Cooling device

Abstract

To provide a cooling device that can determine the degree of deterioration in the cooling performance of the cooling device caused by airborne foreign matter. [Solution] The cooling device 100 includes a compressor 10, a condenser 11, an expansion valve 12, and a cooling evaporator 13, and comprises a refrigerator 1 that cools the air inside the showcase 100a via the cooling evaporator 13, a control unit 4 that controls the operation to alternately switch between normal operation, in which the refrigerator 1 cools the air inside the showcase 100a, and heating operation, in which the temperature of the cooling evaporator 13 is raised to a predetermined temperature, and also controls the operation to switch to heating operation before frost forms on the outer surface 131 of the cooling evaporator 13 during normal operation, and a floating foreign matter amount acquisition unit 7 that acquires floating foreign matter amount information I of floating foreign matter in the air surrounding the refrigerator 1, and the control unit 4 determines the degree of deterioration in the cooling performance of the cooling evaporator 13 of the refrigerator 1 based on the floating foreign matter amount information I acquired by the floating foreign matter amount acquisition unit 7.

Description

[Technical Field] 【0001】 This invention relates to a cooling device, and more particularly to a cooling device comprising a compressor, a condenser, an expansion valve, and a cooling evaporator. [Background technology] 【0002】 Conventionally, cooling systems comprising a compressor, condenser, expansion valve, and cooling evaporator are known (see, for example, Patent Document 1). 【0003】 Patent Document 1 discloses a cooling system comprising a refrigerator including a compressor, a condenser, an expansion valve, and a cooling evaporator, and a control unit. The control unit controls the system to alternately perform normal operation, in which the cooling evaporator cools the air in the cooling space, and heating operation, in which the temperature of the cooling evaporator is raised to a predetermined temperature. The control unit also controls the system to switch to heating operation before frost forms on the outer surface of the cooling evaporator during normal operation, so that defrosting operation is unnecessary. Defrosting operation is an operation in which the temperature of the cooling evaporator is raised to a predetermined temperature higher than the predetermined temperature of the heating operation, thereby removing frost from the outer surface of the cooling evaporator. [Prior art documents] [Patent Documents] 【0004】 [Patent Document 1] Japanese Patent Publication No. 2023-153106 [Overview of the Initiative] [Problems that the invention aims to solve] 【0005】 In the field of cooling devices as disclosed in Patent Document 1, although not explicitly stated in Patent Document 1, there is a need to understand the degree to which the cooling performance of the refrigerator is reduced due to minute suspended foreign matter present in the air surrounding the cooling device. Specifically, when suspended foreign matter present in the air surrounding the cooling device adheres to the outer surface of the cooling evaporator, during normal operation to cool the air in the cooling space, the attached suspended foreign matter acts as a nucleus for frost (ice) formation, making frost more likely to occur. Therefore, there is a need to understand the degree to which the cooling performance of the cooling evaporator is reduced due to suspended foreign matter present in the air. 【0006】 This invention was made to solve the above-mentioned problems, and one of its objectives is to provide a cooling device that can determine the degree to which the cooling performance of a cooling evaporator has deteriorated due to airborne foreign matter. [Means for solving the problem] 【0007】 To achieve the above objective, a cooling device according to one aspect of this invention includes a compressor for compressing a refrigerant, a condenser for condensing the refrigerant discharged from the compressor, an expansion valve for expanding the refrigerant condensed by the condenser, and a cooling evaporator for evaporating the refrigerant expanded by the expansion valve, and a chiller that cools the air in a cooling space via the cooling evaporator; a control unit that switches between normal operation, in which the chiller cools the air in the cooling space, and heating operation, in which the temperature of the cooling evaporator is raised to a predetermined temperature, and also controls the system to switch to heating operation before frost forms on the outer surface of the cooling evaporator during normal operation; and a floating foreign matter amount acquisition unit that acquires floating foreign matter amount information in the air surrounding the chiller, and the control unit is configured to determine the degree of deterioration in the cooling performance of the chiller's cooling evaporator based on the floating foreign matter amount information acquired by the floating foreign matter amount acquisition unit. 【0008】 In one aspect of this invention, the cooling device includes, as described above, a floating foreign matter quantity acquisition unit that acquires information on the amount of floating foreign matter in the air surrounding the refrigerator, and a control unit that determines the degree of deterioration in the cooling performance of the refrigerator's cooling evaporator based on the floating foreign matter quantity information acquired by the floating foreign matter quantity acquisition unit. As a result, the floating foreign matter quantity acquisition unit can acquire the amount of floating foreign matter, which fluctuates depending on various factors such as location, weather conditions, season, and time of day, so that the effect of floating foreign matter, which acts as a nucleus for frost (ice) formation and makes frost formation easier, on the cooling performance of the cooling evaporator can be understood. In other words, the degree of deterioration in the cooling performance of the cooling evaporator caused by floating foreign matter present in the air can be understood. As a result, it becomes possible to take measures such as adjusting the timing of switching from normal operation to continuous operation so that frost does not form on the outer surface of the cooling evaporator. 【0009】 In the cooling device according to the first aspect described above, preferably, the control unit is configured to determine the timing for switching from normal operation to heating operation by obtaining the free-free time, which is the duration during which frost does not form in normal operation, as a measure of the degree of cooling performance degradation, based on the amount of suspended foreign matter information obtained by the suspended foreign matter amount acquisition unit. With this configuration, the free-free time can be obtained based on the amount of suspended foreign matter information, so it is possible to determine the appropriate timing for switching from normal operation to continuous operation while avoiding the formation of frost on the outer surface of the cooling evaporator. 【0010】 In this case, preferably, the control unit is configured to acquire information on the amount of suspended foreign matter by the suspended foreign matter amount acquisition unit each time normal operation is performed, and to acquire the non-freezing time based on the suspended foreign matter amount information, and to determine the timing for switching from normal operation to heating operation. With this configuration, it is possible to switch from normal operation to heating operation at a more appropriate timing according to the amount of suspended foreign matter that changes over time. 【0011】 In the configuration of obtaining the non-freezing time as an indication of the deterioration of the cooling performance, preferably, the control unit obtains the non-freezing time based on the floating foreign matter amount information, determines the continuous operation time of the normal operation that becomes equal to or less than the non-freezing time, and is configured to switch from the normal operation to the heating operation at the end of the continuous operation time. With this configuration, the continuous operation time will not exceed the non-freezing time, so it is possible to more reliably avoid the occurrence of frost on the outer surface of the evaporator for cooling, and to grasp a more appropriate timing for switching from the normal operation to the continuous operation. 【0012】 In the configuration of obtaining the non-freezing time as an indication of the deterioration of the cooling performance, preferably, the control unit is configured to obtain the non-freezing time based on the freezing rate of the adhered foreign matter on the outer surface due to the influence of the foreign matter adhered to the outer surface and the floating foreign matter freezing rate on the outer surface due to the influence of the floating foreign matter around the outer surface, which is a rate obtained based on the floating foreign matter amount information. With this configuration, the non-freezing time can be easily obtained based on the freezing rate of the adhered foreign matter and the floating foreign matter freezing rate considering the floating foreign matter amount information. 