Systems and methods for dynamic coil calibration

Patent metadata

Field	Value
Publication number	US-10830472-B2
Application number	US-201916241594-A
Country	US
Kind code	B2
Filing date	Jan 7, 2019
Priority date	Dec 20, 2018
Publication date	Nov 10, 2020
Grant date	Nov 10, 2020

Abstract

Systems and methods are disclosed that calibrate a defrost threshold used to determine when a heating, ventilating, and air conditioning (HVAC) system enters a defrost mode, and, more particularly, determine frost temperature differences used to determine the defrost threshold when the HVAC system is in a stable condition. A frost temperature difference is a difference between an outdoor ambient temperature and a refrigerant temperature. The HVAC system determines that it is in the stable condition by determining that a standard deviation of a current frost temperature difference from a previous frost temperature difference is below a standard deviation threshold. When the HVAC system is in the stable condition, the frost temperature differences are determined, and the defrost threshold is determined from the frost temperature differences.

First claim

What is claimed is:

1. A heating, ventilation, and air conditioning (HVAC) system at least partially located in an ambient environment, wherein the HVAC system comprises:
a coil configured to transmit refrigerant therethrough;
a first sensor configured to detect a refrigerant characteristic in the refrigerant transmitted through the coil;
a second sensor configured to detect an ambient characteristic of the ambient environment; and
a controller configured to:
receive a first refrigerant characteristic value and a second refrigerant characteristic value from the first sensor;
receive a first ambient characteristic value and a second ambient characteristic value from the second sensor, wherein the first refrigerant characteristic value is correlated to the first ambient characteristic value and the second refrigerant characteristic value is correlated to the second ambient characteristic value;
determine a first temperature difference value based on the first refrigerant characteristic value and the first ambient characteristic value;
determine a standard deviation based on the first temperature difference value and a set of other refrigerant characteristic values and other ambient characteristic values;
determine a defrost threshold based on the first temperature difference value in response to determining that the standard deviation is less than a standard deviation threshold; and
operate the coil in a defrost mode in response to determining that a second temperature difference value based on the second refrigerant characteristic value and the second ambient characteristic value exceeds the defrost threshold.

2. The HVAC system of claim 1 , wherein the coil is configured to:
transfer heat from the ambient environment to the refrigerant in a heating mode; and
transfer heat from the refrigerant to the ambient environment in the defrost mode.

3. The HVAC system of claim 1 , wherein the first sensor comprises a coil temperature sensor configured to detect refrigerant temperature in the coil.

4. The HVAC system of claim 1 , comprising a suction line, wherein the first sensor comprises a suction line temperature sensor configured to detect refrigerant temperature in the suction line.

5. The HVAC system of claim 1 , comprising a suction line, wherein the first sensor comprises a suction line pressure sensor configured to detect refrigerant pressure in the suction line, wherein the controller is configured to determine refrigerant temperature from the refrigerant pressure.

6. The HVAC system of claim 1 , wherein the second sensor comprises an outdoor ambient temperature sensor configured to detect ambient temperature.

7. The HVAC system of claim 1 , wherein the controller is configured to determine the first temperature difference value a duration of time after receiving the first refrigerant characteristic value and the first ambient characteristic value.

8. The HVAC of claim 1 , wherein the controller is configured to determine whether a threshold number of temperature difference values have been determined, wherein determining the standard deviation based on the first temperature difference value and the set of other refrigerant characteristic values and the other ambient characteristic values occurs in response to the controller determining that the threshold number of temperature difference values have been determined.

9. The HVAC of claim 1 , wherein the controller is configured to determine the standard deviation based on the first temperature difference value and a set of other refrigerant characteristic values and other ambient characteristic values by:
determine a threshold number of temperature difference values based on the set of other refrigerant characteristic values and other ambient characteristic values, wherein the threshold number of temperature difference values comprises the first temperature difference value; and
determine the standard deviation based on a difference between the first temperature difference value and the threshold number of temperature difference values.

10. The HVAC of claim 1 , wherein the controller is configured to:
determine whether a calibration time limit has been exceeded; and
determine the defrost threshold in response to determining that the calibration time limit has been exceeded.

11. A controller of a heating, ventilation, and air conditioning (HVAC) system, wherein the controller comprises a memory device and a processor, wherein the memory device comprises instructions for operating the HVAC system, wherein the processor, when executing the instructions, is configured to:
receive a plurality of refrigerant temperatures;
receive a plurality of outdoor ambient temperatures;
determine a plurality of frost temperature differences based on the plurality of refrigerant temperatures and the plurality of outdoor ambient temperatures;
determine a standard deviation based on the plurality of frost temperature differences;
determine a defrost threshold based on the plurality of frost temperature differences in response to determining that the standard deviation is less than a standard deviation threshold; and
after determining the defrost threshold, operate the HVAC system in a defrost mode in response to determining that a frost temperature difference exceeds the defrost threshold.

12. The controller of claim 11 , wherein the processor is configured to receive an additional refrigerant temperature, receive an additional outdoor ambient temperature and determine an additional frost temperature difference based on the additional refrigerant temperature and the additional outdoor ambient temperature, in response to determining that a threshold number of frost temperature differences have not been determined.

13. The controller of claim 12 , wherein the processor is configured to receive the additional refrigerant temperature, receive the additional outdoor ambient temperature, and determine the additional frost temperature difference, in response to determining that a calibration time limit has not been exceeded.

14. The controller of claim 11 , wherein the processor is configured to determine the defrost threshold based on a last threshold number of frost temperature differences of the plurality of frost temperature differences in response to determining that a calibration time limit has been exceeded.

15. A method that calibrates an active defrost threshold, wherein a heating, ventilation, and air conditioning (HVAC) system enters a defrost mode in response to a frost temperature difference exceeding the active defrost threshold, wherein the frost temperature difference comprises a difference between a refrigerant temperature and an outdoor ambient temperature, wherein the method comprises:
receiving information associated with the outdoor ambient temperature and the refrigerant temperature;
determining a measured frost temperature difference based on the outdoor ambient temperature and the refrigerant temperature;
determining a standard deviation based on the measured frost temperature difference; and
determining the active defrost threshold based on the measured frost temperature difference and the standard deviation.

16. The method of claim 15 , comprising receiving an indication that the HVAC system is exiting the defrost mode, wherein receiving the information associated with the outdoor ambient temperature and the refrigerant temperature occurs in response to receiving the indication that the HVAC system is exiting the defrost mode.

17. The method of claim 16 , wherein the indication is received based on the

Assignees

• Johnson Controls Tech Co

Inventors

• Hern Shawn A
• Mccune Tyler P
• Noor Aneek M
• Carlton Drew H
• Kaiser Cody J

Classifications

• F24F2140/20

  Heat-exchange fluid temperature · CPC title

• F24F11/42

  of outdoor units · CPC title

• F24F11/43 Primary

  of indoor units · CPC title

• F24F11/67

  Switching between heating and cooling modes · CPC title

• F24F11/65 Primary

  for selecting an operating mode · CPC title