Method and apparatus for sequencing multistage systems of known relative capacities

A method for automatically ordering a plurality of stages in a multistage control system to provide contiguous capacity control between a minimum and a maximum level, the method comprising the following steps:

• determining the capacity of each of the plurality of stages;
• determining which of the plurality of stages are individually controllable;
• establishing a first stage combination, wherein all stages are off and an individually controllable stage is designated for modulation;
• and
• selecting each successive stage combination to have a minimum capacity equivalent to or less than the maximum capacity of the previous stage combination and to have an individually controllable stage to provide contiguous capacity to the minimum capacity of the next successive stage.

A method for controlling a multistage system comprising a plurality of stages, wherein each of the stages has a defined capacity, and at least one of the stages is individually controllable via pulsing or modulation, the method comprising the following steps:

• obtaining input data from a user indicating the number, type and capacity of each stage in a multistage system;
• automatically ordering a matrix of stage combinations from a first stage combination providing a minimum capacity to a last stage combination providing a maximum capacity, each stage combination having at least one inactive stage that is individually controlled to provide contiguous capacity output control between successive stages;
• periodically monitoring an input main control signal;
• calculating a requested output capacity based on the input main control signal;
• determining a stage combination selected to provide the selected output;
• compare the stage combination to a previous stage combination, and if the stage combination is not equivalent to the previous stage combination, determining whether the requested output capacity exceeds a predetermined deadzone;
• and
• if the deadzone has not been exceeded, saturating the output of the previous stage;
• if the deadzone is exceeded, switching to the selected stage and calculating a split range control signal for controlling the selected stage to provide the selected output capacity.

A multistage system comprising:

• a plurality of stages for controlling an HVAC system, the plurality of stages including at least one individually controllable stage;
• a programmable controller, the programmable controller being coupled to each of the stages, the programmable controller being programmed to:
• receive a setpoint;
• determine which of the stages should be activated based on the requested setpoint;
• calculate a split range signal, the split range signal being used to command the one individually controllable stage to provide the requested output;
• determine whether the main control signal is in a predefined deadzone and saturating the split range signal if the main control signal is in the deadzone.