Building Applications, Opportunities and Challenges of Active Shading Systems: a State-Of-The-Art Review

energies

Review Building Applications, Opportunities and Challenges of Active Shading Systems: A State-Of-The-Art Review

Joud Al Dakheel and Kheira Tabet Aoul * ID

Architectural Engineering Department, United Arab Emirates University, P.O. Box 15551 Al Ain, UAE; [email protected] * Correspondence: [email protected]; Tel.: +971-566-433-648

Academic Editor: Arman Hashemi Received: 28 June 2017; Accepted: 4 August 2017; Published: 23 October 2017

Abstract: Active shading systems in buildings have emerged as a high performing shading solution that selectively and optimally controls daylight and heat gains. Active shading systems are increasingly used in buildings, due to their ability to mainly improve the building environment, reduce energy consumption and in some cases generate energy. They may be categorized into three classes: smart glazing, kinetic shading and integrated renewable energy shading. This paper reviews the current status of the different types in terms of design principle and working mechanism of the systems, performance, control strategies and building applications. Challenges, limitations and future opportunities of the systems are then discussed. The review highlights that despite its high initial cost, the electrochromic (EC) glazing is the most applied smart glazing due to the extensive use of glass in buildings under all climatic conditions. In terms of external shadings, the rotating shading type is the predominantly used one in buildings due to its low initial cost. Algae façades and folding shading systems are still emerging types, with high initial and maintenance costs and requiring specialist installers. The algae façade systems and PV integrated shading systems are a promising solution due to their dual beneﬁts of providing shading and generating electricity. Active shading systems were found to save 12 to 50% of the building cooling electricity consumption.

Keywords: active shading systems; kinetic shading devices; smart glazing; rotating shading systems; folding shading systems; photovoltaic (PV); solar collector; algae façade system; controls

1. Introduction Daylighting in buildings provides multidimensional benefits that have been widely reviewed in the specialized literature [1]. The provision of daylight through building openings permits views to the outdoors [2], which concurrently contributes to visual [3], psychological comforts [4], health [5], and productivity [6]. Additionally, optimum daylighting design strategies reduce reliance on artificial lighting and lessen energy consumption [7,8]. Although daylighting has many benefits, it has however undesirable side effects such as heat gain and glare [9]. Therefore, successful daylighting designs will consider the use of shading devices to reduce glare and excess heat gain in buildings [10]. Shading devices are used in buildings to provide a healthy balance by reducing the excessive glare and heat gain and providing privacy [11].

1.1. Passive versus Active Shading Systems in Buildings Fixed shading devices are a prominent feature in vernacular architecture. They are often designed in response to environmental conditions using locally available materials such as clay, tree branches, concrete, wood planks, bamboo and others to shade the buildings from direct sunlight [12–15]. The modern architectural movement dismissed these strategies until the 1970

Energies 2017, 10, 1672; doi:10.3390/en10101672 www.mdpi.com/journal/energies Energies 2017, 10, 1672 2 of 32 energy crisis, which triggered a renewed interest in passive design strategies as well as pressing for advanced solutions [16]. Conventional static passive shading devices are often categorized first as internal or external based on location of the system [11]. The performance of shading devices including overhangs [17], external roller shades [18], Venetian blinds [19] and internal shadings [20] were investigated in several studies. Furthermore, fixed external shading devices have been widely known as an effective way of controlling heat gain and glare in buildings and reducing cooling energy and cost reductions in different climatic conditions [21–23]. By comparison, external shading devices are more effective than internal shading devices since they are more efficient in decreasing the cooling loads of buildings in hot climate regions [11]. Fixed shading devices have, however, their limitations, the most important of which is their inability to adapt to the external conditions variations as well as blocking the view to the outside [24]. At the other end of the spectrum, active shading strategies try to achieve a balance between sufficient daylighting levels, providing solar protection, energy balance and enabling the occupants with the flexibility to control the shading devices according to their evolving needs [25]. Active shading devices are systems that tend to change their properties in response to exterior climate and interior requirements [26]. The use of active shading systems decreases the undesirable solar heat gain, increase daylight, provide control for the users, may generate on-site energy and increase the use of natural ventilation [25,27,28]. The active systems can be within the glazing of the openings or as an exterior shading system. This is usually achieved through the use of smart glazing technologies [29–31], sensors and control systems [32,33], or through the application of smart dynamic shading devices [34,35].

1.2. Aim of the Review Paper and Objective The main objective of this paper is to establish the extent of knowledge acquired on the subject through a review of the different emerging types of active shading systems and their applications in buildings. The three major types of active shading systems are reviewed; smart glazing systems, automated active (or kinetic) shading systems and shading systems that incorporate renewable energy. The types of control systems and mechanism used in active shading systems were then reviewed, as they are different and have implications on performance. Finally, the review assesses their potential, limitations and opportunities for further development and improvement. The search process consisted of identifying studies with a search strategy across Science-Direct database and Google Scholar. The initial search keywords used were active shading systems, smart glazing, kinetic shading systems, integrated renewable energy and shading systems and it yielded more than 500 papers. However, the papers that were eligible after pre-selection focused on electrochromic (EC) glazing, suspended particle devices (SPDs), liquid crystal devices (LCDs), rotating shading systems, folding shading systems, PV integrated shading systems, algae façade systems and solar collector integrated shading systems. Further focused search considered the types of shading systems along the following related keywords; design principles, types, working mechanism, performances and application in buildings and resulted in a 165 direct relevant papers investigated in this review.

2. Active Shading Systems Active or responsive shading systems, also called dynamic or kinetic shading systems, are often designed to respond to one or multiple environmental situations including: daylighting control [36], solar thermal control, ventilation control, and in addition sometimes energy generation [37,38]. The application of active shading systems is an important step towards improving the energy efﬁciency in the built environment [39]. By using active shading systems, buildings tend to adapt to evolving external conditions [39,40]. These systems can allow or block solar radiation access into the interior space by adjusting a device installed either inside or on the building skin. Energies 2017, 10, 1672 3 of 32

Active shading systems can be classiﬁed into three main categories: the ﬁrst one comprises: (i) the glazing in the form of smart glazing or as (ii) kinetic external shading devices or as (iii) shading devices that incorporate renewable energy generation. These main systems are the target of this review. First, smart glazing devices include suspended particle devices (SPDs), electrochromic (EC) devices and Energies 2017, 10, 1672 3 of 31 liquid crystal devices (LCDs). The second type of active shading is the kinetic external shading systems. This review considers mechanically movable dynamic shading systems which include the rotating include theand rotating folding shading and folding systems. shading The third systems. type is the The integrated third type renewable is the energyintegrated shading renewable systems. energy shading Thesystems. integration The ofintegration renewable energy of renewable can be achieved energy by can using be photovoltaic achieved by panels using (PV) photovoltaic attached on panels (PV) attachedshading deviceson shading [41], or bydevices using algae[41], façade or by systems using which algae can generatefaçade electricitysystems [42which], or through can generate electricitysolar [42], collectors or through attached solar on shading collectors systems atta [43ched]. The activeon shading shading systemssystems types [43]. reviewed The active in this shading systems studytypes are reviewed shown in in Figure this1 .study are shown in Figure 1.

FigureFigure 1. Active 1. Active shading shading systems classiﬁcation classification diagram. diagram

2.1. Smart2.1. Glazing Smart Glazing Systems Systems Windows with dynamic optical properties are a form of building shade. Smart glass, often called Windowssmart windows, with dynamic is defined opti to becal the properties glass whose are light a transmission form of building properties shade. are altered Smart when glass, voltage, often called smart windows,light or heat is is defined applied, byto changing be the fromglass translucent whose light to transparent transmission [44]. properties are altered when voltage, lightThe or functionheat is ofapplied, a smart windowby changing is to control from the translucent transmission to of transparent light into and [44]. out of the glazing Thesystem, function according of a smart to occupants’ window comfort. is to control Smart windows the transmission can also regulate of light lighting into and and heating out of levels the glazing system, accordingfor energy load to occupants’ management. comfort. Smart glassSmart technologies windows includecan also SPDs, regulate EC devices lighting and and LCDs heating [45]. levels Installing smart glass in buildings’ envelope, is similar to creating climate adaptable building shells, for energyin which load costsmanagement. for heating, cooling Smart and glass lighting technologies are reduced [include46,47]. Additionally, SPDs, EC smart devices glass preventsand LCDs [45]. Installing99.4% smart of ultraviolet glass in buildings’ light, which reducesenvelope, furniture is similar and curtain to creating fabric fading climate [44,45 adaptable]. The three building systems shells, in whichrequire costs transparent for heating, conductors cooling as electrical and lighting contacts. are reduced [46,47]. Additionally, smart glass prevents 99.4%SPDs of tend ultraviolet to rapidly switchlight, fromwhich a dark reduces bluish-black furniture state toand a clear curtain greyish fabric appearance fading when [44,45]. The three systemsvoltage require is applied transparent to control the cond amountuctors of light, as electrical glare and heat contacts. passing through [48]. The EC devices use a technology that utilizes an electrical voltage to control the amount of SPDslight tend passing to rapidly through switch the glass from [49]. ECsa dark offer bluish dynamic-black and responsivestate to a controlclear greyish that responds appearance to the when voltage isexternal applied changing to control conditions the andamount controls of visiblelight, transmittance,glare and heat reduce passing glare and through improve [48]. indoor light Theenvironment EC devices when use compareda technology to regular that andutilizes low-E an glass. electrical Additionally, voltage when to control compared the to theamount fixed of light passing throughshading devices, the glass they [49]. offer ECs a dynamic offer dynamic solar radiation and and responsive do not block control the view that [49 responds,50]. to the external changing conditionsLCDs use liquid and crystalscontrols that visible dissolve intotransmittance, a liquid polymer reduce they will, glare in turn, and solidify. improve The liquidindoor light crystals are randomly arranged in the droplets, resulting in scattering of light as it passes through the environmentsmart windowwhen compared assembly and to formingregular a and translucent low-E filmglass. [51 ].Additionally, when compared to the fixed shading devices,The performance they offer ofa smartdynamic glazing solar is first radiation evaluated and through do not the transmittanceblock the view modulation [49,50]. range LCDsin the use visible liquid and crystals whole solar that spectrum. dissolve Secondly, into a liquid the expected polymer lifetime they and will, number in turn, of achieved solidify. cycles The liquid crystals areis considered. randomly Finally, arranged its size in as the the largerdroplets, the devices, resulting the longer in scattering the switching of light time as for it coloration passes through and the smart window assembly and forming a translucent film [51]. The performance of smart glazing is first evaluated through the transmittance modulation range in the visible and whole solar spectrum. Secondly, the expected lifetime and number of achieved cycles is considered. Finally, its size as the larger the devices, the longer the switching time for coloration and bleaching of the glass [45]. Smart glazing acts differently during the transparent and opaque phases to control the transmitted solar radiation. The design principle, types, working mechanism, diagrams, special features and benefits of the three types of smart glazing are summarized in Table 1. The performance of smart glazing devices is indicated by several factors, such as the electrical, optical and thermal properties that depend on the structural composition and configuration of the EC device itself. Typically, the required performance parameters include the specification of: (1) switching speed; (2) switching voltage; (3) optical reflectance; (4) color rendering; (5) solar heat gain coefficient; (6) optical memory coefficients; (7) thermal transmittance; (8) optical transmittance coefficients; (9) lifetime and (10) operating temperature [44,52]. The performance of the three types of smart glazing systems is summarized in Table 2 according to the climatic conditions while highlighting the main variables addressed in the studies.

