ASHRAE-90.1-2022- - Page 312

Extracted Content

Table G3.1 Modeling Requirements for Calculating Proposed Building Performance and Baseline Building Performance (Continued)

Proposed Building Performance	Baseline Building Performance
8. Thermal Blocks—HVAC Zones Not Designed
Where the HVAC zones and systems have not yet been designed, thermal blocks shall be defined based on similar internal load densities, occupancy, lighting, thermal and space temperature schedules, and in combination with the following guidelines: a. Separate thermal blocks shall be assumed for interior and perime- ter spaces. Interior spaces shall be those located greater than 15 ft from an exterior wall or semiexterior wall. Perimeter spaces shall be those located within 15 ft of an exterior wall or semiexterior wall. A separate thermal zone does not need to be modeled for areas adjacent to semiexterior walls that separate semiheated space from conditioned space. b. Separate thermal blocks shall be assumed for spaces adjacent to glazed exterior walls or glazed semiexterior walls; a separate zone shall be provided for each orientation, except that orientations that differ by less than 45 degrees may be considered to be the same orientation. Each zone shall include all floor area that is 15 ft or less from a glazed perimeter wall, except that floor area within 15 ft of glazed perimeter walls having more than one orientation shall be divided proportionately between zones. c. Separate thermal blocks shall be assumed for spaces having floors that are in contact with the ground or exposed to ambient condi- tions from zones that do not share these features. d. Separate thermal blocks shall be assumed for spaces having exte- rior ceiling or roof assemblies from zones that do not share these features.	Same as proposed design.
9. Thermal Blocks—Multifamily Residential Buildings
Residential spaces shall be modeled using at least one thermal block per dwelling unit, except that those units facing the same orientations may be combined into one thermal block. Corner units and units with roof or floor loads shall only be combined with units sharing these features.	Same as proposed design.
10. HVAC Systems
The HVAC system type and all related performance parameters in the proposed design, such as equipment capacities and efficiencies, shall be determined as follows: a. Where a complete HVAC system exists, the model shall reflect the actual system type using actual component capacities and effi- ciencies. b. Where an HVAC system has been designed and submitted with design documents, the HVAC model shall be consistent with design documents. Mechanical equipment efficiencies shall be adjusted from actual design conditions to the standard rating con- ditions specified in Section 6.4.1 if required by the simulation model. Where efficiency ratings include supply fan energy, the effi- ciency rating shall be adjusted to remove the supply fan energy from the efficiency rating in the baseline building design. The pro- posed design HVAC system shall be modeled using manufacturers’ full- and part-load data for the HVAC system without fan power. Exception to (a) and (b): Where part-load performance of chillers in the proposed design is not available, and design temperature across the condenser is 10°F, the performance curves in Nor- mative Appendix L, as referenced in Table J-1, shall be mod- eled for the specified chiller. When using performance curves from Normative Appendix L, chiller minimum part-load ratio (ratio of load to available capacity at a given simulation time step) and minimum compressor unloading ratio (part-load ratio below which the chiller capacity cannot be reduced by unload- ing and chiller is false loaded) shall be equal to 0.25. Simulation programs that do not use performance curves are permitted to use an alternative simulation method that results in the same performance as the curves described in Normative Appendix L. c. Where no heating system exists or no heating system has been sub- mitted with design documents, the system type shall be the same system as modeled in the baseline building design and shall com- ply with but not exceed the requirements of Section 6.	The HVAC systems in the baseline building design shall be of the type and description specified in Section G3.2.1, shall meet the general HVAC system requirements specified in Section G3.2.2, and shall meet any system-specific requirements in Section G3.2.3 that are applicable to the baseline HVAC system types. If the proposed design includes humidification then the baseline building design shall use adiabatic humidification. Exception: If the proposed building humidification system complies with Section 6.5.2.4 then the baseline building design shall use non- adiabatic humidification. For systems serving computer rooms, the baseline building design shall not have reheat for the purpose of dehumidification. Fossil fuel systems shall be modeled using natural gas as their fuel source. Exception: For fossil fuel systems where natural gas is not available for the proposed site as determined by the rating authority, the base- line HVAC systems shall be modeled using propane as their fuel.