Refrigeration system capacity controller and method

A method for control of a refrigeration system having a compressor rack operable at a plurality of capacities, said method comprising:

• determining a rate of change in suction pressure associated with a first capacity;
• determining a rate of change in suction pressure associated with a second capacity;
• determining a desired rate of change in suction pressure;
• determining a first difference between the desired rate of change and the rate of change associated with the first capacity;
• determining a second difference between the desired rate of change and the rate of change associated with the second capacity;
• comparing the first and second differences;
• and
• selecting a capacity based on said comparing.

A controller comprising:

• a first suction pressure rate of change determination module to determine a first rate of change in suction pressure associated with a first capacity of a compressor rack in a refrigeration system;
• a second suction pressure rate of change determination module to determine a second rate of change in suction pressure associated with a second capacity of the compressor rack;
• and
• a suction pressure rate of change evaluation module in communication with said first suction pressure rate of change determination module and said second suction pressure rate of change determination module to determine which of said first and second capacities will produce the least variation between a measured suction pressure and a desired suction pressure based on said first and second rates of change in suction pressure.

A controller comprising:

• a first suction pressure rate of change determination module to determine a first rate of change in suction pressure associated with a first capacity of a compressor rack in a refrigeration system;
• a second suction pressure rate of change determination module to determine a second rate of change in suction pressure associated with a second capacity of the compressor rack;
• a third suction pressure rate of change determination module to determine a desired rate of change in suction pressure;
• a suction pressure rate of change evaluation module in communication with said first, second, and third suction pressure rate of change determination modules to determine a first difference between said desired rate of change and said first rate of change, a second difference between said desired rate of change and said second rate of change, and to evaluate said first and second differences relative to one another;
• and
• a compressor rack capacity selection module in communication with said suction pressure rate of change evaluation module to select a capacity based on the evaluation of said first and second differences.