Zero 'densely occupied space'

The answer is no. If you do not have any densely occupied spaces then there are two possible requirements: 1. Natural ventilation - install CO2 sensors in every occupied space. 2. Mechanical ventilation - install an outside air flow meter for the OA serving occupied spaces.

Valentin, I wanted to piggy-back on Andrew's answer (which is 100% accurate) to point out that you may want to crosscheck what you are submitting under IEQp1: Minimum IAQ Performance. ASHRAE 62.1 will classify spaces as "densely occupied" simply based on the occupant density rates given in Table 6-1 of the Standard. If you are using these rates verbatim in your calculations, the review team may question whether or not there are densely occupied spaces within the project. Just know that you are able to calculate your ventilation requirements not using the default values in ASHRAE 62.1 if the spaces should not be seen as densely occupied. Hope this helps!