【0013】 In the cooling device according to the above aspect, preferably, the evaporator for cooling is coated on the evaporator body for cooling to form the outer surface, and contains a supercooling promoting substance that promotes supercooling of water, and the control unit is configured to switch to the heating operation before frost occurs on the outer surface formed by the supercooling promoting substance during normal operation. With this configuration, water can be cooled to a predetermined temperature below 0°C in a liquid state by the supercooling promoting substance, so it becomes difficult for frost to occur. As a result, it is possible to ensure a longer continuous operation time of the normal operation in a state where frost does not occur. 【0014】 In the cooling device according to the above-described one aspect, preferably, the cooling device further includes a blower that blows air onto the outer surface of the evaporator for cooling, and the control unit, when starting the refrigerator, blows air onto the outer surface of the evaporator for cooling by the blower while driving the refrigerator, so as to maintain the temperature of the evaporator for cooling at 0 degrees or more and the dew point temperature or less, cause dew condensation to occur on the outer surface, and perform a cleaning operation for cleaning the outer surface. With such a configuration, in the cleaning operation, foreign matter adhering to the outer surface of the evaporator for cooling can be washed away, so that foreign matter that causes frost formation can be removed from the outer surface of the evaporator for cooling. Therefore, the normal operation following the cleaning operation performed at startup can always be started in a state where no foreign matter adheres to the outer surface of the evaporator for cooling. 【0015】 In the cooling device according to the above-described one aspect, preferably, the floating foreign matter amount acquisition unit is provided around the refrigerator and is configured to acquire floating foreign matter amount information from a floating foreign matter amount sensor that measures the floating foreign matter amount information. With such a configuration, the floating foreign matter amount information can be easily acquired by the floating foreign matter amount sensor. Also, relatively highly accurate floating foreign matter amount information can be acquired by the floating foreign matter amount sensor. 【0016】 In the cooling device according to the above-described one aspect, preferably, the floating foreign matter amount acquisition unit is configured to acquire floating foreign matter amount information from generally publicly available data regarding floating foreign matter in the area including the installation position of the refrigerator. With such a configuration, the floating foreign matter amount information can be acquired from the generally publicly available data without providing a dedicated configuration for acquiring the floating foreign matter amount information. 【0017】 In the cooling device according to the above-described one aspect, preferably, the refrigerator is provided at a suction port that sucks air from the cooling space into the evaporator for cooling and includes a foreign matter filter that removes floating foreign matter. With such a configuration, the foreign matter filter can suppress floating foreign matter from adhering to the outer surface of the evaporator for cooling. 【Advantages of the Invention】 【0018】 According to the present invention, as described above, it is possible to determine the degree to which the cooling performance of the cooling evaporator is reduced due to suspended foreign matter present in the air. [Brief explanation of the drawing] 【0019】 [Figure 1] This is a block diagram showing the configuration of a cooling device according to an embodiment. [Figure 2] This is a perspective view showing the cooling evaporator of a cooling device according to an embodiment. [Figure 3] This is a flowchart illustrating the control process for the cleaning operation of the cooling device according to the embodiment. [Figure 4] This flowchart shows the control processes for normal operation and heating operation of the cooling device according to the embodiment. [Figure 5] This is a time chart of the cleaning operation of the cooling device according to the embodiment. [Figure 6] This is a time chart of the normal operation and heating operation of the cooling device according to the embodiment. [Figure 7] This is a schematic diagram illustrating the setup configuration of the evaluation sample for evaluating the validity of the above equations (1) to (3) regarding the non-freezing time. [Figure 8] This figure shows the evaluation results, illustrating the relationship between the non-freezing time (vertical axis) and the amount of foreign matter adhering (horizontal axis). [Figure 9] This figure shows a cooling device equipped with a foreign matter filter according to the first modified example. [Figure 10] This is a block diagram showing the configuration of the cooling device according to the second modified example. [Figure 11] This is a block diagram showing the configuration of the cooling device according to the third modified example. [Modes for carrying out the invention] 【0020】 The following describes embodiments of the present invention based on the drawings. 【0021】 [Embodiment] The configuration of one embodiment of the cooling device 100 will be described with reference to Figures 1 to 6. 【0022】 (Cooling system configuration) The cooling device 100 is configured to cool the air inside the showcase 100a. For example, the cooling device 100 may consist of a refrigerated warehouse or freezer warehouse where the showcase 100a is installed, a vending machine, an air conditioner, a refrigerator, etc. The showcase 100a is an example of the "cooling space" in the claims. 【0023】 As shown in Figure 1, the cooling device 100 includes a refrigerator 1, a cooling temperature setting unit 2 for setting the cooling temperature of the air inside the showcase 100a during normal operation (described later), a storage unit 3, a control unit 4, and a floating foreign matter amount acquisition unit 7. The refrigerator 1 includes a compressor 10, a condenser 11, an expansion valve 12, and a cooling evaporator 13, and is configured to cool the air inside the showcase 100a via the cooling evaporator 13. The floating foreign matter amount acquisition unit 7 is configured to acquire floating foreign matter amount information I of floating foreign matter in the air surrounding the refrigerator 1. 【0024】 For example, the above-mentioned suspended foreign matter refers to PM2.5 particles with a particle diameter of approximately 2.5 μm or less that are suspended in the atmosphere. In addition, suspended foreign matter may include various other particles that are suspended in the atmosphere, such as PM10 particles with a particle diameter of approximately 10 μm or less, and ultrafine particles that are even smaller than PM2.5, and may include all particles suspended in the atmosphere that can lead to a decrease in the cooling performance of the cooling evaporator. 【0025】 The cooling evaporator 13 contains a supercooling promoting substance 130 that accelerates the supercooling of water. The supercooling promoting substance 130 is applied to the body of the cooling evaporator, forming the outer surface 131 of the cooling evaporator 13. In other words, the supercooling promoting substance 130 is the surface layer of the cooling evaporator 13. Therefore, water (condensation) adhering to the outer surface 131 formed by the supercooling promoting substance 130 of the cooling evaporator 13 remains in a liquid state as supercooled water without solidifying even when cooled to below 0°C. The supercooling promoting substance 130 is coated over almost the entire surface of the cooling evaporator 13, covering almost the entire surface of the cooling evaporator 13. 【0026】 The cooling device 100 also includes a temperature detection unit 5a for detecting the temperature of the cooling evaporator 13, a temperature detection unit 5b for detecting the temperature of the air inside the showcase 100a, and a blower 6 for supplying air to the outer surface 131 of the cooling evaporator 13 formed by the supercooling promoting substance 130. The cooling device may also include, for example, a backflow prevention valve and a liquid separator to prevent backflow and liquid back. "Liquid back" refers to the phenomenon in which the refrigerant does not become 100% gaseous, and some liquid phase remains before being drawn into the compressor. The temperature detection unit 5a is configured to detect the temperature of the cooling evaporator 13 by detecting the temperature of the refrigerant flowing into the cooling evaporator 13. 