Abstract:
A specially designed electronic expansion valve control system is provided for use with a refrigerant-based air conditioning circuit having a compressor, a condenser coil, an electronic expansion valve and an evaporator coil fluid coupled in series. The control system includes a unit control and an expansion valve control. The unit control is operative to receive compressor operation-related signal information and responsively generate at least one output signal representative of the received compressor operation-related signal information. The expansion valve control is operative to receive from the unit control only the at least one output signal, and to receive from one of the coils coil operation-related signal information, and to responsively output a control useable to control the expansion valve, the control signal being related in a predetermined manner to the signals received by the expansion valve control.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of the filing date of provisional U.S. patent application No. 61/663,960 filed Jun. 25, 2012. The entire disclosure of the provisional application is hereby incorporated herein by this reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to refrigerant circuit control apparatus and methods, and, in a representatively illustrated embodiment thereof, more particularly provides specially designed apparatus and methods for controlling an electronic expansion valve in a heat pump refrigerant circuit. 
     In previously proposed control systems for controlling an electronic expansion valve in a refrigerant circuit, it was necessary to transmit multiple output signals from a unit control to an expansion valve control, such multiple output signals representing a variety of system and component operating characteristics representatively including (1) a first stage compressor operation signal, (2) a second stage compressor operation signal, (3) a heat pump heating mode signal (as determined by a reversing valve position signal), (4) a heat pump cooling mode signal (as determined by a reversing valve position signal), and (5) a defrost mode signal. Multiple corresponding operational characteristic and mode inputs of various types also had to be constructed and connected to the unit control. These previous necessities undesirably increased the complexity and cost of the unit control and thus the overall complexity of the overall air conditioning system, due to the additional structure and signal generating capability required to be incorporated in the unit control. 
     As can be readily seen from the foregoing, a need exists for simpler, less complex, and less expensive apparatus and methods for controlling an electronic expansion valve in an air conditioning system such as a heat pump system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a heat pump refrigerant circuit having therein an electronic expansion valve (EEV) controlled by a specially designed control system embodying principles of the present invention; 
         FIG. 2  is a schematic flow diagram illustrating the operation of the control system utilizing a sensed coil temperature differential to set the EEV to heating or cooling operation; 
         FIG. 3  is a table showing representative operating parameters of the heat pump refrigerant circuit in its cooling and heating modes; 
         FIG. 4  is a schematic diagram of an alternate embodiment of the control system. 
         FIG. 5  is a schematic flow diagram illustrating an optional operation of the control system utilizing the coil outlet temperature to set the EEV to heating or cooling operation; 
         FIG. 6  is a schematic flow diagram illustrating an optional operation of the control system utilizing the coil inlet temperature rise when compared to an off time reference coil saturation temperature to set the EEV to heating or cooling operation; and 
         FIG. 7  is a schematic flow diagram illustrating an optional operation of the control system utilizing the coil inlet temperature rise per unit time to set the EEV to heating or cooling operation; 
     
    
    
     DETAILED DESCRIPTION 
     Schematically depicted in  FIG. 1  is a refrigerant-based air conditioning system  10  having an associated control system  12  embodying principles of the present invention. System  10  is representatively a heat pump system having heating, cooling and defrost modes, but (without a subsequently referenced reversing valve portion) could alternatively be a cooling-only system, and includes a compressor  14 , a condenser coil  16 , an electronic expansion valve (EEV)  18  and an evaporator coil  20  interconnected in series as shown in by a refrigerant line  22  in which a schematically depicted reversing valve  23  is also operatively connected. 
     With the system  10  in its cooling mode the reversing valve  23  in a first position thereof causes the refrigerant to be routed from the compressor  14 , as indicated by the solid line flow arrows C, sequentially through the condenser coil  16 , the expansion valve  18 , the evaporator coil  20  and then back to the compressor  14 . With the reversing valve  23  in a second position thereof and the system  10  in its heating mode, the refrigerant is routed from the compressor  14 , as indicated by the dashed line flow arrows H, sequentially through the evaporator coil  20 , the expansion valve  18 , the condenser coil  16  and then back to the compressor  14 . 
