JPH086996B2 - Cooling water control method in refrigeration system and its control device - Google Patents

Description

The present invention relates to energy saving by automatically controlling the amount of cooling water for a condenser in various water-cooled refrigerators such as compression type, absorption type and adsorption type. The present invention relates to a cooling water control method in a refrigeration system and a control device therefor.

[Prior Art] Cooling water pumps for condensers used in refrigerators and freezer showcases have a constant output (constant flow rate) throughout the year, regardless of whether the refrigeration method is a compression type, an absorption type, or an adsorption type. ) Often drive. However, the rated power of the cooling water pump is 10 to 15% of that of the refrigerator.
Although it is only to a certain degree, normally, a refrigerator is configured to start or stop or control output depending on the load to reduce wasteful power consumption, whereas the cooling water pump described above always outputs maximum power. Since the pump is operated, the actual annual electric power consumption of the pump is 50% of that of the refrigerator.
In fact, it is not uncommon to go up%.

Therefore, recently, in order to reduce the power consumption, in order to change the flow rate of the pump according to the cooling water temperature, for example, the temperature of the cooling water at the outlet of the cooling tower is detected by a thermostat, and the cooling water pump is used. By connecting the drive motor with a mechanical transmission, when the cooling water temperature is higher than the set value, the pump flow rate is operated at 100%, while when the water temperature is low, the flow rate is set to 70%. There are known examples in which the above-mentioned purpose is achieved. However, this method is a method of switching the mode of the transmission (two-stage switching) as described above, and it is not always said that the control corresponds to the refrigeration load. ) Was required, there was a problem that the equipment cost was extra.

Moreover, the rated flow rate of the cooling water pump is often excessive, but in such a case, even if the flow rate is reduced to 70%, the flow rate may still be excessive.

In addition to the above, a method of proportionally adjusting the amount of water by detecting the temperature of the cooling water with a resistance temperature detector or the like and outputting the detected value to an inverter for driving the pump through a proportional controller is also conceivable. That is, the water flow resistance in the cooling water loop pipe is approximately proportional to the square of the amount of water, and the amount of water is proportional to the rotational speed of the pump. On the other hand, pump power is proportional to the product of water flow resistance and water volume, so pump power is 3
Since it will be proportional to the power, based on this idea,
If the rotation speed of the drive motor of the cooling water pump is controlled via the proportional controller and the inverter, the above purpose can be achieved for the time being, but the operating condition of the refrigerator cannot be reflected and the operating power is minimized. And can't.

[Problems to be Solved by the Invention] As is well known, the efficiency of a refrigerator increases as the temperature of cooling water decreases, while the refrigeration efficiency increases as the amount of water increases. Therefore, in general, operating the cooling water pump at a constant output will result in higher efficiency of the refrigerator, but from the above-mentioned viewpoint, the output of the cooling water pump is changed according to the temperature of the cooling water. By controlling, the total power of the refrigerator and the cooling water pump can be reduced accordingly.

However, as is clear from the above description, the above conventional method does not relate to the refrigerating machine power, that is, the refrigerating efficiency, but merely controls the cooling water pump using only the cooling water temperature as an index, so There is no guarantee that the total power of the cooling water pump will always be a minimum, and it cannot be called the best solution. Especially when the flow rate of the cooling water becomes small, for example 50% of the set value,
According to the conventional method, the pump power in that case is the rated value.
It is about 12.5%, but at this time, if the cooling water temperature falls further, there is a possibility that the increase in the refrigerating machine power due to the decrease in the water amount will outweigh the decrease in the pump power obtained by decreasing the flow rate. Since it is high, the difficulty of increasing the total power cannot be eliminated. The present invention
The object of the present invention is to overcome all the above-mentioned drawbacks inevitable in the conventional method and to significantly reduce the transportation power in the refrigerating apparatus by an extremely efficient method and its control device.

[Means for Solving the Problems] The present invention is intended to minimize the refrigeration system input, which is the sum of the pump power of the cooling water and the refrigerating machine power, that is, to maximize the efficiency of the refrigeration system at each cooling water temperature. The following means are adopted.

