System for sequencing chillers in a loop cooling plant and other systems that employ all variable-speed units

A method of sequencing centrifugal chillers in a loop HVAC system having a plurality of variable speed drive centrifugal chillers arrange in parallel and coupled to a common distribution header comprising the steps of:

• commencing operation of the HVAC system with at least one of the chillers on-line;
• monitoring a current compressor operating speed and actual head pressure of the on-line chillers;
• determining a head pressure shedding threshold based on the current compressor operating speed;
• comparing the actual head pressure of the on-line chillers to the head pressure shedding threshold value for the current operating speed;
• if the actual head pressure of the on-line chillers is greater than the head pressure shedding threshold value for the current operating speed, shedding one of the on-line chillers;
• and then increasing the operating speed of the chillers remaining on-line, thereby improving overall operating efficiency.

A method of sequencing centrifugal chillers in a loop HVAC system having a plurality of variable speed drive centrifugal chillers arrange in parallel and coupled to a common distribution header comprising the steps of:

• commencing operation of the HVAC system with at least one of the chillers on-line;
• monitoring compressor operating speed and actual head pressure of the on-line chillers;
• selecting a head pressure adding threshold value based on the current operating speed;
• comparing the actual head pressure of the on-line chillers to the head pressure adding threshold for the current operating speed;
• and
• if the actual head pressure of the on-line chillers is greater than the selected head pressure adding threshold value for the current operating speed, adding another one of the chillers on-line;
• and then reducing the operating speed of all of the on-line chillers, thereby improving overall operating efficiency of the system.

A method of sequencing centrifugal pumps in a variable flow hydronic system having a plurality of variable speed drive centrifugal pumps arranged in parallel and coupled to a common distribution header to circulate chilled or heating water, the method comprising the steps of:

• commencing operation of the hydronic system with at least one of the pumps on-line;
• monitoring operating speed and actual head pressure of the on-line pumps;
• selecting a desired head pressure threshold HPT value based on the current operating speed;
• comparing the actual head pressure of the on-line pumps to the head pressure threshold HPT for the current operating speed;
• and
• if the actual head pressure of the on-line pumps is greater than the head pressure threshold HPT for the current operating speed, shedding one of the on-line pumps, and then increasing the operating speed of the pumps remaining on-line, thereby improving overall operating efficiency of the system.