     The control system  12  includes (1) an electronic expansion valve control  24 , incorporating therein a pre-programmed microprocessor  24   a , operative to output a system operational mode control signal  26  to the valve  18  to position it to optimally control the system superheat and thus the performance of the system  10  in both heating and cooling modes, and (2) a unit control  28  that receives a system operation request  30 , from a room thermostat  32  located in a conditioned space served by the system  10 , and responsively outputs a single digital control signal  36  to the electronic expansion valve control  24 . The single digital signal  36  is indicative of the run state (i.e., “on” or “off”) of the compressor  14 . In addition to uniquely generating the single digital signal  36  which transmits compressor operation-related signal information to the electronic expansion valve control  24 , the unit control  28  is conventionally operative to generate other system control signals which are not illustrated herein and are not pertinent to the present invention. 
     As an alternative to the signal  36  being transmitted from the unit control  28  to the electronic expansion valve control  24 , the signal  36  can be eliminated and replaced with an operation request signal  30   a  sent to the electronic expansion valve control  24  (in addition to the thermostat signal  30  sent to the unit control  28 ) and transmitting similar compressor operation-related signal information to the electronic expansion valve control  24 . 
     Via electrical lead pairs L 1 ,L 2  and L 3 ,L 4  from thermistors TH 1 ,TH 2  respectively sensing evaporator coil refrigerant inlet and outlet temperatures (when the system  10  is in its cooling mode), the valve control  24  also receives evaporator coil operational temperature signals. Using the signals from the evaporator coil  20  and the single digital signal  36  from the unit control  28 , the valve control  24  (via the microprocessor  24   a ) determines the mode of operation of the system  10  (for example, cooling, heating or defrost mode of the heat pump) and responsively adjusts the operational mode control signal  26  output to the expansion valve  18  to appropriately position and/or modulate the expansion valve  18  as determined by the microprocessor  24   a . Both the coil temperature signals transmitted to the valve control  24  via leads L 1 -L 4  and the operation request signals  30 , 30   a  from the thermostat  32  may be generally referred to herein as “compressor operation-related signal information”. 
     While the illustrated expansion valve control technique is illustrated utilized in conjunction with a heat pump system, it could also be implemented in conjunction with a cooling-only refrigerant circuit (i.e., one without the illustrated reversing valve  23 ). Preferably, as just described, the coil inlet and outlet temperatures transmitted to the electronic expansion valve control  24  are those of the evaporator (indoor) coil  20 . However, as will be readily appreciated by those of skill in this particular art, such coil inlet and outlet temperatures could alternatively be those of the condenser (outdoor) coil  16 . 
     In various previously proposed electronic expansion valve control systems, multiple output signals were transmitted from a unit control to an expansion valve control and typically included (1) a first stage compressor operation signal, (2) a second stage compressor operation signal, (3) a heat pump heating mode signal (as determined by a reversing valve position signal), (4) a heat pump cooling mode signal (as determined by a reversing valve position signal), and (5) a defrost mode signal. This undesirably increased the cost and complexity of the unit control due to the additional structure and signal generating capability it required. 
     As illustrated in the representative embodiment of the control system  12  shown in  FIG. 1 , only a single digital output signal (signal  36 ) is needed from the unit control  28 , with the signal  36  representing only compressor operational characteristic information (representatively compressor run/off state information). All of the other input signals (the previously described temperature signals from the evaporator coil  20 ) and their necessary hardware are already available, with such signals being sent from the coil  20  to the valve control  24  instead of to the unit control  28 , thereby permitting the unit control  28  to be appreciably less complex and expensive. 
