Refrigeration – With indicator or tester – Condition sensing
Reexamination Certificate
1999-01-19
2001-03-27
Tanner, Harry B. (Department: 3744)
Refrigeration
With indicator or tester
Condition sensing
C062S131000
Reexamination Certificate
active
06205798
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of refrigeration systems for heating and cooling in a controlled environment. In particular, the invention relates to an algorithm for automatically determining whether there are leaks between the high and low-pressure sides of the refrigeration system.
BACKGROUND OF THE INVENTION
Refrigeration systems are used in many applications for heating and cooling a controlled environment, including homes, buildings and cargo boxes of transport trucks, trains, ships or planes. Before operating a refrigeration system in a cooling or heat/defrost mode, it is desirable to determine whether the refrigeration system
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, is in an operational condition. To determine if the refrigeration system is functioning properly, a diagnostic “pretrip” routine is run to ensure proper operation. Pretrip is a process of testing a refrigeration system before operating the system in a cooling or heat/defrost mode to ensure that the system will operate properly.
To date there have been few attempts to create pretrip testing methods, and those proposed pretrip routines have been inadequate for a variety of reasons. For example, U.S. Pat. No. 5,172,561, discloses a pretrip operational method for automatically checking predetermined functions and the operating performance of a transport refrigeration unit. This system measures the current draw from predetermined electrical components with a prime mover stationary, and compares the measured current draw of those components with an allowable range for the component. When a control unit in the comparison step finds that the current draw for each component checked is in the associated allowable range, the actual speed of the internal combustion engine is determined, and compared to the actual speed of the internal combustion engine to determine if it is in an allowable range. This pretrip method employs temperature sensors which sense the temperatures of the return air, discharge air and ambient air. The system is then commanded to operate in a cooling mode, and the unit is checked for adequate cooling capacity as a function of the temperature values of the return air, discharge air, and ambient air. It is then determined if the transport refrigeration system is operating in the commanded heating mode by comparing the temperatures of the return air and discharge air. Operation of the modulation valve is determined by sensing the speed of the prime mover before and after closing of the modulation valve.
Although this pretrip method attempts to verify whether the system will operate correctly, it suffers from numerous defects. For example, one disadvantage is that the pretrip routine executed is the same regardless of the desired box temperature or ambient temperature. This creates numerous problems especially when heating in warm ambients or cooling in cool ambients. Another limitation of the related art pretrip methods is that they failed to determine the causes of specific problems within the refrigeration system, and even assuming they could determine the cause of the problem, these related art pretrip methods could not determine if problem resulted from the failure of a particular component of the system. Yet another disadvantage of these pretrip routines they only evaluate a change in temperature to determine whether the refrigeration system will function properly. Thus, the related art pretrip methods failed to evaluate whether the system is maintaining necessary pressures at certain points in the system. As a result, alarms in the system would often sound when they were not supposed to (i.e., false failures), or conversely not sound when there were actual problems in the system. Either of these problems is very undesirable. For example, false alarms cause the refrigeration system to be taken out of service and inspected for problems, which takes time and costs money. In addition, a false alarm takes even longer to service because there are no identifiable problems. Furthermore, failing to sound an alarm when there are actual problems in the system often results in destruction of the cargo.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to overcome the limitations of the prior art.
It is an object of the present invention to improve performance and reliability of the refrigeration system by detecting leaks in valves.
It is a further object of the present invention to signal an alarm when there is a leak between a high-pressure side and a low-pressure side of the refrigeration system.
It is yet a further object of the present invention to alert the user of potential problems with a refrigeration system before they adversely affect system performance.
Another object of the present invention is to determine which valves are faulty from many valves in the system. The valves connect the high-pressure side to the low-pressure side.
It is a further object of the present invention to enhance the refrigeration system's ability to heat or cool by maximizing the efficiency of the system.
It is a further object of the present invention to prevent unnecessary shut down of the system by detecting leaks before the system is operational and detrimentally relied upon.
Another object of the present invention is to ensure correct operation by picking up actual problems with the system, and to prevent false failures (i.e., false alarms) of the refrigeration system.
According to the present invention a method of checking for leaks between a high-pressure side and low-pressure side of a refrigeration unit is provided. This method includes the steps of decreasing the suction pressure in the low pressure side, increasing a discharge pressure in a high pressure side of the refrigeration unit, and then checking for leaks between said low pressure side and said high pressure side.
The steps of decreasing the suction pressure in the low pressure side, and increasing a discharge pressure in a high pressure side of the refrigeration unit may be accomplished by pumping down a pressure in the low pressure side, opening a valve, and then verifying that the valve opened. The system is pumped down by continuously removing refrigerant from the low-pressure side until said low-pressure side reaches a first predetermined pressure.
The preferred method of verifying that the valve is operational is by observing significant changes in suction (low) pressure and discharge (high) pressure during opening of the valve.
In one embodiment of the invention, leaks are checked for by turning off a compressor, simultaneously closing any opened valve, waiting momentarily, and then checking for an increase in the suction pressure beyond a specified limit.
In an alternate form of the invention suction pressure may be decreased while discharge pressure may be increased by closing a first valve, decreasing the suction pressure to a first pressure by increasing the discharge pressure, opening the first valve, waiting, and determining if there are any changes in the suction pressure. The process is then repeated by closing the first valve, and decreasing the suction pressure to a predetermined pressure. This also increases the discharge pressure. The process continues by opening a second valve and determining whether the suction pressure or discharge pressure changes. Next, the process continues by further decreasing the suction pressure to an even lower predetermined pressure.
REFERENCES:
patent: 5140825 (1992-08-01), Hanson et al.
patent: 5172561 (1992-12-01), Hanson et al.
patent: 5186014 (1993-02-01), Runk
patent: 5649429 (1997-07-01), Schreber
patent: 5983657 (1999-11-01), Murata et al.
Dobmeier Thomas J.
Kopp Peter H.
Malone Garret J.
Porter Kevin J.
Rabbia Mark R.
Carrier Corporation
Tanner Harry B.
Wall Marjama & Bilinski
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