Window component characteristics

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1 Window component characteristics Content Panes and Screens Shading Devices Frames and Spacers Module 2: Window components characteristics / July 2004 / Slide 1

2 Panes and Screens Most important properties Spectral Selectivity controls visible Transmittance / Reflectance solar Transmittance / Reflectance radiative losses Scattering Behaviour Module 2: Window components characteristics / July 2004 / Slide 2

3 Examples of Important Spectrally Selective Materials in Solar Energy Conversion Glass and glazing products Low emittance coatings Solar gain control coatings Smart windows, e.g. electrochromics Daylighting Redirectional materials Reflectors Radiative cooling Selective paints Absorber surfaces for solar collectors Module 2: Window components characteristics / July 2004 / Slide 3

4 Different Pane Types Clear Float Glass (uncoated) Softcoated Low-E panes Hardcoated low-e panes Absorbing solar control glass Reflecting solar control glass Module 2: Window components characteristics / July 2004 / Slide 4

5 Optical Properties of Clear Float Glass 100 Transmittance / Reflectance (%) T R Wavelength (nm) Module 2: Window components characteristics / July 2004 / Slide 5

6 Glazing used for Heating Dominated Climates Desired properties: High thermal resistance (low U-value to minimise energy loss) High solar gain (maximise potential for passive solar gain) High visible transmittance (maximise potential for use of daylight ) Module 2: Window components characteristics / July 2004 / Slide 6

7 Low-E coated glass (iplus neutral s(89/63): : Tvis= 0.89; Tsol = 0.63; E = 0.04) T Rf Rb Transmittance/Reflectance Wavelength Module 2: Window components characteristics / July 2004 / Slide 7

8 Glazing for maximising passive solar gain: Low-e coating is positioned on Surface 3 - windows can be net gainers of energy even in a cold climate clear outer pane maximises light and solar heat gain low-conductivity gas (e.g. Argon) hard low-e coat (high g-value) reflects longwave heat and is poor emitter of that heat clear inner pane maximises light and solar heat gain Module 2: Window components characteristics / July 2004 / Slide 8

9 Transmittance/Reflectance Low emittance hardcoated glass for high solar gain and low thermal loss (K-glass (82/68): : Tvis= 0.82; Tsol = 0.68; E = 0.17) T Rf Rb Wavelength Module 2: Window components characteristics / July 2004 / Slide 9

10 Infrared spectral reflectance of Pilkington K GLASS (low emittance hard coated glass) Spectral Reflectance ε = U (DGU) cg ~ 1.9 W m -2 C Wavelength (microns) Module 2: Window components characteristics / July 2004 / Slide 10

11 Absorption in solar control coatings 0.6 Transmittance / Absorptance Azurlite T Azurlite A Blue T Blue A Bronze T Bronze A Clear T Clear A Wavelength (nm) Module 2: Window components characteristics / July 2004 / Slide 11

12 Solar Gain Control : the old way & the new way! Two glazings with the same total solar energy transmittance g = 0.40, T vis = 0.14 g= 0.41, T vis = 0.63 High absorption in the glazing leads to a large secondary thermal radiation contribution to the total solar energy transmittance Module 2: Window components characteristics / July 2004 / Slide 12

13 Cool glazing configuration: solar control low-e surface located on Surface 2 - cuts solar heat gain without greatly sacrificing daylight, yet sunlit glass does not become a radiator! Key elements: (optional) selective tint absorbs solar near-infrared more than visible light spectrally selective low-e coating suppresses inward heat flow and reduces near-infrared solar transmission second pane puts convection buffer between outer pane and building s occupants Module 2: Window components characteristics / July 2004 / Slide 13

14 Optical properties of cool silver (reflecting solar control) based coated glass Interpane Ipasol 66/34 Silver Based Low Emittance Glass Transmittance / Reflectance T Rf High visible transmittance T v Low solar transmittance T s Low thermal emittance ε ~ 0.03 U ~ 1.0 W m -2 C Wavelength (nm) Module 2: Window components characteristics / July 2004 / Slide 14

15 Optical properties of Cool silver based coated glass compared to solar spectrum 1 Reflectance / Transmittance / Normalised Solar Irradiance Solar T R Wavelength (µm) Module 2: Window components characteristics / July 2004 / Slide 15

16 Comparison of reflecting solar control glass and hardcoated low-e 1 Reflectance / Transmittance T (Tin Oxide) T (Silver) R (Silver) R (Tin Oxide) Wavelength (nm) Module 2: Window components characteristics / July 2004 / Slide 16

17 Scattering Behaviour When direct beam radiation is reflected or transmitted by a material the reflected component may be either: Specularly reflected (mirror like) directional-directional (regular) Scattered or diffusely reflected near-normal hemispherical Module 2: Window components characteristics / July 2004 / Slide 17

18 Shading Devices Mostly used Devices Types Venetian Blind Fixed slat shading device Concertina blind or pleated blind Screen or Roller blind Lamellas Module 2: Window components characteristics / July 2004 / Slide 18

19 Venetian and fixed slat blind Slat strip width, s (mm) Angle, α ( ) Crown height, c (mm) Chord width, w (mm) Outdoor Indoor Radius of curvature, R (mm) Pitch, p (mm) Thickness, d (mm) Module 2: Window components characteristics / July 2004 / Slide 19

20 Shading devices: illustration Incidence angle 45 degrees Transmission after (multiple) reflections Incidence angle 0 degrees Regular transmission Incidence angle -45 degrees (groundreflection) Module 2: Window components characteristics / July 2004 / Slide 20

