19. METAMATERIALS FOR ”nZEB” BUILDINGS

BSEE IASI-RO DOI: 10.2478/9788395720413-019 METAMATERIALS FOR ”nZEB” BUILDINGS Victoria COTOROBAI1, Ioan Cristian COTOROBAI1, Silviana BRATA2, IonuţCristian BRANCA and Ana- Diana ANCAȘ1 1”Gheorghe Asachi” Technical University from Iași 2 POLITEHNICA University, Timișoara Abstract. Metamaterials are specially designed to interact, in a controlled manner, with various waves. They are very "young" but they have attracted the attention of specialists from the construction area. The buildings have known throughout their existence different approaches in terms of functions, requirements, concepts, materials used, and other, in correlation with the level of civilization, technology, climate characteristics, primary needs, or desire to express the power/the luxury in the different moments and for different people. The concept of the nZEB building was recently promoted. The metamaterials developed so far can also be used in nZEB, such as: for controlling the impact of the different waves with the building; in the equipment of thermal/visual comfort; in the control components; for increasing the performance of power generation equipment. This paper has inventoried some metamaterials that can determine the growth of the building's energetical performances and examples of the growth potential of the thermal and visual performance of glass systems containing metamaterials (static and dynamic). Keywords: metamaterials; metamaterials for roof cooling; waves guide for PV cell; thermal & acoustic metamaterials (aerogels). 1. Introduction 1.1. Buildings of the future. Requirements. Insurance possibilities. The recent climate changes, identified from the studies/measurements/observations made at the level of the planet Earth, have highlighted the need to reduce the concentration of CO 2 in the terrestrial atmosphere, respectively the need to promote the measures of energy efficiency of buildings (reduction emission CO 2 , by reduction energy consumption from fossils resources) [1, 2, 3, 4]. Lately, the measures promoted are completely new (results of the newest research & innovation). These must enable the energy performance of buildings to be increased and in relation to other quality criteria (environmentally friendly, acoustic; ensuring & maintaining human health; be dynamic-adaptable to occupant demands and environmental changes 213 Victoria COTOROBAI et al - interior and exterior; be economical; have a life span correlated with that of the structure; it can be integrated into the structure existing buildings simple and without the significant impact in the occupant's activities [5,6,7]. In existing buildings: it is absolutely necessary to increase the thermal and acoustic protection, by means of interventions, realized in general on the outside of the tire; adaptation of heating/cooling systems to the new requirements imposed on nZEB buildings (reduced loads, uniform energy distribution etc.); the association with systems for generating energy from renewable resources and others [8,9]. 1.2. Metamaterials. Definitions. Types of metamaterials. Applications. Metamaterials know strong development and high worldwide recognition (they are in the top 10 materials that will change the world). Their definition is not unitary. In the specialized literature, various definitions are given, in relation to the experience in the related field of research and to the experience of the authors. The most common definitions: ”A metamaterial = a material designed to have non-existent properties in natural materials” [10, 11]. The materials are the structures usually arranged in repeating patterns, at scales that are smaller than the wavelengths of the phenomena they influence. They derive their properties not from the properties of the base materials, but from their newly designed structures (their geometrical properties, precise shape, size, orientation, and arrangement). The new properties obtained give the metamaterial the quality of the smart material [12, 13]. He becomes capable of control electromagnetic waves by blocking, absorbing, enhancing, or bending waves. The metamaterials obtained can have uses that are impossible to achieve with the classical materials. The metamaterials designed for this purpose can affect/control the waves of electromagnetic, acoustic, or seismic radiation. The many and significant research was attracted by the metamaterials with a negative refractive index. This definition, in its most general expression, shows that the concept of metamaterials can cover all areas of physics: in the fields of electromagnetism including optics, acoustics, fluids, seismic etc [14, 15, 16]. In particular, in design composite metamaterials, electromagnetic waves interact with the inclusions that produce electric & magnetic moments, which in turn affect the macroscopic effective permittivity & permeability of the bulk composite medium [17, 18]. So, metamaterials can be synthesized by embedding artificially fabricated inclusions into a specified host medium and, in consequence, this provides the designer with a large collection of independent parameters such as properties of host materials, size, shape, and compositions of inclusions. In the research metamaterials with the characteristic's deliverables, all these properties can play an important role [19]. By manipulating the inclusions, the designer has at its disposal a new possibility for metamaterial processing. 