Patent Application
20050126190
1. Field of the Invention
This invention generally relates to air conditioning and refrigeration systems. More particularly, this invention relates to detecting a loss of refrigerant charge within an air conditioning or refrigeration system. Furthermore, this invention can also be employed for identifying malfunctioning of the expansion valve.
2. Description of the Related Art
Air conditioning and refrigeration systems need certain refrigerant charge within the system, to achieve a desired amount of cooling within a building, for example. If the refrigerant charge is reduced below a certain level, damage to the system components, such as the compressor, is likely.
Typical causes of inadequate refrigerant charge amounts include insufficient charge at the factory or during installation in the field or leakage through damaged components or loose connections.
It is necessary to detect a loss of refrigerant charge as early as possible to avoid interrupting system operation, especially during high ambient temperature conditions, when adequate cooling at full-load operation is essential to end users. It is also prudent and critical to diagnose a malfunctioning expansion valve as early as possible to avoid system component damage.
While proposals have been made for detecting a loss of refrigerant charge, they are not universally applicable. Further, known arrangements do not provide an early enough indication or are not reliable enough because they can be mistaken for some other system malfunctions such as an evaporator airflow blockage, compressor damage or a plugged distributor. Using known techniques and trying to differentiate between such failure modes requires exhaustive troubleshooting. Furthermore, other consequences of the refrigerant charge loss, such as detection of low suction pressure (i.e., by tripping on a low-pressure switch), usually occur late in the process and applying them may not prevent compressor damage.
In addition, the need for detecting refrigerant charge loss becomes especially acute with the introduction of systems that utilize high pressure refrigerants as R410A and R744. Systems with these refrigerants are more prone to leaks.
Furthermore, expansion valves in refrigerant systems may malfunction (for example, due to contamination). This in turn may lead to improper system operation and other component damage. Timely detection of such problems is useful to prevent extensive damage and to reduce maintenance.
This invention provides a unique early detection of refrigerant charge loss or expansion valve malfunction in the system. The disclosed techniques are useful to prevent compressor damage and to avoid prolonged shutdowns and expensive repairs.
This invention utilizes information regarding a superheat value within a refrigerant system for monitoring an amount of refrigerant charge in the system.
One method includes determining a refrigerant superheat value within the refrigerant system. By determining a difference between the measured superheat value and an expected superheat value and comparing that difference to a selected threshold, a loss of refrigerant charge can be monitored.
One example method includes determining the superheat value based on an actual operating vapor temperature and a saturated vapor temperature. The difference between the saturated vapor temperature and the actual operating vapor temperature is the superheat value.
In one example, the method includes determining a superheat value of refrigerant between the compressor and evaporator coil. In another example, the refrigerant system includes an economizer heat exchanger and an evaporator heat exchanger. In this example, the method includes determining superheat value of the refrigerant between the compressor and the evaporator coil or between the compressor and the economizer heat exchanger.
In another example, a discharge temperature of refrigerant exiting the compressor is determined to provide a confirmation check on the determined superheat value(s). Using known relationships between the superheat value(s) and the discharge temperature provides the ability to verify the superheat information and, therefore, to determine if refrigerant loss of charge occurs within the system. Similar procedures and techniques are useful to identify a malfunctioning expansion valve.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows.
The expansion device 34 operates in a known manner to allow the liquid refrigerant to expand and flow into a conduit 36 in the form of a cold, low pressure refrigerant. This refrigerant then flows through an evaporator 38 where the refrigerant absorbs heat from air that flows across the evaporator coil. Subsequently, cool air cools the desired space as known. The refrigerant exiting the evaporator 38 flows through a conduit 40 to the suction port 24 of the compressor 22 where the cycle continues. In one example, the system 20 may also be used as a heat pump where the just-described flow is reversed as known. Some example systems operate in both modes as known and can be utilized as well.
In the example of
The embodiment of
The controller 50 determines the amount of superheat by subtracting a saturated vapor temperature from the actual operating vapor temperature, which is the temperature of the refrigerant normally determined in the line located between the compressor entrance and exit from the evaporator heat exchanger. The actual operating vapor temperature in
The refrigerant system will normally operate within an acceptable superheat level or range of levels. The controller 50 in this example is programmed to determine a difference between the determined superheat (i.e., based upon the difference between the saturated vapor temperature and the actual operating vapor temperature) and the expected superheat level. When the difference exceeds a selected threshold, the controller 50 determines that the amount of refrigerant within the system is too low.
In another example, the controller monitors the superheat level over time to determine changes in the superheat value. In this embodiment, the controller 50 uses known or predicted temperature patterns and is capable of determining when the superheat value begins increasing as a result of the expansion device 34 not being able to open any further to maintain the required superheat levels. The example arrangements are capable of providing an early indication of low refrigerant amount such that appropriate corrective action can be taken to avoid any potential compressor and system damage.
A conduit 66 carries refrigerant from the economizer heat exchanger 60 to another inlet economizer port 68 of the compressor 22 at some intermediate pressure. In this example, a pressure sensor 72 and a temperature sensor 74 are associated with the conduit 66 to provide pressure and temperature information to the controller 50 regarding the refrigerant entering the compressor economizer port 68.
The superheat value of refrigerant in the section between the economizer heat exchanger 60 and the economizer port 68 of the compressor 22 is determined using sensors 70, 72 and 74 in a fashion similar to the way sensors 42, 44 and 46 are applied in the embodiment of this invention shown in
Like the embodiment of
Given this description, those skilled in the art will be able to determine how to select an appropriate threshold for a particular system arrangement and a particular refrigerant used in that system.
The inventive arrangement not only provides an indication of potentially reduced refrigerant amount, but also provides the ability to determine if the expansion device 34 or 64 is malfunctioning. As noted above, when the superheat is increasing above a predetermined value, that is an indication that the expansion device cannot open any further to maintain the expected superheat level. It is possible under some circumstances for the expansion device 34 or 64 to be malfunctioning and not opening wide enough to accommodate the desired condition. Accordingly, the determination made by the controller 50 provides an indication of a potential expansion device malfunction.
When the controller 50 determines that the superheat value is outside of the expected range, in one example, the controller provides a visual indication on a display screen. In another example, the controller provides an audible alarm or audible signal regarding the determination that the refrigerant amount is too low.
In another example, the controller 50 automatically shuts down the system and provides the indication regarding the reason for the shutdown.
In the embodiments of
It should be noted the previous description would apply to a case of multiple evaporator heat exchangers, multiple economizer heat exchangers or both. In this case the refrigerant superheat can be analyzed independently for each evaporator or economizer heat exchanger section to determine if there is a refrigerant charge loss or malfunctioning expansion valve.
The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this invention. The scope of legal protection given to this invention can only be determined by studying the following claims.
