lecture 4 – insulated glass units · 2014-10-29 · lecture 4 – insulated glass units viorel...
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ADVANCED DESIGN OF GLASS STRUCTURES
Lecture 4 – Insulated glass units Viorel Ungureanu
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards and Catastrophic Events
520121-1-2011-1-CZ-ERA MUNDUS-EMMC
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
Introduction
An insulating glass unit (IGU) is a structural transparent element aiming at providing superior building physics characteristics (reduce thermal losses, improve on the energy savings ....improve transparency by reducing condensation on the warmer side).
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Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
Insulated glass units Components
A multi-glass combination consisting of two or more panes enclosing an hermetically sealed air space. It takes advantage of the fact that air has a low thermal conductivity.
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The space is filled with dehydrated air or gas.
The panes are connected by a spacer, using sealants to reduce water vapour penetration.
The whole unit is hermetically assembled by a secondary edge seal
The spacer contains a desiccant that absorbs humidity from within the air space
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
Insulated glass units Thermal and light physics Light radiation transmission
Glass has very high transparency within the visible range of wavelengths (λ ≈ 380-750 nm).
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32%
3%
Total solar radiation reaching the outer glass pane
Non transmitted
Transmitted
Reflected
Absorbed
3% 55% 42%
Long wave radiation
(thermal effect)
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
Most energy from solar radiation is contained in the IR long wave radiation (55%). Therefore, the strategy for solar protection is to block as much IR as possible without reducing the transmittance in the visible spectrum.
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
▫ Heat transfer through a glass pane:
▫ From warm side to cold side (1)
▫ From the light radiation (2)
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1
2
Heat transfer modes:
Thermal conductivity Heat transfer within a body or between adjacent bodies.
Heat transfer by conductivity
Thermal convection Heat transfer between the surface of a solid body and a surrounding fluid (liquid or gas).
Thermal radiation Heat transfer resulting from a temperature exchange between two neighbour bodies at different temperatures. In the IR region.
Emissivity (εn) is a characteristic of the bodies’ surface associated with thermal radiation. The lower the emissivity the lower the thermal radiation. For glass εn = 0.89. This value may be lowered by special coatings.
Heat transfer by convection
Heat transfer by radiation
Insulated glass units Thermal and light physics Heat transfer
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
6
Thermal resistance (R) | [R] = (m2.k)/W | R =1/U
In an exposed glass pane the three types of heat transfer are present. The sum is expressed by coefficient U.
convection
conductivity
radiation Total thermal transmittance (U) | [U] = W/(m2.K)
U factor is the heat flux crossing 1 m2 of a glass wall for a temperature differential of 1ºC between inside and outside. The lower U value is, the lower are the heat losses.
Total Solar Energy Transmittance (TET) | [g] = dmless a.k.a. Solar factor (SF) or g value (g) in Europe; a.k.a. Solar Heat Gain Coefficient (SHGC) in the USA
g factor is the ratio between the solar radiation that is transferred through the glazing (reaching the interior), and the total solar radiation reaching the outer pane. It is composed of (i) the direct transmittance, (ii) the part of the absorptance that is dissipated inwards and (iii) convection.
The lower it is the less the solar gain is.
Light transmittance | tv value | [tv] = dimensionless
Insulated glass units Thermal and light physics Light radiation related standard parameters
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
Layout & components influening IGUs physics Number of panes, filling gas & low-e coatings
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In order to reduce coefficient U the thermal resistance of the glass element has to be increased.
convection
conductivity
radiation It is not possible to change the convection properties but conductivity can be reduced by adding air space elements (preferably with a heavy gas: lower thermal conductivity) and heat transfer by radiation can be reduced by low emissivity coatings.
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
Low emissivity coatings are sputtered or pyrolytic, transparent or metallic or metallic oxidic coatings that reduce heat losses by a combination of absorbtion and reflection.
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
8
U thermal transmittance
g energy transmittance
tv light transmittance
In order to reduce coefficient U the thermal resistance of the glass element has to be increased.
convection
conductivity
radiation It is not possible to change the convection properties but conductivity can be reduced by adding air space elements (preferably with a heavy gas: lower thermal conductivity) and heat transfer by radiation can be reduced by low emissivity coatings.
