Abstract:
The present invention provides for a system for calibrating operation of a compressor unit in a heating, ventilation, and air conditioning (HVAC) system. A measuring device measures an operating parameter of the HVAC system at a position where the measuring device is mounted on a refrigerant line of the HVAC system. The measuring device switches states when the value of the measured operating parameter reaches a switching value. A controller estimates a value of the first operating parameter at the position where the first measuring device is mounted on the refrigerant line, and the controller determines whether the estimated first operating parameter is within a threshold percentage of the switching value.

Description:
CROSS-REFERENCED APPLICATIONS 
     This application relates to co-pending U.S. patent application Ser. No. 14/173,686, entitled SYSTEM FOR CONTROLLING OPERATION OF AN HVAC SYSTEM, filed Feb. 5, 2014. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to calibration systems used in heating, ventilation, and air conditioning (HVAC) systems and, more particularly, to a system for calibrating operation of a compressor unit in an HVAC system. 
     The discharge pressure and suction pressure of a compressor in a heating, ventilation, and air conditioning (HVAC) system can be used as a diagnostic tool to troubleshoot problems with the system or to confirm that the system is operating normally. A model of the discharge pressure and suction pressure may be created from test data in a laboratory or manufacturing facility. 
     Once the HVAC system is installed, however, use of discharge pressure and suction pressure as a diagnostic tool is time consuming and expensive. Trained technicians may manually determine and utilize discharge and suction pressure in diagnostics. A pressure transducer may also be utilized as a tool for determining these pressures. Because of time and costs involved, suction and discharge pressure cannot often be used in the diagnostic process. What is needed are systems and methods for utilizing suction and discharge pressure as diagnostic tools in the calibration of HVAC systems. 
     SUMMARY 
     The present invention provides for a system for calibrating operation of a compressor unit in a heating, ventilation, and air conditioning (HVAC) system. A controller estimates the value of an operating parameter of the HVAC system at a position on a refrigerant line of the HVAC system where a measuring device is mounted to measure the operating parameter. The controller determines whether the estimated operating parameter is within a threshold percentage of the value of the operating parameter at which the measuring device switches states. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following Detailed Description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates an HVAC system; 
         FIG. 2  illustrates a compressor assembly and a control assembly; 
         FIG. 3  shows a flow chart of steps in a method for calibrating operation of a compressor unit in an HVAC system; and 
         FIG. 4  shows a graph of discharge pressure of a compressor unit versus outside temperature. 
     
    
    
     DETAILED DESCRIPTION 
     In the following discussion, numerous specific details are set forth to provide a thorough understanding of the present invention. However, those skilled in the art will appreciate that the present invention may be practiced without such specific details. In other instances, well-known elements have been illustrated in schematic or block diagram form in order not to obscure the present invention in unnecessary detail. Additionally, for the most part, details concerning well-known features and elements have been omitted inasmuch as such details are not considered necessary to obtain a complete understanding of the present invention, and are considered to be within the understanding of persons of ordinary skill in the relevant art. 
     Referring to  FIG. 1 , a first compressor unit  102  may be configured to operate in a heat pump, such as a heat pump system  100 . The first compressor unit  102  may be configured to compress low pressure refrigerant in vapor form to a higher pressure vapor. It will be understood by persons of ordinary skill that the first compressor unit  102  may operate within the heat pump system  100  in conjunction with other known components. 
     The heat pump system  100  may comprise an outdoor unit  103  operatively connected to an indoor unit  105 . The outdoor unit  103  may comprise the first compressor unit  102  having a suction line  142  and a discharge line  140 . The suction line  142  and the discharge line  140  may operatively connect the first compressor unit  102  with a reversing valve  144  at an output port  143  and an input port  141 , respectively. The reversing valve  144  may be configured to change the direction of flow of refrigerant within the heat pump system  100 . 
     A first transfer line  146  may operatively connect a first reversing port  147  with an outside heat exchanger unit  148  configured to condense high pressure vapor refrigerant to a liquid. An outdoor fan  166  may be configured to blow outside air over the heat exchange section of the outside heat exchanger unit  148 . 
