JPS6157990B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is mainly intended for use in cases where the usage temperature is around 0°C, such as for meat and fresh fish, by circulating cold air inside the refrigerator by operating a refrigerator to display products. Relating to a refrigerated open case for keeping cold.

In order to maintain the quality of products, the refrigerated open store cases installed and used in stores such as supermarkets are subject to fluctuations in the ambient conditions within the store during operation, and regardless of whether the store cases are kept cold or defrosted. It is desirable to be able to perform stable operation so that the temperature of the products in the refrigerator is always maintained at a predetermined temperature.

By the way, as is well known in the above-mentioned refrigerated open-show case, frost forms and adheres to the evaporator due to outside air entering through the opening of the case body as the cold storage operation progresses. If the refrigerant in the evaporator and the evaporation temperature are constant, the amount of frost increases as the cooling operation time of the refrigerator increases and as the humidity of the surrounding outside air increases. Moreover, the frost that accumulates on the evaporator not only covers the surface of the plate fin coil type evaporator and deteriorates the heat exchange efficiency, but also causes frost clogging between the plate fins, which significantly obstructs the ventilation of cold air inside the refrigerator and impairs the cold storage performance. This causes a significant decrease in the amount of water.

For this reason, conventionally, the refrigerator is temporarily stopped after 4 to 6 hours of cold storage operation, and during this stop period, a well-known defrosting means such as an electric heater method or a hot gas method is used to wipe out the frost. Defrosting heat is forcibly applied to the evaporator from the outside to melt and remove the frost. However, during defrosting, the refrigerator is stopped, and the defrosting heat is supplied from outside by a heater, etc., so it is possible to avoid raising the internal temperature and therefore the product temperature to a certain extent. I can't.

Here, the general structure of the above-mentioned refrigerated open show case, as well as a time chart of conventional operation, and changes in product temperature and frost formation will be explained with reference to figures. First, in FIG. 1, 1 is an outer box of the case body, 2 is an inner box, and an evaporator 4 and a blower fan 5 of a refrigerator are installed in a circulation ventilation path 3 formed between the inner and outer boxes. . 6 is a product display shelf installed inside the warehouse. When the refrigerator and fan 5 are operated in this configuration, cold air that has been cooled by heat exchange with the evaporator 4 flows through the ventilation path 3, and a cold air curtain is blown out to the front opening of the case body as shown by arrow A. This keeps the products inside the refrigerator cool while preventing outside air from entering. After a certain predetermined period of time has elapsed in this cold storage operation, the refrigerator is then stopped and switched to defrosting operation, and the electric defrosting heater indicated by reference numeral 7 in the figure is energized to perform heating defrosting. The time chart for this operation is shown in Figure 2. Generally, the standard ambient conditions are a temperature of 25°C and a humidity of 60%, and the freezing capacity of the refrigerator is adjusted to maintain the specified product temperature under these standard ambient conditions. Defrosting is carried out at a rate of approximately 30 minutes every four hours. Further, in this case, the average product temperature of the displayed products and the amount of frost on the evaporator change as shown in FIG. That is, as is clear from the figure, when the refrigerator is operated continuously, the amount of frost increases approximately in proportion to the cold storage operation time. Further, as described above, the greater the amount of accumulated frost, the longer the defrosting time required for defrosting, and the longer the defrosting time, the greater the rise in the temperature of the products in the warehouse. From this point of view, in order to minimize changes in product temperature through the operation of the show case,
The time required for defrosting each time is as short as possible, which means that the amount of frost that accumulates during the cold storage operation up to the start of defrosting is small, and the time required for cold storage operation from one defrost to the next defrost. It is desirable to be able to extend the defrosting period as long as possible and reduce the number of defrosting operations per day. Moreover, since the majority of the heat load on an open show case is heat infiltrated by outside air, the quality of defrosting performance, especially in the overload operation range where ambient conditions are severe, has a large effect on maintaining product temperature.

