Auto-Zone Control Systems Auto-Zone CV-C Controller Installation Guide (Version 01A) - Manual (Page 32)

Section 2 Auto-Zone CV-C
2-22 Sequence of Operation
economizer watches the movement of the controlling temperature to determine if it
should make any further adjustments. If the temperature is dropping but it is still above
setpoint, the economizer will not open any further unless the temperature stops dropping
and becomes stagnant at a level above the setpoint. The same is true if the temperature is
below the setpoint and rising, no adjustments are made unless the temperature stagnates
as some fixed value.
If the economizer is moving too fast or too slow to maintain stable temperature control,
the user can adjust a Control Rate value between a value of 0.1 and 9.9 with 9.9 being the
fastest control and 0.1 being the slowest control.
As mentioned in the DX Cooling and Chilled Water Valve operations, the economizer
must be fully open before mechanical cooling can occur. On the same hand, if mechanical
cooling has been initiated, the economizer must remain fully open until the mechanical
cooling is removed or the supply air temperature drops below 40°F or 4.4°C. If this
occurs, the economizer closes by 5% every 10 seconds until it is fully closed or the
supply air has recovered enough to allow the economizer to be used again. If the supply
air rises above this low limit protection, the economizer will begin to creep open if it
needs to reduce the supply air or mixed air ( not likely ) downward.
One other test that can occur but is not generally required occurs when the user has
installed a return air sensor. If the outside air is within 5° of the return air temperature
then it can’t really be used for cooling the supply air so the economizer is disabled and
maintained at the user defined minimum position.