Christian Kohler

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Highly Insulating Windows Software Tools
Christian Kohler (CJKohler_at_lbl.gov) Lawrence
Berkeley National Laboratory
October, 2007
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Goals for Highly Insulating Windows

• Windows that gain as much heat from the sun as
  they lose.

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Defining Zero Energy Windows

• Zero Energy Windows have a net-zero annual energy
  balance
• Approach
• Model standard houses in 5 different locations
• Vary windows from very insulating to very bad
• Vary windows from high solar gain to low gain
• Plot the results in a graph

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Performance Goals
More Insulating
More solar gain
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Minneapolis
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Non-structural center-layers

• Current technologies for highly insulating
  products use multiple layers of low-e and gas
  fill
• All glass is heavy
• Thin film products expensive
• Multiple spacers can lead to gas leakage
• LBNL research aims to develop lower-cost,
  non-structural center layers
• Utilize available low-e and gas-fill technologies
• Research novel center layer designs and materials

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Non-structural center-layers

• Acrylic center layer

Plastic layer
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FY07 Non-structural center-layersThin glass

• Very thin glass (e.g. .7mm) is now available in
  large sizes as a result of LCD and Plasma TV
  markets
• Prices are falling rapidly as volume increases
• Samples recently received from Corning
• IGs to be built in 08
• Will center layers bow? depends on how they are
  positioned
• Cost and Handling issues?

0.7 mm (0.028)
1.1 mm (0.043)
3 mm (0.118)
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Prototype Testing ResultsSimple insert performs
as well as fixed layer
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Software Tools
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Modeling
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Software Tools
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Chinese version of WINDOW6
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Thank you. Christian Kohler Windows and
Daylighting Research Group CJKohler_at_lbl.gov
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FY07 Non-structural center-layersStructural
Issues Acrylic

• CYRO, leader in production and development of
  acrylic for fenestration products, is supplying
  us with various types of acrylic sheet to better
  understand which type of acrylic sheet is suited
  to center-layer applications

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Heat Transfer through Windows
Low-e coatings
Radiation
Conduction
Special gas fills Multiple cavities
Convection
Low conductance spacers Better frames
Conduction (convrad in cavities)
Primary Driver Indoor/outdoor temperature
difference
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FY07 Non-structural center-layersSpacers and
sealants

• Super spacer, Swiggle-strip grooves for 3 layer
  design used in prototyping
• New BASF TPS technology BASF visit to LBNL and
  continued discussions

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Non-structural center-layers FY08

• Resolve issue of why acrylic layers deflect and
  determine what if any upgrades are needed
• Field-expose (at LBNL) samples
• Understand potentials of thin glass
• Continue/expand contacts with industry to explore
  cost, availability, business issues
• Window and IG manufacturers
• Spacer manufacturers
• Production Equipment manufacturers

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FY07 Low-conductance Frame Heat Transfer

• For residential sized windows (6-10 sf total) the
  frame is 20-30 of area and thus a critical
  element of a high R window
• Little experience in the U.S. with highly
  insulating frames
• Turn to Europe for Review of European
  low-conductance frames
• How do we assess actual performance of a
  low-conductance frame? (see related Software
  Tools effort)

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FY07 Low-conductance Frame Heat Transfer
Review of European frames

• Driven by Passivhaus requirement
• Ult 0.8 W/m2-C (.14 IP)
• Literature review in collaboration with Arild
  Gustavsen, Norway
• Two themes
• More highly insulating frames
• Lower profile frames to capitalize on solar gains

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Low-conductance Frame Heat Transfer Insulating
European frames

• Wood Frame with PUR

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Low-conductance Frame Heat Transfer Insulating
European frames

• Wood Frame with Insulation Filled Al cladding

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Low-conductance Frame Heat TransferFY08 plans

• Analysis of methods used in European frames
• Use/positioning of thermal breaks, cavities
• Hardware impacts
• Spacer impacts
• Analysis of other issues
• low emittance cavities
• phase change frames
• Testing
• IR (LBNL)
• Hot box (Norway)
• Performance issues (see Tools work multi-year
  effort not currently funded)
• Continued collaboration with A. Gustavsen

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Field Tests

• Objectives
• Document field energy performance and non-energy
  benefits of todays highly insulating windows
• Improve homebuilders familiarity with highly
  insulating windows
• Generate manufacturer interest in applications
• Projects
• Field demonstrations in Building America test
  houses
• Installation and monitoring of highly insulating
  windows vs. standard ENERGY STAR in collaboration
  with Cardinal IG in identical houses in Ft.
  Wayne, Indiana

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Low-Energy Home Demonstration FY07

• Affordable home in MA (CARB Building America
  team)
• Heat Mirror (U0.2) windows provided by builders
  normal supplier at no price premium
• Typical price premium strongly related to special
  order process
• Compared window-surface temperatures against
  baseline windows

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Interior Surface Temperatures
Double, clear
Heat Mirror
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Cardinal Test Houses - Indiana

• Standard low-solar gain low-e vs. triple-pane
  with high-solar gain and insulated frames (Ult.2)
• Side-by-side houses have been monitored, empty,
  since Jan 2007
• Prior years data on typical Energy Star windows
  also available