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, an outdoor-air-temperature slope, and a previous runtime of the compressor unit in the second capacity mode during a previous demand period.

2. The climate-control system of claim 1 , wherein the control module is configured to switch the compressor unit between the first capacity mode and the second capacity mode based a current outdoor air temperature.

3. 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.

4. The climate-control system of claim 3 , 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.

5. The climate-control system of claim 4 , 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.

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

7. 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.

8. 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.

9. 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 runtime of the compressor unit in the second capacity mode, a runtime of the compressor unit in the first capacity mode, and a fan speed.

10. The climate-control system of claim 9 , 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.

11. The climate-control system of claim 9 , wherein the control module selects a region based on a comparison of user-selected indoor temperature setpoints with predetermined ranges of indoor temperature setpoints.

12. A climate-control system comprising:

a variable-capacity compressor unit operable in a first capacity mode and in a second capacity mode that is higher than the first capacity mode; and

a control module configured to switch the variable-capacity compressor unit between the first capacity mode and the second capacity mode based on a demand signal, a current outdoor air temperature, an outdoor-air-temperature slope, and a previous runtime of the compressor unit in the second capacity mode during a previous demand period.

13. The climate-control system of claim 12 , wherein the control module is configured to set at least one system operating parameter based on a region in which the climate-control system is installed, wherein the at least one system operating parameter includes at least one of a runtime of the variable-capacity compressor unit in the first capacity mode, a runtime of the variable-capacity compressor unit in the second capacity mode, and a fan speed.

14. The climate-control system of claim 13 , wherein the control module sets the at least one system operating parameter based on a time of day.

15. The climate-control system of claim 14 , wherein the control module approximates the time of day by determining the outdoor-air-temperature slope.

16. The climate-control system of claim 13 , wherein the control module determines which of first, second, third and fourth ranges the outdoor-air-temperature slope is within.

17. The climate-control system of claim 16 , wherein the control module sets a runtime of the variable-capacity 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.

18. The climate-control system of claim 17 , 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.

19. The climate-control system of claim 18 , wherein the control module accounts for relative humidity based on the outdoor-air-temperature slope.

20. The climate-control system of claim 19 , 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.