Method of optimizing and rating a variable speed chiller for operation at part load

A method of rating a chiller's performance, wherein the chiller's performance is of a chiller that includes a compressor adapted to compress a refrigerant whose flow is throttled by an inlet guide vane that can move between a more-open position and a less-open position, wherein the compressor is driven by a motor, which in turn is driven at various speeds by an inverter that creates an electrical output from an electrical input, wherein the electrical output has a variable frequency and the electrical input is at a substantially constant nominal frequency, comprising:

• determining a part load value that reflects the chiller's performance at a part load condition, wherein the variable frequency of the electrical output is at a reduced frequency that is less than the substantially constant nominal frequency of the electrical input and the inlet guide vane is at its less-open position;
• determining a full load value that reflects the chiller's performance at a full load condition, wherein the variable frequency of the electrical output is greater than the reduced frequency and the inlet guide vane is at its more-open position;
• and
• providing a composite rating based on the part load value and the full load value, whereby the composite rating indicates the chiller's performance overall.

A method of rating a chiller's performance, wherein the chiller's performance is of a chiller that includes a compressor adapted to compress a refrigerant whose flow between an evaporator and a condenser is throttled by an inlet guide vane that can move between a more-open position and a less-open position, wherein the compressor is driven by a motor, which in turn is driven at various speeds by an inverter that creates an electrical output from an electrical input, and wherein the electrical output has a variable frequency and the electrical input is at a substantially constant nominal frequency, comprising:

• at a full load condition, conveying into the condenser a heat absorbing fluid at a full load condenser temperature, wherein the heat absorbing fluid once inside the condenser absorbs heat from the refrigerant;
• at the full load condition, conveying into the evaporator a heat emitting fluid at a full load evaporator temperature, wherein the heat emitting fluid once inside the evaporator rejects heat to the refrigerant;
• at a reduced load condition, conveying into the condenser the heat absorbing fluid at a reduced load condenser temperature that is lower than the full load condenser temperature;
• at the reduced load condition, conveying into the evaporator the heat emitting fluid at a reduced load evaporator temperature that is lower than the full load evaporator temperature;
• operating the chiller at the full load condition and at a full load efficiency, wherein the guide vane is at the more-open position, and the variable frequency is at least as great as the substantially constant nominal frequency;
• operating the chiller at the reduced load condition and at a reduced load efficiency that is better than the full load efficiency, wherein the guide vane is at the less-open position, and the variable frequency is less than the substantially constant nominal frequency;
• and
• providing a composite rating based on the full load efficiency and the reduced load efficiency, whereby the composite rating provides an indication of the chiller's performance overall.

A method of optimizing a variable frequency drive controller controlling the motor of a compressor under a variety of conditions, the method comprising the steps of:

• determining part load and full load conditions for a particular set of circumstances;
• selecting a compressor and a motor to optimize their operation at the part load value;
• and
• verifying that the selected compressor and the selected motor can be overspeeded to safely operate at the full load conditions.