Clear Thinking About Windows - Building Knowledge...PowerPoint Presentation Author Jim Larsen...
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Clear Thinking About Windows Spring Training, 2016 Jim Larsen April 25, 2016
Transcript of Clear Thinking About Windows - Building Knowledge...PowerPoint Presentation Author Jim Larsen...
Clear Thinking About Windows
Spring Training, 2016
Jim Larsen
April 25, 2016
Code references
whole window
Window Thermal Components
Outdoors Indoors
#1 #2 #3 #4
Glass/Frame
Interface
Frame
Window
Therm
Edge of Glass
(2.5 inches)
Center of Glass
Aluminumy = 0.82x + 0.42
Alum TBy = 0.79x + 0.22
Clad Woody = 0.69x + 0.18
Wood or Vinyly = 0.63x + 0.14
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55
Win
do
w U
-Fac
tor
IG Glass U-Factor
Operable Window U-Factor vs. Glass Properties
Sunlight on a Window
Solar Heat Gain Coefficient (SHGC) is sum of direct transmission and inward flowing absorptance
Tinted Glass SHGC = 0.52
#3 surface low-E is hot in sunlight
Window Solar Heat Gain
Frame areas can vary from 10% to
40%
X
X
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80
Win
do
w S
HG
C
Glass SHGC
Window SHGC as a Function of Frame Area
15% Frame 25% Frame 35% Frame
The Rule of Panes
• Single Pane ~ R1
• Double Pane ~ R2
Window U 0.55 – 0.80 with Double Pane
More Panes
• Single Pane ~ R1
• Double Pane ~ R2
• Triple Pane ~ R3
• Quad Pane ~ R4
Window U ~ 0.35 with Quad Pane and Non-Metal
Frame
Less Panes with Low-E
• Single Pane ~ R1
• Double Pane ~ R2
• Triple Pane ~ R3
• Quad Pane ~ R4
• 2 Pane + Low-E ~ R3
• 2P + Low-E + Argon ~ R4
Quad Pane Equivalent
Low-E blocks(thermal) radiation
Argon slows conduction
Warm edge reduces conduction losses
Non-Metal Window U ~ 0.302 Pane+ Low-E+ Argon
+ Warm Edge
Back to the Future: More Panes?
• Single Pane ~ R1
• Double Pane ~ R2
• Triple Pane ~ R3
• Quad Pane ~ R4
• 2 Pane + Low-E ~ R3
• 2P+Low-E+Argon ~ R4
• Triple w/2 Low-E + Argon ~ R8
Triple Pane Challenges
• Glass cost about 2X double pane
• 2X IG seal failure risk
• Weight (sash balance)
• Thickness• Vertical sliders (single & double hung) are about 2/3
U.S. window market
Last Step for Double PaneAdd 4th Surface Low-E = R5
Low-E units are warm on winter night. Clear glass is cool.
Traditional Options for Solar Control Glass
Tinted• Adds color to “body” of glass
• Absorbs sunlight and re-radiates to exterior
Reflective• Mirror appearance
• Reflects sunlight out
Clear Window SHGC0.60
The Solar Spectrum
45%3% 52%
2P Clear: Window SHGC ~ 0.6
2P Tinted: Window SHGC 0.4 - 0.5
Today’s Option for Solar Control Glass
Tinted• Adds color to “body” of glass
• Absorbs sunlight and re-radiates to exterior
Reflective• Mirror appearance
• Reflects sunlight out
Spectrally Selective Low-E• Clear glass appearance with solar control
• Reflects solar infrared (invisible to human eye)
High Solar Gain Low-E: Window SHGC ~ 0.5
Low-E Coatings - Circa 1980’s
• 2 processes: Pyrolitic (hard) or Sputtered (soft)
• Pyrolitic low-E coatings are high solar gain and applied to clear glass
• Sputtered low-E coatings are silver based, must be insulated or laminated, are available in wide range of solar gain levels. Only high solar option at this time.
High solar gain low-E is hot in sunlight (#3 surface)
High Solar Gain Low-E
Summer
Transmission SHGC Temperature
#2 Surface 0.56 0.62 87°F
#3 Surface 0.56 0.68 101°F
Medium Solar Gain Low-E: Window SHGC ~ 0.3
Window SHGC ~ 0.30
2 Pane+ Medium Solar
Gain Low-E
| Low-E | Clear GlassMed Solar | High Solar
Low Solar Gain Low-E: Window SHGC ~ 0.2
*
*
*
Unobtanium*
Comfort Science?
55
Metabolic Rate
Comfort @ 70°F
Clothing Insulation
Standard Office Conditions
1. Activity Level
2. Adaptive Clothing
Can a Better Furnace Offset Cold Windows?
No Comfort Science Needed………
Extra Layers Help!
