Systems and methods for head pressure control

Abstract

The present invention relates to systems and methods for controlling head pressure in a vapor compression system, e.g. in a precision air conditioning system. One embodiment of the invention provides a method for regulating working fluid flow in a vapor compression system including a compressor. The method includes: providing a controller; receiving signals at the controller representative of a monitored discharge pressure in a discharge line of the compressor; and using the controller to provide a control signal to an actuator that controls a flow control valve that, in turn, controls working fluid flow into the system, the control signal being responsive at least in part to a difference between a set point pressure and the monitored discharge pressure.

1 . A method for regulating coolant fluid flow in a condenser of a vapor compression refrigeration system including a compressor, the method comprising: 
 providing a vapor compression refrigeration system comprising: 
 a compressor having a discharge for compressed refrigerant;  
 a discharge line attached to the compressor discharge; and  
 a fluid cooled condenser having: 
 a first inlet coupled to the discharge line;  
 a first outlet for passing working fluid to an expansion device;  
 a second inlet for receiving coolant from a coolant recycling system; and  
 a second outlet for returning coolant to the coolant recycling system  
 
 a discharge pressure sensor coupled to the discharge line and operative to provide a discharge pressure signal representative of the discharge pressure;  
 a flow control valve having an inlet for receiving coolant fluid from the coolant recycling system and an outlet, the outlet connected to the second inlet of the condenser, the flow control valve operative to control the flow of the coolant fluid into the condenser;  
 a flow control valve actuator coupled to the flow control valve, the actuator operative to control the flow control valve; and  
 a controller in communication with the discharge pressure sensor and in communication with the actuator, the controller operative to receive the discharge pressure signal and to control the actuator at least in part in response to the discharge pressure signal;  
   receiving signals at the controller representative of a monitored discharge pressure in a discharge line of the compressor; and    using the controller to provide a control signal to an actuator that controls a flow control valve that, in turn, controls coolant fluid flow into the condenser, the control signal being responsive at least in part to a difference between a set point pressure and the monitored discharge pressure.    
   
   
       2 . The method of  claim 1 , wherein the method further comprises: 
 receiving a signal at the controller representative of the position of the flow control valve and wherein the control signal is responsive at least in part to the signal representative of the position of the flow control valve.    
   
   
       3 . The method of  claim 1 , wherein using the controller to provide a control signal to the actuator comprises: 
 if the controller is in a hold position state, if the monitored discharge pressure minus the set point pressure is above a preselected value, and if the monitored discharge pressure is not decreasing,    then entering an opening valve state; and    if the controller is in the hold position state, if the monitored discharge pressure minus the set point pressure is below a preselected value and if the monitored discharge pressure is not increasing, then entering a closing valve state.    
   
   
       4 . The method of  claim 3 , wherein using the controller to provide a control signal to the actuator further comprises: 
 if the controller is in an opening valve state, if the monitored discharge pressure minus the set point pressure is below a preselected value, and if the rate of change in the monitored discharge pressure is below a preselected value,    then entering the hold position state; and    if the controller is in a closing valve state, if the monitored discharge pressure minus the set point pressure is above a preselected value and if the rate of change in the monitored discharge pressure is below a preselected value, then entering the hold position state.    
   
   
       5 . The method of  claim 3 , wherein using the controller to provide a control signal to the actuator further comprises: 
 if the controller is in an opening valve state and if the monitored discharge pressure is decreasing, then entering a pressure decreasing state; and    if the controller is in a closing valve state and if the monitored discharge pressure is increasing, then entering a pressure increasing state.    
   
   
       6 . The method of  claim 5 , wherein using the controller to provide a control signal to the actuator further comprises: 
 if the controller is in the pressure decreasing state and if the monitored discharge pressure is increasing, then entering the opening valve state; and    if the controller is in the pressure increasing state and if the monitored discharge pressure is decreasing, then entering the closing valve state.    
   
   
       7 . The method of  claim 3 , wherein using the controller to provide a control signal to the actuator further comprises: 
 when the controller enters the opening valve state, the controller substantially immediately signals the actuator to open the flow control valve a preselected amount; and    when the controller enters the closing valve state, the controller substantially immediately signals the actuator to close the flow control valve a preselected amount.    
   
