Fault detection and diagnostic system for a refrigeration circuit

Patent metadata

Field	Value
Publication number	US-2016169572-A1
Application number	US-201414572375-A
Country	US
Kind code	A1
Filing date	Dec 16, 2014
Priority date	Dec 16, 2014
Publication date	Jun 16, 2016
Grant date	—

Abstract

A fault detection and diagnostics (FDD) system is provided for a refrigeration circuit having an evaporator and a compressor configured to circulate a refrigerant through the evaporator. The FDD system includes a communications interface configured to receive a measurement of a thermodynamic property affected by the refrigeration circuit and a processing circuit having a processor and memory. The processing circuit is configured to use the measured thermodynamic property to determine an expected suction entropy of the refrigerant at a suction of the compressor, use the expected suction entropy to determine an expected thermodynamic discharge property of the refrigerant at a discharge of the compressor, determine an actual thermodynamic discharge property of the refrigerant at the discharge of the compressor, and detect a fault in the refrigeration circuit by comparing the expected thermodynamic discharge property with the actual thermodynamic discharge property.

First claim

What is claimed is:

1 . A fault detection and diagnostics (FDD) system for a refrigeration circuit having an evaporator and a compressor configured to circulate a refrigerant through the evaporator, the FDD system comprising:
a communications interface configured to receive a measurement of a thermodynamic property affected by the refrigeration circuit; and a processing circuit having a processor and memory, wherein the processing circuit is configured to:
use the measured thermodynamic property to determine an expected suction entropy of the refrigerant at a suction of the compressor;
use the expected suction entropy to determine an expected thermodynamic discharge property of the refrigerant at a discharge of the compressor;
determine an actual thermodynamic discharge property of the refrigerant at the discharge of the compressor; and
detect a fault in the refrigeration circuit by comparing the expected thermodynamic discharge property with the actual thermodynamic discharge property.

2 . The FDD system of claim 1 , wherein:
the refrigerant absorbs heat from a secondary fluid in the evaporator; and the measured thermodynamic property is a measured temperature of the secondary fluid downstream of the evaporator.

3 . The FDD system of claim 2 , wherein determining the expected suction entropy comprises:
using the measured temperature of the secondary fluid and an expected approach of the evaporator to determine an expected suction temperature of the refrigerant at the suction of the compressor; and calculating the expected suction entropy corresponding to a saturated vapor state of the refrigerant at the expected suction temperature.

4 . The FDD system of claim 3 , wherein:
the communications interface is configured to receive a measured discharge pressure of the refrigerant at the discharge of the compressor; and determining the expected thermodynamic discharge property comprises using the measured discharge pressure and the expected suction entropy to calculate an expected isentropic discharge temperature of the refrigerant at the discharge of the compressor.

5 . The FDD system of claim 4 , wherein determining the expected thermodynamic discharge property comprises:
calculating an expected suction enthalpy corresponding to a saturated vapor state of the refrigerant at the expected suction temperature; using the isentropic discharge temperature and the measured discharge pressure to calculate an isentropic discharge enthalpy of the refrigerant at the discharge of the compressor.

6 . The FDD system of claim 5 , wherein determining the expected thermodynamic discharge property comprises:
identifying an isentropic efficiency of the compressor; and using the expected suction enthalpy, the isentropic discharge enthalpy, and the isentropic efficiency to calculate an expected discharge enthalpy of the refrigerant at the discharge of the compressor.

7 . The FDD system of claim 6 , wherein determining the expected thermodynamic discharge property comprises:
using the expected discharge enthalpy and the measured discharge pressure to calculate an expected discharge temperature of the refrigerant at the discharge of the compressor.

8 . The FDD system of claim 1 , wherein:
the expected thermodynamic discharge property is an expected discharge temperature; the actual thermodynamic discharge property is a measured discharge temperature; and detecting the fault in the refrigeration circuit comprises comparing the expected discharge temperature with the measured discharge temperature.

9 . The FDD system of claim 1 , wherein:
the expected thermodynamic discharge property is an expected amount of superheat corresponding to a difference between an expected discharge temperature of the refrigerant and a saturation temperature of the refrigerant at a measured discharge pressure; the actual thermodynamic discharge property is an actual amount of superheat corresponding to a difference between a measured discharge temperature of the refrigerant and the saturation temperature of the refrigerant at the measured discharge pressure; and detecting the fault in the refrigeration circuit comprises comparing the expected amount of superheat with the actual amount of superheat.

10 . The FDD system of claim 1 , wherein detecting the fault in the refrigeration circuit comprises:
calculating an amount by which the actual thermodynamic discharge property exceeds the expected thermodynamic discharge property; comparing the calculated amount with a threshold value; and determining that an evaporator fouling fault is detected in response to the calculated amount exceeding the threshold value.

11 . The FDD system of claim 1 , wherein:
the measured thermodynamic property is a measured suction temperature or pressure of the refrigerant at the suction of the compressor; and determining the expected suction entropy comprises calculating an expected entropy corresponding to a saturated vapor state of the refrigerant at the measured suction temperature or pressure.

12 . The FDD system of claim 11 , wherein:
the expected thermodynamic discharge property is an isentropic discharge property resulting from an ideal isentropic compression of the refrigerant from a saturated vapor at the suction of the compressor to superheated vapor at the discharge of the compressor; the actual discharge property is based on a measured discharge temperature and a measured discharge pressure of the refrigerant at the discharge of the compressor; and detecting the fault in the refrigeration circuit comprises comparing the isentropic discharge property with the actual discharge property.

13 . The FDD system of claim 12 , wherein detecting the fault in the refrigeration circuit comprises determining that a liquid carryover fault is detected in response to the isentropic discharge property exceeding the actual discharge property.

14 . A fault detection and diagnostics (FDD) system for a refrigeration circuit having an evaporator and a compressor configured to circulate a refrigerant through the evaporator, the FDD system comprising:
a communications interface configured to receive measurements from one or more sensors positioned to measure a thermodynamic property of the refrigerant at a suction of the compressor and a thermodynamic property of the refrigerant at a discharge of the compressor; and a processing circuit having a processor and memory, wherein the processing circuit is configured to:
use the measured thermodynamic properties to calculate enthalpy values comprising an actual suction enthalpy of the refrigerant at the suction of the compressor, an actual discharge enthalpy of the refrigerant at the discharge of the compressor, and an isentropic discharge enthalpy of the refrigerant at the discharge of the compressor;
use the calculated enthalpy values to calculate an isentropic efficiency of the compressor;
identify a threshold isentropic efficiency of the compressor; and
detect a fault in the refrigeration circuit by comparing the calculated isentropic efficiency with the threshold isentropic efficiency.

15 . The FDD system of claim 14 , wherein the measurements from the one or more sensors comprise:
a measured suction temperature or pressure of the refrigerant at the suction of the compressor; a measured discharge pressure of the refrigerant at the discharge of the compressor; and a measured discharge temperature of the refrigerant at the discharge of the compressor.

16 . The FDD system of claim 15 , wherein calculating the isentropic efficiency of the compr

Assignees

• Johnson Controls Tech Co

Inventors

• Noboa Homero L
• Boettcher Andrew J
• Beyhaghi Saman

Classifications

• F25B2700/21151

  at the suction side of the compressor · CPC title

• F25B2700/1933

  Suction pressures · CPC title

• F25B2700/1931

  Discharge pressures · CPC title

• F25B2339/047

  Water-cooled condensers · CPC title

• F25B25/005

  using primary and secondary systems · CPC title