JPH0788999B2 - Defrosting method for cold air circulation showcase - Google Patents

Description

TECHNICAL FIELD The present invention relates to a defrosting method for a cold air circulation type showcase.

[Conventional technology]

First, the structure of the cold air circulation type showcase shown in FIG. 3 is shown. In the figure, 1 is a case body of an open showcase having an open front surface, 2 is a product display room inside a storage room equipped with product display shelves 21, and 3 and 4 surround the product display room 2 and partition the inside of the case body 1. Dual inside and outside cold air circulation duct,
Reference numerals 5 and 6 denote fans arranged in the cool air circulation ducts 3 and 4, and reference numeral 7 denotes a cooler of a refrigerator installed in the cool air circulation duct 3 inside. The cooler 7 is a finned coil in which fins are attached to a direct expansion type cooling coil arranged in a meandering shape, and is pipe-connected to a condensing unit of a refrigerator via an expansion valve.

With such a configuration, by operating the refrigerator and the fans 5 and 6 during cold storage, two layers of cold air curtains A and B inside and outside are blown out at the front opening of the case main body 1 to thereby display the products displayed in the warehouse. Is kept cool.

On the other hand, in such a showcase, frost adheres to the surface of the cooler 7 with the lapse of the cool keeping operation. Therefore, the cool keeping operation is periodically stopped and the cooler 7 is defrosted during this period. There is. As the defrosting method, conventionally, an electric heater that is wired in parallel with the fan 5 is energized on the upstream side of ventilation of the cooler 7, and air heated by the heat generated by the heater is blown to the cooler 7 to defrost it. In addition, a defrosting method in which a defrosting operation is terminated by a thermostat arranged downstream of the cooler 7 on the ventilation side to detect and operate the temperature of the air after defrosting the cooler 7 is often adopted.

[Problems to be Solved by the Invention]

By the way, the above-mentioned conventional defrosting method has the following problems. First, in the electric heater defrosting method, the circulating air in the refrigerator is heated by a heater and blown to a cooler, and the sensible heat defrosts the air. Therefore, the temperature of the air that passes through the cooler and blows into the refrigerator rises from a few dozen degrees to around 20 ° C, and as a result, the product temperature of the display case in the refrigerator rises significantly, especially the quality deterioration of products such as meat and fresh fish. Invite.

Further, the frost formed on the cooler due to the cooling operation causes a slight amount of adhesion in the longitudinal direction of the cooler because the air inside the cooler 7 contains a different amount of water depending on the products displayed in the cooler. Then, the amount of the adhered amount causes a temperature difference in the longitudinal direction in the air temperature on the ventilation downstream side of the cooler 7. Therefore, it is extremely difficult to appropriately detect the end of defrosting with a thermostat installed at a specific position. For example, if a thermostat is installed in a place with a small amount of frost, the air temperature in this place will rise faster than in a place with a large amount of frost, and the thermostat's operating time will be accelerated, and frost will still be generated in a place with a lot of frost The defrosting operation ends with the remaining. This residual frost will accelerate frost formation in the next cooling operation and increase the amount of adhesion.
Due to this vicious cycle, the showcase may further deteriorate the cooling performance.

The present invention has been made in view of the above points, and while suppressing a rise in the product temperature of the in-compartment display product at the time of defrosting, it is possible to efficiently defrost the frost attached to the surface of the cooler, Another object of the present invention is to provide a defrosting method for a cold air circulation type showcase capable of appropriately detecting defrosting and ending the defrosting operation without being influenced by the mounting position of the thermostat as in the conventional case.

[Means for Solving the Problems]

In order to solve the above-mentioned problems, the defrosting method of the present invention uses a solenoid valve to connect to the inlet and outlet pipes of a cooler, and conducts heat transfer along a cooling coil outlet pipe arranged at the bottom of the cooler. An electric heater is wired to, the solenoid valve is closed during defrosting, and the electric heater is energized to perform defrosting.
A pressure switch that detects and operates the pressure inside the cooling coil, which is closed by electromagnetic valves on both sides, is provided, and the defrosting operation is terminated by the operation of this pressure switch.

