Honeywell W7750A Modes of Operation, Dirty Filter Monitor, Indoor Air Quality IAQ Override

EXCEL 10 W7750A,B,C CONSTANT VOLUME AHU CONTROLLER

Dirty Filter Monitor

The air filter in the air handler can be monitored by the W7750 and an alarm is issued when the filter media needs replacement. The two methods of monitoring the filter are:

1.Connecting a differential pressure switch to a digital input on the W7750A or W7750B,C.

2.Wiring a 2 to 10V differential pressure sensor to a voltage input on the W7750B,C. If the analog input sensor is used, its measured value 0 to 5 inw (0 to 1.25 kPa) is compared to a user-selectable setpoint (FltrPressStPt— valid range: 0 to 5 inw (0 to 1.25 kPa)), and the Dirty Filter alarm is issued when the pressure drop across the filter exceeds the setpoint.

Indoor Air Quality (IAQ) Override

The Excel 10 W7750 Controller provides IAQ ventilation control using one of two different methods of detecting poor air quality. The first is with an IAQ switch device connected to a digital input on the W7750 Controller, where a contact closure indicates poor air quality, and initiates the IAQ Override mode. The device can detect poor air quality using any desired measure such as CO2, VOC, CO, etc. The second method, which is only available on the W7750B,C, is through an analog input that connects to a CO2 sensor (2 to 10V). The measured value of CO2 from this sensor (0 to 2000 PPM) is compared to the setpoint (IAQSetpt). When the CO2 level is higher than the setpoint (800 PPM adjustable), the

IAQ Override is initiated. The IAQSetpt hysteresis is 50 PPM, IAQ Override is deactivated at a CO2 level less than 50 PPM below setpoint.

The effect of initiating the IAQ Override mode is that the economizer dampers are allowed to open above the standard minimum position setting to allow more fresh air to enter the building. See Appendix B— Sequences of Operation, for further control details.

Smoke Control

The Excel 10 W7750 Controller supports smoke-related control strategies that are initiated either via a network command (DestEmergCmd) or from a local (physically connected) smoke detector digital input. The details of the W7750 smoke-related control operation are described in Appendix B— Sequences of Operation.

Freeze Stat

A freeze stat can be monitored by the W7750 and issue a freeze stat alarm indicating the CVAHU is in danger of freezing its coil. The details of the W7750 freeze stat related control operation are described in Appendix B— Sequences of Operation.

Modes of Operation

The possible modes of operation for the W7750 Controller are listed in Table 5.

Table 5. Modes Of Operation For The Excel 10 W7750 Controller .

Mode	Description	Events causing a controller to switch to this mode
Effective Occupancy (User Address: StatusOcc)
OCCUPIED	Controller is in Occupied mode	Any of the following: Network input (DestSchedOcc) containing a
		time-of-day schedule flag from either the Excel 10 Zone Manager or an
		LONWORKS Bus Controller; Time Clock DI, Occupancy Sensor DI; or
		from Network input (DestManMode) for manual override to OCC mode.
		DestManMode has the highest priority, followed by the Time Clock DI,
		and then DestSchedOcc.
STANDBY	Controller is in Standby mode	Either: (A) Network input (DestSchedOcc) containing a time-of-day
		schedule flag from the Excel 10 Zone Manager or other LONWORKS
		Bus node is STANDBY, or (B) Network input (DestSchedOcc) is
		OCCUPIED and the Occupancy Sensor DI is UNOCCUPIED.
UNOCCUPIED	Controller is in Unoccupied mode	Network input (DestSchedOcc) containing a time-of-day schedule flag
		from the Excel 10 Zone Manager or LONWORKS Bus, or the network
		input DestManOcc has a value of UNOCCUPIED.
BYPASS	Controller is in Occupied mode through	This mode is derived from the schedule occupancy (DestSchedOcc)
OCCUPIED	a Bypass command	having a state of UNOCCUPIED and a manual request for occupancy
		from one of three sources. Two of these are signals originated external
		to the unit, and received by DestManOcc and DestBypass. The third
		source for an occupancy request is from an override button located on
		a wall module. These three sources are arbitrated in a scheme
		determined by the configuration parameter (Network Wins or Last-in
		Wins from OvrdPriority).
Override Modes (User Address: StatusOvrd)
OCCUPIED	Controller occupancy mode was	Network input (DestManOcc) containing a time-of-day schedule
	overridden to Occupied mode	override signal of OCCUPIED from the Excel 10 Zone Manager or
		other LONWORKS Bus device.
STANDBY	Controller occupancy mode was	Network input (DestManOcc) containing a time-of-day schedule
	overridden to Standby mode	override signal of STANDBY from the Excel 10 Zone Manager or other
		LONWORKS Bus device.

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