Auto-Zone Control Systems Auto-Zone Basic Systems Installation & Operation (Version 02C) - Manual (Page 12)

Section 1 Auto-Zone Basic
1-6 Design Guide
temperature, which may result in the supply air temperature reaching the low temp safety
limit. If the supply air low temp safety limit is exceeded, the control system will “cut-off”
the mechanical cooling to protect it from damage. Excessive cycling of the mechanical
system will result if this condition persists. Comfort may also suffer if the system cannot
run long enough to satisfy cooling demands.
A number of things can be done to reduce this problem. Some of these things depend
upon the type of installation.
• Avoid oversizing the unit. Do your load calculations carefully. Since Auto-Zone
directs the heating or cooling to the zones which require it, you may find that you can
use a smaller unit in many cases. Oversizing is the number one cause of excessive
low supply air temperature cycling.
• Increase your cooling minimum airflow or damper position settings to allow more air
during cooling operation. Be careful to avoid settings which are so high you cause
over cooling of the spaces. Find a compromise position.
• Bypass the air into the plenum instead of into the return air intake. Be careful if you
use this method since you may get “dumping” of cold air from your return air grilles.
This method works best with plenum returns. Do not use this method with ducted
returns unless you have carefully considered the consequences.
• Increase your static pressure setpoint to help reduce the amount of air being bypassed.
Be aware of increased noise levels and the cost of operation if you use excessive
static pressures.
Warning : If the fan system has the capability of producing static pressures
which could damage ductwork, you must provide a manual reset high
pressure limit switch to cut-off the fan system in the event of high
duct static. Do not use your Auto-Zone Basic Control System as a
safety device!
• Use an Economizer. Although this is not a cure-all, it greatly improves operation
during cool weather when cooling loads are minimal. Using an Economizer also
improves ventilation and lowers operating costs, both of which are significant.