     Turning now to the flow chart of  FIG. 2 , the operation of the electronic expansion valve control system  12  will be more fully described. A listing of the definitions of the parameters referenced in the flow chart is set forth below: 
     T in =value of a temperature sensor on the input of the coil  20   
     T out =value of a temperature sensor on the output of the coil  20   
     Delay_Control_Time=a variable time to delay 
     Min_Heat_Delta=a variable defining minimum temperature delta across coil  20  expected during heating operation 
     Max_Cool_Delta=a variable defining maximum temperature delta across coil  20  expected during cooling operation 
     Upon start-up of the electronic expansion valve control system  12  at step  40 , a query is made at step  42  as to whether the compressor  14  is active (as indicated by the unit control output signal  36  in  FIG. 1 ). If the compressor  14  is not active a transfer is made to step  44  at which the expansion valve  18  is set for a compressor-off state and the system cycles at step  42  until the compressor  14  is activated, at which point a transfer is made from step  42  to step  46 . At step  46  the value of a delay control timer is set to zero. 
     Next, a transfer is made from step  46  to step  48  at which a query is made as to whether the time on a delay control timer is equal to the predetermined delay control time. If it is not, the system cycles at step  48  until it is, at which point a transfer is made from step  48  to step  50 . At step  50  a query is made as to whether the value of T in −T out  is greater that of Min_Heat_Delta. If it is, a transfer is made from step  50  to step  52  at which the expansion valve  18 , via the control signal  26  from the valve control  24 , is appropriately set for heating operation of the cooling system  10 . A transfer is then made back to step  42 . 
     If at step  50  T in −T out  is not greater than Min_Heat_Delta, a transfer is made from step  50  to step  54  at which a query is made as to whether T in −T out  is less than Max_Cool_Delta. If it is not, a transfer is made from step  54  back to step  46 . If it is, a transfer is made from step  54  to step  56  at which the expansion valve  18 , via the control signal  26  from the valve control  24 , is appropriately set for cooling operation of the system  10 . A transfer is then made from step  56  back to step  42 . If the answer to the query at step  50  is positive, a transfer is made from step  50  to step  52  at which the expansion valve is set to its heating mode. 
     As previously mentioned, the illustrated air conditioning system  10  is representatively a heat pump system capable of both cooling and heating a conditioned space, but could alternatively be a cooling-only system. The same control logic of  FIG. 2  could also be utilized in conjunction with such cooling-only system. However, step  52  in the  FIG. 2  flow chart would not come into play since this alternative system would not have a heating capability. 
     Turning now to the flow chart of  FIG. 5  showing an alternate control scheme to that described in  FIG. 2 , the operation of the electronic expansion valve control system  12  will be more fully described. Steps in the  FIG. 5  flow chart identical to those in the  FIG. 2  flow chart have been given the same reference numbers. A listing of the definitions of the parameters referenced in the  FIG. 5  flow chart is set forth below: 
     T out =value of a temperature sensor on the outlet of the coil  20   
     Delay_Control_Time=a variable time to delay 
     Min_Heat_Range=a variable defining minimum expected temperature value at the outlet of coil  20  during heating operation 
     Max_Cool_Range=a variable defining maximum expected temperature value at the outlet of coil  20  during cooling operation 
     Upon start-up of the  FIG. 5  electronic expansion valve control system, at step  40 , a query is made at step  42  as to whether the compressor  14  is active (as indicated by the unit control output signal  36  in  FIG. 1 ). If the compressor  14  is not active a transfer is made to step  44  at which the expansion valve  18  is set for a compressor-off state and the system cycles at step  42  until the compressor  14  is activated, at which point a transfer is made from step  42  to step  46 . At step  46  the value of a delay control timer is set to zero. 
     Next, a transfer is made from step  46  to step  48  at which a query is made as to whether the time on a delay control timer is equal to the predetermined delay control time. If it is not, the system cycles at step  48  until it is, at which point a transfer is made from step  48  to step  58 . At step  58  a query is made as to whether the value of T out  is greater that of Min_Heat_Range. If it is, a transfer is made from step  58  to step  52  at which the expansion valve  18 , via the control signal  26  from the valve control  24 , is appropriately set for heating operation of the system  10 . A transfer is then made back to step  42 . 
