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Curved and Layer. Struct. 2022; 9:40–53 Research Article Boris Bielek, Daniel Szabó, Josip Klem*, and Kristína Kaniková Application of physical theory of cavity in the construction of double skin facades https://doi.org/10.1515/cls-2022-0004 represents a very important indirect - isolated passive solar Received Aug 06, 2021; accepted Sep 29, 2021 system if the flow of medium - air is realized by natural convection, or a hybrid solar system if the flow of medium - Abstract: The article deals with the issue of double skin air is forced. In both cases, this solar system works on the transparent facades as a new technological-operational principle of a simple solar collector  – Figure 1. Glass system of transparent exterior walls. Especially of high- system (single or double) of exterior transparent wall has rise buildings, which with its operating modes ingeniously the function of the solar radiation collector separating the uses a renewable source of solar energy to reduce the en- cavity from the exterior. The function of the absorber is the ergy needs of the building. The basic precondition for the surface and the accumulator is the mass of the inner heat correct function of the double skin facade is its functional storage wall of the composite structure in its opaque part, aerodynamics in any climatic conditions of the outdoor separating the cavity from the core of the building and also climate. In the critical state of windlessness, the aerody- the shade in front of the transparent surfaces. The function namic quantification of a double skin facade is the total of the regulator and distributor of this solar system is a aerodynamic resistance of the cavity, which consists of the complex mechanism of air holes, vents, blinds and ducts. aerodynamic frictional resistances along the length of the It is based on the theory of aerodynamics, providing oper- air flow line and local aerodynamic resistances of the cav- ational - functional modes of the facade, either with the ity. The article analyses the functional aerodynamics on influence of subjective factor or at a higher level without two frequented types of double skin facades with a nar- it, automated environmental management systems energy row type and corridor type cavity. At the end it confronts processes in an intelligent building. functional aerodynamics with the results of their tempera- In the system of a double skin facade, an indispens- ture, aerodynamic and energy regime obtained from in-situ able element is sun protection (adjustable blinds, pull-out experiments. blinds, etc.). Movable shading systems allow connection Keywords: double skin facade, double skin facade cavity, to a suitable automated control system. This presentation renewable energy source, functional aerodynamics of the intelligent cooperation of the building structure and technical equipment of the building, whose aim is to en- sure the required conditions for the creation of an artificial living - architectural environment depending on the chang- 1 Introduction ing conditions of the outdoor climate, is also inherent in a double skin facade. th At the end of the 20 century, double skinned transpar- In any case, the double skin facade with its energy ent facades began to be applied in the facade technology gains from an alternative energy source - solar radiation, of buildings in the developed countries of the world. Con- contributes to the energy savings of the building in win- struction of double skin facades is based on the theory of ter and also by transforming solar radiation into thermal physical cavities [1, 2]. As a rule, it is basically an energy radiation in the cavity of the facade and justified aerody- impact cavity, the primary function of which is energy. In namics in it, contributes to significant reduction of heat its integrated functions, the double skin facade system also load buildings in summer [1, 3, 4]. The basic precondition for the correct function of the double skin facade is its functional aerodynamics, which Boris Bielek, Daniel Szabó, Kristína Kaniková: Slovak University ensures the constant movement of the air flow through of Technology in Bratislava, Faculty of Civil Engineering, Depart- its cavity in every climatic situation. The critical state is ment of Building Structures without wind, when the movement of air through the cavity *Corresponding Author: Josip Klem: Slovak University of Tech- of a double skin facade is based on natural convection. nology in Bratislava, Faculty of Civil Engineering, Department of Building Structures, E-mail: email@example.com Open Access. © 2022 Bielek et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 License Application of physical theory of cavity in the construction of double skin facades | 41 The functional aerodynamics of the double skin facades (DSF) comes from their correct geometry- construction design (width and effective height of the cavity, geometry of the inlet and outlet openings including the rain louvers and protective screen against birds and insects, type and position of the sun protection device at the cavity and glazing properties), ventilation mode, building orientation, structure and façade design . Ac- cording to Manz and Frank  DSF are in terms of building physics complicated constructions and their construction design must be based on the theory of the natural physical cavities. Mechanism of the airflow in the double skin transpar- ent cavity can be based on: the natural convection (convec- tive buoyancy) during windless condition, natural convec- tive air flow from the pressure effect form the wind, forced airflow