Energies 2017, 10, 1672 4 of 32 bleaching of the glass [45]. Smart glazing acts differently during the transparent and opaque phases to control the transmitted solar radiation. The design principle, types, working mechanism, diagrams, special features and benefits of the three types of smart glazing are summarized in Table1. The performance of smart glazing devices is indicated by several factors, such as the electrical, optical and thermal properties that depend on the structural composition and configuration of the EC device itself. Typically, the required performance parameters include the specification of: (1) switching speed; (2) switching voltage; (3) optical reflectance; (4) color rendering; (5) solar heat gain coefficient; (6) optical memory coefficients; (7) thermal transmittance; (8) optical transmittance coefficients; (9) lifetime and (10) operating temperature [44,52]. The performance of the three types of smart glazing systems is summarized in Table2 according to the climatic conditions while highlighting the main variables addressed in the studies. Energies 2017, 10, 1672 5 of 32

Table 1. Summary of smart glazing types.

System Electrochromic Glazing (EC) Suspended Particle Devices (SPDs) Liquid Crystal Devices (LCDs)

• EC glazing is 1µm thick of purely ionic • SPDs consist of 3–5 layers by which the conductor placed between electrochromic active layer contains needle-shaped dipolar • LCD consist of liquid crystal material and counter electrode layers that are placed particles of polyiodides [54]. positioned between two sheets of glass [56]. Design between transparent electrical conductor • Particles are less than 1 µm in linear size [55]. • LCD has ﬁeld sequential color displays that Principle layers [53]. • The size of the particles is usually less than uses red (R), green (G), and blue (B) light • Change optical properties by switching 200 nm to minimize light scattering and emitting diodes (LEDs) without noticeable between their oxidized and reduced avoid non-desired haze [48]. color breakup [57]. forms [45]. • Conventional Electrochromic (CEC) • Polymer-stabilized blue phase (PSBP) [62]. glazing [58]. • Polymer-dispersed LC (PDLC) reported [63]. Types and • NIR switching electrochromic (NEC) • Evacuated vacuum SPD [61]. • Liquid crystal on silicon (LCoS) displays [64]. Materials glazing [59]. • Optically isotropic LC (OILC) [62]. • “Dual-band” electrochromic (DBEC) [60]. • Gel dispersed liquid crystals (GDLC).

• Liquid crystal molecules are aligned in • EC glazing has a visible light transmission of • During the “off” state, the SPDs are parallel with the glass surface [56]. 62% and allows 47% of the incident solar randomly oriented and absorb/scatter • When voltage is applied, the direction is energy to the building interior in the clear visible light [48]. changed and they become vertical to the state [52]. • Then SPD shows a bluish-black dark color. glass surface. • Amount of incident solar energy going • The scattering effect is due to the particles • Then light passes through the droplets with Working inside the building is reduced by 81% when and is most prominent at short wavelengths. very little scattering and resulting in a Mechanism a low DC voltage is applied [65]. • During the “on” state the electric field is transparent state. • Solar irradiation is absorbed when the films applied and the particles line up • The quantity of light transmission can be are tinted. perpendicularly to the substrates. controlled by combining the motion of liquid • Thermal energy is re-radiated based on the • Then, more light is allowed to pass through crystal molecules and the direction of emissivity’s of the films and the glass [65]. to increase the transmission [48]. polarization of two polarizing plates attached to the both outer sides of the glass sheets [56]. EnergiesEnergies 2017Energies 2017, 10, 1672 102017, 1672 , 10 , 1672 4 of4 31 of 314 of 31

TableTable 1. TableSummary 1. Summary 1. Summary of smarof smart ofglazing tsmar glazingt types.glazing types. types.

SystemSystem System Electrochromic Electrochromic Electrochromic Glazing Glazing (EC) Glazing (EC) (EC) Suspended Suspended Suspended Particle Particle Devices Particle Devices (SPDs) Devices (SPDs) (SPDs) Liquid Liquid Crystal Liquid Crystal Devices Crystal Devices (LCDs) Devices (LCDs) (LCDs) • SPDs• consist• SPDs of 3–5consist layers of 3–5by which layers theby whichactive layerthe active layer • EC• glazing• EC is 1glazingμm thick is 1ofμ mpurely thick ionicof purely conductor ionic conductorplaced placed SPDs consist of 3–5 layers by which the active layer EC glazing is 1μm thick of purely ionic conductor placed contains needle-shapedcontains needle-shaped dipolar particles dipolar of particles polyiodides of polyiodides • LCD• consist• LCD of liquidconsist crystal of liquid material crystal positioned material positioned between electrochrombetween electrochromic and counteric and electrode counter layerselectrode that layers that contains needle-shaped dipolar particles of polyiodides LCD consist of liquid crystal material positioned between electrochromic and counter electrode layers that [54]. [54]. between twobetween sheets two of glass sheets [56]. of glass [56]. Design Designare placedare between placed transparent between transparent electrical conductor electrical conductorlayers layers [54]. between two sheets of glass [56]. Design are placed between transparent electrical conductor layers • Particles• • areParticles less than are 1 less μm than in linear 1 μm size in linear[55]. size [55]. • LCD• has• fieldLCD sequential has field sequentialcolor displays color that displays uses red that uses red Principle Principle[53]. [53]. Particles are less than 1 μm in linear size [55]. LCD has field sequential color displays that uses red Principle [53]. • • • • The• The size size ofThe the of sizeparticlesthe particlesof the is particles usually is usually lessis usually lessthan than 200 less 200nm than nmto 200 to nm to(R), (R),green green (R),(G), (G), greenand and blue (G), blue (B) and light(B) blue light emitting (B) emitting light diodes emitting diodes diodes Change• Change optical Change optical properties optical properties properties by switching by switching by switchingbetween between their between their their minimizeminimize lightminimize light scattering scattering light scatteringand and avoid avoid andnon-desired non-desiredavoid non-desired haze haze haze(LEDs) (LEDs) without(LEDs) without noticeable without noticeable noticeablecolor color breakup breakup color [57]. breakup [57]. [57]. oxidizedoxidized andoxidized and reduced reduced and forms reduced forms [45]. [45].forms [45]. [48].[48]. [48]. • • Polymer-stabilized• Polymer-stabilized Polymer-stabilized blue blue phase phase blue (PSBP) (PSBP)phase [62]. (PSBP) [62]. [62]. • • • • Conventional• Conventional Conventional Electrochromic Electrochromic Electrochromic (CEC) (CEC) glazing (CEC)glazing [58]. glazing [58]. [58]. Polymer-dispersed• Polymer-dispersed Polymer-dispersed LC (PDLC)LC (PDLC) LC reported (PDLC) reported [63]. reported [63]. [63]. TypesTypes and Typesand • and • • • • • NIR• NIR switching switchingNIR switchingelectrochromic electrochromic electrochromic (NEC) (NEC) glazing (NEC)glazing [59]. glazing [59]. [59]. Evacuated• Evacuated Evacuated vacuum vacuum SPD vacuum SPD [61]. [61]. SPD [61]. Liquid• Liquid crystal Liquid crystal on crystalsilicon on silicon (LCoS)on silicon(LCoS) displays (LCoS) displays [64]. displays [64]. [64]. MaterialsMaterials Materials • • • • “Dual-band”• “Dual-band” “Dual-band” electrochromic electrochromic electrochromic (DBEC) (DBEC) [60]. (DBEC) [60]. [60]. Optically• Optically isotropicOptically isotropic LC isotropic (OILC)LC (OILC) LC [62]. (OILC) [62]. [62]. • • Gel• Geldispersed dispersed Gel dispersedliquid liquid crystals liquidcrystals (GDLC). crystals (GDLC). (GDLC). • Liquid• •crystal Liquid molecules crystal moleculesare aligned are in alignedparallel inwith parallel with • During• •the During “off” state, the “off” the SPDs state, are the randomly SPDs are randomlyoriented oriented Liquid crystal molecules are aligned in parallel with • EC• glazing• EC has glazing a visible has light a visible transmission light transmission of 62% and of 62% and During the “off” state, the SPDs are randomly oriented the glass surfacethe glass [56]. surface [56]. EC glazing has a visible light transmission of 62% and and absorb/scatterand absorb/scatter visible light visible [48]. light [48]. the glass surface [56]. allows 47%allows of the 47% incident of the solar incident energy solar to theenergy building to the building and absorb/scatter visible light [48]. • When• voltage• When is applied,voltage is th applied,e direction the is direction changed is and changed and Energies 2017, 10, 1672 allows 47% of the incident solar energy to the building • Then• SPD• Thenshows SPD a bluish-black shows a bluish-black dark color. dark color. When voltage is applied, the direction is changed and 6 of 32 interior in interiorthe clear in state the clear[52]. state [52]. Then SPD shows a bluish-black dark color. they becomethey vertical become to verticalthe glass to surface. the glass surface. interior in the clear state [52]. • The• scattering• The scatteringeffect is due effect to the is dueparticles to the and particles is most and is most they become vertical to the glass surface. Working Working• Amount• • ofAmount incident of solar incident ener gysolar going ener insidegy going the insidebuilding the is building isThe scattering effect is due to the particles and is most • Then• light• Then passes light through passes the through droplets the with droplets very littlewith very little Working Amount of incident solar energy going inside the building is prominentprominent at short wavelengths. at short wavelengths. Then light passes through the droplets with very little MechanismMechanism reduced byreduced 81% when by 81% a low when DC voltagea low DC is appliedvoltage is[65]. applied [65]. prominent at short wavelengths. scattering scatteringand resulting and in resulting a transparent in a transparent state. state. Mechanism reduced by 81% when a low DC voltage is applied [65]. • During• •the During “on” state the “on”the electric state the field electric is applied field isand applied and scattering and resulting in a transparent state. • Solar• irradiation• Solar irradiation is absorbed is whenabsorbed the filmswhen are the tinted. films are tinted. During the Table“on” state 1. theCont. electric field is applied and • The• quantity• The of quantity light transmi of lightssion transmi can bession controlled can be controlledby by Solar irradiation is absorbed when the films are tinted. the particlesthe line particles up perpendicularly line up perpendicularly to the substrates. to the substrates. The quantity of light transmission can be controlled by • • the particles line up perpendicularly to the substrates. Thermal• Thermal energyThermal energy is re-radiated energy is re-radiated is re-radiated based ba sedon the onba sedemissivity’sthe onemissivity’s the emissivity’s of of • of • combiningcombiningcombining the motionthe motion the of motionliquid of liquid crystal of liquidcrystal molecules crystal molecules moleculesand and and Then,• Then, more moreThen, light light more is allowed is light allowed isto allowed pass to pass through to through pass to through increase to increase to increase the filmsthe films andthe and thefilms glassthe and glass [65]. the [65]. glass [65]. the directionthe directionthe of direction polarization of polarization of polarization of two of two polarizing ofpolarizing two polarizing plates plates plates System Electrochromic Glazing (EC)the transmissionthe transmissionthe Suspended transmission [48]. [48]. Particle [48]. Devices (SPDs) Liquid Crystal Devices (LCDs) attachedattached toattached the to boththe bothto outer the outer both sides si outer desof the of si desglassthe glassof sheets the sheets glass [56]. sheets[56]. [56].

