Auto-Zone Control Systems Auto-Zone Basic Systems Installation & Operation (Version 02C) - Manual (Page 11)

Auto-Zone Basic Section 1
Design Guide 1-5
Design Considerations
Consider the following items when designing a system using Auto-Zone.
Zone Diversity
The Auto-Zone Basic Control 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 Basic Control Systems offer a variety of
methods to control additional zone heat to help you avoid problems.
Cooling - Partial Load Conditions
The engineer must be aware of several potential problems when applying the Auto-Zone
Basic Control 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 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 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.
Low Supply Air Temperatures
Under lightly loaded conditions much of the supply air may be bypassed back into the
return airside of the system. This bypassing will result in the lowering of the supply air