[Action]

When the cold insulation operation is switched to defrosting as described above, the electromagnetic valve connected to the inlet and outlet of the cooler is closed to stop the operation of the refrigerator, and at the same time, the electric heater is energized. Among the refrigerants contained in the cooling coil of the cooler, the liquid refrigerant flows down in the cooling coil due to gravity and gathers in the cooling coil outlet pipe installed at the bottom, where it is evaporated and saturated by the heating of the electric heater. Change to gas. Further, this saturated gas diffuses in the coil, radiates heat to the frost adhering to the surface of the cooler, then condenses, flows down in the cooling coil, and is repeatedly heated by the electric heater, and the evaporation / condensation cycle is repeated. . As a result, the cooler itself functions like a heat pipe, and the heat given by the electric heater is spread over the entire length of the cooling coil and radiated from the inside to the frost adhering to the surface in the form of latent heat of condensation. Defrost.
In addition, a part of the heat generated by the electric heater heats and raises the temperature of the air passing through the duct, and in the form of sensible heat, defrost heat is applied to the frost adhering to the peripheral surface of the evaporator.

As a result, the heat generated by the electric heater acts on the cooler from inside and outside as defrosting heat, and particularly from the inside, heat is radiated to the frost in the form of condensation latent heat, which enables efficient defrosting in a short time. Moreover, since most of the heat generated by the electric heater is consumed by the evaporation of the refrigerant, the rate of heating and raising the temperature of the circulating air inside the refrigerator is small, and the rise in the product temperature of the in-store displayed goods can be suppressed to a low level.

Even if some frost is formed in the longitudinal direction of the cooler, the pressure in the cooling coil is uniform due to the gas-liquid mixed refrigerant.
This pressure is increased by melting and removing the attached frost to reduce or eliminate it, whereby the condensation of the refrigerant becomes slower. The pressure switch operates due to the pressure in the cooling coil when the frost is completely removed, and the defrosting operation ends. Therefore, in the showcase, the defrosting operation ends at the most appropriate time when all the frost is removed, and the showcase is switched to the cooling operation.

〔Example〕

FIG. 1 shows the configuration of the embodiment of the present invention. First,
The cooler 7 configured by piping the finned direct expansion cooling coil in a meandering shape has a configuration in which the cooling coil 71 is arranged in a meandering manner,
The expansion valve 8 and the solenoid valve 9 are connected to the cooling coil inlet side which is piped to the upper side, and the cooling coil outlet pipe 72 which is piped to the lower side.
Pressure switch 20 solenoid valve that is electrically connected to an operation control unit (not shown) and communicates with the outlet pipe 72 via the pipe 21.
10 is connected to the condensing unit 11 of the refrigerator to be connected by piping to form a refrigeration cycle. Further, the electric heater 12 is laid out in a heat transfer manner along the outlet pipe 72 that is piped on the bottom side of the cooler 7. Further, an overheat-preventing thermostat 13 arranged in a heat transfer manner on the surface of the cooler 7 is connected in series to a power supply circuit of the electric heater 12.

With such a configuration, the solenoid valves 9 and 10 are opened and the condensing unit 11 is operated in response to a command from an operation control unit (not shown) during the cold insulation operation of the showcase. On the other hand, when switching from cold insulation operation to defrosting periodically by timer control etc.,
The solenoid valves 9 and 10 are closed by a command from the operation control unit. As a result, the low pressure switch provided in the refrigerant pipe is activated to stop the operation of the condensing unit 11. At the same time, the electric heater 12 is energized and controlled.

Here, immediately after the solenoid valves 9 and 10 are closed and the refrigerator is stopped, the refrigerant remaining inside the cooling coil 71 has a form in which the refrigerant gas and the liquid refrigerant coexist at a pressure corresponding to the evaporation temperature. The liquid refrigerant among them is flowed down by gravity in the pipe of the cooling coil 71 and is collected inside the outlet pipe 72. On the other hand, the liquid refrigerant flowing down to the outlet pipe 72 is evaporated by the heating of the electric heater 12 into a saturated gas, rises along the cooling coil 71 from here, diffuses in every corner of the pipe, and is spread on the surface of the cooler 7. Dissipates heat to the frost that adheres. Further, the gas that radiates heat to the surroundings is condensed and liquefied, flows down in the pipe of the cooling coil 71 and recirculates in the outlet pipe 72, where the evaporation / condensation thermostat is repeated so that it is heated by the electric heater 12 and evaporated again. . That is, the cooler 7 functions like a heat pipe, transfers the heat applied from the electric heater 12 over the entire length of the cooling coil 71, and melts the frost adhering to the surface in the form of latent heat of condensation. . During this time, the pressure in the cooling coil 71 is kept substantially constant and the pressure switch 20 does not operate. Further, a part of the heat generated by the electric heater 12 heats the air blown by the fan in the duct, and gives defrosting heat to the cooler 7 from the outside in the form of sensible heat.

