HVAC control using discrete-speed thermostats and run times

1. A method of controlling an air conditioning unit to reduce the use of electricity while maintaining space temperature within a desired range, the method comprising in the following order at least the acts of:

receiving an on-signal from a thermostat located within the space;

operating the unit at an operating speed wherein the act of operating the unit includes running a compressor motor driving a compressor at a compressor speed, running an evaporator fan motor at a blower speed, the evaporator fan motor driving an evaporator fan that moves indoor air through an evaporator and to the space, and running a condenser fan motor at a condenser fan speed, the condenser fan motor driving a condenser fan that moves outdoor air through a condenser;

measuring how long the unit operates;

if the unit operates for longer than a predetermined maximum desired operating time, and if the unit is not already operating at a maximum operating speed, increasing the operating speed, wherein the act of increasing the operating speed includes increasing the compressor speed;

receiving an off-signal from the thermostat located within the space;

after receiving the off-signal, stopping operation of the unit, wherein the act of stopping operation of the unit marks an end to an operating cycle having a final compressor speed at the time the off-signal is received, and wherein the act of stopping operation includes turning off the compressor motor, turning off the evaporator fan motor, and turning off the condenser fan motor;

receiving an on-signal from the thermostat located within the space;

operating the unit at the operating speed wherein:

if the compressor speed was changed during an immediately previous operating cycle, the compressor speed is set at the final compressor speed of the immediately previous operating cycle,

if the compressor speed was not changed during the immediately previous operating cycle, and if the unit operated for less than a predetermined minimum desired operating time during the immediately previous operating cycle, and if the unit did not operate at a minimum non-zero operating speed during the immediately previous operating cycle, decreasing the compressor speed from the final compressor speed of the immediately previous operating cycle, and

if the compressor speed was not changed during the immediately previous operating cycle, if the unit operated for more than the predetermined minimum desired operating time during the immediately previous operating cycle, and if the unit did not operate at a maximum non-zero operating speed during the immediately previous operating cycle, the compressor speed is set at the final compressor speed of the immediately previous operating cycle; and

if the compressor speed was not changed during the immediately previous operating cycle, and if the unit operated at the maximum non-zero operating speed during the immediately previous operating cycle, the operating speed is decreased from the immediately previous operating cycle, including decreasing the compressor speed, even if the unit operated for longer than the predetermined minimum desired operating time during the immediately previous operating cycle; and

returning to the act above of measuring how long the unit operates, and repeating that act and the acts that follow.

2. The method of claim 1 wherein available non-zero compressor speeds consist of a low speed, a high speed, and a boost speed, wherein the low speed is the minimum non-zero speed and the boost speed is the maximum speed.

3. The method of claim 1 further comprising an act of measuring a coil temperature at the condenser.

4. The method of claim 3 wherein the act of operating the unit at the operating speed comprises selecting a higher compressor speed if the coil temperature exceeds a first threshold temperature, and selecting a lower compressor speed if the coil temperature is below the first threshold temperature.

5. A method of controlling an air conditioning unit to reduce the use of electricity while maintaining space temperature within a desired range, the method comprising in the following order at least the acts of:

receiving an on-signal from a thermostat located within the space;

operating the unit at an operating speed wherein the act of operating the unit includes running a compressor motor driving a compressor at a compressor speed, running an evaporator fan motor at a blower speed, the evaporator fan motor driving an evaporator fan that moves indoor air through an evaporator and to the space, and running a condenser fan motor at a condenser fan speed, the condenser fan motor driving a condenser fan that moves outdoor air through a condenser;

measuring how long the unit operates;

if the unit operates for longer than a predetermined maximum desired operating time, and if the unit is not already operating at a maximum operating speed, increasing the operating speed, wherein the act of increasing the operating speed includes increasing the compressor speed;

receiving an off-signal from the thermostat located within the space;

after receiving the off-signal, stopping operation of the unit, wherein the act of stopping operation of the unit marks an end to an operating cycle having a final compressor speed at the time the off-signal is received, and wherein the act of stopping operation includes turning off the compressor motor, turning off the evaporator fan motor, and turning off the condenser fan motor;

receiving an on-signal from the thermostat located within the space;

operating the unit at the operating speed wherein:

