JPH05118732A - Method of controlling defrosting of showcase - Google Patents

Abstract

PURPOSE:To grasp defrosting start deposited frost quantities with high accuracy and prevent useless defrosting and frost residual by determining the amount of deposited frost of a cooler in a showcase by a multiplied value of coefficients based on open air temperature, refrigerator chamber cooling state and an operation status of a refrigerating plant and the performances for each case. CONSTITUTION:During showcase operation, a microcomputer 2 inputs the output of an open air temperature sensor and a chamber temperature sensor 4 for a specified sampling cycle and an opening/closing state of a solenoid valve 7 which controls the distribution of refrigerant to a cooler into an internal memory and computes a state coefficient D of a solenoid valve 7 as open air frost coefficient G (T), chamber status frost coefficient F (t) and a cooling state coefficient based on the specified functions. From the equation FROST= G (T).F(t) D.K (K: performance coefficient), the amount of FROST per unit time of a showcase is computed. When the accumulated amount of frost based on the estimation of the amount of frost reaches a predetermined value, a defrosting command is generated is generated so that defrosting operation may be carried out by supplying power to a defrosting heater.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defrosting control method for a cooler of a showcase, which cools the inside of a refrigerator with a cooler.

[0002]

2. Description of the Related Art Conventionally, in the case of defrosting a cooler in a showcase of this kind, a 24-hour timer is provided and the timer is set to issue a defrosting command every 3 hours, for example, at a fixed time. The defroster of the cooler was being performed. However, according to the constant time defrosting, since the defrosting is performed regardless of the change in the frost formation amount on the cooler due to the change in the outside air temperature,
Especially when the outside air temperature is low and the environment is dry like in winter, and when the amount of frost is small, a so-called premature cut-off state in which defrosting is started and immediately ended is repeated, and wasteful defrosting is repeated. The waste of energy due to frost and the deterioration of products stored in the refrigerator have been problems.

On the contrary, when the outside air temperature is high and the humidity is high like in summer and frost is severe, frost blockage occurs in the cooler in the latter stage of the cooling operation and the circulation of cold air into the refrigerator is disturbed. There was a problem that the temperature inside the cabinet rises and the freshness of stored foods, etc. deteriorates significantly.

That is, when the amount of frost formed is small at the time of entering the defrosting of the cooler, wasteful defrosting is performed, and conversely, there is a problem that frost residue occurs even if it is too large. Is ideal. Therefore, for example, in Japanese Unexamined Patent Publication No. 1-155181 (F25D21 / 06), various temperature and humidity addition constants are determined from the outside air temperature around the case and the relative humidity of the outside air.
It has been attempted to achieve the quantitative defrosting by adding the above values to virtualize the frosting amount, and by comparing the virtual frosting amount with a set value to issue a defrosting command.

[0005]

However, if dust or the like adheres to the sensor for detecting humidity due to long-term use,
This dust absorbs moisture, and accurate humidity detection cannot be performed. Therefore, when the amount of frost is hypothesized with humidity as a factor, there is a problem that accurate calculation cannot be performed due to long-term use.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the conventional problems and provide a defrosting control method for a showcase capable of achieving accurate defrosting.

[0007]

According to the defrosting control method for a showcase of the present invention, an outside air frosting coefficient G derived from the outside air temperature condition and an inside condition frosting coefficient F derived from the inside cooling condition.
And the cooling condition frosting coefficient (state coefficient of the solenoid valve 7) D derived from the operating condition of the refrigerating apparatus and the performance coefficient K determined for each case are multiplied to obtain the frosting amount F per unit time.
When the accumulated frost amount SUM obtained by calculating the ROST and integrating the frost amount FROST reaches a predetermined value, the defrosting command of the cooler is issued.

[0008]

The amount of frost formed on the cooler of the showcase changes depending on the outside air temperature T as shown by the broken line in FIG. Further, it changes as shown by the broken line in FIG. 4 depending on the inside cooling condition (representative temperature t of the inside condition). Furthermore, it is also affected by the operating condition of the refrigeration system (opening / closing of the solenoid valve 7). By determining the coefficients G, F, and D based on these factors and multiplying them by the performance coefficient K for each case, the virtual frost formation amount FROST per unit time can be assumed.
Quantitative defrosting can be realized by issuing a defrosting command when the cumulative amount SUM of the amount of frost formation reaches a set value.

