Water chilling unit multi-unit load allocation system and method

Abstract

The invention discloses a multi-unit load allocation system and method for water chilling units, and aims to realize regulation and control of load distribution of the multiple water chilling units in a reliable manner. And further obtaining a frequency control algorithm of a delivery pump of the chilled water system, a flow guide opening degree calculation method of an inlet shunting device of each water chilling unit, and a corresponding system architecture. The control method suitable for the multi-unit load distribution regulation and control of the water chilling unit is reliable and easy to implement, and complex work of multi-unit communication of the water chilling unit, control protocol butt joint, equipment controller upgrading and the like is omitted.

Description

Technical Field

[0001] The present invention relates to the technical field of refrigeration and air conditioning cold water system control, and in particular to a cold water system variable flow control method and system with constant water supply temperature. Background Art

[0002] Centrifugal and screw chillers have been widely used in park buildings, large single buildings, and regional energy stations, and are developing in the direction of large-scale and centralized. The demand for energy conservation and carbon reduction in large chillers and energy rooms is gradually increasing.

[0003] The optimal efficiency point of centrifugal and screw chillers is usually in the 40-60% load range; while the power configuration of the chiller meets the design load, it also faces the objective situation of intraday partial load fluctuations caused by factors such as weather and insufficient occupancy rate during the cooling season. Therefore, at partial load, for systems with multiple chillers, it is necessary to control the load distribution between units, so as to make each unit run near its optimal efficiency point as much as possible while meeting the total cooling load, thereby reducing the total power consumption. Summary of the invention

[0004] In order to achieve load allocation between multiple chillers, it is necessary to actively control the flow entering the chiller. The conventional method of regulating the flow of the chiller is to install a regulating valve at the outlet of the unit to throttle the flow of chilled water passing through the unit. This method will significantly increase the throttling loss and reduce the overall efficiency of the system fluid transportation.

[0005] In the above context, the purpose of the present invention is to achieve more economical and efficient multi-unit load allocation by controlling the flow ratio entering each chiller and the operating frequency of the chiller pumps for a refrigeration system (many-to-many system) in which multiple chilled water pumps are connected in parallel to deliver chilled water to multiple chillers, while ensuring the safe operation of the units. The present invention adopts the following scheme: A method for load allocation of multiple units of a chiller, firstly records the sequence of opening values ​​of each terminal balancing valve within the current strategy period r (n, j), calculate the delivery frequency of the system chilled water pump at the end of the current strategy period, and adjust the frequency to the calculated value, which is divided into the following 7 steps: (1) Calculate the average opening of each balancing valve during the strategic period. The process is as follows: ; Among them, r(n,j) is the opening value sequence of the jth balancing valve at the end in the current strategy period, and the opening values ​​of each balancing valve total n;

[0006] (2) Calculate the deviation matrix of each balancing valve opening: ; (3) Calculate the correlation coefficient matrix between each balancing valve: ; (4) Take the lower half of the correlation coefficient matrix A, that is: ; (5) Eliminate all valves whose row values ​​in the lower half of the correlation coefficient matrix A are not positive; (6) Calculate the overall opening value of the remaining m balancing valves at the end of the current strategy period after elimination: ; (7) Calculate the chilled water pump delivery frequency: ; Among them, y min and max are the upper and lower limits of the pump operating frequency, k is the steepness coefficient of the frequency conversion curve, z is the overall opening value of the balancing valve at the end of the current strategy period, and c is the center coefficient of the frequency conversion curve. The upper and lower limits of the pump operating frequency need to consider factors such as the performance of the pump inverter, the safe operation requirements of the unit, and the maximum resistance of the system. The purpose of using this function is mainly to reversely adjust the system flow through the overall opening z of the balancing valve: a larger opening of the balancing valve indicates that the flow demand at each end is larger at this time, and the pump operating frequency needs to be increased at this time; a smaller opening of the balancing valve indicates that the flow demand at each end is smaller at this time, and the pump operating frequency needs to be reduced at this time. Since the valve usually has an equal percentage characteristic, this function distribution is adopted. The steepness coefficient of the frequency conversion curve and the center coefficient of the frequency conversion curve are usually determined by the system characteristics.

[0007] According to the cooling load demand during the current strategic period Load , calculate the load distribution value of each chiller in the current strategy period w (j), the prediction method of the total cooling load can be LSTM, historical average, typical daily average, etc., and the calculation of the load distribution value can be calculated by mixed integer linear programming and other methods. Then calculate and adjust the diversion opening of each diversion device. The inlet of the diversion device is connected to the upstream of the chilled water return main, and the two outlets are the return branch pipe at the inlet of the chiller and the downstream of the chilled water return main. By adjusting the diversion opening, the proportion of chilled water to the two outlets can be controlled, but the sum of its flow area remains unchanged, so it basically does not affect the overall along-the-way resistance of the water system. Since the diversion amount of the diversion device is linearly related to its angle, the calculation method of the diversion opening pointing to the chiller is: ; in Reg (j) is the diversion opening of the diversion device pointing to the outlet of the jth chiller at the end of the current strategy period, p(j) is the ratio of the load distribution value of the jth chiller at the end of the current strategy period to the total load demand at the current moment, that is: ; If the overall load demand during the current strategy period Load If it is greater than the value of the previous strategy period, the operating frequency of the chilled water pump is adjusted first. f , then adjust the diversion opening of the diversion device Reg If the overall load demand during the current strategy period is Load If it is less than the value of the previous strategy period, the diversion device opening is adjusted first. Reg , and then adjust the operating frequency of the chilled water pump f .