if the compressor speed was changed during an immediately previous operating cycle, the compressor speed is set at the final compressor speed of the immediately previous operating cycle,

if the compressor speed was not changed during the immediately previous operating cycle, and if the unit operated for less than a predetermined minimum desired operating time during the immediately previous operating cycle, and if the unit did not operate at a minimum non-zero operating speed during the immediately previous operating cycle, decreasing the compressor speed from the final compressor speed of the immediately previous operating cycle, and

if the compressor speed was not changed during the immediately previous operating cycle, if the unit operated for more than the predetermined minimum desired operating time during the immediately previous operating cycle, and if the unit did not operate at a maximum non-zero operating speed during the immediately previous operating cycle, the compressor speed is set at the final compressor speed of the immediately previous operating cycle; and

if the compressor speed was not changed during the immediately previous operating cycle, and if the unit operated at the maximum non-zero operating speed during the immediately previous operating cycle, the operating speed is decreased from the immediately previous operating cycle, including decreasing the compressor speed, even if the unit operated for longer than the predetermined maximum desired operating time during the immediately previous operating cycle; and

returning to the act above of measuring how long the unit operates, and repeating that act and the acts that follow.

6. The method of claim 5 wherein available non-zero compressor speeds consist of a low speed, a high speed, and a boost speed, wherein the low speed is the minimum non-zero speed and the boost speed is the maximum speed.

7. The method of claim 5 further comprising an act of measuring a coil temperature at the condenser.

8. The method of claim 7 wherein the act of operating the unit at the operating speed comprises selecting a higher compressor speed if the coil temperature exceeds a first threshold temperature, and selecting a lower compressor speed if the coil temperature is below the first threshold temperature.

9. A method of controlling an HVAC unit, the HVAC unit having a compressor, wherein the HVAC unit operates the compressor at multiple compressor speeds, the multiple compressor speeds including a low speed, a high speed, and a boost speed, wherein the high speed is higher than the low speed, and the boost speed is higher than the high speed, and wherein the HVAC unit is configured to operate the compressor using a signal from a single-speed thermostat and to select a current compressor speed from the multiple compressor speeds, the method comprising at least the acts of:

when a current run signal is received from the thermostat, starting the compressor;

evaluating whether the compressor speed changed during the immediate prior run, wherein the immediate prior run had a prior run final compressor speed and a prior run time, and if the compressor speed changed during the immediate prior run, operating the compressor at the prior run final compressor speed during the current run signal;

evaluating whether the prior run final compressor speed was the high speed, and if the prior run final compressor speed was the high speed, and if the compressor speed did not change during the immediate prior run, evaluating whether the prior run time was less than a predetermined high speed minimum desired operating time, and if the prior run time was less than the predetermined high speed minimum desired operating time, operating the compressor at a lower speed during the current run signal;

evaluating whether the prior run final compressor speed was the boost speed and if the prior run final compressor speed was the boost speed, and if the compressor speed did not change during the immediate prior run, operating the compressor at the high speed during the current run signal regardless of the prior run time;

measuring a current speed operating time during the current run signal, and if the current compressor speed is the low speed and if the current speed operating time is greater than a predetermined low speed maximum desired operating time, increasing the compressor speed during the current run signal;

measuring the current speed operating time during the current run signal, and if the current compressor speed is the high speed and if the current speed operating time is greater than a predetermined high speed maximum desired operating time, increasing the compressor speed during the current run signal; and

after the current run signal is no longer received from the thermostat, stopping the compressor and repeating the above acts when the run signal is restored.

10. A method of controlling an HVAC unit, the HVAC unit having a compressor, wherein the HVAC unit operates the compressor at multiple compressor speeds, the multiple compressor speeds including an L low speed, an L mid speed, an L high speed, an H high speed and a boost speed, wherein the L mid speed is higher than the L low speed, the L high speed is higher than the L mid speed, the H high speed is higher than the L high speed, and the boost speed is higher than the H high speed, and wherein the HVAC unit is configured to operate the compressor using a signal from a two-speed thermostat and to select a current compressor speed from the multiple compressor speeds, the method comprising at least the acts of:

when a current run signal is received from the thermostat, starting the compressor;

evaluating whether the compressor speed changed during the immediate prior run, wherein the immediate prior run had a prior run final compressor speed and a prior run time, and if the compressor speed changed during the immediate prior run, operating the compressor at the prior run final compressor speed during the current run signal;

