By Tim Shay Chemical Engineering Student. Goal: Reduce our need of fossil fuels How? ◦ Renewable...
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Transcript of By Tim Shay Chemical Engineering Student. Goal: Reduce our need of fossil fuels How? ◦ Renewable...
Window Insulation Technologies
By Tim ShayChemical Engineering Student
Goal: Reduce our need of fossil fuels How?
◦ Renewable resources Solar Biomass Wind Hydro Geothermal
◦ Energy Efficiency Conversion losses Automobiles Heating/cooling
Current Energy Issues
Why care?
Heat flow follows Newton’s law of cooling
◦ U = Heat transfer coefficient◦ A = Area◦ ΔT = Temperature difference
Why Focus on Windows?
Low-end window U-factor = 1.20 BTU/(ft2hr°F)
Home wall U-factor ~ 0.05-0.10 BTU/(ft2hr°F) Windows can lose about 10-20 times more heat per area
The science behind the different technologies
Modeling Testing Quality Assurance Consumer view point
Main Points
Conduction◦ Glass
Gas fill Multi-plane windows
◦ Spacer Structure
◦ Sash Material Design
Convection◦ Weather Strip
Radiation◦ Low-E coatings◦ Heat mirrors
Ways that Heat is Transferred
http://www.uwsp.edu/cnr/gem/SustainableEnergy/energy-statistics.htm
Generic diagram of heat flow with various materials
Temperature Profile Through a Composite Wall
Transport Phenomena, Bird, Stewart and Lightfoot
◦ Fluids cause large change in temperature
◦ Reduces heat transfer
Thermal conductivities of gas greatly affects overall heat transfer◦ Can generally treat as being
stagnant
Gas Fills
Gases used to fill windows
Gas Thermal Conductivity (W/mK)
Air 0.03
Argon 0.016
Krypton 0.009
Gas inside isn’t stagnant◦ Movement increases
heat transfer Heating and cooling
causes convection◦ Taken into account in
FEA models
Modeling with Convective Loops
Hot
Cold
Spacer Type
http://www.vytexwindows.com/homeowners/stay_warm_keep_cool/duratex/
Spacers are what seal the gas in and separate the panes
Spacers come in many different designs and materials
Can have a large affect on◦ Strength of window◦ Conduction of heat
Temperature/pressure changes stress the system◦ Window deflection
Window Deflection
Concave ShapeNormal Shaped IG
unit
Cold Temperatures
High Atmospheric Pressure
Hot Temperatures
Low Atmospheric Pressure
Convex Shape
Intercept spacers◦ Can bend more◦ Let less heat through
Box Spacer◦ More rigid◦ More heat transfer
Allows more conduction
Comparison of Intercept and Box Spacers
http://www.gilkey.com/quality.html
Tri-pane is the highest generally seen in the market
Increases resistance◦ More surfaces to transfer heat through◦ Generally thicker
Multi-Pane Windows
http://www.americandreamwindow.com/doublehung/doublehung.htm
Made from various materials◦ Wood◦ Vinyl◦ Aluminum◦ Special materials
Andersen’s Fibrex Consumer choice also plays a key role in selection Each has it’s own conductivity
Sash Material
http://www.sunrisewindows.com/whyreplace.html
Non solid frames have complex structures◦ Designed to maximize efficiency and for strength◦ Makes use of heat transfer between barriers
Sash Structure
http://www.gilkey.com/quality.html
http://commons.wikimedia.org/wiki/File:5-chamber_plastic_window_profile.JPG
Modeling of the Sash
Air flow will find any open gap between the exterior and interior◦ Create tight seal
Problems◦ Wear and tear
Extensive testing performed◦ 10,000 cycle test
Weather-Stripping
http://www.hometips.com/buying-guides/window-weatherstripping-options.html
The sun emits radiation to the Earth◦ This radiation is generally classified two ways for
window manufactures Solar heat gain Visible light
Light has three options on surfaces◦ Transmittance◦ Absorbance◦ Reflection
Radiation
Coatings of silver and metal oxides can be used to help reflect heat◦ More layers reflects more heat◦ Can go up to 3 layers
Low-e Coatings
Placed on second face◦ Sheltered from
elements◦ Most efficient location
Coating other surfaces◦ Must be resilient to the
elements◦ Must be safe
Tri-pane windows allow more surfaces to apply coating to
Application of low-e Coatings
http://www.taiwanglass.com/en/products/flatglass/processed/leg.html
Effects in Winter and Summer
http://arizona.inetgiant.com/Mesa/AdDetails/LOW-E-WINDOWS-SINGLE-OR-DOUBLE-PANE/7886272
Various Levels of Coatings
http://www.efficientwindows.org/lowe.cfm
More heavy coatings will prevent transmission of solar heat, but also visible light
Heat Mirrors
http://www.buildinggreen.com/live/index.cfm/2010/11/10/Heat-Mirror-for-Structural-Sealant-Glazings
Operates the same as low-e coatings
Made of a thin clear film
Also operates as a divider◦ Creates 2 gaps◦ Decreases conduction
Pricier
Negative Side Affects
The Vdara hotel in Las Vegas
Hotel Vdara “Death Ray” Sunbathers have
been severely burned in as little as 10 minutes
Reflected light is becoming an increasing issue
Affecting buildings that already exist
http://www.amusingplanet.com/2010/10/vdara-hotel-death-ray.html
Low end window U factor ~ 1.2 High end window U factor ~ 0.20 Example
◦ 1 window that is 10ft2
◦ ΔT = 70°F◦ ΔQ = ΔU*A*ΔT
700 BTU/hr◦ Over a 1 day span
16,800 BTU/day = 0.168 Therms/day 1 Therm ~ 1 $
Overall Affects