JPS5947224B2 - How to operate a refrigerated case - Google Patents

Description

[Detailed Description of the Invention] This invention has a freezing or refrigeration specification in which an evaporator is installed inside the case body, and cold air obtained by exchanging heat with the evaporator is circulated and ventilated to keep products displayed in the refrigerator cold. Concerning how to operate a refrigerated showcase.

In order to maintain product quality, it is desirable for the refrigerated showcases mentioned above, which are installed inside stores such as supermarkets, to be able to stably maintain the quality of the products inside at a predetermined refrigerating temperature throughout the entire operating period of the showcase. .

On the other hand, in order to maintain the temperature of the products in the warehouse, the amount of frost that accumulates on the evaporator as the refrigerator operates and the defrosting time required to melt and remove the accumulated frost must be carefully controlled. I'm going to call you.

To discuss this point in detail, first, it is well known that frost grows on the evaporator as the refrigerator continues to operate, and this frost covers the surface of the evaporator and accumulates.

However, if frost adheres and accumulates on the evaporator, it not only reduces the heat exchange efficiency of the evaporator, but also narrows the cross section of the ventilation passage between the fins of the evaporator, making it impossible to obtain a sufficient amount of cold air circulation. Cooling performance deteriorates and quality increases.

Furthermore, the amount of frost formed above is almost proportional to the continuous operation time of the refrigerator (e), and tends to increase as the ambient conditions around the case become more humid.Furthermore, the cold storage performance of the showcase is reduced when the amount of frost formed exceeds the limit of the evaporator. becomes clogged with frost and becomes extremely f4.

On the other hand, as mentioned above, in order to remove the frost accumulated in the evaporator, the refrigerator should be stopped before the frost amount exceeds the limit, and in this state, heater defrosting, hot gas defrosting, or air defrosting can be carried out. Defrosting is carried out using the well-known forced defrosting method, but not only does the refrigerator stop during the defrosting period and the cold storage is not performed, but during defrosting, active defrosting is required from outside. Since defrosting heat is applied, some increase in quality cannot be avoided.

In addition, the greater the amount of frost formation, the more heat and time required for defrosting, which increases the temperature of the product.

By the way, many of the showcases currently on the market have a driving cycle of 4 to 6 times a day, that is, 4 to 6 hours, in order to remove the frost that has accumulated over the course of cold storage operation. After cold storage operation, stop the refrigerator once,
During this stop period, it takes about 30 minutes to perform forced defrosting by applying defrosting heat from the outside, such as by using a heater defrosting method or hot gas defrosting method, and wipe out the accumulated frost using the evaporator. things are being done.

Next, the conventional operating method and operating characteristics described above will be explained with reference to FIG.

First, Figure 1 shows the configuration of a refrigerated open showcase.

In the figure, 1 is an outer box of the case body, 2 is an inner box, and an evaporator 4 and a fan 5 of the refrigerator are installed in a circulation ventilation duct 3 formed between the outer and inner boxes 1 and 2. .

Reference numeral 6 designates a product display shelf provided inside the warehouse, and reference numeral 7 designates a defrosting heater as a forced defrosting means provided on the evaporator inlet side within the duct 3.

Further, the evaporator 4 includes a condensing unit EWJa L/not shown and constitutes a refrigeration cycle.

When the refrigerator and the fan are operated with this configuration, the cold air exchanged with the evaporator 4 and cooled will pass through the duct 3 as shown by the arrow, blowing out a cold air curtain to the front opening of the case body, and discharging the outside air. To keep products in the refrigerator cold while preventing heat from entering.

When this cool operation state has passed for a predetermined period of time, the refrigerator is then temporarily stopped by timer control and the defrosting operation is switched over.
The defrosting heater 7 is energized to perform forced defrosting.

Note that the fan 5 continues to operate.

A circuit for performing such operational control is shown in FIG.

In the figure, CM is the compressor motor of the refrigerator, 52C is the electromagnetic contactor for the compressor motor, FM is the fan motor of the fan 5, H is the defrosting motor, and TM is the defrosting timer that sets the defrosting start time interval.

In order to simplify the explanation, FIG. 2 omits a defrosting termination thermostat, a compressor protection relay circuit, a refrigerator temperature control thermostat, etc., which are not directly related to the present invention.

Further, FIG. 3e shows an operation time chart and operation characteristics based on the above operation control circuit.

Generally, the rated capacity of a refrigerator is selected to maintain a predetermined quality of a product at, for example, 0° C. under standard ambient conditions, such as a case ambient temperature of 25° C. and a temperature of 60%.

When cold storage operation is performed under these conditions, the amount of frost on the evaporator 4 increases over time as shown in the figure.
It's going to increase.

