EP0412473A2 - Method for regulating the internal temperature of a cold load - Google Patents

Abstract

A method for regulating the internal temperature of a cold load 1 is described, which is connected via two refrigerant pipes, one liquid pipe 2 and a suction pipe 3 to a combination refrigerating system (4, 5, 6). In the method, the internal temperature Ti is measured (11) and the throughput is controlled through both or one of the two refrigerant pipes 2, 3. In this connection, at least one of the two refrigerant pipes 2, 3 is closed when the internal temperature Ti lies below a first limit temperature Tu. If Ti lies above a second limit temperature To, To > Tu, both refrigerant pipes 2, 3 are opened. According to the invention, one of the two refrigerant pipes 2, 3, in particular the suction pipe 3, is opened and closed a number of times, while the internal temperature Ti is situated within the hysteresis interval between Tu and To. <IMAGE>

Description

The invention relates to a method for regulating the interior temperature of a refrigeration consumer, which is connected to a composite refrigeration system via two refrigerant lines, a liquid line and a suction line, with the method measuring the interior temperature T _i and the throughput through the liquid line and / or the throughput the suction line is controlled such that at least one of the two refrigerant lines is closed when the interior temperature T _{i is} below a first limit temperature T _u , and that both refrigerant lines are open when the interior temperature T _{i is} above a second limit temperature T _o , T _o> T _u , lies, and also an apparatus for performing the method.

Interior temperature means the temperature within the volume of the refrigeration consumer to be cooled, for example inside the merchandise compartment of a refrigerated display cabinet that is set up in a supermarket and is supplied together with other refrigerated furniture and / or refrigeration rooms by a composite refrigeration system. The refrigeration system supplies liquid refrigerant under pressure in a separate liquid line for every refrigeration consumer. This is relaxed and then passed through the interior of an evaporator.

The outside of the evaporator is surrounded by air, which is brought in by a fan from the room to be cooled (return air from the interior). The air is cooled by indirect heat exchange with the evaporating refrigerant and then returned to the interior of the refrigeration consumer as supply air. The evaporated refrigerant is returned to the compound circuit via a suction line.

A control according to the method described at the outset serves to keep the interior temperature within a preselected temperature range, on the one hand to prevent spoilage of fresh goods stored in the interior of a refrigerator, and on the other hand to avoid unnecessary cold losses due to an excessively high temperature difference for reasons of economy between the interior of the refrigeration consumer and the environment.

In addition to the parameters of the evaporator and the refrigerant used, the interior temperature is mainly determined by the pressure difference during expansion and by the throughput of refrigerant through the evaporator. In principle, it is possible to control any of the quantities that affect the indoor temperature. The setting of the refrigerant flow, which can be carried out by means of easy-to-use solenoid valves, is particularly simple and inexpensive. Such a flow control can be provided either in the liquid and suction line or in one of the two refrigerant lines. The liquid or suction line is either kept closed or opened by a solenoid valve that is switched on or off.

Since the temperature in the interior of the refrigeration consumer is generally subject to spatial fluctuations, the practical control variable generally selected is either the return air from the room to be cooled, which is fed to the outer surface of the evaporator, or the supply air to the cooled space which has flowed past the evaporator. used. This depends on that too expected temporal fluctuations in the interior temperature, which are less when using a night cover, for example, than when a merchandise compartment of a refrigerator is relatively open during sales.

In the previously known control methods of the type mentioned at the outset, a normal hysteresis behavior is used: If the interior temperature (or the corresponding practical control variable) exceeds the upper limit temperature T _o , the refrigerant flow through the evaporator is released, for example by placing the solenoid valve or valves in liquid - And / or suction line are opened. As soon as the interior temperature falls below the lower limit value T _u , the refrigerant flow is interrupted again, for example by closing at least one valve.

This type of control prevents an excessively high switching frequency, which would result in an uneven load on the refrigeration system. However, this advantage is accompanied by strong overshoot of the controlled variable beyond the hysteresis range. This phenomenon can be limited by making the hysteresis interval relatively narrow - however, this easily leads to unstable control behavior.

