ASHRAE-90.1-2022- - Page 317
Extracted Content
For methods describing air leakage as a function of the area of above-grade walls that separate condi- tioned spaces and semiheated spaces from the exterior,
IAGW = 0.112 × I75Pa × S/AAGW When using the measured air leakage rate of the building envelope at a pressure differential of 0.3 in. of water for the proposed design, the air leakage rate shall be calculated as follows:
I75Pa = Q/S
where I75Pa = air leakage rate of the building envelope (cfm/ft [2] ) at a fixed building pressure differential of 75 Pa (0.30 in. of water) Q = volume of air in cfm flowing through the building envelope when subjected to a pressure differential of 75 Pa (0.30 in. of water), in accordance with ASTM E 779, ASTM E1827, or ASTM E3158 S = total area of the building envelope (ft [2] ), including the lowest floor, any below-grade walls or above-grade walls, and roof (including vertical fenestration and skylights ) IFLR = adjusted air leakage rate of the building envelope (cfm/ft [2] ) at a reference wind speed of 10 mph and relative to the gross floor area AFLR = gross floor area, ft [2]
IAGW = adjusted air leakage rate of the building envelope (cfm/ft [2] ) at a reference wind speed of 10 mph and relative to the area of the above-grade walls of the building envelope AAGW = total area of above-grade walls of the building envelope, ft [2]
Exceptions to G3.2.1.7: A multizone airflow model alternative method to modeling building envelope
air leakage may be used, provided the following criteria are met:
- Where the calculations are made independently of the energy simulation program, the proposed method must comply with Section G2.5.
- The method for converting the air leakage rate of the building envelope at 0.3 in. of water, or 1.57 psf, to the appropriate units for the simulation program is fully documented and submitted to the rating authority for approval.
G3.2.2 General Baseline HVAC System Requirements. HVAC systems in the baseline building design shall conform with the general provisions in this section.
G3.2.2.1 Equipment Efficiencies. All HVAC equipment in the baseline building design shall be modeled at the minimum efficiency levels, both part load and full load, in accordance with Tables G3.5.1 through G3.5.6. Where multiple HVAC zones are combined into a single thermal block in accordance with Table G3.1, the efficiencies (for baseline HVAC System Types 3, 4, 9, and 10) taken from Tables G3.5.1, G3.5.2, and G3.5.5 shall be based on the equipment capacity of the thermal block divided by the number of HVAC zones . HVAC System Types 5 or 6 efficiencies taken from Table G3.5.1 shall be based on the cooling equip- ment capacity of a single story when grouping identical stories in accordance with Section G3.2.1.1(a)(4). Fan energy shall be modeled separately according to Section G3.2.1.7.
COPnfcooling and COPnfheating are the packaged HVAC equipment cooling and heating energy efficiency, respectively, to be used in the baseline building design, which excludes supply fan power.
The sets of performance curves specified in Table J-2 should be used to represent part-load performance of chillers in the baseline building design. When using performance curves from Normative Appendix J, 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 unloading 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 J.
G3.2.2.2 Equipment Capacities. System coil capacities for the baseline building design shall be based on sizing runs for each orientation in accordance with Table G3.1, No. 5[a] and Section G3.2.2.2.1, and shall be oversized by 15% for cooling and 25% for heating. The ratio between the capacities used in the annual simulations and the capacities determined by the sizing runs shall be 1.15 for cooling and 1.25 for heating. Plant capacities shall be based on coincident loads.
G3.2.2.2.1 Sizing Runs. Weather conditions used in sizing runs to determine baseline equipment capacities shall be based on design days developed using heating design temperatures, cooling design tem- perature, and cooling design wet-bulb temperature . For cooling sizing runs, schedules for internal loads,
ANSI/ASHRAE/IES Standard 90.1-2022 (I-P) 315