   
       8 . The method of  claim 7 , wherein, while the controller is in the opening valve state, after the controller signals the actuator to open the flow control valve a preselected amount, the controller waits a first off time before signaling the actuator to open the valve further, the first off time being a function of the difference between the monitored discharge pressure and the set point pressure; and 
 wherein, while the controller is in the closing valve state, after the controller signals the actuator to close the flow control valve a preselected amount, the controller waits a second off time before signaling the actuator to close the valve further, the second off time being a function of the difference between the monitored discharge pressure and the set point pressure.    
   
   
       9 . The method of  claim 8 , wherein the first and second off times are re-calculated regularly according to a preselected time period.  
   
   
       10 . The method of  claim 8 , wherein the first off time decreases as the difference between the monitored discharge pressure and the set point pressure increases, and 
 wherein the second off time decreases as the difference between the monitored discharge pressure and the set point pressure increases.    
   
   
       11 . The method of  claim 10 , wherein using the controller to provide a control signal to the actuator further comprises: 
 sending a control signal to the actuator to set the initial position of the flow control valve; and    holding the initial position until the controller receives a transition control signal indicating that the compressor has been turned on.    
   
   
       12 . The method of  claim 5 , wherein, using the controller to provide a control signal to the actuator further comprises: 
 when the controller enters the pressure decreasing state, the controller substantially immediately signals the actuator to close the flow control valve a preselected amount; and    when the controller enters the pressure increasing state, the controller substantially immediately signals the actuator to open the flow control valve a preselected amount.    
   
   
       13 . The method of  claim 12 , wherein, while the controller is in the pressure decreasing state, after the controller signals the actuator to close the flow control valve a preselected amount, the controller waits a first off time before signaling the actuator to open the valve further, the first off time being determined at least in part by the rate at which the pressure is decreasing; and 
 wherein, while the controller is in the pressure increasing state, after the controller signals the actuator to open the flow control valve a preselected amount, the controller waits a second off time before signaling the actuator to open the valve further, the second off time being determined at least in part by the rate at which the pressure is increasing.    
   
   
       14 . The method of  claim 1 , wherein the controller is a microprocessor controller.  
   
   
       15 . The method of  claim 1 , wherein the method further comprises: 
 monitoring the actual discharge pressure using a pressure transducer mounted on the discharge line to produce an analog monitored discharge pressure signal.    
   
   
       16 . The method of  claim 15 , wherein the method further comprises: 
 using an analog op-amp to convert the analog monitored discharge pressure signal to an adjusted monitored discharge pressure signal.    
   
   
       17 . The method of  claim 16 , wherein the method further comprises: 
 using an analog-to-digital converter to convert the adjusted monitored discharge pressure signal to a digital monitored discharge pressure signal for forwarding to the controller.    
   
   
       18 . An air conditioning unit comprising: 
 a compressor having a discharge for compressed refrigerant;    a discharge line attached to the compressor discharge; and    a fluid cooled condenser having: 
 a first inlet coupled to the discharge line;  
 a first outlet for passing working fluid to an expansion device;  
 a second inlet for receiving coolant from a coolant recycling system; and  
 a second outlet for returning coolant to the coolant recycling system;  
   a discharge pressure sensor coupled to the discharge line and operative to provide a discharge pressure signal representative of the discharge pressure;    a flow control valve having an inlet for receiving coolant fluid from the coolant recycling system and an outlet, the outlet connected to the second inlet of the condenser, the flow control valve operative to control the flow of the coolant fluid into the condenser;    a flow control valve actuator coupled to the flow control valve, the actuator operative to control the flow control valve; and    a controller in communication with the discharge pressure sensor and in communication with the actuator, the controller operative to receive the discharge pressure signal and to control the actuator at least in part in response to the discharge pressure signal.    
   
   
       19 . The system of  claim 18 , wherein the discharge pressure sensor comprises: 
 a pressure transducer operative to provide a transducer pressure signal representative of the pressure in the discharge line;    an op-amp coupled to the transducer and operative to convert the transducer pressure signal to provide an amplified signal; and    an analog-to-digital converter coupled to the op-amp to convert the amplified signal to a digital signal.    
   
   
       20 . The system of  claim 18 , wherein the actuator comprises: 
 a feedback potentiometer operative to measure valve position and to provide a signal representative of the valve position, and wherein the controller is operative to receive the valve position signal from the potentiometer and to control the actuator at least in part in response to the valve position signal.    
   
   
       21 . The system of  claim 18 , wherein the controller is further operative to monitor a temperature control state machine to determine cooling demand.  
   
   
       22 . The system of  claim 18 , wherein the controller is a microprocessor controller.  
   
