Honeywell T7350 Product Data page 20

T7350 COMMERCIAL PROGRAMMABLE THERMOSTAT
COOL RECOVERY
RAMP RATE
(DEGREES/HOUR)
MaxClRamp
MinClRamp
OaTempMinClRamp
Fig. 13. Setpoint ramping parameters with ramp rate
calculation.
NOTE: The setpoint used during the cool recovery period is
similar to the heat mode in Fig. 11, except the slope
of the line reverses for cooling.
Advantages:
• Comfort setting is achieved at the programmed time and
maintained regardless of weather conditions; occupants
are comfortable.
• Drafts from low-temperature discharge air are minimized
during Occupied periods.
• Use of the more economical first stage of heat is
maximized during recovery, minimizing use of the
expensive later heat stage(s).
• Comfort and energy savings can be achieved in both
heating and cooling.
• Heat cycling reduced, extending equipment life.
Auxiliary Relay
The auxiliary relay can be used with a variety of controls:
• Time-of-day (TOD).
• Economizer minimum position control.
• Dehumidification (see Dehumidification section).
Relay for Time-Of-Day (Table 16)
Time-of-day (TOD) is the Auxiliary Relay default configuration.
TOD logic operates strictly according to programming:
— Occupied: Relay contacts closed.
— Not Occupied: Relay contacts open.
— Standby (Scheduled): Relay contacts closed.
Relay for Economizers
Mechanical cooling is often used with outside temperatures in
the 50°F (10°C) to 60°F (16°C) range and humidity below 50
percent. In central and northern climates, hundreds of hours
63-2605—5
OUTDOOR AIR
TEMPERATURE
OaTempMaxClRamp
M10111A
20
fall into this temperature category. By permitting 80 to 100
percent outside air into the system, mechanical cooling may
not be needed at all, particularly during Spring and Fall.
Economizers take advantage of outside air. The typical
economizer consists of an outside air damper, motor, outdoor
air changeover control and a minimum position potentiometer.
The motor controls the dampers. Suitability of the outside air
for cooling is determined by the outdoor air changeover
control. The potentiometer adjusts the minimum position of
the economizer dampers, which provide a minimum amount
of fresh air for ventilation.
The economizer reduces compressor run time, thereby saving
energy and extending compressor life. The drawback to using
the economizer is that during the Not Occupied period, if there
is no call for cool or outdoor air is not suitable for free cooling,
the economizer is controlled to minimum position. This
position allows some percentage of outdoor air to enter the
building, regardless of air suitability. The situation can cause
the heating or cooling to run more often than when only
suitable air is permitted to enter the building.
The T7350 can take advantage of an economizer by closing
the auxiliary relay contacts to control the economizer
minimum position potentiometer. (See Table 16 for details.)
— Powered: Allows normal economizer operation.
— Unpowered: Disables the economizer minimum position.
The lack of power causes the economizer to drive dampers
fully closed instead of staying at minimum open position.
This reduces the possibility of unsuitable outdoor air
entering the building, which lowers the internal load on the
HVAC system and saves additional energy.
Table 16. Auxiliary Relay Logic (Economizer and TOD).
Occupancy
Scheduled Sensor Signal
—
Occupied
Occupied Standby
Occupied Standby
Standby Standby
— Not Occupied
— Not Occupied
a
Unless otherwise noted, Economizer logic ignores calls for
heat. TOD logic always observes calls for heat.
b
With fan set to AUTO and call for neither heat nor cool, the
relay is open in order to disable damper minimum position.
Other Uses for the Auxiliary Relay
Examples of other uses of the auxiliary relay are hot water
heaters, lighting, or baseboard heat. The additional loads are
connected to the auxiliary relay contacts on the subbase. The
contacts are rated for 1.5A at 30 Vac, but can be adapted to
higher current applications using an external relay.
(See Fig. 14 through 16.)
Auxiliary Contacts
Call for
a
Cool Economizer TOD
—
b
Closed Closed
Yes Closed Open
No Open Open
— Closed
b
Closed
Yes Closed Open
No Open Open