214 The 30th Conference BSEE 2020, Iasi, Romania They were designed/studied and even (in some cases) made a variety of metamaterials. A classification of the different types of metamaterials developed so far and a characterization of each category are presented in different publications, [21, 22, 23, 24, 25, 26]. 1.3. Applications and research areas of metamaterials in buildings is diverse and multiples. In the field of buildings, the metamaterials can be used to increase [27]: • the performances of buildings (thermo-dynamic; acoustic; seismic; absorption / reflection, refraction, transmission, emission; oxidation; thermal/chemical stability) of the opaque/glazed, vertical/horizontal, exterior/interior; performance of heating / cooling systems and their components; • the performance of indoor lighting systems; • the performance of thermal/electrical/chemical energy storage systems; • seismic performance of buildings; • the performances of the quality control systems of the indoor atmosphere; • the performance of the thermoregulation systems. 2. Method. Theory. Design. Model 2.1. Theory 2.1.1. Metamaterials for the protection of buildings against the action of the exterior acoustics waves (noise due to road traffic) and the ventilation/piping installations The acoustic performance of the buildings is extremely important for the normal activity of the building. The most difficult issues were those related to: the protection of the building from road noise (which is constantly growing); reduction of noise transmitted by installations (with a positive impact on the location of building ventilation plants par example). The evolution of metamaterial research has provided efficient technological solutions for this purpose: a) aerogel for acoustical ant thermic protection building elements structures (presented at the point 2.1.2.); b) metamaterials structure for acoustical protection of installations. A solution in this scope:” Synthetic, sound silencing structures”. Acoustic metamaterials can block 94% of sounds (but not openair). This ring of materials will be able to us in vacuum cleaners, air conditioners, fans, and other devices and products much quieter” [28] . The mathematically designed, 3Dprinted acoustic metamaterial is shaped in such a way that it sends incoming sounds back to where they came from [28] say. Inside the outer ring, a helical pattern interferes with sounds, blocking them from transmitting through the open centre while preserving air's ability to flow through. The image of these acoustic metamaterials and the result of the demonstration for their performances is presented in Fig. 1. 215 Victoria COTOROBAI et al Fig. 1 - Acoustic metamaterial and noise cancellation device noise blocked. Recorded Microphone Signal (V), [28] 2.1.2. Metamaterial for the thermal & acoustical protection of the building • Metamaterials for thermal and acoustic protection: aerogels The material is a gel in which the liquid has been completely replaced with air. The actual matrix of the ring can be made of different substances (silica, metal oxides, graphene). The massive presence of air in the aerogel gives it the quality of excellent thermal insulation material and its special structure gives it a very high mechanical strength. The fatal defect of the aerogel is due to fragility, especially when it is made of silica. This disadvantage has been overcome by scientists from NASA who have made and experienced flexible polymer aerogels. Mixing other compounds in even silicabased aerogels could make them more flexible. So, the main qualities of aerogel are good thermal and sound insulation, high mechanical resistance, low density, many types, and high flexibility. The application of the aerogel in the field of buildings, as thermal and sound insulation, in the form of building blocks for low-density metamaterials is one of the recent initiations. The carbon aerogel is synthesized by sol-gel polymerization of resorcinol with formaldehyde, followed by drying and carbonization of supercritical fluids. The end result is an aero-gel nanostructure, which can be adjusted through the concentrations of reactants and catalysts in the precursor solutions. Negative permittivity and negative permeability are obtained simultaneously in the low-density carbon aerogel. The negative permeability is similar to plasma and can be explained by the low-frequency plasmonic state of the carbon networks. Permissively values have a strong dependence on the frame and carbon aerogel mixers. In Fig.2 is presented the high-frequency magnetic response of the induced circulating currents determines the negative permeability. 