mechanism or combination airflow regime [ 1, 7]. It is not easy to regulate the natural airflow at the cavity and it is not smooth either, because it depends on external weather condition . Mechanical airflow in the cavity is part of the building heating, ventilation and air condition system (HVAC). It can be used for hot air ventilation preheating a fresh outside air in the cavity . Airflow in the double skin transparent facade cavity is affected with several fac- tors which Hazem et al.  divide into the three groups: geometry (inlet and outlet opening dimensions, width of the cavity, angle of the sun protection device and their dis- tance from the inner and outer glazing), material properties (the optical properties of the glazing, the material emissiv- ity, the refraction coefficient and the diffuse fraction) and meteorological parameters (impact of incidence of the solar radiation, angle of incidence of the solar radiation, external temperature, wind direction and velocity). The dimensions (width of the facade, height of the fa- cade, weight of the cavity, inlet and outlet opening dimen- sions) and the size of the window opening into the interior have a primary effect on the natural airflow at the cavity . At the larger width of the cavity, the airflow is more tur- Figure 1: Confrontation of the physical theory of cavity on the prin- bulent and cause that the velocity at the cavity is increased. ciple of a single air collector and a double skin facade A - hot air There is also smaller increase in the average air temperature ventilation mode during the winter period B - circulating air heating in the cavity . The effect of the width of the cavity on the mode during the transition period C - passive cooling mode during airflow was investigated by Rahmani et al.  who used the summer period 1 - global shortwave solar radiation, 2 - reflected shortwave radiation, 3 - glass absorbed radiation, 3a - longwave simulation programme FloVENT with 5 alternative width radiation radiated to the exterior, 3b - longwave radiation radiated (100 mm, 300 mm, 500 mm, 1000 mm and 1500 mm) with to the interior, 4 - transmitted shortwave radiation transformed in typical glazing and reflective glazing at the exterior wall of the cavity into longwave thermal radiation 5 - collector, 6 - absorber, the DSF. Torres et al.  used simulation software TAS in 7 - accumulator, 8 - distributor, 9 - regulator, 10 - intensity of trans- which they made a simulation with four different width of mitted global solar radiation, 11 - heat flow by transmission to the exterior, 12 - heat flow by transmission to the building core, 13A - the cavity (400 mm, 600 mm, 800 mm a 1000 mm) and with heat consumed for heating the air in the cavity - used for hot air ven- three alternative inlet and outlet opening on the two types tilation, 13B - heat consumed for heating the air in the cavity - used of double skin facades (corridor type – one floor and multi- for heating by circulating air, 13C - heat consumed for heating the storey facade) to study natural airflow at the cavity. They air in the cavity, which is dissipated to the exterior, 14 - circulating air supply from the building core, 15 - ventilated air supply from the north side - passive cooling. 42 | Bielek et al. have discovered that at the corridor facade type wider cav- identical to one floor and multistorey facade and concluded ity (1000 mm) functions better than narrower cavity (400 that with increasing area of the openings in the exterior mm). In the case of multistorey facades on higher floors, facade, the intensity of the airflow at the cavity caused by there is a considerable increase on the air temperature in the chimney effect increases. Gratia and De Herde [ 13] anal- the cavity, due to which the convective buoyancy also rises, ysed size of the openings on the facade during four sunny which also increase the airflow at the cavity. days (March, June, September, December) and concluded Gratia and De Herde  analysed 4 different width of that the decrease in air temperature in the cavity did not the cavity (300 mm, 600 mm, 1200 mm and 2400 mm) in Bel- change linearly with increasing size of the inlet and outlet gium. They used simulation software TAS and concluded opening. that when the cavity width increases, the air temperature The airflow in the DSF cavity is significantly affected in the DSF decrease and the temperature decline in the cav- by the sun protection device situated at the cavity. Mingotti ity varies linearly with the size of the inlet and the outlet  claims that properly designed sun protection device at airflow openings. Radhi et al.  showed based on simula- the DSF exposed to solar radiation in warm sunny seasons tion, that optimisation of cavity size between 700 mm and helps airflow. In case of intensive solar radiation during 1200 mm can give a balance between solar gain and heat warm summer days there may be an excessive increase in transmission. air temperature in the cavity, which can also have a nega- Besides the width of the cavity the effective height of tive effect on the lifetime of the components situated in the the cavity is also determinative due to buoyancy effect dur- cavity . Gratia and De Herde  found out that when ing the windless condition. The higher height of the cavity the sun protection device is activated, there may not be the better buoyancy effect and thus a higher air velocity sufficient airflow in the cavity. Published works [ 5, 7, 8] say at the cavity. Ding et al.  researched the natural cross that the heat absorbed on the surface of the sun protection – ventilation of the building at the south oriented DSF fin- device from the