Honeywell W7750A specifications Control Application, Control Provided

EXCEL 10 W7750A,B,C CONSTANT VOLUME AHU CONTROLLER

Control Application

W7750 systems in commercial buildings typically incorporate a packaged air handler system that delivers a constant volume of air at preconditioned temperatures to the zone being served. Each zone is usually serviced by a separate AHU; however, sometimes two or more AHUs service the same zone. Note that the W7750 is not designed to control Variable Air Volume (VAV) air handlers or Multi-Zone air handlers, where one air handler simultaneously controls the space temperature in many zones.

OA TEMP

The W7750 can control staged or modulating heating and cooling coils, mixed air economizer dampers, and the system fan. Control of heat pump units, where the compressor(s) is used for both cooling and heating, is also provided. The zone the W7750 services can use a T7770 or T7650 for space temperature sensing and an LONWORKS Bus network access for users. Fig. 2 shows a typical W7750 control application.

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. 2. Typical W7750 control application.

ROOF

CEILING

DISCHARGE

AIR M17488

Control Provided

The W7750 Controller is designed to control a single air handler to maintain the units space temperature at the current setpoint. Heating and cooling control is provided for either staged or modulating equipment. Up to four stages of mechanical cooling and up to four stages of heating are allowed. Modulating outputs can be either floating type such as a Series 60 control, or Pulse Width Modulated (PWM W7750B,C only) control.

The economizer dampers can be controlled directly with floating or PWM outputs, or indirectly using a digital output as an enable/disable signal to a packaged economizer controller. The economizer enable function, which decides when to allow outdoor air to be used for free cooling, can be configured to

one of ten strategies based on the inputs. For more details, see Appendix B— Sequences of Operation. When the economizer position is controlled from the W7750, the minimum position setting (for ventilation requirements) can be adjusted based on indoor air quality (IAQ) needs in the space. IAQ monitoring is provided through either a CO2 sensor or a digital input from a space-mounted IAQ limit switch.

For heat pump configurations, up to four compressors can be controlled, along with up to four stages of auxiliary heat, and a heat/cool change over valve. Including the supply fan, the combination of these items may not exceed eight outputs if a W7750B,C is used, or six outputs for a W7750A. (The eight outputs on the W7750C consist of five digital and three analog outputs.)

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