阅读说明：本技术 一种多机头冷水机组和控制方法 (Multi-handpiece water chilling unit and control method ) 是由 陈见兴 于 2020-12-30 设计创作，主要内容包括：本发明公开了一种多机头冷水机组和控制方法,控制器被配置为：根据各运行压缩机的吸气压力和吸气温度确定各所述运行压缩机的吸气理论比焓和吸气密度；根据各所述运行压缩机的排气压力和排气温度确定各所述运行压缩机的排气理论比焓；根据各所述运行压缩机的功率、所述吸气理论比焓、所述排气理论比焓和所述吸气密度确定总吸气体积流量；根据所述总吸气体积流量和压比确定所述压缩机的目标运行数量,所述压比为所述冷凝器的冷凝压力与所述蒸发器的蒸发压力的比值,通过机组参数确定最佳负荷分配方案,提高了压缩机运行可靠性和效率。(The invention discloses a multi-handpiece water chilling unit and a control method, wherein a controller is configured to: determining the theoretical specific enthalpy and suction density of suction gas of each running compressor according to the suction pressure and suction temperature of each running compressor; determining the theoretical exhaust specific enthalpy of each operating compressor according to the exhaust pressure and the exhaust temperature of each operating compressor; determining a total suction volume flow from the power of each of the operating compressors, the theoretical specific enthalpy of suction, the theoretical specific enthalpy of discharge, and the suction density; and determining the target operation number of the compressor according to the total suction volume flow and the pressure ratio, wherein the pressure ratio is the ratio of the condensing pressure of the condenser to the evaporating pressure of the evaporator, and the optimal load distribution scheme is determined according to the unit parameters, so that the operation reliability and efficiency of the compressor are improved.)

1. A multi-head chiller comprising:

the compressors are used for compressing the low-temperature and low-pressure refrigerant gas into high-temperature and high-pressure refrigerant gas and discharging the high-temperature and high-pressure refrigerant gas to the condenser;

the condenser is used for condensing the high-temperature and high-pressure refrigerant gas, reducing the pressure of the refrigerant gas through the throttle valve and then discharging the refrigerant gas to the evaporator;

the evaporator is used for evaporating the low-temperature and low-pressure refrigerant to reduce the temperature of the chilled water and sending low-temperature and low-pressure refrigerant gas into the compressor;

characterized in that it further comprises a controller configured to:

determining the theoretical specific enthalpy and suction density of suction gas of each running compressor according to the suction pressure and suction temperature of each running compressor;

determining the theoretical exhaust specific enthalpy of each operating compressor according to the exhaust pressure and the exhaust temperature of each operating compressor;

determining a total suction volume flow from the power of each of the operating compressors, the theoretical specific enthalpy of suction, the theoretical specific enthalpy of discharge, and the suction density;

and determining the target operation number of the compressor according to the total suction volume flow and a pressure ratio, wherein the pressure ratio is the ratio of the condensing pressure of the condenser to the evaporating pressure of the evaporator.

2. The multi-head chiller of claim 1 wherein the control appliance is configured to:

determining the single compressor suction volume flow corresponding to each optional operation quantity according to the ratio of the total suction volume flow to each optional operation quantity;

determining compressor efficiencies corresponding to each of the selectable operating quantities based on the respective single compressor suction volume flows and the pressure ratios;

the target operation number is determined according to a highest efficiency among the respective compressor efficiencies and a current compressor efficiency at a current operation number.

3. The multi-headed chiller according to claim 2 wherein the controller is further specifically configured to:

if the difference value between the maximum efficiency and the current compressor efficiency is not smaller than a preset difference value, taking the selectable operation number under the maximum efficiency as the target operation number;

and if the difference is smaller than the preset difference, taking the current operation quantity as the target operation quantity.

4. The multi-head chiller of claim 1 wherein the control appliance is configured to:

determining the suction mass flow of each operating compressor according to the ratio of the power to the enthalpy difference value, wherein the enthalpy difference value is the difference between the exhaust theoretical specific enthalpy and the suction theoretical specific enthalpy;

determining a suction volume flow rate of each of the operating compressors according to a ratio of the suction mass flow rate to the suction density;

determining the total inspiratory volume flow from the sum of the inspiratory volume flows.

5. The multi-headed chiller according to claim 2 wherein the single compressor suction volume flow is a pre-set filtered single compressor suction volume flow and the pressure ratio is a pre-set filtered pressure ratio.

