JPS5852962A - Defrost control device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] This invention is applicable to freezing, for example, an oven showcase.
The present invention relates to a defrosting control device for refrigeration equipment.

Defrosting in conventional equipment was usually done at regular intervals using a timer. However, in this case, the defrost time interval was set based on the operating conditions that caused the most frost formation, which resulted in defrosting even when defrosting was unnecessary, resulting in a large waste of energy. .

Recently, a method used to defrost refrigerators is to defrost when the cumulative cooling operation time reaches a predetermined value. Since it is set based on the operating conditions that cause the most frost formation, it also has the disadvantage that the frequency of defrosting is too high. Particularly in items such as oven showcases, when the cooler stops cooling operation, the cooler is exposed to relatively high temperature air, so there is little frost formation, and even if this method is used, a lot of energy is wasted. It turns out.

The present inventors determined the time interval between defrosting operations (hereinafter referred to as a defrosting interval) according to the time rate during which the cooler performs cooling operation, that is, the cooling operation rate (hereinafter simply referred to as the operation rate). ), we conducted an experiment to examine the relationship between the operating rate of the cooler and the state of frost formation in various open showcases under different air conditions.

FIG. 1 shows an example of this, showing the relationship between elapsed time and operating rate, where curve A is for a case where the enthalpy of air is larger than curve B. In the case of curve B, the operating rate is almost constant, indicating that there is no reduction in the capacity of the cooler due to frost formation. On the other hand, in the case of curve A, the operating rate gradually increases from around 4 hours, and the operating rate is 100% after that. This is because the capacity of the cooler decreases due to frost formation.

By conducting many such experiments, it is possible to determine the relationship between the operating rate and the appropriate defrosting interval.

FIG. 2 shows an example, and this curve is unique to the showcase and its cooling system. Note that the vertical axis in the figure is the appropriate defrost interval calculated by a coefficient when the appropriate defrost interval during continuous operation is set to 1.

Figures 8 and 4 are an overall diagram and a block diagram of the main parts showing an example of a device that actually performs defrosting at the appropriate interval after determining the relationship between the operating rate and the appropriate defrosting interval as described above. In the figure, (1) is an open showcase for freezing and refrigeration equipment, (1a) is a storage room, and (2)
is a refrigerator consisting of a refrigerant compressor, etc., and the dotted line indicates that a plurality of showcases (1) are connected. (
3) is the refrigerant pipe, (4) is the cutoff valve, (5) is the pressure reducing valve, (
6) is a cooler, (7) is a heater that is a defrosting means for the cooler (6), (8) is a temperature detector that detects the temperature in the storage room (1a), (9) is a controller, The details are shown in FIG.

In FIG. 4, (9a) is a temperature control device that controls on/off the cooling operation of the cooler (6) by opening and closing a shutoff valve, (9b) is a defrosting interval control device, and 01
is the output signal of the temperature detector (8), CI+> is the temperature adjustment circuit, (b) is the temperature range setting signal, (to) is the gate, Q4
is the opening signal of the shutoff valve (4), and (to) is the first signal that integrates the opening time of the shutoff valve (4), that is, the cooling operation time of the cooler (6).
DI is the second timer circuit that counts the elapsed time since the end of the previous defrosting, Ono is the timer circuit θ
An arithmetic circuit that calculates the operating rate based on the output of fll, (g)
is a defrost interval setting circuit that stores the operating rate and a predetermined appropriate defrost interval as shown in Figure 2, and also stores the elapsed time from the end of the previous defrost and the arithmetic circuit. Compare with the appropriate defrost interval corresponding to the determined operating rate. 01 is the initial defrost interval setting signal,
(E) is a defrosting signal that operates the heater (7).

