EP1261830B1 - Method for detecting faults in a cooling system - Google Patents

Description

The invention relates to a method for discovering Faults in a cooling system with several cooling points, in which the according to a predetermined scheme most heavily loaded refrigeration point is determined.

The invention is based on the example of a cooling system described in a supermarket where the Cold stores are formed by individual sales counters. Chilled or frozen goods so ready that a customer can look at them and take them out of the cupboards. The However, invention is not on supermarkets or the like limited, but can basically be anywhere there be used where a cooling system has multiple cooling points has operated with different loads can be. Under the term "cooling system" should fall all systems that are used for refrigeration serve, also those that you would otherwise call Freezers would designate.

JP-A-10 238920 describes an apparatus for discovery of errors and to predict the emergence of Errors in a refrigeration system with multiple refrigerators. The method using the device assumes that an error has occurred when in a predetermined period of time in a temperature Refrigerators are not under certain predetermined temperatures can be held and if in the same period the furniture has a predetermined load value exceeds. In the process of the device for Prediction of errors occurring in the refrigeration system is a database with load data of the individual refrigeration units of the refrigeration system at different Environmental pollution used. These data are with current exposure data under the same environmental exposure compared. If the current load data of a refrigerator over a period of deteriorated for several days over a predetermined amount then an error is predicted. The environmental pollution is calculated using Temperature and humidity measurements in the building where the refrigerators are located.

A method of the type mentioned is from US 4,084,388. Here is the most polluted Cold spot determined to the compressor assembly too Taxes. The compressor arrangement should on the one hand provide so much cooling capacity that the most keep the desired temperature at the refrigerated section under load can. On the other hand, it should also no longer perform provide. In the known case, this is done by that the suction pressure of the compressor assembly is regulated becomes. This results in significant energy savings possible.

With cooling systems of this type, there are always again Error. These errors are critical because that is to be cooled Can spoil well if it's not on the set low temperature remains. A common practice for error monitoring is the Monitor temperature. If the temperature at one Cooling point over a longer period of time a predetermined An error is displayed. This is referred to below as a "temperature warning". Such a warning is often only given for a long time after which the actual error has already occurred is. The error must then be corrected relatively quickly, so that the chilled goods do not spoil or loss of quality suffers. The urgency of troubleshooting is one of the causes of such Repairs are costly. This is especially true then when they perform at night or on weekends are.

The invention has for its object a possible Display errors as early as possible.

This task is carried out in a method of the type mentioned at the beginning Kind of solved by having a stress pattern of the cooling points and if there are any deviations from the Load pattern of at least one predetermined Parameter generates a warning.

Here, the "continuous" determination of the on most heavily loaded cooling point does not necessarily mean that this determination takes place continuously over time. It Rather, the determination in smaller temporal is sufficient Perform intervals, the time intervals adapted to the thermal time constant of the cooling system should be.

Show many of the errors that occur in cooling systems only after a relatively long time as temperature warnings, i.e. than elevated temperatures. For example it can take several days to get into the channels a refrigerated display case, in which air from and to the Evaporator of the showcase flows, a beginning of frosting as a warning. Is the temperature warning in the night or weekend is triggered in many Call a refrigeration technician. An earlier one Warning would make it possible for the operator within the necessary maintenance during normal working hours, for example, defrosting yourself.

If you now create a load pattern for the cooling points, then in the undisturbed case it can be assumed that most or each of the cold spots once as most heavily loaded refrigeration point is determined. If the stress patterns for the undisturbed, i.e. error-free Case determined for a longer period of time certain properties will be recognizable. For example are the load ratios of the individual Cold spots in a certain, almost constant Relationship to each other or at certain times are certain cold spots particularly heavily loaded or the loads on the cooling points change over the time always even. If there is a deviation of such a stress pattern occurs the present invention is believed to be is the announcement of an error, i.e. an error at an earlier stage, the otherwise not noticeable. For this reason a warning is then generated. Because the warning is relative is generated early, the operator of the cooling system troubleshooting during normal working hours go or just do the necessary maintenance carry out.