That is, a cooling tower, a lead-out pipe for guiding the cooling water cooled in the cooling tower to the outside, a refrigerator connected to the lead-out pipe, and cooling water after heat exchange in the refrigerator. A pipe for introduction returning the cooling tower to the cooling tower, and a cooling pump for circulating the cooling water to the cooling tower through the introduction pipe and a pipe for derivation to a refrigerator, and a preset cooling water temperature and Based on a characteristic curve showing the relationship with the cooling water flow rate, in the cooling water control device of the refrigerating device that determines the supply amount of cooling water and controls the operation of the circulation pump, is arranged on the route of the derivation pipe, A first temperature detecting means for measuring the temperature of the cooling tower output water, a second temperature measuring means arranged on the path of the introduction pipe for measuring the temperature of the cooling tower input water, and consumption of the refrigerator. The power measuring means for measuring the power and the first temperature detecting means From the temperature difference obtained by subtracting the measurement result obtained by the second temperature measurement means, the cooling water flow rate obtained from the rotation speed of the circulation pump, and the power consumption measured by the power measurement means. And calculating means for obtaining the output efficiency of the refrigeration system and modifying the characteristic curve so that the output efficiency becomes maximum.

[Embodiment] Hereinafter, a cooling water control method and a control device for the refrigeration apparatus of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of a cooling water control method and its control device in a refrigeration system of the present invention.

First, the main configuration in this block diagram will be outlined. In this figure, reference numeral 1 is a cooling tower, 2 is a pipe for introducing cooling water, 3 is a pipe for introducing cooling water, 4 is a temperature detector, 5 is a refrigerator, 6 is a freezer showcase, 7 is an operating power supply unit, and 8 is A microcomputer control unit, 9 is an inverter circuit, 12 is a cooling water supply pump, and 13 is a branch power supply.

 Next, the details of each configuration will be described.

The cooling tower 1 is a device that can constantly circulate and use cooling water, and is cooled by so-called evaporative cooling.
In this cooling tower 1, an inlet 1a for introducing cooling water, an opening 1b for the inlet and outlet of air, a fan 1c for air cooling the cooling water introduced from the inlet 1a for cooling water, and a motor 1d for operating this fan 1c. , The motor switch 1e for adjusting the start / stop of the motor, the cooling water outlet 1f for guiding the cooling water in the cooling tower 1 to the cooling water outlet pipe 3, and the temperature of the cooling water are detected, and at a predetermined cooling water set temperature. A thermostat 1g for instructing the start / stop of the fan 1c is provided.

The cooling water inlet 1a of the cooling tower 1 is attached to the cooling water introducing pipe 2 for supplying the cooling water from the refrigerator 5 to the cooling tower 1, and is also attached to the cooling water outlet 1f. Is the cooling water outlet pipe 3 for supplying the cooling water from the cooling tower 1 to the refrigerator. In this embodiment, these two pipes 2,
Temperature detectors 4a, 4b formed from thermocouples on the outer surface of 3
Is fixed to each of the pipes 2 and 3, and the temperature of the cooling water introduced or led out of the pipes 2 and 3 is detected. This temperature detector 4a,
4b generates a first voltage and a second voltage depending on the temperature of the cooling water,
The first and second voltages E1 and E2 are applied to a microcomputer control unit (hereinafter abbreviated as "MPU") 8 via signal lines 10 and 11 connected to the temperature detectors 4a and 4b.

The refrigerator 5 is a device for freezing and storing meat, seafood and the like, and is composed of a condenser 5a and a compressor 5b. Cooling water is supplied from the cooling tower 1 to the condenser 5a of the refrigerator 5 through the cooling water outlet pipe 3. In the refrigerator 5 of this embodiment, first, the compressor 5b
Compressed at, for example, high temperature (60-80 ℃), high pressure (18 atm)
The cooled refrigerant gas is sent to the condenser 5a, and the refrigerant gas flowing into the condenser 5a hits a pipe 5e to which cooling water is supplied and is cooled and liquefied. The liquefied refrigerant is temporarily stored in the condenser 5a, and is stored in the freezer showcase 6 in the showcase 6a.
In the case of refrigerating and storing meat and seafood, the liquefied refrigerant (hereinafter abbreviated as “refrigerant liquid”) is stored in the freezer showcase 6 from the condenser 5a via the refrigerant liquid introduction pipe 5c as necessary. Supply to. In the freezing showcase 6, the refrigerant liquid is the expansion valve.
After passing through 6b, it is heated and evaporated by the heat exchanger 6c. on the other hand,
The air circulating in the freezer showcase 6 is cooled when it is supplied to the heat exchanger 6c via the fan 6d, and the showcase is cooled.
The meat and seafood in 6a are frozen and stored at a constant cooling temperature. The refrigerant liquid gasified by the heating and evaporation is led from the freezer showcase 6 to the compressor 5b through the refrigerant gas outlet pipe 5d, is compressed again, and supplies the refrigerant gas to the condenser 5a. In this embodiment, a plurality of freezer showcases 6 are provided, but the function thereof is the same as that described above, so refer to the above description and omit the description here.

