Air conditioning system with cold thermal storage and evaporator temperature control
A system and method of operating a vehicle air conditioning system having an engine driven, fixed capacity refrigerant compressor and a compressor clutch is disclosed. The method may comprises setting a preliminary evaporator air temperature target; charging a cold storage apparatus in the vehicle air conditioning system; determining if the cold storage apparatus has reached a predetermined threshold; if the cold storage apparatus has reached a predetermined threshold, determining a new evaporator air temperature target by: determining a maximum allowable dewpoint evaporator air temperature for maintaining a passenger compartment humidity below a predetermined value; determining a maximum allowable mode evaporator air temperature based on a mode to which the vehicle air conditioning system is set; and setting the evaporator air temperature target to the lower of the dewpoint evaporator air temperature and the mode evaporator air temperature. The compressor clutch is controlled to achieve the evaporator air temperature target.
1. A method of operating a vehicle air conditioning system having an engine driven, fixed capacity refrigerant compressor selectively disengageable from an engine by a compressor clutch, the method comprising the steps of:
(a) setting a preliminary evaporator air temperature target;
(b) charging a cold storage apparatus in the vehicle air conditioning system;
(c) determining when the cold storage apparatus has reached a predetermined threshold;
(d) when the cold storage apparatus has reached the predetermined threshold, determining a new evaporator air temperature target by: determining a maximum allowable dewpoint evaporator air temperature for maintaining a passenger compartment humidity below a predetermined value; determining a maximum allowable mode evaporator air temperature based on a mode to which the vehicle air conditioning system is set; and setting the new evaporator air temperature target to a lower one of the dewpoint evaporator air temperature and the mode evaporator air temperature; and
(e) controlling the compressor clutch to achieve the new evaporator air temperature target.
2. The method of claim 1 including, (f) determining a low charge evaporator air temperature based on air conditioning system low refrigerant charge protection, and (g) setting the new evaporator air temperature target to the higher temperature value of the new evaporator air temperature target and the low charge evaporator air temperature.
3. The method of claim 1 wherein step (d) is further defined by determining a left/right evaporator air temperature based on a difference between a right hand passenger compartment temperature setting and a left hand passenger compartment temperature setting, and wherein the new evaporator air temperature target is set to a lower one of the dewpoint evaporator air temperature, the mode evaporator air temperature, and the left/right evaporator air temperature.
4. The method of claim 1 wherein step (d) is further defined by the mode evaporator air temperature having a higher maximum allowable evaporator air temperature when a mode is one of panel, bi-level and floor than when the mode is one of defrost/defog.
5. The method of claim 1 wherein step (d) is further defined by the maximum allowable for the dewpoint evaporator air temperature being based on air in a vehicle passenger compartment remaining below a predetermined maximum allowable humidity level in the vehicle passenger compartment.
6. The method of claim 1 wherein step (d) is further defined by determining a maximum allowable anti-fogging evaporator air temperature based on an outside ambient air temperature, an in-vehicle air temperature, and a percentage of recirculated air, and wherein the new evaporator air temperature target is set to a lower one of the dewpoint evaporator air temperature, the mode evaporator air temperature, and the anti-fogging evaporator air temperature.
7. The method of claim 1 wherein step (b) is further defined by the cold storage apparatus being a portion of an evaporator assembly including a phase change material therein, with the cold storage apparatus being charged as a cooled refrigerant passes through the evaporator assembly.
8. The method of claim 1 wherein step (b) is further defined by the cold storage apparatus being charged being a cold storage tank located downstream of an outlet of an evaporator assembly and upstream of an inlet to the refrigerant compressor.
9. The method of claim 8 comprising:
(f) prior to step (b), a refrigerant flowing from the evaporator assembly being redirected to bypass the cold storage tank during an initial vehicle cool-down period, and the refrigerant being directed to flow through the cold storage tank after the initial vehicle cool-down period.
10. The method of claim 1 wherein step (b) is further defined by the cold storage apparatus being charged being a refrigerant-to-liquid heat exchanger, and wherein the vehicle air conditioning system includes a primary refrigerant loop directing refrigerant through the refrigerant-to-liquid heat exchanger and a secondary liquid loop directing a liquid through the refrigerant-to-liquid heat exchanger.
11. A vehicle air conditioning system comprising:
an engine driven, fixed capacity refrigerant compressor;
a compressor clutch operatively engaging the refrigerant compressor and configured to selectively disengage the refrigerant compressor from being driven by an engine;
one of an evaporator and a refrigerant-to-liquid heat exchanger;
a cold storage apparatus being located in one of the evaporator, the refrigerant-to-liquid heat exchanger or downstream of the evaporator; and
a controller configured to set a preliminary evaporator air temperature target; charge the cold storage apparatus; determine when the cold storage apparatus has reached a predetermined threshold; and, when the cold storage apparatus has reached the predetermined threshold, determine a new evaporator air temperature target by: determining a maximum allowable dewpoint evaporator air temperature for maintaining a passenger compartment humidity below a predetermined value; determining a maximum allowable mode evaporator air temperature based on a mode to which the vehicle air conditioning system is set; setting the new evaporator air temperature target to a lower one of the dewpoint evaporator air temperature and the mode evaporator air temperature; the controller further configured to control the compressor clutch to achieve the new evaporator air temperature target.
12. The vehicle air conditioning system of claim 11 wherein the cold storage apparatus is located in the evaporator and includes a phase change material.
13. The vehicle air conditioning system of claim 11 wherein the cold storage apparatus is a cold storage tank located downstream of the evaporator assembly and upstream of an inlet to the refrigerant compressor.
14. The vehicle air conditioning system of claim 13 including a bypass valve configured to selectively direct a refrigerant through the cold storage tank or to bypass the cold storage tank.
15. The vehicle air conditioning system of claim 11 wherein the cold storage apparatus is in the refrigerant-to-liquid heat exchanger, and wherein the vehicle air conditioning system includes a primary refrigerant loop directing refrigerant through the refrigerant-to-liquid heat exchanger and a secondary liquid loop directing a liquid through the refrigerant-to-liquid heat exchanger.