ASHRAE-90.1-2022- - Page 319

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accreditation standards, whichever is greater. For systems with multiple zone thermostat set points, use the design set point that will result in the lowest supply air cooling set point or highest supply air heating set point . If return or relief fans are specified in the proposed design, the baseline building design shall also be modeled with fans serving the same functions and sized for the baseline system supply fan air quantity less the minimum outdoor air, or 90% of the supply fan air quantity, whichever is larger.

Exceptions to G3.2.2.7.1:

1. For systems serving laboratory spaces, airflow rate shall be based on a supply-air-to-room temperature set-point difference of 17°F or the required ventilation air or makeup air, whichever is greater.
2. If the proposed design HVAC system airflow rate based on latent loads is greater than the design airflow rate based on sensible loads, then the same supply-air-to-room-air humidity ratio difference (gr/lb) used to calculate the proposed design airflow shall be used to calculate design airflow rates for the baseline building design .

G3.2.2.7.2 Baseline System Types 9 and 10. System design supply airflow rates for the baseline building design shall be based on the temperature difference between a supply air temperature set point of 105°F and the design space -heating temperature set point, the minimum outdoor airflow rate, or the airflow rate required to comply with applicable codes or accreditation standards, whichever is greater. If the pro- posed design includes a fan or fans sized and controlled to provide non- mechanical cooling, the baseline building design shall include a separate fan to provide non- mechanical cooling, sized and controlled the same as the proposed design .

G3.2.2.8 System Fan Power. System fan electrical power for supply, return, exhaust, and relief (excluding power to fan-powered VAV boxes) shall be calculated using the following formulas:

For Systems 1 and 2,

Pfan = CFM s × 0.3

For Systems 3 through 8, and 11, 12, and 13,

Pfan = bhp × 746/fan motor efficiency

For Systems 9 and 10 (supply fan),

Pfan = CFM s × 0.3

For Systems 9 and 10 (non- mechanical cooling fan if required by Section G3.2.2.7.2),

Pfan = CFM nmc × 0.054

where Pfan = electric power to fan motor, W bhp = brake horsepower of baseline fan motor fromTable G3.2.2.8 fan motor efficiency = the efficiency for the next motor size greater than the bhp from Table G3.2.2.8 CFM s = the baseline system maximum design supply fan airflow rate, cfm CFM nmc = the baseline non- mechanical cooling fan airflow, cfm G3.2.2.8.1 The calculated system fan power shall be distributed to supply, return, exhaust, and relief fans in the same proportion as the proposed design .

G3.2.2.9 Exhaust Air Energy Recovery. Individual fan systems that have both a design supply air capacity of 5000 cfm or greater and have a minimum design outdoor air supply of 70% or greater shall have an energy recovery system with at least 50% enthalpy recovery ratio . Fifty percent enthalpy recovery ratio shall mean a change in the enthalpy of the outdoor air supply equal to 50% of the difference between the outdoor air and return air at design conditions . Provision shall be made to bypass or control the heat recovery system to permit air economizer operation, where applicable.

Exceptions to G3.2.2.9: If any of these exceptions apply, exhaust air energy recovery shall not be

included in the baseline building design :

1. Systems serving spaces that are not cooled and that are heated to less than 60°F.
2. Systems exhausting toxic, flammable, or corrosive fumes or paint or dust. This exception shall only be used if exhaust air energy recovery is not used in the proposed design .
3. Commercial kitchen hoods (grease) classified as Type 1 by NFPA 96. This exception shall only be used if exhaust air energy recovery is not used in the proposed design .
4. Heating systems in Climate Zones 0 through 3.

ANSI/ASHRAE/IES Standard 90.1-2022 (I-P) 317