solar radiation increase the air temperature ished by a solar chimney. They made an experiment on a and chimney effect at the cavity. Barbosa and Ip [ 5] and Jiru prototype scale model and made a simulation by numerical  have written about the suitable location of sun protec- computational uid fl dynamics (CFD). The results showed tion device in the cavity. According to them the shading that the height of the solar chimney should be more than device located in the middle of the cavity allows a smoother two storeys, in order to increase the airflow rate in the cavity flow on both sides of the shading device and ensure a lower and achieve a positive distribution of pressure differences surface temperature on the inner glazing. When the shad- (between indoor and outdoor). ing device is placed closer to the inner wall, it may cause For the ventilation efficiency of the DSF the inlet and a risk of heat transfer to the interior (it could be desirable outlet airflow opening are significant. During colder peri- in winter), at this position the turbulent boundary layer ods of the year the smaller openings are more appropriate caused by the blinds overlaps with the turbulent boundary to minimalize heat loss by convection, while in warmer layer of the glass surface and the temperature at the cavity periods of the year the larger ones are more suitable to min- rises. Jiru  claims that the angle of the slat has a lower imize the risk of overheating. The larger area for the inlet effect on the temperature distribution then the position of and outlet openings reduces the airflow resistance which the blinds and that by changing the angle of the slat the leads to a larger amount of airflow into the cavity. The size curves of the velocity profiles of the airflow in the cavity of the inlet opening (actual dimensions including associ- are slightly shifted. Barbosa and Ip  analysed the appro- ated components in these openings) has direct effect on priate angle position of slat of the shading device. They the natural airflow and maximizing the area of the outlet claim that in terms of air circulation, it is more suitable if opening at the upper part of the DSF assists with the higher the slats are in the vertical position, in horizontal position airflow velocities [ 5, 9, 16]. According to Tao et al.  the they cause obstacles to the airflow at the cavity. Hazem optimal height of the opening is about 0.2 – 0.3 m. In addi-  wrote about the ideal angle of the slat in terms of the tion to the size of the openings, the associated components heat ux fl transmitted to the indoor environment. Safer et al. in these openings also have an effect on the air flow, such  analysed the effect of the position of the air inlet and as grids at the inlet and outlet of the air distribution ducts, outlet openings through 2D configuration DSF according floor and ceiling grilles of the distribution ducts. Increase to the slat angle inclination and the location of the blinds the area of the vent openings leads to a laminar airflow in the cavity. Gratia and De Herde  studied the effect of with higher velocity . Torres et al.  researched the the location and colour of the shading device in the cavity effects of the dimensions of the inlet and outlet air opening on the cooling demand of the office building. The results on the facades with corridor type with an effective height showed that the position of the blinds in the cavity and Application of physical theory of cavity in the construction of double skin facades | 43 their colour influence the surface temperature of the inner ing energy simulation and CFD programmes. Alberto  glazing. Ji et al.  researched the effect of the slat an- performed simulation used DesignBuilder software with gle of the shading device on the airflow at the DSF cavity EnergyPlus integration, in which he evaluated the effects using CFD simulations in 2D, which they compared with of geometry, airflow trajectory, width of the cavity, areas experimental measurement and predictions from the nodal of the facade openings and glazing type on facade perfor- model. The results showed that presence of the blinds at mance. Jiru and Haghighat , applied a zonal approach the cavity leads to 35% reduction of the natural airflow in for airflow modelling and air temperature at the ventilated the cavity and 75% reduction of the heat load of the interior. DSF. They used equitation of zone airflow and power low Small changes of the convective heat transfer coefficient for the airflow calculation with integrated shading device. were caused by the rotation of the blinds to various angles. For temperature distribution in the DSF system they used Pappas a Zhai  wrote that when choosing the type of the the energy equitation in the zone. The calculated tempera- shading device, it should be considered how the device will ture distributions were verified using measured values and affect airflow in the cavity and it should also be taken into parametric studies. Von Grabe , developed simulation account the colour of the shading device and thus its ability algorithm for the thermal behaviour and airflow character- to absorb solar gain that will subsequently radiate from it. istics of DSF with an integrated shading device. In order to Eicker et al. , compared an effect of a shading device on determine the degree of accuracy of the algorithm, a dou- the indoor thermal comfort in the mild climate in Stuttgart, ble facade has been monitored under controlled conditions Germany, on a single skin facade with external shading and the results have been compared with the predicted device and on a DSF with a shading device at the cavity. values for