[0008] A multi-unit load allocation system for chillers is applied to a multi-unit load allocation method for chillers, comprising a plurality of chilled water pumps (chilled water pump groups) arranged in parallel, and a plurality of chillers arranged in parallel, wherein a chilled water return main pipe is connected from the outlet of the chilled water pump group to each chilled water return branch pipe, and the chilled water return branch pipe is connected to the inlet of each chiller, and except for the farthest chiller, a diversion device is arranged at the fork of each chilled water return branch pipe and the main pipe, and the chilled water supply branch pipe of the chiller is connected to the outlet of each chiller, and flows to the end user after confluence, and the chilled water is connected to the inlet of the chilled water pump group through the chilled water return main pipe after the end user exchanges heat for cooling and heats up the chilled water.

[0009] The present invention provides a multi-unit load allocation system and method for a chiller, which realizes the regulation and control problem of load distribution of multiple chillers in a relatively reliable manner, including obtaining a frequency control algorithm for a delivery pump of a chilled water system and a method for calculating the diversion opening of an inlet diversion device of each chiller by using a sequence value of an end-user valve opening and a chiller load distribution value, as well as a corresponding system architecture; the present invention realizes a relatively reliable and easy control method suitable for load distribution and regulation of multiple units of a chiller, eliminating the relatively complicated work of multi-unit communication, control protocol docking, equipment controller upgrade, etc. of the chiller.

[0010] The beneficial effects of the present invention are:

[0011] For a system where the chilled water pump group and the chiller are in a many-to-many relationship, the water pump groups can be guaranteed to be mutually redundant, thereby avoiding reliability problems under a one-to-one configuration of the chilled water pump and the chiller. The method of the present invention is suitable for efficient transformation of such a multi-unit cooling system, and can realize the control of the flow of each chiller under a many-to-many relationship between the water pump and the unit.

[0012] The method of the present invention actively reduces or increases the load power of the chiller by controlling the flow rate of each chiller, thereby adjusting the distribution ratio of the cooling load in each chiller, so that each chiller can operate at the power value specified by the optimal scheduling method without changing the set temperature difference during the flow change, thereby realizing the distribution of the cooling load and improving the overall energy efficiency of the system.

[0013] The method of the present invention is highly practical and realizes a relatively reliable and easy control method suitable for load distribution and regulation of multiple units of a chiller, eliminating the relatively complicated work of multi-unit communication, control protocol docking, equipment controller upgrade, etc. of the chiller. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the load allocation system of multiple units of a chiller of the present invention; Figure 2 It is a frequency conversion curve diagram of the delivery frequency of the chilled water pump of the present invention; In the figure: 1. Chilled water pump; 2. Diversion device; 3. Chiller; 4. Chilled water return main pipe; 5. Chilled water return branch pipe; 6. Terminal balancing valve; 7. Each terminal user. DETAILED DESCRIPTION

[0015] Embodiments of the present invention will be described below with reference to the accompanying drawings.

[0016] The chilled water system of a building's cooling room consists of three parallel chilled water pumps (motor power 55kW), three centrifugal chillers and related piping systems. The rated cooling power and cooling COP of the three centrifugal chillers are shown in Table 1: Table 1 ; Under normal operating conditions, the chilled water supply temperature is 7°C and the return water temperature is 12°C.

[0017] There are 5 balancing valves on the user side, and 5 opening values ​​are recorded in the current strategy period. The opening value sequence is as follows: ; Calculate the average of the opening values: ; Calculate the deviation matrix of each balancing valve opening: ; Compute the correlation matrix: ; The lower part of the correlation coefficient matrix is: ; The fifth row is not positive, so it is discarded.