The invention is therefore based on the object which enables stable and economical operation of a refrigeration consumer connected to a composite refrigeration system and in particular keeps the interior temperature very reliably within the preselected range.

This object is achieved in that one of the two refrigerant lines is opened and closed several times, while the interior temperature T _{i is} within the hysteresis interval] T _u , T _o [.

While one refrigerant line is being clocked, the other, if controlled at all, is kept open. The repeated opening and closing of a refrigerant line enables the refrigeration capacity provided on the evaporator to be smoothly adjusted to the current demand. If the interior temperature of the refrigeration consumer rises, the cooling supply can be switched on gradually or smoothly within the hysteresis interval - i.e. before the upper limit temperature T _{o is reached} - so that in most cases an exceeding of the upper limit temperature can be prevented. At least the overshoot is strongly dampened. Of course, this presupposes that the parameters of the refrigeration consumer and refrigeration system, which are not readily controllable, are adapted to the expected refrigeration requirement.

Likewise, it can generally be avoided that the interior temperature falls below the lower limit temperature T _u and thus unnecessary cold losses have to be compensated for. During the drop in the interior temperature, the cooling capacity can already be reduced within the hysteresis interval by a different opening rhythm of the clocked refrigerant line. The slope of the temperature curve is therefore flattened within the hysteresis interval, so that its lower limit is generally not reached.

The method according to the invention also has the advantage that the characteristic of the control can be adapted very flexibly to the respective conditions, for example to more or less high fluctuations in the interior temperature, as can be expected from changing external influences.

It has proven to be advantageous if the refrigerant line is opened and closed periodically within the hysteresis interval. During a period t _p is the refrigerant line in question within the period _a t open. The cooling capacity can be controlled, for example, while the period t _p remains the same, in that the opening period t _{a of} the refrigerant line is selected to be larger or smaller during a period t _p . Thus in principle a sliding adjustment of _a t to the maximum value t _p possible, so a permanent opening and so that maximum cooling capacity.

It is advantageous if, according to a further feature of the invention, the hysteresis interval in n (n> 1) subintervals
I _k = [T _k-1 , T _k ], k = 1, ..., n, T _k > T _k-1
is divided, in which the ratio t ein _{, k-1} / t _{P, k} , the relative opening time, is different. The following then applies: t on _{, k} , / t _{P, k} > t on _{, k-1} / t _{P, k-1}
for k = 2, ... n.

By increasing the number n of subintervals, an almost arbitrarily fine adjustment of the cooling capacity to any desired characteristic can be achieved. However, a range of values for n of 2 to 8, preferably 2 to 4, has proven to be useful for use on supermarket refrigerated cabinets.

It is still favorable to control both refrigerant lines. In the method according to the invention, it is advantageous in this case if the suction line is opened and closed within the hysteresis interval and the liquid line is open while the suction line is clocked.

With this variant, it makes sense to provide a real hysteresis for the non-clocked refrigerant line. For this purpose, within the first sub-interval I _1, an opening period of t = _a 0 chosen, that is clocked at higher temperatures refrigerant line remains within I₁ closed. The non-clocked refrigerant line is opened when T₁ is exceeded and closed when T₀ = T _{u is} undershot.

In principle, it is also possible to cycle the liquid line or even both refrigerant lines. However, the duration of opening of the fluid conduit provides the advantage that always the maximum pressure difference is available while relaxing the refrigerant available, regardless of the relative opening duration t _a / t _P of the clocked suction line, that is, the instantaneous flow rate through the evaporator.

A device for performing the method is by a refrigeration consumer, an evaporator, which is connected via a liquid line and a suction line to a composite refrigeration system, by a measuring device for the interior temperature of the refrigeration consumer, by one or two solenoid valves in the pressure and / or suction line and characterized by a microprocessor-controlled control device that controls the solenoid valve or valves depending on the interior temperature.

Given the complexity of the regulation, an electromechanical control is not advisable. By using a microprocessor, the method according to the invention can, on the one hand - if desired - be carried out in an almost arbitrarily complicated variant; on the other hand, an extremely flexible adaptation to the conditions prevailing at the respective cooling consumer or installation site is possible. In both cases, only the program needs to be changed accordingly, the hardware does not have to be modified.

