Compressor Capacity Control Water Chillers trane

Compressor Capacity Control

Water Chillers trane

Compressor Capacity Control chille trane

Compressor Capacity Control:

 The capacity of the helical-rotary compressor presented in this clinic is controlled by a slide valve that is an integral part of the compressor housing.
Other helical-rotary compressor designs may use a variety of methods to vary capacity. Some of these methods are similar in function to the slide valve presented in this period. One major difference is whether the compressor is designed to unload in steps, like a reciprocating compressor, or if it has variable unloading.

slide valve  :

slide valve 

The position of the slide valve along the rotors controls the volume of refrigerant vapor being delivered by the compressor, by varying the amount of rotor length actually being used for compression.
Note that the compressor discharge has 2 components. First, a port within the slide valve provides a radial discharge path. Second, a port within the end- plate of the compressor housing provides an axial discharge path.

slide valve position  Full Load:

slide valve position  Full Load

At full load, the slide valve is closed. The compressor pumps its maximum volume of refrigerant, discharging it through both the radial and axial ports.

slide valve position  Part Load

slide valve position  Part Load

At part load, the slide valve modulates toward the open position. The opening created by the valve movement allows refrigerant vapor to bypass from the rotor pockets back to the suction side of the compressor. This reduces the volume of vapor available for the compression process. It also reduces the amount of rotor length available for compression. In this manner, the volume of refrigerant that is pumped by the compressor is varied, unloading it to balance the existing chiller load.

compressor capacity control Unloading:

compressor capacity control Unloading

As the slide valve continues to open, further unloading the compressor, its radial discharge port eventually travels past the opening in the compressor housing. Once this occurs, all of the refrigerant vapor being pumped by the compressor is discharged through the axial port in the compressor’s end-plate.
The compressor discharge ports and slide valve are designed to allow the compressor to operate efficiently over a wide range of conditions.

Slide Valve Operation:

Slide Valve Operation

The slide valve is operated by a piston and cylinder assembly. Extension and retraction of the operator shaft positions the slide valve along the compressor rotors.
High-pressure refrigerant vapor, controlled by 2 solenoid valves, is fed to or bled from this assembly in order to position the valve. To close the slide valve and load the compressor, the load valve is opened and the unload valve is closed. This allows high-pressure refrigerant vapor to enter the cylinder from the discharge of the compressor, extending the operator shaft and moving the slide valve so that it covers more of the rotor length.
Conversely, to open the slide valve and unload the compressor, the load valve is closed and the unload valve is opened. This allows the high-pressure refrigerant vapor to bleed out of the cylinder into the low-pressure area within the compressor housing. A spring helps return the piston, retracting the operator shaft and moving the slide valve such that the rotors are more uncovered. This reduces the effective length of the rotors, which are compressing vapor.
On shutdown the unload solenoid valve is energized and the spring drives the slide valve to the fully-unloaded position. This ensures that the compressor always starts fully unloaded.
When both solenoid valves are closed, the operator shaft holds the slide valve at its current position.

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