GB2260816A

GB2260816A - Monitoring fluid quantities

Info

Publication number: GB2260816A
Application number: GB9221939A
Authority: GB
Inventors: David William Vowles
Original assignee: BEAR ORGANISATION Ltd; PARA MECH Ltd
Current assignee: BEAR ORGANISATION Ltd; PARA MECH Ltd
Priority date: 1991-10-21
Filing date: 1992-10-19
Publication date: 1993-04-28
Anticipated expiration: 2012-10-19
Also published as: GB9221939D0; GB9122285D0; GB2260816B

Abstract

Determination of the total quantity of a fluid, for example refrigerant, in a system utilizing the fluid is made by monitoring the level of the fluid in a reservoir 2, and by monitoring one or more operating parameters at at least one operating station 6 at which the fluid is used. The total quantity of fluid, or its rate of change, can be monitored and an alarm given if the total quantity falls below a predetermined threshold, or if the rate of loss is sufficiently high to indicate leakage or unauthorized abstraction. A processor 30 processes through suitable software signals from an opto-electrical reservoir level sensor 26 and sensors 32, 34 and 36 sensing ambient air temperature at condenser 10, temperature of refrigerator unit 6, and operating mode of the unit 6 respectively to assess the total quantity of fluid in the system. <IMAGE>

Description

MONITORING FLUID OUANTITIES This invention relates to the monitoring of the quantity of fluid in a system comprising a reservoir of the fluid and at least one operating station at which the fluid is used.

In systems which utilize a fluid such as a fuel or a refrigerant, it is common to keep the fluid in a reservoir and to monitor its level, for example by means of a sight gauge. It is, however, sometimes desirable to know how much of the fluid is in the system as a whole, rather than only in the reservoir.

For example, in a refrigeration system used in a supermarket, the quantity of refrigerant in the system will normally remain substantially constant, but the level of refrigerant in the reservoir will vary in accordance with the refrigeration demand made on the system. As a result, it is not easily possible to detect an abnormal circumstance such as a refrigerant leak merely by monitoring the level of refrigerant in the reservoir.

According to one aspect of the present invention, there is provided a method of monitoring the quantity of fluid in a system comprising a reservoir of the fluid and at least one operating station at which the fluid is used, the method comprising: (i) monitoring the quantity of the fluid in the reservoir; (ii) monitoring an operating parameter of the system, which parameter influences, or is influenced by, the quantity of fluid required or the rate of use of the fluid at the operating station; and (iii) providing an output signal representing the total quantity of the fluid present in the system on the basis of the quantity of fluid present in the reservoir and of the operating parameter.

By employing a method in accordance with the present invention, it is possible to detect changes in the total quantity of fluid in the system, and consequently to react to abnormal circumstances. For example, it is possible to monitor the rate of change of the output signal, and to generate an alarm signal if the magnitude of the rate of change exceeds a predetermined threshold. By way of example, if a change in the output signal represents an unacceptable rate of loss of fluid from the system, this could represent a fluid leak which would require rapid remedial action.

If the system is to be charged with additional fluid, the alarm signal may be overridden. In addition, the monitoring method in accordance with the present invention can serve as a check on the quantity of fluid added to the system. This enables the user of the system to verify independently that, for example, an outside contractor has supplied the correct quantity of fluid.

According to another aspect of the present invention, there is provided a system comprising a reservoir of fluid and at least one operating station at which the fluid is used, the system also comprising first monitoring means for monitoring the quantity of fluid in the reservoir and second monitoring means for monitoring an operating parameter of the system, processing means being provided, which receives input signals from the first and second monitoring means and which generates an output signal representing the total quantity of fluid present in the system on the basis of the input signals.

In a preferred embodiment of a system in accordance with the present invention, the first monitoring means is an opto-electronic level detector which is capable of providing signals representing the level of fluid in the reservoir to the processing means.