6. A control method of a multi-machine-head water chilling unit is applied to the multi-machine-head water chilling unit comprising a plurality of compressors, a condenser, an evaporator, a throttle valve and a controller, and is characterized by comprising the following steps:

determining the theoretical specific enthalpy and suction density of suction gas of each running compressor according to the suction pressure and suction temperature of each running compressor;

determining the theoretical exhaust specific enthalpy of each operating compressor according to the exhaust pressure and the exhaust temperature of each operating compressor;

determining a total suction volume flow from the power of each of the operating compressors, the theoretical specific enthalpy of suction, the theoretical specific enthalpy of discharge, and the suction density;

and determining the target operation number of the compressors according to the total suction volume flow and a pressure ratio, wherein the pressure ratio is the ratio of the condensing pressure of the condenser to the evaporating pressure of the evaporator.

7. Method according to claim 6, characterized in that a target operating number of said compressors is determined on the basis of said total suction volume flow and pressure ratio, in particular:

determining the single compressor suction volume flow corresponding to each optional operation quantity according to the ratio of the total suction volume flow to each optional operation quantity;

determining compressor efficiencies corresponding to each of the selectable operating quantities based on the respective single compressor suction volume flows and the pressure ratios;

the target operation number is determined according to a highest efficiency among the respective compressor efficiencies and a current compressor efficiency at a current operation number.

8. The method of claim 7, wherein the target operating quantity is determined based on a highest efficiency of the respective compressor efficiencies and a current compressor efficiency at the current operating quantity, by:

if the difference value between the maximum efficiency and the current compressor efficiency is not smaller than a preset difference value, taking the selectable operation number under the maximum efficiency as the target operation number;

and if the difference is smaller than the preset difference, taking the current operation quantity as the target operation quantity.

9. The method according to claim 6, characterized in that the total suction volume flow is determined from the power of each of said operating compressors, said suction theoretical specific enthalpy, said discharge theoretical specific enthalpy and said suction density, in particular:

determining the suction mass flow of each operating compressor according to the ratio of the power to the enthalpy difference value, wherein the enthalpy difference value is the difference between the exhaust theoretical specific enthalpy and the suction theoretical specific enthalpy;

determining a suction volume flow rate of each of the operating compressors according to a ratio of the suction mass flow rate to the suction density;

determining the total inspiratory volume flow from the sum of the inspiratory volume flows.

10. The method of claim 7, wherein said single compressor suction volume flow rate is a pre-set filtered single compressor suction volume flow rate and said pressure ratio is a pre-set filtered pressure ratio.

Technical Field

The application relates to the technical field of water chilling units, in particular to a multi-handpiece water chilling unit and a control method.

Background

The water chilling unit is a main energy consumption device of the air conditioning system of the public building, and the performance of the water chilling unit determines the energy efficiency of the air conditioning system to a great extent.

In the prior art, load control is performed with a target of chilled water (inlet water) and outlet water. And collecting the outlet water temperature of the chilled water in real time, comparing the obtained temperature value with the target water temperature, and loading and unloading the compressor. During loading, the existing running compressors are synchronously loaded until the compressors are loaded to the maximum load, if the water temperature cannot meet the requirement, the compressors are continuously put in and loaded to the same load as other compressors, and then the compressors are synchronously loaded until the water temperature meets the requirement. And during load shedding, synchronously shedding the existing running compressors until the compressors are shed to the minimum load, and if the water temperature cannot meet the requirement, continuously reducing the number of the compressors which are put into operation until the water temperature meets the requirement.

The scheme has a simple control mode, but the online running compressor is usually operated in an inefficient area (maximum or minimum load), the running efficiency is low, and the running cost is high; in addition, when the compressor is under the maximum or minimum load, the stability of the compressor is poor, so that the reliability of the unit is poor, and the service life of the unit is influenced. Taking a 4-machine-head magnetic suspension centrifugal water chilling unit as an example, fig. 1 shows the energy efficiency condition of the unit when the compressor is controlled to increase or decrease load by a traditional control mode: during loading, the unit often has a condition of adding the machine but not adding the machine, so that the online compressor runs in an inefficient large-load area, the running performance of the unit is poor, and the power consumption is high; when the load is reduced, the unit has the condition of reducing the machine without reducing the machine, so that the online compressor operates in an inefficient small load area, the unit has poor operation performance and high power consumption, and the surge is easy to occur.

