How to simulate the baseline enclosed parking garage with exhaust air fan and makeup air fan in the example below?
Example: The designed enclosed parking garage is 10,000 square feet with one makeup air fan at 15 kW and one exhaust air fan at 15 kW, no DCV is needed, and the exhaust air fan and the makeup air fan are running 24/7.
Per LEED interpretation 10371 (https://www.usgbc.org/leedaddenda/10371) 0.75 CFM/sf should be used for the baseline ventilation and the fan power should be 0.3 W/CFM. Per IMC section 403.3.1.1, this 0.75 CFM/sf is exhaust air.
Two opinions have been discussed regarding how to simulate the baseline enclosed parking garage:
a)Total exhaust ventilation is 0.75 CFM/sf * 10,000 sf =75,000 CFM
Total baseline fans’ (makeup air fan and exhaust air fan) power should be 75,000 CFM * 0.3 W/CFM = 22.5 kW
The enclosed parking garage demand saving is: 22.5 kW (baseline)-30 kW (proposed makeup air fan and exhaust air fan) = -7.5 kW.
b) Total exhaust ventilation is 0.75 CFM/sf * 10,000 sf =75,000 CFM
Exhaust fan power should be 75,000 CFM * 0.3 W/CFM = 22.5 kW
Makeup fan power should be identical to the proposed model, which is 15 kW (This suggestion is from LEEDuser: https://leeduser.buildinggreen.com/forum/garage-fan-power-allowance).The enclosed parking garage demand saving is: 37.5 kW (baseline exhaust fan and proposed makeup air fan)-30 kW (proposed makeup air fan and exhaust air fan) = +7.5 kW.
Could you please let me know which one should be the correct method to simulate the enclosed parking gargae ventilation system for the baseline model? I am using ASHRAE 90.1-2013 and hopefully the rule doesn't change for ASHRA 90.1-2019 either.
