Due to the large airflow capacities of larger units, careful consideration is essential when designing an effective zoning system. Consider the following factors when designing a COBP Zoning System with a larger RTU:
- Use constant volume units in your zoning system design.
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Size the bypass dampers for the remaining airflow volume when all zones are at minimum airflow:
Bypass Airflow (cfm) = Unit Airflow (cfm) – All Zones Minimum Airflow (cfm)
- Use rectangular dampers that have a larger air volume capacity than the round dampers. See Table 2 for rectangular damper sizes and cfm ratings.
- To prevent bypassing large amounts of conditioned air, locate bypass dampers toward the end of the main supply duct run.
- Always have a minimum of six zones on large units due to the high airflow capacities.
- Set the zone damper total minimum airflow settings equal to, or preferably greater than, 30% of the unit’s rated cfm to prevent excessive noise in the system.
- To prevent over-pressurization of the duct work, install a high duct static safety switch such as Johnson Controls® P32 Series Sensitive Pressure Switch or similar.