Use of electronic expansion valve to maintain minimum oil flow

• US 6,050,098 A
• Filed: 04/29/1998
• Issued: 04/18/2000
• Est. Priority Date: 04/29/1998
• Status: Expired due to Term

• Current Assignee: Trane International Inc. (Trane Technologies plc)
• Original Assignee: American Standard Companies Incorporated (Ideal Standard International Topco SCA)
• Inventors: Meyer, Jonathan M., Sibik, Lee L.
• Primary Examiner(s): Bennett, Henry
• Assistant Examiner(s): NORMAN, MARC E
• Application Number:
  US09/069,788
• Time in Patent Office: 720 Days
• Field of Search: 62/204, 62/208, 62/210, 62/211, 62/213, 62/222, 62/223, 62/224, 62/218
• US Class Current: 62/213
• CPC Class Codes: F25B 41/315 actuated by floats

Abstract

A method of controlling an expansion valve including the steps of: measuring a primary system condition; determining an error in the primary system condition; measuring a secondary system condition; determining an error in the secondary system condition; and modulating the expansion valve based upon the larger of the first or second error.

Claims

1. A method of controlling an expansion valve to maintain differential pressure in an HVAC system comprising the steps of:

measuring a primary system condition;

determining a first error in the primary system condition wherein the first error is a measure of refrigerant liquid level;

measuring a secondary system condition;

determining a second error in the secondary system condition wherein the second error is a measure of the pressure differential across a compressor; and

modulating the expansion valve based upon the smaller of the first or second error.

2. The method of claim 1 wherein the expansion valve is operably connected to an input of an evaporator and wherein an output of the evaporator is connected to an input of the compressor;

and

wherein the expansion valve is modulated to maintain a mass balance between the flow of refrigerant being removed from the evaporator and between the flow of refrigerant entering the evaporator from the expansion valve.

3. The method of claim 2 wherein the refrigerant liquid level is measured in the evaporator;

and

wherein the expansion valve is modulated to maintain both the refrigerant liquid level and a minimum pressure differential across the compressor.

4. A method of controlling an expansion valve including the steps of:

measuring a refrigerant liquid level;

comparing the measured refrigerant liquid level with a desired refrigerant liquid level to establish a refrigerant level error;

measuring a system pressure differential;

comparing the measured system pressure differential with a desired system pressure differential to determine a system differential pressure error;

comparing the liquid level error to the differential pressure error to determine the smaller error; and

modulating the expansion valve to control the smaller error.

5. The method of claim 4 wherein the liquid level is measured in an evaporator, a condenser, a receiver or a liquid vapor separator.

6. The method of claim 5 wherein the system pressure differential is measured by measuring condenser pressure and evaporator pressure and determining a difference therebetween.

7. The method of claim 6 including establishing a minimum pressure differential between the desired and the measured system pressure differentials.

8. The method of claim 7 including the further step of scaling either the liquid level error or the pressure differential error to correspond in range to the non-scaled error.