ASHRAE-90.1-2022- - Page 266

Extracted Content

A9. DETERMINATION OF ALTERNATE ASSEMBLY U-FACTORS, C-FACTORS,  F-FACTORS, OR HEAT CAPACITIES

A9.1 General. Alternative assembly U-factors, C-factors, F-factors or heat capacities for opaque assemblies shall be determined in accordance with Section A9. The procedures required for each class of construc- tion are specified in Section A9.2. Testing shall be performed in accordance with Section A9.3. Calculations shall be performed in accordance with Section A9.4.

A9.2 Required Procedures. Two- or three-dimensional finite difference and finite volume computer models shall be an acceptable alternative method to calculating the thermal performance values for all assemblies and constructions listed below. The following procedures shall also be permitted to determine all alternative U-factors, F-factors, and C-factors :

a. Roofs

1. Roofs with insulation entirely above deck : Testing or series calculation method.

2. Metal building roofs : Testing, or for single-layer and double-layer systems, calculation method in Section A9.4.6.

3. Attic roofs, wood joists: Testing or parallel path calculation method.

4. Attic roofs, steel joists : Testing or parallel path calculation method using the insulation/framing layer adjustment factors in Table A9.2-1 or modified zone calculation method.

5. Attic roofs, concrete joists: Testing or parallel path calculation method if concrete is solid and uniform, or isothermal planes calculation method if concrete has hollow sections.

6. Other attic roofs and other roofs : Testing or two-dimensional calculation method. b. Above-Grade Walls

7. Mass walls : Testing or isothermal planes calculation method or two-dimensional calculation method. The parallel path calculation method is not acceptable.

8. Metal building walls : Testing, or for single-layer compressed, single-layer in cavity, double-layer sys i. Where the steel-framed wall contains no cavity insulation and uses continuous insulation to satisfy the U-factor maximum, the steel-framed wall member spacing is permitted to be installed at any on-center spacing. ii. Where the steel-framed wall contains framing at 24 in. on center with a 23% framing factor or

iii. Where the steel-framed wall contains less than 23% framing factors, AISI S250 shall be used without any modifications. iv. Where the steel-framed wall contains other than standard C-shape framing members, the AISI S250 calculation option for other than standard C-shape framing is permitted to be used. 4. Wood-framed walls : Testing or parallel path calculation method. 5. Other walls : Testing or two-dimensional calculation method. c. Below-Grade Walls

1. Mass walls : Testing or isothermal planes calculation method or two-dimensional calculation method. The parallel path calculation method is not acceptable.

2. Other walls : Testing or two-dimensional calculation method. d. Floors

3. Mass floors : Testing or parallel path calculation method if concrete is solid and uniform or isothermal planes calculation method if concrete has hollow sections.

4. Steel-joist floors : Testing or modified zone calculation method.

5. Wood-joist floors : Testing or parallel path calculation method or isothermal planes calculation method.

6. Other floors : Testing or two-dimensional calculation method. e. Slab-on-Grade Floors

7. No testing or calculations allowed.

A9.3 Testing Procedures

A9.3.1 Building Material Thermal Properties. If building material R-values or thermal conductivities are determined by testing, one of the following test procedures shall be used:

264 ANSI/ASHRAE/IES Standard 90.1-2022 (I-P)