In addition, as the amount of frost increases, the cooling performance of the funnel as mentioned above decreases, so the product temperature gradually rises, and after approximately 3.5 hours of cooling operation time, the effects of frost clogging become apparent. The cold storage performance deteriorates, and the temperature of the product starts to rise rapidly.

For this purpose, the defrost cycle Tdef, which predetermines the time interval between defrosts using the defrost timer TM, is set for approximately 4 hours (approximately 6 hours for evaporators with high frost tolerance) for cold storage operation. Switch to defrost operation.

However, in the above-mentioned conventional cold storage operation, since the refrigerator remains in continuous operation except for the temperature control thermostat operating during cold storage operation, the amount of frost buildup increases quickly, taking about 4 to 6 hours. Of these, the limit amount Qr reaches which the e-evaporator 4 is no longer able to perform its full function.

Moreover, even after switching to the defrost mode, forced defrosting time of about 30 minutes is required to wipe away the accumulated frost.

As a result, the temperature of the products in the warehouse fluctuates frequently at relatively short time intervals, making it impossible to maintain the quality at a constant temperature throughout the entire operating period of the showcase.

From this point of view, we aim to stabilize the product temperature throughout the showcase operation period by reducing the amount of frost that accumulates on the evaporator to the lowest possible level during the cold storage operation period until the start of the next defrosting period. It is desirable to reduce the number of forced defrosts per day by extending the cold storage operation time from one forced defrost to the next forced defrost as long as possible. It will be done.

The present invention has been made with the above-mentioned considerations in mind, and its purpose is to provide an advantageous method of operating a refrigerated showcase that satisfies the above-mentioned conditions and allows the temperature of refrigerated products to be stabilized. It is in.

This purpose of the present invention is to operate the forced defrosting means periodically or irregularly to clean the frost accumulated on the evaporator as the refrigerator operates.
In addition to performing this forced defrosting, during the cold storage operation period between forced defrosts, the refrigerator is operated and stopped periodically, and the duty cycle is repeated. For each cycle, when the refrigerator is stopped,
This is achieved by having off-cycle defrost performed.

Embodiments of the present invention will be described in detail below with reference to FIG.

First, Fig. 4 shows an operation control circuit that combines fixed period forced defrosting and duty cycle operation, Fig. 5 e shows an operation control circuit that combines irregular period forced defrosting and duty cycle operation, and Fig. 6 e This shows the operating chart and operating characteristics.

In FIGS. 4 and 5, DT is a timer for setting the duty cycle, and X is a timer relay activated by the output signal of the frost amount detection device 8.

The duty cycle timer DT controls the electromagnetic contactor 52C to be turned on and off alternately at a predetermined period.

Timer Marine-X replaces the defrost timer TM in Fig. 4, and switches the contacts by relay operation to switch from cold preservation operation to defrost operation, and performs forced defrost by energizing the heater for a predetermined time limit operation time. .

On the other hand, the frost amount detection device is indicated by reference numeral 8 in Fig. 1e, and either directly detects the amount of frost accumulated on the evaporator 4e with an electrode or optical method, or detects the amount of frost accumulated on the evaporator 4e by detecting the static air pressure at the inlet of the evaporator. Indirect V is detected from the difference in wind speed and temperature between the inlet and outlet sides.

It is configured to output a signal when the amount of accumulated frost exceeds a limit determined based on the cold preservation function of the evaporator compared to a reference value.

In addition, the duty cycle set by the duty cycle timer DT is such that, for example, in one cycle, the duty-on time to close the contact is 25 minutes, and the duty-off time to open the contact is 5 minutes, and the contacts are alternately turned on and off repeatedly. Yoguko is set.

From this point on, during the cold storage operation period other than when forced defrosting is performed, the refrigerator alternately operates and stops in accordance with the above-mentioned cycle, resulting in a so-called duty cycle operation.

This operation chart is shown in FIG. 6, where h and T indicate the 1 cycle time of the duty cycle, Ton indicates the duty on time, and Toff indicates the duty off time.

Moreover, as can be seen from the illustrated operation control circuit, when the duty is off, the defrosting heater H is not energized and only the fan is operated to perform off-cycle defrosting, which sends air from inside the refrigerator to the evaporator. ing.

As mentioned above, V cycle time T'& relatively short time e
By operating the refrigerator in a duty cycle with this setting, the time course of frost formation on the evaporator follows the course shown in FIG. 6.

That is, the frost that occurs during the duty-on time e is defrosted each time during the off-cycle defrosting that is performed during the subsequent duty-off time e.

