48/50PD
(Configuration→CCN→SCH.O→OV.SP) is set to YES. The length of the override period is determined by the
Timed Override Hours setting (Configuration→CCN→SCH.O→OV>EX).
Compressor Operation
The 48/50 PD units use a Copeland Digital Scroll Compressor that can vary the refrigerant capacity between 100 and 15%. This is accomplished by a mechanism in the compressor that separates the two scroll spirals which stops the pumping of the refrigerant gas. This mechanism is operated by the differential pressure between the suction and discharge of the compressor. The pressure to operate the unloading mechanism is controlled by a small solenoid situated in a refrigerant line between the top of the compressor and the suction line. When the solenoid is energized the compressor is unloaded. The solenoid coil is controlled by the Copeland Digital Scroll Controller (DSC) that operates on a 1 to 5V signal from the ComfortLink Auxiliary Board (AUX1) and converts this into a Pulse Width Modulated (PWM) signal to the solenoid valve. The pulse width modulated signal is an on and off signal that repeats every 15 seconds with the off time portion of the 15 seconds representing the % loading of the compressor.
The Compressor Capacity (Outputs→COOL→CAPC) can be monitored on the ComfortLink Scrolling Marquee Display. The Compressor Capacity value is determined by a Proportional, Integral, Derivative (PID) algorithm that controls the Supply Air Temperature (Temperatures→AIR.T→SAT) to the Supply Air Control Point (Run Status→COOL→SA.CP).
The Compressor Minimum Capacity (Configuration→COOL→MIN.C) is configured at the factory to 70%. This is the minimum compressor capacity that gives the highest SEER rating for a 48 series unit with the highest gas heat option and no economizer per AHRI standard 210/240. Since the AHRI rating standard does not account for energy savings that can be realized by displacement ventilation air distribution system and extending economizer cooling operation at higher supply air temperature set points, a complete energy analysis should be conducted before changing the Compressor Minimum Capacity (Configuration→COOL→MIN.C) setting to determine the energy savings at a lower Compressor Minimum Capacity (Configuration→COOL→MIN.C) setting.
Indoor Fan Operation
The indoor fan is controlled by the Indoor Fan VFD Power Relay (Outputs→FANS→IDF) on the MBB (main base board) control, which then operates the indoor fan contactor (IFC). On the 48/50PD units the Indoor Fan VFD Power Relay (Outputs→FANS→IDF) is always on so that power is supplied to the VFD electronic boards. This prevents the formation of condensation on the VFD electronic boards and provides power to the remote VFD display so that error codes and VFD configuration parameters can be verified.
The 48/50PD unit controls require an accurate supply duct CFM at the unit design point where the indoor fan will run at the Supply Fan Maximum Speed (Configuration→UNIT→FS.MX). The Supply Fan Maximum Speed (Configuration→UNIT→FS.MX) is used for operation of the economizer and power exhaust. The supply duct CFM is configured by the Indoor Fan Max Speed CFM (Configuration→ECON→IDF.C). Default values for Indoor Fan Max Speed CFM (Configuration→ECON→IDF.C) are at 400 CFM per ton or 1600 CFM for the 05 size and 2000 CFM for the 06 size. It is preferred to use the supply duct CFM from an air balance report to configure the Indoor Fan Max Speed CFM (Configuration→ECON→IDF.C). If an air balance report is not available then use the fan tables supplied in this book to
determine Fan Max Speed CFM (Configuration→ECON→IDF.C). When using the fan tables to
determine Fan Max Speed CFM (Configuration→ECON→IDF.C) set Economizer Position Test
(Service Test→INDP→ECON) to 0 (Economizer Damper Closed) and Indoor Fan Speed Test (Service Tes→FANS→F.SPD) equal to (Configuration→UNIT→FS.MX). Measure the supply to return duct static pressure difference and indoor fan RPM. Make correction to static pressure for all options installed in the unit per the accessory pressure drop table. Determine Indoor Fan Max Speed CFM (Configuration→ECON→IDF.C) on the fan table where the corrected static pressure and RPM cross.
The supply fan speed range is configured by the Supply Fan Maximum Speed (Configuration→UNIT→FS.MX) and the Supply Fan Minimum Speed (Configuration→UNIT→FS.MN). These configuration values are in units of % speed referenced to a 2 to 10VDC signal to the VFD AI1 input with 2VDC representing 0% speed and 10VDC representing 100% speed or 0 to 60HZ VFD frequency output to the motor.
The Supply Fan Minimum Speed (Configuration→UNIT→FS.MN) can be user configured between 10 and 70%. The Supply Fan Minimum Speed default value is 70%, this provides the greatest energy efficiency rating for a unit without an economizer in a mixed air type duct application.
The Supply Fan Maximum Speed (Configuration→UNIT→FS.MX) can be configured between 80 and 100%. The Supply Fan Maximum Speed default value is 100%. Set the indoor fan pulley to the application design point CFM for heating and cooling at 100% fan speed so that the CFM is not lower than the minimum CFM allowed in the product data. If the exact CFM can not be set by the half turn pulley settings then
adjust the Supply Fan Maximum Speed (Configuration→UNIT→FS.MX) to fine tune the CFM to the application requirements. The Supply Fan Maximum Speed (Configuration→UNIT→FS.MX) RPM must now produce supply CFM that is not lower that the minimum CFM allowed in the product data for heating and cooling.
The indoor fan may operate during cooling with compressors mode, free cooling with outdoor air mode, heating mode, or for ventilation with outdoor air mode.
The indoor fan operation can be affected by the following:
SFan On When Occupied (Configuration→UNIT→OC.FN) S IAQ Analog Fan Config (Configuration→AIR.Q→IA.FN) S IAQ Switch Fan Config (Configuration→AIR.Q→II.FN) S Fan Status Switch (Configuration→UNIT→FN.SW)
When the unit is in occupied or unoccupied cooling mode the supply fan will modulate to maintain the space temperature sensor set point between the configured Supply Fan Maximum Speed (Configuration→UNIT→FS.MX) and the Supply Fan Minimum Speed (Configuration→UNIT→FS.MN).
When the 40PD or 50 PD unit is in occupied or unoccupied heating mode (gas heat or electric heat mode) the indoor fan will operate at the Supply Fan Maximum Speed (Configuration→UNIT→FS.MX) setting.
For 48PD gas heating units, the IGC control fan output is also monitored by the MBB control. This can result in additional modifications of fan delays or other operation due to safety functions of the IGC control.
When the PD unit is in free cooling mode the indoor fan will modulate to maintain The Occupied Cool Set Point (Setpoints→OCSP), the Unoccupied Cool Set Point
(Setpoints→UCSP), Occupied Heat Set Point (Setpoints→OHSP), or the Unoccupied Heat Set Point
(Setpoints→UHSP).
When the PD unit is in ventilation mode and Fan On When Occupied (Configuration→UNIT→OC.FN) the indoor fan will
operate at the Vent Mode Fan Speed (Configuration→UNIT→FS.VM). Vent Mode Fan Speed
(Configuration→UNIT→FS.VM) factory default is 50% and can be user configured between 40 and 100%.
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