JPH0345402B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for predictively controlling a plurality of absorption chiller/heater machines installed in parallel.

BACKGROUND ART An air conditioning system is known in which a plurality of conventional absorption chiller/heater machines are installed in parallel and the temperature of chilled/hot water obtained by controlling the number of absorption chiller/heater machines is controlled at multiple positions. As shown in Figure 1, n
Two absorption cold/hot water machines 1 are arranged side by side, their inlets and outlets are piped in common, and are connected to an air conditioner 3 via a cold/hot water pump. A system temperature detector 4 is attached to the common outlet pipe 2 of the absorption chiller/heater,
Its outlet is connected to the system temperature regulator 5.
The output of this temperature regulator 5 is connected to a fuel control valve 6 that controls the fuel supplied to each absorption chiller/heater 1.

The temperature regulator 5 detects the cold/hot water temperature using the temperature detector 4, compares the temperature with a plurality of preset temperatures, and operates the absorption cold/hot water machine corresponding to each temperature.

FIG. 2 shows the operating state of the absorption chiller/heater when this system is in a cooling operating state. In this example, when the chilled/hot water temperature reaches 10℃ or above, all n absorption chillers/heaters start operating, and if the temperature falls below 4℃, all of them are stopped, and during that time the operation is determined according to the refrigeration capacity of each absorption chiller/heater. The operating time and stop temperature are assigned. For example, the first absorption chiller/heater is controlled in two positions with an operation history of starting operation when the chilled water temperature is 6°C and stopping when the temperature is 4°C. Similarly, the second to n-th absorption chiller/heaters are each controlled in two positions according to mutually different set temperatures. In this way, the system targets the chilled water temperature at 7°C and performs multi-position control with a temperature control range of 4°C to 10°C.

In the conventional control method where each absorption chiller/heater is controlled to start/stop using only the absolute value of the chilled/hot water temperature, when the load fluctuation is large, the absorption chiller/heater is activated in response to the load fluctuation. Operation control is performed by faithfully repeating operation and stopping. However, since the absorption chiller/heater has a large heat capacity, it takes a long time from the start of operation to reach a steady state and from the time of stopping operation to a stopped state, making it difficult to follow large fluctuations in load. For example, if the chilled/hot water temperature changes and an additional absorption chiller/heater is required to start operation, the load may fluctuate and the operation may start before the absorption chiller/heater reaches a steady state. In some cases, an absorption chiller/heater may become unnecessary. That is, since the absorption chiller/heater that has already started operating is stopped at that point, the operation from the start to the stop becomes a wasteful operation. For example, in the example shown in Figure 2, if the chilled water temperature fluctuates greatly between 4.5℃ and 7.5℃, the second absorption chiller/heater will constantly start and stop in response to the fluctuations. The second absorption chiller/heater is always shut down before it is fully functional. As a result, it is not necessary to operate the second absorption chiller/heater when the chilled water temperature fluctuates within the above-mentioned temperature range, which is the biggest cause of lowering the thermal efficiency of the entire system. Furthermore, depending on the selection of the number of multiple positions, the cold/hot water temperature may be controlled excessively, exceeding the control temperature range, resulting in a deterioration in the quality of control.

The present invention was made in view of the above circumstances, and aims to improve the quality of the control results and the thermal efficiency of the entire system in a method for controlling the temperature of cold and hot water at multiple positions using a plurality of absorption chiller/heaters. do.

Preferred embodiments of the present invention illustrated in FIGS. 3 to 6 will be described in detail below.

FIG. 3 shows an air conditioning system implementing the control method according to the invention. According to Figure 3, n
Two absorption cold/hot water machines 1 are arranged side by side, their inlet/outlet pipes are shared, and they are connected to an air conditioner 3 via a cold/hot water pump. A system temperature detector 4 is attached to the common outlet pipe 2 of the absorption chiller/heater 1, and its outlet is connected to a system temperature regulator 5. This system temperature regulator 5 is also connected to each fuel control valve 6, and has the function of inputting the driving state of each fuel control valve 6 and conversely outputting a signal indicating the driving possibility of each fuel control valve. There is. An individual temperature detector 7 is installed in the outlet pipe of each absorption chiller/heater, and each output is connected to a corresponding fuel control valve 8.
The outputs are each connected to a fuel control valve and supplied with a drive signal.

