Method and system for supply-air re-circulation

1. A heating, ventilation, and air conditioning (HVAC) system comprising:

an evaporator coil disposed between a supply air duct and a return air duct;

a re-circulation duct that couples the supply air duct and the return air duct;

a controller operatively coupled to a variable-speed compressor, a variable-speed circulation fan, and a damper, wherein the damper is disposed in the re-circulation duct and is moveable between an open position and a closed position;

wherein the controller is configured to:

determine if the variable-speed circulation fan is operating at a minimum speed;

monitor an operating parameter of the HVAC system;

determine if the operating parameter of the HVAC system exceeds a pre-determined threshold;

responsive to a determination that the variable-speed circulation fan is not operating at the minimum speed or the operating parameter is below the pre-determined threshold, signal the damper to move to the closed position; and

wherein the operating parameter is a refrigerant pressure in a suction line.

2. The HVAC system of claim 1 , wherein:

the variable-speed circulation fan circulates air around the evaporator coil; and

the variable-speed compressor is fluidly coupled to the evaporator coil.

3. The HVAC system of claim 1 comprising:

a pressure sensor disposed in the suction line between the evaporator coil and the variable-speed compressor, the pressure sensor being configured to measure the operating parameter.

4. The HVAC system of claim 1 , wherein the controller is configured to:

responsive to a determination that the variable-speed circulation fan is operating at the minimum speed and the operating parameter exceeds the pre-determined threshold, signal the damper to move to the open position.

5. The HVAC system of claim 4 , wherein, in the open position, air from the supply air duct is diverted to the return air duct via the re-circulation duct.

6. The HVAC system of claim 4 , wherein moving the damper to the open position reduces a volume of air supplied via the supply air duct.

7. The HVAC system of claim 4 , wherein moving the damper to the open position increases latent capacity of the HVAC system.

8. The HVAC system of claim 1 , wherein a speed of the variable-speed circulation fan is modulated responsive to a speed of the variable-speed compressor.

9. The HVAC system of claim 1 , wherein the HVAC system operates in at least one of a cooling mode and a dehumidification mode.

10. The HVAC system of claim 9 , wherein:

the pre-determined threshold is in the range of approximately 130 psi to approximately 150 psi when the HVAC system is operating in the cooling mode; and

the pre-determined threshold is in the range of approximately 110 psi to approximately 130 psi when the HVAC system is operating in the dehumidification mode.

11. A method of utilizing a re-circulation duct, the method comprising:

determining with a heating, ventilation, and air conditioning (HVAC) controller if a variable-speed circulation fan is operating at a minimum speed;

monitoring an operating parameter of an HVAC system;

determining if the operating parameter of the HVAC system exceeds a pre-determined threshold;

responsive to a determination that the variable-speed circulation fan is operating at the minimum speed and the operating parameter exceeds the pre-determined threshold, signaling a damper disposed in a re-circulation duct that fluidly couples a supply air duct and a return air duct to move to an open position;

responsive to a determination that the variable-speed circulation fan is not operating at the minimum speed or the operating parameter is below the pre-determined threshold, signaling the damper to move to a closed position; and

wherein the operating parameter is a refrigerant pressure in a suction line.

12. The method of claim 11 , wherein the monitoring the operating parameter includes monitoring the refrigerant pressure in the suction line with a pressure sensor.

13. The method of claim 11 , comprising diverting air from the supply air duct to the return air duct via the re-circulation duct responsive to opening the damper.

14. The method of claim 11 , wherein moving the damper to the open position reduces a volume of air supplied via the supply air duct.

15. The method of claim 11 , wherein the HVAC system operates in at least one of a cooling mode and a dehumidification mode.

16. The method of claim 15 , wherein:

the pre-determined threshold is in the range of approximately 130 psi to approximately 150 psi when the HVAC system is operating in the cooling mode; and

the pre-determined threshold is in the range of approximately 110 psi to approximately 130 psi when the HVAC system is operating in the dehumidification mode.

17. The method of claim 11 , wherein moving the damper to the open position increases latent capacity of the HVAC system.

18. A heating, ventilation, and air conditioning (HVAC) system comprising:

a controller operatively coupled to a variable-speed compressor, a variable-speed circulation fan, and a damper disposed in a re-circulation duct, wherein the damper is moveable between an open position and a closed position;

wherein the controller is configured to:

determine if the variable-speed circulation fan is operating at a minimum speed and if a suction pressure measured by a pressure sensor disposed in a suction line is above a pre-determined threshold; and

responsive to a determination that the variable-speed circulation fan is operating at the minimum speed and the suction pressure is above the pre-determined threshold, signal the damper to move to the open position to increase latent capacity of the HVAC system.

19. The HVAC system of claim 18 , wherein, responsive to a determination that the variable-speed circulation fan is not operating at the minimum speed or the suction pressure is below the pre-determined threshold, signal the damper to move to the closed position.

20. The HVAC system of claim 18 , wherein the HVAC system operates in at least one of a cooling mode and a dehumidification mode.