# US 12,007,134 B2 · Avoiding coil freeze in HVAC systems > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,007,134 B2 - Document ID: US12007134B2 - Status: Granted - Kind: B2 - Application number: 18/319,971 - Filed: 2023-05-18 - Published: 2023-09-14 - Granted: 2024-06-11 - Earliest claimed: 2019-09-24 - Assignees: Lennox Industries Inc. - Applicants: Lennox Industries Inc. - Inventors: Rakesh Goel - Web page: https://patentgrep.com/patent/US12007134B2 ## CPC - F24F 11/43: of indoor units - F24F 11/64: using pre-stored data - F24F 11/65: for selecting an operating mode - F25B 49/022: {Compressor control arrangements} - G05B 13/024: {in which a parameter or coefficient is automatically adjusted to optimise the performance} - F24F 2013/221: {to avoid the formation of condensate, e.g. dew} - F24F 2140/30: Condensation of water from cooled air - F25B 2600/025: by controlling speed - F25B 2700/197: of the evaporator - F25B 2700/2106: of fresh outdoor air - F25B 2700/21151: at the suction side of the compressor - F25B 2700/21174: of the refrigerant at the inlet of the evaporator - Y02B 30/70: Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating - F24F: AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING (removing dirt or fumes from areas where they are produced B08B15/00; vertical ducts for carrying away waste gases from buildings E04F17/02; tops for chimneys or ventilating shafts, terminals for flues F23L17/02) - F25B: REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS - G05B: CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS (systems for controlling or regulating non-electric variables G05D; systems for regulating electric or magnetic variables G05F; control devices or systems insofar as characterised by mechanical features only G05G) - Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS ## Abstract An HVAC system includes an evaporator. The evaporator includes a sensor configured to measure a property value (i.e., a saturated suction temperature or a saturated suction pressure) associated with saturated refrigerant flowing through the evaporator. The system includes a variable-speed compressor configured to receive the refrigerant and compress the received refrigerant. The system includes a controller communicatively coupled to the sensor and the variable-speed compressor. The controller monitors the property value measured by the sensor and detects a system fault, based on the monitored property value. In response to detecting the system fault, the controller operates the compressor in a freeze-prevention mode, which is configured to maintain the property value above a setpoint value by adjusting a speed of the variable-speed compressor. ## Claims ### Claim 1 A heating, ventilation, and air conditioning (HVAC) system, the HVAC system comprising: an evaporator configured to receive a refrigerant and transfer heat from a flow of air to the refrigerant, the evaporator comprising a sensor configured to measure a property value associated with saturated refrigerant flowing through the evaporator; a variable-speed compressor configured to receive the refrigerant and compress the received refrigerant; a controller communicatively coupled to the sensor and the variable-speed compressor, the controller configured to: monitor the property value measured by the sensor; detect a system fault, based on the monitored property value; and in response to detecting the system fault, operate the variable-speed compressor in a freeze-prevention mode, the freeze-prevention mode configured to maintain the monitored property value above a setpoint value by adjusting a speed of the variable-speed compressor. ### Claim 2 (depends on 1) The HVAC system of claim 1, wherein the controller is configured to detect the system fault by determining that the property value is less than or equal to a predefined threshold value. ### Claim 3 (depends on 1) The HVAC system of claim 1, wherein the controller is configured to: monitor the property value over a period of time; determine, based on a trend of the monitored property value over the period of time, an estimated value of the monitored property value at a future time, the future time following the period of time; detect an anticipated system fault, based on the estimated value of the monitored property value; and in response to detecting the anticipated system fault, operate the variable-speed compressor in the freeze-prevention mode. ### Claim 4 (depends on 1) The HVAC system of claim 1, wherein, during operation in the freeze-prevention mode, a discharge air temperature setpoint of the HVAC system is ignored. ### Claim 5 (depends on 2) The HVAC system of claim 2, wherein the controller is further configured to, in response to detecting the system fault: decrease the speed of the variable-speed compressor to a first decreased speed; following decreasing the speed of the variable-speed compressor to the first decreased speed, determine that the property value is not less than or equal to the predefined threshold value; and in response to determining that the property value is not less than or equal to the predefined threshold value, decrease the first decreased speed of the variable-speed compressor to a second decreased speed, the second decreased speed less than the first decreased speed. ### Claim 6 (depends on 5) The HVAC system of claim 5, wherein the controller is further configured to determine the second decreased speed based on a difference between the monitored property value the predefined threshold value following decreasing the speed of the variable-speed compressor to the first decreased speed. ### Claim 7 (depends on 1) The HVAC system of claim 1, further comprising: a discharge air temperature sensor configured to measure a temperature of a flow of air discharged by the HVAC system; and wherein the controller is communicatively coupled to the discharge air temperature sensor and further configured to: after causing the compressor to operate in the freeze-prevention mode, continue to monitor the property value; determine that the monitored property value is greater than a threshold value; and in response to determining that the monitored property value is greater than the threshold value, operate the variable speed compressor in a normal mode, the normal mode configured to maintain the temperature of the flow of air discharged by the HVAC system near a discharge temperature setpoint value by adjusting a speed of the variable speed compressor. ### Claim 8 A method of operating a heating, ventilation, and air conditioning (HVAC) system, the method comprising: monitoring a property value measured by a sensor, the sensor configured to measure a property value associated with saturated