CompositionCompositionCompositionComposition DiagramDiagramDiagram Diagram

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• Applied on large-size glazing [66]. • Switching speed is influenced by • There is no memory effect for the optical environmental conditions and glazing area. • At opaque state, LCD glazing scatters the properties and the electric field must be The coloring takes longer time than light, become haze, and provides no control maintained for keeping the SPD bleaching [53,67]. of Near-IR [44]. transparent [48]. • Electrically actuated EC glazing absorbs • Operating voltages are in the range of • The light transmission of SPDs is controlled Infra-red spectrum of solar radiation [68]. 20–100 Vrms to maintain the clear state of the by the application of high amplitude Special • The higher the glazing surface temperature, device [73]. alternating current voltage (AC) [48]. Features the lower the power required to switch [69]. • This technology is used in interior and • Controls only the visible solar spectrum and • A typical EC have visible transmission of exterior settings for privacy control. transmit Infra-red (IR) spectrum [44]. Tv = 0.65 − 0.50 and fully colored • The visible transmittance range is typically • Over all heat transfer of 5.9 W/m2 K[71]. transmittance of Tv = 0.25 − 0.10 [44]. 50–80% and the solar heat gain coefficient • Solar heat gain coefficient change from 0.05 • The shading coefficient (SC) is about (SHGC) is 0.55–0.69 [74]. to 0.38 [72]. SC = 0.67 − 0.60 for the bleached condition, and SC = 0.30 − 0.18 for the fully colored condition [70]. Energies 2017, 10, 1672 7 of 32

Table 1. Cont.

System Electrochromic Glazing (EC) Suspended Particle Devices (SPDs) Liquid Crystal Devices (LCDs)

• Requires power only during switching, • SPD glazing is the most suitable among other where they consume a low voltage to switch types of glazing for building application. usually 1–5 V. • Can connect directly with AC main power • Constant dimming and most designs have supply without the need for conversion long-term memory usually 12–48 h [44,53]. system (EC glazing requires an AC to DC • Recent advances in next-generation LCDs • Has a low energy consumption, usually inverter to connect with mains) [76]. with a fast response time [77]. 2 8 W/m , and becomes almost zero when • Controls solar heat gain due to its variable • OILC use makes wide viewing angle without Benefits they are kept at constant conditions, due to transparency [72]. an alignment layer [77]. Optical response their considerable open circuit memory [75]. • Facilitates switchable single or double times are around 1–3 s, which is less than EC • Coloration phases are virtually infinite and glazing systems [71]. devices [48]. are capable of blocking both direct and diffuse solar radiation [52]. Improves the Optical response times are around 1–3 s, daylighting of buildings and offices, which which is the same range as for LCD devices leads to significant cost savings and improve and less than EC devices [48]. labor productivity [50]. Energies 2017, 10, 1672 8 of 32

Table 2. Performance of smart glazing types according to climatic conditions.

Parameters Performance of EC Performance of SPDs Performance of LCDs • Response time Variable • U-Value • Energy saving • Material and optical transmittance addressed • Switching Power • Haze coefﬁcient

• Glass gel-dispersed liquid crystal (GDLC) which has high quality electro-optical behavior was investigated in • Using a thermally insulated test cell yielded a U-value order to overcome the limitations of regular PDLC at 2 of 5.9 W/m K in cold climate in Ireland [71]. While the cold climate in South Korea and showed a fast response use of low heat loss switchable SPD glazing offered a time of ~0.5 and 3 ms which is 10 times shorter than that • Large-size EC windows facing south-east, low overall U-value, which varied between 1.00 and of PDLC, respectively for the on and off processes, high 2 used in a building in Oakland, California 1.16 W/m K in Ireland [61]. contrast and low haziness [78]. during winter was tested and the result • Gosh et al. (2016) also tested the potential of powering • The use of films of silver nanowires was investigated by showed that on a clear winter day, the SPD glazing from photovoltaic device and found that Khaligh et al. (2015) in Ontario, Canada as an alternate Cold climatic 2 average window luminance exceeded 850 for a 1 m of SPD glass under cold climatic conditions in electrode material to the PDLC [79]. It was found that conditions 2 cd/m and the lighting energy was Dublin the switching power consumption is 10.42 kWh the material and fabrication costs of silver nanowire reduced by 6–24% in the 11% glazing, which can be supplied by 1 W PV. Thus, there is a films are lower than ITO and enable transparency of while the energy was 3% reduced when potential combination for SPD and PV for future low ∆Ton – off = 57% versus ∆Ton – off = 46% for the 13% glazing was used [53]. building annual energy consumption [76]. A 40 Wp PV ITO-based devices and a lower voltage supply [79]. device continuously powered a 0.07 W SPD glazing. • A 20 µm commercial PDLC layer has been developed in Low sizing ratio of 1.12 between PV and inverter South Korea between ITO coated polyester films to offered less power losses from inverter output [76]. achieve a device with haze coefficient changing from 0.09 to 0.90. The device exhibits good temperature stability between 0 and 60 ◦C[80].

Variable • • Power and energy consumption U-values and SHGC • Light transmittance addressed • Transmittance reﬂectance, color appearance and haze.

• It was claimed by Gosh et al. (2016) that high U-values and variable SHGC makes the SPD glazing to be suitable for summer. • The light-controlled transmittance in a • EC devices can lead to a 30% reduction in • (SHGC) varied between 0.05 (when opaque) and 0.38 polymer-dispersed liquid crystals (PDLC) device was the annual power consumption and in (when transparent) and U-value varied between investigated by Cupelli et al. (2009) during warm peak demand by 23% in large area 2 2 Warm and hot 5.02 W/m K and 5.2 W/m K for the two states and climate in Calabria, Italy. It was claimed to self-increase buildings in hot climatic conditions [81]. climatic showed 6 kW h cooling load reduction [72]. scattering as a function of the light intensity and • Up to 50% of the primary energy conditions • Total and diffuse components of transmittance and self-control the incident daylight and glare as a function consumed in air-conditioning is saved by reﬂectance, along with color appearance and haze were of incident intensity both in building and automotive the use of EC windows [82]. used in model calculations to predict the thickness of applications [83]. the active layer during summer period and showed thicknesses of 200–300 µm as most optimum for SPD-based smart window applications [48]. Energies 2017, 10, 1672 9 of 32

Table 2. Cont.

Parameters Performance of EC Performance of SPDs Performance of LCDs

Variable • Energy consumption -- addressed • Energy savings

• The energy consumption of EC windows was tested in cold and hot climates in two prototype buildings in Chicago and Houston. The results suggested that the annual peak electric demand was reduced by 7–8% for moderate-area windows and by 14–16% for large-area windows in either climates [46]. • The performance of near-infrared switching electrochromic (NEC) window glazing was tested, using the COMFEN software to simulate a broad range of NEC performance levels, for commercial and residential buildings in 16 climatic Mixed climatic variations-representative reference cities. -- conditions The results showed an annual HVAC energy savings up to 11.6% with potential as high as 11 kWh/m2 per year for commercial buildings, and up to 13% with 15 kWh/m2 per year for residential over the highest performing static glazing [84]. • EnergyPlus software was used to simulate annual energy performance of the dual-band electrochromic (DBEC) glazing and indicated that DBEC is capable of achieving annual primary energy savings between 64.5 and 322.9 kWh/m2 of window area from reduced heating, cooling, and lighting demand [58]. Energies 2017, 10, 1672 10 of 32

2.2. Kinetic External Shading Systems Kinetic shading systems follow the same concept as dynamic facades and were introduced to satisfy some of the energy characteristics of the building envelope. The Lawrence Berkeley National Laboratory (LBNL) in the U.S. describes kinetic shading systems (dynamic façades) as systems that enable a building to reduce its lighting and cooling loads [85]. The development of these systems was a response to the growing awareness of energy reduction in buildings. Their adaptability offers the potential to achieve an energy-efﬁcient environment, improve the comfort, balances indoor environmental quality (IEQ), such as, reduced glare, view to outside, privacy, thermal comfort and air quality and increase satisfaction and productivity of the occupants while minimizing the energy cost and environmental impact [86–88]. The systems move in response to mechanical, chemical or electrical stimuli by which folding, sliding, expanding, shrinking and transforming in the shading devices take place [89]. The development of kinetic facades presented in the literature are mainly concerned with the functional possibilities and enabling technology [37]. The mechanism in the kinetic shading depends on mechanical, chemical and electrical engineering where folding, sliding, expanding, shrinking and transforming in the shading devices takes place [89,90]. In this literature review the dominant types; rotating and folding shading systems have been explored.

2.2.1. Rotating Shading Systems (a) Design Principle and Performance

As discussed earlier, rotating shading systems consist of a shading device made of either glass, metal, fabric or timber and is designed to rotate around either a horizontal or vertical axis depending on the position of its slates [91]. Glass lamella device have a better utilization of daylight over other systems [92]. The rotational movement of kinetic facades creates slow responses on every panel of the facade, which prevents any noise or distraction for the building’s occupants throughout the day [88]. The influence of external dynamic louvers with light dimming strategies in an office building at hot and humid climate in Abu Dhabi, UAE was explored. The results showed that the dynamic louvers with inclination angle of −20◦ for the south had 30.31% energy savings, while with a 20◦ inclination angle for the east and west orientations the savings were 34.02% and 28.57%, respectively [93]. Similarly, a new double skin façade with movable integrated shading louvers was investigated and showed that during the entire year the proposed façade significantly improved the building energy behavior, especially when the winter configuration forced convection was considered [94]. The cooling and heating energy savings of four types of kinetic façade systems; the overhang, folding, horizontal louver, and vertical louver were investigated by Kensek and Hansanuwat (2011) at hot climate in California in U.S. It was found out that the most optimal shades are overhang and horizontal louvers and were able to rotate for 90 degrees, and decreased the energy consumption by 33% for cooling and 30% for heating [95].

