Phase change material evaporator charging control

1. A method of controlling an air conditioning (A/C) compressor in a heating ventilation and air conditioning (HVAC) system having an evaporator including a phase change material, the method comprising the steps of:

measuring an evaporator output air temperature (EOAT);

determining a state of charge (SoC) value based on the EOAT;

determining an upper limit value and a lower limit value for the SoC;

initiating operation of the A/C compressor when the SoC value is less than or equal to the lower limit value; and

discontinuing operation of the A/C compressor when the SoC value is greater than or equal to the upper limit value.

2. The method according to claim 1 , further comprising the steps of:

determining whether the HVAC system is operating in a defog mode; and

operating the A/C compressor according to a freeze control method when the HVAC system is operating in the defog mode.

3. The method according to claim 1 , further comprising the steps of:

determining a humidity value within a vehicle cabin; and

operating the A/C compressor according to a freeze method when the humidity value exceeds a threshold.

4. The method according to claim 1 , further comprising the step of:

determining an outside ambient air temperature, wherein the upper limit value is based on the outside ambient air temperature.

5. The method according to claim 1 , further comprising the step of:

determining an average vehicle stop time, wherein the lower limit value is based on the average vehicle stop time.

6. The method according to claim 1 , further comprising the step of:

providing the evaporator that includes the phase change material.

7. The method according to claim 1 , further comprising the steps of:

providing a variable displacement A/C compressor; and

operating the A/C compressor in full displacement mode.

8. The method according to claim 1 , wherein a mass of phase change material in the evaporator is Mss+Ma, where Mss is a phase change material mass required for start-stop operation and Ma is an additional phase change material mass and wherein the lower limit value is Mss/(Mss+Ma).

9. The method according to claim 1 , wherein the step of determining the state of charge (SoC) value further includes the steps of:

determining the SoC value by calculating a difference between an estimated refrigerant temperature based on the EOAT and a phase change material freeze temperature and integrating the difference over time; and

applying a calibratable factor to the SoC value so that the SoC value indicates a percentage of phase change material charged.

10. The method according to claim 9 , further comprising the steps of:

initializing the SoC value to zero after a prolonged calibratable period of HVAC system off time; and

truncating the value of the SoC value to 1 (100%) when the SoC value is greater than 1 (100%).

11. A method of recovering braking energy in a vehicle having a HVAC system having the evaporator including the phase change material, the method comprising the steps of:

converting a portion of the vehicle's kinetic energy to mechanical energy;

providing a portion of the mechanical energy to an A/C compressor;

operating the A/C compressor to compress a refrigerant to a liquid state;

evaporating the refrigerant to a gaseous state within the evaporator, thereby changing a liquid state of the phase change material to a solid state and thereby storing energy from the A/C compressor, wherein the A/C compressor is controlled by the method of claim 1 .

12. The method according to claim 11 , further comprising the steps of:

converting a portion of the mechanical energy to electrical energy; and

providing a portion of the electrical energy to an electrical motor driving the A/C compressor.

13. A method of recovering braking energy in a vehicle having a HVAC system having an evaporator including a phase change material, the vehicle having a kinetic energy, the method comprising the steps of:

converting a portion of the vehicle's kinetic energy to mechanical energy;

providing a portion of the mechanical energy to an A/C compressor;

operating the A/C compressor to compress a refrigerant to a liquid state;

evaporating the refrigerant to a gaseous state within the evaporator, thereby changing a liquid state of the phase change material to a solid state and thereby storing energy from the A/C compressor.

14. The method according to claim 13 , further comprising the steps of:

converting a portion of the mechanical energy to electrical energy; and

providing a portion of the electrical energy to an electrical motor driving the A/C compressor.

15. The method according to claim 13 , further comprising the steps of:

detecting whether the vehicle is driving downhill;

determining a downhill driving time period;

operating the A/C compressor according to sub-freeze control when the downhill driving time is within the downhill driving time period; and

operating the A/C compressor according to standard freeze control when the downhill driving time period is exceeded.

16. The method according to claim 13 , further comprising the steps of:

detecting whether the vehicle is decelerating;

determining a deceleration time period; and

operating the A/C compressor according to sub-freeze control when the deceleration time is within the deceleration time period; and

operating the A/C compressor according to standard freeze control when the deceleration time period is exceeded.

17. A method of controlling an A/C compressor in a HVAC system having an evaporator including a phase change material, the method comprising the steps of:

determining an increased engine load;

determining an increased engine load time period; and

discontinuing operation of the A/C compressor until the increased engine load time period exceeds a threshold; and

operating the A/C compressor according to a Series Reheat Reduction (SRR) method when the increased engine load time period exceeds the threshold.

18. The method according to claim 17 , further comprising the steps of:

detecting whether the vehicle is driving uphill;

determining an uphill driving time period;

operating the A/C compressor according to the SRR method control when the downhill driving time is within the downhill driving time period; and

operating the A/C compressor according to standard freeze control when the PCM charge is below a SoC threshold.

19. The method according to claim 17 , further comprising the steps of:

detecting whether the vehicle is accelerating;

determining an acceleration time period; and

operating the A/C compressor according to the SRR method when the acceleration time exceeds the acceleration time period; and

operating the A/C compressor according to standard freeze control when the PCM charge is near a low threshold.