Layout & components influening IGUs physics Example
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
Edge seal material:
Polyurethane edge seal
Silicon edge seal
Polysulphide edge seal
drier 1 sealing (butyl)
2 sealing (polysulphide, silicone)
aluminium spacer synthetic spacer
soft spacer (butyl) with integrated drier
2 sealing (polysulphide, silicone)
Spacer material:
Steel/aluminum spacer
Synthetic spacer
Soft spacer
Steel spacer Synthetic spacer Soft spacer
Aluminum Stainless steel
Thermix (Stainless steel + plastic sheet)
Ext
erio
r -
10º
C
Inte
rior
+ 2
0ºC
Ext
erio
r -
10º
C
Inte
rior
+ 2
0ºC
Ext
erio
r -
10º
C
Inte
rior
+ 2
0ºC
Layout & components influening IGUs physics Spacer
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
Insulated glass units Shapes
Flat glass units -Rectangular, triangular…… Curved glass units - Cylindrical, conical, free shaped…
Joanneumsviertel, Graz
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
Noise is any type of sound that is disturbing, annoying or painful. Ambient noise consists of a multitude of sounds of different frequencies and intensities. To represent the volume perceived by the human ear, a logarithmic scale has been chosen for acoustic measurements. The unit of measurement is the decibel (dB). The auditory threshold is the value of 0 dB and the pain threshold has a value of about 130 dB.
Effective sound control means controling the two physical effects of wave propagation:
Noise sorces: Airborne (e.g. Outdoor and indoor noise in buildings, internal inherent noise) Impact (internal noise, mostly footsteps) Structure-borne (equipment noise, building services)
• Noise insulation by reflection (sound insulation) the sound energy is not converted into a different energy form, but its direction of propagation is changed by reflection. • Noise damping by absorption (sound absorption) sound energy is essentially converted into heat (dissipation).
Insulated glass units Sound physics
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
The sound insulation provided by a partition is defined by an index that represents the difference between internal and external noise (sound attenuation R).
Insulated glass units Sound physics
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
For each relevant construction partition element the parameter R must be such that the sound insulation it provides may meet the terms of the code regulation. These are established in terms of a normalized acoustic insulation (DnT).
R depends on the sound frequency. The best behaviour of an insulating element is obtained when it provides insulation for the frequencies were the noise is stronger. By choosing apropriate materials and layout it is possible to tailor a glass pane for insulation for a precise type of sound.
Sound profile 1
Sound profile 2
Window sound spectrum
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
Insulated glass units Support systems
Typical linear glass support
The self weight of glass is transferred to the frame through setting blocks at the bottom glass edge. Lateral loads are resisted by clamping the glass between the frame system and clamping/pressure plate on the other side.
Panels are fixed to the sub-structure at discrete points by clamps. The self weight is transferred through setting blocks and the lateral loads through low friction clamps.
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
Insulated glass units Support systems
Watch out for building physics!
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
Insulated glass units Design External and internal actions
External loads Wind loads Snow loads Dead loads Thermal loads Dynamic loads
Hail loads Earthquake Bomb blast Impact loads Internal loads
Internal loads Temperature difference ∆T Meteorological pressure change ∆pmet Change of altitude ∆H
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
Insulated glass units Design Durability and Service Life Expectancy
Fogging
Glass fracture
Maintainability and Repairability
Sustainability
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
Insulated glass units Design Durability and Service Life Expectancy Fogging
Fogging of IGU’s is caused by condensation of moist air that penetrates into the air space of IGU’s through or around the hermetic seal of the unit.
Seal failure is usually caused by: ▫ Prolonged water exposure of the perimeter seal ▫ Absence of functional weep holes to drain water leakage ▫ Discontinuities, poor bond or thin applications of the perimeter seals.
To assess the susceptibility of IGU’s to seal failures: ▫ Test by cycling through heating and cooling cycles (ASTM E-774)
▫ Units that pass the test are grouped in three performance levels: Class C (15% failure rate after 20 years) Class CB (15% failure rate after 20 years) Class CBA (25% failure rate after 20 years)
The desiccant contained in the spacer helps condensation resistance by absorbing moisture built into the unit.
Spacers with bent, welded, or soldered corners, rather than corners constructed with slip-in corner keys, are more reliable because they provide a stable surface for seal adhesion.
Similar to IGU’s seal failure, laminated glass can delaminate when the edge of the laminated glass is in contact with water over extended periods, causing the interlayer to debond from the glass surface.
