US20070256434A1

US20070256434A1 - Monitoring System for Detecting Low-Charge Condition in a Heat-Exchange System

Info

Publication number: US20070256434A1
Application number: US11/381,596
Authority: US
Inventors: Kwangtaek Hong; Gary Baker
Original assignee: DaimlerChrysler Co LLC
Current assignee: Old Carco LLC
Priority date: 2006-05-04
Filing date: 2006-05-04
Publication date: 2007-11-08

Abstract

A monitoring system for detecting a low-charge condition in a heat-exchange system is provided. The monitoring system has a first set of sensors located at the outlet of a compressor of the heat-exchange system. The first set of sensors monitor a plurality of first parameters. Based on the plurality of first parameters, a processor determines the low-charge condition in the heat-exchange system.

Description

FIELD OF THE INVENTION

The present invention generally relates to a heat-exchange system. More particularly, the present invention relates to a monitoring system for the heat-exchange system.

BACKGROUND OF THE INVENTION

A heat-exchange system such as an air-conditioning system or a refrigeration system helps to maintain a constant temperature of the surrounding environment. The heat-exchange system works with a specified amount of refrigerant and a specified amount of lubricating fluid. It maintains temperature of the environment by exchanging heat with the surroundings. The exchange of heat may include either heating or cooling the environment. However, the exchange of heat can reduce significantly if the amount of refrigerant is less than the specified amount. This condition is referred to as a low-charge condition. The exchange of heat can also reduce significantly if the heat-exchange system is overheated due to lack of proper lubrication. This condition is referred to as a low-lube condition. The low-charge condition and the low-lube condition may be caused due to leakage of refrigerant or due to leakage of lubricating fluid from the heat-exchange system. This adversely affects the performance of the heat-exchange system as its capacity to transfer heat is reduced. Thus, the heat-exchange system may take more time to cool or to heat the surroundings to a certain temperature, thereby increasing the fuel consumption. The low-lube condition can also damage the moving parts of the heat-exchange system such as a compressor due to lack of proper lubrication. Operating the compressor in a low-charge condition or a low-lube condition for a long period may cause excessive wear and may finally lead to a breakdown of the compressor. Further, the leakage of refrigerants, such as chlorofluorocarbons, may damage the environment by depleting the ozone layer. Thus, it is imperative to detect the low-charge and low-lube condition accurately and reliably to prevent the above-mentioned problems.
In an existing method for detecting a low-charge condition in a heat-exchange system, a sensor is installed at the outlet of a condenser. The sensor measures the temperature and pressure of the refrigerant at the outlet of a condenser. Based on the temperature and pressure, a sub-cool is calculated to detect a low-charge condition. However, such a system can reliably detect a low-charge condition only when the heat-exchange system employs a fixed displacement compressor. When a variable displacement compressor is employed, which is nowadays common in air-conditioners in automobiles, the temperature measured by the sensor is very close to ambient temperature. Thus, the sub-cool cannot be measured accurately and reliably. Further, the detection of the low-charge condition becomes even more difficult and unreliable in mid-ambient conditions (60-70 deg. F.).
In the light of the foregoing discussion, there is a need for a system which can accurately detect a low-charge and a low-lube condition in a heat-exchange system. The system should be capable of detecting the low-charge condition in a variable displacement compressor such as those employed in automobiles. Further, the system should be able to reliably detect the low-charge condition in mid-ambient conditions.

SUMMARY OF THE INVENTION

It is an object of the present invention to accurately detect a low-charge in a heat-exchange system.
Another object of the present invention is to accurately detect a low-lube condition in a heat-exchange system.
Another object of the present invention is to detect a low-charge condition even when the heat-exchange system employs a variable displacement compressor, such as in air-conditioners in automobiles.
Yet another object of the present invention is to reliably detect a low-charge condition when a heat-exchange system is operating in mid-ambient conditions.
Yet another object of the present invention is to provide a system for detecting a low-charge condition that can be economically implemented in a heat-exchange system.
The present invention provides a monitoring system to detect a low-charge condition in a heat-exchange system. The monitoring system includes a first set of sensors and a processor. The first set of sensors is located at an outlet of a compressor of the heat-exchange system and monitors a plurality of first parameters. Based on the plurality of first parameters, the processor determines the low-charge condition in the heat-exchange system.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments of the invention will hereinafter be described in conjunction with the appended drawings, provided to illustrate and not to limit the invention, wherein like designations denote like elements, and in which:
FIG. 1 shows a heat-exchange system, in accordance with an embodiment of the present invention;
FIG. 2 shows a monitoring system for detecting a low-charge condition in a heat-exchange system, in accordance with an embodiment of the present invention;
FIG. 3 is a flow-chart illustrating a method for detecting a low-charge condition in a heat-exchange system, in accordance with an embodiment of the present invention; and
FIG. 4 represents a graph illustrating variation of degree of superheat with respect to time for different percentages of refrigerant, in accordance with an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE VARIOUS EMBODIMENTS