     If at step  58  T out  is not greater than Min_Heat_Range, a transfer is made from step  58  to step  60  at which a query is made as to whether T out  is less than Max_Cool_Range. If it is not, a transfer is made from step  60  back to step  42 . If it is, a transfer is made from step  60  to step  56  at which the expansion valve  18 , via the control signal  26  from the valve control  24 , is appropriately set for cooling operation of the system  10 . A transfer is then made from step  56  back to step  42 . 
     As previously mentioned, the illustrated air conditioning system  10  is representatively a heat pump system capable of both cooling and heating a conditioned space, but could alternatively be a cooling-only system. The same control logic of  FIG. 5  could also be utilized in conjunction with such cooling-only system. However, step  52  in the  FIG. 5  flow chart would not come into play since this alternative system would not have a heating capability. 
     Turning now to the flow chart of  FIG. 6  showing an alternate control scheme to that described in  FIG. 2 or 5 , the operation of the electronic expansion valve control system  12  will be more fully described. Steps in the  FIG. 6  flow chart identical to those in the  FIG. 2  flow chart have been given the same reference numerals. A listing of the definitions of the parameters referenced in the flow chart is set forth below: 
     T in =Value of a temperature sensor on the input of evaporator coil  20   
     T inoff =Temperature on the input of the coil with system in off state 
     T inon =Temperature on the input of the coil with system in on state 
     Delay_Control_Time=a variable time to delay 
     Heat_Cycle_Max_Delta=A variable that defines the maximum temperature differential expected during heating operation across coil  20 . 
     Cool_Cycle_Min_Delta=a variable defining minimum temperature differential expected during cooling operation across coil  20 . 
     Upon start-up of the  FIG. 6  electronic expansion valve control system, at step  40 , a query is made at step  42  as to whether the compressor  14  is active (as indicated by the unit control output signal  36  in  FIG. 1 ). If the compressor  14  is not active a transfer is made to step  62  at which the expansion valve  18  is set for a compressor-off state, the Tinoff variable is set equal to Tin measured value, and the system cycles at step  42  until the compressor  14  is activated, at which point a transfer is made from step  42  to step  46 . At step  46  the value of a delay control timer is set to zero. 
     Next, a transfer is made from step  46  to step  48  at which a query is made as to whether the time on a delay control timer is equal to the predetermined delay control time. If it is not, the system cycles at step  48  until it is, at which point a transfer is made from step  48  to step  64 . At step  64  the T inon  variable is set equal to T in  and a transfer is made from step  64  to step  66 . At step  66  a query is made as to whether the value of T inoff −T inon  is less than that of Heat_Cycle_Max_Delta. If it is, a transfer is made from step  66  to step  52  at which the expansion valve  18 , via the control signal  26  from the valve control  24 , is appropriately set for heating operation of the cooling system  10 . A transfer is then made back to step  42 . 
     If at step  66  T inoff −T inon  is greater than Heat_Cycle_Max_Delta, a transfer is made from step  66  to step  68  at which a query is made as to whether T inoff −T inon  is greater than Cool_Cycle_Min_Delta. If it is not, a transfer is made from step  68  back to step  42 . If it is, a transfer is made from step  68  to step  56  at which the expansion valve  18 , via the control signal  26  from the valve control  24 , is appropriately set for cooling operation of the system  10 . A transfer is then made from step  56  back to step  42 . 
     As previously mentioned, the illustrated air conditioning system  10  is representatively a heat pump system capable of both cooling and heating a conditioned space, but could alternatively be a cooling-only system. The same control logic of  FIG. 6  could also be utilized in conjunction with such cooling-only system. However, step  52  in the  FIG. 6  flow chart would not come into play since this alternative system would not have a heating capability. 