Building Envelope Design Guide – Glazing by Nik Vigener, PE and Mark A. Brown
http://www.wbdg.org/design/env_fenestration_glz.php
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
Insulated glass units Design Durability and Service Life Expectancy Maintainance and reparability
The glazing seals between the glass and framing must be replaced periodically to maintain good performance. Properly installed silicone wet seals should last 10 to 20 years; gaskets 15 to 20 years.
Fogged IGU’s cannot be repaired.
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
Insulated glass units Design Durability and Service Life Expectancy Sustainability
IGU’s have a shorter service life (most practitioners estimate it at 15 to 30 years) compared to monolithic glass, which, if not physically damaged, has an infinite lifespan.
The energy savings afforded by IGU’s usually pays for the replacement cost if the units last more than 15 years.
On the downside, IGU’s are typically not recycled: since they consist of a mix of glass, metallic glass coatings, sealants, and aluminum spacers, IGU’s require significant and costly effort to separate the constituent materials. Furthermore, glass is manufactured from relatively inexpensive and abundant raw materials, which makes glass recycling unattractive.
At the end of their service life, IGU’s are generally discarded as general trash. Crushed glass is sometimes utilized as hard fill. Most glass manufacturing plants recover glass discarded during the float glass manufacturing process and combine them with other batch materials for subsequent production. Overall, the most promising strategy to limit the amount of glazing in the waste stream is find ways to extend the service life of IGU’s.
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
Insulated glass units Design procedure Load distribution
In case of double glazing, with panes of thickness h1 and h2, the distribution of external uniformly distributed loads (e.g. wind, snow, self weight) is essentially determined by the distribution of the stiffness of the panes, that is:
32
31
31
1 hh
h
+=δ
132
31
32
2 1 δδ −=+
=hh
h
a
b
h1 h2 s
Additionally, the distribution of external loads is determined by the insulating unit factor ϕ. 4*)/(1
1
aa+=ϕ
The length “a” gives the actual dimension of the unit (e.g. in a rectangular unit the length of the short edge) while “a*” is the characteristic length of the unit, depending on the thickness of the glass panes (h1 and h2) the gas space (s), and the shape of the unit (λ).
( )25,0
532
31
32
319,28*
⋅+⋅⋅⋅=
khh
hhsa
λ=a/b
p* (internal initial pressurization)
0 5 10 20 30 50 100 200 300 500
1,0 0,019 0,019 0,019 0,018 0,017 0,015 0,011 0,008 0,007 0,005
0,9 0,024 0,024 0,023 0,022 0,020 0,017 0,013 0,009 0,007 0,006
0,8 0,029 0,029 0,028 0,026 0,023 0,020 0,015 0,010 0,008 0,007
0,7 0,035 0,035 0,034 0,031 0,028 0,023 0,017 0,012 0,010 0,008
0,6 0,042 0,042 0,040 0,037 0,033 0,027 0,020 0,014 0,012 0,009
0,5 0,050 0,050 0,048 0,044 0,040 0,033 0,025 0,018 0,014 0,011
0,4 0,059 0,058 0,057 0,053 0,049 0,042 0,031 0,022 0,018 0,014
0,3 0,068 0,067 0,066 0,064 0,061 0,054 0,042 0,031 0,025 0,020
0,2 0,077 0,077 0,076 0,076 0,074 0,071 0,062 0,048 0,040 0,031
0,1 0,086 0,086 0,086 0,086 0,086 0,085 0,084 0,081 0,077 0,068
0 0,095 0,095 0,095 0,095 0,095 0,095 0,095 0,095 0,095 0,095
Coefficient k5 for calculation of the volume change Linear interpolation apply. For small deflections (linear theory) p*=0 may be considered.