【0027】 The cooling device 100 also includes an input unit 2a for inputting various information and an output unit (not shown) which has a display unit or the like for outputting various information. The input unit 2a may be integrated with the cooling temperature setting unit 2. The input unit 2a is also configured to allow setting of the maximum temperature that the cooling evaporator 13 can reach during the heating operation described later. 【0028】 The cooling device 100 (control unit 4) is configured to control and alternately perform normal operation, in which the refrigerator 1 cools the air inside the showcase 100a, and heating operation, in which the temperature of the cooling evaporator 13 is raised to a predetermined temperature (maximum temperature). 【0029】 Furthermore, the cooling device 100 (control unit 4) is configured to switch to heating operation before frost forms on the outer surface 131 formed by the supercooling promoting substance 130 during normal operation. In other words, the cooling device 100 is configured to be able to perform normal operation with no frost forming on the cooling evaporator 13 at all times. 【0030】 In this embodiment, the cooling device 100 (control unit 4) is configured to determine the degree of deterioration in the cooling performance of the cooling evaporator 13 of the refrigerator 1 based on the floating foreign matter amount information I acquired by the floating foreign matter amount acquisition unit 7. Details will be described in the configuration of the control unit 4 later. 【0031】 Furthermore, the cooling device 100 is configured to perform a defrosting operation instead of a heating operation if frost occurs in the cooling evaporator 13 as an exception. A defrosting operation is an operation to remove frost by raising the temperature of the cooling evaporator 13 to a higher defrosting temperature (for example, 30°C to 40°C) than that of a heating operation. 【0032】 Furthermore, the cooling device 100 (control unit 4) is configured to perform a cleaning operation to clean the outer surface 131 of the cooling evaporator 13, which is formed by the supercooling promoting substance 130, before the start of normal operation and heating operation when the cooling device 100 is started. Details of each operation of the cooling device 100 will be described later. 【0033】 (Refrigeration unit configuration) The compressor 10 is configured to compress a refrigerant. The compressor 10 consists of a drive unit and a compressor body that is driven by the drive unit to discharge the refrigerant. For example, the compressor body of the compressor 10 is driven and controlled by an inverter (not shown), which is the drive unit. This allows the compressor 10 to adjust the flow rate of the refrigerant discharged from the compressor body. For example, the refrigerant may be R410A, R404A, R32, or carbon dioxide. 【0034】 The condenser 11 is configured to condense the refrigerant discharged from the compressor 10. The condenser 11 is equipped with a heat dissipation fan 11a. The heat dissipation fan 11a is configured to supply air to the condenser 11. As a result, the heat from the refrigerant in the condenser 11 is transferred to the air supplied by the heat dissipation fan 11a. In other words, heat is dissipated from the condenser 11. 【0035】 The expansion valve 12 is configured to expand the refrigerant condensed by the condenser 11. For example, the expansion valve 12 is composed of a needle valve. The opening degree of the expansion valve 12 is adjusted by a stepping motor (not shown) attached to the expansion valve 12. By adjusting the opening degree of the expansion valve 12, the flow rate of the refrigerant to the downstream cooling evaporator 13 is adjusted. When the opening degree of the expansion valve 12 is adjusted to be larger, the temperature of the refrigerant flowing to the downstream cooling evaporator 13 rises, and the temperature of the cooling evaporator 13 rises. When the opening degree of the expansion valve 12 is adjusted to be smaller, the temperature of the refrigerant flowing to the downstream cooling evaporator 13 falls, and the temperature of the cooling evaporator 13 falls. 【0036】 As shown in Figure 2, the cooling evaporator 13 is configured to evaporate the refrigerant expanded by the expansion valve 12. The cooling evaporator 13 is a so-called fin-and-tube heat exchanger and has a plurality of flat plates 13b and a refrigerant flow path 13c. 【0037】 The multiple flat plates 13b are formed of, for example, aluminum. The refrigerant flow path 13c penetrates the multiple flat plates 13b and is arranged in a meandering manner. The flat plates may be formed of a material other than aluminum. The cooling evaporator can be applied to all other types of air-cooled heat exchangers, such as fin and flat-tube heat exchangers, rather than being configured as a fin and tube heat exchanger. 【0038】 The supercooling-promoting substance 130 has the function of promoting the supercooling of water adhering to the outer surface 131 (cooling evaporator 13). The supercooling-promoting substance 130 covers the outer surface of the cooling evaporator 13. That is, the supercooling-promoting substance 130 covers multiple flat plates 13b and refrigerant flow paths 13c. As an example, the supercooling-promoting substance 130 is formed by a coating of a functional paint on the outer surface of the cooling evaporator 13 by dip coating. 【0039】 The method for producing the supercooling-promoting substance 130 will now be explained in detail. The supercooling-promoting substance 130 is produced by dissolving a supercooling accelerator containing the supercooling-promoting substance 130 in a soluble solvent to create a functional paint, and then applying this functional paint as a coating to the flat plate 13b and refrigerant flow path 13c of the cooling evaporator 13. As a result, the cooling evaporator 13 becomes a so-called ice-free heat exchanger that does not require defrosting in principle. 【0040】 For example, supercooling-promoting substance 130 is obtained by synthesizing polymethyl methacrylate (PMMA), which enables the formation of a coating film, three tyrosine residues that promote supercooling, and five glycine residues that assist the supercooling-promoting performance of the three tyrosine residues. The above polymethyl methacrylate is polymerized using 4-cyanovaleric acid (ACVA) as an initiator. In the above functional coating, the supercooling-promoting agent is dissolved in tetrahydrofuran (THF) and used as the coating. 【0041】 As shown in Figure 1, the blower 6 is configured to supply air to the outer surface 131 formed by the supercooling promoting substance 130 of the cooling evaporator 13, as described above. As a result, heat is transferred from the refrigerant of the cooling evaporator 13 to the air supplied by the blower 6. Consequently, cold air is supplied from the cooling evaporator 13 into the showcase 100a. 【0042】 (Memory Unit Configuration) The storage unit 3 includes, for example, a non-volatile storage device such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive). The storage unit 3 stores various temperature information and time information used for normal operation, heating operation, and cleaning operation described later. For example, the storage unit 3 stores information such as the cooling temperature of the air inside the showcase 100a during normal operation, which is set by the user via the cooling temperature setting unit 2. In addition, the storage unit 3 stores the floating foreign matter amount information I when the floating foreign matter amount acquisition unit 7 acquires the floating foreign matter amount information I. 【0043】 (Configuration of the floating foreign matter quantity acquisition unit) The floating foreign matter quantity acquisition unit 7 is installed around the refrigerator 1 and is configured to acquire floating foreign matter quantity information I from the floating foreign matter quantity sensor P, which measures floating foreign matter quantity information I. For example, the floating foreign matter quantity acquisition unit 7 is a wireless communication unit for acquiring floating foreign matter quantity information I from the floating foreign matter quantity sensor P, and includes a communication module and a communication antenna. The floating foreign matter quantity acquisition unit may also be a wired communication unit connected to the floating foreign matter quantity sensor via a wired connection. Furthermore, for example, the floating foreign matter quantity sensor P measures the amount of floating foreign matter [mg / m³] of PM2.5. 3 This is a sensor that measures [part. / m³]. As another example, a floating foreign matter amount sensor may be constructed using a particle counter. The particle counter measures the foreign matter concentration [part. / m³], which will be described later. 3 It is possible to measure [the amount of airborne foreign matter]. Also, as an example, the airborne foreign matter sensor P is placed in the same area (same room) as the refrigerator 1 in the store where the refrigerator 1 is located. 【0044】 (Configuration of the control unit) The control unit 4 includes a CPU (Central Processing Unit), RAM (Random Access Memory), and ROM (Read Only Memory). The control unit 4 stores control programs for performing cleaning, normal operation, and heating operation. These control programs may be stored in a separate memory unit. 