Below Grade Garage Exhaust with CO Monitoring

Condition: I have a completely unconditioned garage located in the cellar. There is no heating. No cooling. Only an exhaust fan and an opening in the entry gate to the garage to provide unconditioned fresh air. This garage fan operates via VFD as there are carbon monoxide monitoring controls that allow fan speed to modulate based on those levels. I am NOT modeling this as a system as I am not required to given the fact that there is no cooling or heating (unconditioned spaces have neither heating nor cooling systems). The exhaust CFM and the fan power remains the same (as shown in the design dwgs) in the baseline and proposed cases. The only difference is that fan operating schedule: baseline is 100% on during occupied hours and the proposed case fluctuates based on a similar type of people schedule throughout the day. The LEED reviewer has indicated this as a DCV system (?!) and has noted that I should be treating my exhaust fan according to the baseline fan power calcs AND the ASHRAE minimum ventilation rates. The reviewer is treating my system as DCV even though the ASHRAE application of DCV applies to CO2 sensors and modulating occupancy, not CO (related to toxins in the air; as a result of increased intermittent occupancy). In my opinion, this should be treated as an exceptional calc following the method I described earlier because fans that ventilate only, ie garage exhaust fans, are NOT qualified as a fan system, meaning that the fan power remain equal in both modeling cases. Additionally, the rules for modeling DCV do not apply in this case, for the reasons listed above. Please let me know your thoughts.