216 The 30th Conference BSEE 2020, Iasi, Romania Fig. 2 - The NASA processes to made flexible air-gel (Source: [29]) Following the analytical calculations, the specialists demonstrated that the permeability values have a linear relationship with (ω) 0.5. This shows a relaxation spectrum, as opposed to "magnetic plasma" of typical metamaterials. The use of the aerogel is unique and has a high potential for the realization of metamaterials with ultralow density at the nano-scale and also presents the ability to expand the potential applications of metamaterials, for different purposes and under extreme conditions. Very recently the aerogel has been used in the field of buildings, as thermal and sound insulation and for fuel protection. • Metamaterial for cooling the roof He determines radiation to the celestial vault. It is a covering the mirrors for cooling the buildings by pumping the interior heat into space (Fig. 3). For this action are realized “an air conditioning system for structures” (an engineered material): ”it has the ability to cool objects even under direct sunlight with zero energy and water consumption”. The metamaterial film, applied to a surface, cools the object underneath: a) it efficiently reflects incoming solar energy back into space while b) simultaneously, it allows the discharge of the energy accumulated by the surface, towards the underside of this film, in the form of infrared thermal radiation. 217 Victoria COTOROBAI et al Fig. 3 - Metamaterial radiative-cooling film (Source: [29]) The objective of the inventors of the "Radi-Cool" group consists of ecological cooling technologies with zero energy consumption. The metamaterial system "Optical metamaterials that cool objects underneath (cooling materials)" [29] present diverse properties: a)The system exploits a passive peak cooling technology: it dissipates the heat of objects wrapped on Earth and is covered with radiative cooling film in outer space (the celestial vault is temperature T = ~ 3 K), in the form of infrared radiation (813 μm), through the atmospheric transparency window; b) The cooling film was a radiative or hybrid film (glass microscope-metamaterial plastic), completely transparent to radiation from the solar spectrum, with infrared emission greater than 0.93 in the window atmosphere; c) Silver coating of the metamaterial film determined or with average cooling power Pc>110 W in three consecutive days and the night cooling power of 93 W between 11:00 and 14:00; d) The radiative cooling film can have objects below this level with 10 K (below ambient temperature during the day) and 16 K (respectively at night); e)Relatively low cost; f)Production technology: roll-to-roll type; g) By integrating into the silicon photovoltaic cells, it increases the efficiency by 5% and the amount of life (by cell cooling by over 10 K) with 5 years; h) Cooling an nZEB singlefamily with S = 50 m2 with a radiative cooling film with the same surface, it can ensure cases where no energy can be brought; This result is possible in South and South-East emplacement from the Romanian area; i) The application of the film directly on the roof leads to a decrease in the cooling necessary energy. This solution with the isolated roof with this film for the large urban area urban eliminates la need to use the "split" cooling peak systems type; j) The application of the film directly on the roof leads to a decrease in the cooling necessary energy. This solution with the isolated roof with this film for the large urban area urban eliminates la need to use the "split" cooling peak systems type. 2.1.3. Metamaterials for increasing the widow’s performance. The metamaterials were included in the most important windows from the Middle Ages. But the developments can carry out their research and allow them to create multi218 The 30th Conference BSEE 2020, Iasi, Romania functionalities and to create a special operation to allow them to be transformed into a multifunctional wall-mounted appliance rather when it is a single piece of coated glass. The "window of the future" (according to the emerging concept), it becomes extremely sensitive to change the parameters of the external and internal environment and it is necessary to adapt with regard to the environmental conditions and the requirements of the occupants (processing carried out inside). These include: switchable windows [30] and shading systems [31]. They have variable optical and thermal properties (they can be adapted to the climatic conditions and occupational preferences) [30]. By managing the lighting and cooling activity, a potential intelligent / dynamic adaptive: reducing the peak electric charges [30]; the well-being of the world grows during the day; I can offer comfort and energy production in high temperatures and radiation conditions. An ideal window is needed to be able to propose variable options, with a prompt response to change the climatic conditions and the occupied demands, respectively