CNT-SVX17G-EN 45
Sequence of Operations
Air Valve Control in Space Temperature Control Operation
The Tracer® VV550/VV551 controllers support one modulating air valve for heating and
cooling operation. Air delivered to the space is controlled with a three-wire floating-point
actuator that modulates the air valve. The controller positions the modulating air valve
to deliver the desired airflow (cooling or heating capacity). The desired airflow is called
the active-flow setpoint. The controller positions the modulating air valve to deliver the
desired airflow (cooling and heating capacity) to within +/-2% of nominal airflow.
The airflow control algorithm compares the active airflow setpoint with the measured
ai
rflow and calculates the necessary air valve movement to minimize error. The airflow
setpoint is limited by applicable minimum and maximum flow setpoints.
Reheat Control
There are two types of reheat control: hydronic heat and electric heat. Reheat is allowed
to turn On if the zone temperature is below the heating setpoint. Space temperature
control can use reheat if the following conditions are
all true:
• The unit is not calibrating;
• Reheat is enabled (communicated auxiliary heat enable);
• For local reheat only, the fan, if present,
is not being overridden to Off (communicated
fan speed command);
• The primary air temperature is less than the configured reheat enable setpoint (5°F
[2
.78°C]);
• Local heat minimum airflow is used for both local and remote reheat.
Hydronic Heat
Two types of control of hydronic heat are supported: On/Off and modulating.
Note: Steam is not supported.
Hot < Active Heat Stpt Modulate from heat max to highest min:
• Local heat min airflow
• Heating min airflow
• Effective ventilation setpoint
Series On
Parallel Off
Reheat Off
HSP < ZT < HSP + 2 At the highest min position:
• Heating min airflow
• Effective ventilation setpoint
Series On
Parallel Off
Reheat Off
> Active Cool Stpt At the highest min position:
• Heating min airflow
• Effective ventilation setpoint
Series On
Pa
rallel Off
Reheat Off
a. Primary air temperature is derived from either the communicated source temperature or the primary/discharge air temperature sensor
when configured for primary air temperature. Cold; PAT< configured auto-changeover setpoint minus 10°F. Warm; configured auto-
changeover setpoint < PAT < configured reheat enable setpoint minus 5°F. Hot; configured reheat enable setpoint < PAT. Rover
™will
check the range of the configured reheat enable setpoint, 70°F to 100°F (21.11°C to 37.78°C) for electric heat and 70°F to 200°F (21.11°C
to 93.33°C) for hot water heat.
Table 30.Controller operation during occupied heating and cooling (continued)
PAT
(a)
Space Temperature
Primary airflow control active minimum
airflow setpoints
Fan control Reheat control
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