GB2267582A - Control of refrigeration in a supermarket - Google Patents

Abstract

A control system for a plurality of refrigerated containers (2, 3, 4) comprises means for sensing a condition of system breakdown; means for control the valves (14, 15, 16) to connect or disconnect the containers to or from the compressor (18) according to signals from the sensing means; and means for sequencing the connection of the containers to the compressor after a system shutdown, so as to avoid a high demand to the compressor. Individual conditions for each container can be input into the system via a microprocessor keyboard and can be displayed on a display module. The strategy involves giving cases a priority of order in reconnection. <IMAGE>

Description

CONTROL OF REFRIGERATION This invention relates to control of refrigeration in the context where a plurality of refrigerated containers are supplied from a common compressor of refrigerant medium.

Within the term refrigerated containers we include display and storage devices and also devices for freezing, for chilling or for cooling.

It is nowadays common, forexample in supermarkets, that a large number of deep-freeze and chilled containers such as display cabinets are coupled from a common compressor via headers, one of which contains refrigerant liquid under pressure, and the other is a return header for evaporated refrigerant. There also may be a third header for defrosting gas or liquid. Each container or small group of containers is fed from the header by branches which are known as stubs.

Electromechanical valves in the stubs are operable to effect the condition in the container (or group of containers) fed by the stubs so as, for example, to initiate automatically a defrosting period and then to terminate the defrosting period and recommence the feed of refrigerating liquid in that stub.

The conventional layout of such a system has all the valves of the stubs, and their electromechanical timers and controllers, gathered together in a single massive panel, usually on a gallery or mezzanine floor above the level of the refrigerated containers.

The present invention seeks to simplify, and to make more compact and more flexible the control of such refrigeration systems. We provide a solid-state system for the programming of individual containers and/or stubs and/or for the separation of a control board from any necessary proximity with the containers or the actual valves of the stubs and/or for automatically sequencing reintroduction of feed of refrigerant liquid to the containers after a breakdown of the system.

Such a breakdown may occur in the event of lack of proper supply of refrigerant liquid or of proper return of the vaporised refrigerant, and the system will shut down. The causes of loss could be manifold. The most obvious would be power failure, but could include also compressor failure or a leakage developing somewhere in the mains. In such an event the whole system is shut down, all containers being isolated from the mains.

If upon restoration of ordinary service, for example by the restoration of power or by the replacement of a faulty compressor, all the containers were allowed to resume normal operation at once, all would be demanding a maximum flow of refrigerant liquid. This demand which could be many times the design capacity of the compressor could overwhelm the compressor and lead to dangerous failure.

We therefore preferably provide in our control system for the sequential and progressive introduction of refrigerant containers after shut-down.

In the drawings, Figure 1 is a schematic diagram of mechanical elements of the refrigeration system and Figure 2 is a schematic circuit diagram of electrical elements of it.

Referring now to Figure 1, a retail floor 1 has refrigerated containers 2, 3, 4 which are display cases.

Above the ceiling 5 of the retail hall are a set of headers 6, 7, 8 containing respectively refrigerant liquid, returned evaporated refrigerant and defrosting medium. Stubs 9, 10 lead from these headers to either an individual display case e.g. stub 9 to case 2 or to a group of display cases, e.g. stub 10 to cases 3,4. Each stub comprises pipes 11, 12, 13. Under normal operation pipe 11 carried refrigerant liquid to each case and pipe 12 carries returned evaporated refrigerant from each case.

Pipe 13 connects the defrosting medium header 6 to the returned refrigerant pipe 12, and when a defrosting operation is carried out, defrosting medium is carried to a case along pipes 13, 12 and from the case along pipe 11 i.e in a reverse direction to normal flow.

Each stub leading to or from a container is fitted with electromechanical valves 14, 15, 16 which control flow in pipes 11, 12 and 13 respectively.

Refrigerant liquid valve 14 is usually located in a container, whilst suction valve 15 and defrost valve 16 are usually located in the vicinity of their respective headers. All the valves are under the control of the controller 17. Since controller 17 is a solid-state controller, considerable size-reduction is possible compared to previous stub valve control systems. A compressor 18 for returned evaporated refrigerant is usually sited either on a ground floor or a roof mounted plantroom and passes refrigerant via condenser 19 to a liquid tank for return to the refrigerant liquid header 6.

In Figure 2 a pair of containers, for example display cases 3 and 4, are indicated schematically at 20 and 21 and are supplied by a single stub (not shown in Fig. 2). Power for the cases is derived from distributor 22 in the control panel 17 via sub-distributor 23 and powers, inter alia, an integrated case control circuit 24 in each of the cases, one connection of which provides a low voltage direct current signal taken via lead 26 to and from a plug-in module 33 in a programmable control rack 27. The control panel may be situated on an upper level of the retail hall, as shown in Fig. 1, and may be remote from the compressor and other equipment used to refrigerate the cases.

Input to the integrated case control circuits 24, so as to set required temperature or other data for each case is achieved from a personal computer 28 via panel 29 in the control panel 17. As may be readily appreciated, the personal computer may be remote from the control panel 17. The required operating conditions for each case are displayed via an LED display module on each case, and the module permits direct entry of new data (and alteration of existing data) by a user via e.g. a keypad.

There is also indicated a general alarm panel 30 to alert an operator to malfunction of the system as a whole, and a trip switch 31 to enable the alarm panel to be triggered manually or by a particular piece of equipment, e.g. the compressor.