【0045】 The control unit 4 is configured to perform control for cleaning, normal operation, and heating operation. The control unit 4 performs cleaning, normal operation, and heating operation based on various temperature information and time information stored in the memory unit 3 and the detection results of the temperature detection unit 5a. Each operation will be described below. Note that the information used for cleaning, normal operation, and heating operation is not limited to that described above, and other information may be used. 【0046】 (Washing operation) The control unit 4 is configured to perform a cleaning operation when the refrigerator 1 is started. This operation involves driving the refrigerator 1 and using the blower 6 to send air to the outer surface 131 of the cooling evaporator 13, which is formed by the supercooling promoting substance 130. This maintains the temperature of the cooling evaporator 13 above 0 degrees Celsius and below the dew point temperature, causing condensation to form on the outer surface 131 and then removing the condensation to clean the outer surface 131. As an example, "startup" refers not only to the first startup but to all startups when the power to the refrigerator 1 is turned on. As another example, "startup" may include the first startup and startups after a predetermined period has elapsed since the first startup, or it may be configured to perform the cleaning operation when a predetermined cleaning instruction is received from the user at each startup. 【0047】 For example, the control unit 4 is configured to drive the refrigerator 1 while simultaneously supplying air via the blower 6 to the outer surface 131 of the cooling evaporator 13 formed by the supercooling promoting substance 130 for approximately 5 hours (cleaning duration t_clean). Also, for example, during the cleaning operation, the control unit 4 maintains the temperature of the cooling evaporator 13 at approximately 5°C (cleaning temperature T_clean). 【0048】 The cooling device 100 is configured to remove foreign matter adhering to the outer surface 131 formed by the supercooling promoting substance 130 by repeatedly generating and removing condensation during the cleaning operation. By removing the foreign matter adhering to the outer surface 131, it is possible to prevent the formation of frost nucleated by the foreign matter during normal operation. In short, the control unit 4 performs control such that by executing the cleaning operation, it is possible to secure a longer continuous operation time (the time from the start to the end of normal operation) as described later in normal operation. 【0049】 The control unit 4 is configured to dry the outer surface 131 formed by the supercooling promoting substance 130 by driving the blower 6 while driving the refrigerator 1 during the cleaning operation, and then stopping the refrigerator 1 and driving the blower 6. In other words, the control unit 4 is configured to remove water adhering to the outer surface 131 before starting normal operation. As an example, the control unit 4 is configured to continue stopping the refrigerator 1 and driving the blower 6 for approximately 2 hours (blowering duration t_fan). 【0050】 As described above, the cleaning operation performed by the control unit 4 removes foreign matter adhering to the outer surface 131. This results in the wall surface foreign matter density ρ in equation (2) of the non-freezing time, which will be described later. p to [part. / m 2 ] can be set to approximately zero. 【0051】 (Normal operation) The control unit 4 is configured to drive the chiller 1 during normal operation to perform heat exchange between the condenser 11 and the cooling evaporator 13, thereby cooling the air in the showcase 100a. In normal operation, the blower 6 is also driven. 【0052】 The control unit 4 is configured to determine the continuous operating time for normal operation, which is the time from the start of normal operation until switching to heating operation, based on the cooling temperature set by the cooling temperature setting unit 2, so that frost does not form on the outer surface 131 formed by the supercooling promoting substance 130. 【0053】 In detail, the control unit 4 increases the continuous operating time of normal operation as the cooling temperature set via the cooling temperature setting unit 2 increases, and decreases the continuous operating time of normal operation as the cooling temperature set via the cooling temperature setting unit 2 decreases. 【0054】 For example, if the set temperature (threshold temperature T_cool) is -6°C or lower, the control unit 4 uniformly sets the continuous operation time to 2 hours (t_cool1), and if the set temperature is greater than -6°C, it uniformly sets the continuous operation time to a predetermined time longer than 2 hours (t_cool2). 【0055】 The control unit 4 is configured to determine the timing for switching from normal operation to heating operation by acquiring the freezing time, which is the duration during which frost does not form in normal operation, as a measure of the degree of cooling performance degradation, based on the freezing foreign matter amount information I acquired by the freezing foreign matter amount acquisition unit 7. As a specific example, while the freezing time in an ideal situation where no freezing foreign matter is present is 6 hours, in a situation where freezing foreign matter is present, the freezing time acquired based on the freezing foreign matter amount information I will be a predetermined time shorter than 6 hours (for example, 5 hours). 【0056】 The control unit 4 is configured to acquire the non-freezing time based on the amount of suspended foreign matter I, determine the continuous operation time for normal operation that is less than or equal to the non-freezing time, and switch from normal operation to heating operation at the end of the continuous operation time. As a specific example, the control unit 4 is configured to use the non-freezing time as the continuous operation time. However, in order to more reliably prevent frost from forming on the outer surface of the supercooling promoting substance, the control unit may set the continuous operation time to a predetermined time shorter than the non-freezing time. As a specific example, if the non-freezing time is 5 hours, the control unit 4 may set the continuous operation time to 4.9 hours, which is 0.1 hours shorter than 5 hours. 【0057】 Each time the control unit 4 performs normal operation, it acquires the floating foreign matter amount information I by the floating foreign matter amount acquisition unit 7, acquires the non-freezing time based on the floating foreign matter amount information I, and determines the timing to switch from normal operation to the temperature increase operation. 【0058】 The control for acquiring the non-freezing time t executed by the control unit 4 will be described. The control unit 4 is the adhesion foreign matter freezing speed f on the outer surface 131 due to the influence of the foreign matter adhering to the outer surface 131 s and the speed acquired based on the floating foreign matter amount information I, and the floating foreign matter freezing speed f on the outer surface 131 due to the influence of the floating foreign matter around the outer surface 131 a and is configured to acquire the non-freezing time t based on them. The control for acquiring the non-freezing time t is performed in steps S10 and S13 in the flow of the control process shown in FIG. 4 described later. Details will be described below. 【0059】 The control unit 4 acquires the non-freezing time t based on the following formula (1) of the non-freezing time. 【0060】 t = 1 / (α(f s + f a )) ···(1) 【0061】 α in formula (1) is the ice nucleation activity rate, and the unit is dimensionless. The ice nucleation activity rate is a value indicating the probability of ice generation on the outer surface 131 formed on the supercooling promoting substance 130. When comparing the outer surface 131 with the supercooling promoting substance 130 and the outer surface without the supercooling promoting substance, the outer surface 131 with the supercooling promoting substance 130 has a smaller ice nucleation activity rate and a longer non-freezing time t. The higher the supercooling promoting performance of the supercooling promoting substance 130, the smaller the ice nucleation activity rate. As described above, f in formula (1) s indicates the adhesion foreign matter freezing speed. The adhesion foreign matter freezing speed f s is the speed acquired based on the floating foreign matter amount information I, and the unit is [part. / s]. As described above, f in formula (1) a indicates the floating foreign matter freezing speed. The floating foreign matter freezing speed f aThis is the freezing rate obtained based on the amount of suspended foreign matter I, and also the freezing rate on the outer surface 131 due to the influence of suspended foreign matter around the outer surface 131, and its unit is [part. / s]. 