In many cases, an error is not due to elements the cooling system itself, but by human misconduct. For example, the door left on a refrigerated display case or in a cold room. Another example using a temperature warning system cannot be recorded immediately, is the false stacking of goods, where goods are in one Refrigerated display case are stacked too high, so that the cold layer not be maintained in the showcase can. The showcase is therefore uneconomical, because surrounding warm air flows into the refrigerated display case and must be cooled. The refrigerated display case must therefore provide more cooling capacity to the desired temperature to keep. This doesn't just mean an uneconomical one Operation of the individual refrigerated display case, but also an uneconomical operation of the associated Compressor system, because here the suction pressure, for example regulated by the most heavily used refrigeration point becomes. In the example, however, the burden would be caused by the error at this stage could still be eliminated relatively easily. If recognize such a false load early, then there is no risk of being out of the ordinary Working time caused by overwork Failure occurs after an expensive repair pulls itself.

It is preferable to determine locally at each cooling point continuously the burden. In this case, you can determine the most heavily used cooling point at any time, because the load data is locally available at every cooling point To be available. You can, for example, with a Microprocessor when the most stressed Cold store should be determined, all the cold stores Query sequentially and by comparing the load data find out the most polluted refrigeration point. Here, too, the term "continuous" means not necessarily continuously, but the load data can also be determined discretely.

It is preferable to filter the load over time. In order to one avoids that impact shocks, such as those by opening or closing a door Refrigerated display case can be caused a wrong one Resulting load picture. Rather, the stress flows the one to be raised over a certain period of time Cooling capacity.

The load criterion is preferably used a temperature-dependent variable at the cooling point. A temperature dependent size can be done with relatively simple Determine measures, namely with a temperature sensor, which is almost always already there. There are therefore no interference in the refrigerant circuit necessary. A display system by the process So it can also be used with existing systems can be easily installed. The effort to determine the load so stay small.

The temperature-dependent variable is preferably used .DELTA.T REL = T V - T CutOut T cuTiN - T CutOut where T _{V is} the temperature at the cold store, for example in the refrigerated display case, T _CutOut a temperature at which the cold store is switched off and T _CutIn the temperature at which the cold store is switched on. In other words, ΔT _REL expresses the deviation from the temperature T _CutOut to the current cooling point, weighted in relation to the distance between the temperatures T _CutIn and T _CutOut . In particular in connection with a "two-point control", in which the temperature T _{CutIn is used} for switching on and the temperature T _CutOut for switching off the cooling point, this load variable can be obtained relatively easily. Filtering can take place, for example, by _newly determining a load L from L New = L Old • const , + Δ T REL const + 1 where L _{ALT is} the previously determined and, if applicable, filtered load.

This filter eliminates sudden changes in the load expression.

After the determination of the most heavily loaded refrigeration point as long as heavily loaded refrigeration point until their condition changes or a predetermined time is exceeded and only then determines the most heavily polluted Cool place. This procedure has the advantage that the effort to identify the most can be kept small. When a cold store is identified as the most polluted then this first assumes that this cooling point cools. If the cooling point the necessary or has reached the desired low temperature, then it turns off. One can change this state use as a signal for it again after the most to look for a contaminated cooling point. Another criterion would be, for example, that a defrost process on this Refrigeration point, which either starts from time to time or depending on other criteria, like a frost load. After all, it is possible that the cooling point over a predetermined Period does not change their state. In this case one uses a safety barrier and so to speak checked after the lapse of this predetermined period, whether the cold spot is still the strongest is burdened.

The times are preferably added up for each cooling point, in which the cooling point in question as the most polluted refrigeration point is considered. This simplifies the evaluation and creation of a load pattern. It is only checked how long a cold store as the most heavily used cold store can be seen. Only these times are then for the Evaluation used.

The evaluation can now be done in different ways. An immediate warning is preferably generated, if a refrigeration point has more than a predetermined one contiguous period the most stressed Cold spot is. This can indicate a mistake which should be checked as soon as possible. The predetermined continuous period of time can for example be on the order of an hour. On Such errors result, for example, when the door of a cold room or a refrigerated display case open has been left or goods in the refrigerated display case have been piled high. Such a mistake not immediately noticeable. But it has the consequence that the corresponding cooling point over a relative long term as the most heavily used refrigeration point must be viewed. In this case, a Warning issued to the operator of the cooling system has the possibility of an intervention.