several design situations. The results showed that the shading device can effectively reduce the total solar energy transmission to the building in summer period even with slightly opened blinds, for both 2 Methods cases simple and double skin facade. The highest energy priority is to reduce shortwave solar radiation, which is the 2.1 Aerodynamic quantification of double dominant heat ux. fl Poirazis [ 23] says that the choice of the skin facade suitable type of the glazing and shading device is decisive for the proper function of DSF. The glazing properties (ab- To work properly, double skin facade has to have func- sorption, reflection, and convection) and its geometry can tional aerodynamics, which means a constant flow of the affect the airflow velocity field at the cavity. For more exten- air through its cavity in every climatic condition. sive projects it is useful to find the correct combination of The aerodynamic quantification of a double skin trans- glazing and the position of the shading device at the cavity. parent facade is its total aerodynamic resistance Z (-), in Experimental and numerical models and experiments which: for naturally ventilated facades with shading devices and mechanically ventilated facades are used for study and – aerodynamic frictional resistances along the length the optimisation of the DSF . Significant process has L (m) of the airflow line Z (-) along the double skin been made in terms of evaluation methods, in particu- facade height of section H (m) characterized by a lar advances in analytical tools for computational uid fl coefficient of friction resistance λ (-), dynamics (CFD), such as analytical and lumped models, – local aerodynamic resistances Z (-) characterized non-dimensional analysis, network models, control vol- by aerodynamic coefficients of local resistances ξ (-) ume models, zonal models, and computational uid fl dy- namics (CFD), which allows a better understanding of the (︁ )︁ complex behaviour of DSF and its interactions with the ∑︁ ∑︁ ∑︁ ∑︁ λ · (H + b) Z = 1 + Z + Z = 1 + + ξ (−) 1 m x building without resorting to expensive experiments [5, 24]. x=1 The evaluation software tools should meet all three levels (1) of modelling: spectral optical model (using the spectral where: ∑︀ method), thermodynamic and uid fl dynamics (using CFD) Z - sum of the frictional resistances along the height of and the building energy simulation (using building energy the cavity (-), ∑︀ simulation tools). Compared to nodal models, which are Z - sum of the local aerodynamic resistances (-), often used in building design, this method significantly H - effective height of the cavity (m), increases the reliability of prediction . Pappas and Zhai b - width of the cavity (m), 2008  used in their research the combination of build- 44 | Bielek et al. Figure 2: Basic scheme for the definition and quantification of aerodynamic resistances of double skin transparent facade with open circuit A – convection anti rain or aerodynamic shutter, B – inlet air channel, C – bird and insect net, D – cavity of climate facade, E – walkable removable – openable grate, F – floor grate, G – outlet air channel, H – height of the cavity section (m), h – height of the openings of the distribution air channels (m), b – width of the cavity, L – length of the cavity section (m), M – air flow trajectory. ξ - aerodynamic coeflcient of local resistance of airflow, in particular: ξ - at inlet on aerodynamic louvers "A", ξ - on protective screen "C" at inlet, ξ - where flow 1 2 3 direction changes from inlet channel "B" to the cavity "D", ξ - on grille - grid "E" during flow from inlet channel "B" to the cavity "D", ξ - 4 5 upon sudden increase in diameter during movement of airflow from inlet channel "B" to cavity "D", ξ - on grid "F" during flow from cavity "D" to outlet channel "G", ξ - upon sudden decrease in diameter during movement of airflow from cavity "D" to outlet channel "G", ξ - 7 8 upon change of direction of movement from cavity "D" to outlet channel "G", ξ - on protective screen "C" at outlet, ξ - on aerodynamic 9 10 louvers "A" at outlet. λ - coefficient of the friction along the height of the cavity 2.2 Quantification of aerodynamic (-), λ = f(Re), Re (-) is Reynolds number, which gives the resistances of double skin facade ratio of inertial forces and viscous forces acting on the flow of liquids and its value determines whether uid fl flow is The methodology of quantification of aerodynamic resis- laminar or turbulent, tances of the cavity of a double skin facade will be docu- ξ - aerodynamic coefficients of local resistances along the mented on the facade according to Figure 2. This is a quan- height of the air flow trajectory through the cavity (-) as tification of two basic types of aerodynamic drag: explained in Figure 2, - aerodynamic frictional resistance along the height of ∑︀ ∑︀ λ·(H+b) D - aerodynamic diameter of the cavity (m). h the section of the double skin facade Z = (-), If the total aerodynamic drag of the cavity is less than - local aerodynamic resistances along the height of the ∑︀ the force of the convective buoyancy of the air, then in each moving air stream line of the double skin facade Z = ∑︀ climatic condition the air moves in the cavity of the double ξ . x=1 skin facade. The coefficient of friction resistance along the height of the section of the double skin facade λ (-) - Figure 3, Application of physical theory of cavity in the construction of double skin facades | 45 Figure 4: Graphic representation of a coeflcient of friction as a function of the cavity height λ = f (Re). Figure 3: Coeflcient of friction resistance along the height of the