(b) Material

The rotating shading devices are made of different materials, but predominantly use: (i) glass louvers, (ii) metal louvers and (iii) timber louvers. Examples of building applications with their performance are illustrated in Table3.

The carrier system of the shading device may vary depending on the application type, the size of the louver and the span (Table4). Energies 2017, 10, 1672 11 of 32 Energies 2017, 10, 1672 9 of 31

Energies 2017, 10, 1672 Table 3. Application of materials of external shading systems. 9 of 31 Table 3. Application of materials of external shading systems. Material Glass Rotating Shading System [96,97] Reproduced with the Permission from COLT Company, 2017. Material Glass RotatingTable Shading 3. Application System of [96,97] materials Reproduc of externaled with shading the Permission systems. from COLT Company, 2017.

Material Glass Rotating Shading System [96,97] Reproduced with the Permission from COLT Company, 2017.

BuildingBuilding application application example example

Building application example

EuropeanEuropean Commission Commission He Headquarters,adquarters, Brussels Brussels The façade was renovated using glass rotating systems which respond to the changes in light intensity and temperature. It is a Shading system design description The façade was renovated using glass rotating systems which respond to the changes in light intensity and temperature. It Shading system design description Europeansolar-controlled Commission glass withHeadquarters, high reflectance Brussels coatings. Theis afaçade solar-controlled was renovated glass using with highglass reﬂectancerotating systems coatings. which respond to the changes in light intensity and temperature. It is a Shading system design description • Reduces solar heat gain and cooling loads. solar-controlled•• PrimaryReduces energy solarglass consumption heatwith gain high and reflectance of cooling the building loads.coatings. was reduced by 50% lower than a similar building as modeled. Benefits • •• ReducesViewsPrimary are solar available energy heat gain consumptionwhen and gl coolingass louvers of loads. the buildingare in use. was reduced by 50% lower than a similar building as modeled. Beneﬁts • ••Primary energy consumption of the building was reduced by 50% lower than a similar building as modeled. Benefits CanViews be used are in available residential when buildings glass louvers and mass are inhousing. use. • Material Metal•ViewsCan rotating are be available used shading in residentialwhen device glass [97,98]buildings louvers Reproduc are and in massuse.ed with housing. the permission from COLT company, 2017. • Can be used in residential buildings and mass housing. MaterialMaterial Metal Metal rotating rotating shading shading device device [97,98] [97,98 Reproduc] Reproduceded with with the the permission permission from from COLT COLT company, company, 2017. 2017.

Building application example

BuildingBuilding application application example example

Zurich Airport, Switzerland • Perforated metal rotating shading system was used to reduce the extensive use of glass over the large area to avoid excessive Shading system design description ZurichZurichheat Airport, gain Airport, within Switzerland Switzerland the building. • • PerforatedThe system metal rotates rotating in response shading to system changing was climate used to conditions reduce th ande extensive available use daylight. of glass over the large area to avoid excessive • Perforated metal rotating shading system was used to reduce the extensive use of glass over the large area to avoid Shading system design description •heat gain within the building. Reductionsexcessive in heat cooling gain loads within and the glare. building. Shading system designBenefits description • •The system rotates in response to changing climate conditions and available daylight. • CanThe be used system in rotatesresidential in response buildings to and changing mass climatehousing. conditions and available daylight. • Reductions in cooling loads and glare. BenefitsMaterial Anodized aluminum shading device [99] Reproduced with the permission from COLT company, 2017. • Can be used in residential buildings and mass housing. • Reductions in cooling loads and glare. Beneﬁts Material Anodized• Can aluminum be used in shadingresidential device buildings [99] Reproduc and massed housing. with the permission from COLT company, 2017.

Energies 2017, 10, 1672 12 of 32

Table 3. Cont. Energies 2017, 10, 1672 10 of 31 Material Anodized aluminum shading device [99] Reproduced with the permission from COLT company, 2017.

Building application example Building application example

University of Potsdam, Germany Shading system design description Vertically folding shutters which open and closed according to the position of the sun. Shading system design description Vertically folding shutters which open and closed according to the position of the sun. • Dynamic and variable according to the weather situation. Benefits • Aesthetical kinetic appearance for the building. • Reduction in cooling energy and glare from direct sunlight.

Beneﬁts • Dynamic and variable according to the weather situation. • Aesthetical kineticTable appearance 4. Carrier for systems the building. of shading device. • Reduction in cooling energy and glare from direct sunlight. Carrier Diagram Description Application Suitable for use with a variety of louver materials including glass, metal, fabric and timber wood.

Intended for wider spans, carrier system 1 System 1: Straight incorporates a central aluminum torsion tube carrier bracket [100] along the entire length of the louver, and is ideal for continuous facades, as well as for roofs.

Energies 2017, 10, 1672 10 of 31

Building application example Building application example

University of Potsdam, Germany

Shading system design description VerticallyUniversity folding shutters of Potsdam, which Germany open and closed according to the position of the sun. • Shading system design description Dynamic Vertically and variable folding according shutters which to the openweather and situation. closed according to the position of the sun. Energies 2017, 10, 1672 • 13 of 32 Benefits Aesthetical• Dynamic kinetic and appearance variable accordingfor the building. to the weather situation. • Benefits Reduction• Aesthetical in cooling kinetic energy appearance and glare fromfor the direct building. sunlight. • Reduction in cooling energy and glare from direct sunlight. Table 4. CarrierTable 4. systems Carrier systems of shading of shading device. device.

Carrier DiagramTable 4. Carrier Description systems of shading device. Application Carrier Diagram Description Application Carrier Diagram Description Suitable for use with a varietyApplication of louver materials Suitable for use with a variety of louver materials includingSuitable glass, metal,for use fabric with anda variety timber of wood.louver materials including glass, metal, fabric and timber wood. including glass, metal, fabric and timber wood.

Intended for wider spans, carrier system IntendedIntended for wider for spans, wider carrier spans, system carrier 1 system 1 System 1: Straight incorporates1 incorporates a central aluminum a central aluminum torsion tube System 1: Straight carrierSystem bracket 1: Straight [100] incorporatestorsion tube alonga central the aluminum entire length torsion of tube carrier bracket [100] along the entire length of the louver, and is ideal carrier bracket [100] alongthe louver, the entire and islength ideal of for the continuous louver, and is ideal for continuous facades, as well as for roofs. forfacades, continuous as well facades, as for roofs. as well as for roofs. Energies 2017, 10, 1672 11 of 31 Energies 2017, 10, 1672 11 of 31

EnergiesEnergies 2017, 10 2017, 1672, 10 , 1672 Suitable for use with a variety of louver materials11 of 3111 of 31 Suitable for use with a variety of louver materials including glass, metal, fabric and timber wood. including glass, metal, fabric and timber wood. Suitable Suitable for use for with use a withvariety a variety of louver of louvermaterials materials

Suitableincludingincluding for glass, usewith metal,glass, a varietymetal,fabric andfabric of louver timber andmaterials timberwood. wood. Intended for shorter spans or where frequent including glass, metal, fabric and timber wood. Intended for shorter spans or where frequent anchor support points are available. anchor support points are available. System 2: Bracket IntendedItIntended providesIntended for shorter forminimum for shorter spans shorter orobstructionspans spanswhere or or wherefrequent where from frequent the System 2: Bracket It providesfrequent minimum anchor obstruction support pointsfrom the are carrier [100] anchorlouveranchor support so support when points used poinare available.withts are glass available. louvers it carrier [100] louver soavailable. when used with glass louvers it SystemSystem 2: Bracket 2: Bracket It providesmaximizesIt provides minimum the minimum natural obstruction daylight obstruction from and the from enhances the the System 2: Bracket carrier [100] maximizesIt providesthe natural minimum daylight obstruction and enhances from the carrier carrier[100] [100] louver louverso when so usedwhen with used glass with louvers glass louvers it it viewsthe to louver the outside. so when used with glass viewsmaximizes to the the outside. natural daylight and enhances the maximizeslouvers it the maximizes natural thedaylight natural and daylight enhances the views to the outside. viewsand enhancesto the outside. the views to the outside.

Suitable for use with a variety of louver materials Suitable for use with a variety of louver materials including glass, metal, fabric and timber wood. Suitableincluding for glass, use withmetal, a varietyfabric and of louver timber materials wood. Suitable Suitable for use for with use a withvariety a variety of louver of louvermaterials materials including glass, metal, fabric and timber wood. includingincluding glass, metal,glass, metal,fabric andfabric timber and timberwood. wood.

Like carrier system 1, carrier system 3 is Like carrierLike system carrier 1, system carrier 1, system carrier 3 systemis 3 is intended for wider spans and incorporates a System 3: Torsion bar intendedintended for wider for spans wider and spans incorporates and a System 3: Torsion bar Like carrierdiscreetLikeincorporates carriersystem central system 1, aluminum acarrier discreet 1, carriersystem central torsion system 3 aluminumis tube 3 alongis the System 3: Torsion barcarrier carrier [100] [100 ] discreet central aluminum torsion tube along the carrier [100] intendedentireintendedtorsion for length wider tubefor of spanswider alongthe louver. andspans the incorporates entire andIt is idealincorporates length for a of a SystemSystem 3: Torsion 3: Torsion bar bar entire length of the louver. It is ideal for discreetcontinuousdiscreet thecentral louver. central aluminum facades It isaluminum ideal as torsion well for as continuoustorsion tube for roofs. along tube thealong the carrier carrier[100] [100] continuous facades as well as for roofs. entire lengthentirefacades lengthof the as well louver.of the as louver. forIt is roofs. ideal It is for ideal for

continuous continuous facades facades as well as as well for roofs.as for roofs.

Energies 2017, 10, 1672 14 of 32

Energies 2017, 10, 1672 Table 4. Cont. 12 of 31 EnergiesEnergies 2017, 10 2017, 1672, 10 , 1672 12 of 3112 of 31 Carrier Diagram DescriptionSuitable for use with Application a variety of louver materials includingSuitableSuitable for glass, use for withmetal, use a with varietyfabric a varietyand of louvertimber of louver materials wood. materials Suitable includingincluding for glass, usewith glass,metal, a metal, varietyfabric fabricand of louver timber and materialstimber wood. wood. including glass, metal, fabric and timber wood. Carrier system 4 provides a back hung end Carrier system 4 provides a back hung end pivotedCarrier solutionCarrier system system with 4 hidden provides 4 provides control a back a back hung hung end mechanismspivotedpivoted solutionend pivotedintegrated solution with solution hidden with within hidden withcontrol the hiddenmain control vertical control System 4: Hung mullionmechanismsmechanisms mechanismssupports. integrated integrated integrated within within the within main the the verticalmain main vertical designSystem carrierSystem 4: Hung [100] 4: Hung System 4: Hung design carrier [100] mullionmullion verticalsupports. supports. mullion supports. designdesign carrier carrier [100] [100] This allows for seamless continuous louvers with unobtrusiveThis allowsThisThis allows for supports allows seamless for for seamless wh seamless continuousen viewed continuous continuous fromlouvers the louvers with with outside.unobtrusiveunobtrusive louvers supports with supports unobtrusivewhen whvieweden supportsviewed from thefrom when the outside.outside. viewed from the outside.