When the defrosting progresses as described above and the adhered frost decreases and disappears, the refrigerant condenses slowly and the cooling coil 71
The pressure inside rises gradually. Then, the pressure switch 20 whose operating pressure is set to the pressure at which frost formation has just disappeared operates to send a defrosting completion signal to the operation control unit. Then, the open showcase is switched from the defrosting operation to the cooling operation.

When the surface temperature of the cooler 7 rises to a predetermined temperature as the defrosting progresses, the overheat prevention thermostat 13 operates to cut off the electric heater 12, but for a while after the electric power is stopped, the electric heater 12 is stopped. The evaporation / condensation cycle described above continues inside the cooler 7 due to the residual heat of 12.

In this way, the heat of the electric heater 12 is applied to the defrosting heat from inside and outside of the cooler 7, whereby the defrosting temperature is set to be low and the temperature rise of the circulating air blown into the refrigerator is kept low, while cooling is performed. The frost adhering to the surface of the vessel 7 can be efficiently defrosted.

In addition, since the defrosting operation is ended and the operation shifts to the cooling operation at an appropriate time when all the frost is removed, the operation is always performed with a high cooling performance. In this way, it is possible to suppress the temperature rise of the products displayed in the warehouse and maintain the quality.

Next, as the defrosting method for the showcase, in addition to the above-mentioned electric heater, a hot gas defrosting method is conventionally known. However, the present inventor has proposed a conventional hot gas defrosting method and an electric heater defrosting method. FIG. 2 shows the result of the defrosting test of the actual machine, which was performed in comparison with the defrosting method according to the invention. In the defrosting method of the present invention, the operation set temperature of the overheat preventing thermostat 13 was set to 5 ° C. as a defrosting condition. As is clear from this characteristic diagram, according to the defrosting method of the present invention, the conventional electric heater defrosting method (the operation set temperature of the thermostat is 20 ° C.)
The defrosting time is significantly shortened as compared with, and the defrosting can be completed in about the same time as the hot gas defrosting method. Moreover,
The rise in the temperature inside the chamber due to defrosting can be significantly reduced compared to the conventional defrosting methods. Further, there is no fear that an excessive thermal stress is generated in the cooling coil as seen in the hot gas defrosting method.

〔The invention's effect〕

According to the defrosting method of the present invention, a solenoid valve is interposed and connected to the cooler inlet and outlet pipes of the cooler of the refrigerator, which is a direct expansion type cooling coil arranged in the cool air circulation duct in the showcase. Along with the cooling coil outlet pipe that is piped at the bottom of the cooler, the electric heater is heat-transferred, the electromagnetic valve is closed at the time of defrosting, and the electric heater is energized for defrosting. Is equipped with a pressure switch that detects and operates the pressure inside the cooling coil blocked by the solenoid valve, and the defrosting operation is terminated by the operation of this pressure switch. Compared with the frost method, the frost generated on the surface of the cooler can be efficiently defrosted in a short defrosting time while minimizing the temperature rise in the refrigerator and hence the product temperature. Compared to the electric heater defrosting method of It is possible to set the frost end time very properly, it is possible to prevent the degradation of the cooling performance due to residual frost after defrosting operation. As a result, it is possible to improve the reliability of the showcase by solving the problem of product quality deterioration such as fresh meat and fresh fish due to defrosting.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, and FIG. 2 is a defrosting characteristic diagram showing the conventional defrosting method and the defrosting method of the present invention in comparison.
FIG. 3 is a configuration diagram of the entire cold air circulation type showcase.
In the figure, 7 ... Cooler, 71 ... Cooling coil, 72 ... Cooling coil outlet pipe, 8 ... Expansion valve, 9,10 ... Solenoid valve, 12 ... Electric heater, 20 ... Pressure switch.

Claims (1)

[Claims] 1. An inlet pipe of a cooling coil located on the upper side of the cooler of a refrigerator, which is a direct expansion type cooling coil arranged in a cool air circulation duct in a showcase,
A solenoid valve is connected to each outlet pipe of the cooling coil located on the bottom side, and a defrost heater is thermally arranged along the outlet pipe of the cooling coil located on the bottom side of the cooler. After closing the solenoid valves on the inlet and outlet pipes, the defrost heater is energized to defrost, and a pressure switch is installed to detect and operate the pressure inside the cooling coil blocked by the solenoid valves on both sides. A defrosting method for a cold air circulation showcase, characterized in that the defrosting operation is terminated by the operation of this pressure switch.