JPH06159904A - Low temperature showcase - Google Patents

Abstract

PURPOSE:To appropriately control the calorific value of a heater for preventing dew condensation on a glass door. CONSTITUTION:A heater 22 for preventing dew condensation on a glass door is provided. A control device 2 is provided with a variable resistor 19, which reduces the calorific value of the heater 22 when the temperature of a storing chamber goes above a prescribed temperature increases the calorific value of the heater 22.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low temperature showcase in which an opening of a storage chamber is openably and closably closed by a glass door.

[0002]

2. Description of the Related Art A conventional low temperature showcase of this type is disclosed, for example, in Japanese Patent Laid-Open No. 62-294887 (F25D21 / 0).
As shown in 4), the storage chamber formed in the heat insulating wall is cooled to a set temperature by a cooling device, and the front opening of the storage chamber is closed by a transparent glass door so as to be openable and closable. Also, because the storage room is cooled to a low temperature,
Dew forms on the outer surface of the glass door due to the temperature difference between the inside and outside, and this dew reduces the visibility of the storage room,
This causes inconveniences such as the customer's clothes getting wet.

Therefore, conventionally, in a low temperature showcase, a film heater is attached to the glass door as described in the above publication to prevent dew on the outer surface of the glass door due to heat generated by the heater.

[0004]

However, since the heating value of the heater provided on the glass door is constant in the past, if the heating value of the heater is set to a large value when the preset temperature in the storage chamber is low, the storage When the set temperature in the room is increased, the amount of heat generated by the heater becomes excessive and the glass becomes too hot, and there is a risk that a customer who touches the glass may get burned or feel uncomfortable. Conversely, if the heating value of the heater is set to a low value when the set temperature in the storage room is high, then the heating value of the heater will be insufficient when the set temperature in the storage room is lowered, and dew will not form on the outer surface of the glass. There was a problem that would occur.

Therefore, conventionally, it has been considered that a humidity sensor for detecting the humidity of the outer surface of the glass of the door is provided and the heat generation amount of the heater is adjusted according to the humidity of the outer surface of the glass detected by the humidity sensor. However, there is a problem in that the control becomes unstable because the addition of the above increases the cost and it is difficult to obtain a representative value of the humidity on the outer surface of the glass. In addition, since a foreign substance called a sensor must be attached to the outer surface of the glass of the door, there is a problem that the display effect of the product in the storage room is impaired.

The present invention has been made in order to solve the above-mentioned conventional technical problems, and provides a low-temperature showcase capable of appropriately controlling the heat generation amount of a heater for preventing dew on the glass door. The purpose is to do.

[0007]

A low temperature showcase 1 of the present invention has a glass door 6 for opening and closing an opening of a storage chamber 4 formed in a heat insulating wall 3 so as to be openable and closable. Cooling device (evaporator) 14 for cooling the inside of 4 and storage chamber 4
Temperature setting device (variable resistor) for setting the set temperature of 19
A control device 2 for controlling the cooling device based on the temperature set by the temperature setting device (variable resistor) 19 and the temperature in the storage chamber 4, and a heater 22 for preventing the dew of the glass door 6. When the set temperature is raised by the temperature setting device (variable resistor) 19, the control device 2 reduces the heat generation amount of the heater 22 and when the set temperature is lowered, It is characterized in that the amount of heat generated by the heater 22 is increased.

[0008]

That is, when the set temperature of the storage chamber 4 is increased, the temperature difference between the inside and the outside of the glass door 6 is reduced, and it is difficult for dew condensation to occur. Therefore, the amount of heat generated by the heater 22 can be small. on the other hand,
When the set temperature in the storage chamber 4 is lowered, the temperature difference between the inside and outside of the glass door 6 becomes large, and the outer surface of the glass door 6 becomes cooler due to the cooling from the storage chamber 4, so that dew condensation easily occurs.

According to the present invention, when the temperature setting device (variable resistor) 19 raises the set temperature of the storage chamber 4, the control device 2 reduces the heat generation amount of the heater 22, so that the door 6 is abnormal. Overheat and temperature rise of the storage chamber 4 due to the heater 22 are prevented, and a temperature setting device (variable resistor)
When the set temperature of the storage chamber 4 is lowered by 19, the control device 2 increases the heat generation amount of the heater 22, so that the outer surface of the glass 7 of the door 6 is strongly heated to effectively prevent dew condensation. Can be prevented.

