Bryant 580G Smoke Control Modes, Smoke Detector, Indoor Air Quality Control, Time Guard Circuit

controls up to 2 stages of power exhaust to maintain building pressure. The power exhaust package can be con®gured to deliver positive or negative building pressure. These power exhaust stages are staged according to a percentage of the economizer dampers position. Default values are 25% for Stage 1 and 75% for Stage 2.

D. Smoke Control Modes

The 580G,H units with an optional expansion board perform ®re and smoke control modes. The expansion board provides 4 modes which can be used to control smoke within the con- ditioned area. The modes of operation are ®re shutdown, pres- surization, evacuation, and smoke purge. See Table 7.

E. Smoke Detector

A smoke detector can be used to initiate ®re shutdown. This can be accomplished by a set of normally closed pilot relay contacts which will interrupt power from the 24-v trans- former, secondary ``B'' terminal to the control circuit breaker (CB4). See Fig. 33. The wire that connects these two points is white and labeled ``W78.''

NOTE: On standard gas models, the indoor fan will continue to run 45 seconds after the call for heat has been terminated. If ®re shutdown is initiated the fan will stop immediately. No 45-second delay will occur.

The smoke detector may be mounted in the return air duct or the supply duct.

F. Indoor Air Quality Control

The accessory expansion board and accessory IAQ sensor are required for IAQ control. The IAQ sensors operate with a 4 to 20 mA signal. The 4 to 20 mA signal is connected to T11 (+) and T12 (−) on the expansion board for the IAQ sen- sor, and T13 (+) and T14 (−) on the expansion board for the OAQ (Outdoor Air Quality) sensor. The sensor is ®eld- mounted and wired to the expansion board installed in the unit main control box. The IAQ sensor must be powered by a ®eld-supplied 24-v power supply (ungrounded). Do not use the unit 24-v power supply to power the sensor.

Once installed, the sensor must be enabled. The sensor is con- ®gured with default values which may be changed through network access software. To work properly, the IAQ sensor high and low reference points for the sensor that is used must match the con®gured values. The expansion board reacts to a 4 to 20 mA signal from the IAQ sensor. The low reference (4 mA output) must be con®gured to the minimum IAQ sensor reading. The high reference (20 mA output) must be con®gured to the maximum IAQ sensor reading.

The IAQ sensor can be con®gured to either low or high pri- ority. The priority value can be changed by the user. The default is low.

Low Priority

When the priority is set to low, the initial control is to the IAQ set point, but the outside air damper position will change to its minimum position when the space temperature is greater than the occupied cooling set point plus 2° F or when the space temperature is less than the occupied heating set point minus 2° F. The damper will also change to minimum posi- tion when the outdoor air quality is greater than the outdoor air quality set point (ppm).

High Priority

When the priority is set to high, the IAQ set point controls the outside air damper exclusively, with no regard to comfort conditioning.

G. Time Guard Circuit

The Time Guard function (built into the rooftop control board) maintains a minimum off time of 5 minutes, a minimum on time of 10 seconds, and a 10-second delay between compres- sor starts.

H. Crankcase Heater

Unit main power supply must remain on to provide crank- case heater operation. The crankcase heater in each compres- sor keeps oil free of refrigerant while compressor is off.

Table 7 Ð Smoke Control Modes

DEVICE	PRESSURIZATION	SMOKE PURGE	EVACUATION	FIRE SHUTDOWN
Economizer	100%	100%	100%	0%
Indoor Fan	ON	ON	OFF	OFF
Power Exhaust (all outputs)	OFF	ON	ON	OFF
Heat Stages	OFF	OFF	OFF	OFF

Fig. 33 Ð Field-Supplied Smoke Detector Wiring

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