Next, the operating power supply unit 7 and the branch power supply, which are the main power supplies of this embodiment, will be described.

In the operating power supply unit 7, a power detector (or current detector) 7a is attached to each power source of the cooling tower 1, the refrigerator 5, and the cooling water pump 12, and a power / voltage converter (or current / voltage converter) is provided. ) At 7b the power is converted to a voltage signal. Alternatively, an ammeter that directly measures the detection output of the current detector may be used without using such a power / voltage converter.

Power supplies 7c, 7d, 7e are connected to the power detector 7a, and the power supply 7c is connected to the branch power supply 13. The power source 7d is the power source of the refrigerator 5, and the power source 7e is the fan 6d of the refrigeration showcase 6.
It is a power source for driving the etc. The common power supply 13a is connected to the power supply 7c of the branch power supplies 13, and the branch power supply 13 is a motor switch power supply 13b connected to the fan motor switch 1e and an inverter power supply connected to the inverter circuit 9. It is composed of 13c. The output signal of the operating power supply unit 7 is connected to the MPU 8 via a signal line 16. The power of the refrigerator 5, the freezer showcase 6, and the inverter circuit 9 can be detected by the power detector 7a, and the third voltage converted into a voltage signal by the power / voltage converter 7b is MPU8.
Apply to.

An example of the MPU8 is shown in FIG. The MPU 8 is composed of an A / D conversion circuit 8a, a CPU 8b, a storage circuit 8c, an arithmetic circuit 8e and a D / A conversion circuit 8e. The A / D conversion circuit 8a digitally converts the third voltage and the first and second voltages (analog amount) converted into the voltage (analog amount) by the power / voltage converter 7b of the operating power supply unit 7. Convert to. The CPU 8b is a central processing unit that commands each job in the MPU 8. Memory circuit
8c stores the first cooling water temperature, the second cooling water temperature, and the total electric power of the refrigerator system. The arithmetic circuit 8e integrates the first to third voltages input from the operating power supply unit 7 and the temperature detector 4 to the MPU 8 via the respective signal lines and the respective electric powers that change momentarily from the third voltage. . Further, the CPU 8b issues a command to read the first cooling water temperature, the second cooling water temperature, and the total electric power of the refrigerator system stored in the storage circuit 8c. Therefore, the MPU 8 outputs a control signal corresponding to the third electric power and the first and second cooling water temperatures to the inverter circuit 9.

The inverter circuit 9 is a circuit for converting the frequency to a signal, and normally closes the inverter power switch 9a and operates the inverter 9b. The inverter 9b supplies power to the pump motor 17 connected to the inverter output terminal 9c at a frequency according to the signal supplied from the MPU 8 via the signal line 18. The rotation speed of the pump motor 17 increases or decreases in proportion to the frequency.

The power switch 9e is connected in parallel with the power switch 9a, but the power switch 9e is a bypass power switch. When the inverter 9b is out of order, or when it is desired to operate the pump motor 17, for example, the power switch 9a is opened and the power switch 9e is closed to bypass the current.

Next, the cooling water control method in the refrigerating apparatus of this embodiment and the operation of the control apparatus will be described with reference to the flowchart of FIG.

Before explaining this action, it is assumed that the cooling tower heat radiation amount, the refrigerator system efficiency, and the cooling water amount are formed by the following relational expressions (1) to (3).

[Cooling tower heat dissipation] = [Refrigeration output] + [Refrigerator power] + [Cooling water pump power] (1) [Cooling tower heat dissipation] = [Cooling tower inlet / outlet temperature difference] x [Cooling water flow rate] (1) ′ [Refrigerator system efficiency] = [Refrigerator output] / ([Cooling water pump power] + [Refrigerator power]) (2) [Cooling water amount] = Rated flow rate × Pump rotation speed / Rated rotation speed ≈Rating Flow rate x (inverter output frequency / power frequency)
(3) Based on the expressions (1), (2), and (3), the flowchart will be described below. First, the cooling water control in the refrigeration system of this embodiment is started by the MPU 8 (step 1).
Next, the relationship between the amount of cooling water sent from the cooling tower 1 and the water temperature (T) of the cooling water in the outlet pipe 3 is stored under constant conditions in the memory circuit.
It is set and stored in 8c as an initial value (step 2). At this time, the water temperature (T) and the water amount have the relationship shown in FIG. 4, for example. Here, the constant condition is that the minimum flow rate required for the refrigerator 5 or more, the fluctuation of the designated flow rate with respect to the cooling water temperature does not become too large, and the flow rate increases up to the cooling water pump maximum flow rate as the cooling water temperature rises. It is a rising value. That is, if the output of the refrigerator 5 is constant, a larger flow rate is required as the temperature of water supplied to the refrigerator 5, that is, the water output from the cooling tower 1 is higher. Therefore,
As shown in FIG. 4, the water amount changes monotonically with respect to the water temperature, and the upper limit value and the lower limit value are set so that the water amount does not become zero or the supply amount becomes excessive.