One use of a method and system in accordance with the present invention is for monitoring the level of refrigerant in a refrigeration system. In particular, a supermarket may have, in addition to chill and freezer cabinets in the sales area, many other areas in which refrigeration equipment is employed. For example, there may be cold rooms and other storage areas for storing goods and produce away from the sales area, and the supermarket itself may be air conditioned. Very large quantities of refrigerant are often required to operate the refrigeration equipment throughout the supermarket and this refrigerant may have a high value. Furthermore, there is increasing sensitivity over the deliberate or accidental release of some refrigerants into the atmosphere as a result of the environmental damage which they are believed to cause.By using a method or system in accordance with the present invention, it is possible for the supermarket operator to monitor closely, and maintain a record of, refrigerant use within the supermarket. As a result, the supermarket operator is able to react quickly to any suspected leaks of refrigerant which may not otherwise become apparent. Also, the supermarket operator will be in a position to detect any unauthorized extraction of refrigerant from the system, or any instance of short quantities being supplied when the system is charged.

The operating stations may comprise refrigerated cabinets, air conditioning units, cold stores or any other unit of the system which employs the refrigerant.

The operating parameters may, for example, be the outside ambient temperature, but other operating parameters which may be monitored, either alone or in combination, are interior ambient temperature in the vicinity of the refrigeration equipment, and the operating mode of the refrigeration equipment (e.g.

whether or not the equipment is undergoing a defrost cycle).

For additional refrigerant leak detection, the method and system in accordance with the present invention may be operated in conjunction with a sensor system as disclosed in British Patent Specification GB 2239952A. Not only does such a system provide detection of refrigerant leakage by the use of sensors, but it also assists in locating the source of any detected leak.

Although the present invention is described in the specification with particular reference to refrigeration equipment, it is also applicable to other types of system. For example, it may be applied to a combustion process in which fuel is stored in a reservoir. By monitoring operating parameters of the combustion device, it is possible to detect loss of fuel by leakage or evaporation. Also, by providing an accurate indication of the total quantity of fuel in the system, it is possible to check the quantity of fuel introduced into the reservoir during filling.

For a better understanding of the present invention, and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawing, which diagrammatically represents a refrigeration system for a supermarket.

The system comprises a reservoir 2 for refrigerant, which is connected to the evaporator 4 of refrigeration equipment 6 by means of a liquid header 8. The refrigeration equipment 6 constitutes an operating station of the system, and may, for example, be a freezer cabinet for frozen foodstuffs. Although only one such operating station is shown in the Figure, a supermarket will have several other operating stations in the form of freezer cabinets, chill cabinets, frozen food cold stores, chilled food cold stores, and air conditioning units. A typical supermarket may, for example, have fifty refrigerated cabinets on the sales floor, ten or more cold stores, and several other refrigeration units as well as an air conditioning system. All of these units will be provided with refrigerant from the single reservoir 2.

The outlet of the evaporator 4 is connected to a condenser 10 via a compressor 11 provided with an oil separator 12.

Refrigerant is returned to the reservoir 2 from the condenser 10. A fan 14 creates a forced air flow across the condenser 10.

The system is provided with a charging point 16 by which liquid refrigerant can be supplied to the system through a valve 18. A drier 20 is connected in a bypass circuit, circulation of refrigerant through the drier being controlled by valves 22,24. When refrigerant is to be introduced into the system, a refrigerant container is connected to the charging point 16, the valve 18 is opened and the valve 22 is closed.

A level sensor 26 is provided on the reservoir 2.

The level sensor 26 is an opto-electronic device and provides an output on a line 28 to a processor 30. The processor 30 also receives input signals from three sensors 32,34,36. The sensor 32 responds to the air-on temperature at the condenser 10, which corresponds to the ambient outside temperature. The sensor 34 responds to the inside temperature in the vicinity of the refrigeration unit 6, and consequently provides a measure of the temperature difference between the set point temperature inside the refrigerated cabinet and the ambient temperature. The sensor 36 responds to the operating mode of the refrigeration unit 6. Primarily, the sensor 36 is provided in order to indicate to the processor 30 whether the refrigeration unit 6 is operating normally, or whether it is operating on a defrost cycle.

The sensors 32,34,36 thus provide indications to the processor 30 of operating parameters of the refrigeration unit 6, and their signals enable an assessment to be made of the refrigerant demand generated by the refrigeration unit 6. Similar signals are provided to the processor 30 in relation to the other refrigeration units of the system. Each refrigeration unit may have its own sensor responsive to its operating mode, corresponding to the sensor 36 shown in the Figure, but a single sensor corresponding to the sensor 34 may be adequate for more than one refrigeration unit. For example, a single sensor 34 may be provided in the sales area for a group of refrigeration units 6. Similarly, the sensor 32 may be sufficient for all of the refrigeration units in the system.

