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Julien, thanks for your suggestions, much appreciated. I tried a number of items and have narrowed it down to some sort of AHU heating/cooling control issue.

For anyone running into a similar issue, I made the following changes to my model and saw some improvement. Hourly airflow is still higher in the summer months compared to the autosized model, but the VAV system airflow over the course of the year looks more "normal" and annual energy use is now almost identical to the autosized fan model.

1. Disabled SAT reset - this was causing the flat airflow profile during the summer months and increasing fan energy
2. Added heating coils at the zone level instead of at the system level
3. The AHU in question is serving one interior zone modeled with a floor multiplier. Changing the zone's throttling range from 4F to 0.1F reduces the model's heating, cooling, and fan energy use without changing unmet load hours.

I'm still not exactly sure what was happening and why these changes helped. I'll post back if I get a better understanding of it later on.

Thanks again!

Holly