Building was Built in the 70s What would I use for Design OA and Infiltration

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If you are looking for the efficiency level and air flow rates that make sense for a building that age you might want to take a look at reference buildings that NREL has modeled for pre-1980. The models are for reference buildings but the assumptions made in them might help you figure out the assumptions for both questions. My instinct is that a window A/C unit from that era has a 6 EER to 8 EER for efficiency when new. With the amount of maintenance that window A/C unit usually get, the efficiency probably has dropped significantly since the units were new.

For window AC, use PTAC. For the unit ventilators, I would use PTAC with outdoor air supply. If the unit ventilators have energy recovery device, then you will need to use an air loop and an AHU. You then use schedules to control the OA.