21 Incident angle and solar transmission shortwave transmission venetian blinds slats at 45 degrees total shortwave transmission transmission Regular transmission between successive slats transmission after (multiple) reflection doorlating via (evt. meervoudige) reflecties Incidence angle Transmission for ground reflected radiation angles Transmission for sky and sun radiation angles Module 2: Window components characteristics / July 2004 / Slide 21

22 Module 2: Window components characteristics / July 2004 / Slide 22 Screen or roller blind

23 Mounting possibilities of Blinds Blind may be positioned in one of three positions: Internal (inside of the glazing) External (outside of the glazing) Between the glazing panes (Interstitial) Module 2: Window components characteristics / July 2004 / Slide 23

24 Ventilated or unventilated Gaps Pane or shading T b_i T gap_i,out T f_i+1 Pane or shading L i s i T gap i H i h cv,i h cv,i q v,i T gap_i,,in Module 2: Window components characteristics / July 2004 / Slide 24

25 Ventilated cavity ISO DIS Outlet air temperature, T gap,i_out H i Air flow ϕ v,i Average air temperature, T gap,i Average surface temperature, T ave,i H 0,i Height h Inlet air temperature T gap,i_in Air temperature T gap,i (h) Module 2: Window components characteristics / July 2004 / Slide 25

26 Solar Protection : Internal Blind Maximising the Blind solar reflectance minimises the total solar gain Blind on the inside of the glazing Formula and coefficient according to pren (1998) Glazing Blind g = g(1 gρ α Λ ) total SB SB Λ 2 Where Λ represents the effective heat transfer through the configuration defined as Λ= 1 withλ = 18Wm 2K 1 ( ) 2 U Λ 2 where U is the thermal transmittance, or heat loss coefficient, of the glazing without the blind and Λ2 assumes the value 18 W m -2 o K -1. Module 2: Window components characteristics / July 2004 / Slide 26

27 Solar Protection : External Blind Total solar energy transmittance g-value Blind on the outside of the glazing Formula and coefficients according to pren (1998) g total Λ = τ B g + α B + τ B (1 g) Λ 2 Λ Λ 1 where Λ = 1 U Λ Λ 3 where Λ 1 = 6 W/m 2 K; Λ 2 = 18 W/m 2 K Blind Glazing Module 2: Window components characteristics / July 2004 / Slide 27

28 Solar Protection : Interstitial Blinds (for unventilated air spaces) Blind in between the glazing Formula and coefficient according to pren (1998) g Glazing Blind Glazing total where = gτ B + g ( α B + (1 g) ρ B Λ = 1 U Λ where Λ 3 = 3 W/m 2 K 3 ) Λ Λ 3 Module 2: Window components characteristics / July 2004 / Slide 28

29 Integrated optical properties of blinds Solar Solar Solar Types of blinds Reflectance Transmitance Absorptance ρ_sb τ_sb α_sb Absorptive Blind Reflective Blind Transmissive blind Module 2: Window components characteristics / July 2004 / Slide 29

30 Spectral optical properties of blind materials Absorptive blinds 100 Highly Absorbing Blind Reflectance / Transmittance (%) R T Wavelength (nm) Module 2: Window components characteristics / July 2004 / Slide 30

31 Spectral optical properties of blind materials Reflective blinds 100 Blind with Low Transmittance Reflectance / Transmittance (%) R T Wavelength (nm) Module 2: Window components characteristics / July 2004 / Slide 31

32 Spectral optical properties of blind materials: Transmissive blinds 100 Blind with Finite Transmittance Reflectance / Transmittance (%) R T Wavelength (nm) Module 2: Window components characteristics / July 2004 / Slide 32

33 Frames and Spacers Mostly used Frame Types Wooden Frame Plastic Frame Metall Frame thermally broken profile thermally unbroken profile Frames composed of Materialcombinations Module 2: Window components characteristics / July 2004 / Slide 33

34 Glazing Schematic (ignoring the Frame) Glazing (e.g. Glass) Gas fill (e.g. Air, Argon) Surface Spacer Seal Module 2: Window components characteristics / July 2004 / Slide 34

35 Categories of Spacer Types Aluminium Spacer Stainless Steel Spacer Synthetic Material Spacer Spacer of a combination of different Materials Module 2: Window components characteristics / July 2004 / Slide 35

36 Examples of Spacer Module 2: Window components characteristics / July 2004 / Slide 36

37 Examples of Ψ-values of Spacers for common types of glazing spacer bars (e.g. aluminium or steel) Frame Type Wood or PVC Metal with a thermal break Metal without a thermal break Double or triple glazing uncoated glass air or gas filled 0,06 0,08 0,02 Glazing type Double or triple glazing low emissivity glass (1 pane coated for double glazed) (2 panes coated for triple glazed) air or gas filled 0,08 0,11 0,05 Module 2: Window components characteristics / July 2004 / Slide 37

38 Examples of Ψ-values of Spacers for glazing spacer bars with improved thermal performance Frame Type Wood or PVC Metal with a thermal break Metal without a thermal break Double or triple glazing uncoated glass air or gas filled 0,05 0,06 0,01 Glazing type Double or triple glazing low emissivity glass (1 pane coated for double glazed) (2 panes coated for triple glazed) air or gas filled 0,06 0,08 0,04 Module 2: Window components characteristics / July 2004 / Slide 38

Ph P y h s y i s c i s c s R ev e i v e i w e : R ad a i d a i t a io i n o UV VIBGYOR infra-red

Ph P y h s y i s c i s c s R ev e i v e i w e : R ad a i d a i t a io i n o UV VIBGYOR infra-red Glass, Glazing and Window Energy Performance by Alex McGowan, P.Eng. Levelton Consultants Limited Victoria, British Columbia, Canada AIBC Module V Skin Problems April 26, 2007 Outline of Presentation Physics