The present invention relates to a monitoring system for detecting a low-charge condition in a heat-exchange system. The monitoring system has a first set of sensors and a processor. The first set of sensors is located at an outlet of a compressor in the heat-exchange system. The first set of sensors monitors a plurality of first parameters. Based on the plurality of first parameters, the processor determines the low-charge condition.
FIG. 1 shows a heat-exchange system 100, in accordance with an embodiment of the present invention. The examples of heat-exchange system 100 include, but are not limited to, an air-conditioning system and a refrigerator. Heat-exchange system 100 includes a compressor 102, at least one condenser-coil 104, at least one expansion-valve 106 and at least one evaporator-coil 108. Compressor 102 compresses a charge (or a refrigerant). It is lubricated using lubricating fluids such as silicon lubricants, synthetic lubricants, oils and greases. Examples of a compressor include, a reciprocating compressor, a rotary compressor, a screw compressor, a scroll a screw compressor, a centrifugal compressor, a screw compressor, and so forth. A charge is a chemical substance having a low boiling point that absorbs heat from the environment while evaporating. Examples of charge include, but are not limited to, ammonia, fluorocarbons, chlorofluorocarbons and carbon dioxide. Due to the compression, the temperature and pressure of the charge is raised. The charge flows into at least one condenser-coil 104 from compressor 102. In at least one condenser-coil 104, the charge condenses to a liquid state and thus dissipates heat to the environment. Thereafter, the charge flows through at least one expansion-valve 106 where its pressure drops quickly. The charge at low pressure, in at least one evaporator-coil 108, absorbs heat from the environment thereby producing a cooling effect.
In an exemplary embodiment of the present invention, heat-exchange system 100 can be an air-conditioning system. The air-conditioning system can include a first set of sensors 110 located at an outlet of compressor 102 and a processor 112. First set of sensors 110 measures a plurality of first parameters such as pressure and temperature of refrigerant in the air-conditioning system. Based on the plurality of first parameters, processor 112 determines a low-charge condition in the air-conditioning system. In an embodiment of the present invention, processor 112 can calculate a degree of superheat to determine the low-charge condition based on the plurality of first parameters. A degree of superheat for a fluid at a specific pressure is defined as the difference between the temperature of the fluid and the saturation temperature of the fluid at the specific pressure.
In an embodiment of the present invention, processor 112 can include a comparator 114. Comparator 114 can ascertain a low-charge condition based on a comparison between a degree of superheat of the refrigerant in the air-conditioning system and a pre-defined degree of superheat. The comparison is further described in detail in conjunction with FIG. 4.
In an embodiment of the present invention, the air-conditioning system can also include a second set of sensors 116. Second set of sensors 116 can monitor a plurality of second parameters associated with the air-conditioning system. Example of the plurality of second parameters include, a blower speed, a relative humidity, a temperature, an engine rotation per minute (RPM), and so forth. Based on the plurality of second parameters, the low-charge condition can be determined.
FIG. 2 shows a monitoring system 202 for detecting a low-charge condition in heat-exchange system 100, in accordance with an embodiment of the present invention. Heat-exchange system 100 operates compressor 102 to enable exchange of heat with the environment through the charge in heat-exchange system 100. The monitoring system 202 includes first set of sensors 110 and processor 112. First set of sensors 110 is located at the outlet of compressor 102 and monitors a plurality of first parameters. The plurality of first parameters includes the temperature and pressure of the charge at the outlet of compressor 102. Based on the plurality of first parameters, processor 112 determines the low-charge condition in heat-exchange system 100. In an embodiment of the present invention, processor 112 can compute a degree of superheat based on the plurality of first parameters to determine the low-charge condition.
In an embodiment of the present invention, processor 112 can include comparator 114. Comparator 114 can ascertain a low-charge condition based on a comparison between a degree of superheat of the charge in heat-exchange system 100 and a pre-defined degree of superheat. The comparison is further described in detail in conjunction with FIG. 4. At a specific pressure, the degree of superheat increases as the amount of charge in heat-exchange system 100 reduces. In an exemplary embodiment of the present invention, the pre-defined degree of superheat can be a degree of superheat corresponding to a condition when 100% charge is present in heat-exchange system 100.
