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ZONE SIZING EXAMPLE:
The zone size has a direct impact on system operation and homeowner comfort. The system uses zone sizes
to determine the air handling capability of each zone and determines the amount of excess air that has to be
managed. Incorrect zone sizes will undermine the performance and comfort levels within the space.
NOTE:
For zoning, the duct system should be sized to handle the peak load of each zone. Therefore, the duct system
is typically sized larger than a conventional non-zoned application.
EXAMPLE:
A 4-zone system is installed on a two compressor system. Each zone can handle 40% of the system air flow.
All zones are set to off at the . The homeowner now turns one zone to cool and lowers the setting to 5 degrees
below the current temperature. Since this zone can handle a maximum of 40% of the system capacity, the zone
control will lock the system in first stage operation. There is no reason to move to second stage operation
since all the additional air flow and capacity would be forced into non-calling zones.
The system would be allowed to energize second stage if another zone is calling. The total zone size would
now be 80% and first stage operation may not be enough to satisfy this demand.
•
On a two compressor system, the sum of the calling zone sizes must be at least 51% to enable second
stage operation.
•
On a single compressor, two stage system, the sum of the calling zone sizes must be at least 68% to
enable second stage operation.
•
On a two stage furnace, the sum of the calling zone sizes must be at least 66% to enable second stage
operation.
•
On a three stage furnace, the sum of the calling zone sizes must be at least 41% to enable second stage
operation. Third stage is not inhibited.
STEP 7 - Voting Zones
A voting zone has the ability to turn on the HVAC
system.
A non-voting zone has the ability to control the
damper, but does not have the ability to turn on
the system. A non-voting zone cannot keep the
system running if all voting zones are satisfied.
