Xavier,

I would check the minimum airflows for the VAV zones. 30% of maximum air flow is generally a code minimum (unless there is a critical space that needs a high fraction of ventilation, such as a conference room, or the cfm/sf is near 0.4). If your percentage is abnormally high, then the system will have a lot of reheat. Unfortunately the eQUEST wizard limits assigning different minimum airflow percentages to only two types of zones - core and perimeter - so it's harder to deal with a critical space that affects the ventilation fraction.

Sincerely,

Keith Swartz, PE, LEED? AP