Auto-Zone Control Systems Auto-Zone Basic Systems Installation & Operation (Version 02C) - Manual (Page 13)

Auto-Zone Basic Section 1
Design Guide 1-7
Heating - Partial Load Conditions
Heating difficulties are less common than cooling difficulties. They are similar in nature,
however, and the cures are generally the same.
• Increase the Heating minimum setpoints on as many zones as possible.
• Increase the static pressure setting as high as is practical. Increasing static pressure
does not help if you are using pressure independent operation.
• Bypass to plenum instead of the return air intake if acceptable.
• Do not oversize your equipment.
• Use auxiliary heat in either your VAV boxes or baseboard.
Auto-Zone has a number of auxiliary heat control options which provide solutions to
most problems. Refer to the Auxiliary Heat Control Options topic near the end of this
section.
Override Conditions
After-hours overrides can produce aggravated partial load conditions in both the heating
and cooling modes. The problem is most commonly caused by a single zone being
overridden for after-hours use. This causes the rooftop equipment to operate for only one
zone. The Auto-Zone Basic Control System offers an improved solution to this common
problem by allowing a single override to trigger a group of zones via a “global” override.
This allows the system to operate with sufficient load to reduce cycling caused by light
load conditions.
Building Pressurization
If you are using an economizer, building pressurization must be addressed. Failure to
properly handle building pressurization may result in doors remaining open when the
economizer is operating. Pressurization problems can render economizer operation
useless. The following suggestions will help to avoid potential problems.
• Use powered exhaust when the system uses ducted returns. The return duct pressure
drop will cause most barometric relief dampers to function poorly or not at all. Auto-
Zone has the ability to control a powered exhaust whenever the economizer is
operating.
• Use a separate building pressure control which operates a relief fan or dampers.