System and method for controlling an air conditioner or heat pump
View Patent ↗A control procedure operates an expansion valve of an air conditioning system. The control procedure utilizes a first control procedure to bring a calculated superheat value within a range of a target superheat value, and a second control procedure to cause the calculated superheat value to match the target superheat value. Both the first and second control procedures preferably use Proportional, Integral, Derivative control algorithms.
1. A method for controlling an expansion valve of an air conditioning system having an evaporator configured to evaporate a refrigerant, the expansion valve having an open position, a closed position and a plurality of intermediary positions, the method comprising:
calculating a superheat value of the refrigerant exiting the evaporator;
determining whether the calculated superheat value matches a target superheat value;
if the calculated superheat value matches the target superheat value, leaving the expansion valve at its current position;
operating the expansion valve according to a first control procedure for adjusting the position of the expansion valve, the first control procedure implementing first and second Proportional, Integral, Derivative (PID) control algorithms where the first and second PID control algorithms are different from each other;
determining whether the calculated superheat value is within a preset range of a target superheat value;
if the calculated superheat value is outside of the preset range, operating the expansion valve in accordance with a third PID control algorithm to bring the calculated superheat within the preset range; and
if the calculated superheat value is within the preset range, operating the expansion valve in accordance with a second control procedure for adjusting the position of the expansion valve to cause the calculated superheat to match the target superheat, wherein
the first and second control procedures are different.
2. The method of claim 1 wherein the calculating is based on a pressure value and a temperature value of the refrigerant.
3. The method of claim 2 wherein:
the first PID control algorithm is implemented for a first predetermined control loop count; and
the second PID control algorithm is implemented for a second predetermined loop count.
4. The method of claim 3 wherein the second PID control algorithm uses a superheat set point determined as follows:
SuperheatSetting=superheat+((40+(pidcount−pidstart))/(2+(pidcount−pidstart)))−1
where,
superheat is the target superheat,
pidcount is the loop count, and
pidstart is a constant.
5. The method of claim 4 wherein the pidstart constant is between 2 and 12.
6. The method of claim 3 wherein the first PID control algorithm employs a Proportional value between 10 and 40, an Integral value between 0 and 30, and a Derivative value between 0 and 30.
7. The method of claim 3 wherein the second PID control algorithm employs a Proportional value between 10 and 50, an Integral value between 0 and 30, and a Derivative value between 0 and 30.
8. The method of claim 3 wherein the second control procedure includes:
implementing a fourth PID control algorithm if a total loop count is below a threshold; and
implementing a fifth PID control algorithm if the total loop count exceeds the threshold.
9. The method of claim 1 wherein the air conditioning system further includes a compressor, the method further comprising, in response to detecting a shut-down of the compressor, moving the expansion valve to a closed position.
10. The method of claim 9 further comprising holding the expansion valve in the closed position until a subsequent start-up of the compressor.
11. A method for controlling an expansion valve of an air conditioning system having an evaporator configured to evaporate a refrigerant, the expansion valve having an open position, a closed position and a plurality of intermediary positions, the method comprising:
calculating a superheat value of the refrigerant exiting the evaporator;
determining whether the calculated superheat value matches a target superheat value;
if the calculated superheat value matches the target superheat value, leaving the expansion valve at its current position;
if the calculated superheat value does not match the target superheat value, operating the expansion valve in accordance with a PID control procedure for adjusting the position of the expansion valve that employs a temporary SuperheatSetting based on the target superheat value, wherein the temporary SuperheatSetting is determined as follows:
SuperheatSetting=superheat+((40+(pidcount−pidstart))/(2+(pidcount−pidstart)))−1
where,
superheat is the target superheat,
pidcount is a loop count, and
pidstart is a constant.
12. The method of claim 11 further comprising repeating the calculating, determining, leaving, and operating steps, wherein each calculating step is one loop count.
13. A method for controlling an expansion valve of an air conditioning system having an evaporator configured to evaporate a refrigerant, the expansion valve having an open position, a closed position and a plurality of intermediary positions, the method comprising:
calculating a superheat value of the refrigerant exiting the evaporator;
determining whether the calculated superheat value matches a target superheat value;
if the calculated superheat value matches the target superheat value, leaving the expansion valve at its current position;
if the calculated superheat value is outside of the present range of the target superheat value, operating the expansion valve in accordance with a first control procedure for adjusting the position of the expansion valve, the first control procedure implementing first and second Proportional, Integral, Derivative (PID) control algorithms where the first and second PID control algorithms are different from each other; and
determining whether the calculated superheat value is within a preset range of a target superheat value;
if the calculated superheat value does not match the target superheat value following the first control procedure, operating the expansion valve in accordance with a second control procedure for adjusting the position of the expansion valve to cause the calculated superheat to match the target superheat, wherein
the first and second control procedures are different, and
one of the first and second PID control algorithms of the first control procedure uses a superheat set point determined as follows:
SuperheatSetting=superheat+((40+(pidcount−pidstart))/(2+(pidcount−pidstart)))−1
where,
superheat is the target superheat,
pidcount is the loop count, and
pidstart is a constant.
14. The method of claim 13 wherein the pidstart constant is between 2 and 12.
15. The method of claim 14 further comprising repeating the calculating, determining, leaving, and operating steps, wherein each calculating step is one loop count.