Refrigeration – Automatic control – Refrigeration producer
Reexamination Certificate
1999-01-19
2001-01-09
Ferensic, Denise L. (Department: 3744)
Refrigeration
Automatic control
Refrigeration producer
C062S196200, C062S196300, C062S228500, C062SDIG001
Reexamination Certificate
active
06170277
ABSTRACT:
FIELD OF INVENTION
The present invention relates to the field of refrigeration systems for heating and cooling in a controlled environment, and in particular to a control algorithm for a refrigeration system which automatically maintains the discharge pressure in the refrigeration system below a predetermined limit.
BACKGROUND OF THE INVENTION
Refrigeration systems are used in many applications for heating and cooling a controlled environment, including a cargo box on a transport truck, train, ship or plane. An important objective of any refrigeration system is to absorb heat by evaporating at low pressure and temperature, and to give up heat by condensing at a higher temperature and pressure. A system's ability to move heat energy in this manner depends primarily on the magnitude of the pressure difference. Consequently, there is a need to establish a large difference in pressure between the high pressure side and the low pressure side of the refrigeration system. To create a large pressure difference it is necessary to establish a high pressure on one side and a low pressure on the other. Unfortunately, the components of a refrigeration system are only designed to withstand certain pressure ratings. If the pressure difference is too great these ratings can be exceeded, then the system components can be damaged. Prior art systems addressed this problem by configuring a control unit to shut a refrigeration system down completely if the system pressures being monitored increased beyond a specified level. As a result, the refrigeration system had to be taken out of service and inspected for problems. Such refrigeration system outages are generally time consuming and costly.
SUMMARY OF THE INVENTION
According to its major aspects and broadly stated, the present invention provides a method of controlling the discharge pressure in a refrigeration system. Steps are provided according to this method for determining if a discharge pressure is below a predetermined upper limit, and adjusting the discharge pressure to bring the discharge pressure below the predetermined upper limit.
According to another aspect of this invention, steps are also provided for determining if a discharge pressure is within a specified pressure range, and adjusting the discharge pressure within the specified pressure range.
According to yet another aspect of the present invention, the above steps of determining and adjusting are continuously repeated.
According to one aspect of the invention, the step of determining if a discharge pressure is within a specified pressure range may be accomplished by determining if the discharge pressure is greater than a predetermined pressure, and determining if the discharge pressure is less than a second predetermined pressure.
According to yet another aspect of the invention, the step of adjusting a valve to increase or decrease the discharge pressure to bring the discharge pressure within the specified pressure range can be implemented by closing a first valve if the discharge pressure is less than said second predetermined pressure until the discharge pressure is within a specified pressure range, and repeating the method if the discharge pressure is greater than the second predetermined pressure.
According to another feature of the present invention, the discharge pressure is lowered if it is too high.
According to yet another feature of the present invention, the processor sends a signal to open condenser pressure control valve if the discharge pressure is too high.
Therefore, it is an object of the present invention to overcome the limitations of the prior art. It is a further object of the present invention to provide a method for maintenance of discharge pressure in a refrigeration system regardless of the ambient temperature conditions to thereby increase the ambient temperature range over which the system is operable.
It is yet a further object of the present invention to provide a control algorithm that maintains adequate, but not excessive discharge pressure in a refrigeration system.
It is a further object of the present invention to signal and alarm when the discharge pressure drifts above or below predetermined limits.
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.
It is a further object of the present invention to selectively open and close a valve to maintain discharge pressure within specified limits.
It is a further object of the present invention to alert the user to the actual problems in the system.
These and other features of the invention, as well as additional objects, advantages, and other novel features of the invention, will become apparent to those skilled in the art upon reading the following detailed description and accompanying drawings.
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Dobmeier Thomas J.
Malone Garret J.
Porter Kevin J.
Carrier Corporation
Ferensic Denise L.
Norman Marc
Wall Marjama & Bilinski
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