[0009]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram of a control circuit 1 for implementing the defrosting control method of the present invention, and FIG. 2 is a flow chart showing a program of a microcomputer 2. The control circuit 1 is composed of a general-purpose microcomputer 2. The microcomputer 2 receives an output of an outside air temperature sensor 3 for detecting an ambient temperature where a low-temperature showcase (not shown) is installed, that is, the outside air temperature T, and the above-mentioned The output of the in-compartment temperature sensor 4 that detects the representative temperature t of the in-compartment situation of the low temperature showcase is input. The in-compartment temperature sensor 4 includes a circulating cold air discharge temperature of the low-temperature showcase, a circulating cold air suction temperature (including a calculated in-compartment temperature calculated from both temperatures), an evaporating temperature of a cooler (not shown), a cooler outlet temperature or a cooler It is provided in a low temperature showcase (not shown) so as to detect any one of the internal air temperatures or a plurality of these values.

A microcomputer 2 is provided for each low-temperature showcase, and its output is connected to a controller 6 of a compressor which constitutes a refrigerating device (not shown) together with the cooler. The output of the microcomputer 2 is further connected to an electromagnetic valve 7 that controls the flow of the refrigerant to the cooler of the low temperature showcase and a defrost heater 8 of the cooler. Each low temperature showcase has one or more coolers, and these low temperature showcases are connected to a plurality of single compressors, and the refrigerant flow to the coolers of each low temperature showcase is electromagnetic by the microcomputer 2. It is controlled by opening and closing the valve 7.

That is, the microcomputer 2 issues an operation command to the controller 6 of the compressor on the basis of the output of the internal temperature sensor 4 when the case needs to be cooled, and the controller 6 operates from any one of the microcomputers 2. When the instruction is received, the compressor is operated, and when the operation instruction is not received from any of the low temperature showcase microcomputers 2, the compressor 6 is stopped. That is, the microcomputer 2 supplies the refrigerant to the cooler by issuing the operation command and opening the solenoid valve 7 based on the output of the inside temperature sensor 4 of the low temperature showcase in which the microcomputer 2 is provided. The inside temperature of the low temperature showcase is controlled to a set value by evaporating to cool the inside of the refrigerator, or when cooling is not necessary, the operation command is stopped and the electromagnetic valve 7 is closed.

Next, the defrosting control operation of the microcomputer 2 will be described with reference to the flow chart of FIG. In step S1, the microcomputer 2 sets the outside air temperature T (° C.) based on the output of the outside air temperature sensor 3 and the representative temperature t of the inside condition based on the inside temperature sensor 4 at a predetermined sampling cycle (for example, 1 second). (° C.) and the open / closed state of the solenoid valve 7 controlled by itself are input to an internal memory, and in step S2, the outside air frosting coefficient G is calculated from the function shown in FIGS.
(T), the inside condition frosting coefficient F (t), and the state coefficient D of the solenoid valve 7 as the cooling state coefficient are calculated.

Now, the functions shown in FIGS. 3 to 5 will be described.
It has been known that the amount of frost on the cooler increases as the outside air temperature T increases, and exhibits a tendency like a broken line curve in FIG. The outside air frosting coefficient G (T) is defined by a function shown by a solid line in FIG. That is, the outside air frosting coefficient G (T) is given as a function that does not change with a small value when the outside air temperature T is low, rises from a certain temperature with a predetermined slope, and does not change again when the outside air temperature T is high, 2 stores this, and in step S2, the outside air temperature T obtained from the outside air temperature sensor 3 is added to this function.
The outside air frosting coefficient G (T) is calculated by substituting The above function is not limited to the one shown in FIG. 3, and is generally a positive number at least at a certain outside air temperature and 1 at a certain outside air temperature, and the number is larger or equal as the outside air temperature is higher. That is, if the outside air temperature T1
<If the outside air temperature is T2, it is defined by a function of G (T1) ≦ G (T2).

Further, it has been known that the amount of frost on the cooler increases as the representative temperature t in the inside of the refrigerator decreases, and exhibits a tendency as shown by the broken line curve in FIG. The inside condition frosting coefficient F (t) is defined by a function indicated by a solid line in FIG. That is, the inside condition frosting coefficient F (t) is large and does not change when the representative temperature t is low, falls from a certain temperature with a predetermined slope, and does not change again when the representative temperature t is high. The computer 2 stores this, and in step S2, the representative temperature t of the inside situation obtained from the inside temperature sensor 4 is substituted into this function to calculate the inside situation frosting coefficient F (t). ..
The above-mentioned function is not limited to the one shown in FIG. 4, and is generally a positive number at least at a representative temperature of a certain inside condition and is 1 at a certain representative temperature.
The lower the representative temperature is, the larger or equal the number is, that is, if the representative temperature t1> the representative temperature t2, F (t1) ≦ F (t
2) is a function.

