double-skin façade Figure 3. Coefficient of friction as a function of Re number. Figure 4. Description and quantification of aerodynamic resistances. 463 M. Franek, B. Bielek, M. Macák, J. Klem Acta Polytechnica Figure 5. Friction resistance along the height of the convective air flow (Re – Reynolds number [-], vam – air flow velocity in the cavity [m/s], ν – coefficient of kinematic viscosity of air [m2/s], g – gravitational acceleration coefficient [9.81 m/s2], θam – increase in tempretature in the cavity [K], θam,T – temperature in the centre of mass A = f(H, ∆θam) [°C]). Figure 6. Coefficients of local resistances ξ2, ξ3, ξ4, ξ52, ξ6, ξ7, ξ8, ξ9 [-] in the air flow movement (a – net area opening for air movement, A – total area of the air inlet including its solid parts, b – planar width of the rectangular cross-section, h – height of rectangular cross section). 464 vol. 62 no. 4/2022 Functional aerodynamics of a naturally ventilated double-skin façade Figure 7. The local drag of the air flow at the inlet. Left picture illustrates the conventional rain louvers, Right picture shows aerodynamic louvers (A – total area of the inlet air, including the louvers, a – net opening area for air flow). Figure 8. The local drag of the air flow at the outlet. Left picture shows conventional rain louvers, Right picture illustrates aerodynamic louvers (A – total area of the inlet air, including the louvers, a – net opening area for air flow). Figure 9. Simulation of the local aerodynamic drag coefficients ξ1 and ξ10 in ANSYS FLOTRAN. Velocity contour plot at the inlet [20]. 465 M. Franek, B. Bielek, M. Macák, J. Klem Acta Polytechnica Figure 10. Aerodynamic loads on the DSTF with open circuit under wind condition a) Leeward side of the building, b) Windward side of the building. can be quantified: qV = A.vam = L.b.vam, (9) qm = qV .ρam,T = L.b.vam.ρam,T , (10) where ρam,T is the air density in the centre of mass „C“ at the temperature θam,T [kg/m3] in Figure 2. The main requirement of the air flow in the cavity of DSTF in windless climate conditions is that Z [-] must be less than the force of the convective air buoy- ancy [6]. Natural convection is a phenomenon, which describes the dynamics of fluid (air) and depends on the difference of the temperature and density as a consequence of gravitational forces. 3.2. Aerodynamic quantification of the building – external pressure coefficient The external pressure coefficient has to be known to determine the airflow rate in the cavity qm [kg/s] for wind conditions (Fig. 10): cpe = p − p0 1 2 ρ0.v2 w,0 , (11) The total pressure is defined as: cp = cp + cpm, (12) where cpm is the cavity pressure coefficient [-]. Air flow rate is defined as: qV = 2 (L.h) . √ cp v2 w,z.ρae 2 , (13) where vw,z is the gust velocity of wind [m/s], and ρae is the density of the external air [kg/m3]. Wind loads on buildings can be evaluated from codes [21], wind tunnel tests, CFD and in-situ mea- surements. The data contained in standards are issued from wind tunnel experiments, performed on an iso- lated building in open exposure. Measurements by several works have shown that wind loads on buildings in close vicinity are considerably different from those on an isolated building. These effects arise because of the modifications of the flow field due to the surround- ings. The experimental determination of the pressure coefficients is a typical aerodynamic task. It is solved on a „rigid model“ in a wind tunnel. Boundary layer wind tunnel (BLWT) is an experimental facility used for modelling the Earth’s atmosphere and it allows the experimental measurement of static and dynamic effects of wind on scale models – Figure 11. Wind tunnels with a developed atmospheric boundary layer provide a complete statistical description of the load test objects in a wind flow with a natural structure. For acquisition of external pressures from the mea- surement, a pressure transducer, which is conducted with plastic tubes and pressure taps with the rigid model, is used. The transducer records differential pressure. Then, according to Eq. 11, the differential pressure is divided by dynamic pressure. It is the prin- ciple of experimental measurement with a pressure transducer. The simulated boundary layer requires similarity criteria in four basic parameters: 466 vol. 62 no. 4/2022 Functional aerodynamics of a naturally ventilated double-skin façade Figure 11. View of the measured buildings in the BLWT in Bratislava [22]. Figure 12. Properties of ABL in BLWT Bratislava: a) Mean wind velocity, b) Intensity of turbulence profile [23]. (1.) longitudinal mean velocity profile, (2.) longitudinal turbulence intensity profile, (3.) turbulence integral length scale, (4.) non-dimensional power spectral density function. Longitudinal mean wind velocity follows the log- arithmic law according to Eq. 14. The longitudinal turbulence intensity is found to agree well with Eq. 15. The illustrative profile of mean wind velocity and turbulence intensity