ASHRAE-90.1-2022- - Page 379
Extracted Content
f. For a building model with multiple blocks, each block facade input shall provide adequate information to identify the outside boundary condition (outside, inside to adjacent block, ground contact, or adiabatic) of each facade or portion of each facade that match the actual proposed design .
Informative Note: The simulation program may automatically identify the adjacent block facade outside boundary conditions through a graphic input process.
L2.2.2 Building Envelope Components. Building envelope thermal properties used in the proposed design shall be based on the actual proposed design using documented user-defined values and shall comply with all of the following:
a. Where different roof thermal properties are present in a single block, an area-weighted U-factor shall be
used. b. Where different wall constructions exist on the facade of a block, an area-weighted U-factor shall be used. c. Where different below-grade wall constructions exist in a block, an area-weighted C- factor shall be used. d. Where different floor constructions exist in the block , an area-weighted U-factor shall be used. e. Where different slab-on-grade floor constructions exist in a block, an area-weighted F-factor shall be used. f. Where different vertical fenestration types or sill heights exist, area-weighted sill heights, U-factor, and SHGC values shall be used. g. Where different skylight types exist, area-weighted U-factor and SHGC values shall be used. h. Permanent shading devices such as overhangs shall be modeled only if >50% of the area of vertical fen-
estration on a facade is shaded by the same.
L2.2.3 HVAC System Components. The HVAC system parameters shall be provided for the proposed design at design conditions unless otherwise stated with clarifications and simplifications as described in Table L2.2.3 and as follows:
a. All HVAC zones within a block shall be served by the same HVAC system type as listed in Table L.1.1.1. b. Where multiple system components serve a block, average values weighted by the appropriate metric as
described in Section L2.2.3.1 shall be used. c. The Table L2.2.3 parameter requirements are based on input of full-load. equipment efficiencies with
adjustment using part-load curves integrated in the simulation program . Where other approaches to partload adjustment are used, it is permitted for specific input parameters to vary.
Informative Note: Table L2.2.3 includes both user-defined parameters and parameters that are fixed in the simulation program and may not be changed by the user. They are maintained in one table here so related items can be viewed together in context.
L2.2.3.1 Proposed Building HVAC System Aggregation. Projects using the Mechanical System Performance Rating Method shall comply with all the following requirements.
a. Where multiple fan systems serve a single block, fan power shall be based on weighted average using the
design supply air (cfm). b. Where multiple cooling systems serve a single block, COP shall be based on a weighted average using
cooling capacity. DX coils shall be entered as multistage if more than 50% of coil capacity serving the block is multistage with staged controls. c. Where multiple heating systems serve a single block, thermal efficiency or heating COP shall be based
on a weighted average using heating capacity. d. Where multiple boiler s or chillers serve a heating-water or chilled-water loop, efficiency shall be based
on a weighted average for using heating or cooling capacity. e. When multiple cooling towers serving a condenser water loop are combined, the cooling tower effi-
ciency, cooling tower design approach, and design range are based on a weighted average of the design water flow rate through each cooling tower. f. Where multiple pumps serve a heating-water, chilled-water, or condenser water loop, pump power shall be based on a weighted average for using design water flow rate. g. When multiple system types with and without economizers are combined, the economizer maximum out-
door air fraction of the combined system shall be based on weighted average of 100% supply air for sys- tems with economizers and design outdoor air for systems without economizers. h. Multiple systems with and without ERVs cannot be combined. i. Systems with and without supply air temperature reset cannot be combined. j. Systems with different fan control (constant volume, multispeed, or VAV ) for supply fans cannot be combined.
ANSI/ASHRAE/IES Standard 90.1-2022 (I-P) 377