Non-invasive temperature diagnostic method

Abstract

A Non-invasive Temperature Diagnostic (NTD) method for evaluating proper operation, undercharge, or other faults of a Heating, Ventilating, Air Conditioning (HVAC) system based on measurements of temperature or HVAC system airflow. Measurements may comprise return-air wetbulb temperature (RWT), return-air drybulb temperature (RDT), supply-air drybulb temperature (SDT), actual temperature split (ATS) equals RDT minus SDT, required temperature split (RTS) based on RDT and RWT, delta temperature split (DTS) equals ATS minus RTS, outdoor-air temperature (OAT), suction temperature (ST), liquid temperature (LT), or liquid over ambient (LOA) based on LT minus OAT. The method can diagnose at least one HVAC system fault selected from a group consisting of: refrigerant restriction, low airflow, low-cooling capacity, condenser/evaporator heat exchanger fault, refrigerant undercharge/overcharge, non-condensables, failed capacitor, HVAC blower fan relay fault, and condenser contactor fault. The ATS and airflow measured before and after correcting HVAC system faults are used to calculate an energy-efficiency improvement.

1 . A Non-invasive Temperature Diagnostic (NTD) method for a Heating, Ventilating, Air Conditioning (HVAC) system, the method comprising:
 measuring HVAC system temperatures comprising a Return-air Drybulb Temperature (RDT), a Return-air Wetbulb Temperature (RWT), a Supply-air Drybulb Temperature (SDT), an Outdoor Air Temperature (OAT), a refrigerant Suction Temperature (ST), and a refrigerant Liquid Temperature (LT); and   entering the HVAC system temperatures into a processor memory and the processor performing processing steps comprising:
 calculating an Actual Temperature Split (ATS) across an evaporator coil based on the RDT minus the SDT; 
 calculating a Required Temperature Split (RTS) based on the RWT and the RDT; 
 calculating a Delta Temperature Split (DTS) based on the ATS minus the RTS; 
 calculating a Liquid Over Ambient (LOA) temperature based on the LT minus the OAT; 
 diagnosing a proper Refrigerant Charge and Airflow (RCA) based on the DTS and the LOA or diagnosing at least one HVAC system fault; and 
 providing at least one message from the processor to a visual display or an audible device, wherein the at least one message is selected from the group consisting of:
 verifying the proper RCA indicating acceptable HVAC system performance, and 
 reporting the at least one HVAC system fault with information to enable repair of the at least one HVAC system fault. 
 
   
     
     
         2 . The method of  claim 1 , wherein diagnosing the proper RCA or diagnosing the at least one HVAC system fault is performed without currently connecting refrigerant pressure sensors to the HVAC system or obtaining prior pressure measurements of the HVAC system. 
     
     
         3 . The method of  claim 1 , wherein and the at least one HVAC system fault comprises a refrigerant undercharge fault with the processor estimating a refrigerant undercharge amount based on the DTS and at least one other temperature measurement selected from the group consisting of: the ST, and the LOA; when the refrigerant undercharge fault is diagnosed and reporting the refrigerant undercharge fault and the refrigerant undercharge amount to add to the HVAC system to correct the refrigerant undercharge fault. 
     
     
         4 . The method of  claim 1 , wherein the diagnosing the proper RCA or the diagnosing the at least one HVAC system fault is based on at least one diagnosing selected from the group consisting of:
 diagnosing a failed capacitor fault when a measured capacitance (μF) of a capacitor serving a condenser fan motor, a compressor, or an HVAC system blower fan is less than 80 percent of a rated capacitance of the capacitor,   diagnosing an HVAC system blower fan relay fault or a condenser contactor fault based on at least one second diagnostic wherein a measured fan G current serving the HVAC system blower fan is greater than 0.1 Amps (A) or a condenser contactor is pitted,   diagnosing a refrigerant restriction fault or an evaporator heat exchanger fault based on at least one third diagnostic selected from the group consisting of: the DTS is between minus 11 degrees Fahrenheit (F) and −6 F, the ST is greater than the SDT, the LT is less than the OAT, and the LOA is less than −2 F,   diagnosing a low airflow fault based on at least one fourth diagnostic selected from the group consisting of: a measured airflow is less than 350 cubic feet per minute per ton (CFM/ton) of cooling, the DTS is greater than 2 F when the ST is less than 50 F, and the DTS is greater than 3 F when the ST is less than 53 F,   diagnosing a low cooling capacity fault based on at least one fifth diagnostic selected from the group consisting of: the DTS is negative, and the SDT is greater than the RDT,   diagnosing a condenser heat exchanger fault based on at least one sixth diagnostic selected from the group consisting of: the DTS is less than −0.5 F when the LOA is greater than 9 F, the ST is less than 55 F when the OAT is less than or equal to 100 F, and the ST is less than 60 F when the OAT is greater than 100 F,   diagnosing the proper RCA based on at least one seventh diagnostic selected from the group consisting of: the DTS is between −2 F and 2 F when the LOA is between 4 F and 10 F, and an estimated refrigerant undercharge based on the DTS is less than a minimum threshold,   diagnosing a refrigerant undercharge fault based on at least one eighth diagnostic selected from the group consisting of: the DTS is less than or equal to −2 F when the ST is greater than the SDT, and the LOA is greater than 3 F,   diagnosing a refrigerant overcharge fault based on at least one ninth diagnostic selected from the group consisting of: the DTS is between −4 F and 0 F when the LOA is between 0 F and 8 F and the ST is less than 53 F, the DTS is between −1 F and 0.5 F when the LOA is between −1 F and 11 F and the ST is less than 57 F, and the DTS is between −5 F and −1 F when the LOA is between 0 F and 4 F and the ST is between 62 F and 66 F, and   diagnosing a non-condensable fault based on at least one tenth diagnostic selected from the group consisting of: the DTS is between −9 F and 1 F when the OAT is less than 80 F, the DTS is between −10 F and −1 F when the OAT is greater than or equal to 8° F., the ST is between 52 F and 76 F, and the LOA is between 0 F and 6 F.   
     