In a preferred embodiment of the present invention, each absorption chiller/heater has a chilled water temperature of 8°C during cooling operation, for example.
It is assumed that two-position control is performed with a target value of 7°C, such that operation starts when the temperature is 6°C and stops when the temperature is 6°C. In the case of heating operation, a temperature setting having a similar operation history is made, so the following explanation will be made for the case of cooling operation.

The system temperature controller 5 has an average load factor necessary to determine the number of absorption chiller/heaters to be operated.
Find _QL .

For example, when the first absorption chiller/heater is operated with the temperature set by its individual temperature detector 7 as shown in FIG. 2, fuel is supplied as shown in FIG. The duty ratio T _ON1 /(T _OFF1 + T _ON1 ) between the operating time T _ON1 during which the fuel supply is stopped and the stop time T _OFF1 during which the fuel supply is stopped is regarded as the heat load factor, and this is defined as the load factor Q _L. If there are multiple absorption chiller/heater units in operation, the average of their respective load factors is determined. For example, when i units of absorption chiller/heater are in operation, the average load factor _L is expressed as _L = _o 〓 ⁱ⁼¹ {T _ONi / (T _OFFi + T _ONi )}/n.

Since each absorption chiller/heater is controlled by its own temperature controller 8 as shown in Fig. 4,
There is no relationship between each operation and stop timing.

Next, the system temperature regulator 5 determines the temperature gradient M based on the change in the cold water temperature detected by the system temperature detector 4. As shown in FIG. 5, this temperature gradient M is the rate of change in the cold water temperature from a time G _i a certain time ago in the past to a current time G _j and is expressed as follows.

M=(θ _j −θ _i )/(G _j −G _i ) The system temperature controller 5 then calculates the chilled water temperature from the current chilled water temperature and the temperature gradient M to the lower limit temperature L ₁ (= 4℃) or upper limit temperature L ₂
(=10℃) (in the example in Figure 5, the lower limit temperature
The time (G _k −G _j ) until the control limit slope of L ₁ ) is reached by linear approximation is calculated.

Finally, the system temperature controller 5 determines whether to increase or decrease the number of absorption chiller/heaters up to the number of operating units corresponding to the average load factor _L determined previously. For this determination, the temperature gradient M and arrival time (G _k −G _j )
will be considered preferentially. For example, as in the example shown in Fig. 5, even if the sign of the temperature gradient M is negative and the arrival time is short, due to large load fluctuations, the number of operating machines corresponding to the average load factor is the current number of operating machines. It may indicate that the amount should be increased. In this way, when the average load factor indicates an increase in the number of operating vehicles, a contradiction arises in which the number of operating vehicles is increased even though the chilled water temperature is decreasing. There is no need to increase the number of units, as it is possible to control the chilled water temperature at two positions within the current number of units in operation using each temperature controller 8 and keep the overall chilled water temperature within the specified temperature range (L ₁ to L ₂ ). do not have. Of course, even if the temperature gradient M is negative, the predicted time to reach the lower limit temperature _L1 is longer than the predetermined time,
If the number of operating absorption chiller/heaters corresponding to the average load factor has increased by calculation, the absorption chiller/heater to be operated next is placed in a ready state, and the temperature controller 8 associated with that chiller/heater is placed in a ready state. It is independently controlled in two positions by.