The invention and further details of the invention are explained in more detail below with reference to drawings and tables. Here show:
FIG. 1 shows a schematic illustration of an embodiment of the device according to the invention,
Figures 2 and 3 tabular representations of a special embodiment of the method according to the invention for increasing or decreasing interior temperature and
Figure 4 is a flowchart which schematically illustrates the sequence of an embodiment of the method according to the invention.

In the diagram of Figure 1, a refrigeration consumer 1 is indicated as a rectangle. It is connected to a compound refrigeration system via two refrigerant lines, a liquid line 2 and a suction line 3. The refrigeration system has one or more compressors 4 and a condenser 5, which is cooled by air which is conveyed by the fan or fans 6. Additional cooling consumers which are not shown in the drawing can be connected via additional liquid and suction lines 2a, 3a.

Within the refrigeration consumer 1, liquid, pressurized refrigerant from the liquid line 2 is expanded with the aid of an expansion valve 7 and evaporated in an evaporator 8. In this case, cold is given off to cooling air, which is drawn in from the interior of the refrigeration consumer 1 to be cooled, flows around the evaporator 8 and is returned to the interior. The throughput through the liquid line 2 is controlled by a solenoid valve 9; the suction line 3 can be closed by a further solenoid valve 10. The solenoid valves 9, 10 are switched by relays.

The interior temperature in the refrigeration consumer 1 is measured with a temperature sensor 11, for example a thermal resistor or a thermocouple. In general, a value averaged over the volume of the interior is determined by arranging the temperature sensor 11 in the supply air flow to the evaporator 8 or in the return air flow from the evaporator 8.

The temperature sensor 11 is connected to a control device 13 via a measuring line 12 shown in broken lines. Control lines 14, 15, which are drawn with dashed lines in FIG. 1, also emanate from this. The solenoid valves 9, 10 in the liquid or suction line 2, 3 can be actuated via these control lines 14, 15.

The control device 13 has a microprocessor which is controlled by a program, which is preferably stored in an electrically erasable, permanent read-only memory (EEPROM) and implements the control method according to the invention. On the one hand, the EEPROM is not erased when the control device 13 is switched off, on the other hand, it allows any access to the individual memory cells, both for reading and for writing. Both the program and, above all, the control parameters can therefore be changed during operation and these changes remain saved even in the event of an interruption in operation, for example due to a brief power failure. The control unit is equipped with an input keyboard and an output display for entering the control parameters and for outputting measurement and control data.

The control device 13 can take on additional tasks by means of additional hardware (not shown in FIG. 1) and by correspondingly adapting the program. In particular, defrost control is available, which of course requires corresponding measuring devices on the outer surface of the evaporator 8. In addition, when determining the controlled variable interior temperature, it is favorable if supply air from and return air to the interior are measured at different points and via the individual measured values is averaged. Weights dependent on the respective operating state (for example day or night operation) can be included in the averaging. When using a processor-controlled control device, very sophisticated methods for averaging can be used. For example, the operating history can also be taken into account in order to adapt the control to special requirements.

In addition, additional digital inputs and outputs for the exchange of data with other devices, for example with a controller for the composite refrigeration system or with a computer for central control and / or monitoring.

An example of the practical functioning of a program which controls the control device 13 can be seen from the flow chart in FIG. After switching on or resetting (reset) the device (step 1.1), the configuration is first checked in step 1.2 (for example the type of refrigeration consumer and the system, etc.) and the corresponding default setting of the control device. In the following step 1.3, certain parameters are preset. This applies, for example, to the limit temperatures T _u and T _{o of} the hysteresis interval, the temperature values T₁ to T _n-1 , which limit the subintervals I₁ to I _n , and / or the switching parameters for the clocked refrigerant line, namely the clock period t _{P, k} and the Opening period during a period t on _{, k} . The program then enters an endless loop from which only switching off or resetting the device results.