     
         5 . The method of  claim 1 , further including calculating an energy efficiency improvement of the HVAC system based on a ratio of the ATS measured before correcting the at least one HVAC system fault to the ATS measured after correcting the at least one HVAC system fault. 
     
     
         6 . The method of  claim 1 , further including diagnosing the proper RCA or the at least one HVAC system fault, based on at least one diagnosing step selected from the group consisting of: diagnosing a failed capacitor, diagnosing an HVAC system blower fan relay fault, diagnosing a condenser contactor fault, diagnosing a refrigerant restriction fault, diagnosing a low airflow fault, diagnosing a low cooling capacity fault, diagnosing a condenser heat exchanger fault, diagnosing evaporator heat exchanger fault, diagnosing the proper RCA, diagnosing a refrigerant undercharge fault, diagnosing a refrigerant overcharge fault, and diagnosing a non-condensable fault, wherein the diagnosing steps of the at least one diagnosing step performed are performed in an order comprising: diagnosing the failed capacitor fault, diagnosing the failed HVAC blower fan relay fault, diagnosing the failed condenser contactor fault, diagnosing the refrigerant restriction fault, diagnosing the low airflow fault, diagnosing the low cooling capacity fault, diagnosing the condenser heat exchanger fault, diagnosing the evaporator heat exchanger fault, diagnosing the proper RCA, diagnosing the refrigerant undercharge fault, diagnosing the refrigerant overcharge fault, diagnosing the non-condensable fault. 
     
     
         7 . A Non-invasive Temperature Diagnostic (NTD) method for a Heating, Ventilating, Air Conditioning (HVAC) system, the method comprising:
 measuring HVAC system temperatures comprising a Return Drybulb Temperature (RDT), a Return Wetbulb Temperature (RWT), a Supply Drybulb Temperature (SDT), an Outdoor Air Temperature (OAT), a Suction Temperature (ST), and a refrigerant Liquid Temperature (LT); and   entering the HVAC system temperatures into a processor memory and the processor performing processing steps comprising:
 monitoring the HVAC system temperatures reaching an equilibrium condition based on a rate of change of the HVAC system temperatures with respect to time; 
 calculating an Actual Temperature Split (ATS) across an evaporator coil based on the RDT minus the SDT; 
 calculating a Required Temperature Split (RTS) based on the RWT and the RDT; 
 calculating a Delta Temperature Split (DTS) based on the ATS minus the RTS; 
 calculating a Liquid Over Ambient (LOA) temperature based on the LT minus the OAT; 
 diagnosing a proper Refrigerant Charge and Airflow (RCA) based on the DTS and the LOA or diagnosing at least one HVAC system fault; and 
 reporting at least one message from the processor to a visual display or audible device, wherein the at least one message is selected from the group consisting of:
 the HVAC system has not reached the equilibrium condition for diagnostic testing, 
 the proper RCA indicating the HVAC system is operating properly, and 
 the at least one HVAC system fault with information to enable repair of the at least one HVAC system fault. 
 
   
     
     
         8 . The method of  claim 7 , wherein diagnosing the proper RCA or diagnosing the at least one HVAC system fault is performed without currently connecting refrigerant pressure sensors to the HVAC system or obtaining prior refrigerant pressure measurements of the HVAC system. 
     
