Honeywell TB6575B1000/U Installation Instructions - Page 15

TB6575/TB8575 DIGITAL FAN COIL THERMOSTATS Fig. 26 illustrates the relationship between setpoints, Remote Setback, and deadband for auto changeover with heat and cool setpoints. UNOCCUPIED DEADBAND REMOTE SETBACK COOL SETPOINT COOL SETPOINT DEADBAND UNOCCUPIED DEADBAND HEAT SETPOINT REMOTE SETBACK HEAT SETPOINT M27562 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. REMOTE SETBACK COOL SETPOINT UNOCCUPIED DEADBAND COOL SWITCHING POINT SETPOINT UNOCCUPIED DEADBAND HEAT SWITCHING POINT REMOTE SETBACK HEAT SETPOINT M31331 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 +4°F DIFFERENCE BETWEEN +2°F RT AND SETPOINT -2°F -4°F FAN SPEED IS HIGH FAN SPEED IS MEDIUM FAN SPEED IS LOW FAN SPEED IS LOW FAN SPEED IS MEDIUM FAN SPEED IS HIGH COOL SETPOINT HEAT M27563 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 Pipe Temperature after purge System Mode >Threshold for Heating (ISU code #7) Heat Between Thresholds After Purge Occurs Fan Only* < Threshold for Cooling (ISU code #6) Cool *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". 15 62-0311-05