As the first step 2.1 of the loop, the current control parameters are read from the EEPROM. These are, for example, the specifications for defrost control and the number and the respective type (supply or return air) of the temperature sensors. In the following step 2.2 the keyboard and the digital inputs are queried. If parameters are requested to be changed using the keyboard, this will be done in 2.3 performed. If required, step 2.4 enables the output of specially selected data, such as the individual measured temperature values and their setpoints, on the display. The device also communicates the request for output via the keyboard.

Then (2.5) the temperature measurements for the interior temperature are read in, a weighted average is calculated depending on the specific type and use of the refrigeration consumer, and the latter is stored temporarily. In step 2.6, the type of control of the refrigerant lines according to the invention is carried out. This is further explained in detail with the aid of FIGS. 2 and 3. Before returning to the start of the loop, other services are processed, for example the notification of the cooling consumer's current cooling requirement to a higher-level control device or to a computer which centrally monitors the control.

A special, simple example of the method according to the invention will now be explained with reference to FIGS. 2 and 3, which has proven its worth in tests in which the conditions of a refrigerated cabinet set up in a supermarket were simulated.

The hysteresis interval between the temperatures T _u and T _o is divided here into three equally large subintervals I₁ to I₃.

Both refrigerant lines 2, 3 are controlled, the suction line 3 being clocked with a cycle period t _P of 10 to 100 seconds, preferably 30 to 300 seconds. The period t _P is chosen to be the same for all subintervals. The periodic opening and closing of the suction line takes place when the interior temperature T _{i is} in the temperature range between T₁ and T₃, ie in one of the sub-intervals I₂ or I₃. The suction line is then opened during 35% or 70% of the period t _P and remains closed for the rest of the time. Both refrigerants are above the upper limit temperature T _o Lines 2, 3 open continuously, below the lower limit temperature t _u they are closed by the solenoid valves 9 and 10, respectively. Within the hysteresis interval] T _u , T _o [the opening state of the liquid line 2 depends on the time profile of the interior temperature T _i (t): it is opened when the temperature T 1 is exceeded (FIG. 2) and when T _u = T _{o is} undershot closed (Fig. 3). In contrast to the suction line 3, the liquid line 2 therefore experiences a real hysteresis, but only in the sub-interval I 1.

Claims (5)

1.Method for regulating the interior temperature of a refrigeration consumer, which is connected to a composite refrigeration system via two refrigerant lines, a liquid line (2) and a suction line (3), with the method measuring the interior temperature T _i and the throughput through the liquid line (2 ) and / or the throughput through the suction line (3) are controlled so that at least one of the two refrigerant lines (2, 3) is closed when the interior temperature T _{i is} below a first limit temperature T _u , and that both refrigerant lines (2, 3) are open when the interior temperature T _{i is} above a second limit temperature T _o , T _o > T _u , characterized in that one (3) of the two refrigerant lines (2, 3) is opened and closed several times while the Interior temperature T _{i is} within the hysteresis interval] T _u , T _o [. 2. The method according to claim 1, characterized in that the opening and closing of the refrigerant line (3) is done periodically within the Hystereseintervalles, wherein during a period t _P, the refrigerant line in question (3) within the time period t _a is open. 3. The method according to claim 2, characterized in that the hysteresis interval in n (n> 1) subintervals
I _k = [T _k-1, T _k ], k = 1, ..., n, T _k > T _k-1 , in which the ratio t _{a, k} / t _{P, k} , the relative opening time , is different, with t on _{, k} / t _{P, k} > t on _{, k-1} / t _{P, k-1}
for k = 2, ... n. 4. The method according to any one of claims 1 to 3, characterized in that both refrigerant lines (2, 3) are controlled so that the suction line (3) is opened and closed within the hysteresis interval and the liquid line (2) is constantly open. 5. Device for performing the method according to one of claims 1 to 4, characterized by a refrigeration consumer (1), an evaporator (8) via a liquid line (2) and via a suction line (3) to a composite refrigeration system (4, 5 , 6) is connected, by a measuring device (11) for the interior temperature of the refrigeration consumer (1), by one or two solenoid valves (9, 10) in the liquid (2) and / or suction line (3) and by a microprocessor-controlled control device ( 13), which controls the solenoid valve (s) (9, 10) depending on the interior temperature.

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