Controlling HVAC Condenser Fans Using Pressure Sensors

• US 20140360211A1
• Filed: 06/07/2013
• Published: 12/11/2014
• Est. Priority Date: 06/07/2013
• Status: Active Grant

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Incorporated
• Inventors: Hovel, Douglas J., Njos, Erick A., Spurgeon, Daniel A.
• Granted Patent: US 9,809,088 B2
• Time in Patent Office: Days
• US Class Current: 62/89
• CPC Class Codes: B60H 1/00828 Ventilators, e.g. speed control B60H1/00864 takes precedence
• CPC Class Codes: B60H 1/3205 Control means therefor
• CPC Class Codes: B60H 2001/3277 to control the air flow

Abstract

A heating, ventilation and air conditioning (HVAC) unit may both save energy and monitor for fault conditions by monitoring an ambient air temperature, compressor discharge pressure, and evaporator suction pressure and using these measurements to identify known conditions. Compressor discharge pressure and ambient temperature may be used as indices to a look up table or map to determine a speed and direction for a condenser fan. In some cases, the look up table may direct the fan to be reversed at full power in an attempt to remove a suspected buildup of dirt or debris at the condenser. Ambient temperature and evaporator suction pressure may be monitored for a combination of conditions that indicate low refrigerant levels, allowing the compressor to be turned off before damage to the compressor is sustained.

Claims

1. A method of operating a heat, ventilation, and air conditioning (HVAC) unit operated in an earthmoving machine, the method comprising:

sensing a compressor output pressure;

sensing a compressor input pressure;

during a time period when the compressor output pressure is in an operating pressure range, controlling a speed of a condenser fan responsive to the compressor output pressure; and

operating the condenser fan in a reverse direction responsive to the compressor output pressure being above the operating pressure range.

2. The method of claim 1, further comprising:

turning off a compressor of the HVAC unit when the ambient temperature is above a threshold temperature value.

3. The method of claim 2, wherein the threshold suction pressure is less than a predetermined pressure and the threshold temperature exceeds a value from a map of temperature values.

4. The method of claim 1, wherein operating the condenser fan in the reverse direction comprises operating the condenser fan in the reverse direction not to exceed a predetermined a duty cycle.

5. The controller of claim 4, operating the condenser fan in the reverse direction comprises operating the condenser fan at full forward speed prior to reverse operation.

6. A controller for use in heat, ventilation, and air conditioning (HVAC) equipment operated in an earthmoving machine, the controller comprising:

a compressor control signal output operatively coupled to a compressor of the HVAC equipment;

a condenser fan control signal output operatively coupled to a condenser fan of the HVAC equipment;

a first pressure sensor input that receives an output pressure of the compressor;

a second pressure sensor input that receives a suction pressure between an evaporator of the HVAC equipment and the compressor;

a temperature input that receives an ambient air temperature;

a processor coupled to the compressor control signal output, the condenser fan control signal output, the first pressure sensor input, the second pressure sensor input, and the temperature input; and

a computer-readable memory that stores i) operating characteristics including condenser fan control data and ii) instructions that when executed by the processor cause the controller to;

turn on the compressor via the compressor control signal output based on a request for air conditioning and an ambient temperature being above a first threshold temperature;

select a condenser fan speed from the condenser fan control data responsive to the ambient air temperature and the output pressure of the compressor; and

set the condenser fan speed to the selected condenser fan speed via the condenser fan control signal.

7. The controller of claim 6, wherein computer-readable memory has further instructions that when executed by the processor, cause the controller to turn off the compressor via the compressor control signal output when the suction pressure is less than a threshold suction pressure level and the ambient temperature is above a second threshold temperature.

8. The controller of claim 7, wherein the threshold suction pressure a compressor minimum effective suction pressure.

9. The controller of claim 7, wherein the second threshold temperature is an ambient temperature above a predetermined temperature for a minimum time duration.

10. The controller of claim 6, wherein the computer-readable memory has further instructions that when executed by the processor cause the controller to reverse the condenser fan direction via the condenser fan control signal output responsive to:

the condenser fan control data indicating a reverse direction based on the ambient air temperature and the output pressure of the compressor; and

a previous reverse operation of the condenser fan occurred outside a minimum reverse cycle time.

11. The controller of claim 10, wherein the minimum reverse cycle period is based on maintaining an acceptable cooling capacity.

12. The controller of claim 10, wherein the instructions cause the controller to operate the condenser fan in the reverse direction for a period of time in a range of one minute to three minutes.

13. The controller of claim 10, wherein a second reverse operation within the minimum reverse cycle time sets a fault condition.

14. The controller of claim 10, wherein reverse operation of the condenser fan is further responsive to the condenser fan operating at 100% forward speed prior to reverse operation.

15. A heat, ventilation, and air conditioning (HVAC) unit operated in an earthmoving machine, the HVAC unit comprising:

a compressor that is selectively operable, responsive to a compressor control signal;

a condenser fluidly coupled to the compressor;

an expansion valve fluidly coupled to the condenser;

an evaporator fluidly coupled to the expansion valve and the compressor;

a first pressure sensor that measures an output pressure of the compressor;

a second pressure sensor that measures a suction pressure between the expansion valve and the compressor;

an ambient temperature sensor;

a condenser fan that provides cooling to the condenser, the condenser fan having variable speed and reversible direction responsive to a condenser fan control signal; and

a controller electrically coupled to the first pressure sensor, the second pressure sensor, the ambient temperature sensor, and the fan, the controller configured to;

i) provide the compressor control signal to selectively operate the compressor, and ii) provide the fan control signal, the controller including;

a processor;

a compressor control signal output;

a condenser fan control signal output;

a first pressure sensor input coupled to the first pressure sensor;

a second pressure sensor input coupled to the second pressure sensor;

an ambient temperature input coupled to the ambient temperature sensor;

a computer-readable memory that stores instructions that when executed by the processor cause the controller to;

turn on the compressor via the compressor control signal output based on a request for air conditioning;

select a condenser fan speed from condenser fan control data stored in the computer readable memory responsive to the ambient air temperature and the output pressure of the compressor;

set the condenser fan speed to the selected condenser fan speed via the condenser fan control signal; and

send an alarm signal via the alarm output when the suction pressure is less than a threshold suction pressure level and the ambient temperature is above a threshold temperature.

16. The HVAC unit of claim 15 wherein the computer-readable memory has further instructions that when executed by the processor, cause the controller to send an alarm signal via the alarm output when the output pressure of the compressor is less than about 28 pounds per square in gauge (PSIG) and the ambient temperature is above about 5 degrees Celsius.

17. The HVAC unit of claim 15, wherein the computer-readable memory has further instructions that when executed by the processor, cause the controller to turn off the compressor via the compressor control signal output when the suction pressure is less than the threshold suction pressure level and the ambient temperature is above the threshold temperature.

18. The HVAC unit of claim 17, wherein the threshold suction pressure is less than 5 pound per square inch gauge (PSIG) and the ambient temperature is above about 18 degrees Celsius for a duration of greater than about 8-12 seconds.

19. The HVAC unit of claim 15, wherein the computer-readable memory has further instructions that when executed by the processor cause the controller to reverse the condenser fan direction via the condenser fan control signal output responsive to:

the condenser fan control data indicating a reverse direction based on the ambient air temperature and the output pressure of the compressor; and

a previous reverse operation of the condenser fan occurred outside a minimum reverse cycle time.

20. The HVAC unit of claim 19, wherein the minimum reverse cycle period is in a range of 25 minutes to 30 minutes.