is in Figure 12. U(z) = u∗ κ ln z z0 , (14) Iu = √ u′2 Uz , (15) where U(z) is the mean wind velocity at the height z [m/s], u∗ is the shear velocity [m/s], z0 is the rough- ness length [m], Iu is the longitudinal turbulence in- tensity [-], √ u′2 is RMS of the turbulent velocity fluctuations [m/s]. Non-dimensional power spectral density is illustrated in Figure 13. The second possible way to quantify the aerody- namic coefficients of the external pressure on the surface of a building envelope is a simulation using Computational Fluid Dynamics (CFD). CFD is a fluid mechanics division that uses numerical analyses and algorithms to solve problems including fluid flow, heat and mass transfer and other related phenomena. There are some mathematical evaluations of an at- mospheric flow simulation [25], [26]. For a simulation of convection, Navier-Stokes equations are used. The flow is treated as incompressible because the Mach number for our tasks is below 0.3. The Navier-Stokes equations for incompressible flow can be written as: ∂p ∂t + ∂ ∂xi (ρūi) = 0 , (16) ∂ ∂t (ρūi)+ ∂ ∂xj (ρūiūj) = ∂ ∂xj (σij)− ∂p̄ ∂xi − ∂τij ∂xj , (17) where p is the pressure of the flow [Pa], t is the time duration [s], x is the dimension [s], u is the velocity of flow [m/s], ρ is the density of flow [kg/m3], σij is the stress tensor [-], τij is the subgrid-scale stress [-]. In general, there are four methods for solving N-S equations. First one is the Direct Numerical Sim- ulation (DNS), when a problem in space and time is 467 M. Franek, B. Bielek, M. Macák, J. Klem Acta Polytechnica Figure 13. Power spectral density in BLWT Bratislava [23]. Figure 14. Distribution of external pressure coefficient on the envelopes of a group of buildings received from the ANSYS Fluent [22]. Figure 15. Distribution of external pressures of the building of the National Bank of Slovakia (NBS) in Bratislava on the 17th floor, H = 56.3 m [24]. 468 vol. 62 no. 4/2022 Functional aerodynamics of a naturally ventilated double-skin façade Figure 16. Geometry of DSTF and drawing of measured points. solved, the second one are Reynolds Averaged N-S equations (RANS). The third method is a combina- tion of both previous methods, which simulates large vortices and modells small structures with the help of Reynolds equations. It is called the Large Eddy Simulation (LES). Current methods for solving RANS are Scale-Resolving Simulation models (SRS). An ex- ample of a graphical output of a quantification of external pressures on a building façade from the CFD calculation program is documented in Figure 14. To obtain the overall aerodynamic pressure coef- ficient, it is necessary to evaluate the pressure over the entire height of a building, which is documented in Figure 15. The CFD model has to be correctly validated with experimental or situ measurements to achieve correct results. The validation procedure in- volves an exact modelling of the boundary conditions with experimental or situ measurements. The results are then statistically evaluated to see if they correlate with the experiment. Deviations from the experiment are then assessed, and a numerical model is calibrated to achieve the most accurate results. 4. In situ measurement-preparation An in-situ measurement experimentally confirmed the above theory on a double-skin facade with a corridor- type cavity width = 600 mm, with an effective height of the cavity identical to the height of the floor = 3450 mm, Fig. 16. The total aerodynamic resistance of the facade was evaluated according to Eq. 3 max Z = 1 + 0.20 + 14.94 = 16.14 < 18, which expresses the convective buoyancy of the air. It can be stated that in terms of functional aerody- namics of the cavity, the airflow through the cavity is ensured in any climatic situation. The measuring setup monitored the temperature and aerodynamic regimes of DSTF during 18 months on the 17th floor of a southwest façade, which was 56.3 m in height. The 469 M. Franek, B. Bielek, M. Macák, J. Klem Acta Polytechnica Figure 17. Measured variables from the experiment for the typical period of clear windless warm weather. recorded parameters were the temperature, relative humidity, and wind velocities in the control points, as is shown in Fig. 16. Due to the large volume of measuring points and results, we will focus on the critical state of windless conditions in this article. When the airflow in the cav- ity of DSTF is based on natural convection. Recording of the measured variables in the cavity for the period of clear windless warm weather is illustrated in Fig. 17. 