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
Insulated glass units Design procedure Load distribution
Internal pressure transmits the external loads (e.g. wind on pane 1) from one pane to the next (“Coupling Effect”)
External load Part of the external
load carried by pane 1 Part of the external
load carried by pane 2
Fd;2 acting on pane 2
Fd;1 acting on pane 1 ( ) 1;21 dF⋅⋅− δϕ
( ) 2;11 dF⋅⋅− δϕ
( ) 1;21 dF⋅⋅+ δϕδ
( ) 2;21 dF⋅+⋅ δδϕ
The internal loads, given by the isochore pressure, are reduced by a factor proportional to the relative flexibility of the panes. “Climatic Load”
Internal load Part of the internal
load carried by pane 1 Part of the internal
load carried by pane 2
Isochore pressure Dp p∆⋅ϕ p∆⋅ϕ
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
summer winter pressure suction
o i o i o i o i
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
Insulated glass units Design Example
h1 = 6 mm h2 = 6 mm s = 16 mm
b = 1500 mm
a = 750 mm
external load: wind w = 1,2 kN/m²
internal load: Dp = ±16,0 kN/m²
k5 factor
λ=a/b=750/1500=0,5 � k5= 0,050
p* = 0 50,0
66
633
3
32
31
31
1 =+
=+
=hh
hδ
50,050,0166
633
3
2 =−=+
=δ
External load distribution:
1 2
λ=a/b
p* (internal initial pressurization)
0 5 10 20
1,0 0,019 0,019 0,019 0,018 0,017
0,9 0,024 0,024 0,023 0,022 0,020
0,8 0,029 0,029 0,028 0,026 0,023
0,7 0,035 0,035 0,034 0,031 0,028
0,6 0,042 0,042 0,040 0,037 0,033
0,5 0,050 0,050 0,048 0,044 0,040
0,4 0,059 0,058 0,057 0,053 0,049
0,3 0,068 0,067 0,066 0,064 0,061
0,2 0,077 0,077 0,076 0,076 0,074
0,1 0,086 0,086 0,086 0,086 0,086
0 0,095 0,095 0,095 0,095 0,095
07,0)1,394/750(1
1
*)/(1
144
=+
=+
=aa
ϕ
insulating unit factor ϕ ( ) ( ) 1.39405,066
66169,289,28*
25,0
33
3325,0
532
31
32
31 =
⋅+⋅⋅⋅=
⋅+⋅⋅⋅=
khh
hhsa
characteristic length a*
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
internal loads 33,10,1607,0 ±=⋅±=∆⋅± pϕ kN/m²
kN/m²
external loads
( ) ( ) ( ) 64,02,150,0077,050,0211;21 =⋅⋅+=⋅⋅+=⋅⋅+ wFd δϕδδϕδ
( ) ( ) ( ) 56,02,150,007,0111 21;2 =⋅⋅−=⋅⋅−=⋅⋅− wFd δϕδϕ kN/m² pane 1
pane 2
+ summer - winter
Insulated glass units Design Example
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
External
load
Part of the external load
carried by pane 1
Part of the external load
carried by pane 2
Fd;2 acting on pane 2
Fd;1 acting on pane 1
( ) 1;21 dF⋅⋅− δϕ
( ) 2;11 dF⋅⋅− δϕ
( ) 1;21 dF⋅⋅+ δϕδ
( ) 2;21 dF⋅+⋅ δδϕ
Internal load
Part of the internal load carried by
pane 1
Part of the internal load
carried by pane 2
Isochore pressure Dp
p∆⋅ϕ p∆⋅ϕ
External load
Part of the external load
carried by pane 1
Part of the external load
carried by pane 2
0.56 0.64
Fd;2 acting on pane 2
- -
Fd;1 acting on pane 1
Internal load
Part of the internal load carried by
pane 1
Part of the internal load
carried by pane 2
Isochore pressure Dp
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
internal loads kN/m²
kN/m²
external loads kN/m² pane 1
pane 2
+ summer - winter
Lc 1: summer + suction Lc 2: winter + pressure
summer winter pressure suction
o i o i o i o i
1 2 1 2 1 2 1 2
Lc 3: summer + pressure Lc 4: winter + suction
pane 1
pane 2
79,1=q kN/m²
88,1=q kN/m²
Insulated glass units Design Example
Introduction
Components
Thermal/light
physics
Shapes
Sound physics
Support systems
Design
232,10,16077,0 ±=⋅±=∆⋅± pϕ
( ) ( ) ( ) 646,02,150,0077,050,0211;21 =⋅⋅+=⋅⋅+=⋅⋅+ wFd δϕδδϕδ
( ) ( ) ( ) 554,02,150,0077,0111 21;2 =⋅⋅−=⋅⋅−=⋅⋅− wFd δϕδϕ
L4 Insulated glass units
European Erasmus Mundus Master Course
Sustainable Constructions under Natural Hazards
and Catastrophic Events
25
This lecture was prepared for the 1st Edition of SU SCOS (2012/14) by Prof. Sandra Jordão (UC).
Adaptations brought by Prof. Viorel Ungureanu (UPT) for 2nd Edition of SUSCOS