[0010]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a control device 2 of a low temperature showcase 1 of the present invention.
2 is a vertical side view of the low temperature showcase 1 of the present invention, and FIG. 3 is a front view thereof. 2 and 3, the low temperature showcase 1 includes a heat insulating wall 3 that opens forward,
The storage chamber 4 formed in the heat insulating wall 3 and the storage chamber 4
Glass doors 6, 6 that open and close the front opening of the
It consists of and. A transparent glass 7 is fitted inside the peripheral frame of the glass door 6, so that the inside of the storage chamber 4 can be seen through from the outside.

Inside the adiabatic wall 3, a series of cold air ducts 11 from the lower part to the upper part of the storage chamber 4 are constituted by the bottom plate 8 and the partition plate 9 of the storage chamber 4.
The upper and lower ends of are open to the inside of the storage chamber 4 at the cold air discharge port 12 and the cold air suction port 13 located above and below the front opening of the storage chamber 4. Cold air duct 1 below the bottom plate 8
An evaporator 14 and a blower 16 which constitute a cooling device
An electromagnetic valve 17 is connected to the evaporator 14 to control the supply of the refrigerant from the refrigerator, which is a separately installed cooling device.

The cool air cooled by the evaporator 14 is forcibly blown out into the cool air duct 11 by the blower 16 as shown by the arrow in FIG. 2, and is discharged from the cool air discharge port 12 into the storage chamber 4 and the storage chamber. After circulating through the inside of 4, the cold air suction port 13 returns to the cold air duct 11. The inside of the storage chamber 4 is cooled by such cold air circulation. The cold air outlet 12
A temperature control sensor 18 for substantially detecting the temperature in the storage chamber 4 based on the temperature of the discharged cold air is attached to the cold air duct 11 side. Further, a knob 21 of a variable resistor 19, which will be described later, as a temperature setting device is arranged at the upper end of the front surface of the heat insulating wall 3. Further, on the peripheral frame of the glass door 6 or the surface of the glass 7, a dew condensation preventing heater 22 for heating the glass 7 to prevent dew condensation (condensation) on its outer surface is attached. The dew-prevention heater 22 may be a conductive coating adhered to the glass 7 as described in the above publication, or may be an electric heating element provided on the glass 7 by printing or the like.

Next, in the control device 2 of FIG. 1, the temperature control sensor 18 comprises a thermistor whose resistance value increases when the temperature decreases and decreases when the temperature rises. DC power supply V
A capacitor 28 for noise prevention is further connected in parallel to the temperature control sensor 18, which is connected between cc and ground. on the other hand,
The variable resistor 19 comprises variable resistors 31 and 32,
By turning the knob 21, the variable resistors 31 and 3
It is a uniaxial two-unit volume in which the resistance value of 2 simultaneously increases and decreases. The resistor 33, the variable resistor 31 and the resistor 34
Is connected between the DC power supply Vcc and the ground.

The terminal voltage A of the resistor 27 and the terminal voltage B of the variable resistor 31 are connected to the non-inverting input terminal (+) and the inverting input terminal (-) of the OP amplifier 36, respectively. A positive feedback resistor 37 for setting hysteresis is connected between the output of the OP amplifier 36 and the non-inverting input terminal (+), and the output of the OP amplifier 36 is a resistor 38,
The voltage is divided by 39 and connected to the base of the transistor 41. The emitter of the transistor 41 is grounded, and the collector is connected to the DC power supply Vcc in series with the coil 42C of the relay 42. The relay 42 has a normally open contact a, a normally closed contact b, and a common contact c. The normally open contact a and the common contact c are connected in series with the solenoid valve 17 to an AC power supply AC.

On the other hand, the dew condensation prevention heater 22 is connected to an AC power supply AC in series with a switching element 43 composed of a bidirectional three-terminal thyristor. A series circuit of the variable resistor 32, a resistor 47 and a capacitor 48 is connected between the anode and cathode of the switching element 43, and protective capacitors 44 and 46 are connected. The variable resistor 32, the resistor 47 and the capacitor 48 constitute a CR time constant circuit, and a trigger element 49 is connected between the terminal of the capacitor 48 and the gate of the switching element 43.