Furthermore, the amount of frost formed on the cooler is large when the refrigerant flows into the cooler and is evaporated, and is small when the supply of the refrigerant is stopped. The state factor D of the solenoid valve 7 is 1 when the solenoid valve 7 is open, and 0.5 when the solenoid valve 7 is closed.
Is defined by a function as shown in FIG. The microcomputer 2 stores this, and in step S2, the state coefficient D of the solenoid valve 7 is calculated according to the open / closed state of the solenoid valve 7 controlled by itself. The above function is not limited to the one shown in FIG. 5, but is generally a function determined by the state of the solenoid valve 7, that is, opening and closing, and is always a positive number, and the value when the solenoid valve 7 is open is A number equal to or greater than the value at close,
That is, it is defined by a function of D (open) ≧ D (closed).

Next, in step S3, the microcomputer 2 calculates the frost formation amount FROST per unit time (1 second in this case) of the low temperature showcase by the calculation formula shown in Formula 1.

[0017]

[Equation 1]

K in the equation (1) is a coefficient of performance determined by the performance of each low-temperature showcase. If the low-temperature showcase is, for example, an open showcase, it is given as an outside air entrainment constant or variable determined by the performance of the air curtain. The unit is g / sec. As is clear from Equation 1, the frost formation amount FROST per unit time is calculated in step S2.
Outside air frosting coefficient G (T) and inside situation frosting coefficient F obtained in
It is calculated by multiplying (t) by the state coefficient D of the solenoid valve 7 and the performance coefficient K, and the unit is g. That is,
By giving the effect of each of the above-mentioned factors that changes with the change of the frost formation on the cooler to the FROST, it is possible to accurately estimate the frost formation per unit time.

Next, in step S4, the microcomputer 2 adds a new accumulated frost formation amount SUM (by adding the accumulated frost formation amount SUM per unit time calculated in step S3 to the accumulated value SUM of frost formation up to the previous time. The unit is g), and in step S5, it is determined whether or not the cooling elapsed time from the previous defrosting is equal to or longer than the minimum cooling time such as 2 hours. If not, the process returns to step S1. By thus ensuring the minimum cooling time, frequent defrosting is eliminated. If cooling has been performed for at least the minimum cooling time in step S5, it is determined in step S6 whether or not the cumulative frost formation amount SUM calculated in step S4 is equal to or greater than the preset preset frost formation amount of the cooler optimum for starting defrosting. And SU
If the value of M has not reached the set amount of frost, the process returns to step S1 and is repeated thereafter.

When the accumulated frost amount SUM reaches the set frost amount in step S6, the microcomputer 2 proceeds to step S6.
In step 7, the defrosting request signal is issued to issue a defrosting command to itself, and the defrosting heater 8 provided in the cooler is energized to start defrosting the cooler. Then, in step S8, the cumulative frost formation amount SUM is reset and the process returns to step S1.

Next, the operation of calculating the accumulated frost amount will be executed assuming the actual operating conditions. Outside temperature T is now +25
C., the representative temperature t of the inside condition is 0.degree. C., the solenoid valve 7 is open, and each state remains unchanged. The low-temperature showcase has a coefficient of performance of 0.2 g / sec and a set frost amount of 2160.
g.

The outside air frosting coefficient G (+ 25 ° C.) when the outside air temperature T is + 25 ° C. is 1, as is clear from FIG. 3, and the inside situation frosting coefficient F when the representative temperature t of the inside situation is 0 ° C. (0 ° C.) is also 1 as apparent from FIG. Further, when the solenoid valve 7 is open, the state coefficient D (open) is 1 from FIG. 5, so the frost formation amount FROST per unit time (1 second) obtained by the equation 1 is 0.2 g.

Frost amount FROST of 0.2 g per second
In the case of, the accumulated frost amount SUM becomes 2160 g after reaching the set frost amount 3 hours after the start of the cooling operation, and defrosting is started. Therefore, the cooling operation time until defrosting of the cooler in this case is calculated to be 3 hours.

Here, if the outside air temperature T decreases, the amount of frost decreases, but since the outside air frosting coefficient G (T) also decreases, the frosting amount FROST per unit time also decreases, so defrosting starts. The cooling operation time before the operation is extended and defrosting is started with an appropriate amount of frost formation. This also applies to the case where the representative temperature t in the inside situation rises, and the inside operation situation frosting coefficient F (t) becomes small, so that the cooling operation time is similarly lengthened. Also, when the electromagnetic valve 7 is closed for a long period of time, the defrosting start with an appropriate amount of frost is realized by extending the cooling operation time by decreasing the value of the state coefficient D.