The signals received by the processor 30 from the level sensor 36 and the sensors 32;34,36 are processed by appropriate software to yield an output signal which represents the total quantity of refrigerant in the system. The processor 30 is connected to alarm circuitry which gives an alarm if the total quantity of refrigerant drops below a predetermined level, indicating that the system needs to be recharged.

By monitoring this signal over time, it is possible to produce a rate of change signal. In normal operating conditions, there is always some loss of refrigerant, although this is very small. Also, transient conditions may cause the output signal to represent a temporary loss of refrigerant. However, by appropriate programming, the processor 30 can ignore such changes, and react only to situations which are likely to result from an abnormal situation, such as a serious leak or unauthorized abstraction of refrigerant. An alarm can then be given and, in serious situations, emergency automatic shut-off valves can be operated in order to isolate the cause of any leak and minimize the escape of refrigerant.

The output signal from the processor can also be used to determine the quantity of refrigerant added at the charging point 16. This provides a check on metering equipment at the charging point 16. It is important for charging to be done relatively quickly, in order to minimize errors resulting from changes in operating parameters while charging is proceedings.

The processor 30 may be connected to a memory which is capable of providing a record of the total quantity of refrigerant in the system over a predetermined period of time. For example, it is possible to provide graph data at five minute intervals of total refrigerant quantity, with history going back at least one week, and to provide graph data showing daily averages of total refrigerant quantity, with history going back at least one month.

Although the system shown in the Figure has all three sensors 32, 34 and 36, it is possible to simplify the operations required of the processor 30, without any significant loss of accuracy, by providing only the sensor 32, responsive to the outside air temperature.

Variations of the inside air temperature, and the defrost cycles of the refrigeration equipment 6, will tend to occur on a cyclical pattern and current output data can thus be compared with historical data to determine whether variations in the output signal represent normal cyclical variations, or whether they indicate a leak or other abnormality.

Claims

1. A method of monitoring the quantity of fluid in a system comprising a reservoir of the fluid and at least one operating station at which the fluid is used, the method comprising: (i) monitoring the quantity of the fluid in the reservoir; (ii) monitoring an operating parameter of the system, which parameter influences, or is influenced by, the quantity of fluid required or the rate of use of the fluid at the operating station; and (iii) providing an output signal representing the total quantity of the fluid present in the system on the basis of the quantity of fluid present in the reservoir and of the operating parameter.

2. A method as claimed in claim 1, in which an alarm signal is generated if the output signal represents a total quantity of the fluid below a predetermined value.

3. A method as claimed in claim 1 or 2, in which the rate of change of the output signal is monitored, and in which an alarm signal is generated if the magnitude of the rate of change exceeds a predetermined threshold.

4. A method as claimed in claim 3, in which the alarm signal is overridden when additional fluid is supplied to the system.

5. A method as claimed in any one of the preceding claims, in which the quantity of fluid in the reservoir is monitoring by means of an opto-electronic level detector.

6. A method as claimed in any one of the preceding claims, in which at least one of the operating stations includes refrigeration equipment, and in which the fluid is refrigerant.

7. A method as claimed in claim 6, in which the monitored operating parameter of the operating station is the of outside ambient temperature.

8. A method as claimed in claim 6 or 7, in which the operating parameter comprises the interior ambient temperature in the vicinity of the refrigeration equipment, and/or the operating mode of the refrigeration equipment.

9. A system comprising a reservoir of fluid and at least one operating station at which the fluid is used, the system also comprising first monitoring means for monitoring the quantity of fluid in the reservoir and second monitoring means for monitoring an operating parameter of the operating station, processing means being provided, which receives input signals from the first and second monitoring means and which generates an output signal representing the total quantity of fluid present in the system on the basis of the input signals.

10. A system as claimed in claim 9, in which the first monitoring means is an opto-electronic level detector.

11. A system as claimed in claim 9 or 10, in which the operating station includes refrigeration equipment and in which the fluid is refrigerant.

12. A method of monitoring the quantity of fluid in a system, as claimed in claim 1 and substantially as described herein.

13. A refrigeration system substantially as described herein with reference to, and as shown in, the accompanying drawing.