ASHRAE-90.1-2022- - Page 310
Extracted Content
Table G3.1 Modeling Requirements for Calculating Proposed Building Performance and Baseline Building Performance (Continued)
| Proposed Building Performance | Baseline Building Performance |
|---|---|
| 5. Building Envelope (continued) | |
6. Manual fenestration shading devices, such as blinds or
shades, shall be modeled or not modeled the same as in the
baseline building design. Automatically controlled fenestra-
tion shades or blinds shall be modeled. Permanent shading
devices, such as fins, overhangs, and light shelves shall be
modeled.
7. Automatically controlled dynamic glazing may be modeled.
Manually controlled dynamic glazing shall use the average of
the minimum and maximum SHGC and VT.
8. The above-grade wall surface shall be modeled using the ini-
tial solar reflectance and thermal emittance determined in
accordance with the test methods identified in Section
5.5.3.2.2(a). Where initial test data are unavailable, the wall
surface may be modeled with a solar reflectance of 0.25 and a
thermal emittance of 0.90.
b. To simulate air leakage, infiltration shall be modeled using the
same methodology and adjustments for weather and building
operation in both the proposed design and the baseline building
design. These adjustments shall be made for each simulation time
step and must account for but not be limited to weather conditions
and HVAC system operation, including strategies that are intended
to positively pressurize the building. The air leakage rate of the
building envelope shall be converted to appropriate units for the
simulation program using one of the methods in Section G3.2.1.7.
1. When whole-building pressurization testing is required or
specified during design, and completed in accordance with
Section 5.4.3.1.4, the measured air leakage rate of the build-
ing envelope (I75Pa) at a fixed building pressure differential
of 75 Pa (0.30 in. of water) shall be modeled for purposes of
demonstrating compliance with this standard.
Informative Note: Before the start of pressurization testing,
the maximum air leakage rate of the building envelope
(I75Pa) specified in Section 5.4.3.1.4 or as specified in design
documents may be simulated to estimate the energy impact of
building envelope air leakage. The final measured value is
used for compliance; therefore, care should be taken when
using estimated air leakage as a trade-off for performance-
based code compliance.
2. For buildings providing verification in accordance with Sec-
tion 5.9.1.2, the air leakage rate of the building envelope
(I75Pa) at a fixed building pressure differential of 75 Pa (0.30
in. of water) shall be 0.45 cfm/ft2. | • Roofs with insulation entirely above deck (A2.2).
• Above-grade walls—steel-framed (A3.3).
• Below-grade walls—concrete block (A4).
• Floors—steel-joist (A5.3).
• Slab-on-grade floors shall match the F-factor for unheated
slabs from the same tables (A6).
• Opaque door types shall be of the same type of construction
as the proposed design and conform to the U-factor require-
ments from the same tables (A7).
e. Vertical Fenestration Areas. For building area types included in
Table G3.1.1-1, vertical fenestration areas for new buildings and
additions shall equal the percentage in Table G3.1.1-1 multiplied
by the gross area of above-grade walls that are part of the exte-
rior building envelope and semiexterior building envelope.
Where a building has multiple building area types, each type
shall use the values in the table. For building areas not shown in
Table G3.1.1-1, vertical fenestration areas for new buildings and
additions shall equal that in the proposed design or 40% of gross
area of above-grade walls that are part of the exterior building
envelope and semiexterior building envelope, whichever is
smaller, and shall be distributed on each face of the building in
the same proportions in the proposed design.
The vertical fenestration shall be distributed on each face of the
building in the same proportion as in the proposed design. If this
would cause the combined vertical fenestration and opaque door
area on a given face to exceed the gross above-grade wall area on
that face, then the vertical fenestration area on other faces shall be
increased in proportion to the gross above-grade wall area of these
faces such that the total baseline building vertical fenestration area
is equal to that calculated following Table G3.1.1-1.
The fenestration area for an existing building shall equal the
existing fenestration area prior to the proposed work and shall
be distributed on each face of the building in the same
proportions as the existing building.
f. Vertical Fenestration Assemblies. Fenestration for new build-
ings, existing buildings, and additions shall comply with the fol-
lowing:
• Fenestration U-factors shall match the appropriate require-
ments in Tables G3.4-1 through G3.4-8 for the applicable
glazing percentage for Uall.
• Fenestration SHGCs shall match the appropriate requirements
in Tables G3.4-1 through G3.4-8 using the value for SHGCall
for the applicable vertical glazing percentage.
• All vertical fenestration shall be assumed to be flush with the
exterior wall, and no shading projections shall be modeled.
• Manual window shading devices such as blinds or shades are
not required to be modeled.
• Automatic fenestration shading devices shall not be modeled.
g. Skylights and Glazed Smoke Vents. Skylight area shall be equal
to that in the proposed design or 3%, whichever is smaller. If the
skylight area of the proposed design is greater than 3%, baseline
skylight area shall be decreased by an identical percentage in all
roof components in which skylights are located to reach 3%. Sky-
light orientation and tilt shall be the same as in the proposed
design. Skylight U-factor and SHGC properties shall match the
appropriate requirements in Tables G3.4-1 through G3.4-8 using
the value and the applicable skylight percentage.
h. Roof Solar Reflectance and Thermal Emittance. The exterior
roof surfaces shall be modeled using a solar reflectance of 0.30
and a thermal emittance of 0.90.
i. The air leakage rate of the building envelope (I75Pa) at a fixed
building pressure differential of 0.3 in. of water shall be 1.0 cfm/ft2.
j. Wall Solar Reflectance and Thermal Emittance. Above-grade
wall surfaces shall be modeled with a solar reflectance of 0.25
and a thermal emittance of 0.90. |
308 ANSI/ASHRAE/IES Standard 90.1-2022 (I-P)