Glazing Systems: Balancing Aesthetics, Performance & Cost

Compare today’s glass options to the ideal glass

Discuss trade-off between aesthetics & thermal performance

Advantages/Disadvantages of sealed insulating glass vs. dual glazing systems

Mount St. Helen’s Visitors CenterCastle Rock, WASRG Partnership

Glazing Systems -Overview Architectural Trends Review of Heat Transfer

Mechanisms & Definitions

Glass Thermal

Performance Comparison of Insulating

glass and Dual glazing Specifications

Worthington High SchoolWorthington, OHNBBJ

Top Interests in Glass Aesthetics Initial Cost/Life Cycle Cost Durability Fading Blockage Warranty Energy Performance Options Safety Resistance to Condensation

Long-term Care FacilityWashington, DCSmith, Hinchman & Grylls Associates, Inc.

Architectural Trends Higher % of glass use in

building skin in conjunction w/ energy conscious design

High visible light transmission, Low infrared transmission

Low reflectance, clear appearance

Low-E coatings gain share– standard on all buildings in 5

years

– lower heating and cooling loads than an R19 wall

The Lansburg CondominiumsWashington, DCGraham Gund.

Heat Transfer Heat flows through a window assembly in

three ways:– Conduction (heat traveling thru a solid material)– Convection (heat transfer by air movement)– Radiation (movement of heat energy thru space)

Heat Transfer Heat flow measured in terms of:– Insulating value (U-value)– Heat Gain from solar radiation (Solar Heat Gain

Coefficient or Shading Coefficient)– Air Infiltration (cfm/sq ft)

Other Considerations– Visible Light– Comfort– Fading

Heat Transfer Insulating value

(U-value & Emissivity)– Design conditions

15 mph, 70 F inside,

0 F outside– combination of conduction,

convection, & radiation– Measured in terms of

Btu/hr-sq. ft.-degree F– R-value = 1/U-value

Heat Transfer Insulating value

(U-value)– center of

glass– edge of

glass– window sash

and frame

75.0° F @edge offrame

57.4° F @ center of glass

24.4° F @ edge of glass

-15° F +75° F

51.5° F @ edge ofsash

Heat Transfer Heat Gain from solar radiation

Double -glazedwindow

Solar transmittance

Absorbedradiation

Inward flowingcomponentof absorbedradiation

Reflectedradiation

OUTDOORS INDOORS

Heat Transfer Heat Gain from solar radiation– Solar Heat Gain Coefficient (SHGC)

that fraction of incident solar radiation that actually enters a building thru the window as heat gain

center-glass or total unit SHGC = SC x 0.87 (approximate)

– Shading Coefficient (SC) the ratio of solar heat gain thru the system relative to

that thru 1/8” clear glass at normal incidence center-glass only not recognized by NFRC

Impact of Glass Performance

Minneapolis Case Study - NSP Energy Assets Program– Energy analysis as part of design process– more than 75 buildings since 1994– Energy consultant is The Weidt Group– Buildings use 30-35% less energy than a code-

compliant building (average of 32% savings)– Daylighting & specification of correct glass result

in 10-15% of the savings

Glass Thermal Performance(center-glass values)

Sealed Insulating Glass Dual Glazing

Glass Thermal Performance (center-glass values)

Ultra-Violet Transmission (Fading) Visible Transmission (Seeing) Infrared Transmission (Heat)– Near Infrared - Solar Heat Gain Coefficient

(Keeping Heat Out)– Far Infrared - U-Value and Emissivity (Keeping

Heat In)

Ideal Glass Spectrum

0%

100%

0% 0%0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Ultra-Violet Visible Near IR Far IR

Clear InsulatingGlass UV Light is Transmitted Visible Light is Transmitted Near Infrared is Transmitted Far Infrared is Transmitted

(E=0.84)

Solar Spectrum

0%

100%

0% 0%

56%

76%84%81%

0%10%20%30%40%50%60%70%80%90%

100%

Ultra-Violet

Visible Near IR Far IR

Ideal Glass

Clear Glass

Tinted Gray Glass Ultra-violet Light is Absorbed Visible Light is Absorbed Near Infrared is Absorbed Far Infrared is Absorbed

(E=0.84)