evaluating whether the prior run final compressor speed was the L high speed, and if the prior run final compressor speed was the L high speed, and if the compressor speed did not change during the immediate prior run, evaluating whether the prior run time was less than a predetermined L high speed minimum desired operating time, and if the prior run time was less than the predetermined L high speed minimum desired operating time, operating the compressor at a lower speed during the current run signal;

evaluating whether the thermostat is calling for stage one or stage two;

if the thermostat is calling for stage one, evaluating whether the thermostat called for stage two after a start of an immediate prior run, and if the thermostat called for stage two after the start of the immediate prior run, operating the compressor at the L High speed during the current run signal;

if the thermostat is calling for stage two, and if the thermostat did not call for stage two during the immediate prior run, operating the compressor at the H high compressor speed during the current run signal;

if the thermostat is calling for stage two, if the thermostat called for stage two during the immediate prior run, and if the compressor speed changed during stage two of the immediate prior run, operating the compressor at the boost speed during the current run signal;

if the thermostat is calling for stage two, if the thermostat called for stage two during the immediate prior run, and if the compressor speed did not change during stage two of the immediate prior run, operating the compressor at the H high speed during the current run signal regardless of the prior run time;

measuring a current speed operating time during the current run signal, and if the current compressor speed is the L low speed and if the current speed operating time is greater than a predetermined L low speed maximum desired operating time, increasing the compressor speed during the current run signal;

measuring the current speed operating time during the current run signal, and if the current compressor speed is the L high speed and if the current speed operating time is greater than a predetermined L high speed maximum desired operating time, increasing the compressor speed during the current run signal;

measuring the current speed operating time during the current run signal, and if the current compressor speed is the L mid speed and if the current speed operating time is greater than a predetermined L mid speed maximum desired operating time, increasing the compressor speed to the L high speed during the current run signal;

measuring the current speed operating time during the current run signal, and if the current compressor speed is the H high speed and if the current speed operating time is greater than a predetermined H high speed maximum desired operating time, increasing the compressor speed to the boost speed during the current run signal; and

after the current run signal is no longer received from the thermostat, stopping the compressor and repeating the above acts when the run signal is restored.

11. The method of claim 10 wherein the HVAC unit has a two-speed indoor air fan configured to operate at a low speed and at a high speed, wherein the method comprises:

operating the indoor air fan at the low speed when the compressor is operating at the L low speed;

operating the indoor air fan at the low speed when the compressor is operating at the L mid speed;

operating the indoor air fan at the high speed when the compressor is operating at the H high speed; and

operating the indoor air fan at the high speed when the compressor is operating at the boost speed.

12. An HVAC unit comprising a compressor, wherein the HVAC unit operates the compressor at multiple compressor speeds, the multiple compressor speeds including an L low speed, an L mid speed, an L high speed, an H high speed, and a boost speed, wherein the HVAC unit comprises a controller configured to operate the compressor using a signal from a two-speed thermostat and to select a current compressor speed from the multiple compressor speeds, wherein the controller is configured to perform at least the acts of:

when a current run signal is received from the thermostat, starting the compressor;

evaluating whether the thermostat is calling for stage one or stage two;

if the thermostat is calling for stage one, evaluating whether the thermostat called for stage two after a start of an immediate prior run, and if the thermostat called for stage two after the start of the immediate prior run, operating the compressor at the L High speed during the current run signal;

if the thermostat is calling for stage one, and if the thermostat has not called for stage two since before the immediate prior run, evaluating whether the compressor speed changed during the immediate prior run, wherein the immediate prior run had a prior run final compressor speed and a prior run time, and if the compressor speed changed during the immediate prior run, operating the compressor at the prior run final compressor speed during the current run signal;

if the thermostat is calling for stage one, if the thermostat has not called for stage two since before the immediate prior run, and if the compressor speed did not change during the immediate prior run, evaluating whether the prior run final compressor speed was the L low speed, the L mid speed, or the L high speed, and if the prior run final compressor speed was the L mid speed, evaluating whether the prior run time was less than a predetermined L mid speed minimum desired operating time, and if the prior run time was less than the predetermined L mid speed minimum desired operating time, operating the compressor at the L low speed during the current run signal;