On the other hand, conventional show cases are equipped with temperature control thermostats (hereinafter referred to as "temperature control thermostats") for the purpose of regulating the internal temperature of the refrigerator, especially in the winter or during nighttime operation under good ambient conditions and under light loads. The operation of refrigerators is controlled to prevent cooling. In other words, the refrigerator operation control circuit shown in Fig. 3 is constructed by incorporating a thermostat 9 with a temperature-sensing tube 8 installed on the evaporator outlet side in Fig. 1 into the circuit, and CM in the figure is the compressor motor, and 52C is the compressor motor. The electromagnetic contactor, FM is the fan motor of the blower fan 5 in Figure 1, TM is the defrost timer that sets the defrost cycle, H is the defrost heater 7 in Figure 1,
23I indicates the temperature control thermostat 9 described above. Contact 23I of the temperature control thermo switches to the high temperature contact H when the cold air temperature is higher than the set temperature, and to the low temperature contact L when the cold air temperature is lower than the set temperature, and this contact switching action causes the temperature of the air exiting the evaporator to become the set temperature. If the temperature falls below the set temperature, the refrigerator will stop, and if the temperature rises above the set temperature again, the refrigerator will operate to keep the product at an appropriate temperature during cold storage operation. Controlling the operation of the refrigerator based on this temperature control thermostat is called thermocycle operation, and the operation pattern, average product temperature, and changes in frost amount are shown in FIG. 4. Furthermore, the fourth
The figure shows the operating characteristics in a light load operation range where the ambient conditions are slightly better than the standard ambient conditions mentioned above. As is clear from FIG. 4, in this thermocycle operation, the operation of the refrigerator is controlled by the operation of the temperature control thermostat so that it repeatedly starts and stops even during the cold preservation operation. On the other hand, the refrigerator fan is operated to blow and form an air curtain even when the refrigerator is stopped.
Therefore, during this period when the refrigerator is stopped, so-called off-cycle defrosting, in which air at a temperature of 0° C. or higher circulating through the ventilation path flows through the evaporator to defrost, is performed each time. Therefore, compared to the characteristics shown in Figure 2 when the refrigerator is operated continuously throughout the cold storage operation period, the amount of accumulated frost during the cold storage operation is reduced, so the defrosting when switching from cold storage operation to defrosting operation is reduced. Since the defrosting time required for this process can be shortened, as a result, there is less fluctuation in the average product temperature and the product temperature can be maintained stably. However, the range in which the above thermocycle operation can be performed is based on the isenthalpy line passing through the points under standard ambient conditions or the isoabsolute humidity line, which is the thermocycle operation boundary line B in Figure 5 (this is theoretically It is limited to the area to the left of the (equal refrigeration load line). Point X in the figure shows the standard ambient conditions of temperature 25℃ and humidity 60%, points Y and X indicate the ambient conditions shifted left and right from boundary line B with point X as a reference, and Figure 4 shows the standard ambient conditions at point Y. Indicates thermocycle operation. If we consider cold storage operation at point Z, which has an ambient condition that is harsher than the standard ambient condition, contrary to point Y, point Z is in the shaded area to the right of boundary line B, and the refrigerator is slightly overheated. Since it is a load operation, the temperature sensing part of the temperature control thermostat 9 does not fall below the set temperature, so the thermocycle operation is not performed and the refrigerator is not operated until it switches to defrosting operation as described in Fig. 2. It becomes continuous operation. Moreover, since the ambient conditions are harsher than standard ambient conditions, the amount of accumulated frost during cold storage operation increases significantly, causing frost clogging even before defrosting, deteriorating the heat exchange rate of the evaporator and the performance of the air curtain. . As a result, as shown in Figure 6, the operating characteristics are such that as the amount of frost increases, the defrosting time required for defrosting increases. The rise in temperature of the product will be significant, and there is a risk that the quality of the product will deteriorate.

In this way, with the conventional show case cold storage operation method, excellent product cold storage properties can be obtained when thermocycle operation is performed in light load operating ranges, but on the other hand, it is difficult to maintain cold storage properties under harsh ambient conditions such as in the summer when thermocycle operation cannot be performed. In the load operation range, the refrigerator is operated continuously, so the amount of accumulated frost during cold storage operation increases significantly, resulting in a significant deterioration of cold storage performance, making it difficult to maintain stable product temperatures. It was extremely difficult to do so. In this case, it would of course be possible to use an overspecified refrigerator with a higher refrigerating capacity than necessary so that thermocycle operation can be performed with sufficient margin even in the summer when the ambient conditions are harsh. is expensive, and economical operation throughout the year cannot be expected.

The present invention was conceived in consideration of these points, and its purpose is to employ a refrigerator whose refrigerating capacity is selected so as to maintain a predetermined product temperature under standard ambient conditions. It is possible to reduce the amount of frost that accumulates during cold storage operation even in the severe overload operation range of To obtain a refrigerated open case with good performance, which can reduce the number of defrosting operations per day by heating type defrosting, etc., and can always stabilize product temperature throughout the year.

