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CNT-SVX07D-EN
Sequence of operations
position, causing the discharge air temperature to fall below the Discharge Air Control Point Low
Limit.
Morning warm-up
Morning warm-up can occur any time the controller is in the occupied mode. The controller supply
fan always runs in the occupied mode.
Morning warm-up is initiated when the zone temperature is more than 2°F (1.1°C) below the
occupied heating setpoint. Morning warm-up is terminated when the zone temperature is less than
2°F (1.1°C) below the occupied heating setpoint.
When morning warm-up is terminated, the ZN520 runs in occupied heat mode. The outdoor air
damper will be closed when the zone temperature is 3°F (1.7°C) or more below the occupied heating
setpoint. The outdoor air damper will be at the minimum position when the zone temperature is
2°F (1.1°C) or less below the occupied heating setpoint. The outdoor air damper modulates
between the minimum position and closed as the zone temperature goes from 2°F (1.1°C) below
the occupied heating setpoint to 3°F (1.7°C) below the occupied heating setpoint.
Morning cool-down
Morning cool-down is initiated when the controller transitions from unoccupied to occupied and
the zone temperature is 3°F (1.7°C) above the occupied cooling setpoint. The fan will turn on and
the outdoor air damper will remain closed. The damper modulates between closed and the
minimum position as the zone temperature cools down toward the occupied cooling setpoint.
The damper will be closed when the zone temperature is more than 3°F (1.7°C) above the occupied
cooling setpoint. The damper will be at the minimum position when the zone temperature is less
than 2°F (1.1°C) above the occupied cooling setpoint. If economizing is possible, the damper will
open up above the minimum position. Cool down can only happen once.
When the outdoor air damper gets to its minimum position, morning cool-down is over and cannot
happen again until the next transition from unoccupied to occupied.
The controller will be in the occupied cooling mode when morning cool-down is over.
Heating or cooling mode
The heating or cooling mode can be determined in one of two ways:
•
By a communicated signal from a BAS or a peer controller
•
Automatically, as determined by the controller
A communicated heating signal permits the controller to heat only. A communicated cooling signal
permits the controller to cool only. A communicated auto signal allows the controller to
automatically change from heating to cooling and vice versa.
In heating and cooling mode, the controller maintains the zone temperature based on the active
heating setpoint and the active cooling setpoint, respectively. The active heating and cooling
setpoints are determined by the occupancy mode of the controller.
For two-pipe and four-pipe changeover units, normal heat/cool operation will not begin until the
ability to conduct the desired heating or cooling operation is verified. This is done using the
entering water temperature sampling function, for which a valid entering water temperature is
required. When neither a hard-wired nor a communicated entering water temperature value is
present on changeover units, the controller will operate in heating mode only and assume the coil
water is hot. The sampling function is not used.
The entering water temperature sampling function is used only for changeover applications. It is
used for information and troubleshooting only and does not affect the operation of the controller.
(For more information, see
Содержание Tracer ZN521
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