trajectory of the convective air flow (Re - Reynolds criterial num- ber (-),v – air flow velocity in the cavity (m/s), ν – coeflcient of am kinematic viscosity of air (m /s), g – gravitational acceleration co- eflcient (9,81 m/s ), ∆Θ – temperature increase in the cavity (K), am Θ – temperature in the centre mass point of the triangle surface am,T A = f(H,∆Θ ) ( C)). am is determined from the graphical dependence showed on Figure 4. for Reynolds number: v.2D Re = (2) To quantify it, we need to know: – aerodynamic diameter of the cavity D (m). We de- termine it using the definition of the aerodynamic radius: S L.b R = = (m) (3) O 2L + 2b D = 2.R (m) (4) h h – velocity of convective air flow in (m/s). This value is Figure 5: Aerodynamic coeflcients of local resistances ξ , ξ , ξ , 2 3 4 determined from the known temperature differences ξ , ξ , ξ , ξ , ξ (-) in the trajectory of air flow (a – net area opening 5 6 7 8 9 between the air entering and leaving the cavity ∆Θ am for air movement, A – total area of the air inlets including its solid (K) and the known temperature at the centre of linear parts, b – planar width of the rectangular cross-section, h – height gradient of the cavity Θ ( C), by: of rectangular cross section). am , CENTR √︃ g · H · ∆θ am Vam = (5) Z · θ am,CENTR 46 | Bielek et al. Figure 6: The local aerodynamic drag of the air flow at the inlet part. Upper picture illustrates the conventional rain screen louvers. Lower picture shows aerodynamic louvers (a – net opening area for air flow, A – total area of the inlet air, including the louvers). Figure 8: Basic geometry of a double skin facade. – kinematic viscosity coefficient of air ν (m /s). Coefficients of local resistances along the height of the moving line of the air flow of the double skim facade – Figure 5, is determined as: – aerodynamic coefficient of local resistance ξ (-) of air flow at the entrance with louver "A" – Figure 2. which characterizes the swirling of the air flow at the en- trance to the supply channel "B" is determined from the graphical dependences in Figure 6 depending on the type of blinds. – aerodynamic coefficients of local resistance ξ ξ 2, 4, ξ ξ (-) of air ow fl on the mesh or grate – Figure 2, 6, 9 which characterize the swirling of the air flow when overcoming the mesh or grate, we determine as: (︃ )︃ (︂ )︂ 0, 7 A ξ = 1 + √︀ · − 1 (6) 2,4,6,9 1 − a/ where: Figure 7: The local aerodynamic drag of the air flow at the outlet A – the total area of the net or grate, including their part. Upper picture shows conventional rain screen louvers. Lower fixed surfaces (m ) picture illustrates aerodynamic louvers (a – net opening area for air a – area of the air openings (m ). flow, A – total area of the inlet air, including the louvers). Application of physical theory of cavity in the construction of double skin facades | 47 – aerodynamic coefficient of local resistance ξ (-) in case of sudden narrowing of the cross-section during the movement of the air stream from the cavity "D" to the exhaust duct "G" – Figure 2, which character- izes the swirling of the air stream in case of sudden narrowing of the cross-section “G" is determined by the relation : (︁ )︁ ξ = 1 − (9) where the meaning of the symbols is the same as in relation (8). – aerodynamic coefficient of local resistance ξ (-) of air flow at the outlet with louver "A" – Figure 2, which characterizes the turbulence of the air flow at the out- let of the drainage channel "G" is determined from the graphical dependence on Figure 7 again depend- ing on the type of blinds. 2.3 Alternative possibilities of construction for double skin facades Figure 9: The characteristic vertical section of the double skin fa- cade showing the compatibility of its basic and complementary From the point of view of its fundamental concept, a double theoretically justified structural elements and details into a com- skin facade can be developed in broad modifications of its plete structural system. construction, which influences: choice of cavity geometry (width and height zoning), approach to cavity aerodynam- ics (natural or forced air movement), choice of glass system – aerodynamic coefficients of local resistance ξ ξ (-) 3, 8 of suspended transparent wall (single or double, without of air flow when changing direction – Figure 2, which or with other special functions) and a conceptual approach characterizes the vortex - impact of air flow when to the use of the physical functions of the cavity (open or changing direction, we determine as: closed circuit facades). The wide variability of these factors √︂ determines the wide variability of facades of this kind. ξ = 1, 1. (7) 3,8 The current trend in the design of project applications where: of double skin facades, corresponding to the current level b – plan width of the rectangular cross-section (m) of theoretical knowledge of the problem, focuses on double h – height of the rectangular cross-section (m) ( for skin facades with the corridor type cavity (width 500 mm - ≤ 1) 1500 mm) with section height identical to the height of one – aerodynamic coefficient of local resistance ξ (-) at floor and also economical double skin facades with the slot sudden widening of the cross-section during the type cavity (width 100 mm - 300 mm) with the height of the movement of the air flow from the supply duct "B" section also identical with the height of one floor, realized to the cavity "D" – Figure 2, which characterizes the in the form of a spatial completed part - element. swirling of the air stream at sudden widening of the Let’s demonstrate the structural creation of the two cross-section between the supply duct "B" and the development types of double skin facades, including their cavity "D" is determined by the relation: physical assessment based on in-situ experiments. (︁ )︁ ξ = 1 − (8) where: A – larger extended cross - sectional area (m ), a – smaller original cross - sectional area (m ). 