Energies 2017, 10, 1672 12 of 31

Applied for metal louvers. Applied AppliedAppliedApplied forfor for metalmetal metalfor louvers.metallouvers. louvers. louvers.

The patentedTheThe patented louver patented clip louver louveris adjustable clip clip is adjustable is inadjustable in in incrementsThe patentedThe patented incrementsof louver15 degrees. louver clip of is 15The clipadjustable degrees. plastic is adjustable Theclip in plasticallows in SystemSystem 5: Metal5: Metal increments of 15 degrees. The plastic clip System 5: Metal support clip [100] forincrements thermalincrementsallows clip ofexpansion 15 forallows degrees.of thermal 15 forofdegrees. the Thethermal expansion blade plastic The expansion and plastic clip of ensures the allows clip of allowsthe supportSystemsupportSystem clip5: clipMetal [100] 5:[100] Metal for thermalforblade thermal expansion and expansion ensures of the that ofblade the louver bladeand blades ensures and ensures supportsupport clip [100] clip [100] that louver bladeblades and cannot ensures rattle that against louver the blades rafters.that louverthat cannot louver cannotblades rattle blades rattlecannot against againstcannot rattle the againstrattlethe rafters. rafters. against the the rafters.rafters.

Energies 2017, 10, 1672 15 of 32

2.2.2. FoldingEnergies 2017 Shading, 10, 1672Systems 13 of 31 (a) Design Principle and Performance 2.2.2. Folding Shading Systems An effective type of shading systems is the shape morphing solar shading also called the folding (a) Design Principle and Performance shading system or the Origami shading device. This type of shading had been applied in several engineeringAn ﬁelds, effective in adjustable type of shading and systems reconﬁgurable is the shape structures. morphing solar Folding shading geometries also called the have folding been used shading system or the Origami shading device. This type of shading had been applied in several in biomedical devices [101], and in space and aircraft applications [102]. However, in architecture engineering fields, in adjustable and reconfigurable structures. Folding geometries have been used the usein of biomedical folding Origami devices [101], has and only in space been and recently aircraft experimented,applications [102]. especiallyHowever, in asarchitecture a shading the device. When installed,use of folding they Origami usually has have only different been recently typologies experimented, of movement especially such as a as, shading translation, device. rotationWhen and scaling, whereinstalled, external they usually forces have are required.different typologies Recent trends of movement in shading such device as, translation, design have rotation been and trying to replace traditionalscaling, where mechanical external forces systems are required. with integratedRecent trends multifunctional in shading device and design smart have actuators been trying and are responsibleto replace for moving traditional or controllingmechanical systems the mechanism with integrated [103 ].multifunctional and smart actuators and are responsible for moving or controlling the mechanism [103]. Usually,Usually, sensors sensors are ableare able to analyzeto analyze the the variationvariation of of an an external external stimulus stimulus and transfer and transfer the the informationinformation to the actuator, to the whichactuator, provides which theprovides structure the withstructure a change with ina onechange of its in properties one of its [104 ,105]. The applicationproperties of [104,105]. shape morphing The application solar of shading shape mo inrphing buildings solar shading depends in buildings on the following depends on criteria the that are consideredfollowing to criteria identify that and are analyze considered in detailto identify the most and analyze suitable in smart detail materialsthe most suitable [106]: smart materials [106]: • Corrosion resistance. • Corrosion resistance. • Durability• Durability (life cycle (life cycle of the of smartthe smar movement/shapet movement/shape memory memory effect) effect) • Stimulus• Stimulus responsiveness responsiveness (solar (solar radiation, radiation, outside outside air temperature, temperature, electrical electrical stimulus) stimulus) • Workability• Workability (process (process and adaptability)and adaptability) • • AchievableAchievable movements movements • Impressing force • Impressing force (b) Materials (b) MaterialRecently, there are no solar shading devices that are entirely made of smart materials due to the Recently,material there properties are no and solar costs. shading Therefore, devices smart that ma areterials entirely are still made used of either smart asmaterials sensors or due as to the actuators. material properties and costs. Therefore, smart materials are still used either as sensors or as actuators. The types of smart materials of folding shading systems (either sensors or actuators) are Theillustrated types of smartin Figure materials 2 [106]. of folding shading systems (either sensors or actuators) are illustrated in Figure2[106].

Shape Change Materials Shape Memory Stimulus- (SCMs) Alloys (SMAs) Smart responsive Materials Materials Shape Memory Shape Memory (SRMs) Materials Polymers (SMMs) (SMPs) Shape Memory Hybrids (SMHs)

Figure 2. Smart materials types for folding shading systems. Figure 2. Smart materials types for folding shading systems.

Stimulus-responsiveStimulus-responsive materials materials (SRMs) (SRMs) are are the the mostmost suitable suitable smart smart materi materialsals for shape for shape morphing morphing solar skins.solar Thisskins. isThis due is todue their to their ability ability to to respond respond to external external stimulus stimulus through through a change a change of their of their physicalphysical or chemical or chemical properties properties [107 [107].]. This This type type of of smartsmart materials materials is grouped is grouped into intotwo main two types main as types as shown inshown Figure in 2Figure: 2: 1. Shape change materials (SCMs) [106]: They are able to change their shape when right stimulus is present commonly a potential difference. 2. Shape memory materials (SMMs) [106]: “They are included in all the materials that are able to hold the modiﬁed shape until the appropriate stimulus is applied to activate the shape recovery cycle” [107,108]. Usually, those materials are activated by a difference in temperature. Energies 2017, 10, 1672 16 of 32

EnergiesEnergies 20172017,, 1010, , 16721672 1414 ofof 3131 A study compared, described and listed the properties of the three types of SMMs that are used 1.1. ShapeShape changechange materialsmaterials (SCMs)(SCMs) [106]:[106]: TheyThey areare ableable toto changechange theirtheir shapeshape whenwhen rightright stimulusstimulus either as sensorsisis presentpresent or actuators commonlycommonly for aa potentialpotential solar shading difference.difference. devices [106]. The comparison showed that the SMPs is the most2.2. promisingShapeShape memorymemory system, materialsmaterials due (SMMs)(SMMs) to the [106]:[106]: fact that“They“They their areare includedincluded global in deformationin allall thethe materialsmaterials is that sensiblythat areare ableable higher toto (800%) than Shape Memoryholdhold thethe modifiedmodified Alloys shapeshape (SMAs) untiluntil (up thethe appropriateappropriate to 10%) and stimstim Shapeulusulus isis appliedapplied Memory toto activateactivate Hybrids thethe shapeshape (SMHs) recoveryrecovery (up to 6–8%). cycle” [107,108]. Usually, those materials are activated by a difference in temperature. However, in thecycle” time [107,108]. being, Usually, SMAs those are thematerials most ar durablee activated shape by a difference memory in temperature. materials since they are able to exceed 200,000AA studystudy cycles, compared,compared, where describeddescribed SMPs andand have listedlisted been thethe propertiesproperties tested onlyofof thethe three upthree to typestypes 200 ofof cycles SMMsSMMs thatthat and areare SMHs usedused have not eithereither asas sensorssensors oror actuatorsactuators forfor solarsolar shadingshading devicesdevices [106].[106]. TheThe comparisoncomparison showedshowed thatthat thethe SMPsSMPs undergone any tests [106]. isis thethe mostmost promisingpromising system,system, duedue toto thethe factfact thatthat theirtheir globalglobal deformationdeformation isis sensiblysensibly higherhigher (800%)(800%) thanthan ShapeShape MemoryMemory AlloysAlloys (SMAs)(SMAs) (up(up toto 10%)10%) andand ShapeShape MemoryMemory HybridsHybrids (SMHs)(SMHs) (up(up toto 6–8%).6–8%). (c) BuildingHowever,However, Applications inin thethe timetime being,being, SMAsSMAs areare thethe mostmost dudurablerable shapeshape memorymemory materialsmaterials sincesince theythey areare ableable toto exceedexceed 200,000200,000 cycles,cycles, wherewhere SMSMPsPs havehave beenbeen testedtested onlyonly upup toto 200200 cyclescycles andand SMHsSMHs havehave notnot Thereundergoneundergone are different anyany teststests types [106].[106]. of shape morphing shading systems that can be applied in buildings. They usually(c)(c) moveBuildingBuilding in ApplicationsApplications responseto variable external conditions, and they have the ability of minimizing energy required to perform adaptation. The movement of the folding shading systems has two main ThereThere areare differentdifferent typestypes ofof shapeshape morphingmorphing shadshadinging systemssystems thatthat cancan bebe appliedapplied inin buildings.buildings. typologiesTheyThey [106 usuallyusually]: movemove inin responseresponse toto variablevariable exteexternalrnal conditions,conditions, andand theythey havehave thethe abilityability ofof minimizingminimizing energyenergy requiredrequired toto performperform adaptationadaptation.. TheThe movementmovement ofof thethe foldingfolding shadingshading systemssystems 1. Translationalhashas twotwo mainmain movement typologiestypologies which[106]:[106]: performs a bi-dimensional change of shape. It is linear and allows adjustment levels in the building skins by size-opening variation and by overlapping layers. 1.1. TranslationalTranslational movementmovement whichwhich performsperforms aa bi-dimensionalbi-dimensional changechange ofof shape.shape. ItIt isis linearlinear andand 2. Rotationalallowsallows movement adjustmentadjustment which levelslevels in performsin thethe buildingbuilding a tri-dimensional skinskinss byby size-openingsize-opening change variationvariation of shape; andand byby and overlappingoverlapping performs swivel motion bothlayers.layers. in the same axis and/or around a different axis. 2.2. RotationalRotational movementmovement whichwhich performsperforms aa tri-dimensionaltri-dimensional changechange ofof shape;shape; andand performsperforms swivelswivel In both typologiesmotionmotion bothboth aninin thethe actuator samesame axisaxis is and/orand/or required, aroundaround and aa differentdifferent it can be axis.axis. completely embedded into the device or strategically locatedInIn bothboth typologiestypologies to trigger anan actuator aactuator speciﬁc isis required,required, action. andand The itit cancan different bebe completelycompletely typologies embeddedembedded of intofoldinginto thethe devicedevice shading oror devices applied instrategicallystrategically buildings locatedlocated are shown toto triggertrigger in Tableaa specificspecific5. action.action. TheThe differentdifferent typologiestypologies ofof foldingfolding shadingshading devicesdevices appliedapplied inin buildingsbuildings areare shownshown inin TableTable 5.5. Table 5. Different types of folding shading systems. TableTable 5.5. DifferentDifferent typestypes ofof foldingfolding shadingshading systems.systems.