In such a configuration, the control temperature range in the storage room (la) is set by the signal (6), and the signal 0
1 to set the initial defrost interval and start operation. At that time, the circuit 0η outputs the open signal Q4 and the shutoff valve (4)
, the cooler (6) starts cooling operation. When the temperature of the storage room (1a) reaches the lower limit set temperature, the signal Q41 is stopped, the shutoff valve (4) is closed, and the cooler (6) thereafter performs on/off operation. - The force calculation circuit Qη calculates the operating rate of the cooler (6) and inputs the value to the circuit (to). The circuit (to) repeats the operation of calling the appropriate defrosting interval corresponding to the input operation rate and comparing it with the elapsed time counted by the circuit α. In the process, when the elapsed time and the appropriate defrost interval match, the circuit (to) generates a defrost signal (e) to operate the heater (7), and the signal (e) that enters gate 0 is cut off. Stop the opening signal a◆ of valve (4). As a result, the cooler (6) is turned off and defrosted by the heater (7).

In such a device, defrosting is performed at the appropriate time, so that appropriate defrosting can be performed with the minimum amount of energy.

However, as shown in FIG. 2, as the operating rate decreases, the appropriate defrosting interval becomes longer, and when the operating rate reaches about 45%, defrosting is no longer performed.

However, in such a low load state with a low operation rate, even if the cooler (6) is off, the inlet air temperature is extremely low, for example around 2°C, and the heat transfer surface of the cooler (6) is extremely low. Although some of the surface of the frost melts, it does not melt completely; rather, it becomes denser and some parts of it freeze. If frost formation, partial melting of frost, and freezing are repeated for a long time under such a low operating rate, the surface of the cooler (6) will be covered with ice-like blocks, making it impossible to defrost easily. If the cooler (6) is operated in such a state, the heat exchange efficiency is reduced, and there is a risk that the liquid phase refrigerant will flow back into the refrigerator (2) and cause damage to the compressor, etc. there were.

This invention was made in view of the above circumstances, and aims to prevent the above-mentioned danger by operating a defrosting means when the elapsed time from the end of the previous defrosting reaches a predetermined value. In other words, for example, in a configuration as shown in FIG. 4, the timer circuit in FIG. 2 (Iej is an example of the predetermined value in FIG. If you count the elapsed time of
Regardless of the appropriate defrost interval called in the defrost interval setting circuit 0, the circuit αQ is
A defrost command (No. 1) is sent to the circuit (G), and the circuit (G) outputs a defrost signal (E) based on that signal. Therefore, even at low operating rates, the heater is activated before freezing of the cooler (6) progresses. (7
), defrosting is performed, and liquid phase refrigerant no longer flows back into the refrigerator (2), and there is no fear of damage to the compressor or the like.

As explained above, the present invention prevents frost from forming on the cooler by activating the defrosting means when the elapsed time from the end of the previous defrosting reaches a predetermined value, and prevents frost from forming on the compressor. The effect is that proper defrosting can be achieved with minimal energy without worrying about damage to the frost.

[Brief explanation of the drawing]

FIGS. 1 and 2 are explanatory diagrams of the present invention, and FIGS. 8 and 4 are an overall view and a block diagram of essential parts showing a conventional equipment and an embodiment of the present invention. In the figure, (1) is the refrigeration equipment, ((, > is the cooler, (7) is the defrosting means, (9a) is the temperature control device, (9b
) is a defrost interval control device. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent: Kazuno Ia - Continuation of Figure 1, Page 1 ■Applicant: Mitsubishi Electric Corporation 2-2-3 Marunouchi, Chiyoda-ku, Tokyo

Claims (1)

[Claims] A defrosting means for the cooler, a temperature control device that controls on/off the cooling operation of the cooler, and a relationship between the cooling operation rate of the cooler and a predetermined appropriate defrosting inlet, and A defrosting interval control device is provided to calculate the cooling operation rate of the cooler within the elapsed time from the end of defrosting, and the appropriate defrosting interval control device calculates the cooling operation rate of the cooling unit <
), wherein the defrosting interval control device is configured to operate the defrosting means when the elapsed time reaches a predetermined value; A defrosting control device characterized by: