Honeywell TB6575B1000/U Installation Instructions - Page 16

TB6575/TB8575 DIGITAL FAN COIL THERMOSTATS 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 deenergized. 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 Cool Mode > Threshold Valve (W/Y) Changeover. for Heating energized on calls Mode changes to (ISU code #7) for heat Heat. Between Thresholds After Purge Occurs Aux Heat (Y/A) energized on calls for heat Changeover. Mode changes to Heat because Cool is not available. < Threshold Mode stays in Heat Valve (W/Y) for Cooling but Aux Heat (Y/A) energized on calls (ISU code #6) energized on calls for cool for heat 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 ISU code #10. SWITCHING DIFFERENTIAL COOL SWITCHING POINT SETPOINT 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. A 5 minute purge will occur every 2 hours 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, and if the power is reset. NOTE: For the 2 Pipe with Auxiliary Heat application, the thermostat must be in the "Off" position for more than 30 minutes before a 5 minute purge will occur when it is switched back into "Heat" or "Cool". HEAT SWITCHING POINT M31330 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 ISU code #10. COOLING SETPOINT DEADBAND HEATING SETPOINT M27565 Fig. 30. 4 Pipe Auto Changeover setpoints and deadband. 62-0311-05 16