ReferenceReference Reference Study ShapeShape MotionMotion Motion SmartSmart ActuatorSmartActuator Actuator StudyStudy

Three-dimensionalThree-dimensionalThree-dimensional movementmovementmovement (swivel (swivel FlectoﬁnFlectofinFlectofin [109 [109][109]] -- - motion—Bothmotion—Bothmotion—Both inin in thethe the samesame sameaxis).axis). axis).

[106 [106][106]]

Three-dimensionalThree-dimensionalThree-dimensional SolarSolar KineticKinetic movementmovementmovement (swivel (swivel ShapeShapeShape MemoryMemory Memory Solar Kinetic [110] [110][110] motion—Bothmotion—Bothmotion—Both inin in thethe the samesame AlloysAlloysAlloys (SMA)(SMA) (SMA) sameaxis).axis). axis). Energies 2017, 10, 1672 15 of 31 [ [106]106[106]]

Three-dimensionalThree-dimensional Ocean ThematicOcean Thematic Pavilion movementmovement (swivel (swivel - - Pavilion[111] [111] motion—aroundmotion—around a a differentdifferent axis). axis).

[106 [106]]

Three-dimensional movement (swivel Shape Memory Air Flow [112] motion—around a Alloys (SMA) different axis).

[106]

Shape Memory Three-dimensional Alloys/ Shape Sun Shading movement (swivel Memory [113] motion—around a Polymers different axis) (SMA/SMP) [106]

Bi-Dimensional Movement Smart Screen Shape Memory (Translational Movement [114] Alloys (SMA) by overlapping layers)

[106]

Shape Variable Bi-Dimensional Movement Not Available Mashrabiya (Translational Movement (N/A) [115] by overlapping layers)

[106] Reproduced with permission from Elsevier and Copyright Clearance Center, 2017.

Energies 2017, 10, 1672 15 of 31 EnergiesEnergiesEnergies 2017, 10 2017 2017, 1672, 10, 10 , 1672, 1672 15 of 311515 of of 31 31

Energies 2017, 10, 1672 Three-dimensional 17 of 32 Three-dimensionalThree-dimensionalThree-dimensional Ocean Thematic movement (swivel OceanOcean ThematicOcean Thematic Thematic movementmovementmovement (swivel (swivel (swivel - Pavilion [111] motion—around a - - - PavilionPavilionPavilion [111] [111] [111] motion—aroundmotion—aroundmotion—around a a a different axis). differentdifferent axis). axis). Table 5. Cont. different axis).

Reference Study Shape Motion Smart Actuator [106] [106] [106] [106]

Three-dimensionalThree-dimensional Three-dimensionalThree-dimensionalThree-dimensional movementmovement (swivel (swivel Shape ShapeMemory Memory AirAir Flow Flow [112 [112]] movementmovementmovement (swivel (swivel (swivel Shape ShapeMemoryShape Memory Memory Air FlowAirAir [112] Flow Flow [112] [112] motion—aroundmotion—around a a AlloysAlloys (SMA) (SMA) motion—aroundmotion—aroundmotion—around a a a AlloysAlloys (SMA)Alloys (SMA) (SMA) differentdifferent axis). axis). differentdifferentdifferent axis). axis). axis).

[106 [106]] [106] [106] [106]

Shape Memory Three-dimensional Shape ShapeMemoryShape Memory Memory Three-dimensionalThree-dimensionalThree-dimensionalThree-dimensional Alloys/Shape Shape Memory Sun Shading movement (swivel Alloys/Alloys/ Alloys/Shape Shape Shape Sun ShadingSunSun Shading Shading movementmovementmovementmovement (swivel (swivel (swivel (swivel MemoryAlloys/ Shape Sun Shading[113] [113] motion—around a MemoryMemoryMemory [113] [113][113] motion—aroundmotion—aroundmotion—aroundmotion—around a a a PolymersMemory Polymers different axis) PolymersPolymersPolymers differentdifferentdifferentdifferent axis) axis) axis) (SMA/SMP)(SMA/SMP) (SMA/SMP)(SMA/SMP)(SMA/SMP) [106] [106] [ [106]106 [106]]

Bi-Dimensional Movement Smart Screen Bi-DimensionalBi-DimensionalBi-DimensionalBi-Dimensional Movement Movement Movement Shape Memory Smart SmartScreenSmart Screen Screen (Translational Movement Shape ShapeMemoryShapeShape Memory Memory Memory Smart Screen[114] [114] (Translational(Translational(Translational(Translational Movement Movement MovementMovement byAlloys (SMA) [114] [114][114] by overlapping layers) AlloysAlloys (SMA)AlloysAlloys (SMA) (SMA) (SMA) by overlappingoverlappingbyby overlapping overlapping layers) layers) layers) layers)

[106] [106 [106]] [106] [106]

Shape Variable Bi-Dimensional Movement Shape ShapeVariableShape Variable Variable Bi-DimensionalBi-DimensionalBi-Dimensional Movement Movement Movement Not Available Mashrabiya (TranslationalBi-Dimensional Movement Movement Not AvailableNotNot Available Available ShapeMashrabiya VariableMashrabiya (Translational(Translational Movement Movement (N/A) Mashrabiya (Translational(Translational Movement Movement(N/A) by (N/A)Not Available (N/A) Mashrabiya[115][115][ 115 ] by overlappingby overlapping layers) layers) (N/A) [115] [115] by overlappingoverlappingby overlapping layers) layers) layers)

[106] [106] [ 106[106] [106]] Reproduced with permission from Elsevier and ReproducedReproducedReproducedReproduced with permission with with with permission permission permission from Elsevier from from fromElsevier Elsevier and Elsevier and and and Copyright Clearance Center, 2017. CopyrightCopyrightCopyrightCopyright Clearance Clearance Clearance Clearance Center, Center, Center,2017. Center, 2017. 2017. 2017.

2.3. Integration of Renewable Energy Systems

2.3.1. PV Integrated Shading Device (a) Design Principle and Performance

The integration of PV materials into shading systems was introduced in 1998 [116]. Integration of renewable energy generation can be applied in a very effective way in the shading devices, combining a dual beneﬁt: shading and production of electricity. Integrated PV shadings could be used to provide energy controlling shape morphing devices. Several studies were done on integrating PV panels as solar shadings and providing maximum PV performance. Researches were carried out different studies during 2002 and 2011 about integrating PV in the building as shading devices, the results showed that the use of BIPV as exterior solar shading devices produces on-site electricity and reduces cooling loads by 10% and 9.2% in building [117,118]. In another study, a prototype of a PV-integrated shading device on venetian blinds was built and monitored, where each blind consisted of a glazed static concentrator and of crystalline silicon bifacial solar cells. The result showed that the efﬁciency of PV cells was improved by 85% and represented a very good result for facades’ applications [119]. Building integrated PV (BIPV) systems are used for generating electricity and as shading devices, they can be integrated into the building envelope, such as the roof, cladding, window shading, semi-transparent windows and façades. Additionally, they can reduce the use of building materials and electricity costs, reduction in use of fossil fuels and emission of ozone depleting gases [120]. Energies 2017, 10, 1672 18 of 32

Visual and the thermal performances of transparent BIPV on windows have been compared and revealed that in residential buildings in hot humid climate regions BIPV with slat angles of 60◦ and 68◦ provided good visual and thermal effect [121]. Mandalaki et al. also carried out several studies during 2012 and 2014 in hot climatic conditions on the visual and thermal comfort of PV-integrated with ﬁxed shading devices. It was found out that shading devices with integrated south facing PV can produce electricity to be used for lighting and that the theoretical efﬁciency of 12% is satisfactory for simple geometries [41]. A prototype of a solar-powered automatic shading device was built and tested in Indonesian climatic conditions. The results showed a 3 ◦C decrease in the indoor air temperature due to the control of incoming solar radiation [122]. Kim et al. performed a study on a PV-integrated adjustable shading device combined with daylight responsive dimming system in Korea and results showed 32% increase of power production and a 35% reduction of energy consumed by lighting systems [123].

(b) Building applications

The design characteristics of shading devices (SDs) with integrated photovoltaic panels (PVs) for residential building facades were studied for cooling and heating weather conditions in Crete. The results defined the best position PV-integrated shading devices according to the best lighting levels for tasks [124]. Thirteen different forms of monocrystalline PV panels mounted on south-facing shading devices of office buildings in Mediterranean region were evaluated [125]. The results showed that the best form of shading device integrated with PV was the “Brise-soleil full façade” which had the best optimization in the heating, cooling and lighting loads [125]. Integration of PV panels on louvers is another alternative in which the blade is exposed to provide full ventilation and can be tilted to maximize the efficiency [126]. The integration of PV panels on several fixed shading systems was tested by Mandalaki et al. (2014) for cooling purposes in Crete and found that the Brise–Soleil systems is the most efficient system where it ensures visual comfort and sufficient energy production [126].

2.3.2. Solar Collectors Integrated Shading Devices (a) Design Principle and Performance

Solar collectors are used in buildings to reduce energy consumption and carbon emissions [127]; they are usually installed on building facades, roofs, balconies, awnings and outdoor spaces, which are called building-integrated solar thermal (BIST) systems [128,129]. Integration of solar collectors with exterior shading devices can reduce solar radiation and at the same time generate heat. Solar collector devices have been investigated in some researches, and research methods typically include heat output estimation, numerical model calculation [43,130] and simulation analysis [131]. A study integrated shading device with a solar thermal system for water heating and analyzed the system in buildings in temperate and Mediterranean climatic conditions of Portugal and Spain [132]. The two cases were compared; a real case that has a completely sunlit louver and two shaded louvers, and an ideal one with three completely sunlit louvers. For the real case, the shadings reduced transmitted energy by 7% for the 15◦ inclination on horizontal plane, 12% for the 30◦ inclination and 17% for the 45◦ inclination. For the ideal case, the optimum angle was 25◦ [132]. The payback period was 6.5 years and the CO2 savings was 8.6 tons [132].

(b) Building applications

A full-size prototype of solar collector was installed on a shading louver and showed that when the solar radiation was enough, the systems did not require auxiliary heating equipment and the performance was 20% more than the performance of conventional solar collectors with natural circulation function [133]. The integration of solar collectors in buildings at hot and humid weather in Kuala Lumpur has been investigated by Saadatian et al. and the results highlighted that there are several ways of Energies 2017, 10, 1672 19 of 32 integration including mounting on a structure on the roof or window separated from the building or superimposed, where the collectors are mounted on a structure of the building envelope and are arranged in parallel [134]. Another study evaluated the heat pipe solar collector attached on a louver under a range of climatic conditions in the UK [133]. The indoor experimental results showed the performance of the new design to be very promising, even though the collector materials were not carefully selected. Increased collector efﬁciency can be achieved by increasing the number of heat pipes in the louver with only minimal increase in louver cost [131].