     A distributor  158  may be operatively connected to the outlet of the outside heat exchanger unit  148  at a first end  160  and operatively connected to the inlet of an outside heater exchanger unit  148  at a second end  162 . Liquid tubing  164  may span the first end  160  and the second end  162  for transporting substantially liquid refrigerant from the outside heat exchanger unit  148  to an inside heat exchanger unit  154 . The distributor  158  may function as a metering device to regulate the amount of liquid refrigerant flowing into the inside heater exchanger unit  154 . 
     The inside heat exchanger unit  154  may be configured to evaporate liquid refrigerant to a vapor. An indoor blower  156  may be configured to pull air over coils of the inside heat exchanger unit  154  and to circulate air into the enclosed space. A second transfer line  150  may operatively connect a second reversing port  152  with the inside heat exchanger unit  154  to transfer refrigerant in low pressure vapor form back into the compressor unit  102  through the suction line  142 . 
     It will be understood by persons of ordinary skill that operation of the heat pump system  100  may be changed from heating to cooling by reversing flow within the system so that the inside heat exchanger unit  154  operates as a condenser and the outside heat exchanger unit operates as an evaporator. 
     Referring to  FIG. 2 , a control assembly  110  may be operationally coupled to the first compressor unit  102 . The control assembly  110  may comprise an electrical power converter, such as a first inverter  104  and an electronic first controller  106 . The first inverter  104  may be operationally connected to the first compressor unit  102  and configured to adjust the input voltage delivered to the first compressor unit  102 . 
     The first inverter  104  may be operationally connected to a first controller  106  configured to receive and send operation signals for operation of the HVAC system  100 . The first controller  106  may be an outside unit controller. 
     The first inverter  104  may be operationally coupled to the first compressor unit  102  and configured to modify the input voltage delivered to the first compressor unit  102 . The first inverter  104  may be operationally coupled to a first controller  106  configured to receive and send control signals for operation of the HVAC system  100 . 
     A compressor speed of the first compressor unit  102  may be controlled by the first inverter  104  receiving control signals from the first controller  106 . It will be understood that the compressor speed may be controlled without the use of an inverter as part of the control assembly  110 . In those embodiments, the first controller  106  may be configured to utilize other known variable-speed solutions, including but not limited to pulse width modulation of the compression process, or modulating the capacity by bypassing some of the refrigerant around the compression process (referred to as “unloading”). 
     The control assembly  110  may further comprise other control devices, such as an inside control unit  170  and a thermostat  172 . The inside control unit  170  may operate in conjunction with the first controller  106  to control operation of the indoor blower  156  and compressor unit  102 . The thermostat  172  may adjust the target temperature and have other commonly-used functions to control the environmental conditions of the enclosed space. 
     Referring to  FIG. 1 , the HVAC system  100  may further comprise a measuring device configured to measure an operating parameter of the HVAC system  100 . In some embodiments, the measuring device comprises a pressure switch  121  mounted on the discharge line  140  configured to monitor the discharge pressure of the first compressor unit  102 . The first controller  106  may be operationally connected to the pressure switch  121  to control the monitoring process and store data. 
     The pressure switch  121  may comprise an actuation pressure and a reset pressure. The actuation pressure is the discharge pressure at which the switch opens or closes from a normal position, and the reset pressure is the discharge pressure at which the switch returns to a normal position. It will be understood by persons of ordinary skill in the art that the pressure switch  121  may be configured to monitor other pressure values or operating parameters in the HVAC system that may be useful in the systems and methods disclosed in this description, including but not limited to the suction pressure. 
     Referring to  FIGS. 3 and 4 , the first controller  106  may be configured to perform one or more methods for calibrating operation of the HVAC system  100 . The HVAC system  100  may be configured to operate in a calibration mode. Calibration of the HVAC system  100  may comprise a comparison between a normal operation model  130  of the HVAC system  100  and a measured operating parameter of the HVAC system  100 . The model  130  may characterize normal operation as a function of one or more operating conditions. The model  130  shown in  FIG. 4  was prepared in laboratory tests using an HVAC system having a variable capacity compressor unit of 5 tons. It will be understood by persons of ordinary skill in the art that a model of normal operation may be prepared for different types of HVAC systems having one or more compressor units of different capacities. 