48 | Bielek et al. Figure 11: View into the cavity of a double skin facade with installed sensors of physical quantities . ∑︁ ∑︁ λ · (H + b) Z = 1 + + ξ = 1 + 0, 20 + 14, 94 = x=1 = 16, 14 < 18 = Z conv Figure 10: Examined physical parameters of the double skin trans- (10) parent facade. A1 – vertical section – inlet module, A2 – vertical which expresses the convective buoyancy of the air in section – outlet module, B – horizontal section through inlet and outlet modules. Θ – measuring points for temperature monitoring x the cavity of a double skin facade. Based on the above, it can ( C), v - measuring points for monitoring air velocity (m/s), ϕ - x a be stated that in terms of functional aerodynamics of the measuring points for monitoring relative humidity (%) . cavity, the above-mentioned facade is designed correctly and that airflow through its cavity is ensured in any climatic situation. 2.4 Double skin facade with corridor type We monitored the temperature, aerodynamic and en- cavity ergy regime of the double skin facade for 18 months with an in-situ experiment. The experiment was carried out on The first example documents the structural creation of a 17th floor, 56.3m above the terrain. Orientation of the exper- double skin facade with corridor type cavity, width b = imentally examined part of the cavity was SW (240 ). The 600 mm, with an effective height of the cavity identical recorded physical parameters of the double skin facade are to the height of one floor (H = 3450 mm) - Figure 8. The shown in Figure 10. The view of the installed sensors for detailed construction solution of the double skin facade is measuring physical quantities in the cavity of the facade documented in Figure 9. The facade was realized by multi- is documented in Figure 11. From the whole range of re- phase assembly technology. sults of the in-situ experiment, in this article we will focus The airflow in the cavity of the facade is based on natu- on the critical state of windlessness in terms of functional ral flow - a combination of natural convection and the effect aerodynamics, when the movement of air in the cavity of of wind. The total aerodynamic resistance of the facade was a double skin facade is based on natural convection. An quantified as: example of the recording of measured physical quantities Application of physical theory of cavity in the construction of double skin facades | 49 Figure 14: Construction diagram of the double skin facade element with a narrow type cavity. in the cavity of a double skin facade in the period of clear Figure 12: The example of measured values from the experiment for windless warm weather is documented in Figure 12. the typical period of clear windless warm weather (v ≤ 0.5 m/s). Following the processing – research into the long-term experiments of loads on natural physical cavity of the dou- ble skin transparent facade only by effects of outdoor tem- peratures, relative humidity and effects of global solar ra- diation (windless) we can state : – convective airflow occurs in the cavity in every stress interval and its velocity ranges from 0.05 ≤ v (m/s) ≤ 0.2 to 0.3, – under the effect of global solar radiation (900 - 1800) the convective velocity increases, – as a result of alternating position of air inlet and air outlet modules the energy regime in the cavity is char- acterized by inhomogeneity – Figure 13, – there are 3 characteristic areas for the thermal and aerodynamic regime in the cavity: • area of increasing temperatures along height of the cavity in the air inlet module – convective air flow move- ment, • small area of particularly high temperatures in the upper part of air inlet module of the cavity – stagnation of warm air, Figure 13: Natural physical cavity of double skin facade. Climate situation: period of clear windless warm weather v ≤ 0.5 m/s. Dis- w • large area of high temperatures in air outlet module tribution of characteristic temperatures. Characteristic movement of of the cavity – stagnation of warm air – Figure 13. convective air flow. Based on the results of a long-term in-situ experiment of the physical regime of the mentioned double skin facade, 50 | Bielek et al. we can state that in its cavity there is a constant airflow in any climatic situation (even in windless condition). This fact is a confirmation of the correct physical function of the cavity and testifies to the quality design of the facade in terms of its aerodynamic dimensioning. Figure 16: Scheme of distribution of measuring points for measured parameters of the cavity in the completed part of double skin facade Θ , x - measuring points for temperature measurement ( C), v - a x Figure 15: Characteristic sections of the double skin facade element. measuring points for measuring air velocity (m/s), ϕ - measuring points for measuring relative humidity (%). characterized by high coefficients of local aerody- namic resistance of air outlet, and thus a high value 2.5 Double skin facade with narrow type of the total aerodynamic resistance of the physical cavity cavity. The second example documents - the structural creation Total aerodynamic resistance of the facade was calcu- of a double skin facade of a narrow type cavity, width b lated in the value of: = 162 mm, with an effective height of the cavity identical to the height of one floor (H = 3000 mm) – Figure 14. The ∑︁ ∑︁ λ · (H + b) facade was constructed by a