System and method for controlling a system that includes fixed speed and variable speed compressors

Patent metadata

Field	Value
Publication number	US-9599118-B2
Application number	US-201414244684-A
Country	US
Kind code	B2
Filing date	Apr 3, 2014
Priority date	Apr 4, 2013
Publication date	Mar 21, 2017
Grant date	Mar 21, 2017

Abstract

A system and method for controlling a system that includes fixed speed and variable speed compressors are described. The method generally allows the system, for example, a heating, ventilating, and air condition (HVAC) system that includes fixed speed and variable speed compressors, to maximize unit modulating capability. The method allows the use of a variable speed compressor that is relatively smaller, which can lead to cost savings, easier installation, manufacturing, etc.

First claim

What is claimed is:

1. A system for controlling the operation of a variable speed compressor and a fixed speed compressor,
wherein the system comprises
a fixed speed compressor;
a variable speed compressor, and
a control unit that includes a PI controller and is configured to:
(a) determine a first parameter value;
(b) determine a first PI capacity value based on the first parameter value determined in (a) and a set point using the PI controller;
(c) determine a first operating mode based on the first PI capacity value determined in (b);
(d) operate the fixed speed and variable speed compressors based on the determination made in (c);
(e) determine a second operating mode after (d);
(f) determine an operational state of the fixed speed compressor;
(g) operate the fixed speed compressor based on the determination made in (f);
(h) determine a speed of the variable speed compressor using the PI controller; and
(i) operate the variable speed compressor according to an operational state based on the determination made in (h).

2. The system of claim 1 , wherein the fixed speed compressor includes a plurality of fixed speed compressors, and the plurality of fixed speed compressors includes a first fixed speed compressor and a second fixed speed compressor.

3. The system of claim 2 , wherein the variable speed compressor and the first and second fixed speed compressors have one or more operational stages: Stage 0, Stage 1 min, Stage 1 max, Stage 2 min, Stage 2 max, Stage 3 min and Stage 3 max, wherein each of the operational stages are different from one another, the one or more operational stages corresponds to the operational state.

4. The system of claim 3 ,
wherein at the Stage 0, the first and second fixed speed compressors and the variable speed compressor operate in the off state so that the speeds of the fixed speed compressors and the variable speed compressor are at 0 revolutions per second (rps);
wherein at the Stage 1 min, the speed of the variable speed compressor ramps up from 0 rps until a minimum speed is reached, and the first and second fixed speed compressors operate in the off state so that the speeds are at 0 rps;
wherein at the Stage 1 max, the speed of the variable speed compressor ramps up from a minimum speed to a maximum speed, and the first and second fixed speed compressors operate in the off state so that the speeds are at 0 rps;
wherein at the Stage 2 min, the first fixed speed compressor operates in the on state and the second fixed speed compressor operates in the off state so that the speed of the second fixed compressor is at 0 rps, and the speed of the variable speed compressor is set at a minimum speed;
wherein at the Stage 2 max, the first fixed speed compressor operates in the on state and the second fixed speed compressor operates in the off state so that the speed of the second fixed compressor is at 0 rps, and the speed of the variable speed compressor ramps up from a minimum speed to a maximum speed;
wherein at the Stage 3 min, both the first fixed speed compressor and the second fixed speed compressor operate in the on state, and the speed of the variable speed compressor is set at a minimum speed; and
wherein at the Stage 3 max, both the first fixed speed compressors and the second fixed speed compressor operate in the on state, and the speed of the variable speed compressor ramps up from a minimum speed to a maximum speed.

5. The system of claim 4 , wherein a capacity/stage overlap of the variable speed compressor relative to the fixed speed compressor is present, and the operating mode includes one or more of Stage 0, Stage 1 min capacity, Stage 1 max capacity, Stage 1 max capacity+X, Stage 2 max capacity, Stage 2 max capacity+X and Stage 3 max capacity, wherein X is a dynamic buffer value expressed as a percentage.

6. The system of claim 5 , wherein the Stage 0 capacity references a unit capacity when the first and second fixed speed compressors and the variable speed compressor operate in the off state; the Stage 1 min capacity references the unit capacity when the variable speed compressor is operating at Stage 1 min, where both the first fixed speed compressor and the second fixed speed compressor are turned off; wherein the Stage 1 max capacity references the unit capacity when the variable speed compressor is operating at Stage 1 max, where both the first fixed speed compressor and the second fixed speed compressor are turned off; wherein the Stage 2 max capacity references the unit capacity when the variable speed compressor is operating at Stage 2 max, where the first fixed speed compressor is turned on and the second fixed speed compressor is turned off; and wherein the Stage 3 max capacity references the unit capacity when both the first fixed speed compressor and the second fixed speed compressor operate in the on state.

7. The system of claim 5 , wherein X is between about 0 to about 20%.

8. The system of claim 2 , wherein a capacity/stage gap of the variable speed compressor relative to the fixed speed compressor is present, and the operating mode includes Stage 0, Stage 1 min capacity, Stage 1 max capacity, Stage 2 min capacity, Stage 2 max capacity, Stage 3 min capacity and Stage 3 max capacity.

9. The system of claim 8 , wherein the Stage 0 capacity references a unit capacity when the first and second fixed speed compressors and the variable speed compressor operate in the off state; wherein the Stage 1 min capacity references the unit capacity when the variable speed compressor is operating at Stage 1 min, where both the first fixed speed compressor and the second fixed speed compressor are turned off; wherein the Stage 1 max capacity references the unit capacity when the variable speed compressor is operating at Stage 1 max, where both the first fixed speed compressor and the second fixed speed compressor are turned off; wherein the Stage 2 min capacity references the unit capacity when the variable speed compressor is operating at Stage 2 min where the first fixed speed compressor is turned on; wherein the Stage 2 max capacity references the unit capacity when the variable speed compressor is operating at Stage 2 max, where the first fixed speed compressor is turned on and the second fixed speed compressor is turned off; wherein the Stage 3 min capacity references the unit capacity when the variable speed compressor is at Stage 3 min and both the first fixed speed compressor and the second fixed speed compressor are turned on; and wherein the Stage 3 max capacity references the unit capacity when both the first fixed speed compressor and the second fixed speed compressor operate in the on state.

10. The system of claim 1 , wherein in (c), the first PI capacity value is compared to one or more predetermined values to determine the applicable operational stage.

11. A method of controlling the operation of a variable speed compressor and a fixed speed compressor in a refrigeration or a heating, ventilating and air conditioning system, the method comprising:
(a) determining a discharge air temperature (DAT);
(b) determining a PI capacity value based on the DAT determined in (a) and a set point using a PI controller;
(c) determining a first operating mode based on the PI capacity value determined in (b);
(d) operating the fixed speed compressors and the variable speed compressor based on the determination made in (c);
(e) determining a second operating mode after (d);
(f) determining the operational state of the fixed speed compressor;
(g) operating the fixed speed compressor based on the determination made in (f);
(h) determining a speed of the variable speed compressor using the PI controller; and
(i) operating the va

Assignees

• Trane Int Inc

Inventors

• Zhou John Qianghua
• Voorhis Roger Joseph
• Joiner Caleb Ryan
• Hayes Benjamin
• Crolius James Philip
• Hansen William

Classifications

• F04B49/065 Primary

  and making use of computers · CPC title

• F04D27/0269 Primary

  by changing flow path between different stages or between a plurality of compressors; load distribution between compressors · CPC title

• F04B2203/0209

  Rotational speed · CPC title

• F25B2400/0751

  the compressors having different capacities · CPC title

• F25B2600/0253

  with variable speed · CPC title