     In some embodiments, as shown in  FIG. 4 , the model  130  may comprise a characterization of the discharge pressure of the HVAC system  100  as a function of the outside ambient temperature in which the compressor unit  102  operates. The model  130  may be compared to a measured value of discharge pressure. The comparison may be used for diagnostic purposes or to determine or infer other useful information about the operation of the HVAC system  100 . 
     Referring to  FIG. 4 , a normal operation model  130  of discharge pressure as a function of the outside ambient pressure may comprise a data set  132 . The data set  132  may comprise one or more pressure curves  134   a - d  which represent the discharge pressures of the HVAC system at a set of outside ambient temperatures expected under normal operating conditions for a specific compressor speed where Speed 4 is the maximum speed of the compressor, Speed 1 is the minimum Speed of the compressor and Speeds 2 and 3 are between Speeds 1 and 4. For example, in some embodiments, Speed 1 corresponding to curve  134   d  may equal about 22 Hertz (Hz); Speed 2 corresponding to curve  134   c  may equal about 34 Hz; Speed 3 corresponding to curve  134   b  may equal about 46 Hz; and Speed 4 corresponding to curve  134   a  may equal about 58 Hz. It will be understood that range of speed used to characterize the normal operation model  130  may vary according to the configuration and capacity of the compressor used . . . . The data set  132  may be stored in a memory of the first controller  106 . 
     It will be further understood that other measuring devices may be used in place of the pressure switch  121  to obtain measured operating parameters of the HVAC system  100  that would be useful in the calibration processes disclosed in this description. For example, a bimetal temperature switch may be operationally coupled to the HVAC system and configured to measure a condensing temperature of the outdoor coil. A data set for normal operation of the HVAC system  100  may be developed as function of at least the condensing temperature in order to allow for a comparison to be made between normal expected operation and the measured operating parameter. 
     Referring to  FIG. 3 , a method for controlling operation of an HVAC system may comprise a first step  202  of verifying normal operation of the system  100 . This operation may include verifying that the compressor unit  102  is currently on. In other embodiments, the HVAC system may be in setback or away mode, when demand on the compressor unit  102  is low. 
     In a second step  204 , the controller assembly may verify that the outdoor temperature is in a calibration range. A calibration range may comprise a range of temperatures for a given range of operating speeds of the compressor unit  102  at which the pressure switch  121  changes states. For example, as shown in  FIG. 4 , the pressure switch  121  may be configured to reset at a discharge pressure of about 280 pounds per square inch gauge (psig) in a first temperature range T1 for a first speed range S1 of the compressor unit  102 . The pressure switch  121  may be configured to open at a discharge pressure of about 340 psig in a second temperature range T2 for the speed range S1 of the compressor unit  102 . 
     In a third step  206 , the first controller  106  may initiate a calibration mode, based on the verification that the outdoor temperature is in the calibration range. If the temperature is not in the calibration range, then the HVAC system  100  may continue in normal operation (step  202 ). 
     In a fourth step  208 , the first controller  106  may set the compressor unit  102  to operate at a first operating speed. For example, the compressor unit  102  may be operated at the Speed 4, which may correlate to a maximum demand on the compressor unit  102 . It will be understood by persons of ordinary skill in the art that the maximum demand will be compressor-specific and will vary based on the configuration and size of the compressor. 
     In a fifth step  210 , the compressor unit  102  may be operated for a first time period t 1 . The time period t 1  may comprise a pre-determined amount of time configured to increase the discharge pressure of the compressor unit  102  by a pre-selected amount. For example, the time period t 1  may comprise about 5 minutes, which may elevate the discharge pressure by about 127%, when the compressor unit  102  is operating at the Speed 2 and at an outside temperature of about 90° F. 