Alternatively or in addition, a long-term warning can be given generated when a refrigeration point over more than a predetermined portion of a predetermined period is the most polluted refrigeration point. Usually, i.e. in the undisturbed case, will during a predetermined Period, for example during opening hours a supermarket of 12 hours, that each cold spot has a certain percentage the times when it was the most stressful Cold spot is. Due to different positions or different loads of course, the proportions of the individual cooling points somewhat move. This statistical division can be broken down into in most cases arithmetically or by trying it out determine. If this division is something changes without external influences such as regrouping of the display cases or the like, can be seen, then this indicates a developing error, which must be examined and, if necessary, eliminated.

Finally, one can generate a warning if there is the load pattern of a period by more than one Tolerance range from a load pattern of a predetermined one earlier period differs. In statistical Means can be assumed that the stress pattern remains unchanged over time. smaller Fluctuations are of course possible at any time without these must immediately indicate an error. If however, if there are major deviations, then interpret this indicates an error that must be warned of. You can do this for consecutive periods, for example, successive sales days a supermarket, compare them. One can but also compare other periods with each other, for example all assembly, Tuesdays, etc. For larger ones However, there are differences in time intervals the stress patterns more noticeable. You have to choose the intervals so that a warning is generated early enough, but differences are clear become recognizable when they occur.

Fig. 1

den schematischen Aufbau einer Kühlanlage,

Fig. 2

eine schematische Darstellung zur Erläuterung der Temperaturregelung einer Kühlstelle,

Fig. 3

ein Flußdiagramm zur Erläuterung der Steuerung eines Verdampfers und

Fig. 4

ein Flußdiagramm zur Erläuterung der Ermittlung eines Belastungsmusters.

The invention is described below with reference to a preferred embodiment in connection with the drawing. Show here:

Fig. 1

the schematic structure of a cooling system,

Fig. 2

1 shows a schematic illustration to explain the temperature control of a cooling point,

Fig. 3

a flow chart for explaining the control of an evaporator and

Fig. 4

a flow chart to explain the determination of a load pattern.

1 shows a cooling system 1 with a cooling circuit, the three connected in parallel in the present case Has cooling points 2, 3, 4. Each cold store points Expansion valve 5, an evaporator 6 and an evaporator control unit 7 on. To indicate that with similar elements of the cooling points 2, 3, 4 need not be the same elements, they are Additional elements with a, b, c for the cooling points 2, 3, 4 marked.

The evaporators are connected to a compressor system 8, which in turn is connected to a capacitor 9 are, which has a plurality of fans 10 to heat dissipate. The capacitor 9 is connected to a collector 11 connected. The compressor system 8 and the condenser are controlled by a control unit 13, for example with the help of a pressure sensor 12 the condenser pressure regulates.

The entire cooling system is operated by a central control unit 14 controlled and / or monitored.

The basic mode of operation of such a cooling system is known. A coolant in the gas phase is in compresses the compressors 8. His temperature rises on. The heated, compressed gas is through the Condenser 9 passed. There with the help of the fans 10 dissipated heat so that the gas liquefies. The liquid coolant is in the collector 11 collected, which acts as a coolant buffer. From the Collector 11 passes the coolant through the expansion valves 5a, 5b, 5c in the evaporators 6a, 6b, 6c, where it evaporates from the environment with heat absorption, in turn as a gaseous coolant to the compressors reach.

Each cooling point 2, 3, 4 is now assigned by the Evaporator control unit 7a, 7b, 7c controlled. This local evaporator control devices 7a, 7b, 7c with the central control unit 14 in connection. each Control unit 7 controls the expansion valve in dependence from the temperature with a temperature sensor 15 is determined in the following manner based on 2 is to be explained.

The temperature sensor 15 determines a temperature T _V , for example the temperature in a refrigerated display case. Two temperatures T _CutIn and T _{CutOut are specified} . As long as T _{V is} less than T _CutIn , there is no cooling (t <t ₂ in FIG. 2), ie no coolant is passed into the evaporator 6. If T _V exceeds the temperature T _CutIn , the cooling of the cooling point begins (t ₂ <t <t ₃ ) and coolant is introduced into the evaporator 6. Cooling continues until T _{V falls} below T _CutOut again. At this moment (t ₃ ) the expansion valve 5 will close and only open when T _V again exceeds the temperature T _CutIn .

