Sequence of Operation
Fan Coil CARRIER CORPORATION ©2020
Integration Guide All rights reserved
23
If all the above conditions are met, the heating outputs are energized as required, otherwise they are de-
energized. If the heating is active and the SAT approaches the maximum SAT limit, the heating valve modulates
closed. For electric heating, if the SAT rises above the configured Maximum SAT limit minus 10 °F (5.5 °C), the
fan is indexed to a higher speed. If this is insufficient and the SAT rises above the maximum limit, the EH heating
stage is disabled. After the electric heater stage is turned off, it may be restarted again after the supply air
temperature falls below the Maximum Heating SAT limit minus 15 °F (8.3 °C). There is a 2-minute minimum
off-timer for the electric heater stage to insure protection against excessive cycling.
The configuration screens contain the Max SAT parameter as well as Heating Lockout based on outdoor air
temperature (OAT). Both can be adjusted to meet various specifications.
Modulating Hot Water / Steam Heating - The control can operate a modulating (0-10 Vdc) type, NO or NC, hot
water or steam valve, connected to the heating coil of the unit and supplied by a boiler in order to maintain the
desired heating setpoint. The valve is controlled so the SAT does not exceed the Maximum Heating SAT limit. If
the fan is off, the valve modulates to maintain the SAT at the configured Fan Off Value temperature.
2- Position Hot Water / Steam Heating - The control can operate a 2-position, NO or NC, hot water or steam valve,
connected to the heating coil of the unit and supplied by a boiler in order to maintain the desired heating setpoint.
The valve is controlled so the SAT does not exceed the Maximum Heating SAT limit. If the fan is off, the valve
opens and closes to maintain the SAT at the configured Fan Off Value.
Single Stage Electric Heat - The control can operate a single stage of electric heat in order to maintain the desired
heating setpoint. The heat stage is controlled so the SAT does not exceed the Maximum Heating SAT limit. The
electric heat output is not energized unless the SAT is < Maximum Heating SAT limit minus 15 °F (8.3 °C) and,
once disabled, cannot be restarted for at least 2 minutes to prevent excessive cycling.
Combination Heating - The control can operate a modulating (0-10 Vdc) type, or 2-position type, NO or NC, water
valve connected to a 2-pipe heating/cooling coil of the unit and also a single stage of electric heat in order to
maintain the desired heating setpoint. The valve is used to meet the heating requirements in the space when the
changeover mode is heat. The electric heater is used when the changeover mode is cool. The heat is controlled so
that the SAT does not exceed the Maximum Heating SAT limit. If the fan is off and the changeover mode is heat,
the valve is controlled to maintain the SAT at the configured Fan Off Value temperature.
Changeover mode detection
The Fan Coil control determines the changeover mode for 2-pipe heating/cooling systems. The controller monitors
a local changeover thermistor sensor or switch, dependent upon configuration. User-configurable temperature
setpoints determine the heat or cool mode. When the sensed temperature exceeds the Changeover Heat Limit,
the system changeover mode is set to heat. When the sensed temperature falls below the Changeover Cool Limit,
the system changeover mode is set to cool. For applications using a switch, the heat mode is determined when
the input is open, while a closed switch indicates cool mode.
Additionally, an Analog Network Input point and a BACnet Analog Value input variable are also provided to allow a
network-supplied analog value of the system water temperature to determine the changeover mode. The Analog
Network Input point has the highest priority, followed by the BACnet AV point, then the local input, if multiple
inputs are supplied simultaneously.
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