The operation will be described with the above configuration. Now, when the knob 21 of the variable resistor 19 is turned to increase the resistance value of the variable resistor 31 (the resistance value of the resistor 32 also increases in conjunction), the terminal potential B of the variable resistor 31 rises. The threshold value of the OP amplifier 36 is raised by such a setting operation, so that the set temperature in the storage chamber 4 is +9, for example.
Assuming that the temperature of the storage chamber 4 has risen, the resistance value of the temperature control sensor 18 decreases as the temperature of the storage chamber 4 rises, and the terminal potential A of the resistor 27 exceeds the terminal potential B when the temperature reaches + 10 ° C. become. OP when terminal potential A exceeds terminal potential B
The output of the amplifier 36 becomes "H" (high potential), the transistor 41 becomes conductive, the coil 42C is energized, and the relay 4
2 closes the normally open contact a to energize the solenoid valve 17, so that the solenoid valve 17 opens to supply the refrigerant to the evaporator 14, thereby cooling the storage chamber 4.

Due to such cooling, the temperature of the storage chamber 4 drops, the resistance value of the temperature control sensor 18 increases accordingly, and the terminal potential A of the resistor 27 becomes equal to + 8 ° C. due to the hysteresis due to the resistor 37. When the potential becomes lower than the terminal potential B, the output of the OP amplifier 36 becomes "L" (low potential), the transistor 41 becomes non-conductive, the current supply to the coil 42C is stopped, the relay 42 is closed to the normally closed contact b, and the electromagnetic wave is closed. Since the valve 17 is de-energized, the solenoid valve 17 is closed and the evaporator 1
The supply of the refrigerant to 4 is stopped. Due to such temperature control, the temperature in the storage chamber 4 is maintained at + 9 ° C., which is the increased set temperature, on average.

When the knob 21 of the variable resistor 19 is turned to decrease the resistance value of the variable resistor 31 (the resistance value of the resistor 32 also decreases in conjunction with it), the terminal potential B of the variable resistor 31.
Descends. The threshold value of the OP amplifier 36 is lowered by such a setting operation, and if the set temperature in the storage chamber 4 is lowered to + 5 ° C., for example, the temperature of the storage chamber 4 rises to + 6 ° C. When
The decrease in the resistance value of the temperature control sensor 18 causes the terminal potential A of the resistor 27 to exceed the terminal potential B. As a result, the output of the OP amplifier 36 becomes “H” as described above, and as a result, the solenoid valve 17 is opened to supply the refrigerant to the evaporator 14, thereby cooling the storage chamber 4.

Further, the temperature of the storage chamber 4 is lowered by such cooling, and due to the hysteresis due to the resistance 37, for example, +
When the terminal potential A of the resistor 27 becomes lower than the terminal potential B due to the increase of the resistance value of the temperature control sensor 18 at the time of 3 ° C., the output of the OP amplifier 36 also becomes “L”, and as a result, the solenoid valve. 17 is closed to stop the supply of the refrigerant to the evaporator 14. By such control, the temperature in the storage chamber 4 is maintained at the lowered set temperature of + 5 ° C. on average.

As described above, the inside of the storage chamber 4 is cooled and maintained at the set temperature arbitrarily set by the variable resistor 19, and the capacitor 48 has the resistance values of the variable resistors 32 and 47 and the capacitor. It is charged with a time constant determined by the capacity of 48, and the trigger element 49 triggers the gate of the switching element 43 to be conductive at a predetermined charging potential. When the switching element 43 is turned on, the dew condensation prevention heater 22 provided on the glass door 6 is energized to heat the glass 7 of the glass door 6 by its heat generation and prevent the dew condensation on the outer surface thereof.

At this time, the knob 21 controls the variable resistor 3
When the resistance value of No. 1 is increased and the set temperature in the storage chamber 4 is increased, the resistance value of the variable resistor 32 is also increased as described above. The phase in which 49 conducts is delayed, and thus the phase in which the switching element 43 conducts is also delayed. Due to this phase delay, the energization rate to the dew condensation prevention heater 22 is reduced, so that the heat generation amount of the dew condensation prevention heater 22 is reduced.

