Windows in the United States use aproximately 2 quads a year in heating
energy, approximately one third of all building space heating energy
used and the largest single end use attributed to windows. Even if all
existing windows were replaced with today’s ENERGY STAR low-e products
(U values < 0.35 Btu/hr-ft2-F), windows related heating would still be
over 1 Quad.
Because heating loads are strongly tied to conductive losses,
technologies which lead to lower window U-factors are the key to reducing
heating energy. A 0.1 Btu/hr-ft2-F window is targeted as a product, which
will meet the requirements of zero-energy homes. Dynamic control of solar
gains will further reduce heating needs by allowing winter solar heat gains
to be effectively utilized while limiting cooling season gains. Significant
cooling load savings can also be expected from lower U-factor windows in
certain climates and from dynamic windows in all climates.
Current strategies used to reduce heat loss through windows are triple or
quadruple glazing, which adds significant weight, or suspended films, which
are costly. Because of these weight and cost disadvantages, very highly
efficient multi-layer, low-emissivity (low-E) gas-fill window products
account for less than one percent of today’s window sales.
In existing multi-layer units, the center layer is positioned between two
spacers. This adds to production costs and doubles the path length for gas
loss leakage. In this project, we examine the thermal potentials of three
layers designs utilizing various means of positioning a non-structural
center layer between the inner and outer layers of a standard IG (i.e. a
drop-in insert in a typical IG). Some designs had thermal performance
similar to that of a standard three layer low-e/gas filled unit, indicating
the possibility of developing a lower cost, more durable, lighter, highly
insulating glazing system.
This project focuses on high performance glazing systems; other R&D efforts
are needed to focus on reductions in frame/edge heat transfer.
Optimal Gap Width study
We performed a brief study on the
optimal gap width of double and triple glazing systems. Comparing
US/NFRC standards with European EN 673 standards.
Advanced Windows for Zero-Energy Homes, J. Apte, D. Arasteh, J. Huang,
2003 ASHRAE Annual Meeting, 2002
Performance Criteria for Residential Zero Energy Windows,
D. Arasteh, H. Goudey, J. Huang, C. Kohler, R. Mitchell,
2006, submitted to ASHRAE
Windows, D. Arasteh, S. Selkowitz, J. Apte, M. LaFrance,
2006 ACEEE Summer Study on Energy Efficiency in Buildings,2006
Highly Insulating Glazing Systems
using Non-Structural Center Glazing Layers, D. Arasteh,
H. Goudey, C. Kohler, 2006, Submitted to ASHRAE for review.
more information contact Robert Hart
Traditional triple glazed window with
4 paths for gas leakage.