Compressor And Vfd Cooling; Vfd Cooling; Figure 8 - Vfd Cooling Path - Danfoss Turbocor VTT Series Service Manual

2.4 Compressor and

VFD Cooling

2.5 VFD Cooling

Figure 8 - VFD Cooling Path

Air Inlet for
Front Channel
Sheet Metal
Gland
Heat Sink Fan
20 of 165
M-SV-VT-001-EN Rev. A
Compressor Fundamentals
Liquid refrigerant, having at least 2⁰C (Kelvin)/ 3.6°F (Rankine) sub-cooling at connection point, must
be piped to both the Compressor cooling inlet connection and the VFD cooling inlet connection.
Refer to the VTT Applications Manual for cooling connections sizes.
To cool the motor, sub-cooled liquid refrigerant enters the Compressor through the EXV and passes
through a groove surrounding the motor Stator. At the groove outlet, the superheated refrigerant gas
is channeled back to the exit port via the motor cavity, thereby cooling the Rotor.
The superheat level of the gas entering the motor cavity is measured using a temperature sensor
inside the end cap and the saturated temperature of the suction gas is measured at the suction
inlet of the Compressor. The expansion valve at the motor cooling inlet modulates to maintain a
pre-determined superheat level based off of this reading.
The VFD is cooled through a combination of air flow and refrigerant cooling of the back plate. Under
most operating conditions, all heat is removed by air flow through the VFD heat sinks. Monitoring
the insulated-gate bipolar transistor (IGBT) temperatures indicate peak power requirements which
activates additional refrigerant cooling when required.
The VFD module is equipped with cooling fans to provide airflow along the heat sink. Units have a
fan mounted in the enclosure door to provide additional airflow to the unit. Each fan has tachometer
feedback to the VFD Control Card to confirm that the fan is operating correctly. On/off and speed
control of the fans is provided to reduce overall acoustical noise and extend the life of the fans. The
fans are activated as needed by VFD module control logic. Figure 8 (VFD Cooling Path) illustrates the
air flow through the VFD.
Air Outlet for
Front Channel
Front Channel
Air Flow
Back Channel