Figure 6 shows an example of the number of units in operation with respect to the average load factor _L when an air conditioning system is configured with four absorption chiller/heaters (i.e. n = 4), and in particular the capacity of each absorption chiller/heater. This shows the case where are the same. The number of operating units shown in FIG. 6 is preset regardless of the temperature gradient M and arrival time described above. In this example, if the calculation result of the average load factor shows, for example, _L = 75%, the first
In addition to the third absorption chiller/heater, the fourth absorption chiller/heater should be placed in an operable state simply. However, while the first to third absorption chiller/heaters are individually controlled in two positions by their associated temperature regulators 8, the operability of the fourth absorption chiller/heater is limited by the temperature gradient and the limit temperature. Depends on arrival time. If the arrival time is longer than the predetermined time regardless of the sign of the temperature gradient M, the fourth absorption chiller/heater is controlled to be ready for operation; For example, the fourth absorption chiller/heater is forcibly shut down. Similarly, if the average load factor _L is 75% or less,
The number of operable vehicles is 3, if it is 50% or less, it is 2, and if it is 25% or less, it is 1.

According to the present invention, each of the absorption chiller/heaters connected in parallel has an individual temperature detector 7 and a temperature controller 8.
At the same time, determine the average load factor of the entire system, set the number of operationable absorption chiller/heaters corresponding to this average load factor, and calculate the temperature gradient at that point. The optimal number of units to be operated is determined by relating the time to reach the limit temperature. In conventional multi-position control, when the air load is light, for example, when there are large load fluctuations in the spring and autumn seasons, or when there are large load fluctuations during the day, the absorption chiller/heater's initial response cannot keep up with the changes in the chilled/hot water temperature. The resulting dead time increases, resulting in a decrease in total thermal efficiency, but according to the present invention, the changing temperature is predicted and the absorption chiller/heater is given priority and the number of units is controlled, eliminating unnecessary control. , leading to a significant improvement in thermal efficiency. Furthermore, the quality of control is improved because predictive control is performed before the temperature is about to deviate from the temperature range to be controlled.

Although the present invention has been described above with reference to preferred embodiments, particularly taking the case of cooling operation as an example, the present invention is not limited to this specific embodiment, and may be modified in any number of ways without departing from the spirit of the present invention. Variations and transformations are possible. For example, in the preferred embodiment, each absorption chiller/heater is described as being controlled in two positions, but it is also possible to obtain the average load factor in the same manner for absorption chiller/heaters controlled in multiple positions.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating a conventional air conditioning system, FIG. 2 is a diagram illustrating conventional multi-position temperature control, FIG. 3 is a diagram illustrating an air conditioning system according to the present invention, and FIG. 4 is a diagram illustrating a conventional air conditioning system. FIG. 5 is an explanatory diagram for calculating the average load factor, FIG. 5 is an explanatory diagram for calculating the temperature gradient, and FIG. 6 is an explanatory diagram showing the relationship between the load factor and the number of operating vehicles. 1...Absorption chiller/heater, 2...Common outlet pipe, 3...
...Air conditioner, 4...System temperature detector, 5...
...System temperature regulator, 6...Fuel control valve, 7...
...Individual temperature detector, 8...Temperature controller.

Claims (1)

[Claims] 1 In a method in which multiple absorption chiller/heaters are installed in parallel and the chilled/hot water temperature at their common inlet or inlet is controlled at multiple locations, each absorption chiller/heater is controlled individually based on the chilled/hot water temperature detected at each outlet. The system calculates the average load factor from the sum of the fuel supply and stop time duty ratios of each absorption chiller/heater and the total number of absorption chiller/heaters, detects the common chilled/hot water temperature, and Calculate the temperature gradient for a predetermined time, calculate the arrival time to the control limit temperature from the temperature gradient and the last detected temperature, and if this arrival time is longer than the predetermined time, it corresponds to the average load factor. A predictive control method for a water chiller/heater, characterized in that the optimum number of absorption chiller/heater units in operation at the present time is calculated, and the operation of only a predetermined number of absorption chiller/heater units corresponding to this number of units in operation can be individually controlled.