     Turning now to the flow chart of  FIG. 7  showing an alternate control scheme to that described in  FIGS. 2, 5, and 6 , the operation of the electronic expansion valve control system  12  will be more fully described. Steps in the  FIG. 7  flow chart identical to those in the  FIG. 2  flow chart have been given the same reference numerals. A listing of the definitions of the parameters referenced in the flow chart is set forth below: 
     T in-1 =Value of a temperature sensor on the input of the evaporator coil at time t n-1    
     T in =Value of a temperature sensor on the input of the evaporator coil at time t n    
     t n-1 =sample time at which a compressor operation call is made as seen by the electronic expansion valve control  12  via signal  36  from the unit control  28 . 
     t n =sample time at which T in  is taken 
     m n =The slope of the T in  temperature change over time t n −t n-1    
     Delay_Control_Time=a variable time to delay 
     Min_Heat_Slope=a variable that defines the minimum temperature change per unit time expected during heating operation across coil  20 . 
     Max_Cool_Slope=a variable defining maximum temperature change per unit time expected during cooling operation across coil  20 . 
     Upon start-up of the electronic expansion valve control system  12  at step  40 , a query is made at step  42  as to whether the compressor  14  is active (as indicated by the unit control output signal  36  in  FIG. 1 ). If the compressor  14  is not active a transfer is made to step  62  at which the expansion valve  18  is set for a compressor-off state, the T inoff  variable is set equal to T in  measured, and the system cycles at step  42  until the compressor  14  is activated, at which point a transfer is made from step  42  to step  46 . At step  46  the value of a delay control timer is set to zero. 
     Next, a transfer is made from step  46  to step  48  at which a query is made as to whether the time on a delay control timer is equal to the predetermined delay control time. If it is not, the system cycles at step  48  until it is, at which point a transfer is made from step  48  to step  70 . At step  70  a sample Ti n-1  is taken at time t n-1  stored in the electronic expansion valve control board  24  and a transfer is made to step  72 . At step  72  an additional sample T in  is taken at predetermined interval of time t n  from t n-1 . A transfer is then made from step  72  to step  76  where the rate of temperature change per unit time, t n-1 −t n , is calculated. Following the rate of temperature change calculation a transfer is made from step  76  to step  78 . At step  78  a query is made as to whether the value of m n  is greater than that of Min_Heat_Slope. If it is, a transfer is made from step  78  to step  52  at which the expansion valve  18 , via the control signal  26  from the valve control  24 , is appropriately set for heating operation of the cooling system  10 . A transfer is then made back to step  42 . 
     If at step  78  m n  is less than Min_Heat_Slope, a transfer is made from step  78  to step  80  at which a query is made as to whether m n  is less than Max_Cool_Slope. If it is not, a transfer is made from step  80  to step  74  where the coil temperature variable T in-1  is set equal to the instantaneous measurement of T in  at the evaporator coil  20  outlet  48  and the temperature variable T n-1  is then set to 0. A transfer is then made back to step  72 . If mn is less than Max_Cool_Slope, a transfer is made from step  80  to step  56  at which the expansion valve  18 , via the control signal  26  from the valve control  24 , is appropriately set for cooling operation of the system  10 . A transfer is then made from step  56  back to step  42 . 
     As previously mentioned, the illustrated air conditioning system  10  is representatively a heat pump system capable of both cooling and heating a conditioned space, but could alternatively be a cooling-only system. The same control logic of  FIG. 7  could also be utilized in conjunction with such cooling-only system. However, step  52  in the  FIG. 7  flow chart would not come into play since this alternative system would not have a heating capability. 
     The table shown in  FIG. 3  sets forth, by way of non-limiting example, illustrative parameter values for the heating and cooling modes of the system  10 —namely, representative examples of compressor outlet temperature and evaporator coil inlet and outlet temperatures in the heating and cooling modes. Such temperatures are for a representative medium temperature air conditioning type system design. The fundamental relationships among the three points will remain somewhat constant for high temperature and low temperature refrigeration, but the absolute values of the tabled points will be variable. 