2.3.3. Algae Façade Systems (a) Design principle

Algae façade systems grow micro-algae in order to generate heat and electricity and are used as external cladding elements and dynamic shading devices [42]. Double skin façades were developed for the purpose of protecting curtain walls from the sun. Several transparent façade technologies have been introduced in buildings, such as insulated glass unit (IGU) and shading device (such as stretched metal, frit, suspended film) [135]. The use of those technologies in buildings is to protect the building from excessive heat gain and improve the performance of the building. However, those technologies are not enough for achieving high performance building. In order to do that, energy generation must be achieved from the integration of those technologies; such as Photovoltaic and solar thermal systems. As an alternative for high performance facade, an algae facade system has been introduced. Kim investigated the algae façade system, which consists mainly of an algae panel, aluminum framing and algae growing apparatus in the University of North Carolina in the U.S. as illustrated in (Figure3)[ 42]. The size of the system is 1.5 m wide by 3.65 m tall or taller depending on building conditions, consisting of both vision zone and algae zone [42]. The purpose of the clear vision zone is for view, daylight and ventilation, while the algae zone is for growing algae. The algae growing Energies 2017, 10, 1672 18 of 31 apparatus is comprised of intake systems for supplying CO2, and growing algae (e.g., algae, nutrients, medium etc.) and discharging systems for emitting O2 and collecting grown algae [42]. The mechanism medium etc.) and discharging systems for emitting O2 and collecting grown algae [42]. The of workmechanism in this system of work is in achieved this system first is byachieved water first being by filledwater inbeing the filled vertical in the glass vertical louvers glass that louvers contains nutrientsthat contains which convertnutrientsdaylight which convert and COdaylight2 to algaland CO biomass2 to algal through biomass thethrough bio-chemical the bio-chemical process of photosynthesis;process of photosynthesis; at the same time at the the same water time is beingthe wa heatedter is being up. heated Secondly, up. theSecondly, biomass the andbiomass the heatand that is generatedthe heat bythat the is generated façade elements by the façade are transported elements are by transported a closed loopby a closed system loop to thesystem plant to the room, plant where both formsroom, ofwhere energy both are forms exchanged of energy by are a separatorexchanged and by a a separator heat exchanger and a heat respectively. exchanger Therespectively. temperature levelsThe of thetemperature heat generated levels of can the beheat adjusted generated by can using be aadjusted hot water by using pump a forhot thewater supply pump of for hot the water and forsupply heating of hot the water building and for [136 heating]. the building [136].

Figure 3. Algae façade system details [42]. Reproduced with the permission from author Kyoung-Hee Kim. Figure 3. Algae façade system details [42]. Reproduced with the permission from author Kyoung-Hee Kim. (b) System Performance Kim has performed a few studies about the performance of algae façade systems. In one of the studies [42] the aim was to identify the feasibility of the algae façade system through schematic design and prototyping. The mechanism of algae facades was explained. Tests were conducted in a sunny winter noon in outdoor environment using a FLUKE (2006, SmartView (Version 3.2), NC, USA) thermography system with its software package. The result showed that the algae façade system has the future potential for sustainable façade alternatives and energy generation possibilities. The computer simulation on structural behaviors provided alternative design solutions to meet stress and stiffness criteria under various loadings, in addition to fabrication challenges associated with watertight interfaces between the vision zone and the algae zone [42]. Another study by Kim about bio-facades or algae façade systems showed a retrofitting case of a building [137]. The result showed that the algae facades reduces the energy consumption and CO2 emissions, where the retrofitted building energy consumption was reduced by 30% compared to an existing building due to the thermal and daylighting performance improvements. Moreover, the retrofitted façade reduces the life cycle cost by $110,000 and reduces the life cycle by 200 tons, and CO2 generation due to the photosynthesis process, which was 150 tons over the 30-year life cycle [136]. Usually, about 40 °C heat is obtained from the façade and is either used directly to heat water or stored in the ground to be used in a geothermal system. The efficiency of the conversion of light to biomass is 10% and to heat 38%. For comparison, photovoltaic systems have an efficiency of 12–15% and solar thermal systems 60–65% [136]. Therefore, algae façade is a competitive opportunity relative to these other technologies. Additionally, the algae façade helps improve the overall CO2 balance by removing CO2 from flue gas at quantities equivalent to the build-up of biomass [136].

Energies 2017, 10, 1672 20 of 32

(b) System Performance

Kim has performed a few studies about the performance of algae façade systems. In one of the studies [42] the aim was to identify the feasibility of the algae façade system through schematic design and prototyping. The mechanism of algae facades was explained. Tests were conducted in a sunny winter noon in outdoor environment using a FLUKE (2006, SmartView (Version 3.2), NC, USA) thermography system with its software package. The result showed that the algae façade system has the future potential for sustainable façade alternatives and energy generation possibilities. The computer simulation on structural behaviors provided alternative design solutions to meet stress and stiffness criteria under various loadings, in addition to fabrication challenges associated with watertight interfaces between the vision zone and the algae zone [42]. Another study by Kim about bio-facades or algae façade systems showed a retrofitting case of a building [137]. The result showed that the algae facades reduces the energy consumption and CO2 emissions, where the retrofitted building energy consumption was reduced by 30% compared to an existing building due to the thermal and daylighting performance improvements. Moreover, the retrofitted façade reduces the life cycle cost by $110,000 and reduces the life cycle by 200 tons, and CO2 generation due to the photosynthesis process, which was 150 tons over the 30-year life cycle [136]. Usually, about 40 ◦C heat is obtained from the façade and is either used directly to heat water or stored in the ground to be used in a geothermal system. The efficiency of the conversion of light to biomass is 10% and to heat 38%. For comparison, photovoltaic systems have an efficiency of 12–15% and solar thermal systems 60–65% [136]. Therefore, algae façade is a competitive opportunity relative to these other technologies. Additionally, the algae façade helps improve the overall CO2 balance by removing CO2 from flue gas at quantities equivalent to the build-up of biomass [136].

The ﬁrst algae façade integrated in a building was in the BIQ which is a part of the International Building Exhibition (IBA) 2013 in Hamburg, Germany [136]. The building used 129 "bioreactors” or algae façade, when sunlight hits the facade, photosynthesis process causes the microorganisms to multiply and causes the water to go about 40 ◦C , the heat then stored to be used for other uses [136]. Currently, the building reduces the overall energy needs by 50%, and the designer of the system says 100% is achievable by combining it with solar panels to power the pumps and heat exchangers [136]. Another application of the algae façade system was in the GSA Federal Building in Los Angeles that won ﬁrst place scheme for the 2011 Ideas competition, where an “algae photo bioreactor tube” was attached to the top surface of the opaque building envelopes [136]. Similarly, the same company made a net energy zero Battery Park project in San Francisco that applied “algae photo bioreactor panels” to grow algae and reduce CO2 [136].

3. Controls of Active Shading Systems The control of the movement of dynamic shading can be either user manual control strategy or automatic control strategy.

3.1. User Control Shading Devices Shading devices in buildings are linked to occupants’ behavior. There are many studies that focused on the relationship between user comfort and shading operation. Most of the researches done on user’s response to these systems are related to the manual use of blinds [138]. A survey explored the factors that affect the occupants’ comfort in Danish residential buildings [139]. The results suggested that most of the occupants preferred manually-controlled, especially for artificial light, windows opening and solar shading [139]. In another study, 800 building occupants were interviewed, and 90% preferred the use of automatic blinds because they thought they provided a better indoor quality [140]. The position of remotely controlled blinds in eight individual Energies 2017, 10, 1672 21 of 32 offices for 30 weeks was evaluated and showed that remotely controlled blinds were used three times more often than manually controlled ones [141]. Galasiu and Veitch pointed out that the results of the studies on manually operated blinds are helpful in favoring automated ones in Ontario, Canada [142]. Reinhart and Voss studied the reasons that trigger occupants’ reaction to shading devices in Germany and found out that they tend to close their blinds to avoid direct sunlight above 50 W/m2 on the work plane surface [143]. Wienold analyzed different shadings control strategies in Germany in order to design a shading system based on real user behaviors and the result showed that when a manual control is provided especially in summer, the shading device is rarely activated [144]. It was claimed that occupants had a positive experience when automated dynamic shading was applied [145]. It is concluded that automated control strategies of shading systems are preferred and are more beneficial in buildings.

3.2. Automatic Control Strategies The use of sensors and actuators for controlling the movement of dynamic shading devices is more beneﬁcial when it comes to adapting to various external environmental conditions. Control strategies and advanced control shading systems have positive impact on both the occupants’ comfort and the energy performance of the building [146]. The operation of the façade components could be by occupancy, environmental variable, time or utility price signals. Two types of loop controls can be used in buildings; open and closed loop control systems [147,148]. The open loop motorized shading systems working mechanism depends on the pre-calculated angle of incidence of sun light [149–151], or the illuminance sensor measurements of the façade [143]. The control of the shading is based on three main types of control algorithms that depend on the performance criteria they address [30]:

1. Threshold controllers: where the shading device gets activated when an external solar illuminance or irradiance limit is exceeded. 2. Sun blocking controllers: moves the shading system or adjust the blind slat angle depending on the sun position. 3. Mode and scene controllers: use a variety of sensors and different control algorithms [30].

Three types of control of the external shading devices were analyzed [152]. The first type was based on external vertical irradiation level only; the second type was based on the interior temperature level only, while the third type was the most effective one which was a combination of both types. The external shadings are closed when both conditions are met and opened when at least one of the conditions is met. A scaled model was built to test two types of control strategies for external venetian blinds [153]. One strategy provided maximum slat openness, while the other one provided maximum work-plane illuminance. The results indicated that for the low ground reflectance the energy savings was 38.1%, while for the high ground reflectance, the energy savings was 55.3%. Bauer et al. developed a logic based control algorithm that minimized thermal and artificial lighting energy demand [154]. The result showed that the smart blind controller achieved saving of 11% for the artificial lighting and between 20% and 50% savings for heating/ cooling. A significant application of sensors application in buildings is the case of the “Arab World Institute” in Paris, which is the one of first buildings to apply sensor based automated response shading systems based on the environmental conditions. The lens opens or closes according to the light quality inside the building. The system consisted of photosensitive mechanical automated devices, 30,000 light sensitive diaphragms on 1600 elements, which function like, a lens of the camera and all the mechanical devices are connected to a central computer [155]. Examples of innovative controls of shading devices that depends on different strategies for their movement are discussed in Table6 below. Energies 2017, 10, 1672 22 of 32 Energies 2017, 10, x 21 of 31 Energies 2017, 10, x 21 of 31 Table 6. Innovative shading control systems. Table 6. Innovative shading control systems. Table 6. Innovative shading control systems. Control Type Description Working Mechanism Diagram Control Type Description Working Mechanism Diagram Control Type Description Working Mechanism Diagram

Consist of two fiber-reinforced polymer absorber tubes. The tubes are filled with Consist of two fiber-reinforced polymer absorber tubes. The A self sun-trackingA self device sun-tracking designed device to designedConsist of totwo fiber-reinforcedspecial thermo-hydraulic polymer absorber fluid. tubes. When The A self sun-tracking device designed to tubes are filled with special thermo-hydraulic fluid. When the Non electrical thermo- control the externalcontrol shading the external louvers. shading tubes louvers. are filled withthe special sun moves, thermo-hydraulic one tube isfluid. more When the NonNon electrical electrical thermo-hydraulic thermo- control the external shading louvers. sun moves, one tube is more irradiated to sun and heats up hydraulic controlling system Controls the louversControls without the louvers the use withoutsun the moves, use of one tubeirradiated is more irradiated to sun and to heatssun and up heats more up than controllinghydraulic systemcontrolling [156 system]. Controls the louvers without the use more than the other tube. This causes the hydraulic cylinder to [156]. of electrical powerelectrical or digital power electronic or digital electronicmore than the otherthe tube. other This tube. causes This the causes hydraulic the cylinder hydraulic to [156]. of electrical power or digital electronic move and rotate the louvers into optimal shading position devices [156,157].devices [156,157]. move and rotate thecylinder louvers to into move optimal and shading rotate theposition louvers devices [156,157]. throughout the day [156,157]. throughout the dayinto [156,157]. optimal shading position throughout the day [156,157].