【0062】 The control unit 4 calculates the freezing rate of attached foreign matter f based on the following equation (2) for the non-freezing time. s Obtain it. 【0063】 f s =( A l ×ρ p ) / t l ...(2) 【0064】 A in equation (2) l This indicates the condensation area, and the unit is [m²]. 2 ]. ρ in equation (2) p This is the density of foreign matter on the wall surface, and its unit is [part. / m]. 2 ]. As a result of the cleaning operation, the density of foreign matter on the wall surface ρ p Since it becomes approximately zero, the freezing rate of the attached foreign matter f s This also becomes approximately zero. Therefore, in equation (1), the freezing rate of the attached foreign matter f s This has little effect on the change in the non-freezing time t, and the freezing rate of suspended foreign matter f a This is a variable that particularly affects the change in the non-freezing time t. The variable t in equation (2) l This represents the dew time, and its unit is [s]. 【0065】 The control unit 4 calculates the freezing rate of floating foreign matter f based on the following equation (3) for the non-freezing time. a Obtain it. 【0066】 f a =A l ×(ρ´×ρ m ) × h p ...(3) 【0067】 In equation (3), ρ' is the unit number of suspended particles, and its unit is [part. / mg]. The unit number of particles is a value determined by the type of suspended particles that make up the suspended matter, such as PM2.5 and PM10. mThis represents the amount of suspended foreign matter, and its unit is [part. / mg]. Suspended foreign matter amount ρ m This is measured by the suspended foreign matter quantity acquisition unit 7. Unit particle number ρ' and suspended foreign matter quantity ρ m By multiplying by , the concentration of suspended foreign matter is obtained. h in equation (3) p This is the mass transfer coefficient, and its unit is [m / s]. Mass transfer coefficient h p This value is determined by factors such as the shape of the gas flow path around the cooling evaporator 13, the temperature of the gas, and the humidity of the gas. 【0068】 (Temperature increase operation) The control unit 4 is configured to start the heating operation when no frost has accumulated on the outer surface 131 of the cooling evaporator 13, which is formed by the supercooling promoting substance 130. During the heating operation, the control unit 4 is configured to raise the temperature of the cooling evaporator 13 to a predetermined temperature T_rise, which is the temperature at which ice nuclei contained in the water that accumulate on the outer surface 131 during normal operation are eliminated. 【0069】 The control unit 4 is configured to increase the temperature of the cooling evaporator 13 by increasing the opening degree of the expansion valve 12 during the heating operation. 【0070】 The control unit 4 is configured to raise the temperature of the cooling evaporator 13 to a predetermined temperature T_rise greater than 0°C and 10°C or less during the heating operation. For example, the control unit 4 is configured to raise the temperature of the cooling evaporator 13 (maximum temperature reached) to 2°C (predetermined temperature T_rise) during the heating operation. 【0071】 The control unit 4 is configured to stop the blower 6 during the heating operation, at least while the temperature of the cooling evaporator 13 is being raised. In other words, the control unit 4 is configured to stop the blower 6 during the heating operation, at least while it is outputting a command D_rise to increase the opening degree of the expansion valve 12. 【0072】 Furthermore, the control unit 4 is configured to stop the blower 6 during the heating operation, not only while the temperature of the cooling evaporator 13 is being raised, but also from the time the temperature of the cooling evaporator 13 has finished rising (from the point where it reaches its highest temperature) until the temperature detection unit 5a detects that the temperature of the cooling evaporator 13 has dropped to the threshold temperature (T_cool). In other words, the control unit 4 is configured to stop the blower 6 from the time it starts outputting the command D_cool to reduce the opening of the expansion valve 12 until the temperature of the cooling evaporator 13 reaches the threshold temperature (T_cool), which is the cooling temperature. 【0073】 The control unit 4 is configured to stop the blower 6, thereby suppressing the rise in the temperature of the air in the showcase 100a during the heating operation, which would otherwise occur if air were blown from the blower 6 to the heating evaporator 13 when it is in a heated state. 【0074】 (Control processing for cleaning operation, normal operation, and heating operation) Referring to Figures 3 to 6, the flow of control processing for cleaning operation, normal operation, and heating operation performed by the control unit 4 will be described. 【0075】 In step S1, the refrigerator 1 is started. Then, the process proceeds to step S2. 【0076】 In step S2, the cleaning operation is started. That is, the chiller 1 (compressor 10) and the blower 6 are started. When the chiller 1 (compressor 10) and the blower 6 are started, the temperature detected by the temperature detection unit 5a decreases from the ambient temperature T_amb to the cleaning temperature T_clean. Then, the process proceeds to step S3. 【0077】 The cleaning operation in step S2 described above begins at the time when the compressor command and cleaning command shown in Figure 5 are output, which is the time of t_off. The compressor command is a drive command for the compressor 10 output from the control unit 4. The cleaning command is a drive command for the blower 6 output from the control unit 4. 【0078】 In step S3, it is determined whether the cleaning temperature T_clean has been maintained for a cleaning duration t_clean or longer since the cleaning operation started. If the cleaning temperature T_clean has been maintained for a cleaning duration t_clean or longer (step S3, Yes), proceed to step S4. If the cleaning temperature T_clean has not been maintained for a cleaning duration t_clean or longer (step S3, No), repeat step S3. 【0079】 In step S4, the chiller 1 (compressor 10) is stopped, and the blower 6 is driven independently. Then, the process proceeds to step S5. 【0080】 In step S5, it is determined whether the independent operation of the blower 6 has continued for a duration of t_fan or longer. If the independent operation of the blower 6 has continued for a duration of t_fan or longer (step S5, Yes), proceed to step S6. If the independent operation of the blower 6 has not continued for a duration of t_fan or longer (step S5, No), repeat step S5. 【0081】 In step S6, the washing operation is completed; that is, the blower 6 is stopped. Then, the process proceeds to step S7. 【0082】 In step S7, the chiller 1 (compressor 10) and the blower 6 are started. In other words, normal operation begins. Then, the process proceeds to step S8. 【0083】 In step S8, it is determined whether the cooling temperature of the air in the showcase 100a, as set by the cooling temperature setting unit 2, is less than or equal to T_cool. If the cooling temperature of the air in the showcase 100a, as set by the cooling temperature setting unit 2, is less than or equal to T_cool (step S8, Yes), the process proceeds to step S9. If the cooling temperature of the air in the showcase 100a, as set by the cooling temperature setting unit 2, is greater than T_cool (step S8, No), the process proceeds to step S12. 【0084】 In step S9, floating foreign matter quantity information I is acquired via the floating foreign matter quantity acquisition unit 7. Then, the process proceeds to step S10. 【0085】 In step S10, the degree of deterioration in the cooling performance of the cooling evaporator 13 of the refrigerator 1 due to suspended foreign matter is obtained. That is, the non-freezing time t_cool1 is obtained. Then, the process proceeds to step S11. Note that the non-freezing time t_cool1 obtained in step S10 is also the continuous operating time t_cool1 during normal operation. Steps S9 and S10 make it possible to determine the optimal length of the continuous operating time t_cool1 during normal operation, taking into account the surrounding suspended foreign matter. 【0086】 In step S11, it is determined whether normal operation has been continued for a continuous operating time of t_cool1 or longer. If normal operation has been continued for a continuous operating time of t_cool1 or longer (step S11, Yes), proceed to step S15. If normal operation has not been continued for a continuous operating time of t_cool1 or longer (step S11, No), repeat step S11 to continue normal operation. 【0087】 Meanwhile, in step S12, floating foreign matter quantity information I is acquired via the floating foreign matter quantity acquisition unit 7. After that, the process proceeds to step S13. 【0088】 In step S13, the degree of deterioration in the cooling performance of the cooling evaporator 13 of the refrigerator 1 due to suspended foreign matter is obtained. That is, the non-freezing time t_cool2 is obtained. Then, the process proceeds to step S14. Note that the non-freezing time t_cool2 obtained in step S13 is also the continuous operation time t_cool2 under normal operation. Note that if the amount of suspended foreign matter obtained in step S12 is the same as the amount of suspended foreign matter obtained in step S9, the non-freezing time t_cool2 will be a predetermined time longer than the non-freezing time t_cool1. 