refrigerant flowing through an evaporator; detecting a system fault, based on the monitored property value; and in response to detecting the system fault, operate a variable-speed compressor of the HVAC system in a freeze-prevention mode, the freeze-prevention mode configured to maintain the monitored property value above a setpoint value by adjusting a speed of the variable-speed compressor. ### Claim 9 (depends on 8) The method of claim 8, further comprising detecting the system fault by determining that the property value is less than or equal to a predefined threshold value. ### Claim 10 (depends on 8) The method of claim 8, further comprising: monitoring the property value over a period of time; determining, based on a trend of the monitored property value over the period of time, an estimated value of the monitored property value at a future time, the future time following the period of time; detecting an anticipated system fault, based on the estimated value of the monitored property value; and in response to detecting the anticipated system fault, operating the variable-speed compressor in the freeze-prevention mode. ### Claim 11 (depends on 8) The method of claim 8, wherein during operation in the freeze-prevention mode, a discharge air temperature setpoint of the HVAC system is ignored. ### Claim 12 (depends on 9) The method of claim 9, further comprising, in response to detecting the system fault: decreasing the speed of the variable-speed compressor to a first decreased speed; following decreasing the speed of the variable-speed compressor to the first decreased speed, determining that the property value is not less than or equal to the predefined threshold value; and in response to determining that the property value is not less than or equal to the predefined threshold value, decreasing the first decreased speed of the variable-speed compressor to a second decreased speed, the second decreased speed less than the first decreased speed. ### Claim 13 (depends on 12) The method of claim 12, further comprising determining the second decreased speed based on a difference between the monitored property value the predefined threshold value following decreasing the speed of the variable-speed compressor to the first decreased speed. ### Claim 14 (depends on 8) The method of claim 8, further comprising: after causing the compressor to operate in the freeze-prevention mode, continuing to monitor the property value; determining that the monitored property value is greater than a threshold value; and in response to determining that the monitored property value is greater than the threshold value, operating the variable speed compressor in a normal mode, the normal mode configured to maintain a temperature of a flow of air discharged by the HVAC system near a discharge temperature setpoint value by adjusting a speed of the variable speed compressor. ### Claim 15 A controller for operating a heating, ventilation, and air conditioning (HVAC) system, the controller comprising: a memory configured to store a setpoint value associated with operating the HVAC system in a freeze-prevention mode; an input/output interface configured to: receive measurement data from a sensor, the configured to measure a property value associated with saturated refrigerant flowing through the evaporator; and transmit a control signal to a variable-speed compressor of the HVAC system; and a processor coupled to the memory and the input/output interface, the processor configured to: monitor the property value measured by the sensor; detect a system fault, based on the monitored property value; and in response to detecting the system fault, cause the input/output interface to transmit the control signal, the control signal instructing the variable-speed compressor to operate in the freeze-prevention mode, the freeze-prevention mode configured to maintain the monitored property value above the setpoint value by adjusting a speed of the variable-speed compressor. ### Claim 16 (depends on 15) The controller of claim 15, wherein the processor is configured to detect the system fault by determining that the property value is less than or equal to a predefined threshold value. ### Claim 17 (depends on 15) The controller of claim 15, wherein the processor is further configured to: monitor the property value over a period of time; determine, based on a trend of the monitored property value over the period of time, an estimated value of the monitored property value at a future time, the future time following the period of time; detect an anticipated system fault, based on the estimated value of the monitored property value; and in response to detecting the anticipated system fault, cause the input/output interface to transmit the control signal, the control signal instructing the variable-speed compressor to operate in the freeze-prevention mode. ### Claim 18 (depends on 15) The controller of claim 15, wherein during operation in the freeze-prevention mode, a discharge air temperature setpoint of the HVAC system is ignored. ### Claim 19 (depends on 16) The controller of claim 16, wherein the processor is further configured to, in response to detecting the system fault: decrease the speed of the variable-speed compressor to a first decreased speed; following decreasing the speed of the variable-speed compressor to the first decreased speed, determine that the property value is not less than or equal to the predefined threshold value; and in response to determining that the property value is not less than or equal to the predefined threshold value, decrease the first decreased speed of the variable-speed compressor to a second decreased speed, the second decreased speed less than the first decreased speed, wherein the second decreased speed is determined based on a difference between the monitored property value the predefined threshold value following decreasing the speed of the variable-speed compressor to the first decreased speed. ### Claim 20 (depends on 15) The controller of claim 15, wherein the processor is further configured to: after causing the compressor to operate in the freeze-prevention mode, continue to monitor the property value; determine that the monitored property value is greater than a threshold value; and in response to determining that the monitored property value is greater than the threshold value, cause the input/output interface to transmit a second control signal, the second control signal instructing the variable speed compressor to operate in a normal mode, the normal mode configured to maintain the temperature of the flow of air discharged by the HVAC system near a discharge temperature setpoint value by adjusting a speed of the variable speed compressor.