Therefore, how to provide a multi-machine-head water chilling unit for improving the operation reliability and efficiency of a compressor is a technical problem to be solved at present.

Disclosure of Invention

The invention provides a multi-handpiece water chilling unit, which is used for solving the technical problems of poor reliability and low efficiency of a compressor of the multi-handpiece water chilling unit in the prior art.

This multimachine head cooling water set includes:

the compressors are used for compressing the low-temperature and low-pressure refrigerant gas into high-temperature and high-pressure refrigerant gas and discharging the high-temperature and high-pressure refrigerant gas to the condenser;

the condenser is used for condensing the high-temperature and high-pressure refrigerant gas, reducing the pressure of the refrigerant gas through the throttle valve and then discharging the refrigerant gas to the evaporator;

the evaporator is used for evaporating the low-temperature and low-pressure refrigerant to reduce the temperature of the chilled water and sending low-temperature and low-pressure refrigerant gas into the compressor;

further comprising a controller configured to:

determining the theoretical specific enthalpy and suction density of suction gas of each running compressor according to the suction pressure and suction temperature of each running compressor;

determining the theoretical exhaust specific enthalpy of each operating compressor according to the exhaust pressure and the exhaust temperature of each operating compressor;

determining a total suction volume flow from the power of each of the operating compressors, the theoretical specific enthalpy of suction, the theoretical specific enthalpy of discharge, and the suction density;

and determining the target operation number of the compressor according to the total suction volume flow and a pressure ratio, wherein the pressure ratio is the ratio of the condensing pressure of the condenser to the evaporating pressure of the evaporator.

In some embodiments of the present application, the control appliance is configured to:

determining the single compressor suction volume flow corresponding to each optional operation quantity according to the ratio of the total suction volume flow to each optional operation quantity;

determining compressor efficiencies corresponding to each of the selectable operating quantities based on the respective single compressor suction volume flows and the pressure ratios;

the target operation number is determined according to a highest efficiency among the respective compressor efficiencies and a current compressor efficiency at a current operation number.

In some embodiments of the present application, the controller is further specifically configured to:

if the difference value between the maximum efficiency and the current compressor efficiency is not smaller than a preset difference value, taking the selectable operation number under the maximum efficiency as the target operation number;

and if the difference is smaller than the preset difference, taking the current operation quantity as the target operation quantity.

In some embodiments of the present application, the control appliance is configured to:

determining the suction mass flow of each operating compressor according to the ratio of the power to the enthalpy difference value, wherein the enthalpy difference value is the difference between the exhaust theoretical specific enthalpy and the suction theoretical specific enthalpy;

determining a suction volume flow rate of each of the operating compressors according to a ratio of the suction mass flow rate to the suction density;

determining the total inspiratory volume flow from the sum of the inspiratory volume flows.

In some embodiments of the present application, the suction volume flow of the single compressor is a suction volume flow of the single compressor after a preset filtering process, and the pressure ratio is a pressure ratio after the preset filtering process.

Correspondingly, the invention also provides a control method of the multi-handpiece water chilling unit, which is applied to the multi-handpiece water chilling unit comprising a plurality of compressors, condensers, evaporators, throttle valves and controllers, and the method comprises the following steps:

determining the theoretical specific enthalpy and suction density of suction gas of each running compressor according to the suction pressure and suction temperature of each running compressor;

determining the theoretical exhaust specific enthalpy of each operating compressor according to the exhaust pressure and the exhaust temperature of each operating compressor;

determining a total suction volume flow from the power of each of the operating compressors, the theoretical specific enthalpy of suction, the theoretical specific enthalpy of discharge, and the suction density;

and determining the target operation number of the compressors according to the total suction volume flow and a pressure ratio, wherein the pressure ratio is the ratio of the condensing pressure of the condenser to the evaporating pressure of the evaporator.

In some embodiments of the present application, a target operating number of the compressor is determined based on the total suction volume flow and the pressure ratio, specifically:

determining the single compressor suction volume flow corresponding to each optional operation quantity according to the ratio of the total suction volume flow to each optional operation quantity;

determining compressor efficiencies corresponding to each of the selectable operating quantities based on the respective single compressor suction volume flows and the pressure ratios;

the target operation number is determined according to a highest efficiency among the respective compressor efficiencies and a current compressor efficiency at a current operation number.