According to the present invention, the operation of the refrigerator is controlled by the operation of the thermostat for regulating the internal temperature in the light load operation region where the ambient temperature of the case is lower than the preset temperature based on a preset temperature, and When the ambient temperature reaches an overload operating range higher than the set temperature, the operation switching control device switches the refrigerator to duty-cycle operation, in which the refrigerator is alternately operated and stopped at a predetermined cycle, thereby controlling the operation of the refrigerator. This is achieved by arranging that off-cycle defrosting is performed during the operation of the thermostat and the stop period of the refrigerator due to duty cycle operation.

The present invention will be described in detail below based on illustrated embodiments.

First, FIG. 7 shows an operation control circuit for a refrigerator including an operation switching control device according to the present invention. This circuit is based on the circuit shown in FIG.
Both are installed in the case body 1 shown in FIG. As shown in FIG. 7, the internal circuit of the device 10 includes an operation switching thermostat 12 (hereinafter referred to as "switching thermostat 12") that operates in response to the ambient temperature of the case, and a thermostat 12 that is energized depending on the operating conditions of the thermostat 12. It is equipped with a timer DT for duty cycle operation connected to the high temperature contact H of the switching thermometer 12 and an auxiliary relay X for thermocycle operation connected to the low temperature contact L so that the switching thermometer 12 is controlled. The contacts are connected in parallel to the temperature control thermostat 9, and the a contact of the auxiliary relay X is connected in series to the temperature control thermostat 9, as shown in the figure, in the control circuit of the refrigerator. Among these, the switching thermostat 12 has a set temperature that is slightly higher than the standard ambient temperature of 25°C mentioned above, for example 28°C, and when the ambient temperature of the case is higher than 28°C, the contact is changed to the high temperature contact H, and when the temperature is higher than 28°C. In a low range, it operates to switch to the low temperature contact L. In addition, the duty cycle operation timer DT forcibly turns on the timer contact according to a predetermined cycle after the timer starts operating.
An example of its operation pattern is to turn it on for 10 minutes and then turn it off for the next 5 minutes.

Next, the operation control operation of the refrigerator based on the circuit shown in FIG. 7 will be described. First, in the light load operating range where the ambient temperature of the case is lower than the set temperature (28°C) of the switching thermostat 12, the a contact of the auxiliary relay X closes, and the refrigerator operates in the operating pattern shown in FIG. The operation is controlled according to the following. Of course, once the predetermined cold storage operation time (4 hours) has elapsed, the defrost timer will start.
The refrigerator is stopped by TM, and the defrosting heater H is energized to enter heating type defrosting operation, as in the conventional case. When the ambient conditions change from this operating state and the ambient temperature of the case reaches a point higher than 25°C, for example, the overload operating region at point Z in Fig. 5, the contact of the switching thermostat 12 switches from L to H. The a contact of relay X opens to disconnect temperature control thermostat 9 from the circuit. At the same time, the duty cycle operation timer DT starts its timer operation, and the refrigerator switches to so-called duty cycle operation, in which the refrigerator alternately starts and stops at a predetermined cycle even during the cold storage operation period. . The operating pattern and operating characteristics of this duty cycle operation are shown in FIG. In the figure, DTon and DToff indicate the operating and stopping periods of the refrigerator based on the duty cycle. Moreover, during the stop period DToff, the refrigerator fan continues to operate and off-cycle defrosting is performed in the same way as described in FIG. 4. Therefore, as is clear from Fig. 8, even in the overload operation region where the ambient conditions are harsher than the standard ambient conditions during cold storage operation, the operation is controlled just as if the thermocycle operation was extended. Since the amount of accumulated frost is small, the evaporator can be operated efficiently, and no frost clogging occurs, so good air curtain performance can be maintained. As a result, the outside air intrusion load increases due to the harsh ambient conditions, resulting in overload operation, and the average product temperature increases slightly overall, but the amount of accumulated frost on the evaporator is reduced, so the amount shown in Figure 6. Compared to the characteristics of continuous operation shown above, the temperature of the product is also more stable, and the cold storage performance of the product can be significantly improved. The range of the above-mentioned switching operation can be expressed graphically as shown in FIG. 9. In other words, in the light load operation region on the left side of the operation switching boundary line C in Fig. 9, the refrigerator is operated in thermocycle mode, and in the overload operation region indicated by diagonal lines on the right side, the refrigerator in cold storage operation is controlled by duty cycle operation. be done. For the sake of clarity, we have explained that the operating method is immediately switched at boundary line C, but as is well known in thermostats, this operation is accompanied by hysteresis, so in Fig. 9, boundary line C is There is a range of degrees.