if the thermostat is calling for stage one, if the thermostat has not called for stage two since before the immediate prior run, if the compressor speed did not change during the immediate prior run, and if the prior run final compressor speed was the L high speed, evaluating whether the prior run time was less than a predetermined L high speed minimum desired operating time, and if the prior run time was less than the predetermined L high speed minimum desired operating time, operating the compressor at the L mid speed during the current run signal;

if the thermostat is calling for stage two, and if the thermostat did not call for stage two during the immediate prior run, operating the compressor at the H high compressor speed during the current run signal;

if the thermostat is calling for stage two, if the thermostat called for stage two during the immediate prior run, and if the compressor speed did not change during stage two of the immediate prior run, the controller performs acts of operating the compressor at the H high speed during the current run signal regardless of the prior run time;

measuring a current speed operating time during the current run signal, and if the current compressor speed is the L low speed and if the current speed operating time is greater than a predetermined L low speed maximum desired operating time, increasing the compressor speed to the L mid speed during the current run signal;

measuring the current speed operating time during the current run signal, and if the current compressor speed is the L mid speed and if the current speed operating time is greater than a predetermined L mid speed maximum desired operating time, increasing the compressor speed to the L high speed during the current run signal;

measuring the current speed operating time during the current run signal, and if the current compressor speed is the H high speed and if the current speed operating time is greater than a predetermined H high speed maximum desired operating time, increasing the compressor speed to the boost speed during the current run signal; and

after the current run signal is no longer received from the thermostat, stopping the compressor and repeating the above acts when the run signal is restored.

13. The HVAC unit of claim 12 wherein the controller is configured so that when the current run signal is first received from the thermostat, the controller performs acts of:

starting the compressor;

ramping the compressor up to a start speed; and

operating the compressor for a predetermined desired start time at the start speed;

wherein the start speed is substantially the same regardless of the prior run final compressor speed.

14. The HVAC unit of claim 12 wherein the controller is configured so that if the compressor speed did not change during the immediate prior run, the controller performs acts of:

evaluating whether an outdoor temperature parameter is beyond a first threshold; and

if the outdoor temperature parameter is beyond the first threshold, operating the compressor at a higher speed during the current run signal.

15. The HVAC unit of claim 14 wherein the HVAC unit has an outdoor coil and the outdoor temperature parameter is a temperature of the outdoor coil.

16. The HVAC unit of claim 14 wherein the controller is configured to perform an act of varying the boost speed as a function of the outdoor temperature parameter.

17. The HVAC unit of claim 14 wherein the controller is configured so that if the thermostat is calling for stage two, if the thermostat called for stage two during the immediate prior run, and if the compressor speed did not change during stage two of the immediate prior run, the controller performs an act of operating the compressor at the H high speed during the current run signal regardless of the outdoor temperature parameter.

18. The HVAC unit of claim 12 wherein the HVAC unit has a variable-speed drive for the compressor, wherein the HVAC unit operates the compressor at only a limited whole number of steady compressor speeds, wherein the steady compressor speeds include the L low speed, the L mid speed, the L high speed and the H high speed, and wherein the L mid speed is higher than the L low speed, the L high speed is higher than the L mid speed, the H high speed is higher than the L high speed, and the boost speed is higher than the H high speed.

19. The HVAC unit of claim 12 wherein the controller is configured to operate the compressor at no steady speeds other than the L low speed, the L mid speed, the L high speed, the H high speed, the boost speed, and a start speed.

20. The HVAC unit of claim 12 wherein the HVAC unit has a two-speed indoor air fan configured to operate at a low speed and at a high speed, and wherein the controller is configured to perform acts of:

operating the indoor air fan at the low speed when the compressor is operating at the L low speed;

operating the indoor air fan at the low speed when the compressor is operating at the L mid speed;

operating the indoor air fan at the high speed when the compressor is operating at the H high speed; and

operating the indoor air fan at the high speed when the compressor is operating at the boost speed.

21. The HVAC unit of claim 12 wherein the controller is configured so that if the thermostat is calling for stage two, if the thermostat called for stage two during the immediate prior run, and if the compressor speed changed during stage two of the immediate prior run, the controller will perform an act of operating the compressor at the boost speed during the current run signal without first operating the compressor at the H high speed for the predetermined H high speed maximum desired operating time.