Condenser Pressure Control System and Method

Abstract

A method of controlling a condenser fan of a heating, ventilating, and air-conditioning (HVAC) system based on a comparison of a refrigerant flow rate to maintain a valve position of an expansion valve. In the method, a controller modulates the condenser fan to maintain the valve position of the expansion valve at a valve position setpoint when the refrigerant flow rate is higher than the critical flow rate. The method also comprises controlling the speed of the condenser fan of the HVAC system to maintain a condensing measurement at a plurality of condensing measurement setpoints when the refrigerant flow rate is higher than the critical flow rate. The method also comprises controlling the speed of the condenser fan to maintain a condensing measurement at a plurality of condensing measurement setpoints when the condensing temperature measurement is higher than an ambient air temperature value plus at or around 5° F.

What is claimed is: 
     
         1 . A method of controlling a condenser fan to maintain a valve position of an expansion valve of a heating, ventilating, and air-conditioning (HVAC) system at a valve position setpoint, said method comprising:
 providing a controller in communication with said expansion valve of said HVAC system, said controller operable to receive a signal indicating said valve position;   providing a refrigerant flow rate sensing device in communication with said HVAC system and said controller and operable to measure a refrigerant flow rate of said HVAC system;   configuring said controller with a critical flow rate value and said valve position setpoint;   comparing, by said controller, said refrigerant flow rate with said critical flow rate value;   modulating, by said controller, said condenser fan to maintain said valve position of said expansion valve at said valve position setpoint when said refrigerant flow rate is higher than said critical flow rate value.   
     
     
         2 . The method of  claim 1 , further comprising inactivating, by said controller, said condenser fan when said refrigerant flow rate value is lower than said critical flow rate value. 
     
     
         3 . The method of  claim 1 , further comprising activating, by said controller, said condenser fan when said refrigerant flow rate value is higher than said critical flow rate value. 
     
     
         4 . A method of controlling a condenser fan of a heating, ventilating, and air-conditioning (HVAC) system to maintain a liquid condensing measurement of a refrigerant at a plurality of condensing measurement setpoints, said HVAC system comprising at least one evaporator, expansion valve, condenser, and compressor configured in a refrigerant circuit, said method comprising:
 providing a condensing measurement device in communication with said condenser and controller and configured to provide a condensing measurement;   providing a sensing device in communication with said controller and operable to sense a flow rate value of said refrigerant;   determining, by said controller, a system load ratio (ω) for said HVAC system;   programming said controller with a plurality of variables for said HVAC system comprising a critical flow rate value of said refrigerant, a design flow rate value of said refrigerant, said system load ratio value (ω), a subcooling liquid temperature value for said refrigerant, a saturated pressure measurement (P evaporator ) from said evaporator; and a sum of a pressure loss value from said expansion valve and a pressure loss value in a liquid line of said refrigerant circuit at said design flow rate value (ΔP);   determining, by said controller, a condensing pressure setpoint (P set ) of said condenser based on said plurality of variables, wherein P set =P evaporator +ω 2 ΔP;   modulating, by said controller, said speed of said condenser fan to maintain said condensing measurement value at said plurality of condensing measurement setpoints when said flow rate value of said refrigerant is higher than said critical flow rate value.   
     
     
         5 . The method of  claim 4 , wherein said condensing measurement device is a pressure measurement device, said condensing measurement is a pressure measurement at said liquid line of said refrigerant circuit, and said plurality of condensing measurement setpoints is said condensing pressure setpoint (P set ). 
     
     
         6 . The method of  claim 4 , wherein said condensing measurement device is a temperature measurement device, said condensing measurement is a temperature measurement at said liquid line of said refrigerant circuit, and said plurality of condensing measurement setpoints is a saturated temperature value of said refrigerant at said condensing pressure setpoint (P set ). 
     
     
         7 . The method of  claim 4 , wherein said sensing device is a flow meter and wherein determining, by said controller, said system load ratio (ω) for said HVAC system further comprises dividing, by said controller, said flow rate value over said design flow rate value. 
     
     
         8 . The method of  claim 4 , wherein said sensing device is a compressor status device operable to collect and transmit to said controller a signal indicating when said compressor is in an active state of operation and wherein determining, by said controller, said system load ratio (ω) for said HVAC system further comprises:
 providing at least one additional compressor in communication with said compressor status device and said controller; 
 transmitting, by said compressor status device, said compressor status signal for said at least one additional compressor to said controller; and 
 dividing, by said controller, a sum of said compressor status signal for said compressor and said compressor status signal for said at least one additional compressor over a sum of said compressor and said at least one additional compressor. 
 
     
     
         9 . The method of  claim 4 , wherein said sensing device is a compressor speed device operable to collect and transmit to said controller a signal indicating a speed of said compressor and wherein determining, by said controller, said system load ratio (ω) for said HVAC system further comprises:
 providing said controller with a design speed for said compressor; 
 transmitting, by said compressor status device, said signal indicating said speed of said compressor to said controller; and 
 dividing, by said controller, said speed of said compressor over said design speed. 
 