Then, the amount of water is obtained from the cooling water temperature value in the cooling tower 1 measured by the temperature detector 4b based on FIG. 4, and the pump 17 is driven at the frequency corresponding to this (steps 3 and 4). Here, if the diameter of the pipe and the pump performance curve of the pump 17 are known, the amount of water and the frequency can be associated.

Then, the pump 17 is driven, and the actual cooling water temperature is detected by the two temperature detectors 4a and 4b (step 5). The first voltage (current) and the second voltage (current) corresponding to the first cooling water temperature and the second cooling water temperature detected by the temperature detectors 4a and 4b are A / D converted by the MPU8. The analog amount is converted into a digital amount by the device 8a, and then stored in the memory circuit 8c under the command of the CPU 8b. Further, in the arithmetic circuit 8d shown in FIG. 2, the cooling tower heat radiation amount is estimated from the cooling tower inlet / outlet temperature difference of the cooling water from the equation (1) ′ and the cooling water flow rate value obtained from the equation (3). be able to. That is, since the output frequency of the inverter 9 is determined so that the flow rate corresponding to the temperature measured by the temperature detector 4b can be supplied at the start of the operation, this inverter frequency is substituted into the above-mentioned formula (3) to perform cooling. The amount of water can be obtained, and the amount of heat radiated from the cooling tower can be obtained by substituting the obtained amount of water and the temperature difference between the inlet and outlet of the cooling tower into the equation (1) '.

When actually calculating this heat radiation amount, confirm that the measured values (electric power, water temperature) do not fluctuate significantly, and check the cooling water temperature (first temperature, second temperature) at the inlet / outlet of the cooling tower. ) Is performed a plurality of times (N times in FIG. 3), the integrated value of these data is obtained (steps 6 and 7), and the heat radiation amount is obtained based on the average value of the temperature differences.

After that, the coefficient of performance is calculated using the following equation (5) from the heat radiation amount obtained by the MPU8 and the power value measured by the power detector 7a.
Calculate the COP (step 8).

The formula (5) is substantially the same as the formula (2), but the formula (2) is a theoretical formula.
Expression (5) is an expression used in actual measurement.

Next, the inverter output frequency H = H (T) is + α
When changing (second time), inverter output frequency H
= H (T) is changed by -α (third time), the cooling water flow rate is forcibly changed, and each coefficient of performance in three cases is obtained. (Step 9). In this embodiment, the inverter output is changed only three times, but it may be changed plural times. If the fluctuation of the water temperature or the like is large during this trial, the process returns to step 3 and the measurement is performed again. In addition, when the swing width is small and stable, three pairs of (COPi, Hi) (i = 1, 2,
Adopt 3). From these three sets of values, the frequency H is the coefficient of performance
As a relational expression of COP, a quadratic curve of COP = aH2 + bH + c (6) can be created (step 10). This quadratic curve is a curve as shown in FIG. 6, for example.

Next, the frequency Hm that gives the maximum COP is obtained from this quadratic curve within the above-mentioned frequency range (H-α to H + α) (step 11). If this quadratic curve does not have the maximum value as shown in FIG. 6, it can be determined that there is no optimum value in this range (H−α to H + α), but in reality, this range does not exist. Since it is dangerous to set the frequency deviating from the optimum value to the optimum value, the frequency Hm that gives the maximum COP within this range is set to the optimum value.

Then, the inverter output H = H (T) is changed to H (T) = Hm
Then, the value up to the previous time is corrected (step 12). Then, the corrected inverter output H (T) is used as a reference value instead of the initial value, and the process returns to step 3. In this way, the relationship between the water temperature and the inverter is modified so that the maximum COP in water temperature and water volume can always be obtained.

That is, the characteristic curve showing the relationship between the water temperature and the water amount shown in FIG. 4 is roughly determined, and the coefficient of performance COP is not always maximized. Therefore, in the present embodiment, by performing the processing of each step described above,
By sequentially modifying the curve shown in Fig. 5 and obtaining the characteristic curve shown by the solid line in Fig. 5, the pump can be operated with optimum efficiency.

