Apparatus and method for subcooling control based on superheat setpoint control

1. A system comprising:

a setpoint module configured to indirectly control subcooling of a condenser by adjusting a superheat setpoint based on (i) a return air temperature setpoint or a supply air temperature setpoint, and (ii) an outdoor ambient temperature, wherein the setpoint module is configured to set the superheat setpoint by calculating the superheat setpoint based on values of (i) the return air temperature setpoint or the supply air temperature setpoint, and (ii) the outdoor ambient temperature;

a summer configured to determine an error between the superheat setpoint and a superheat level of a compressor;

a control module configured to generate a control signal based on the error; and

an expansion valve module configured to electronically control a state of an expansion valve based on the control signal,

wherein the setpoint module is configured to

obtain a plurality of adjustment factors for adjusting the superheat setpoint, wherein the plurality of adjustment factors are predetermined values selected based on one of a plurality of setups and one of a plurality of types of the system,

select an operating mode from a plurality of operating modes, wherein the setpoint module, while operating in each of the plurality of operating modes, calculates the superheat setpoint differently than while operating in the other ones of the plurality of operating modes, and wherein each of the plurality of operating modes uses a corresponding two or more of the plurality of adjustment factors, and

adjust the superheat setpoint based the selected operating mode.

2. The system of claim 1 , wherein the setpoint module is configured to adjust the superheat setpoint based on an initial predetermined superheat level of the compressor.

3. The system of claim 1 , wherein the setpoint module is configured to adjust the superheat setpoint based on (i) the return air temperature setpoint, (ii) the outdoor ambient temperature, and (iii) an initial predetermined superheat level of the compressor.

4. The system of claim 1 , wherein the setpoint module is configured to adjust the superheat setpoint based on (i) the supply air temperature setpoint, (ii) the outdoor ambient temperature, and (iii) an initial predetermined superheat level of the compressor.

5. The system of claim 1 , further comprising a mode selection module configured to select an operating mode,

wherein the setpoint module is configured to, based on the selected operating mode, adjust the superheat setpoint based on (i) the return air temperature setpoint, or (ii) the supply air temperature setpoint.

6. The system of claim 1 , wherein the setpoint module is configured to adjust the superheat setpoint based on an average of iterative determinations of the outdoor ambient temperature over a predetermined period of time.

7. The system of claim 1 , wherein setpoint module is configured to (i) detect a loss in an outdoor ambient temperature signal, and (ii) use a previous outdoor ambient temperature as a current outdoor ambient temperature to prevent changing the superheat setpoint due to the loss in the outdoor ambient temperature signal.

8. The system of claim 1 , wherein:

setpoint module is configured to determine, based on a discharge comparison signal, whether to refrain from changing the superheat setpoint;

the discharge comparison signal indicates a difference between a discharge pressure of the compressor and a predetermined pressure; and

the setpoint module is configured to refrain from changing the superheat setpoint based on a result of the determining whether to refrain from changing the superheat setpoint.

9. The system of claim 1 , wherein:

the summer is configured to determine an error between the adjusted superheat setpoint and the superheat level of the compressor; and

the control module is configured to generate the control signal based on the error between the adjusted superheat setpoint and the superheat level.

10. The system of claim 1 , wherein the setpoint module is configured to:

operate in an additional operating mode not included in the plurality of operating modes; and

refrain from adjusting the superheat setpoint while operating in the additional operating mode.

11. The system of claim 1 , wherein:

the plurality of operating modes include a first operating mode, a second operating mode, and a third operating mode;

the plurality of adjustment factors include a first adjustment factor, a second adjustment factor and a third adjustment factor; and

the setpoint module is configured to:

during the first operating mode, use the first adjustment factor and the second adjustment factor to adjust the superheat setpoint,

during the second operating mode, use the third adjustment factor and the second adjustment factor to adjust the superheat setpoint, and

during the third operating mode, use the first adjustment factor, the second adjustment factor and the third adjustment factor.

12. The system of claim 1 , wherein:

the plurality of operating modes include a first operating mode, a second operating mode and a third operating mode;

the plurality of adjustment factors include a first adjustment factor and a second adjustment factor; and

the setpoint module is configured to:

during the first operating mode, adjust the superheat setpoint based on the first adjustment factor and a first predetermined temperature,

during the second operating mode, adjust the superheat setpoint based on the second adjustment factor and a second predetermined temperature, and

during the third operating mode, adjust the superheat setpoint based on the first adjustment factor, the second adjustment factor, the first predetermined temperature and the second predetermined temperature.

13. The system of claim 12 , wherein:

the plurality of adjustment factors comprise a third adjustment factor; and

during the third operating mode, the setpoint module is configured to adjust the superheat setpoint based on (i) a weighting of a difference between the return air temperature setpoint and the first predetermined temperature, and (ii) a weighting of a difference between the return air temperature setpoint and the second predetermined temperature.

14. The system of claim 1 , wherein the setpoint module is configured to:

during a first operating mode, adjust the superheat setpoint based on the return air temperature setpoint, one of the plurality of adjustment factors and a predetermined temperature, and

during a second operating mode, adjust the superheat setpoint based on a weighting of the one of the plurality of adjustment factors and a difference between the return air temperature setpoint and the predetermined temperature.

15. The system of claim 8 , wherein the setpoint module is configured to:

if the discharge comparison signal is greater than a predetermined value, disable adjusting the superheat setpoint; and

if the discharge comparison signal is less than or equal to the predetermined value, enable adjusting the superheat setpoint.

16. The system of claim 1 , wherein the plurality of adjustment factors include one or more indoor adjustment factors and one or more outdoor adjustment factors.

17. The system of claim 14 , wherein the one of the plurality of adjustment factors is an indoor adjustment factor.

18. A system comprising:

a setpoint module configured to indirectly control subcooling of a condenser by adjusting a superheat setpoint based on (i) a return air temperature setpoint or a supply air temperature setpoint, and (ii) an outdoor ambient temperature, wherein the setpoint module is configured to set the superheat setpoint by calculating the superheat setpoint based on values of (i) the return air temperature setpoint or the supply air temperature setpoint, and (ii) the outdoor ambient temperature;

a summer configured to determine an error between the superheat setpoint and a superheat level of a compressor;

a control module configured to generate a control signal based on the error; and

an expansion valve module configured to electronically control a state of an expansion valve based on the control signal,

wherein the setpoint module is configured to

obtain a plurality of adjustment factors for adjusting the superheat setpoint,

adjust the plurality of adjustment factors based on the return air temperature setpoint and a plurality of predetermined temperatures,

determine resultant values based on adjustments to the plurality of adjustment factors,

determine a sum of the resultant values, and

if the superheat setpoint is permitted to decrease and is not permitted to increase and the sum is negative, use the resultant values to adjust the superheat setpoint.

19. The system of claim 18 , wherein the plurality of adjustment factors include one or more indoor adjustment factors and one or more outdoor adjustment factors.