Why Zone a SpacePak Central Air System?
Uniform Comfort in Multilevel Construction
When two or more levels are connected by an open stairwell or a balcony, the tendency is for the upper level to be too warm and the lower level to be too cold. (manual D, section 1, pg-1)
To compensate for this difference in temperature, a second unit can be added, or the mini-duct system can be divided into zones.
Energy and Cost Savings
Typical HVAC system design is based on both average loads and peak loads. Peak demand is required less than 10% of the seasonal run time (manual J, 8th Edition). Room CFM quantities based on average load requirements will be undersized during times of peak load.
A fixed branch damper setting will not balance the cooling (or heating) of the supply air with the room load because the room load continually changes as the outdoor temperature, solar gain and internal loads vary. (manual D, section 1, pg 1)
Small Duct High Velocity requires a higher than average investment for a "No Compromise" benefit to the home owner, space is at a premium. Adding multiple units to meet variable load requirements is typically not an option due to space and cost limitations.