     As can be seen from the  FIG. 3  table, during the cooling mode the temperature at the inlet to the evaporator coil  20  (point  1  in the table) will be between 35-55° F. depending on the indoor and outdoor ambient loads. At this time the evaporator coil outlet/suction temperature (point  2  in the table) will be in the 45-65° F. range with a discharge temperature (point  3  in the table) in the range of 110-220° F., which is common for medium temperature air conditioning systems. In the heating mode, the evaporator inlet temperature will be in the −5-+60° F. range and the evaporator coil outlet temperature will be in the 5-70° F. range with discharge temperatures fluctuating between 145° F. and 180° F. 
     When the representatively illustrated heat pump system  10  is operating in a heating mode, the coil  20  will be functioning as a condenser and thus have refrigerant entering temperatures in the range of 145-180° F. The control system  12  would thus have ample difference between the discharge temperatures at point  3  in heating mode and the evaporator outlet/suction temperature during cooling mode to perform a simple relative analysis. 
     Therefore, with respect to the indoor coil  20 , the electronic expansion valve  18  would cease to modulate/meter the refrigerant flow if the absolute value of the temperature sensed by thermistor TH 2  rose to above a predefined point selected between the minimum discharge temperature in heating and the maximum evaporator coil outlet temperature in the cooling mode or vice versa for the outdoor coil  16  in the opposite modes). During this condition the expansion valve  18  would either open to a fully stroked position or remain static at the last modulated position. In either event it would be desirable, to minimize the pressure drop across the expansion valve  18  during the heating mode (with no expansion valve modulation being performed) to utilize a check valve (not shown herein) device that permits refrigerant flow to bypass the expansion valve. 
     An alternate embodiment  12   a  of the previously described  FIG. 1  control system  12  portion of the refrigerant-based air conditioning system  10  is schematically shown in  FIG. 4 . The control system  12   a  is identical to the control system  12  with the exceptions that in addition to the previously described compressor run state signal  36  (i.e., compressor on/off) the electronic expansion valve control  24  also receives from the unit control  28  an operating stage signal  80  (i.e., compressor first stage/second stage. Via the microprocessor  24   a  the output signal  26  to the electronic expansion valve  18  is controlled as a function of the signals  36 , 80 , and the evaporator coil operational signals (transmitted via the leads L 1 ,L 2 ,L 3  and L 4 ) received by the electronic expansion valve control  24 . 
     The representatively illustrated control systems  12  and  12   a  provide several advantages over previously proposed systems used to control an electronic expansion valve in a refrigerant-based air conditioning circuit. For example, in such previously proposed systems it was necessary to transmit multiple output signals from the unit control to the expansion valve control, such multiple output signals representing a variety of system and component operating characteristics which, as previously mentioned herein, including (1) a first stage compressor operation signal, (2) a second stage compressor operation signal, (3) a heat pump heating mode signal (as determined by a reversing valve position signal), (4) a heat pump cooling mode signal (as determined by a reversing valve position signal), and (5) a defrost mode signal. Multiple corresponding operational characteristic and mode inputs of various types also had to be constructed and connected to the unit control. These previous necessities undesirably increased the complexity and cost of the unit control, and thus the overall complexity of the overall air conditioning system, due the additional structure and signal generating capability required to be incorporated into the unit control. 
     In contrast, in the representatively illustrated expansion valve control systems  12  and  12   a  of the present invention only compressor-related information is output from the unit control  28  to the valve control  24 —compressor run state information in the control system  12 , and compressor run state and stage information in the control system  12   a . Moreover, in each of the control systems  12  and  12   a  coil information (via leads L 1 -L 4 ) is routed to the expansion valve control  24  instead of to the unit control  28 . 
     The foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.