Modelling Basement Parking

If the supply flow rate = exhaust flow rate, just double the fan pressure rise to double the fan electric consumption, or if you need to be more exact you can calculate the equivalent pressure rise to account for the energy consumption of both exhaust and supply fans.

Don't do #2. Not sure why you can't model exhaust fans in the simulation, seems like a pretty basic function.

If you are attempting to claim savings for CO DCV you need to make the case that it is not standard practice in the project locale. You will also need to do an exceptional calculation.

See section 1.7 of the EAp2 prerequisite form for details. You need to do an exceptional calculation if: 1) your modeling software cannot model a strategy directly and you are performing a workaround; 2) you need to violate a modeling protocol (like a schedule change) in order to show savings; and 3) to claim energy savings related to non-regulated or process loads.

A narrative should describe all Baseline and Proposed case assumptions included for this measure as well as the calculation methodology used to determine the projected savings. The narrative and energy savings should be reported separately from the other efficiency measures in Section 1.7 - Table EAp2-7. The Baseline case description should provide evidence that garage demand control ventilation is not standard practice for similar newly constructed facilities where the project is located. Additionally, sufficient information must be provided to justify all Baseline and Proposed Case assumptions used for the calculation of savings including the Baseline ventilation rates, the Proposed Ventilation rates, the Baseline fan power, the Proposed fan power, and the Baseline and Proposed operating schedules. Note that the Baseline fan volume should not exceed the minimum required ASHRAE 62.1 parking ventilation rates of 0.75 cfm/square foot.

1) if you want to take credit for DCV, check out CIR 10371 on 04.02.2014. This is a new ruling.
2) Unless you try 1), the fresh air ventilation rates for baseline = proposed.
3) for a parking garage, the 62.1 required min fresh air rate = 0, so you have met the minimum.
4) for a parking garage 50% open to outside on two or more sides, the 62.1 required exhaust rate = 0, so this requirement is met.
5) If you are not conditioning your zone with the supply air, you can consider the fan(s) a process load.

They are process as Jean indicates.

Jean it is my understanding that the minimum ventilation rate for an underground (enclosed) parking garage is 0.75 cfm/sf.

Funny, that. Underground may make it difficalt to get the opening area to outside to be larger than 50% on two sides...but I've seen enough exceptions. We're working on a (non-LEED) project, where, for political reasons and budget application, they dug a gap down to the slab level of the underground parking all the way around, so that the requirement to sprinkler the underground parking falls away. They have a natural smoke exhaust system with plenty of opening.

I am assuming that underground = enclosed and that the 50% cannot be obtained.