Honeywell SuitePRO TB8575 Installation Instructions Manual page 17

Table 6. Logic for 2 Pipes with Auto Changeover
Pipe Temperature after purge
>Threshold for Heating (IS code #7)
Between Thresholds
After Purge Occurs
< Threshold for Cooling
*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".
Operation:
After exiting the installer setup, the thermostat will perform
a 5 minute purge. During this time, the valve (W/Y) will
energize and the fan and auxiliary heat (Y/A) will be de-
energized. After the 5 minute purge, the thermostat will go
into the appropriate mode as described by Table 7.
Table 7. Logic for 2 Pipes with Auxiliary Heat
Pipe
Temperature
After Purge Heat Mode
> Threshold Valve (W/Y)
for Heating energized on calls
(IS code #7) for heat
Between Aux Heat (Y/A)
Thresholds energized on calls
After Purge for heat
Occurs
< Threshold Mode stays in Heat
for Cooling but Aux Heat (Y/A)
(IS code #6) energized on calls
for heat
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 auxiliary heat will be
available for heating.
Auxiliary heat (Y/A) always de-energizes during purges.
Purge Cycles for 2 Pipe Seasonal Changeover
Applications
For 2 Pipe with Auto Changeover and 2 Pipe with
Auxiliary Heat applications, the thermostat will run purge
cycles to determine if there is hot or cold water in the
pipes.
For the 2 Pipe with Auxiliary Heat application, the thermostat must be in the
1
before a 5 minute purge will occur when it is switched back into "Heat" or "Cool".
TB6575/TB8575 SUITEPRO™ DIGITAL FAN COIL THERMOSTATS
System Mode
Heat
Fan Only*
(IS code #6) Cool
Cool Mode
Changeover.
Mode changes to
Heat.
Changeover. Mode
changes to Heat
because Cool is not
available.
Valve (W/Y)
energized on calls
for cool
A 5 minute purge will occur every 2 or 24 hours (IS 25) to
ensure that the pipe sensor is sensing the correct mode
during seasonal changeover months.
A 5 minute purge will also occur anytime the installer
setup or installer test menus are exited, whenever the
thermostat is switched from its "Off" position
power is reset.
4 PIPES AUTO CHANGEOVER
Single Set Point Method
In 4 pipe auto changeover with a single setpoint, the
temperature is always controlled to the setpoint. Switching
points are used to determine when to switch between
heating and cooling modes. If the current mode is heat
and the temperature drifts above the cool switch point
(Setpoint + Switching Differential), the thermostat will
switch to heat operation and will heat the space until
setpoint is reached.
For this application, the setpoint setting and switching
points are illustrated in Fig. 29. The switching differential
is defined via IS code #10.
SWITCHING
DIFFERENTIAL
Fig. 29. 4 Pipe Auto Changeover with Single Setpoint
and Switching Points
Heat/Cool Setpoint Method
In 4 pipe auto changeover with heat and cool setpoints,
the system key is used to switch between the heating
setpoint and cooling setpoints. Use the Up and Down
arrow buttons to change the setpoint.
For this application, the setpoint settings and deadband
are illustrated in Fig. 30. The deadband is changed via IS
code #10.
DEADBAND
Fig. 30. 4 Pipe Auto Changeover setpoints and
Off
" "
17
1
COOL SWITCHING POINT
SETPOINT
HEAT SWITCHING POINT
COOLING SETPOINT
HEATING SETPOINT
M27565
deadband.
position for more than 30 minutes
, and if the
M31330
62-0278—13