ASHRAE Journal - March 2022 - 52

TECHNICAL FEATURE
Thin-Glass, Triple-Pane Technology Explained
The thin-glass triplepane
IGU allows for
R-5 (U-0.20) or better
double-hung and R-6.5
(U-0.15) or better picture
windows in place
of today's R-3.7 Energy
Star products. The
Typical Double Pane Thin-Triple Pane
design uses a combination of thin-glass (0.7-1.6 mm)
for the center layer, two low-e coatings and krypton
gas fill. The thin glass keeps IGU weight and width to
a minimum, enabling the use of frame profiles optimized
for double-pane.
The thin-glass triple-pane concept is based on the
novel use of components that have been available for
years. This technology is a high- performance solution
for the mass-market and is ready for industry
adoption.
IECC Residential Model Code
The IECC envelope and air-sealing requirements are
designated for eight different climate zones (CZ) in
the U.S. (Figure 3). Over the past decade, as residential
building energy codes have become more stringent,
homebuilders have had to adopt new approaches to
constructing single-family homes to meet these tighter
envelope requirements. For example, when wood-frame
wall insulation requirements were increased to R-20
(in the 2009 IECC for CZ 5 through CZ 8 and the 2012
IECC for CZ 3 through CZ 4), wall construction with 2 × 6
wall studs was required to accommodate the additional
cavity insulation. In subsequent versions of the code,
options were added to use rigid foam insulation in place
of (or in addition to) cavity insulation. Other insulation
requirements for ceilings and floors have also steadily
increased; the 2021 IECC ceiling R-value requirements
are now R-60 for CZ 4 through CZ 8 (Table 1). Other significant
changes included the addition of air leakage
testing with 3 ACH required in CZ 3 through CZ 8.
In builder surveys, the IECC air tightness requirements
are consistently identified as one of the biggest
challenges in constructing new homes to meet energy
codes.5 While window U-factors have also become more
stringent, the code can still be met with a double-pane
low-e window.
52
ASHRAE JOURNAL ashrae.o rg M A R CH 2022
Two types of compliance paths exist to meet the IECC
code: a prescriptive path and performance-based paths.
Some trade-offs between envelope components (e.g.,
wall, ceiling or floor insulation and window performance)
are acceptable within the prescriptive path. A
simple envelope component trade-off is allowed based
on the overall U-factor times area (i.e., the heat loss/gain
rate) for all components of the envelope, referred to
as the " UA " trade-off approach. For example, one can
trade decreased wall efficiency (lower R-value, higher
U-factor) for increased window efficiency (lower
U-factor).
Additionally, the same type of envelope component
trade-offs, as well as air tightness, can be made within
performance-based paths. The traditional performance
path requires that the building as a whole performs to a
certain standard and has lower annual energy costs than
the same building built to a prescriptive code and, starting
with the 2015 IECC, there is also a new energy rating
index (ERI) option that rates the home's energy use on a
scale of 100 to 0. The performance path requires the use
of a code-compliant software. In all cases, the 2021 IECC
also includes certain limitations on how much envelope
components can be traded off.
Envelope Provisions of 2021 IECC
Table 1 summarizes the 2021 IECC envelope insulation
and air-sealing requirements for a wood-framed house.
The key changes relative to the previous 2018 version of
the IECC are shaded and summarized as follows:
* Windows: Reduces U-factor for CZ 3 and CZ 4 (except
Marine) down to 0.30.
FIGURE 2 Top left: Thin-triple windows with vinyl frames and stainless steel spacers
are installed in a new home site (Twin Cities, Minn.). Bottom left: Thin-triple
with vinyl frames and a foam spacer are installed in a new home site (Rotterdam,
N.Y.). Middle: Installation of thin triple-pane window at PNNL Lab Homes
(Richland, Wash.). Right: Thin triple-pane double-hung window with fiberglass
frames are installed in a new home site (Kalamazoo, Mich.).
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