[157][157 Reproduced] Reproduced with with the permission the permission from [157] Reproduced with the permission from COLTfrom company, COLT company, 2017. 2017. COLT company, 2017.

When the sun is direct, the motor sends The electric control operation The electric controlThe electric operation control operationWhen adjustment the sun is direct,data the to motor the holder sends ofdata the to gearthe holder which of is adjustmentThe electric of control motors operation could be manual When the sun is direct, the motor sends data to the holder of adjustment ofof motors motors could could be manual be manual the switchesWhen gear thewhich orsun is is retracted direct,retracted the and motor and pulls pullssends smoothly smoothlydata tothe the rod theholder of rodthe of of Electrical controlling system switchesadjustment or automatic. of motors Automatic could be manual the gear which is retracted and pulls smoothly the rod of the Electrical controlling system switches or automatic.automatic. Automatic Automatic controlledlouversthe gear downwards system which is retractedthe to close louvers theand louvers downwardspulls smoothly and block to the close the rod sun. theof the Electrical[157]Electrical controlling controllingsystem system [157controlled]switches systemor automatic. consists Automatic of various louvers downwards to close the louvers and block the sun. [157] controlled systemconsists consists of various of various sensors The andlouvers sensors has downwards a control louversthe to shading close and the by blocklouvers rotating the and the sun. block louvers the sun. [157] sensorscontrolled and hassystem a fully consists controlling of various The sensors control the shading by rotating the louvers sensors and hasfully a fully controlling controlling over the internalfollowingThe sensors the suncontrol rotation.The the sensors shading controlby rotating the the shading louvers by oversensors the internal and has climate. a fully controlling following the sun rotation. over the internalclimate. climate. following the sun rotatingrotation. the louvers following the sun over the internal climate. rotation. [129] Reproduced with the permission from [[129]129] Reproduced Reproduced with with the the permission permission from COLT company, 2017. fromCOLT COLT company, company, 2017. 2017.

Built robotic controlling Built robotic controlling Hypothetical fleet of small robots These small robots could detect building Builtsystem robotic [158] controllingReproduced systemwith [158Hypothetical] Hypothetical fleet of small ﬂeetrobots of smallThese robots small called robots could detect building facade, and regulate system [158] Reproduced with called “Edge monkeys”. To protect These small robotsfacade, could detect and regulatebuilding energyfacade, and usage regulate and Reproducedthe permission with from the authors permission fromcalled “Edge“Edge monkeys”. monkeys”. To protect To protectenergy building usage and indoor conditions in order to close windows, the permission from authors building facades, regulate energy energy usage and indoorindoor conditions conditions in inorder order to close to close windows, authorsStephen Stephen Gage and Gage William and Williambuilding facades,facades, regulate regulate energy energy usagecheck andthermostats, and adjust blinds. Stephen Gage and William usage and indoor conditions. check thermostats,windows, and adjustcheck blinds. thermostats, and adjust Thorne,Thorne, 2017.2017. usage and indoorindoor conditions. conditions. Thorne, 2017. blinds.

Energies 2017, 10, 1672 23 of 32

4. Challenges, Limitations and Future Opportunities in Active Shading Systems The application of dynamic smart shading has grown widely in order mitigate the building conditions against excessive heat gain and glare. However, there are some challenges inherent to these systems that should be considered in future research. Challenges, limitations and opportunities of active shading systems are discussed in Table7.

Table 7. Challenges and future developments of dynamic shading systems.

Dynamic Shading Type Challenges and Limitations Opportunities and Development

• High initial cost (between 100–1000 US $/m2) and is more expensive than other smart glazing types [44]. • Improve the Electrochromic glazing life time • High labor and maintenance cost compared to other expectancy and durability to be similar to conventional glazing types [44]. those of standard coated windows [44]. • The optical properties that change the Near-infrared • Develop faster switching speeds (<5, 6 min) in Electrochromic Glazing switching electrochromics (NIC) are still little known [68]. order to promote better savings in energy and • The performance of the NIC glazing might be affected by occupants’ visual comfort [161]. the present climate changes [68]. • Develop higher visible transmittances in the • Low durability (sensitive to UV) [159] bleached state (τV > 0.6) to allow more • High increased surface temperature and slow coloration daylight [161]. process [160].

• Improve the properties of the SPD glazing • Lower transparency in the SPDs’ bleached state, and increase its transparency. SPDs compared with the EC glazing [48]. • Remove haze from the SPD glazing. • Undesirable haze [48]. • Further research is required on the integration of SPD glazing in buildings.

• Remove the haze from the LCD glazing. • Improve the properties of the LC glazing to • LCD glazing is hazy because it scatters rather than absorb have intermediate states between opaque and light, so there is a fog factor even when the device is in transparent states. • Investigate the application of the emerging LCD transparent state [44,82]. • LC glazing is either transparent or opaque with no (GDLC) which less haze and yellowing than in-between states [44]. conventional LCDs in different climate conditions [78]. • Carry out further researches on the integration of LCD glazing in buildings.

• Further studies should be undertaken on the use of shape memory actuators in the building industry; life cycle, solar activation, • Variable external conditions could limit the efﬁciency and and resistance to external weather the movement of the folding shading systems [106]. conditions [106]. Folding shading systems • The behavior of the SMPs is limited to one-dimensional • Further research on the use of smart materials deformation which limits their movement [162]. with dynamic shading devices [106]. • Further research on the control of the folding shading systems in response to the climate variations.

• Higher temperatures will decrease the power production • Further research required on cost assumption of the PV panels. of PV shading systems, particularly for • Dust accumulation and limited tolerance to overheating movable PV shading devices. PV mounted shading will restrict the expected performance and lower • To investigate materials that have long-term the efﬁciency. durability and can stand the various climate • Gap in PV shading systems in Mediterranean countries conditions (Snow, heat, dust, wind and air where the amount of solar radiation is high. tightness) [163].

• More research is required on working mechanism alternates of the algae façade systems in order to reduce their initial cost. • More research to test its performance under several climate conditions. • High initial cost (approximately $2500 per square meter • As relatively new, the Verde system was Algae Façade System for the bioreactor system alone) [164]. introduced in the market after the • High maintenance cost. development of algae façade system. Its main function is to collect light and transfer it through ﬁber optic cables, then algae is grown within the bioreactor to generate energy. More research is necessary to establish its properties and part of the market [165]. Energies 2017, 10, 1672 24 of 32

5. Conclusions This paper reviewed the current status of active shading systems in buildings, exploring their design principle, performance, working mechanism and building application. Six types of active shading systems including the electrochromic glazing, the automated shading systems consisting of the rotating and folding shading devices and the shading systems that integrated renewable energy generation such as the PV, algae façade and solar thermal collectors were discussed. The design principle, performance and application of each system were explored. Additionally, the control strategies of the systems including user control automated control were reviewed. In this literature review, 165 papers were examined to evaluate the different types of active shading systems. The signiﬁcant conclusions inferred from the reviewed studies states that:

1. The use of electrochromic windows is increasing; however, its high cost is still a challenge. 2. The electrochromic windows have always progressed in their performance and there is always an emergence of new types such as the NIR and POMs which have better performance. However, they are hindered by their high initial costs. 3. The use of folding shading systems is still limited because of the need of expensive smart actuators and sensors. 4. Rotating shading system is the most applied and studied system among active shading systems. Its low initial cost and available resources and materials including glass, metal, timber and fabric make it attractive. 5. The use of automatic control strategies has been proven to be much more effective than the use of manual user controlled systems due to the beneﬁts they provide including the adaptation to the external conditions. 6. The use of robotic controlling systems and the thermo-hydraulic controlling systems are emerging automatic control systems that requires further investigation as there are limited number of studies done on their performance, building application and use in varying climate conditions. 7. Additionally, more studies should be done on the integration of PV panels on this emerging type of shading devices.

Furthermore researches must be done on to develop faster switching speeds of electrochromic glazing to increase energy savings. Additionally the SPDs and LCDs suffer from haze in the glazing, thus, further research must be carried out in order to decrease the haze and test their integration in buildings. The movement of folding shading systems could be limited by the variable external conditions, therefore further investigation under different climatic conditions is required. Finally, the algae façade system is a promising immerging system that needs further exploration in terms of performance and building application.

Acknowledgments: The authors gratefully acknowledge financial support from the United Arab Emirates University through the Emirates Centre for Energy and Environment Research funded research project (31R054). Author Contributions: Kheira Tabet Aoul conceived and guided the review; Joud Al Dakheel conducted the literature data collection and analysis. Both authors wrote the paper. Conflicts of Interest: The authors declare no conflict of interest. Energies 2017, 10, 1672 25 of 32

Nomenclature

PV Photovoltaic SPDs Suspended particle devices EC Electrochromic devices LCD Liquid crystal devices LEDs Light emitting diodes CEC Conventional electrochromic glazing NEC Near-infrared Switching Electrochromic DBEC Dual-band Electrochromic PSBP Polymer-stabilized Blue Phase PDLC Polymer-dispersed Liquid Crystal LCoS Liquid crystal on silicon displays OILC Optically isotropic LC GDLC Gel dispersed liquid crystals AC Alternating current IR Infra-red SHGC Solar heat gain coefﬁcient Tv Visible transmission SC Shading coefﬁcient ITO Indium tin oxide IEQ Indoor environmental quality SRMs Stimulus-responsive materials SCMs Shape change materials SMMs Shape memory materials BIPV Building integrated PV BIST Building-integrated solar thermal IGU Insulated glass unit

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