ASHRAE-90.1-2022- - Page 322
Extracted Content
load and above to space temperature at 0% cooling load. In heating mode supply air temperature shall be modulated to maintain space temperature, and fan volume shall be fixed at the minimum airflow.
G3.2.3.18 Dehumidification (Systems 3 through 8 and 11, 12, and 13). If the proposed design HVAC systems have humidistatic controls, then the baseline building design shall use mechanical cooling for dehumidification and shall have reheat available to avoid overcooling. When the baseline building design HVAC system does not comply with any of the exceptions in Section 6.5.2.3, then only 25% of the system reheat energy shall be included in the baseline building performance . The reheat type shall be the same as the sys- tem heating type.
G3.2.3.19 Preheat Coils (Systems 5 through 8). The baseline system shall be modeled with a preheat coil controlled to a fixed set point 20°F less than the maximum design heating temperature set point of the HVAC zones served by the system.
G3.3 Performance Calculations for Other Alterations
G3.3.1 Proposed Building Performance. The simulation model for calculating the proposed building performance shall be developed in accordance with the requirements in Table G3.1, Proposed Building Performance column and the following additional requirements:
a. New and retrofitted systems and equipment shall be consistent with design documents. b. Systems and equipment excluded from the scope of retrofit shall reflect the existing conditions.
G3.3.2 Baseline Building Performance
G3.3.2.1 General Approach. System and equipment included in the scope of retrofit shall be modeled at efficiency levels meeting the mandatory and prescriptive requirements in Sections 5 through 10 and as described in this section. All other baseline systems and equipment shall be modeled the same as in the pro- posed design.
G3.3.2.2 Schedules. Schedules modeled in the baseline design are allowed to differ from the proposed design following Table G3.1(4), Baseline Building Performance column, Exceptions 1 through 3.
G3.3.2.3 Opaque Assemblies. Opaque assemblies shall be modeled with U-factors meeting the requirements in Section 5.1.3.
G3.3.2.4 Fenestration. Fenestration U-factor, SHGC, and VT shall be modeled as meeting the requirements in Section 5.1.3.
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.
G3.3.2.5 Air Leakage. When Section 5.4.3.1.3 applies, the air leakage rate of the building envelope ( I75Pa ) shall be equal to 0.35 cfm/ft [2] of building envelope area at a pressure differential of 75 Pa (0.30 in. of water). The air leakage rate shall be converted to appropriate units for the simulation software using the same method as the proposed design .
G3.3.2.6 Interior Lighting. Interior lighting power density shall be modeled as meeting Section 9.1.1.3.1 using applicable allowances in Section 9.5.2.1. Lighting controls shall be modeled as meeting Section 9.1.1.3.1.
G3.3.2.7 Exterior Lighting. Tradable exterior lighting shall be modeled as meeting Section 9.1.1.3.2.
G3.3.2.8 HVAC Systems
a. Baseline HVAC system types shall be the same as the proposed design .
Exception to G3.3.2.8(a): If the proposed design includes variable refrigerant flow heat pumps or sin-
gle-zone systems with electric resistance heat, then air source heat pumps shall be used in the base- line design . b. Baseline systems shall meet the requirements in Section 6.1.3. Chillers shall meet the efficiency require ments in Table 6.8.1-3 using Path A or Path B, the same as the proposed design . If the proposed design meets both Path A and Path B requirements, Path A shall be used. c. Where the efficiency rating includes supply fan energy, calculate the minimum COPnfcooling and COPnf-
heating [ in accordance with Section 12.5.2(c).] d. Fan system efficiency (bhp per cfm of supply air, including the effect of belt losses but excluding motor
and motor drive losses) shall be the same as the proposed design or up to the limit prescribed in Section 6.5.3.1, whichever is smaller. If this limit is reached, each fan shall be proportionally reduced in brake horsepower until the limit is met. Fan electrical power shall then be determined by adjusting the calcu
320 ANSI/ASHRAE/IES Standard 90.1-2022 (I-P)