     
     
         10 . The method of  claim 4 , further comprising inactivating, by said controller, said condenser fan when said refrigerant flow rate value is lower than said critical flow rate value. 
     
     
         11 . The method of  claim 4 , further comprising activating, by said controller, said condenser fan when said refrigerant flow rate value is higher than said critical flow rate value. 
     
     
         12 . A method of controlling a condenser fan of a condenser of a heating, ventilating, and air-conditioning (HVAC) system to maintain a liquid condensing measurement of a refrigerant at a plurality of condensing measurement setpoints, said HVAC system also comprising an evaporator and expansion valve connected in a refrigerant circuit, said method comprising:
 providing a controller in communication with said HVAC system;   providing an ambient air temperature sensor in communication with and operable to measure and send to said controller an ambient air temperature value (T amb );   providing a condensing measurement device in communication with said controller and operable to measure and send to said controller a condensing measurement value;   determining, by said controller, a condensing temperature value (T cond );   programming said controller with a ratio of a speed of said condenser fan over a design speed of said condenser fan (ω), a design condenser split temperature value of said HVAC unit (ΔT), an on/off heat transfer coefficient ratio for said condenser fan (α), a suction pressure value (P suc ) of said evaporator, a subcooling liquid temperature value of said refrigerant, and a sum of a pressure loss value across a liquid line and suction line of said refrigerant circuit and said expansion valve of said HVAC unit under a design refrigerant flow rate (ΔP d );   determining, by said controller, a cooling load ratio (β) of said condenser, wherein:   
       
         
           
             
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         determining, by said controller, a condensing liquid pressure set point (P cond.set ) of said refrigerant based on said cooling load ratio (β), wherein:
     P   cond.set   =P   suc +β 2   ΔP   d  
 
 
         determining, by said controller, a plurality of condensing measurement setpoints based on said condensing measurement value and said condensing liquid pressure set point (P cond.set ); 
         modulating, by said controller, said speed of said condenser fan to maintain said condensing measurement at said plurality of condensing measurement setpoints when said condensing temperature value is higher than said ambient temperature value plus at or around 5° F. 
       
     
     
         13 . The method of  claim 12 , wherein determining, by said controller, said condensing temperature value (T cond ) further comprises:
 providing a temperature sensor in communication with and operable to measure and send to said controller said condensing temperature value (T cond ) of said refrigerant.   
     
     
         14 . The method of  claim 12 , wherein determining, by said controller, said condensing temperature value (T cond ) further comprises the steps of:
 providing a pressure sensor in communication with said condenser and controller operable to measure and send to said controller a condensing pressure value of said refrigerant; and   determining a saturated temperature of said refrigerant at said condensing pressure value.   
     
     
         15 . The method of  claim 12 , further comprising:
 providing a pressure sensor in communication with and operable to measure and send to said controller a liquid pressure measurement value (P cond );   determining, by said controller, said plurality of condensing measurement setpoints as a plurality of condensing pressure setpoints (P set );   modulating, by said controller, said speed of said condenser fan to maintain said pressure measurement value (P cond ) at said plurality of condensing measurement setpoints when said pressure measurement value (P cond ) is higher than said saturated pressure under said ambient temperature value plus at or around 5° F.   
     
     
         16 . The method of  claim 12 , further comprising:
 providing a temperature sensor in communication with and operable to measure and send to said controller said liquid temperature condensing measurement value (T cond );   determining, by said controller, said plurality of condensing measurement setpoints as a corresponding plurality of saturated refrigerant temperatures at said condensing liquid pressure setpoint (P cond.set );   modulating, by said controller, said speed of said condenser fan to maintain said temperature measurement value (T cond ) at said plurality of condensing temperature measurement setpoints when said temperature measurement value (T cond ) is higher than said ambient air temperature value plus at or around 5° F.   
     
     
         17 . The method of  claim 15 , further comprising inactivating, by said controller, said condenser fan when said condensing pressure value (P cond ) is less than said corresponding saturated pressure value at said ambient air temperature value plus at or around 5° F. 
     
     
         18 . The method of  claim 15 , further comprising activating, by said controller, said condenser fan when said condensing pressure value (P cond ) is higher than said corresponding saturated pressure value at said ambient temperature value plus at or around 5° F. 
     
     
         19 . The method of  claim 16 , further comprising activating, by said controller, said condenser fan when said condensing temperature value (T cond ) is higher than said ambient air temperature value plus at or around 5° F. 
     
     
         20 . The method of  claim 16 , further comprising inactivating, by said controller, said condenser fan when said condensing temperature value (T cond ) is less than said ambient air temperature value plus at or around 5° F.