【0089】 In step S14, it is determined whether normal operation has been continued for a continuous operating time of t_cool2 or longer. If normal operation has been continued for a continuous operating time of t_cool2 or longer (step S14, Yes), proceed to step S15. If normal operation has not been continued for a continuous operating time of t_cool2 or longer (step S14, No), repeat step S14 to continue normal operation. Note that the continuous operating time t_cool2 is longer than the continuous operating time t_cool1. 【0090】 Next, in step S15, the heating operation is started. That is, the blower 6 is stopped, and a D_rise signal is output to the expansion valve 12, increasing the opening degree of the expansion valve 12. As a result, the temperature of the cooling evaporator 13 rises. Then, the process proceeds to step S16. 【0091】 The point at which the heating operation described in step S15 above begins is the point at which the heating command shown in Figure 6 is output. The heating command is a drive command output from the control unit 4 to increase the opening degree of the expansion valve 12, and is also a command to start the shutdown of the blower 6. 【0092】 In step S16, it is determined whether the predetermined temperature T_rise of the cooling evaporator 13 has been maintained for a heating duration t_rise or longer. If the predetermined temperature T_rise has been maintained for a heating duration t_rise or longer (step S16, Yes), the process proceeds to step S17. If the predetermined temperature T_rise has not been maintained for a heating duration t_rise or longer (step S16, No), step S16 is repeated. As an example, the heating duration t_rise is approximately 5 minutes (0.08 hours), which is an extremely short time compared to the continuous operating time of normal operation (t_cool1 and t_cool2). 【0093】 Furthermore, the heating duration in step S16 (the period during which the D_rise signal is output to the expansion valve 12) may be set to an extremely short time. Also, in step S16, instead of deciding to terminate the heating of the cooling evaporator based on the heating duration, the decision to terminate the heating of the cooling evaporator may be made based on temperature information such as the maximum temperature reached by the heating evaporator. Alternatively, the decision to terminate the heating of the cooling evaporator may be made based on both the heating duration and temperature information such as the maximum temperature reached by the heating evaporator. 【0094】 In step S17, the D_cool signal is output to the expansion valve 12, causing the opening degree of the expansion valve 12 to decrease. Then, the process proceeds to step S18. 【0095】 In step S18, it is determined whether the temperature detection unit 5a has detected that the temperature of the cooling evaporator 13 has dropped to the threshold temperature T_cool. If the temperature detection unit 5a has detected that the temperature of the cooling evaporator 13 has dropped to the threshold temperature T_cool (step S18, Yes), the process proceeds to step S19. If the temperature detection unit 5a has not detected that the temperature of the cooling evaporator 13 has dropped to the threshold temperature T_cool (step S18, No), step S18 is repeated. 【0096】 In step S19, the heating operation is terminated. That is, the process returns to step S8, the blower 6 is started, and normal operation resumes. At the point when the heating operation is terminated, the temperature inside the showcase 100a detected by the temperature detection unit 5b reaches its highest temperature. This temperature is lower than the upper limit temperature T_limit, which is considered undesirable for the preservation of products inside the showcase 100a. 【0097】 (Effects of the embodiment) In this embodiment, the following effects can be obtained. 【0098】 In this embodiment, as described above, the system includes a floating foreign matter quantity acquisition unit 7 that acquires floating foreign matter quantity information I in the air surrounding the refrigerator 1, and a control unit 4 that determines the degree of deterioration in the cooling performance of the cooling evaporator 13 of the refrigerator 1 based on the floating foreign matter quantity information I acquired by the floating foreign matter quantity acquisition unit 7. As a result, the floating foreign matter quantity acquisition unit 7 can acquire the amount of floating foreign matter, which fluctuates depending on various factors such as location, weather conditions, season, and time of day, so that the effect of floating foreign matter, which acts as a nucleus for frost (ice) formation and makes frost formation easier, on the cooling performance of the cooling evaporator 13 can be understood. In other words, the degree of deterioration in the cooling performance of the cooling evaporator 13 caused by floating foreign matter present in the air can be understood. As a result, it becomes possible to take measures such as adjusting the timing of switching from normal operation to continuous operation so that frost does not form on the outer surface 131 of the cooling evaporator 13. 【0099】 In this embodiment, as described above, the control unit 4 is configured to determine the timing for switching from normal operation to heating operation by acquiring the freezing time, which is the duration during which frost does not form in normal operation, as a measure of the degree of cooling performance degradation, based on the freezing foreign matter amount information I acquired by the freezing foreign matter amount acquisition unit 7. As a result, since the freezing time can be acquired based on the freezing foreign matter amount information I, it is possible to determine the appropriate timing for switching from normal operation to continuous operation while avoiding the formation of frost on the outer surface 131 of the cooling evaporator 13. 【0100】 In this embodiment, as described above, the control unit 4 is configured to acquire floating foreign matter amount information I from the floating foreign matter amount acquisition unit 7 each time normal operation is performed, and to acquire the non-freezing time based on the floating foreign matter amount information I, and to determine the timing to switch from normal operation to heating operation. This makes it possible to switch from normal operation to heating operation at a more appropriate timing according to the amount of floating foreign matter that changes over time. 【0101】 In this embodiment, as described above, the control unit 4 is configured to acquire the free-free time based on the amount of suspended foreign matter I, determine the continuous operation time for normal operation that is less than or equal to the free-free time, and switch from normal operation to heating operation at the end of the continuous operation time. As a result, the continuous operation time will never exceed the free-free time, so it is possible to determine a more appropriate timing for switching from normal operation to continuous operation while more reliably avoiding the formation of frost on the outer surface 131 of the cooling evaporator 13. 【0102】 In this embodiment, as described above, the control unit 4 is configured to acquire the non-freezing time based on the freezing rate of foreign matter attached to the outer surface 131 due to the influence of foreign matter attached to the outer surface 131, and the freezing rate of floating foreign matter on the outer surface 131 due to the influence of floating foreign matter around the outer surface 131, which is a rate acquired based on the amount of floating foreign matter I. This makes it possible to easily acquire the non-freezing time based on the freezing rate of attached foreign matter and the freezing rate of floating foreign matter considering the amount of floating foreign matter. 【0103】 In this embodiment, as described above, the cooling evaporator 13 includes a supercooling promoting substance 130 that is applied to the cooling evaporator body to form an outer surface 131 and promotes the supercooling of water. The control unit 4 is configured to switch to heating operation before frost forms on the outer surface 131 formed by the supercooling promoting substance 130 during normal operation. As a result, the water can be cooled to a predetermined temperature below 0°C while remaining in liquid state by the supercooling promoting substance 130, making frost less likely to form. Consequently, the continuous operation time during normal operation, which is performed without frost formation, can be extended. 