Cold Weather Analysis
• Assume large window (patio door) and close proximity (3’ away)
Cold Weather Analysis
• Assume large window (patio door) and close proximity (3’ away)
• Limit increase in PPD to 10% over baseline
– Cold threshold set to 56°F for “average” roomside surface temperature
MRT Analysis (window size & proximity)
2P Clear @ 0°F = +12% in PPD
Cold Weather Analysis
• Assume large window (patio door) and close proximity (3’ away)
• Limit increase in PPD to 10% over baseline
– Cold threshold set to 56°F for “average” roomside surface temperature
• Calculate hourly roomside glass surface temperature for no wind conditions(use weather data file: 8760 hours)
Cold Weather Analysis
• Assume large window (patio door) and close proximity (3’ away)
• Limit increase in PPD to 10% over baseline
– Cold threshold set to 56°F for “average” roomside surface temperature
• Calculate hourly roomside glass surface temperature for no wind conditions
• Hour counts as Discomfort if window temperature falls below threshold
Glazing
Layers U-factor SHGC VT
1 Single Metal 1.29 0.73 0.69
2 Double Metal 0.83 0.65 0.63
3 Double Tinted Metal 0.83 0.54 0.47
4 Double Low-E, Hi SHGC yes Metal 0.65 0.58 0.61
5 Double Low-E, Med SHGC yes Metal 0.64 0.38 0.56
6 Double Low-E, Lo SHGC yes Metal 0.63 0.26 0.49
7 Double Metal, Thermal Break 0.60 0.62 0.63
8 Double Tinted Metal, Thermal Break 0.60 0.51 0.47
9 Double Low-E, Hi SHGC yes Metal, Thermal Break 0.42 0.55 0.61
10 Double Low-E, Med SHGC yes Metal, Thermal Break 0.42 0.35 0.56
11 Double Low-E, Lo SHGC yes Metal, Thermal Break 0.41 0.23 0.49
- Double 4th Low-E Hi SHGC yes Metal, Thermal Break 0.38 0.51 0.60
- Double 4th Low-E, Med SHGC yes Metal, Thermal Break 0.37 0.34 0.54
- Double 4th Low-E, Lo SHGC yes Metal, Thermal Break 0.37 0.23 0.49
12 Single Non-metal or metal clad 0.88 0.64 0.65
13 Double Non-metal or metal clad 0.52 0.57 0.59
14 Double Tinted Non-metal or metal clad 0.52 0.47 0.44
15 Double Low-E, Hi SHGC yes Non-metal, thermally improved 0.29 0.50 0.57
16 Double Low-E, Med SHGC yes Non-metal, thermally improved 0.28 0.31 0.52
17 Double Low-E, Lo SHGC yes Non-metal, thermally improved 0.27 0.20 0.4621 Double 4th Low-E Hi SHGC yes Non-metal, thermally improved 0.25 0.46 0.56
22 Double 4th Low-E, Med SHGC yes Non-metal, thermally improved 0.24 0.30 0.51
23 Double 4th Low-E, Lo SHGC yes Non-metal, thermally improved 0.24 0.21 0.46
18 Triple Low-E Hi SHGC yes Non-metal, thermally improved 0.20 0.41 0.50
19 Triple Low-E, Med SHGC yes Non-metal, thermally improved 0.19 0.28 0.45
20 Triple Low-E, Lo SHGC yes Non-metal, thermally improved 0.19 0.18 0.37
Frame
Values for simulation2016 EWC
window # Glazing Type Argon Gas
Low-E History
• 1980’s High Solar Gain
I’m too damn hot!
Low-E History
• 1980’s High Solar Gain
• 1990’s Medium Solar Gain• No more field complaints
• 2000 Low Solar Gain• Low-E now in building code from Muskoka to Miami
• Mandate for low-solar in South
• Northern users beware of overheat with high solar
“Hot” Window Analysis
• Assume occupant is in direct sunlight
• Limit increase in PPD to 10% over baseline
– Solar gain < 70 Btu/hr·ft²
Window Comfort Research
WarmCool
+1 +2 +3
Cold Cool
Slightly
Neutral
Slightly
Warm Hot
-3 -2 -1 0
“Hot” Window Analysis
• Assume occupant is in direct sunlight
• Limit increase in PPD to 10% over baseline
– Solar gain < 70 Btu/hr·ft²
• Hour counts as Discomfort if transmitted solar exceeds threshold
– Calculate gain on 4 orientations (N, E, S, W)
Summary
• “Cold” discomfort is climate specific• Northern latitudes require lower U-Factors due to colder
extreme winter ambient temperatures
• Risk of “Hot” discomfort exists in all climates• Solar radiation levels similar across North America
• Orientation specific
• Beware overheat risks as building performance improves