That is, according to the present invention, when the set temperature in the storage chamber 4 is increased and the temperature difference between the inside and the outside of the glass 7 is reduced to make it difficult for dew condensation, the heat generation amount of the dew condensation prevention heater 22 is reduced. Therefore, it is possible to prevent the glass door 6 including the glass 7 from being abnormally overheated while preventing the dew on the outer surface of the glass 7, and to eliminate the occurrence of burns and discomfort of the customer. Further, since the glass 7 is not unnecessarily heated, energy is saved, and the heat effect of the dew condensation preventing heater 22 on the storage chamber 4 is reduced, so that the cooling effect in the storage chamber 4 can be improved. become able to.

On the other hand, when the resistance value of the variable resistor 31 is reduced by the knob portion 21 and the set temperature in the storage chamber 4 is lowered, the resistance value of the variable resistor 32 is also reduced as described above. The charging speed to 48 becomes faster, and the phase in which the trigger element 49 conducts becomes faster, so that the phase in which the switching element 43 conducts also becomes faster. As the phase is advanced in this way, the dew condensation prevention heater 2
Since the duty ratio to No. 2 increases, the amount of heat generated by the dew condensation prevention heater 22 increases.

That is, according to the present invention, when the set temperature in the storage chamber 4 is lowered, the temperature difference between the inside and outside of the glass 7 becomes large, the outer surface of the glass 7 is cooled, and it is easy for dew to condense there. Since the heating value of the prevention heater 22 is increased,
By strongly heating the outer surface of the glass 7, it is possible to reliably prevent the dew condensation. In the embodiment, the energization rate of the dew condensation prevention heater 22 is adjusted by phase control. However, the present invention is not limited to this, and the energization rate may be adjusted by changing the number of energization waveforms by so-called zero volt switching. Further, if an outside air temperature sensor for detecting the temperature around the low temperature showcase 1 is added to the embodiment and the outside air temperature based on the outside air temperature sensor is also added to adjust the heat generation amount of the dew prevention heater 22, the dew prevention control can be performed. Can be performed more precisely.

[0025]

As described in detail above, according to the present invention, when the temperature setting device raises the set temperature of the storage chamber and it becomes difficult for the dew condensation on the glass door, the control device reduces the heat generation amount of the heater. Therefore, it is possible to prevent the customer's discomfort due to abnormal overheating of the door while preventing dew on the glass door. Further, since unnecessary heat generation is prevented, power is saved, and adverse effects of the heat of the heater on the cooling effect of the storage chamber are suppressed.

On the other hand, when the set temperature of the storage chamber is lowered by the temperature setting device and the dew condensation on the glass door becomes easy,
Since the controller increases the amount of heat generated by the heater, it is possible to strongly heat the glass door and effectively prevent the dew on the glass. In general, the visibility in the storage room from the glass door can always be maintained in a good state.
In particular, in this case, since it is not necessary to attach a sensor or the like to the glass door surface, there is no risk of impairing the effect of displaying the products in the storage room.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram of a low temperature showcase of the present invention.

FIG. 2 is a vertical sectional side view of the low temperature showcase of the present invention.

FIG. 3 is a front view of the low temperature showcase of the present invention.

[Explanation of symbols]

 1 Low Temperature Showcase 2 Control Device 3 Insulation Wall 4 Storage Room 6 Glass Door 7 Glass 14 Evaporator 17 Solenoid Valve 18 Temperature Control Sensor 19 Variable Resistor 21 Handle 22 Dew Prevention Heater 31 Variable Resistance 32 Variable Resistance 36 OP Amp 43 Switching element 48 capacitor

Claims (1)

[Claims] 1. A low-temperature showcase having a glass door that opens and closes an opening of a storage chamber formed in a heat insulating wall, and sets a cooling device for cooling the storage chamber and a set temperature of the storage chamber. A temperature setting device, a control device that controls the cooling device based on the temperature set by the temperature setting device and the temperature in the storage chamber, and a heater for preventing dew on the glass door. When the set temperature is raised by the temperature setting device, the control device reduces the heat generation amount of the heater, and when the set temperature is lowered, increases the heat generation amount of the heater. A low-temperature showcase characterized by that.