Auto-Zone Control Systems Auto-Zone Plus Systems Installation & Operation (Version 03A) - Manual (Page 14)

Section 1 Auto-Zone Plus
1-10 Design Guide
Design Considerations
Consider the following items when designing an Auto-Zone Plus system.
Zone Diversity
An Auto-Zone Plus system is designed to improve tenant comfort by dynamically re-
balancing the air distribution when used with a typical constant volume rooftop
heating/cooling unit. If zones with extremely different load conditions are serviced by a
single rooftop unit, the result will be poor control and excessive wear due to cycling of
the equipment.
It is especially important to avoid mixing interior zones (which require cooling all year)
with exterior zones (which may require constant heat during winter months). If you must
mix zones under these conditions, consider using either VAV boxes with heat or separate
baseboard heat on exterior zones. Auto-Zone Plus systems offer a variety of methods to
control additional zone heat to help you avoid problems.
Group similar loads on an individual unit and use more than one zoned unit if required.
Any special loads can be handled by using separate constant volume units.
The Auto-Zone Plus system offers the designer considerable flexibility by allowing both
multiple-zoned units and single-zone units to be connected within a single simple system.
Cooling - Partial Load Conditions
The engineer must be aware of several potential problems when applying an Auto-Zone
Plus system during cold weather operation.
Low Ambient Temperature Lockout
During very cold weather it is common for mechanical systems to have “low temp
lockouts” which protect equipment from damage if operated under these conditions.
Auto-Zone Plus also provides user programmed lockouts for protection purposes,
although mechanical safeties should always be used as the final stage of protection.
If the rooftop unit services interior zones with thermal loads which require cooling when
outside temperatures are below the safe operating limits for your equipment, you should
seriously consider installing an economizer on your rooftop unit. The Auto-Zone Plus
control system is designed to take advantage of an economizer if it is installed. The use of
an economizer will save money on utilities and provide comfort under conditions when it
is not possible to operate the mechanical cooling system.