Honeywell W7750A specifications Temperature Control Operations, Dirty Filter Monitor

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 issued when the filter media needs replacement. The two methods of monitoring the filter are:

1.A differential pressure switch whose contacts are con- nected to a digital input on the W7750A or W7750B,C; and

2.A 2-to-10V differential pressure sensor wired to a current 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.

START-UP

START_UP_WAIT is the first mode after application restart or power-up.During START_UP_WAIT, the analog and digital inputs are being read for the first time, no control algorithms are active, and the physical outputs (fan and heat/cooling stages) are in the de-energized position. The node remains in

OA TEMP

the START_UP_WAIT mode for a pseudo-random period (depending on neuron_id) between 12 and 22 seconds and then transitions to one of the operating modes, depending on the inputs that are read from the physical and network inputs. The pseudo random period prevents multiple controllers from simultaneously starting major electrical loads when power is restored to a building.

NOTES: After a controller download via Care/E-Vision, the delayed reset time is bypassed and the controller starts after a 40-second initialization.

Not all network inputs can be received during the START_UP_WAIT period because many network variables are updated at a slower rate; therefore some control decisions can be considered tempo- rarily inappropriate.

Temperature Control Operations

See Fig. 49 for a diagram of a typical W7750 Unit.

OUTDOOR AIR

	COOL	HEAT
FILTER	COIL	COIL
	FAN
	-	+
M

EXCEL 10

W7750

CVAHU

DA TEMP

RA TEMP

OCCUPANCY

SENSOR

RETURN	T7770 OR T7560A,B
AIR
	WINDOW CONTACT

Fig. 49. Schematic diagram for a typical W7750B Unit.

ROOF

CEILING

DISCHARGE

AIR M17488

59 74-2958— 1