     
         9 . The method of  claim 7 , wherein the at least one message is selected from the group consisting of: check and repair the HVAC system to achieve the equilibrium condition for diagnostic testing, check for proper airflow, check a capacitor, check a fan relay, check or replace an air filter, check or clean the evaporator coil, check or clean a condenser coil, check for refrigerant leaks with an electronic leak detector or soap solution, check an expansion valve or a heat pump reversing valve, check for a refrigerant restriction, check for non-condensable nitrogen, air, water vapor in the HVAC system, check HVAC compressor faults such as a failed capacitor or a failed contactor, or check other faults. 
     
     
         10 . The method of  claim 7 , wherein the processor diagnoses the proper RCA or the at least one HVAC system fault, in a processing order comprising: diagnosing a refrigerant restriction fault, diagnosing a low airflow fault, diagnosing a low cooling capacity fault, diagnosing a condenser heat exchanger fault, diagnosing an evaporator heat exchanger fault, diagnosing the proper RCA, diagnosing a refrigerant undercharge fault, diagnosing a refrigerant overcharge fault, and diagnosing a non-condensable fault. 
     
     
         11 . The method of  claim 7 , further including calculating an energy efficiency improvement of the HVAC system based on a ratio of the ATS measured before correcting the HVAC system fault to the ATS measured after correcting the HVAC system fault. 
     
     
         12 . The method of  claim 7 , wherein the at least one HVAC system fault comprises a refrigerant undercharge with the processor estimating a refrigerant undercharge amount based on the DTS and at least one other temperature measurement selected from the group consisting of: the ST, and the LOA; when the refrigerant undercharge fault is diagnosed and reporting the refrigerant undercharge fault and the refrigerant undercharge amount to add to the HVAC system to correct the refrigerant undercharge fault. 
     
     
         13 . The method of  claim 12 , wherein diagnosing and estimating the refrigerant undercharge amount further includes subsequently correcting the refrigerant undercharge by adding an amount of refrigerant through a suction line without connecting a pressure sensor to a liquid line to reduce refrigerant venting. 
     
     
         14 . A Non-invasive Temperature Diagnostic (NTD) method for a Heating, Ventilating, Air Conditioning (HVAC) system, the method comprising:
 measuring HVAC system temperatures comprising a Return-air Drybulb Temperature (RDT), a Return-air Wetbulb Temperature (RWT), a Supply-air Drybulb Temperature (SDT), an Outdoor Air Temperature (OAT), a refrigerant Suction Temperature (ST), and a refrigerant Liquid Temperature (LT);   measuring an HVAC system airflow; and   entering the HVAC system temperatures and the HVAC system airflow into a processor memory and the processor performing processing steps comprising:
 calculating an Actual Temperature Split (ATS) across an evaporator coil based on the RDT minus the SDT; 
 determining a Required Temperature Split (RTS) based on the RWT and the RDT; 
 calculating a Delta Temperature Split (DTS) based on the ATS minus the RTS; 
 calculating a Liquid Over Ambient (LOA) temperature based on the LT minus the OAT; 
 diagnosing a proper Refrigerant Charge and Airflow (RCA) based on the DTS and the LOA or diagnosing at least one HVAC system fault to subsequently correct when the at least one HVAC system fault is diagnosed; and 
 reporting at least one message to a visual display or an audible device wherein the at least one message is selected from the group consisting of:
 verifying the proper RCA indicating the HVAC system is operating properly, and 
 reporting the at least one HVAC system fault with information to enable repair of the at least one HVAC system fault. 
 
   
     
     
         15 . The method of  claim 14 , further including diagnosing the at least one HVAC system fault comprising a refrigerant undercharge fault and estimating a refrigerant undercharge amount based on the DTS and at least one other measurement selected from the group consisting of: the ST, the LOA, and the HVAC system airflow; and reporting the refrigerant undercharge fault and the refrigerant undercharge amount to add to the HVAC system to correct the refrigerant undercharge fault. 
     
     
         16 . The method of  claim 14 , further including correcting a refrigerant undercharge fault by adding an amount of refrigerant through a suction line without connecting a pressure sensor to a liquid line to reduce refrigerant venting. 
     
     
         17 . The method of  claim 14 , further including calculating an energy efficiency improvement of the HVAC system based on a ratio of the ATS times the HVAC system airflow measured before correcting the at least one HVAC system fault to the ATS times the HVAC system airflow measured after correcting the at least one HVAC system fault. 
     