[0018] Calculate the overall opening value of the remaining 4 balancing valves at the end of the current strategy period: ; According to the performance of the water pump inverter in the system, the safe operation requirements of the unit, the maximum resistance of the system, etc., the minimum frequency is 25Hz and the maximum frequency is 50Hz. The steepness coefficient of the frequency conversion curve is 10, and the center coefficient of the frequency conversion curve is 0.4. Substituting it into the calculation of the delivery frequency of the chilled water pump, we get f=46.75, and the frequency is rounded to 46.8Hz; Figure 2 As shown; Using the prediction algorithm and the historical load data of the dispatching system, the cooling load in the current strategy period is 2900kW. Using the mixed integer linear programming algorithm, the optimal cooling load of chillers 1 and 3 under this cooling load is 900kW, and the optimal cooling load of chiller 2 is 1100kW. ;

[0019] According to the load distribution value of each chiller, calculate the diversion opening of each diversion device: Diversion opening of No. 1 diversion device: ; Diversion opening of No. 2 diversion device: ; In the previous strategy period, the cooling load was 3500kW. The overall load demand of the current strategy period is 2900kW, which is less than the value of the previous strategy period. f , Reg (1) Reg (2) After that, first adjust the diversion opening of the diversion device, and then adjust the operating frequency of the water pump.

[0020] Compared with existing technologies: Compared with the same system without the present invention, if three chillers are turned on, the cooling load will be passively shared evenly, i.e. w (1) = 966.6kW, w (2) = 966.6kW, w (3) = 966.6kW. If two chillers are turned on, then w (1) = 1450kW, w (2) = 1450kW, w (3) = 0kW. At the same time, the pump delivery frequency is 46.8Hz, and the power is further reduced compared to the non-frequency reduction. The final comparison results are shown in Table 2: Table 2 ; The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A multi-unit load allocation system for chillers, characterized by: The invention comprises a plurality of chilled water pumps (1), a plurality of chillers (3), a chilled water return main pipe (4), a chilled water return branch pipe (5) and a diverter device (2); the plurality of chilled water pumps (1) are arranged in parallel, and the outlet of each chilled water pump is connected to the chilled water return main pipe (4); the plurality of chillers (3) are arranged in parallel, and the chilled water return main pipe (4) is connected to each chilled water return branch pipe (5); except for the farthest chiller (3), a diverter device (2) is arranged at the bifurcation between each chilled water return main pipe (4) and the chilled water return branch pipe (5); the chilled water return branch pipe (5) is connected to the inlet of each chiller (3); the outlet of the chiller (3) is connected to the chilled water supply branch pipe; after confluence, the chilled water is led to the end user through the end balancing valve; after the chilled water is heated by heat exchange for cooling at the end user, it is connected to the inlet of the chilled water pump (1) through the chilled water return main pipe.

2. A method for adjusting loads of multiple units of a chiller, used in the system for adjusting loads of multiple units of a chiller as claimed in claim 1, characterized in that: The following steps are involved: S1. Obtain the sequence of opening values ​​of each terminal balancing valve within the current strategy period r (n,j); S2. According to the sequence of opening values ​​of each terminal balancing valve in the current strategy period r (n,j), calculate and adjust the system chilled water pump delivery frequency; S3. Based on the cooling load demand during the current strategic period Load , calculate the load distribution value of each chiller in the current strategy period w (j); S4. According to the load distribution value of each chiller in the current strategy period w (j) Calculate and adjust the diversion opening of each diversion device.

3. A method for load allocation of multiple chillers according to claim 2, characterized in that: In S2, the method for calculating the delivery frequency of the chilled water pump is as follows: 2.1) Calculate the average opening of each balancing valve within the strategic period. The process is as follows: ； in, r (n,j) is the opening value sequence of the jth balancing valve at the end in the current strategy period, and the opening values ​​of each balancing valve total n; 2.2) Calculate the deviation matrix of each balancing valve opening: ； 2.3) Calculate the correlation coefficient matrix between each balancing valve: ； 2.4) Take the lower half of the correlation coefficient matrix A, that is: ； 2.5) Eliminate all valves whose row values ​​in the lower half of the correlation coefficient matrix A are not positive; 2.6) Calculate the overall opening value of the remaining m balancing valves at the end of the current strategy period after elimination: ； 2.7) Calculate the chilled water pump delivery frequency: ； Among them, y min and max are the upper and lower limits of the pump operating frequency, k is the steepness coefficient of the frequency conversion curve, z is the overall opening value of the balancing valve at the end of the current strategy period, and c is the center coefficient of the frequency conversion curve.

4. A method for load allocation of multiple chillers according to claim 2, characterized in that: In S4, the method for calculating the diversion opening of each level of diversion device is as follows: ； in Reg (j) is the diversion opening of the diversion device pointing to the outlet of the jth chiller at the end of the current strategy period, p (j) is the ratio of the load distribution value of the jth chiller at the end of the current strategy period to the total load demand at the current moment, that is: ； in w (j) is the load distribution value of the jth chiller at the end of the current strategy period, and Load is the predicted total cooling load of the current strategy period.

5. A method for load allocation of multiple chillers according to claim 2, characterized in that: If the overall load demand during the current strategy period Load If it is greater than the value of the previous strategy period, the operating frequency of the chilled water pump is adjusted first. f , then adjust the diversion opening of the diversion device Reg ; If the overall load demand during the current strategy period Load If it is less than the value of the previous strategy period, the diversion device opening is adjusted first. Reg , and then adjust the operating frequency of the chilled water pump f .

Images