As is clear from the above, according to the present invention, the amount of frost that accumulates on the evaporator is significantly reduced due to duty cycle operation during cold storage operation even under harsh ambient conditions compared to conventional methods. The heat exchange rate hardly decreases, and the air curtain performance is stable, allowing the temperature of the products in the refrigerator to be maintained at an appropriate temperature. Also, when switching from cold preservation operation to defrost operation, the amount of accumulated frost on the evaporator is small, so the time required for heating defrost using a heater etc. is shortened.
Furthermore, the number of defrosting operations per day can be reduced from 6 times/day to 3 to 2 times/day, which reduces the number of defrosting operations performed by heating, which has the greatest impact on maintaining product quality. It is possible to suppress the rise in product temperature to a low level. Moreover, thermocycle operation is performed in the light load operation range, and the above-mentioned duty cycle operation and thermocycle operation can be switched automatically according to changes in ambient conditions, allowing for a wide range of ambient conditions throughout the year. It is possible to provide a refrigerated open case with excellent performance capable of suppressing the rise in product temperature during defrosting and keeping products refrigerated at an appropriate temperature despite changes.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the refrigerated open shower case, and Figures 2, 4, 6, and 8 are continuous operation under standard ambient conditions, thermocycle operation under light overload operation, and overload operation, respectively. An operation characteristic diagram showing the operation pattern, average product temperature, and changes in frost amount in continuous operation in the load operation region and duty cycle operation in the overload operation region according to the present invention. Figure 3 shows the conventional thermocycle. Refrigerator control circuit diagram for operation, Figure 5 is an explanatory diagram showing the range of ambient conditions in which thermocycle operation is possible, Figure 7
The figure is a circuit diagram of an embodiment of the operation switching control device based on the present invention, and FIG. 9 is an operation switching chart according to the present invention. 1... Case body, 4... Evaporator, 5...
...Interior ventilation fan, 7... Defrosting heater, 9... Thermostat for controlling temperature in the oven, 10... Operation switching control device, 12... Operation switching thermostat,
DT...Duty cycle operation timer, X...
...Auxiliary relay.

Claims (1)

[Claims] 1. An evaporator and an internal ventilation fan are installed in the case body, and the cold air obtained by exchanging heat with the evaporator by operating a refrigerator is circulated and ventilated by operating the internal ventilation fan. In a refrigerated open case that keeps products displayed in the refrigerator cold, in a light load operation range where the ambient temperature of the case is lower than a preset temperature, the refrigerator is controlled by the operation of the thermostat for regulating the internal temperature. In an overload operation range higher than the set temperature, the refrigerator is equipped with an operation switching control device that controls the operation of the refrigerator by switching to a duty cycle operation in which the refrigerator is alternately operated and stopped at a predetermined cycle, and furthermore, it has a thermostat. 2. A refrigerated open-shuttle case characterized in that an off-cycle defrosting operation is performed in which the internal ventilation fan continues to operate during a period when the refrigerator is stopped due to the operation and duty cycle operation. 2. In the refrigerated open case as set forth in claim 1, the operation switching control device detects the ambient temperature of the case and operates in response to the operation switching thermostat, and the operation switching thermostat is connected to a high temperature contact. and is connected to the low-temperature contact of the operation switching thermostat and a duty cycle operation timer that starts timer operation in the overload operation region in response to the operating conditions of the operation switching thermostat, and is connected to the low-temperature contact of the operation switching thermostat and starts the timer operation in the overload operation region in response to the operating conditions of the operation switching thermostat. The contacts of the thermostat for controlling the temperature inside the refrigerator and the auxiliary relay are connected to the drive coil of the electromagnetic contactor, which is equipped with an auxiliary relay that closes the contacts in the area, and is connected to the operation control circuit that controls the energization of the electric motor for driving the refrigerator. A refrigerated open case in which a series circuit with a contact point is connected in series, and the duty cycle operation timer contact point is connected in parallel to this series circuit.