to adapt to them. To this goal, it is currently: a) passive devices: photochromic and thermochromic; b) active devices: with liquid crystals; with suspended particles; electrochromic. The metamaterials are present in both passive devices and active devices [30]. The spectacular evolution of research in the field of nano, electro, optical allowed the emergence of the most efficient glazed system, by combining electrochromic windows obtained through nano technologies, with thermochromic windows. These are the windows obtained by "heliotrope" technology, which has the following major performances: the transmission of visible light through the window is electronically modulated, from <3% to> 50% in a time of τ ≤ 5 min; retains the neutral grey appearance, aesthetically pleasing, over the entire range of fading; maintains a neutral grey appearance throughout the fading range; can be electrically connected both wired and wireless; have low power consumption (<3V) and controlled state memory functions; can hold comfortably in confined spaces; no installation, maintenance and replacement costs associated with shading systems are required; has a good ability to connect to the HVAC system in buildings; installation costs are lower compared to conventional systems that have associated / integrated shading systems; has an excellent aesthetic; can be controlled on request; they are light; has the best performance compared to other dynamic systems. 2.1.4. Perovskites — Cheap Solar Cells Solar cells made of perovskites. In the global efforts to reduce the costs of PV cells and to increase the efficiency of conversion of perovskite technologies, the evolution of this is important [32]. Since 2009, when the first cells with perovskite products had η = 3.9, until now, when their efficiency has reached η = 31.3 for exterior PV and η = 36.3 to the interior PV (for recovery interior light). Furthermore, the cost of care is much smaller. Perovskites are a class of materials defined by a certain crystalline structure. They can contain any number and type of elements (perovskites and silica, graphene, lead etc). They can be sprayed on glass rather than meticulously assembled in clean 219 Victoria COTOROBAI et al rooms. A special category in this class of metamaterials is perovskite-graphene cells is presented in Fig. 4 [32]. These are very recently developed solar cells, with an excellent quality-efficiency-cost ratio and great flexibility. The perovskite photocells contain in the active layer a natural mineral structure with special properties and it is expected to become a market leader in the field of photoelectric solar energy technologies. a) PV tandem structure with perovskites b) Efficiency of the PV with perovskite Fig. 4 - PV with perovskite ([23], Image credit: University of Oxford) Perovskite site presents: a) the possibility of combining several semiconductor materials in order to expand the spectral domain of the solar radiation that can be used with consequences in increasing their efficiency: a cell with perovskite has been recently investigated which has reached the efficiency η = 31% (2018). Considering the much lower price (at least ... times lower than other cells with similar performance), they can become a major option for future technologies in the field; b) ever-increasing efficiency: photovoltaic cells with perovskite increased, from the end of 2009, from η = 3.8%, to η = 27% at the beginning of 2017 and 31% at the beginning of 2018. The band structure of the perovskite ore is adjustable: an optimized structure can be designed to allow the exploitation of a proportion of the spectrum of the net solar radiation superior to the cells that use only the visible spectrum. This structure allows the maximum efficiency given by the Shockley - Queisser limit (approximately 31% under the conditions: solar spectrum: AM1.5G; irradiance: 1,000 W / m2, perovskite bandwidth: 1.55 eV); c) other embedded materials: c1) Initially, lead was used to make them; c2) the technology has advanced and very recently, in 2017, it was proposed to combine perovskite with graphene. They have: eliminated the major disadvantages of lead; added benefits to graphene; c3) the use of graphene has led to multiple innovations and high performances: super-flexible films; increased efficiency; high robustness; low cost price (for portable applications I am a market leader); c4) the possibility of further development / growth. We are adding another new type of perovskite cell designed especially for the use of light energy from inside in order to power the laptops and other [33,34,35]. These very recently discovered PV cells, together with those integrated in the building envelope to 220 The 30th Conference BSEE 2020, Iasi, Romania which dynamic active/passive windows can be added, can ensure the autonomy of the buildings in the south, south-east. 2.1.5. Metamaterials for to increase the performance of the heating/cooling systems These metamaterials have been developed and diversified very