In an embodiment of the present invention, monitoring system 202 can also include second set of sensors 116. Second set of sensors 116 monitors a plurality of second parameters associated with heat-exchange system 100. The plurality of second parameter includes a blower speed, a relative humidity, a temperature, and an engine rotation per minute (RPM). The plurality of second parameters can be used to determine a low-charge condition in heat-exchange system 100.
FIG. 3 is a flow-chart illustrating a method for detecting a low-charge condition in heat-exchange system 100, in accordance with an embodiment of the present invention. At step 302, a plurality of first parameters such as the pressure and temperature of the charge in heat-exchange system 100 is monitored at an outlet of compressor 102 in heat-exchange system 100. At step 304, a degree of superheat of the charge is calculated based on the plurality of first parameters. Thereafter, at step 306, the low-charge condition is ascertained based on a comparison between the degree of superheat of the charge and a pre-defined degree of superheat. The comparison is further described in detail in conjunction with FIG. 4. In an embodiment of the present invention, a plurality of second parameters such as a blower speed, a relative humidity, a temperature, and an engine rotation per minute (RPM) associated with heat-exchange system 100 can also be monitored for determining the low-charge condition.
In an embodiment of the present invention, a plurality of first parameters, associated with a lubricating fluid in heat-exchange system 100, is monitored. Examples of a first parameter include, but are not limited to, the pressure and temperature of the lubricating fluid. Based on the plurality of first parameters, a degree of superheat of the lubricating fluid is computed. Thereafter, a low-lube condition is ascertained based on a comparison between the degree of superheat of the lubricating fluid and a pre-defined degree of superheat.
FIG. 4 represents a graph 400 illustrating a variation of a degree of superheat with respect to time for different percentages of refrigerant, in accordance with an exemplary embodiment of the present invention. In graph 400, the X-axis represents time expressed in seconds; and the Y-axis represents a degree of superheat expressed in degree Fahrenheit (deg. F.). Hereinafter, graph 400 is explained with reference to a refrigerant in an air-conditioning system for the sake of clarity, though it is obvious to a person ordinarily skilled in the art that graph 400 is also applicable to the charge in heat-exchange system 100 associated with monitoring system 202. The degree of superheat bears an inverse relationship with the amount of the refrigerant in the air-conditioning system. When the amount of the refrigerant is 100%, the degree of superheat remains around 40 deg. F. at all instants of time for the refrigerant at a temperature of 50 deg. F. and a relative humidity (RH) of 20. Even with a slight reduction in the amount of refrigerant, the degree of superheat increases significantly. The degree of superheat increases to around 70 deg. F., when the amount of the refrigerant is reduced to 50%. The pre-defined degree of superheat, as described with reference to FIG. 1, FIG. 2 and FIG. 3, can be a degree of superheat corresponding to a specified amount of refrigerant in the air-conditioning system. For example, the pre-defined degree of superheat can be 70 deg. F. corresponding to 100% refrigerant. When the degree of superheat is higher than 70 deg. F., the low-charge condition can be ascertained. Similarly, the pre-defined degree of superheat can be 47 deg. F. corresponding to 85% refrigerant. When the degree of superheat is higher than 47 deg. F., the low-charge condition can be ascertained.
An advantage of the monitoring system as described earlier is that it accurately detects a low-charge and a low-lube condition in a heat-exchange system. The monitoring system also detects the low-charge condition even when the heat-exchange system is employing a variable displacement compressor such as in air-conditioners fitted in automobiles. The monitoring system also reliably detects the low-charge condition in mid-ambient condition. Further, the monitoring system can be economically implemented in the heat-exchange systems.
While the various embodiments of the invention have been illustrated and described, it will be clear that the invention is not limited only to these embodiments. Numerous modifications, changes, variations, substitutions, and equivalents will be apparent to those skilled in the art, without departing from the spirit and scope of the invention, as described in the claims.