     
         18 . The method of  claim 14 , wherein the diagnosing the proper RCA or the diagnosing the at least one HVAC system fault is based on at least one diagnosing selected from the group consisting of:
 diagnosing a failed capacitor fault when a measured capacitance in micro Farads (μF) of a capacitor serving a condenser fan motor, a compressor, or an HVAC system blower fan is less than 80 percent of a rated capacitance of the capacitor,   diagnosing an HVAC system blower fan relay fault or a condenser contactor fault based on at least one second diagnostic wherein a measured fan G current serving the HVAC system blower fan is greater than 0.1 Amps (A) or a condenser contactor is pitted,   diagnosing a refrigerant restriction fault or an evaporator heat exchanger fault based on at least one third diagnostic selected from the group consisting of: the DTS is between minus 11 degrees Fahrenheit (F) and −6 F, the ST is greater than the SDT, the LT is less than the OAT, and the LOA is less than −2 F,   diagnosing a low airflow fault based on at least one fourth diagnostic selected from the group consisting of: a measured airflow is less than 350 cubic feet per minute per ton (CFM/ton) of cooling, the DTS is greater than 2 F when the ST is less than 50 F, and the DTS is greater than 3 F when the ST is less than 53 F,   diagnosing a low cooling capacity fault based on at least one fifth diagnostic selected from the group consisting of: the DTS is negative, and the SDT is greater than the RDT,   diagnosing a condenser heat exchanger fault based on at least one sixth diagnostic selected from the group consisting of: the DTS is less than −0.5 F when the LOA is greater than 9 F, the ST is less than 55 F when the OAT is less than or equal to 100 F, and the ST is less than 60 F when the OAT is greater than 100 F,   diagnosing the proper RCA based on at least one seventh diagnostic selected from the group consisting of: the DTS is between −2 F and 2 F when the LOA is between 4 F and 10 F, and an estimated refrigerant undercharge based on the DTS is less than a minimum threshold,   diagnosing the refrigerant undercharge based on at least one eighth diagnostic selected from the group consisting of: the DTS is less than or equal to −2 F when the ST is greater than the SDT, and the LOA is greater than 3 F,   diagnosing a refrigerant overcharge fault based on at least one ninth diagnostic selected from the group consisting of: the DTS is between −4 F and 0 F when the LOA is between 0 F and 8 F and the ST is less than 53 F, the DTS is between −1 F and 0.5 F when the LOA is between −1 F and 11 F and the ST is less than 57 F, and the DTS is between −5 F and −1 F when the LOA is between 0 F and 4 F and the ST is between 62 F and 66 F, and   diagnosing a non-condensable fault based on at least one tenth diagnostic selected from the group consisting of: the DTS is between −9 F and 1 F when the OAT is less than 80 F, the DTS is between −10 F and −1 F when the OAT is greater than or equal to 80 F, the ST is between 52 F and 76 F, and the LOA is between 0 F and 6 F.   
     
     
         19 . The method of  claim 14 , further including;
 diagnosing the at least one HVAC system fault comprising a refrigerant undercharge based on the DTS and at least one other measurement;   estimating a refrigerant undercharge amount based on the HVAC system airflow and a Delta Superheat (DSH) temperature wherein the DSH is based on an Actual Superheat (ASH) minus a Required Superheat (RSH) temperature and the ASH equals the ST minus an Evaporator Saturation Temperature (EST) and the EST is based on a Suction Pressure (SP) measurement and the RSH is based on the OAT and the RWT; and   reporting the at least one HVAC system fault and indicating the refrigerant undercharge amount.   
     
     
         20 . The method of  claim 14 , further including:
 diagnosing the at least one HVAC system fault comprising a non-condensable fault based on the DTS and at least one other measurement;   diagnosing the non-condensable fault further based on a Condenser Over Ambient (COA) temperature being greater than a calculated COA threshold temperature wherein the COA is based on the OAT and the COA is equal to a Condenser Saturation Temperature (CST) minus the OAT and the CST is based on a Liquid Pressure (LP) measurement; and   reporting the at least one HVAC system fault indicating the non-condensable fault.   
     
     
         21 . The method of  claim 14 , further including:
 diagnosing the at least one HVAC system fault comprising a refrigerant restriction based on the DTS and at least one other measurement;   diagnosing the refrigerant restriction further based on the LT is less than the OAT, and the LOA is less than minus 2 degrees Fahrenheit (F) or −2 F;   diagnosing the refrigerant restriction further based on an Evaporator Saturation Temperature (EST) being less than a calculated EST threshold temperature and the EST is based on a Suction Pressure (SP) measurement; and   reporting the at least one HVAC system fault indicating the refrigerant restriction fault.   
     
     
         22 . The method of  claim 14 , further including:
 diagnosing the at least one HVAC system fault comprising a refrigerant overcharge based on the DTS and at least one other measurement;   estimating a refrigerant overcharge amount based on a Delta Subcooling (DSC) temperature wherein the DSC is based on an Actual Subcooling (ASC) temperature minus a Required Subcooling (RSC) temperature and the ASC is equal to a Condenser Saturation Temperature (CST) minus the LT and the CST is based on a Liquid Pressure (LP), wherein the RSC provided by a manufacturer or is a default value; and   reporting the at least one HVAC system fault indicating the refrigerant overcharge amount.