Trane VAV VV550 LonTalk, Руководство по установке и эксплуатации

Страница: 76 / 116

76 VAV-SVP01A-EN
Sequence of Operations
Freeze Protection (Hot Water Only)
Units with hot water coils installed are susceptible to freezing. It is important to prevent the water
coils from freezing. Freeze protection occurs only when the controller is in the Off state or during
the unoccupied period when the primary air valve is closed and the reheat is disabled. During
occupied operation, the control algorithm indirectly provides freeze protection.
Note: See CNT-SVX17*-EN for details on BAS system control of VV550 controller.
Stand-alone Controller Freeze Protection
Controllers operating without communications do not have the source temperature available to
them. In these cases, the discharge air temperature sensor is assumed to provide a reasonable
representation of the coil temperature at conditions with no airflow if the sensor is close to the coil.
If the discharge air temperature, at no airflow, falls below the configured outdoor air low limit, the
hot water valve is fully opened. The hot water valve remains open until the discharge air
temperature is 10°F (5.56°C) above the configured outdoor air low limit or occupied operation
begins. If the communicated source temperature is invalid and the local discharge air temperature
sensor has failed, freeze protection is active and the water valve is open.
Unoccupied Ventilation Flow Control
The controller closes the air valve. Local electric heat and hot water heat are disabled. The hot water
valves open if needed for freeze protection. The operation of freeze protection for local hot water
heat depends on whether the controller is operating as a network controller or a stand-alone
controller.
Table 15, p. 76 shows unoccupied VFC control freeze protection for hot water reheat.
Flow Tracking
Flow Tracking Control Mode
Flow tracking control (FTC) is one of three supported control algorithms. Two VAV VV550
Controllers work together to provide flow tracking control. See
Figure 50, p. 77 .The space
temperature controller outputs the airflow (reported airflow). The space temperature controller
airflow output (reported airflow) is bound to the flow tracking controller airflow setpoint input
(communicated airflow setpoint). The flow tracking controller adds the configured airflow tracking
offset (positive or negative) to the airflow setpoint (communicated airflow setpoint) and controls
the airflow to this setpoint. The flow tracking controller does not require a space temperature
sensor or a discharge air temperature sensor. If the calculated airflow setpoint is less than 10% of
the configured nominal airflow and the configured airflow tracking offset is less than zero, the air
valve is closed. If the calculated airflow setpoint is less than 10% of the configured nominal airflow
and the configured airflow tracking offset is greater than or equal to zero, the air valve is positioned
Table 15. Unoccupied VFC control, freeze protection for hot water reheat
Controller operation Air valve position Condition
Hot water valve
position
Networked and valid
communicated source
temperature Closed no flow Communicated source temperature greater than configured
outdoor air low limit
Closed
Communicated source temperature less than or equal to
configured outdoor air low limit, freeze protection active diagnostic
(with 10°F hysteresis)
Open to 100%
Stand-alone, coil
temperature sensed at
discharge air
temperature
(a)
Closed no flow
Discharge air temperature greater than configured outdoor air low
limit
Closed
Discharge air temperature less than or equal to configured outdoor
air low limit, freeze protection active diagnostic (with 10°F
hysteresis)
Open to 100%
(a) Place the discharge temperature sensor in close proximity to the hot water coil discharge. The sensor effectively reports coil temperature when there
is no airflow through the coil. Therefore, the coil can be freeze-protected by the discharge air temperature sensor.