In fact, the results of actual machine tests conducted by repeatedly changing the duty-on time Ton in the range of 10 to 60 minutes and the duty-off time Toff'aj in the range of about 10 to 20 minutes show that the evaporator t produces a large amount of frost. No accumulation is seen.

If the ambient conditions of the special case are almost the same as the standard ambient conditions, even if the duty cycle is operated continuously for a long period of time, there will be almost no residual frost formed on the evaporator, and the temperature will be higher and more humid than the standard ambient conditions. Even under such severe ambient conditions, only a small amount of frost remains after each cycle and gradually accumulates over the course of the duty cycle.

Moreover, the rate of increase in the amount of frost over time changes very gradually, as shown in the frost formation characteristics shown in the figure.

Therefore, the cold storage operating time until reaching the frost limit amount Q&, which significantly reduces the performance of the evaporator, is significantly longer than the operating characteristic of the conventional system described in FIG.

As a result, the practical time interval for forced defrosting to wipe out the frost that has accumulated on the evaporator has traditionally been 4 to 40 minutes.
However, by combining e-duty cycle operation as in the present invention, it is possible to extend the time to 12 to 24 hours depending on the degree of ambient conditions.

In other words, even if the defrost cycle Tdef set by the defrost timer TM in FIG. 4 is set to about 12 to 24 hours, the cold storage operation can be performed while maintaining high cold storage performance.

In addition to using the defrost timer TM in the embodiment shown in FIG. 4, the time setting of the defrosting cycle Tdef for performing forced defrosting at a predetermined period can also be done by counting the number of duty cycles. It is also possible to switch from duty cycle operation to forced defrosting operation when the number reaches a predetermined number.

In addition, as in the operation control circuit shown in Fig. 5, the command for forced defrosting operation is sent to the evaporator by detecting the amount of frost formed on the evaporator, and therefore at irregular intervals.
Even with this method, by combining duty cycle operation, the forced defrost cycle Tdef' is lower than that of the conventional method.
It can be extended by r wide e.

Moreover, according to the method shown in Figure 5, a command for forced defrosting can be given at an appropriate timing in accordance with changes in ambient conditions. It is also possible to further extend the defrost time interval.

As a further embodiment, the sequence may be configured to perform forced boxing using the duty-off time.

As is clear from the above explanation, according to the operating method of the present invention, forced defrosting and duty cycle operation during cold storage operation are combined, and off cycle defrosting is performed during duty off. As the time passes during cold storage operation, the rate of increase in frost that accumulates on the evaporator becomes extremely small, and the number of forced defrosts that were conventionally performed 4 to 6 times per day has been reduced to 1 to 2 times per day. e can be reduced.

Moreover, during the long period of cold storage operation,
Since the amount of frost accumulation is small, the evaporator can be operated at a high heat exchange rate and exhibit sufficient cold storage performance.As a result, as shown in the product temperature characteristics in Figure 6, the conventional The temperature stability of refrigerated products can be improved compared to the product temperature characteristics.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a refrigerated open showcase, Figure 2 is a conventional operation control circuit diagram, Figure 3 is an operation time chart and operation characteristic diagram based on the circuit in Figure 2, Figures 4 and 5. is a different operation control circuit diagram for implementing the present invention, No. 6
The figures are an operation time chart and an operation characteristic diagram based on the present invention. 1... Outer box of the case body, 2... Inner box, 4... Evaporator, 5... Fan, I... Defrosting heater. DT...Duty cycle timer, T...
...One cycle time of duty cycle, Ton
...Dution time, Toff...
...Duty off time, Tdef...Forced defrost cycle.

Claims (1)

[Scope of Claims] 1. A refrigerated showcase in which a -C/〈porator is installed inside the case body, and cold air obtained by exchanging heat with the evaporator from the operation of the refrigerator is circulated to keep the products displayed inside the refrigerator cold. , the forced defrosting means is operated at regular or irregular intervals, and the evaporator is
In addition to performing forced defrost to wipe away the accumulated frost, the refrigerator is operated and stopped periodically during the cold storage operation period between forced defrosts. A method for operating a refrigerated showcase, characterized in that the refrigerator is operated in a utility cycle, and furthermore, in each cycle of the duty cycle, off-cycle defrosting is performed when the refrigerator is stopped. 2. A method of operating a refrigerated showcase in which forced defrosting is performed periodically at predetermined time intervals by timer control or the like, in accordance with the operating method according to claim 1. 3 In the operating method e described in claim 1, the frosting state of the evaporator is constantly monitored, and when the amount of accumulated frosting reaches a predetermined limit, this is detected and forced defrosting is performed. How to operate a refrigerated showcase.