【0104】 In this embodiment, as described above, a blower 6 is further provided to supply air to the outer surface 131 of the cooling evaporator 13. The control unit 4 is configured to perform a cleaning operation when the refrigerator 1 is started, by driving the refrigerator 1 and supplying air to the outer surface 131 of the cooling evaporator 13 using the blower 6, thereby maintaining the temperature of the cooling evaporator 13 above 0 degrees Celsius and below the dew point temperature, causing condensation to form on the outer surface 131 and cleaning the outer surface 131. As a result, foreign matter adhering to the outer surface 131 of the cooling evaporator 13 can be washed away during the cleaning operation, thus removing foreign matter that could trigger frost formation from the outer surface 131 of the cooling evaporator 13. Therefore, normal operation following the cleaning operation performed at startup can always be started with no foreign matter adhering to the outer surface 131 of the cooling evaporator 13. 【0105】 In this embodiment, as described above, the floating foreign matter quantity acquisition unit 7 is provided around the refrigerator 1 and is configured to acquire floating foreign matter quantity information I from a floating foreign matter quantity sensor P that measures floating foreign matter quantity information I. This allows floating foreign matter quantity information I to be easily acquired by the floating foreign matter quantity sensor P. Furthermore, the floating foreign matter quantity sensor P can acquire floating foreign matter quantity information I with relatively high accuracy. 【0106】 (Evaluation to confirm the validity of the above formulas (1) to (3) regarding the non-freezing time) Referring to Figures 7 and 8, we will explain the evaluations conducted to confirm the validity of the above equations (1) to (3) regarding the non-freezing time t. 【0107】 As shown in Figure 7, the evaluation involved placing the evaluation sample on a Peltier cooling stage that cools the evaluation sample from the back side, and generating condensation (up to the maximum amount) on the front surface of the evaluation sample, which was previously positioned horizontally under a wind speed of 1.2 [m / s]. Then, the evaluation sample with this condensation attached was placed in a closed space, and the effect of only the amount of attached foreign matter on the non-freezing time t was evaluated. The evaluation was performed with the amount of suspended foreign matter and the amount of condensation fixed. Furthermore, the various parameters in the above equations (1) to (3) were set to predetermined values ​​using JIS standards, etc. 【0108】 As shown in Figure 8, the mathematically calculated non-freezing time t, obtained by substituting various values ​​into equations (1) to (3) above, gradually decreases with increasing foreign matter adhesion on the horizontal axis, and the rate of decrease gradually slows down. The various values ​​plotted in Figure 6, which are evaluation values ​​(experimental values), are close to the line representing the mathematically calculated non-freezing time t. When the correlation coefficient, which indicates the strength of the relationship between the mathematically calculated non-freezing time t and the evaluation value (experimental value), was calculated, it was found to be 0.94, indicating a strong correlation between the mathematically calculated non-freezing time t and the evaluation value (experimental value). 【0109】 [Differentiation] It should be noted that the embodiments disclosed herein are illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims rather than by the description of the embodiments, and further includes all modifications (exceptions) within the meaning and scope equivalent to the claims. 【0110】 For example, as a first modification, as shown in Figure 9, in the configuration of the above embodiment, the showcase 102 of the cooling device 101 may further include a foreign matter filter 103. More specifically, it may include a foreign matter filter 103 provided at the intake port 102a of the showcase 102 that draws air into the cooling evaporator 13, to remove floating foreign matter. The foreign matter filter 103 can suppress the adhesion of floating foreign matter to the outer surface 131 of the cooling evaporator 13. In this case, the control unit performs control to acquire the non-freezing time, taking into consideration the effect of the foreign matter filter 103 on the floating foreign matter amount information acquired by the floating foreign matter amount acquisition unit 7. 【0111】 In the above embodiment, an example was shown in which the temperature of the cooling evaporator was increased by an expansion valve during the heating operation, but the present invention is not limited thereto. In the present invention, as in the cooling device 200 equipped with the refrigerator 201 of the second modified example shown in Figure 10, the temperature of the cooling evaporator 13 may be increased by switching the four-way valve 201a without changing the opening degree of the expansion valve 12 during the heating operation. In detail, the control unit 4 is configured to switch between normal operation and heating operation by switching the four-way valve 201a. In the above normal operation, low-temperature, low-pressure refrigerant flows from the cooling evaporator 13 to the compressor 10, and high-temperature, high-pressure refrigerant flows from the condenser 11 to the expansion valve 12. In the above heating operation, high-temperature, high-pressure refrigerant flows from the compressor 10 to the cooling evaporator 13 which functions as a condenser, and low-temperature, low-pressure refrigerant flows from the expansion valve 12 to the condenser 11 which functions as an evaporator. 【0112】 Furthermore, as an example different from the second modified example described above, in the cooling device 300 equipped with the refrigerator 301 of the third modified example shown in Figure 11, the temperature of the cooling evaporator 13 may be raised by the electric heater 301a without changing the opening degree of the expansion valve 12 during the heating operation. Specifically, the electric heater 301a is attached to the cooling evaporator 13. The control unit 4 is configured to switch from normal operation to heating operation by outputting a drive signal to the electric heater 301a. In this case, the temperature detection unit 5a is provided on the electric heater 301a so as to be able to detect the temperature of the electric heater 301a. 【0113】 Furthermore, while the above embodiment shows an example in which the floating foreign matter amount acquisition unit is provided around the refrigerator and acquires floating foreign matter amount information from a floating foreign matter amount sensor that measures floating foreign matter amount information, the present invention is not limited to this. In the present invention, the floating foreign matter amount acquisition unit may be configured to acquire floating foreign matter amount information from publicly available data on floating foreign matter in the area including the installation location of the refrigerator. As an example, publicly available data is measurement data on PM2.5 published by the Ministry of the Environment. This makes it possible to acquire floating foreign matter amount information from publicly available data without providing a dedicated configuration for acquiring floating foreign matter amount information. In addition, the cooling device may include a floating foreign matter amount sensor as a component of the cooling device. In this case, the floating foreign matter amount sensor itself becomes the floating foreign matter amount acquisition unit. 【0114】 Furthermore, while the above embodiment shows an example in which control is performed to acquire the free-free time after each normal operation, the present invention is not limited to this. In the present invention, control may be performed to acquire the free-free time after a predetermined number of normal operations. 【0115】 Furthermore, although the above embodiment shows an example in which the outer surface is formed by coating the outer surface of the cooling evaporator with a supercooling promoting substance, the present invention is not limited to this. In the present invention, the outer surface may be formed by fixing the supercooling promoting substance to the outer surface of the cooling evaporator using vapor deposition or the like. 【0116】 Furthermore, although the above embodiment shows an example in which a supercooling promoting substance is provided on the outer surface of the cooling evaporator, the present invention is not limited thereto. In the present invention, it is not necessary to provide a supercooling promoting substance on the outer surface of the cooling evaporator. 【0117】 Furthermore, although the above embodiment shows an example in which a blower is driven independently to dry the outer surface during the cleaning operation, the present invention is not limited to this. In the present invention, it is not necessary to drive the blower independently during the cleaning operation. That is, steps S4 and S5 in Figure 3 may be omitted. 