Controlling multiple variable speed compressors

• US 5,797,729 A
• Filed: 02/16/1996
• Issued: 08/25/1998
• Est. Priority Date: 02/16/1996
• Status: Expired due to Fees

• Current Assignee: Aspen Systems, Inc.
• Original Assignee: Aspen Systems, Inc.
• Inventors: Borhanian, Hamed S., Rafuse, Lenley J. Jr., Pope, Willard C.
• Primary Examiner(s): Sheikh, Ayaz R.
• Assistant Examiner(s): THAI, XUAN MARIAN
• Application Number:
  US08/602,584
• Time in Patent Office: 921 Days
• Field of Search: 417/3, 417/4, 417/5, 417/6, 417/7, 417/8, 417/17, 417/18, 417/19, 417/20, 417/22, 417/42, 417/45, 417/44.2, 417/53, 415/1, 415/17, 62/126, 62/196.2, 62/196.4, 62/222, 62/228.4, 62/228.3
• US Class Current: 417/3
• CPC Class Codes: F04B 2205/01 Pressure before the pump inlet
• CPC Class Codes: F04B 2205/10 Inlet temperature
• CPC Class Codes: F04B 49/20 by changing the driving speed
• CPC Class Codes: F04C 28/08 characterised by varying the rotational speed
• CPC Class Codes: F25B 2400/075 with parallel compressors
• CPC Class Codes: F25B 2600/021 Inverters therefor
• CPC Class Codes: F25B 2600/0251 with on-off operation
• CPC Class Codes: F25B 49/025 Motor control arrangements
• CPC Class Codes: Y02B 30/70 Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating

Abstract

A refrigeration system having a plurality of variable speed compressors, each variable speed compressor operating at a speed substantially the same as the other energized variable speed compressors, the speed being below a maximum speed of the compressors.

Claims

1. A refrigeration system comprising a plurality of variable speed compressors and a controller, the controller being configured to energize a subset of the variable speed compressors, the subset being determined by comparing a capacity requirement of the refrigeration system against a stored set point table stored in the controller, the stored set point table defining a plurality of ranges of required rack capacity over which defined subsets of the plurality of variable speed compressors provide a greater energy efficiency ratio than any other subsets when each energized variable speed compressor operates at a speed substantially the same as the other energized variable speed compressors, the speed being below a maximum speed of the compressors.

2. The refrigeration system of claim 1 wherein the plurality of variable speed compressors share a common discharge line and a common suction line.

3. The refrigeration system of claim 1 further comprising a plurality of fixed capacity compressors sharing the common discharge line and the common suction line.

4. A method for controlling combinations of a plurality of variable speed compressors sharing a common discharge line and a common suction line, comprising

calculating a required rack capacity to satisfy a refrigeration load,

energizing a subset of the variable speed compressors, the subset determined by comparing the required rack capacity to a stored set point table, and

the stored set point table defining a plurality of ranges of required rack capacity over which defined subsets of the plurality of variable speed compressors provide a greater energy efficiency ratio than any other subsets when the energized variable speed compressors operate at substantially a same speed.

5. The method of claim 4 further comprising

determining the speed at which the chosen combination of compressors provides the required compressor capacity.

6. In a refrigeration system comprising a plurality of variable speed compressors sharing a common discharge line and a common suction line, each compressor operating at a speed substantially the same as the other energized compressors, a first combination of compressors capable of providing a first range of percentage of a maximum capacity provided by the plurality of compressors, and a second combination of compressors capable of providing a second range of percentage of the maximum capacity provided by the plurality of compressors, a method for determining a range of compressor speeds at which the first combination of compressors is more energy efficient than the second combination of compressors, comprising

measuring a first energy efficiency ratio of the first combination of compressors over the first range of percentage of the maximum capacity,

measuring a second energy efficiency ratio of the second combination of compressors over the second range of percentage of the maximum capacity,

calculating a third range of percentages of the maximum capacity over which the first energy efficiency ratio is greater than the second energy efficiency ratio and a fourth range of percentages of the maximum capacity over which the second energy efficiency ratio is greater than the first energy efficiency ratio, and

storing the third range and the fourth range in a set point table in a memory in a controller.

7. In a refrigeration system comprising a plurality of variable speed compressors, each variable speed compressor having a maximum capacity, a method for controlling the compressors, comprising

determining a total capacity equal to the sum of the maximum capacities of the energized variable speed compressors, determining a required capacity required to meet a refrigeration load,

calculating a required compressor speed equal to a scaled ratio of the required capacity to the total capacity,

comparing the required compressor speed to a stored set point table to determine a subset of the plurality of variable speed compressors that provides a greater energy efficiency ratio than any other subset of the plurality of variable speed compressors at the required compressor speed, and

energizing the subset of the plurality of compressors to operate at a speed substantially identical to the required speed.

8. A refrigeration system controller configured to energize a subset of a plurality of commonly piped variable speed compressors, the controller further configured to determine the subset of compressors by comparing a required rack capacity against a stored set point table defining a plurality of ranges of required rack capacity over which different subsets of the plurality of variable speed compressors provide a greater energy efficiency ratio than any other subsets when each compressor operates at a speed substantially the same as the other energized variable speed compressors.

9. A refrigeration system controller configured to control a plurality of variable speed compressors by calculating a required rack capacity, the controller further configured to choose a subset of compressors to energize by comparing the required rack capacity to a stored set point table defining a plurality of ranges of required rack capacity over which defined subsets of the plurality of variable speed compressors provide a greater energy efficiency ratio than any other subsets when each compressor operates at a speed substantially the same as the other energized variable speed compressors.

10. A refrigeration system controller configured to calculate a required rack capacity, the controller being further configured to determine a subset of compressors to energize by comparing the required rack capacity against a stored set point table defining a plurality of ranges of required rack capacity over which defined subsets of the plurality of variable speed compressors provide a greater energy efficiency ratio than any other subsets when each compressor operates at a speed substantially the same as the other energized variable speed compressors, the controller further comprising

a single speed control output signal for controlling the speed of the determined subset of variable speed compressors.

11. The refrigeration system controller of claim 10 further comprising

a plurality of energize signals, each energize signal configured to cause one of the plurality of variable speed compressors to activate.

12. A method for controlling a plurality of variable speed compressors sharing a common discharge line and a common suction line, a first combination of the plurality of variable speed compressors operating at a same speed, comprising

determining a required compressor capacity,

if the required compressor capacity is above an upper threshold stored in a set point table containing a plurality of ranges of required rack capacity over which defined subsets of the plurality of variable speed compressors Provide a greater energy efficiency ratio than any other subsets, energizing a second combination of the plurality of variable speed compressors having a greater energy efficiency ratio than the first combination at the required compressor capacity and changing the speed of the second combination of energized compressors to provide the required compressor capacity, and

if the required compressor capacity is below a lower threshold stored in the set point table, energizing a third combination of variable speed compressors and changing the speed of the third combination of energized compressors to provide the required compressor capacity.

13. A refrigeration controller capable of controlling a plurality of variable speed compressors sharing a common discharge line and a common suction line, comprising

a plurality of combinations of energized variable speed compressors,

a compressor capacity threshold stored in a set point table containing a plurality of ranges of required rack capacity over which defined subsets of the plurality of variable speed compressors provide a greater energy efficiency ratio than any other subsets,

a first combination of compressors having a greater energy efficiency ratio than the other combinations for compressor capacities greater than the compressor capacity threshold, and

a second combination of compressors having a greater energy efficiency ratio than the other combinations for compressor capacities less than the compressor capacity threshold.