Further, this makes it possible to predict the amount of frost on the cooler over time, so that the accumulated amount of frost SU
As M increases, it is possible to perform predictive control such as increasing the number of rotations of the cold air circulating fan motor in the refrigerator, lowering the set temperature in the refrigerator, or increasing the performance coefficient K. That is, when the amount of frost on the cooler increases, the circulation of circulating cold air is also obstructed, and the air curtain weakens in the open showcase. Since the temperature also rises, it tends to decrease the set temperature in the refrigerator to supplement the cooling capacity,
Further, the performance coefficient K, which is an outside air entrainment constant, is increased in accordance with an increase in outside air entrainment due to the weakening of the air curtain, and the defrosting start time is advanced.

When a plurality of low temperature showcases are connected to the compressor, the temperature rise in the refrigerator and the number of times of defrosting are reduced,
In addition, in order to shorten the defrosting time, it is necessary to simultaneously start defrosting of a plurality of connected defrosters. However, since the inside condition and the outside air temperature are different for each case, the defrost request signal is separately issued for each microcomputer 2.

Therefore, the defrosting command is issued to the microcomputers 2 in all cases by the defrosting request signal of the microcomputer 2 designated in advance. Alternatively, this problem is solved by adopting a configuration in which the microcomputer 2 that has issued the defrosting request signal earliest after defrosting issues a defrosting command to all the cases or the parent case microcomputer 2 that commands defrosting. To do.

Further, when a failure occurs in each of the sensors 3 and 4, since the input value and the actual temperature are different, the calculated frost formation amount per unit time is deviated. Therefore, when a sensor malfunctions, the corresponding coefficient is set to standard value 1 to prevent this.

[0029]

According to the defrosting control method for a showcase of the present invention, the amount of frost formed on the cooler of the showcase is based on the outside air temperature, the cooling condition inside the refrigerator, the operating condition of the refrigeration system, and the performance of each case. Since it is calculated by multiplying the coefficient, the defrosting start frost formation amount can be accurately grasped. Thereby, wasteful defrosting and residual frosting can be prevented, and smooth defrosting control can be realized.

The defrosting control method for a showcase according to the present invention does not require a humidity sensor, and has excellent effects such as no control error due to long-term use.

[Brief description of drawings]

FIG. 1 is a block diagram of a control circuit.

FIG. 2 is a flowchart showing a program of a microcomputer.

FIG. 3 is a diagram showing a relationship between an outside air temperature and an outside air frosting coefficient.

FIG. 4 is a diagram showing a relationship between a representative temperature of the inside situation and an inside situation frosting coefficient.

FIG. 5 is a diagram showing a relationship between a state of a solenoid valve and a state coefficient of the solenoid valve.

[Explanation of symbols]

 1 Control Circuit 2 Microcomputer 3 Outside Air Temperature Sensor 4 Inside Temperature Sensor 8 Defrost Heater

Claims (5)

[Claims] 1. An outside air frosting coefficient derived from an outside air temperature condition, an inside condition frosting coefficient derived from an inside cooling condition, a cooling condition frosting coefficient derived from an operating condition of a refrigerating device, and for each case. The amount of frost formation per unit time is calculated by multiplying it with the performance coefficient that is determined, and when the accumulated frost formation amount obtained by integrating the frost formation amount reaches a predetermined value, the cooling device is removed. A defrost control method for a showcase that issues a frost command. 2. A defrosting control method for a showcase according to claim 1, wherein the outside air frosting coefficient has a standard value of 1, and the outside air frosting coefficient becomes larger or equal as the outside air temperature becomes higher. 3. The showcase according to claim 1 or 2, wherein the standard value of the frost formation coefficient in the inside of the chamber is set to 1 and is set to be larger or equal as the representative temperature of the inside of the chamber is lower. Defrost control method. 4. The cooling condition frosting coefficient is set to 1 when the refrigerant is supplied to the cooler, and is set to a value smaller than 1 when the refrigerant supply is stopped. The defrosting control method for a showcase according to claim 3. 5. The defrosting control method for a showcase according to claim 1, claim 2 or claim 3 or claim 4, wherein the coefficient of performance is an outside air entrainment constant or a variable determined by the performance of the air curtain of the case.