In the cooling water control system and its control device in the refrigeration system of this embodiment, the MPU 8 automatically controls the amount of cooling water so that the total efficiency of the refrigeration showcase 6, the cooling tower 1 and the cooling water pump 12 is optimized. Therefore, the power of the refrigeration system can be significantly reduced.

In addition, the cooling water control system and its control device in this refrigeration system can maintain the minimum amount of cooling water so that the cooling water amount does not become extremely small in order to protect the refrigerator from high pressure and prevent the cooling tower from freezing in winter. Control can also be performed.

In the present embodiment, the case where the number of cooling water pumps is one has been described, but the number of cooling water pumps is not limited to one. Needless to say, the number of cooling water pumps may be plural as long as it does not deviate from the range of the configuration of the present embodiment.

EFFECTS OF THE INVENTION According to the present invention, the amount of cooling water can be automatically controlled according to the cooling water temperature so that the total efficiency of the refrigerator and the cooling water pump is maximized. Power can be significantly reduced. Further, in the present embodiment, since the flow rate can be estimated from the output of the inverter without using an expensive flow rate measuring device, there is an effect that the cost of the facility can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a cooling water control method and its control device in a refrigerating apparatus of the present invention, FIG. 2 is a block diagram showing an example of a microcomputer control unit, and FIG. 3 is this embodiment. FIG. 4 is a flow chart showing the action, FIG. 4 is a diagram showing the relationship between the cooling water temperature (T) and the flow rate in the case of initial setting, and FIG. 5 is a diagram showing the relationship between the corrected cooling water temperature (T) and the flow rate, Figure 6 shows the frequency that maximizes the coefficient of performance
It is explanatory drawing which shows the quadratic curve used when calculating | requiring Hm. 1 ... Cooling tower, 2 ... Cooling water introducing pipe, 3 ... Cooling water leading pipe, 4 (4a, 4b) ... Temperature detector, 5 ... Refrigerator, 6 ... Freezing showcase, 7 ...... Operating power supply section, 8 ...
… Microcomputer control unit, 9 …… Inverter circuit, 12 …… Cooling water circulation pump, 13 …… Power supply.

Claims (2)

[Claims] 1. A cooling tower, a lead-out pipe for guiding the cooling water cooled in the cooling tower to the outside, a refrigerator connected to the lead-out pipe, and after heat exchange in the refrigerator. Of the cooling water to the cooling tower, and a cooling pump that circulates the cooling water to the cooling tower and the refrigerator via the piping for introduction and the piping for derivation, and a preset cooling In a cooling water control method of a refrigerating device, which determines a supply amount of cooling water and controls the operation of the circulation pump, based on a characteristic curve showing a relationship between a water temperature and a cooling water flow rate, The temperature difference between the cooling water at the inlet and outlet of the cooling tower is obtained by measuring the temperature of the cooling water of No. 1 and the temperature of the second cooling water flowing in the introduction pipe, and the cooling water is calculated from the rotation speed of the circulation pump. The flow rate of A cooling water control method in a refrigeration system, characterized in that the output efficiency of the refrigeration system is obtained from the temperature difference, the flow rate, and the power consumption, and the characteristic curve is modified so that the output efficiency becomes maximum. 2. A cooling tower, a lead-out pipe for guiding the cooling water cooled in the cooling tower to the outside, a refrigerator connected to the lead-out pipe, and after heat exchange in the refrigerator. Of the cooling water to the cooling tower, and a cooling pump that circulates the cooling water to the cooling tower and the refrigerator via the piping for introduction and the piping for derivation, and a preset cooling Based on a characteristic curve showing the relationship between the water temperature and the cooling water flow rate, in the cooling water control device of the refrigerating device for determining the supply amount of cooling water and controlling the operation of the circulation pump, on the path of the derivation pipe A first temperature detecting unit arranged to measure the temperature of the cooling tower output water; a second temperature measuring unit arranged on the path of the introduction pipe to measure the temperature of the cooling tower input water; Power measuring means for measuring the power consumption of the machine, and the first temperature detector. A temperature difference obtained by subtracting the measurement result by the output means and the measurement result by the second temperature measurement means, the cooling water flow rate obtained from the rotation speed of the circulation pump, and the power consumption measured by the power measurement means. And a calculation unit that corrects the characteristic curve so that the output efficiency is maximized, and a control device for the refrigeration apparatus.