System and method of controlling a variable-capacity compressor

1. A climate-control system comprising a variable-capacity compressor unit and a control module controlling the compressor unit, the compressor unit operable in a first capacity mode and in a second capacity mode that is higher than the first capacity mode, the control module configured to switch the compressor unit between the first capacity mode and the second capacity mode based on a demand signal, a current outdoor air temperature, and an outdoor-air-temperature slope.

2. The climate-control system of claim 1 , wherein the control module determines which of first, second, third and fourth ranges the outdoor-air-temperature slope is within.

3. The climate-control system of claim 2 , wherein the control module sets a runtime of the compressor unit in the first capacity mode according to one of four columns in a lookup table based on which one of the first, second, third and fourth ranges the outdoor-air-temperature slope is within.

4. The climate-control system of claim 3 , wherein the first range includes an outdoor-air-temperature slope of zero, the second range corresponds to a positive outdoor-air-temperature slope, the third range corresponds to a negative outdoor-air-temperature slope, and the fourth range corresponds to an extreme negative outdoor-air-temperature slope.

5. The climate-control system of claim 4 , wherein the control module switches the compressor unit between the first and second capacity modes based on a compressor runtime.

6. The climate-control system of claim 5 , wherein the compressor runtime is a runtime of the compressor unit in the second capacity mode.

7. The climate-control system of claim 6 , wherein the runtime of the compressor unit in the second capacity mode is equal to a previous runtime in the second capacity mode during a previous demand period.

8. The climate-control system of claim 1 , wherein the control module accounts for relative humidity based on the outdoor-air-temperature slope.

9. The climate-control system of claim 1 , wherein the control module accounts for a thermal load of a building to be heated or cooled by the climate-control system based on the outdoor-air-temperature slope.

10. The climate-control system of claim 1 , further comprising an indoor blower forcing air over an indoor heat exchanger, the indoor blower having a speed setting determined based on a region in which the climate-control system is installed.

11. The climate-control system of claim 1 , wherein the control module sets system operating parameters based on a region in which the climate control system is installed, the system operating parameters including one or more of a high-capacity runtime of the compressor unit, a low-capacity runtime of the compressor unit, and a fan speed.

12. The climate-control system of claim 11 , wherein the control module selects a region based on a comparison of outdoor-air-temperature values and outdoor-relative-humidity values with predetermined ranges of outdoor-air-temperature and outdoor-relative-humidity values.

13. The climate-control system of claim 11 , wherein the control module selects a region based on a comparison of user-selected indoor temperature setpoints with predetermined ranges of indoor temperature setpoints.

14. The climate-control system of claim 1 , wherein the outdoor-air-temperature data is obtained from an outdoor-air-temperature sensor.

15. The climate-control system of claim 1 , wherein the outdoor-air-temperature data is determined based on a heat exchanger coil temperature.

16. A climate-control system comprising a variable-capacity compressor unit and a control module controlling the compressor unit, the compressor unit operable in a first capacity mode and in a second capacity mode that is higher than the first capacity mode, the control module configured to switch the compressor unit between the first capacity mode and the second capacity mode based on a demand signal, outdoor-air-temperature data, and a time of day.

17. The climate-control system of claim 16 , wherein the control module switches the compressor unit between the first and second capacity modes based on a runtime of the compressor unit in the second capacity mode.

18. The climate-control system of claim 17 , wherein the runtime of the compressor unit in the second capacity mode is equal to a previous runtime in the second capacity mode during a previous demand period.

19. The climate-control system of claim 16 , wherein the control module approximates the time of day by determining an outdoor-air-temperature slope.

20. The climate-control system of claim 19 , wherein the control module determines which of first, second, third and fourth ranges the outdoor-air-temperature slope is within, and wherein the first range includes an outdoor-air-temperature slope of zero, the second range corresponds to a positive outdoor-air-temperature slope, the third range corresponds to a negative outdoor-air-temperature slope, and the fourth range corresponds to an extreme negative outdoor-air-temperature slope.

21. The climate-control system of claim 20 , wherein the control module sets a runtime of the compressor unit in the first capacity mode according to one of four columns in a lookup table based on which one of the first, second, third and fourth ranges the outdoor-air-temperature slope is within.

22. A method of controlling a compressor operable in a first capacity mode and in a second capacity mode that is higher than the first capacity mode, the method comprising:

receiving a demand signal from a thermostat;

obtaining an outdoor-air-temperature value;

setting a first-capacity-runtime of the compressor in the first capacity mode based on the outdoor-air-temperature value;

comparing a total runtime of the compressor to the first-capacity-runtime; and

switching the compressor from the first capacity mode to the second capacity mode in response to the comparison of the total runtime and the first-capacity-runtime.

23. The method of claim 22 , wherein the first-capacity-runtime is set based on a previous second-capacity-runtime of the compressor in the second capacity mode.

24. The method of claim 22 , further comprising determining an outdoor-air-temperature slope.

25. The method of claim 24 , wherein determining the outdoor-air-temperature slope accounts for relative humidity based.

26. The method of claim 24 , wherein determining the outdoor-air-temperature slope accounts for a thermal load of a building to be heated or cooled.

27. The method of claim 24 , further comprising determining which of first, second, third and fourth ranges the outdoor-air-temperature slope is within, wherein the first range includes an outdoor-air-temperature slope of zero, the second range corresponds to a positive outdoor-air-temperature slope, the third range corresponds to a negative outdoor-air-temperature slope, and the fourth range corresponds to an extreme negative outdoor-air-temperature slope.

28. The method of claim 27 , wherein the first-capacity-runtime is set according to one of four columns in a lookup table based on which one of the first, second, third and fourth ranges the outdoor-air-temperature slope is within.