     The time period t 1  may be configured to change the discharge pressure so that the discharge pressure crosses the threshold at which pressure switch  121  changes state. For example, operating the compressor unit  102  at the Speed 2 for 5 minutes may result in the pressure switch  121  actuating. 
     In step  212 , the actuate event of the pressure switch  121  may be recorded in a memory of the first controller  106 . If the pressure switch  121  does not change states, the first controller  106  may generate a signal (step  214 ) to the compressor unit  102  to change demand to operate the compressor unit at a second operating speed. The change in demand may comprise a pre-selected percentage of change from the initial demand load, where the pre-selected percentage is configured to change the discharge pressure of the compressor unit  102 . In some embodiments, the discharge pressure is elevated to change the state of the pressure switch  121 . 
     In step  210 , the compressor unit  102  may be operated for a second time period t 2 . The time period t 2  may comprise a pre-determined amount of time configured to change the discharge pressure of the compressor unit  102  by a pre-selected amount. It will be understood that the time periods t 1  and t 2  may be based on the expected operational characteristics of the HVAC system  100 , including but not limited to the compressor unit capacity. 
     In step  216 , the current operating state of the HVAC system at the actuate event (recorded in step  212 ) may be recorded in a memory of the first controller  106 . The operating state may comprise known values of the HVAC system  100  and other data readily accessible through measurement by sensors or calculable based on known or measured data within the control assembly  110 , including data regarding operation of the compressor unit  102  taken from the inverter  104 . 
     In step  218 , the discharge pressure of the compressor unit  102  may be determined based on the operating state. For example, the discharge pressure may be calculated according to the systems and methods described in U.S. Application entitled “SYSTEM FOR CONTROLLING OPERATION OF AN HVAC SYSTEM”, which is here incorporated by reference. In other embodiments, a data set containing a characterization of discharge pressure, for example in a table format, may be stored in memory and the predicted discharge pressure may be determined by correlating one or more parameters of the operating state of the compressor unit  102  with the stored estimated value of the predicted discharge pressure. Alternatively, the estimated discharge pressure may be received by the first controller  106  from a separate device, including but not limited to a pressure transducer operationally connected to the HVAC system. 
     In step  220 , the first controller  106  may compare the calculated discharge pressure of step  218  to the value of the pressure at which the pressure switch  121  is configured to change states (referred to as the “switch setting”). The first controller  106  may determine whether the calculated discharge pressure is within a threshold percentage of the switch setting. In some embodiments, the threshold percentage may be in a range of −10% to +10% of the switch setting. The threshold percentage may be pre-selected and programmed into the controller  106  based on the acceptable operational tolerances of the HVAC system  100 . 
     In step  222 , the first controller  106  may be configured to generate and send a communication based on whether the calculated discharge pressure is within the pre-selected percentage of the switch setting. For example, if the calculated discharge pressure is outside the threshold percentage of the switch setting, the first controller  106  may send a communication indicating that the HVAC system  100  is not operating within acceptable parameters. 
     The communication may comprise a textual or visual summary of data regarding operation of the HVAC system  100 , including a characterization of discharge pressure of the compressor unit  102 , such as a chart, graph, or table. The communication may be sent to a display, stored in memory, or communicated directly to a third party. Referring to  FIG. 2 , the communication may be stored in a memory log  112  operationally connected to the first controller  106 . The predicted pressure may be sent to a display  114 . For example, a diagnostician may be connected to a port operationally connected to the controller  106  and may request a reading of the predicted discharge pressure, or may access the memory log  112  that contains a history of the predicted pressure for a given time period. In other embodiments, the communication generated by the first controller  106  in step  222  may be sent via a wireless device, for example as an email or text message. 
     In other embodiments, the measuring device, such as the pressure switch  121 , may be positioned at other positions within the HVAC system  100  for calibrating the pressure at that position, including but not limited to positioning a pressure switch  120  positioned on the suction line  142  for measuring suction pressure, as shown in  FIG. 1 . 
     Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Many such variations and modifications may be considered desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.