single-phase assembly tech- Z = 1 + + ξ = 1 + 0, 37 + 12, 88 = nology from a spatially assembled part - element. Figure x=1 15 documents a detailed structural solution of the facade = 14, 25 > 12 = Z conv element. (11) The functional aerodynamics of above mentioned dou- which expresses the convective buoyancy of the air ble skin facade - the movement of air in the cavity - was in the cavity of a double skin facade. This aerodynamic based on natural flow - a combination of natural convection quantification of the cavity of the double facade is without and the effect of the wind. Natural physical cavity of the considering the local resistances on the lowered lamellas assembled panel of the double skin facade is due to : of the screening device. If the quantification of the total aerodynamic resis- – the relative complexity of air inlet and outlet open- tance of the facade also takes into account the triggered sun ings – Figure 14, protection situated in this cavity, which occupies approxi- – relatively small cross-sectional area of these open- ∑︀ mately 1/3 of the cavity and its local aerodynamic resistance ings ( A ≈ 0,05 m / per meter of panel, OPENING represents up to 25% of the total aerodynamic resistance of – geometric disproportion of air on exhaust from the the cavity of the facade. : cavity (from two panels and 14 openings of area ∑︀ A ≈ 0,1 m – Tab.1, into the collecting chan- OPENING nel of cross-sectional area A ≈ 0,0064 m ) VERT.CANAL Application of physical theory of cavity in the construction of double skin facades | 51 Figure 18: The example of measured values from the experiment for the typical period of nice warm weather. Figure 17: View of the installed sensors for measuring the physical parameters of the cavity of the double skin facade element. can state that in the cavity of the facade in certain time periods there is air stagnation, which confirms the theoreti- cal assumption of significantly higher total aerodynamic ∑︁ ∑︁ resistance of the double skin facade than the convective λ · (H + b) Z = 1 + + ξ = 1 + 0, 37 + 19, 11 = lift force. air in its cavity. This is also supported by the fact x=1 that in the scheme of air movement in the cavity according = 20, 48 ≫ 12 = Z conv to Figure 19 the measured values of air velocity v (m/s) at (12) inlet openings v , v (m/s) are significantly higher than at 2 5 Based on the above, it can be stated that from the point outlet openings v , v (m/s) or in the middle of cavity v , 13 14 8 of view of functional aerodynamics, the facade mentioned v (m/s). As a result, despite the relatively small effective above has a significant problem resulting in the stagnation height, there is a significant increase in the air temperature of air in its cavity during windlessness. in the cavity in windless conditions – Figure 18 and Figure This facade was also subjected to in-situ experiments to verify its physical regime. The experiment was carried As a result of geometric disproportion in cross sections out on 6th floor, 22.19 m above the terrain. Orientation of the of airflow trajectory through the natural physical cavity of experimentally examined part of the cavity was SW (240 ). the double skin facade, there is : The recorded physical parameters of the double transparent – high value of its total aerodynamic resistance, caus- facade are shown in Figure 16. The view of the installed ing stagnation of air in the cavity under still air (aero- sensors for measuring physical quantities in the cavity of dynamic resistance of the cavity is higher than con- the facade is documented in Figure 17. An example of the vective air buoyancy)  recording of measured physical quantities in the cavity of a – low airflow rate through the cavity (q ≈ 0,04 kg/s.m double facade in the period of warm weather is documented « 0,2 kg/s.m = q ) [1, 3], causing low energy m,REQUIRED in Figure 18. efficiency of the double skin facade. Based on the results of monitoring the physical regime of the double skin facade from the in-situ experiment, we 52 | Bielek et al. Figure 19: Scheme of air movement in the cavity of a double facade Figure 20: Schemes of air temperature rise in the cavity of a double A - windows of the inner wall of the double facade open B - windows facade ∆Θ (K). A - windows of the inner wall of the double facade am of the inner wall of the double facade closed. closed B - windows of the inner wall of the double facade open. These two facts are responsible for high temperature in its cavity, resulting that during the solar radiation there rise in the physical cavity (Figure 15) as well as high air is significant increase in air temperature in the cavity with temperatures of indoor climate during the typical summer a negative impact on the temperature inside the building. period. They are caused by underestimation of the phys- Double skin facade with a narrow type cavity are sig- ical dimensioning of the double skin facade in two main nificantly more demanding on their physical-structural di- interrelated and mutually influencing fields, in the field of mensioning in terms of their functional aerodynamics than aerodynamics  and in the field of solar thermal technol- facades with a corridor cavity. This fact is significantly influ- ogy in buildings . enced by the sun protection in the form of shading mobile blinds situated in this cavity, which in the lowered state occupies a large part of the cavity and represents a signifi- 3 Conclusions cant increase in the overall aerodynamic resistance of the cavity of the double skin facade. Its local aerodynamic re- Physical-structural dimensioning and design of individual sistance can represent up to 25% of the value