Proper air and water balancing is critical to HVAC system performance. No amount of commissioning will make a system function as intended if it isn’t balanced. Design air and water flows need to be achievable in all modes of operation. Typical modes in an HVAC system include occupied, unoccupied, morning warm-up, morning cool-down, airside economizer, minimum outside air, water-side economizer, etc. This column is dedicated to the importance of testing and documenting system airflows in both the minimum outside air mode and the 100% outside air economizer mode.
Systems often experience different pressure relationships as the outside air, return air, and relief air dampers (mixing dampers) modulate from their minimum outside air positions to their 100% outside air positions. If the system cannot achieve design airflows under certain mixing damper conditions, it will result in intermittent and challenging-to-diagnose problems after occupancy.