Method for optimizing pressure equalization in refrigeration equipment

1. A method for operating a compressor ( 22 ) having an inlet ( 26 ) and an outlet ( 28 ), the method comprising:

running the compressor to compress a fluid;

shutting down the compressor;

determining a condition-dependent threshold restart pressure difference (threshold) across the compressor;

relieving a pressure difference across the compressor to reach the threshold; and

after the threshold is reached, restarting the compressor,

wherein said condition comprises:

average operating pressure difference across the compressor during a period of time immediately prior to said shutdown where a higher average pressure difference results in a lower threshold.

2. The method of claim 1 wherein said condition further comprises one or more of:

time since said shutdown of the compressor;

operating pressure difference across the compressor immediately prior to shutdown of the compressor;

temperature of any part of the compressor or a point on tubing connected to the compressor; and

outside air temperature.

3. The method of claim 1 wherein said condition further comprises one or more of:

time since said shutdown of the compressor where a longer time results in a higher threshold;

operating pressure difference across the compressor immediately prior to shutdown of the previous operation where a higher pressure difference results in a lower threshold;

temperature of any part of the compressor or a point on tubing connected to the compressor where a higher temperature results in a lower threshold; and

outside air temperature where a higher air temperature results in a lower threshold.

4. The method of claim 1 wherein the determining the condition-dependent threshold restart pressure difference across the compressor comprises:

estimating the motor temperature; and

from the estimated motor temperature, determining the threshold restart pressure difference.

5. The method of claim 1 wherein the determining the condition-dependent threshold restart pressure difference across the compressor comprises:

during a shutdown, compensating for motor cooling to allow an increase in said threshold restart pressure difference.

6. The method of claim 1 wherein the compressor is in a vapor compression system ( 20 ), the vapor compression system comprising:

said compressor ( 22 ) having said inlet ( 26 ) and said outlet ( 28 ) along a refrigerant flowpath ( 24 );

a first heat exchanger ( 30 ) downstream of the outlet along the refrigerant flowpath;

an expansion device ( 32 ) downstream of the first heat exchanger along the refrigerant flowpath;

a second heat exchanger ( 34 ) downstream of the expansion device along the refrigerant flowpath; and

a valve ( 50 ) having a closed condition and an open condition and positioned so as to relieve a pressure difference between the inlet and the outlet in the open condition.

7. The method of claim 1 wherein the determining is performed by a controller ( 200 ).

8. A vapor compression system ( 20 ) comprising:

a compressor ( 22 ) having an inlet ( 26 ) and an outlet ( 28 ) along a refrigerant flowpath ( 24 );

a first heat exchanger ( 30 ) downstream of the outlet along the refrigerant flowpath;

an expansion device ( 32 ) downstream of the first heat exchanger along the refrigerant flowpath;

a second heat exchanger ( 34 ) downstream of the expansion device along the refrigerant flowpath;

a valve ( 50 ) having a closed condition and an open condition and positioned so as to relieve a pressure difference between the inlet and the outlet in the open condition;

means ( 210 , 212 ) for detecting a pressure difference between the outlet and the inlet; and

a controller ( 200 ) configured to:

determine a condition-dependent threshold restart pressure difference (threshold) across the compressor; and

relieve the pressure difference to reach the threshold,

wherein said condition comprises:

average operating pressure difference across the compressor during a period of time immediately prior to said shutdown where a higher average pressure difference results in a lower threshold.

9. The system of claim 8 wherein the means for detecting the pressure difference comprises:

a low side pressure sensor ( 212 ) positioned to detect a pressure proximate the inlet; and

a high side pressure sensor ( 210 ) positioned to detect a pressure proximate the outlet.

10. The system of claim 8 wherein the controller is further configured to determine the threshold based on one or more of:

time since said shutdown of the compressor;

operating pressure difference across the compressor immediately prior to shutdown of the compressor;

temperature of any part of the compressor or a point on tubing connected to the compressor; and

outside air temperature.

11. The system of claim 8 wherein the controller is further configured to determine the threshold based on one or more of:

time since said shutdown of the compressor where a longer time results in a higher threshold;

operating pressure difference across the compressor immediately prior to shutdown of the previous operation where a higher pressure difference results in a lower threshold;

temperature of any part of the compressor or a point on tubing connected to the compressor where a higher temperature results in a lower threshold; and

outside air temperature where a higher air temperature results in a lower threshold.

12. The system of claim 8 wherein the controller is further configured to determine the threshold by:

estimating a motor temperature; and

from the estimated motor temperature, determining the threshold restart pressure difference.

13. The system of claim 8 wherein the controller is configured to determine the threshold by:

during a shutdown, compensating for motor cooling to allow an increase in said threshold restart pressure difference.

14. The system of claim 8 wherein:

the compressor is a rotary compressor.

15. The system of claim 8 further comprising:

an outdoor air temperature sensor ( 220 ).

16. The system of claim 8 further comprising:

a compressor temperature sensor ( 224 ).

17. A method for using the system of claim 8 , the method comprising:

running the compressor to compress refrigerant and drive the refrigerant along the refrigerant flowpath;

shutting down the compressor;

the controller determining said threshold;

the controller opening the valve to relieving the pressure difference to reach the threshold; and

after the threshold is reached, the controller closing the valve; and

restarting the compressor.

18. The method of claim 17 wherein:

the restarting is performed by the controller.

19. The method of claim 17 wherein:

the controller opening the valve is responsive to a restart command.