For the following explanation, the evaporator is in the T _CutIn state when it cools and in the T _CutOut state when there is no cooling.

From time to time, i.e. at fixed time intervals, can the respective evaporator 6 can be defrosted. Defrosting can be done in different ways, for example by electrical heating of those surrounding the evaporator 6 Air, or by hot refrigerant, which is not shown in more detail, but is known per se. The hoarfrost which sits on and around the evaporator will melt in the process. This state of Evaporator during defrosting is called defrosting.

In addition to the three states mentioned above, the The cooling point is in a closed state, for example when it is turned off, or it can be loaded with sensor errors, which the Evaporator control unit 7 can determine each.

The compressor control unit 13 regulates on the basis of the Suction pressure, which is determined by the sensor 12, the capacity of the compressor system. The compressor capacity the system is increased or decreased, depending from that for maintaining the desired suction pressure required capacity. The compressor control unit 13 also controls the fans 10, i.e. the ventilation system, thus the desired pressure in the condenser is maintained. This pressure can be caused by a Increase or decrease in airflow over the capacitor can be reached to a sufficient level To achieve heat emission to the environment.

The central control unit 14 identifies the am most heavily loaded refrigeration point based on that determined by the respective evaporator control unit 7 Load, which is explained below and warns an operator after also specified below Principles.

The specific way in which the burden of the individual Evaporator is determined, plays only a subordinate Role. Basically you can get the warning at top different systems. In addition to the above A cooling system can also be in the same state work more or less states, for example with suction pressure control or modulating thermostat control, where the degree of filling of the evaporator 6 is regulated to a predetermined temperature, on systems on which the evaporator, the compressor systems and condenser ventilation from a central one Control unit can be controlled, or on other types of cooling systems, for example brine systems or Forced circulation systems.

The basis of the warning generation is the load on each individual cooling point. In the present example, the determination of the load takes place in the control unit 7 of each individual cooling point 2, 3, 4 and the difference between the desired temperature and the current temperature at the cooling point, ie T _V , is used as the starting point. Of course, other methods can also be used. The design of the cooling system often decides how the load must be determined. However, it is not critical for the present invention how the current load is actually determined.

Fig. 3 shows schematically how the load is determined at each individual cooling point 2-4. First, it is checked whether the cooling point is defrosting, i.e. is in the defrosting state. If the cooling point is currently in the defrosting state, go back to the beginning of the diagram. If the cooling point is not in the defrosting process, check whether it is in the T _CutIn state, _i.e. is currently cooling. If this is not the case, the load is set to zero. This also applies if, for another reason, it cannot be positively determined that the cooling point is in the T _CutIn state.

If it is in the T _CutIn state, the load is determined according to the following scheme. The current load is calculated using the following formula L New = L Old • const , + Δ T REL const + 1 where ΔT _REL means: .DELTA.T REL = T V - T CutOut T cuTiN - T CutOut ΔT _REL expresses the deviation from the temperature T _CutOut to the current cooling point, whereby this deviation is weighted to the bandwidth between T _CutIn and T _CutOut . Basically, this expression could already be used as a value for the load. However, in order to avoid sudden changes in the load expression, the calculation of the load expression is provided with a simple filter which avoids such sudden changes.

L _Old is the load on refrigeration point 2-4, as it resulted from the previous run. Then the current load L _{New is} saved.

The scheme shown in Fig. 3 is predetermined go through small intervals. It's not necessary, that one run connects seamlessly to the other. This scheme is local to every evaporator control unit 7 settled. At the start of this flow chart is still the temperature and the control state registered. This step can also be done elsewhere this flowchart.

This means that there is continuous information about the load available at every cold store.

4 will now be explained how a Warning is generated.

The sequence shown in FIG. 4 also applies to this run through repeatedly.