【0118】 Furthermore, while the above embodiment shows an example where the continuous operating time for normal operation is set to one of two predetermined continuous operating times according to the set cooling temperature, the present invention is not limited to this. In the present invention, the continuous operating time for normal operation may be set to two different unique continuous operating times according to the set cooling temperature. In this case, for example, the higher the set cooling temperature, the longer the freezing time can be secured, so a longer continuous operating time can be set. In addition, the continuous operating time for normal operation may be set to one of three or more predetermined continuous operating times according to the set cooling temperature. 【0119】 Furthermore, while the above embodiment shows an example in which the cooling device is configured to perform a cleaning operation, a normal operation, and a heating operation, the present invention is not limited thereto. In the present invention, the cooling device may be configured to perform a normal operation and a heating operation without performing a cleaning operation. 【0120】 Furthermore, although the above embodiment shows an example where the maximum temperature reached by the cooling evaporator during the heating operation is 2°C, the present invention is not limited to this. In the present invention, the maximum temperature reached by the cooling evaporator during the heating operation may be set to any temperature greater than 0°C and 10°C or less. 【0121】 Furthermore, the various temperature and time conditions for performing the cleaning operation, normal operation, and heating operation in the above embodiment are merely examples. The cleaning operation, normal operation, and heating operation may be performed under different temperature and time conditions than those in the above embodiment. 【0122】 Furthermore, in the above embodiment, an example was shown in which the supercooling promoting substance forming the outer surface was produced by synthesizing polymethyl methacrylate (PMMA), 5 glycine residues, and 3 tyrosine residues, but the present invention is not limited thereto. In the present invention, the supercooling promoting substance forming the outer surface may be produced using antifreeze polysaccharides. Specifically, the supercooling promoting substance forming the outer surface may be produced by adding an appropriate amount of antifreeze polysaccharide to an appropriate amount of hydrophilic coating main component consisting of an appropriate amount of PVA (polyvinyl alcohol), silicate, and inorganic aluminum compound, and mixing. In addition, the supercooling promoting substance forming the outer surface may be produced using catechin-type tannins such as lychee fruit-derived low molecular weight polyphenols, lychee fruit-derived polyphenols (LFP), and grape seed-derived polyphenols (GSP). In addition, the supercooling promoting substance forming the outer surface may be produced to contain one or more substances selected from N-long-chain acyl acidic amino acids or their salts. Note that the supercooling promoting substance forming the outer surface is not limited to those exemplified above, and any substance capable of promoting the supercooling of water adhering to the outer surface is acceptable. 【0123】 Furthermore, in the above embodiment, for the sake of explanation, an example was shown in which the control processing of the control unit was explained using a flow-driven flowchart that processes sequentially according to the processing flow, but the present invention is not limited to this. In the present invention, the control processing of the control unit may be performed by event-driven processing that executes processing on an event-by-event basis. In this case, it may be performed as a completely event-driven system, or a combination of event-driven and flow-driven systems may be used. [Explanation of symbols] 【0124】 1, 201, 301 Refrigeration Units 4. Control Unit 6. Blower 7. Unit for acquiring the amount of floating foreign matter 10 Compressor 11 Condenser 12 Expansion valve 13. Cooling evaporator 100, 101, 200, 300 cooling device 100a Showcase (Cooling Space) 102a Inlet 103 Foreign object filter 130 Supercooling accelerator 131 Outer surface (formed by a supercooling promoting substance) I. Information on the amount of suspended foreign matter P Floating foreign matter quantity sensor

Claims

[Claim 1] A refrigerator includes a compressor for compressing a refrigerant, a condenser for condensing the refrigerant discharged from the compressor, an expansion valve for expanding the refrigerant condensed by the condenser, and a cooling evaporator for evaporating the refrigerant expanded by the expansion valve, and cools the air in the cooling space via the cooling evaporator. The control unit performs control to alternately execute a normal operation in which the refrigerator cools the air in the cooling space and a heating operation in which the temperature of the cooling evaporator is raised to a predetermined temperature, and also performs control to switch to the heating operation before frost forms on the outer surface of the cooling evaporator during the normal operation. The refrigerator is equipped with a floating foreign matter quantity acquisition unit that acquires information on the amount of floating foreign matter in the air surrounding the refrigerator, The control unit is configured to determine the degree of deterioration in the cooling performance of the cooling evaporator of the refrigerator based on the floating foreign matter amount information acquired by the floating foreign matter amount acquisition unit. [Claim 2] The cooling device according to claim 1, wherein the control unit is configured to determine the timing for switching from the normal operation to the heating operation, based on the floating foreign matter amount information acquired by the floating foreign matter amount acquisition unit, by acquiring the non-freezing time, which is the duration during which no frost occurs in the normal operation, as the degree of deterioration in cooling performance. [Claim 3] The cooling device according to claim 2, wherein the control unit is configured to acquire information on the amount of suspended foreign matter using the suspended foreign matter amount acquisition unit each time the normal operation is performed, acquire the non-freezing time based on the information on the amount of suspended foreign matter, and determine the timing for switching from the normal operation to the heating operation. [Claim 4] The cooling device according to claim 2, wherein the control unit is configured to acquire the non-freezing time based on the amount of suspended foreign matter information, determine the continuous operation time of the normal operation that is less than or equal to the non-freezing time, and switch from the normal operation to the heating operation at the end of the continuous operation time. [Claim 5] The cooling device according to claim 2, wherein the control unit is configured to obtain the non-freezing time based on the freezing rate of foreign matter on the outer surface due to the influence of foreign matter adhering to the outer surface, and the freezing rate of floating foreign matter on the outer surface due to the influence of floating foreign matter around the outer surface, which is obtained based on the amount of floating foreign matter information. [Claim 6] The cooling evaporator includes a supercooling promoting substance that is applied to the cooling evaporator body to form the outer surface and promotes the supercooling of water. The cooling device according to claim 1, wherein the control unit is configured to switch to the heating operation before frost forms on the outer surface formed by the supercooling promoting substance during normal operation. [Claim 7] The cooling evaporator is further equipped with a blower that supplies air to the outer surface thereof. The cooling apparatus according to claim 1, wherein the control unit is configured to perform a cleaning operation in which, when the refrigerator is started, the control unit drives the refrigerator and blows air onto the outer surface of the cooling evaporator with the blower to maintain the temperature of the cooling evaporator at 0 degrees Celsius or above and below the dew point temperature, thereby causing condensation to form on the outer surface and cleaning the outer surface. [Claim 8] The cooling device according to claim 1, wherein the floating foreign matter quantity acquisition unit is provided around the refrigerator and is configured to acquire floating foreign matter quantity information from a floating foreign matter quantity sensor that measures the floating foreign matter quantity information. [Claim 9] The cooling device according to claim 1, wherein the floating foreign matter quantity acquisition unit is configured to acquire floating foreign matter quantity information from publicly available data concerning the floating foreign matter in a region including the installation location of the refrigerator. [Claim 10] The cooling apparatus according to claim 1, wherein the refrigerator is provided at an intake port that draws air from the cooling space to the cooling evaporator and includes a foreign matter filter for removing the floating foreign matter.

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