Honeywell W7750A Window Sensor StatusWndw, Smoke Control, FAN Operation, Demand Limit Control DLC

EXCEL 10 W7750A,B,C CONSTANT VOLUME AHU CONTROLLER

OCC setpoint

UN_OCC setpoint

OR

STANDBY setpoint

HEAT PUMP

SETPOINT

(FOR COMPRESSORS)

AUX HEAT

SETPOINT

RECOVERY TIME

OCCUPIED TIME

Standby or Unoccupied modes, the fan cycles on with a call for cooling (or heating if the FanOnHtMode parameter is set). In Intermittent Fan mode, the fan cycles on with a call for cooling (or heating if the FanOnHtMode parameter is set), and cycles off when the space temperature control is satisfied.

The fan control supports an optional (Proof of Air Flow) digital input, that allows monitoring of the supply fans status. If the fan is commanded on, the Proof of Air Flow digital input is checked up to three times to verify that the fan is running after an initial delay of FanOnDelay seconds (user-settable). If the fan fails to start the CVAHU must be reset by first cycling CVAHU power. If this does not work, set DestManMode to Manual and then back to Enable. After a reset the application restarts— all outputs switch off and auto control is enabled.

M10110

Fig. 47. Setpoint ramping parameters with setpoint

calculation.

During the COOL recovery period, the setpoint changes at a rate in degrees per hour relative to the outdoor air temperature. If there is no outdoor air temperature sensor available, the MinClRamp is used as the recovery rate.

See Fig. 48 for the various setpoints.

COOL RECOVERY
RAMP RATE
(DEGREES/HOUR)
MaxClRam
MinClRam
	OUTDOOR AIR
	TEMPERATURE
OaTempMinClRa	OaTempMaxClRam
	M10111

Also, the W7750 Controller provides fan-run-on operation that keeps the fan running for a short time after heating or cooling shuts off. The amount of time that the fan continues to run is set in FanRunOnHeat for heating mode and FanRunOnCool for cooling mode.

WINDOW SENSOR (StatusWndw)

The digital input for a window contact provides the algorithm with a means to disable its temperature control activities if someone has opened a window or door in the room. When a window is detected to be Open (digital input contacts Open equals window open), the normal temperature control is disabled, and the W7750 Controller enters the Freeze Protect mode. Freeze Protect mode sets the space setpoint to 46.4 °F (8°C) and brings on the fan and heat if the space temperature falls below this setpoint. Normal temperature control resumes on window closure. The Window sensor signal can also be a network input from another LONWORKS Bus device, so that no physical sensor is required at the receiving W7750 Controller.

SMOKE CONTROL

The Excel 10 W7750 Controller supports three smoke-related control strategies:

1.Emergency Shutdown (all outputs off).

2.Depressurize (fan on, outdoor air damper closed).

3.Pressurize (fan on, outdoor air damper open).

Fig. 48. Setpoint ramping parameters with ramp rate

calculation.

NOTES: The setpoint used during the COOL recovery period is similar to the heat mode in Fig. 46, except the slope of the line reverses for cooling.

Recovery ramping applies between scheduled heat- ing or cooling setpoint changes from UNOCCUPIED to STANDBY, UNOCCUPIED to OCCUPIED, and STANDBY to OCCUPIED. Scheduled setpoint changes from OCCUPIED to UNOCCUPIED or OCCUPIED to STANDBY do not use a ramped set- point, but instead, use a step change in setpoint. Recovery ramps begin before the next scheduled occupancy time and are ramped from the setpoint for the existing scheduled occupancy state to the set- point for the next occupancy state.

FAN OPERATION

The W7750 supply fan can be controlled in one of two different ways. In Continuous Fan mode, the fan runs whenever the controller is in Occupied mode. When in

The controller is placed in one of these three control states whenever the W7750 mode becomes SMOKE_EMERGENCY, which can be initiated via a network command (DestEmergCmd) or from a local (physically connected) smoke detector digital input. When in SMOKE_EMERGENCY mode, the W7750 Controller uses the control strategy found in SmkCtlMode (one of the three listed above), and the normal temperature control function is disabled. If a W7750 local smoke detector trips, the SrcEmerg network variable (for other LONWORKS Bus devices to receive) is set to the Emergency state.

DEMAND LIMIT CONTROL (DLC)

When The LONWORKS Bus network receives a high-electrical- demand signal, the controller applies a DlcBumpTemp amount to the current actual space temperature setpoint value. The setpoint is always adjusted in the energy-saving direction. This means that if the W7750 Controller is in Cooling mode, the DLC offset bumps the control point up, and when in Heating mode, bumps the control point down.

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