Avoiding coil freeze in HVAC systems

Patent metadata

Field	Value
Publication number	US-11460207-B2
Application number	US-201916580486-A
Country	US
Kind code	B2
Filing date	Sep 24, 2019
Priority date	Sep 24, 2019
Publication date	Oct 4, 2022
Grant date	Oct 4, 2022

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. This prevents or delays freezing of the evaporator during operation of the system during the detected system fault.

First claim

What is claimed is:

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, wherein the property value is one of a saturated suction temperature and a saturated suction pressure;
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, thereby delaying freezing of the evaporator during operation of the HVAC system during the detected system fault.

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

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, wherein the property value is one of a saturated suction temperature and a saturated suction pressure;
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, thereby delaying freezing of the evaporator during operation of the HVAC system during the detected system fault.

9. 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.

10. 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.

11. The method of claim 8 , wherein during operation in the freeze-prevention mode, a discharge air temperature setpoint of the HVAC system is ignored.

12. 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.

13. 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.

14. 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.

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, wherein the property value is one of a saturated suction temperature and a satur

Assignees

• Lennox Ind Inc

Inventors

• Goel Rakesh

Classifications

• F25B49/022 Primary

  Compressor control arrangements · CPC title

• F24F11/64

  using pre-stored data · CPC title

• G05B13/024

  in which a parameter or coefficient is automatically adjusted to optimise the performance · CPC title

• F25B2700/21151

  at the suction side of the compressor · CPC title

• F24F2140/30

  Condensation of water from cooled air · CPC title