Claims

1. A monitoring system for detecting a low-charge condition in a heat-exchange system, the heat-exchange system comprising a compressor, the monitoring system comprising:

a. a first set of sensors located at an outlet of the compressor, the first set sensors monitoring a plurality of first parameters; and

b. a processor for determining the low-charge condition based on the plurality of first parameters.

2. The monitoring system according to claim 1, wherein the processor further computes a degree of superheat based on the plurality of first parameters.

3. The monitoring system according to claim 2, wherein the processor comprises a comparator for ascertaining the low-charge condition, wherein the low-charge condition is ascertained based on a comparison between the degree of superheat and a pre-defined degree of superheat.

4. The monitoring system according to claim 1, wherein the plurality of first parameters comprises pressure and temperature at the outlet of the compressor.

5. The monitoring system according to claim 1 further comprising a second set of sensors for monitoring a plurality of second parameters associated with the heat-exchange system, the plurality of second parameters being used for determining the low-charge condition.

6. The monitoring system according to claim 5, wherein the plurality of second parameters is selected from the group comprising a blower speed, a relative humidity, a temperature, and an engine rotation per minute (RPM).

7. An air-conditioning system comprising:

a. a compressor for compressing a refrigerant;

b. at least one condenser-coil for dissipating heat to environment, the heat being dissipated by the refrigerant in the at least one condenser-coil;

c. at least one expansion-valve for dropping pressure of the refrigerant;

d. at least one evaporator-coil for absorbing the heat from the environment, the heat is being absorbed by the refrigerant in the at least one evaporator-coil;

e. a first set of sensors located at an outlet of the compressor, the first set of sensors measuring a plurality of first parameters; and

f. a processor for determining a low-charge condition in the air-conditioning system based on the plurality of first parameters.

8. The air-conditioning system according to claim 7, wherein the processor further calculates a degree of superheat based on the plurality of first parameters.

9. The air-conditioning system according to claim 8, wherein the processor comprises a comparator for ascertaining the low-charge condition, wherein the low-charge condition is ascertained based on a comparison between the degree of superheat and a pre-defined degree of superheat.

10. The air-conditioning system according to claim 7, wherein the plurality of first parameters comprises pressure and temperature at the outlet of the compressor.

11. The air-conditioning system according to claim 7 further comprising a second set of sensors for monitoring a plurality of second parameters associated with the air-conditioning system.

12. The air-conditioning system according to claim 11, wherein the plurality of second parameters is selected from the group comprising a blower speed, a relative humidity, a temperature, and an engine rotation per minute (RPM).

13. A method for detecting a low-charge condition in a heat-exchange system, the heat-exchange system comprising a compressor, the method comprising:

a. monitoring a plurality of first parameters, wherein the plurality of first parameters is monitored at an outlet of the compressor;

b. calculating a degree of superheat based on the plurality of first parameters; and

c. ascertaining the low-charge condition based on a comparison between the degree of superheat and a pre-defined degree of superheat.

14. The method of claim 13, wherein the plurality of first parameters comprises pressure and temperature at the outlet of the compressor.

15. The method of to claim 13 further comprising monitoring a plurality of second parameters associated with the heat-exchange system, the plurality of second parameters being used for determining the low-charge condition.

16. The method of claim 15, wherein the plurality of second parameters is selected from the group comprising a blower speed, a relative humidity, a temperature, and an engine rotation per minute (RPM).

17. A method for detecting a low-lube condition in a heat-exchange system, the method comprising:

a. monitoring a plurality of first parameters associated with a lubricating fluid in the heat-exchange system;

b. computing a degree of superheat of the lubricating fluid based on the plurality of first parameters; and

c. ascertaining the low-lube condition based on a comparison between the degree of superheat of the lubricating fluid and a pre-defined degree of superheat.