In normal operation, detectors in the cases 20, 21 "feel" the conditions obtained within them and transmit data to the case controller 24. The controller 24 compares these conditions with the desired conditions set by the computer or directly via the display module and issues demand signals to the valves 14, 15, 16 via lead 26 and a plug-in module in the control rack 27. Appropriate signals issued from that module will cause the opening or closing of the relevant valves associated with the case "making" the demands and will control the flow of refrigerant liquid, returned evaporated liquid and, in a defrosting cycle, defrosting medium. Other valves or control parameters, such as a drain-down valve in the set of headers or a hot gas bypass valve in each case, may also be included in the control system. Thus each case will effectively initiate its own defrosting cycle, regulate its own temperature and so-forth in accordance with the desired conditions set by the operator using the personal computer 28. Statistically the various types of demand will be evenly distributed over the whole of the retail floor (as many as 60 to 70 refrigerated cases may be supplied in common such a system). A defrosting cycle is usually activated and terminated according to an internal calendar clock in each case controller.

The control panel may also monitor the operating conditions of the compressor 15, condensor 16 and liquid receiver 17, by means of conventional control circuitry such as the trip switch 31, in order to check that these units are functioning correctly.

As stated above, the low voltage current signal 26 is transmitted to a plug-in module 33 in the programmable control rack 27. The control rack contains a number of modules, each one controlling the stub valves for a particular case (or group of cases connected to one stub). Each module provides an indication of the state of the refrigerant liquid, returning evaporated liquied and defrosting medium valves for that stub. Each module also allows for the operator to select "Manual" defrost mode, "Fans Only" mode (where only the fan in the case is on prior to case cleaning), and "off" (during and after case cleaning).

In order for the modules 33, and hence the containers, to be operating at all, they must be receiving a 'run' signal, which is usually provided upon correct operation of the compressor.

In the event, however, of a total failure of the system, due for example to power failure or to breakdown of the compressor, the run signal will be terminated and the modules will initiate a close-down of all valves for all cases so that they are isolated from fault, i.e. the "off" mode for each module is triggered.

Inevitably this will mean a rise in temperature of those cases, as time goes on. The panel 29 in the control panel 17 activates the alarm panel 30, alerting an operator to the malfunction of the system. This alarm may be aural or visual. The alarm may also be activated by one of a number of trip switches 31, which may be operated manually, or by a particular piece of apperatus in the system.

When the cause of the shut-down is removed, i.e. power is restored or the compressor signals to the system that it is again supplying refrigerant liquid, the 'run' signal will be reinstated and the cases will be progressively reintroduced into operation, ensuring that not all demand from all cases is met at once. The 'off' signal on each module is released, and the module is returned to 'auto' mode. A pre-determined sequencing strategy controlled by the case controllers 24 will be initiated in which only "n"cases will be supplied at any given time according to their "demands" for refrigerant liquid, this "n" representing that level of demand which is safely within the design demand of the compressor. The strategy to be followed in such a sequencing can be one of many, but a particularly preferred strategy is to allocate numbers to each case giving each case an "address". A number of cases on the same stub will have the same address. Then, according to a pre-determined priority, fo supply refrigerant liquid only to particular addresses, or groups of addresses, i.e. the reintroduction strategy may be to sequentially supply all cases of which the last identifying digit is 0 and then all whose last identifying digit is 1 and so-forth.

Each case controller may be pre-programmed so that, upon the 'run' signal being reinstated, the controller will not demand re-supply of refrigerant until a pre-determined time has elapsed - the time period being determined according to the priority given to the case.

Claims (12)

CLAIMS :

1. A control system for refrigeration facilities having means for compressing a refrigerant medium; a plurality of refrigerated containers connected to said compressing means for circulating said medium; and valve means to selectively control the connection between each said container and said compressing means; said control system comprising: means for sensing a condition of system breakdown; means for selectively controlling said valve means to connect or disconnect one or more of containers to or from said compressing means according to signals from said sensing means.

2. A control system according to claim 1 wherein the control system includes means for sequencing the connection of said containers to said compressing means after a system shut-down by said valve control means.

3. A control system of claim 1 or claim 2, wherein said sequencing means comprises means for allocating a priority number to each said container so that the connection of each said container to the compressing means is sequentially made according to said priority member.

4. A control system of claim 1, claim 2 or claim 3 wherein said sensing means comprises means for sensing power failure; and/or means for sensing fault in said compressing means; and/or means for sensing leakage in said connection between said compressing means and the containers and/or in said valve means.

5. A control system of any preceding claim, further comprising controller means for fitting in at least one said container so that said valve control means can operate according to the conditions in said container.

6. A method for control refrigeration facilities having means for compressing a refrigerant medium; a plurality of refrigerated containers connected to said compressing means for circulating said medium; and valve means to control the connection between each said container and said compressing means; said method comprising the steps of: a) detecting a condition of system breakdown in said refrigeration facilities; b) shutting down said valve means to disconnect one or more of said containers selectively from said compressing means in response to the detection of said condition of system breakdown.

7. A method of claim 6 which includes connecting said containers sequentially to said compressing means upon the removal of said condition of system breakdown.

8. A method of claim 7, wherein said connecting step c) is conducted automatically upon the detection of the removal of said condition of system breakdown.

9. A method of claim 7 or claim 8, wherein said condition of system breakdown comprises power failure, failure of said compressing means, or leakage in said connection between said compressing means and the containers and/or in said valve means.

10. A method of any one of claims 6 to 9, further comprising steps of: d) detecting the operational conditions in each said container; and e) regulating the operation of each said container by operating said valve means associated with said container in response to the detected conditions of said container.

11. A control system constructed substantially as described herein with reference to the accompanying drawings.

12. A method for control refrigeration facilities performed substantially as described herein with reference to the accompanying drawings.