Hot gas bypass control for centrifugal chillers

A method for automatically calibrating a surge control of a refrigeration system including a centrifugal compressor having pre-rotational vanes, a condenser, an evaporator, and a hot gas bypass line between the compressor and the evaporator, said method comprising the steps of:

• sensing a surge condition when the refrigeration system is operating under surge conditions;
• and
• sensing a head parameter representative of the head of the compressor;
• sensing a load parameter representative of a load;
• and
• storing the head parameter and the load parameter when the surge condition is sensed as control data to be used by the control of the refrigeration system.

The method of 20, further comprising:

• sensing a present head parameter representative of the present head of the compressor;
• sensing a present load parameter representative of the load;
• and
• controlling the hot gas bypass valve so as to avoid surging in the compressor in response to the present head parameter, the present load parameter, and the stored head and load parameters.

A method for controlling a hot gas bypass valve in a refrigeration system including a centrifugal compressor having pre-rotational vanes, a condenser, an evaporator, and a hot bas bypass line between the compressor and the evaporator, said method comprising:

• sensing a present head parameter representative of the present head of the compressor;
• sensing a present load parameter representative of the load;
• and
• controlling the hot gas bypass valve so as to avoid surging in the compressor in response to the present head parameter, the present load parameter, and stored head and load parameters.

An apparatus for controlling a hot gas bypass valve in a refrigeration system including a centrifugal compressor having pre-rotational vanes, a condenser, an evaporator, and a hot gas bypass line between the compressor and the evaporator, said apparatus comprising:

• means for continuously sensing for a surge condition during operation of the refrigeration system;
• means for indicating a surge condition when the refrigeration system is operating under surge conditions;
• and
• means for opening at least partially the hot gas bypass valve in response to the sensed surge condition to return the refrigeration system to operating under non-surge conditions.