5. Results and discussion The following conclusions were found based on long- term measurements of temperatures, the effects of solar radiation and relative humidity in-situ conditions when the facade was treated under windless conditions, Fig. 18: • the convection occurs in the cavity at every time step with the velocity ranging from 0.05 ≤ v [m/s] ≤ 0.2 to 0.3, • the convective velocity through the cavity increases due to the growth of global solar radiation, • the energy regime in the cavity is characterised by inhomogeneity due to the alternating position of the air inlet and air outlet modules, • in the cavity, there are 3 characteristic zones for aerodynamic and thermal regimes: zone of increasing temperatures (around 29 °C) along the height of the cavity in the inlet – the movement of convective airflow, a large area with temperatures in the air outlet-stagnation of air (around 47 °C) a small area with particularly high tempera- tures in the upper part of the inlet (around 53 °C) – the state of no flow, stagnation of air. This means a 29 °C temperature gradient as compared to the outside temperature. Based on these results, we can evaluate a constant airflow in any climatic situation, even in windless conditions. It confirms the correct physical function of the cavity and testifies to the quality of DSTF in terms of its aerodynamic dimensions. 470 vol. 62 no. 4/2022 Functional aerodynamics of a naturally ventilated double-skin façade Figure 18. The resulting temperature zones during the clear windless warm weather. 6. Conclusions The theory and practice of natural physical cavities is a very significant area of the future façade technologies of intelligent buildings. It is directly connected with two very efficient and available alternative energy sources, solar radiation and wind energy, but most often, their very significant combinations. Natural physical cavities allow for wide modifications in the creation of the new façade technology of buildings in the material-structural and shape-aesthetic concepts of modern architecture. The functional aerodynamics of the cavity of the DSTF in any climatic situation (even in a critical windless state) is an essential precondition for its optimal temperature and energy regime. It can be seen from the experience of the implementation of naturally ventilated DSTF in the modern world that underestimating the dimensioning of elements can lead to severe defects. It can lead to an uncomfortable temperature regime (stagnation of hot air in the cavity in summer). To quantify the temperature and energy regime of DSTF, we must know two basic aerodynamic inputs: (1.) aerodynamic quantification of the building char- acterised by an external pressure coefficient, which we can obtain from experimental measurements in the BLWT or from CFD simulations, (2.) aerodynamic quantification of the interspace char- acterised by its total aerodynamic resistance. With their help, we can quantify the air flow through the cavity, the increase in temperature and the result- ing energy efficiency of the façade. In-situ measure- ments of the temperature, aerodynamic, and energy regime of the DSTF during its operation can serve as a standard for debugging and refining calculation procedures and simulation programs. These results significantly contribute to the development of the sci- ence and practice. The design of DSTF has to integrate the multidisci- pline approach to ensure the low energy needs. Only a global view can provide a development in the field of architecture. Acknowledgements This work was supported by the Scientific Grant Agency MŠVVŠ SR and SAV under VEGA 1/0113/19, Slovak Research and Development Agency under the contract No. APVV-21-0144. References [1] B. Bielek, J. Híreš, D. Lukášik, M. Bielek. Development of technology in architecture for sustainable society. Nakladatel’stvo STU, Bratislava, 2012. [2] B. Todorovic, B. Maric. The influence of double facades on building heat losses and cooling loads. 471 M. Franek, B. Bielek, M. Macák, J. Klem Acta Polytechnica Faculty of Mechanical Engineering, Belgrade University, Belgrade, Yugoslavia, 1999. [3] D. M. Arons. Properties and applications of double-skin building facades. Ph.D. thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/8724. [4] G. Gan. Thermal transmittance of multiple glazing: computational fluid dynamics prediction. 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Cambridge University Press, 2011. 472 http://hdl.handle.net/1721.1/8724 https://doi.org/10.1016/S1359-4311(01)00016-3 https://doi.org/10.1106/CU0X-XL16-6QTA-29QC https://doi.org/10.1016/j.enbuild.2003.10.008 https://doi.org/10.1016/S0378-7788(02)00065-8 https://doi.org/10.1016/j.buildenv.2010.09.015 https://doi.org/10.1016/j.buildenv.2010.02.014 https://doi.org/10.1016/j.buildenv.2014.08.007 https://doi.org/10.1201/9781003078852-71 https://doi.org/10.1016/j.buildenv.2012.04.007 https://doi.org/10.3390/en8064882 https://doi.org/10.1080/17512549.2007.9687267 https://doi.org/10.4028/www.scientific.net/AMR.1057.137 https://doi.org/10.4028/www.scientific.net/AMR.1057.137 Acta Polytechnica 62(4):459–472, 2022 1 List of Acronyms 2 Introduction 3 Theoretical background 3.1 Aerodynamic quantification of the cavity 3.2 Aerodynamic quantification of the building – external pressure coefficient 4 In situ measurement-preparation 5 Results and discussion 6 Conclusions Acknowledgements References