Solar Spectrum

0%

100%

0% 0%

21%

50%

84%

45%

0%10%20%30%40%50%60%70%80%90%

100%

Ultra-Violet

Visible Near IR Far IR

Ideal Glass

Gray Tint

Reflective Gray Glass UV Light is Reflected Visible Light is Reflected Near Infrared is Reflected Far Infrared is Transmitted

(E=0.84)

Solar Spectrum

0%

100%

0% 0%7%

34%

84%

18%

0%10%20%30%40%50%60%70%80%90%

100%

Ultra-Violet

Visible Near IR Far IR

Ideal Glass

Reflective Gray

Low Emissivity Coatings UV Light is Reflected Visible Light is Transmitted Near Infrared is Reflected Far Infrared is Reflected (E=0.04)

Solar Spectrum

0%

100%

0% 0%

16%

41%

4%

72%

0%10%20%30%40%50%60%70%80%90%

100%

Ultra-Violet

Visible Near IR Far IR

Ideal Glass

Clear LoE2 IG

Clear / Low E Dual Glazed UV Light is Transmitted Visible Light is Transmitted Near Infrared is Transmitted Far Infrared is Reflected

(E=0.15)

Solar Spectrum

0%

100%

0% 0%

45%

71%

15%

75%

0%10%20%30%40%50%60%70%80%90%

100%

Ultra-Violet

Visible Near IR Far IR

Ideal Glass

Clear LoE DG

Low EmissivityCoatings

UV Light is Reflected Visible Light is Transmitted Near Infrared is Reflected Far Infrared is Reflected

Solar Spectrum

0%

100%

0% 0%

11%

36%

4%

60%

0%10%20%30%40%50%60%70%80%90%

100%

Ultra-Violet

Visible Near IR Far IR

Ideal Glass

Clear LoE2 IG w/LoE DG

Compare Thermal Performance

Compare Center Glass U-value

Compare Cost

Comparison of Glazing Systems

Warm Edge Mechanical Seal for

Long Life Re-glazing Between Glass

Options Thermal Performance Cost

InsulatingGlass

DualGlazed

Hamilton Lakes Itasca, IL Architect: Skidmore, Owings, & Merrill

Office Building - Insulating Glass

Nestle Corporate Offices Solon, OHArchitect: Voinovich Architects, Inc

Office Building - Dual Glazed

Dual Glazed Systems

Wood Frame Aluminum Frame

Warm Edge

Double-seal Stainless Silicone Foam Wood Spacer Aluminum spacer at IG aluminum spacer Steel spacer spacer Wood spacer

Warm Edge/Comfort

Mechanical Seal for Long Life

+

Residence Halls 12 dorms University of Wisconsin at Madison 6428 sash

Re-glazing

Between-Glass Options Tilt-only blinds Muntins Pleated shades Raise-and-lower

blinds Provide lower

SHGC than room-side blinds

Extra insulating value by reducing convective loops w/in air space

Compare Thermal Performance

Compare Total Unit U-value

Compare Dual Glazing with Blinds

Compare Blind Options

Source: 1997 ASHRAE Fundamentals Handbook, Chapter 29 - Fenestration

Comparison Summary

Specifications 11/99 AIA Masterspec - Section 08550– Thermal transmittance per NFRC 100

insert appropriate whole-window U-value

– Solar Heat Gain Coefficient per NFRC 200 insert appropriate whole-window SHGC

– No other thermal performance values noted

– Masterspec IG warranty of [5] [10] [insert number] years

– Choose insulating glass or dual glazing (for venetian blinds)

Specifications Specifying Glass Performance– Choose insulating glass or dual glazing

– Determine Center-glass or Whole-window Values

– Coordinate with Section 08800 - Glazing

– Maximize warranty on insulating glass

– Visible Light Transmission

– Ultra-violet Light Transmission or LBL Fading Damage Function

– Solar Heat Gain Coefficient (Near Infrared)

– U-value (Far Infrared)

Glazing Systems: Balancing Aesthetics, Performance & Cost

Compare today’s glass options to the ideal glass

Discuss trade-off between aesthetics & thermal performance

Advantages/Disadvantages of sealed insulating glass vs. dual glazing systems

Mount St. Helen’s Visitors CenterCastle Rock, WASRG Partnership