recently. Among these we mention the graphene radiators. E.g.: Radiator SOLUS (design by KOLEDA) (Fig. 5.) could save you over 80% on your next heating bill due to its clever use of the completely new graphene-based technology.” The nanotech coating has returned test results that are 5x more efficient than conventional radiator” [33]. Fig. 5 - Heating radiator with graphene [33], (Source: www.uberdesign.co.uk) 2.1.6. Metamaterials for to increase the performance of power generation systems The metamaterials have found important use in the field of direct conversion of solar energy into electricity. Is used to increase their efficiency by concentrating solar radiation with the help of so-called waveguides or increasing the performance relative to the absorption of solar energy, respectively radiation in the visible and infrared spectrum (for about 95% of incident solar energy). Researchers in the field have proposed numerous technical solutions, which are becoming more and more efficient [36,37,38]. One of the latest solutions proposed in this field is an ultrafine device (with a thickness of 90 nm) capable of absorbing a large part of the solar radiation from the visible spectrum, in the broadband as well as from the non-polarized light, in a wide range of angles. The technology can be used for photovoltaic conversion but also for photodetectors, thermal transmitters, and optical modulators. So far, it has been difficult to simultaneously meet these requirements, but the discovery and development of graphene research have allowed these desires to be realized. 221 Victoria COTOROBAI et al Fig. 6 - Schematic of graphene-based metamaterial absorber [ 39], (Source: U. Sydney / NPG) Australian researchers [39] have proposed a metamaterial of "graphene 12.5 cm2, 90 nm thick, with approximately 85% absorption of visible polarized light and infrared radiation, covering almost the entire solar spectrum (300-2500 nm)" [40]. The metamaterial is composed of a package made of graphene and dielectric layers, arranged alternately; to achieve broadband absorption over incident angles up to 60 ° used a grating couple the light into waveguide modes. For solar thermal applications, the use of an absorber with very wide spectral and angular responses is ideal (it has been shown that heating at 160 ° C under the influence of natural sunlight is a good solution). So, ”is open a new approach for the applications of the strong absorption of large surface photonic devices based on 2D materials”. 3. Case study. Metamaterials for increasing the widow’s performance. Results and Discussion The authors conducted a case study, meant to present a comparison between the performances (visual, solar transmission, coefficient of heat transfer) of the different glass systems to highlight the importance of a preliminary analysis of the performances of some glass systems, in different hypotheses of design and location / irradiation (Table 1.), for the selection of the best performing concepts. The simulations were performed in WINDOW 10 for windows and TRNSYS for simulation comportment of the room / building delimited by glazed surfaces. The important results obtain after simulation the comportment of glasses systems is: • The U-factor of a fenestration assembly which characterizes the thermal performance of the glazed system separating the indoor environment from the outdoor one between which there is a thermal gap. The thermal transfer processes include the combined effects of conduction, convection, and radiation [41,42]. 222 The 30th Conference BSEE 2020, Iasi, Romania • • • • Solar Gain (by direct or indirect solar radiation), characterized by gain coefficient (SHGC) of the glazing [40] Shading coefficient (SC) of the window [43,44] Infiltration, represented by heat loss and gain also occur by infiltration through cracks in the fenestration assembly and measured in terms of the ”amount of air (cubic feet or meters per minute) that passes through a unit area of fenestration product (square foot or meter) under given pressure conditions”. The infiltration varies with wind-driven and temperature-driven pressure changes. Graph of the daily & annual variation of luminous variation transmittance/ reflectance flux and energy transmittance/reflectance flux by frontal & dorsal face (Fig. 7). The 2001 ASHRAE Handbook of Fundamentals contains the following equation for calculating the energy flow through a fenestration product (assuming no humidity difference and excluding air infiltration) [45,46]: q =U t •(Apf(tout−tin))+(SHGCt•Apf •Et) • [1] where: q = instantaneous energy flow in W; Ut = overall coefficient of heat transfer (U-factor), in W/m2, K; tin = interior air temperature, in oC; tout = exterior air temperature, in oC ; Apf = Total projected area of fenestration, in m2 ; SHGCt = overall solar heat gain coefficient, non-dimensional; Et = incident total irradiance, in W/m2. • the properties U-factor, SHGC, and infiltration determine the energy flow through the system windows [47,48,49]. Our analyses