It is first assumed that the most heavily used refrigeration point is known. Their temperatures (T _V , T _CutOut , T _CutIn ) and their control status are registered. Then it is checked whether this cooling point is still in the T _CutIn state. It must have been before. Otherwise, it would not have been selected as the most heavily used refrigeration point. If it is in this state, it is checked whether this state is already present over a period t that is greater than a predetermined period t _cycle . If this is not the case, the loop returns to the beginning.

If the condition of the cooling point has changed or the cycle time t _{cycle has been} exceeded, the central control unit 14 searches again for the most heavily loaded cooling point. Here, it simply compares the load information provided by the evaporator control units 7.

If it turns out that another cooling point the most polluted is the data on Cold store identification and the time saved. This data is then used for a new run to calculate loading times.

If it turns out that the most heavily loaded cooling point is the same as before, a loading time t _{MLC is} calculated from the previously stored time and the now determined time. This loading time t _MLC is then checked to determine whether it exceeds a predetermined maximum value t _LIMIT . Such a maximum value t _LIMIT is typically one hour. If this value has been exceeded, a warning is issued. Such a warning may indicate, for example, that the door to a cold store or showcase has been left open or that goods in a showcase are stacked too high.

The stored data are processed statistically, i.e. the duration is saved for the individual cooling point their exposure time. But this always only applies for the most heavily used refrigeration point.

This results in all cooling points of the cooling system Loading times, i.e. Times when each one Cold store is the most heavily used cold store is. You can now statistically evaluate whether this Share of a cooling point in the total time, for example at the opening period of a supermarket, about the time changes or if there are any changes that this time is increasing. If such Changes can result in relation to the respective A cold spot will be issued a warning.

This warning informs the operator of the cooling system that there may be a problem. In most cases, he can solve this problem through a Maintenance or through a change in the cooling point itself, for example closing a door or the Modify a stack of goods, help. Other typical Errors, such as a damaged fan, a damaged defrost heating element, a loss of Coolant filling are also detectable. such Errors are characterized by the fact that a cooling point or a group of cooling points the desired temperature can only keep up with problems and therefore more often than the others as the most heavily used refrigeration point is identified. If a cold spot problems has to maintain the desired temperature, this will Initially do not trigger a temperature warning because a such an error is not yet so serious that the Cooling point the temperature is not below the warning limit can hold. With the procedure shown but it becomes possible to detect an error for a long time before such a fault triggers a temperature warning and makes maintenance work urgent.

There are no additional ones for operating the cooling system Measures required. One only has to have existing ones Evaluate sensors accordingly.

Claims (10)

1. Method for detecting faults in a refrigeration system with several refrigeration locations, in which the most heavily loaded refrigeration location is currently determined in accordance with a predetermined schedule, characterised in that a load pattern of the refrigeration locations is created and that a deviation of the load pattern from at least one predetermined parameter generates a warning.
2. Method according to claim 1, characterised in that the load is currently determined locally for each refrigeration location.
3. Method according to claim 2, characterised in that the load is filtered with regard to time.
4. Method according to one of the claims 1 to 3, characterised in that a temperature-dependent quantity at the refrigeration location is used as load criterion.
5. Method according to claim 4, characterised in that the temperature-dependent quantity used is: ΔTREL = TV - TCutOut TCutIn - TCutOut
6. Method according to one of the claims 1 to 5, characterised in that, after determining the most loaded refrigeration location, this refrigeration location is regarded as the most loaded, until its state changes or a predetermined period is exceeded, and not until then a new determination of the most loaded refrigeration location is performed.
7. Method according to one of the claims 1 to 6, characterised in that for each refrigeration location the periods are summed up, in which the refrigeration location in question is regarded as the most loaded refrigeration location.
8. Method according to claim 7, characterised in that an immediate alarm is generated, when, for more than a predetermined continuous period, one single refrigeration location is the most loaded refrigeration location.
9. Method according to claim 7 or 8, characterised in that a long-time alarm is generated, when, for more than a predetermined share of a predetermined period, one single refrigeration location is the most loaded refrigeration location.
10. Method according to one of the claims 1 to 9, characterised in that an alarm is generated, when the load pattern of a period deviates by more than a tolerance area from a load pattern of a predetermined former period.

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