   
       23 . An apparatus for regulating coolant fluid flow in a vapor compression refrigeration system, the apparatus comprising: 
 a compressor having a suction and a discharge for a refrigerant;    a discharge line attached to the compressor discharge;    a fluid cooled condenser having: 
 a first inlet coupled to the discharge line;  
 a second inlet for receiving-coolant fluid from a conventional coolant recycling system;  
 a first outlet for passing working fluid to an expansion device;  
 a second outlet for returning coolant to the coolant recycling system  
   a pressure transducer coupled to the discharge line and operative to provide a transducer pressure signal representative of the pressure in the discharge line;    an op-amp coupled to the transducer and operative to convert the transducer pressure signal as necessary to provide an amplified signal; and    an analog-to-digital converter coupled to the op-amp to convert the amplified signal to a digital pressure signal;    a flow control valve having an inlet for receiving coolant fluid and an outlet, the outlet connected to the condenser's second inlet, the flow control valve operative to control the flow of the coolant fluid into the condenser;    a flow control valve actuator coupled to the flow control valve, the actuator operative to control the flow control valve, the actuator having a feedback potentiometer operative to measure valve position and to provide a signal representative of the valve position; and    a controller in communication with the analog-to-digital converter and in communication with the actuator, the controller operative to receive a digital pressure signal from the analog-to digital converter, and to control the actuator at least in part in response to the digital pressure signal.    
   
   
       24 . A method for regulating coolant fluid flow in a fluid cooled condenser of a vapor compression system including a compressor, the method comprising: 
 providing,    providing a discharge pressure sensor coupled to a discharge line of the compressor and operative to provide a discharge pressure signal representative of the discharge pressure;    providing a flow control valve having an inlet for receiving coolant fluid and an outlet, the outlet connected to an inlet of the condenser, the flow control valve operative to control the flow of Coolant fluid into the condenser;    providing a flow control valve actuator coupled to the flow control valve, the actuator operative to control the flow control valve;    providing a controller in communication with the discharge pressure sensor and in communication with the actuator, the controller operative to receive a discharge pressure signal and to control the actuator at least in part in response to the discharge pressure signal;    receiving signals at the controller representative of a monitored discharge pressure in a discharge line of the compressor; and    using the controller to provide a control signal to an actuator that controls a flow control valve that, in turn, controls coolant fluid flow into the condenser, the control signal being responsive at least in part to a difference between a set point pressure and the monitored discharge pressure.    
   
   
       25 . An apparatus for regulating coolant fluid flow, the apparatus comprising: 
 a vapor compression refrigeration system comprising:    a compressor having a discharge for compressed refrigerant;    a discharge line attached to the compressor discharge; and    a fluid cooled condenser having: 
 a first inlet coupled to the discharge line;  
 a first outlet for passing working fluid to an expansion device;  
 a second inlet for receiving coolant from a coolant recycling system; and  
 a second outlet for returning coolant to the coolant recycling system;  
   discharge pressure sensor means coupled to the discharge line for providing a discharge pressure signal representative of the discharge pressure;    flow control valve means having an inlet for receiving coolant fluid and an outlet, the outlet connected to the second inlet of the condenser, the flow control valve means for controlling the flow of the coolant fluid into the condenser;    flow control valve actuator means coupled to the flow control valve, the actuator means for controlling the flow control valve; and    controlling means in communication with the discharge pressure sensor and in communication with the actuator, the controlling means for receiving the discharge pressure signal and for automatically controlling the actuator at least in part in response to the discharge pressure signal.    
   
   
       26 . The apparatus of  claim 26 , wherein the fluid cooled condenser comprises: 
 a coolant-cooled heat exchanger.    
   
   
       27 . An apparatus for regulating coolant fluid flow, the apparatus comprising: 
 a discharge pressure sensor adapted to couple to a discharge line of a compressor and operative to provide a discharge pressure signal representative of a discharge pressure of the compressor;    a flow control valve having an inlet for receiving coolant fluid from a coolant recycling system and an outlet connected to an inlet of a fluid cooled condenser, the flow control valve operative to control the flow of the coolant fluid into the condenser;    a flow control valve actuator coupled to the flow control valve, the actuator operative to control the flow control valve; and    a controller in communication with the discharge pressure sensor and in communication with the actuator, the controller operative to receive the discharge pressure signal and to control the actuator at least in part in response to the discharge pressure signal.