ASHRAE Journal - March 2022 - 56

TECHNICAL FEATURE
0.2 U-value windows at 3 ACH at 50 Pa and 4 ACH and
5 ACH at 50 Pa. Using these three data points, linear
interpolation was used to determine at what ACH 50 at
50 Pa would the home with 0.2 U-value windows result
in equal energy use as a home with 0.3 U-value windows
with 3 ACH at 50 Pa of envelope leakage.
The wall insulation trade-off analysis was a home with
2018 IECC prescriptive code requirements for the walls
but with 0.2 U-value windows compared with a home
with 2021 IECC prescriptive code requirements for the
walls and 0.3 U-value windows.
Trade-off scenarios are evaluated in six different mixed
and cold climate locations (Table 2) where the benefits of
insulated windows (and other envelope insulation) are
expected to yield the most significant energy savings.
Figure 4 shows the whole house site energy use for the
modeled home following both the 2018 IECC versus the
2021 IECC prescriptive envelope requirements. The
shaded green area in Figure 4 shows the percentage of
site energy savings that comes from moving from 2018 to
2021 IECC requirements. The savings reflect the relative
changes in stringency requirements between the two
IECC versions, where the move to more stringent window,
wall, slab and ceiling insulation in CZ 3 through
CZ 5 are reflected in the higher percentage savings
between 2018 and 2021 IECC prescriptive measures.
To develop window performance trade-off scenarios,
we focused on air-leakage requirements and wall
insulation requirements. These two components were
selected, as they are perceived as the most challenging
areas for builders where simple trade-off options may
offer opportunities to reduce costs and risks associated
with adopting new building practices.
The cost and non-energy benefits elements of this article
are sourced from real purchases made to procure windows
for the PNNL Lab Homes and High-R Window field
test sites located across the U.S. and sensor and observational
data by researchers, builders, and the occupants.
Site Energy Savings Trade-Off Results
The IECC performance path trade-offs require equivalence
in terms of annual energy cost, applying different
fuel prices appropriate for the home's equipment and
region. Because the trade-offs being discussed here are
primarily heating-related in mixed and cold regions, the
trade-offs are described in site energy use (MMBtu/yr),
which gives a reasonable assessment of what can and
56
ASHRAE JOURNAL ashrae.o rg M A R CH 2022
TABLE 2 Locations used in trade-off scenarios.
SIMULATION LOCATION
Oakland, Calif.
Washington, D.C.
Seattle
Denver
Minneapolis
Fairbanks, Alaska
IECC CLIMATE ZONE
3C
4A
4C
5B
6A
8
DOE BUILDING AMERICA
CLIMATE ZONE
Marine
Mixed-Humid
Marine
Cold
Cold
Very Cold
FIGURE 4 Site energy use and savings comparison between 2018 and 2021 IECC
envelope requirements.
250
200
150
100
50
3C
15
2018 IECC
2021 IECC
Energy Savings
10
5
4C
4A
5B
Climate Zone
cannot be traded off between various measures. Energy
saving trade-offs vary by component and climate zones,
and the results suggest several envelope trade-offs exist
where window upgrades fare well in comparison to
other envelope upgrades.
Air-Leakage 5 ACH50 to 3 ACH50
For all climate zones modeled, the 2021 IECC prescriptive
whole-house air leakage limit is 3 ACH50 (air
changes per hour at 50 Pascals pressure difference)
with a maximum air leakage of up to 5 ACH for performance
trade-offs. The blue bars in Figure 5 depict the
maximum air leakage allowable* to still achieve equal
energy site use to the 2021 benchmark home when high
R-value windows are used. The results demonstrate
that triple-pane windows could provide the full energy
use trade-off (to the " backstop " maximum of 5 ACH) in
Oakland and Seattle (CZ 3A, CZ 4C) and close to a full
trade-off in Denver (5B). Results suggest that installation
of high R-value windows could enable trade-offs of
*Note that 2021 IECC limits the trade-off for air infiltration to
5 ACH50 in all climate zones.
6A
8
Site Energy Use (MMBtu/yr)
Energy Savings (%)
http://ashrae.org
ASHRAE Journal - March 2022

Table of Contents for the Digital Edition of ASHRAE Journal - March 2022
