Fan Power Credits

ASHRAE 90.1-2019

Note 1 and 2 under Table G3.1.2.9 indicate that the baseline fan brake horsepower adjustment factor, A, is calculated according to Section 6.5.3.1.1 using the pressure-drop adjustment from the proposed design and the design flow rate of the baseline building system. The pressure-drop adjustment for evaporative coolers or heat recovery devices that are not required in the baseline system by Section G3.1.2.10.

Code Requirement Interpretation

Section 6.5.3.1.1 include credits but also deductions. Following an internal discussion we concluded that the intent of Appendix G should be to base the deduction on the baseline building design and not the proposed design.

Implementation

Fan power credits are provided by the user via the userdata_airloop_hvac.csv and userdata_zone_hvac.csv files. The deductions are only applicable to system 6 and 8 and are handled in the code in air_loop_hvac_fan_power_limitation_pressure_drop_adjustment_brake_horsepower(). Credits and deduction are stored as an additionaProperty at the ThermalZone and AirLoopHVAC level. The baseline fan power credits/deductions are calculated for each zone as follows: Az = sum(PD_sum * CFM_d_baseline/4131), where CFM_d_baseline is the baseline zone design air flow and PD_sum. The system A is obtained by summing all the zone Az.

Key Ruby Methods