of the total elements and the whole system of a double skin facade aerodynamic resistance of the cavity of the double skin is a demanding process, based on the theory of natural facade. physical cavities. The theory of cavities results in a double skin facade in the quantification of the physical regime Acknowledgement: This work was supported by the Sci- of its cavity. It is a matter of knowing the aerodynamic, entific Grant Agency of the Ministry of Education, Science, temperature and energy regime in time, while it should be Research and Sport of the Slovak Republic and the Slovak noted that there are strong bonds between them expressed Academy of Sciences in the project VEGA 1/0113/19 and by by the laws of physics. the Slovak Research and Development Agency under the Properly functioning double skin transparent facade contract No. APVV-16-0126. has to be able to eliminate the thermal load from shortwave solar radiation through its transformation into long-wave Funding information: The authors state no funding in- thermal radiation in the physical cavity. Underestimation of volved. functional aerodynamics in the construction and technical design of a double skin facade results in stagnation of air Application of physical theory of cavity in the construction of double skin facades | 53 Author contributions: All authors have accepted responsi-  Torres M, Alavedra P, Guzmán A, Cuerva E, Planas C, Raquel C et al. Double skin façades – cavity and exterior openings dimen- bility for the entire content of this manuscript and approved sions for saving energy on mediterranean climate. Build Simul. its submission. 2007;198-205.  Gratia E, De Herde A. Greenhouse effect in double-skin facade. Conflict of interest: The authors state no conflict of inter- Energy Build. 2007;39(2):199-2011. est.  Radhi H, Sharples S, Fikiry F. Will multi-facade systems reduce cooling energy in fully glazed buildings? A scoping study of UAE buildings. Energy Build. 2013;56:179-188.  Ding W, Hasemi Y, Yamada T. Natural ventilation performance of a double-skin façade with a solar chimney. Energy Build. References 2005;37(4):411-418.  ingotti N, Chenvidyakarn T, Woods AW. The fluid mechanics of  Bielek B, Bielek M, Palko M. Double-skin transparent facades of st the natural ventilation of a narrow-cavity double-skin facade. buildings. 1 volume : History, development, classification and Build Environ. 2011;46(4):807–23. theory of design. Bratislava: Coreal. 2002.  Gratia E, DeHerde A. Optimal operation of a south double-skin  Bielek B, Bielek M, Kusý M, Paňák P. Double-skin transparent nd facade. Energy Build. 2004;36(1):41-60. facades of buildings. 2 volume : development, simulation, ex-  Safer N, Woloszyn M, Roux JJ. Three-dimensional simulation with periment and design of the facade of the Slovak National Bank a CFD tool of the airflow phenomena in single floor double-skin fa- building in Bratislava. Bratislava: Coreal. 2002. cade equipped with a venetian blind. Sol Energy. 2005;79(2):193-  Compagno A. Inteligent Glass Facades – Material Practice Design. 1st ed. Basel, Boston, Berlin: Birkhäuser Verlag. 1995.  Gratia E, De Herde A. The most eflcient position of shading de-  Oesterle E, Lieb RD, Lutz M, Heusler W. Doppelschalige Fassaden, vices in a double-skin facade. Energy Build. 2007;39(3):364-373. Ganzheitliche Plannung. München: Callwey Verlag. 1999.  i Y, Cook MJ, Hanby VI. D. Infield DGG, Loveday DLL, Mei L. CFD  Barbosa S, Ip K. Perspectives of double skin façades for nat- modelling of double-skin facades with venetian blinds. J Build urally ventilated buildings: A review. Renew Sust Energy Rev. Perform Simul. 2007;1(3):185-196. 2014;40:1019-1029.  Pappas A, Zhai Z. Numerical investigation on thermal perfor-  Manz H, Frank T. Thermal simulation of buildings with double- mance and correlations of double skin façade with buoyancy- skin façades. Energy Build. 2005;37(11):1114-1121. driven airflow. Energy Build. 2008;40(4);466-475.  Jiru TE, Taob YX, Haghighat F. Airflow and heat transfer in double  Eicker U, Fux V, Bauer U, Mei L, Infield D. Facades and summer skin facades. Energy Build. 2011;43(10):2760-2766. performance of buildings. Energy Build.2008;400(4):600-611.  Hazem A, Ameghchouche M, Bougriou C. A numerical analysis of  Poirazis H. Double-skin façades for oflce buildings–literature re- the air ventilation management and assessment of the behavior view, Report EBD-R-04/3, Division of Energy and Building Design, of double skin facades. Energy Build. 2015;102:225-236. Department of Construction and Architecture, Lund Institute of  Tao Y, Zhang H, Zhang L, Zhang G, Tu J, Shi L. Ventilation perfor- Technology. Lund; 2004. mance of a naturally ventilated double-skin façade in buildings.  De Gracia A, Castell A, Navarro L, Oró E, Cabeza LF. Numerical Renew Energy. 2021;167(C):184-198. modelling of ventilated facades: A review. Renew Sust Energy  Alberto A, Ramos NM, Almeida RM. Parametric study of double- Rev. 2013;22:539-549. skin facades performance in mild climate countries in J. J Build  Jiru TE, Haghighat F. Modeling ventilated double skin façade-A Eng. 2017;12:87–98. zonal approach. Energy Build. 2008;40(8):1567–1576.  Rahmani B, Kandar MZ, Rahmani P. How double skin Façade’s air-  Von Grabe J. A prediction tool for the temperature field of double gap sizes effect on lowering solar heat gain in tropical climate? facades. Energy Build. 2002;34(9):891-899. World Appl Sci J. 2012;774–8.
Curved and Layered Structures – de Gruyter
Published: Jan 1, 2022
Keywords: double skin facade; double skin facade cavity; renewable energy source; functional aerodynamics
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