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TB6575/TB8575 DIGITAL FAN COIL THERMOSTATS

62-0311—05

Fig. 26 illustrates the relationship between setpoints,
Remote Setback, and deadband for auto changeover with
heat and cool setpoints.

Fig. 26. Auto Changeover with Heat/Cool Setpoints

deadband illustration.

For 4 pipe applications with Auto Changeover and a
single setpoint, when Economy Setback is enabled, the
setpoint will revert to a dual heat/cool setpoint approach.
The remote setback heating and remote setback cooling
setpoints will be used to create an effective unoccupied
deadband.

Fig. 27 illustrates the unoccupied deadband when
Economy Setback is enabled for 4-pipe single setpoint
auto changeover.

Fig. 27. 4 Pipe Auto Changeover with Single Setpoint

and Economy Setback Deadband Illustration

Fan Modes

VERSASPEED™ FAN RAMPING

When the fan switch is in auto, the thermostat will cycle
the fan using the fan ramping algorithm. The appropriate
fan speed is selected according to Fig. 28.

The fan ramping algorithm is illustrated in Fig. 28

Fig. 28. VersaSpeed™ fan ramping algorithm

illustration.

AUTO FAN RESET (ISU CODE #24)

If Auto Fan Reset is enabled, and a constant fan speed is
selected, the thermostat resets the fan to Auto.
• Value = 1: The fan resets back to Auto after 2 hours.
• Value = 2: The fan resets back to Auto after 4 hours.
The start time is calculated after the initial call for Heat/
Cool is satisfied. Then, the two or four hour timing begins.
The fan is set back to Auto when the 2-hour or 4-hour
delay expires.

Application Modes

2 PIPE SEASONAL CHANGEOVER APPLICATIONS

These applications require the pipe sensor as a N.O,
N.C., or Analog Input to detect seasonal changeover:

• 2 pipes with auto changeover
• 2 pipes with auxiliary heat
Changeover occurs when the system has been changed
over from the boiler to the chiller. This occurs on a
seasonal basis from winter to summer months. When
using a pipe sensor as an analog input, the thermostat
can use the logic below to determine what mode to
operate in. A changeover will occur when the pipe
temperature goes above the threshold for heating or
below the threshold for cooling. If a purge has not
occurred or a call has not been satisfied in awhile, the
pipe temperature may start to get close to the ambient
temperature. In this case, the thermostat will only
changeover once the temperature falls into the opposite
threshold.

2 Pipes with Auto Changeover

For this application the system switch only provides “Off”
and "Auto". When in "Auto" mode the water temperature
will indicate if the thermostat should operate in heating or
cooling.

Operation:

After exiting the installer setup, the thermostat will perform
a 5 minute purge. During this initial 5 minute purge, the
valve (W/Y) will energize and the fan will be de-energized.
After the 5 minute purge, the thermostat will go into the
appropriate mode as described in Table 6.

Table 6. Logic for 2 Pipes with Auto Changeover

*If pipe temperature is between the two threshold values
after the 5 minute purge occurs, the thermostat will
activate a second 5 minute purge to double check the
water temperature. If after the second 5 minute purge, the
water temperature is still between the two thresholds, the
valve output will be disabled and only manual fan will be
available. It will stay in this operation until the next purge
cycle occurs.

2 Pipes with Auxiliary Heat

For this application, when there is hot water in the pipes,
the system switch provides "Off" and "Heat". When there
is cold water in the pipes, the system switch provides
"Off", "Heat", and "Cool".

UNOCCUPIED DEADBAND

DEADBAND

REMOTE SETBACK COOL SETPOINT

UNOCCUPIED DEADBAND

COOL SETPOINT

HEAT SETPOINT

REMOTE SETBACK HEAT SETPOINT

M27562

M31331

HEAT SWITCHING POINT

REMOTE SETBACK HEAT SETPOINT

REMOTE SETBACK COOL SETPOINT