Orion System Zoning User Manual
Page 29
Orion Systems
29
Zoning Design Guide
Application Notes:
Zoning Large Units
Zoning systems work very well for HVAC units up to
40 tons. It is reccommended that HVAC units larger
than 40 tons should be designed as true VAV systems
due to the large number of zones involved. When using
HVAC units that are 25 to 40 tons, for zoning applica-
tions, several rules must be considered to prohibit po-
tential problems. If
Because of the larger air flow capacities of these units,
great care must be taken in sizing zone and bypass damp-
ers.
Use these guidelines to help keep you out of trouble.
• Always specify that the unit is equipped with
hot gas bypass on the first stage of cooling.
• Always use a VFD instead of using a bypass
damper for controlling duct pressure
• The unit should be equipped with the maxi-
mum number of heating and cooling stages
available.
• Avoid large zones served by a single damper.
Try to break the larger zones up into multiple
zones.
• Large units should always have a minimum
of 6 zones due to the high air flow capacities.
On larger tonnage units, the more zones the
better
• To prevent excessive noise in the system,
zone damper total minimum airflow settings
should be equal to or preferably greater than
30% of the units rated CFM.
As an added precaution, we recommend a high duct
static safety switch be installed (Dwyer Model 1900-
5-MR or equal) to prevent over pressurization of the
ductwork.