Refrigerant Subcooling in a Vehicle HVAC System

1 . An HVAC system for use in a vehicle comprising:

an evaporator having a drain configured to receive condensate that drips from the evaporator;

a refrigerant compressor configured to receive a refrigerant from the evaporator and compresses the refrigerant;

a condenser configured to receive the refrigerant from the compressor; and

a condensate-to-refrigerant heat exchanger configured to receive the refrigerant from the condenser and the condensate from the drain, whereby the condensate absorbs heat from the refrigerant as the condensate flows through the condensate-to-refrigerant heat exchanger.

2 . The HVAC system of claim 1 wherein the condensate-to-refrigerant heat exchanger includes a central conduit through which one of the refrigerant and the condensate is directed and an outer concentric conduit surrounding the central conduit through which the other of the refrigerant and the condensate is directed.

3 . The HVAC system of claim 2 wherein the central conduit is configured to receive the condensate and the outer concentric conduit is configured to receive the refrigerant.

4 . The HVAC system of claim 1 wherein the condensate-to-refrigerant heat exchanger includes a condensate inlet, and the condensate inlet is at a lower elevation than the drain.

5 . The HVAC system of claim 4 wherein the condensate-to-refrigerant heat exchanger includes a condensate outlet, and the condensate outlet is at a lower elevation than the condensate inlet.

6 . The HVAC system of claim 1 further including an expansion device configured to receive the refrigerant from the condensate-to-refrigerant heat exchanger.

7 . A method of operating an HVAC system in a vehicle, the method comprising the steps of:

(a) directing air and a refrigerant through an evaporator to cause the refrigerant to absorb heat from the air;

(b) directing condensate from the evaporator through an evaporator drain to a condensate-to-refrigerant heat exchanger;

(c) compressing the refrigerant;

(d) directing the refrigerant through an expansion device; and

(e) directing the refrigerant through the condensate-to-refrigerant heat exchanger after the refrigerant is compressed and before the refrigerant is directed through the expansion device to thereby cause the condensate to absorb heat from the refrigerant.

8 . The method of claim 7 including step (f) directing the refrigerant through a condenser to remove heat from the refrigerant, and wherein step (e) is further defined by directing the refrigerant through the condensate-to-refrigerant heat exchanger after the refrigerant leaves the condenser and before the refrigerant is directed through the expansion device.

9 . The method of claim 7 wherein step (b) is further defined by directing the condensate through a central conduit in the condensate-to-refrigerant heat exchanger, and step (e) is further defined by directing the refrigerant through an outer concentric conduit surrounding the central conduit in the condensate-to-refrigerant heat exchanger.

10 . The method of claim 7 including step (f) directing the condensate from an outlet of the condensate-to-refrigerant heat exchanger to atmosphere.

11 . The method of claim 7 wherein step (b) is further defined by locating the condensate-to-refrigerant heat exchanger at a level below the evaporator drain to thereby employ gravity to cause the condensate to move from the evaporator drain to the condensate-to-refrigerant heat exchanger.