51
modulated by rapidly switching a normally closed (N.C.) unloader
solenoid on and off. When the solenoid is energized, i.e., open, the
compressor is unloaded. When the solenoid valve is not energized,
the compressor is loaded. Varying the length of time the solenoid
is energized provides a modulating effect and determines the aver-
age capacity of the compressor. Units equipped with the digital
compressor will incorporate a digital compressor controller. The
digital compressor controller provides the interface between the
62X controller and the digital compressor. The device provides
control, protection and diagnostics. The control can detect faults
and provides 3 levels of protection: reduced capacity, trip, and
lockout.
Inverter Driven Compressor
62X units, 20 tons and larger, will have a standard lead circuit in-
verter driven compressor. The lag circuit will have a standard
scroll with hot gas bypass. Inverter driven compressors shall be
capable of modulating from 58-100% of nominal compressor ca-
pacity. All circuits with inverter compressors shall be equipped
with a minimum load control valve.
Condenser Fan Motors and
Head Pressure Control
The 62X unit may be equipped with head pressure (discharge
pressure) control.
ā¢ Vari-Speed - Variable Speed condenser fan control
All sizes use three-phase condenser fan motors (OFM). With the
variable-speed head pressure control and the condenser fan VFD,
speed will be controlled by a discharge pressure transducer (0 to
500 psig, 2 to 10 VDC pressure transducer). The motor speed is
controlled by a VFD. Condenser fan is off if discharge pressure is
less than 310 psig. The condenser fan motor is at full speed if dis-
charge pressure is greater than 410 psig. See Table 22 for condens-
er fan head pressure control parameters.
Table 22 ā Condenser Fan Head Pressure Control
Parameters
Fig. 81 ā Condenser Head Pressure Control using an AC Tech VFD w Pressure Transducer
ID Value Description
P-04 30 s t-dec
P-05 1: Coast to Stop Stop Mode
P-08
Set Per Serial Tag if a Single
Motor is Wired to the VFD
Motor Nom Current
P-12
5: PI-Controller, external
feedback
Local Process Data
Source
P-14 101 Password
P-15 0 DI Config Select
P-20 60 Hz f-Fix1
P-30 3: Auto-2 Start Mode
P-43 1: Inverse Operation PI1 Mode
P-45 50.6% PI1 Set Point Digital
P-46 5: max value of AI1 and AI2 PI1 Feedback 1 Source
To Next Page
Loading...