is ample but, for this work I have retained an analysis of the graphs with daily and annual variation of light and solar energy through the glass system (glass system with 2 windows: glass 1, gas layer 1, glass 2; glass system with three windows: glass 1, gas layer 1, glass 2; gas layer 2, glass 3) for the retained variants highlights the following aspects. There are other factors that determine the performance of windows: window thickness, gas blades; type of gas used; glass configuration-types and position of windows) types and position of shading systems but in the paper, we focused only on the impact of dynamic / intelligent, active or passive glass with metamaterials, on energy performance (solar flux / light). The resultants of the case study are relevant for demonstrations les performance for the windows with metamaterials. The simulation results are shown in Fig.8, 9,10 and 11. • V1 is a classic glazed system for the beginning of the third millennium (two windows + air layer in the cavity): much of the sunlight and energy is transmitted through the front but also through the back, without being able to control, in the absence of shading, transmission / reflection process; • V2, V3, represent classic glazed systems for the 1st decade of the third millennium (two clear windows + a double-glazed window, interior / exterior, air layer in the cavity): solar energy transmitted through the front and back is less transmitted and in the case of Low-e glass -is on the inside, the solar energy is strongly reflected, so the system becomes a solar trap; 223 Victoria COTOROBAI et al Case V1 V2 V3 Triple clear glass -air -blades Triple window: outer Low-E layer- - Triple glass: - 2 clear - air blades 2 clear windows -air blades -Low-e interior layer Structure Month Month Month Month Reflected Visible Light Solar energetic reflected Transmitted Solar Energy Transmitted Visible Light Front surface glasses system hours hours hours Fig. 7 - Graphs with daily and annual variation of luminous and solar fluxes through the glass systems glass system  continuation 224 The 30th Conference BSEE 2020, Iasi, Romania Case V1 V2 V3 hours hours hours Month Month Month Month Reflected Visible Light Reflected Solar Energy Transmitted Solar Energy Transmitted Visible Light Structure Fig. 8 - Graphs with daily and annual variation of luminous and solar fluxes through the glass system  continuation 225 Victoria COTOROBAI et al Case V4 V5 V6 Structure Month Month Month Month Solar fl energetic reflected Reflected Visible Light Transmitted Solar Energy Transmitted Visible Light Front surface glasses system hours hours hours Fig. 9 - Graphs with daily and annual variation of luminous and solar fluxes through the glass system  continuation 226 The 30th Conference BSEE 2020, Iasi, Romania Case Structure V4 V5 V6 Month Month Month Month Reflected Visible Light Solar energetic reflected flux Transmitted Solar Energy Transmitted Visible Light Back surface glasses system hours hours hours Fig. 10 - Graphs with daily and annual variation of luminous and solar fluxes through the glass system  continuation 227 Victoria COTOROBAI et al V7 Transmitted Visible Light Transmitted Solar Energy Reflected Visible Light Reflected Solar energetic Month Front surface glasses system Back surface glasses system Fig. 11 - Graphs with daily and annual variation of luminous and solar fluxes through the glass system  continuation • Other simulations, for glasses systems with aerogel, are demonstrated the very good thermal isolation by this system; • A wrong configuration can turn the glazed system and the room into a solar trap that requires a high amount of cooling energy • The use of high-performance dynamically adaptive glazed systems can substantially reduce the cooling load (with ca. 50%). The exceeded flux is transformed into energy. • A favourable behaviour is presented by systems with thermochromic windows (V4, V7): the visible flux transmitted/reflected by electrochromic and thermochromic face glasses is low. 4. Conclusions • The development of research in the field of metamaterials has opened a huge window to possible applications in the field of buildings. • Some of these possible uses were exposed within the paper, which could lead to a paradigm shift in the concept of new buildings but especially in increasing the performance of existing buildings (thermal, acoustic, seismic protection measures are 228 The 30th Conference BSEE 2020, Iasi, Romania targeted; heating/cooling equipment; CO2 collection and recovery equipment; technologies to increase the performance of direct solar energy conversion systems); Example: heliotrope glass, thermochromic glass, nanoelectrochromic glass etc. • Basically, the pandora's box was opened, physicists, mathematicians, and theorists respectively know what they have deposited in it but the engineers have to select what is useful today and tomorrow, analysing the performances & risks & evolutions possible over time. 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