In some embodiments of the present application, the determining the target operation number according to a highest efficiency of the compressor efficiencies and a current compressor efficiency under a current operation number specifically includes:

if the difference value between the maximum efficiency and the current compressor efficiency is not smaller than a preset difference value, taking the selectable operation number under the maximum efficiency as the target operation number;

and if the difference is smaller than the preset difference, taking the current operation quantity as the target operation quantity.

In some embodiments of the present application, a total suction volume flow is determined according to the power of each of the operating compressors, the suction theoretical specific enthalpy, the discharge theoretical specific enthalpy, and the suction density, and specifically is:

determining the suction mass flow of each operating compressor according to the ratio of the power to the enthalpy difference value, wherein the enthalpy difference value is the difference between the exhaust theoretical specific enthalpy and the suction theoretical specific enthalpy;

determining a suction volume flow rate of each of the operating compressors according to a ratio of the suction mass flow rate to the suction density;

determining the total inspiratory volume flow from the sum of the inspiratory volume flows.

In some embodiments of the present application, the suction volume flow of the single compressor is a suction volume flow of the single compressor after a preset filtering process, and the pressure ratio is a pressure ratio after the preset filtering process.

Compared with the prior art, the invention has the following beneficial effects:

the invention discloses a multi-handpiece water chilling unit and a control method, wherein a controller is configured to: determining the theoretical specific enthalpy and suction density of suction gas of each running compressor according to the suction pressure and suction temperature of each running compressor; determining the theoretical exhaust specific enthalpy of each operating compressor according to the exhaust pressure and the exhaust temperature of each operating compressor; determining a total suction volume flow from the power of each of the operating compressors, the theoretical specific enthalpy of suction, the theoretical specific enthalpy of discharge, and the suction density; and determining the target operation number of the compressor according to the total suction volume flow and the pressure ratio, wherein the pressure ratio is the ratio of the condensing pressure of the condenser to the evaporating pressure of the evaporator, and the optimal load distribution scheme is determined according to the unit parameters, so that the operation reliability and efficiency of the compressor are improved.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

FIG. 1 is a schematic diagram showing a comparison between a conventional control mode and an optimization control mode of a 4-handpiece magnetic suspension centrifugal chiller;

fig. 2 is a schematic structural diagram of a multi-head water chilling unit according to an embodiment of the present invention;

fig. 3 shows a refrigeration cycle pressure-enthalpy diagram of a multi-head water chiller according to an embodiment of the present invention;

fig. 4 is a schematic diagram illustrating the effect of the control method for a multi-head water chilling unit according to an embodiment of the present invention;

fig. 5 is a schematic flow chart illustrating a control method for a multi-head water chiller according to another embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

In the description of the present application, it is to be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience in describing the present application and simplifying the description, but do not indicate or imply that the referred device or element must have a particular orientation, be constructed in a particular orientation, and be operated, and thus should not be construed as limiting the present application.

The terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present application, "a plurality" means two or more unless otherwise specified.

In the description of the present application, it is to be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present application can be understood in a specific case by those of ordinary skill in the art.

Fig. 2 is a schematic structural diagram of a multi-head water chiller according to an embodiment of the present invention, and as shown in fig. 2, the multi-head water chiller may include a compressor 100, a condenser 200, an evaporator 300, and a throttle valve 400. The compressor 100, the condenser 200, the throttle valve 400, and the evaporator 300 are sequentially connected to form a refrigerant circulation circuit. It should be noted that, in the embodiment of the present invention, the sequential connection only illustrates a sequential relationship of connection between the respective devices, and other devices, such as a stop valve, may also be included between the respective devices.

During refrigeration, the compressor 100 compresses low-temperature and low-pressure refrigerant gas into high-temperature and high-pressure refrigerant gas, the high-temperature and high-pressure refrigerant gas is discharged to the condenser 200, the high-temperature and high-pressure refrigerant gas exchanges heat with cooling water in the condenser 200, the refrigerant releases heat, the released heat is brought into outdoor environment air by the cooling water, and the refrigerant is condensed into liquid or gas-liquid two-phase refrigerant through phase change. The refrigerant flows out of the condenser 200 and enters the throttle valve 400 to be cooled and decompressed into a low-temperature and low-pressure refrigerant. The low-temperature and low-pressure refrigerant enters the evaporator 300, and the refrigerant absorbs the heat of the chilled water in the evaporator 300, so that the temperature of the chilled water in the evaporator 300 is reduced, and the refrigeration effect is realized. The refrigerant is phase-changed and evaporated into a low-temperature and low-pressure refrigerant gas, and the refrigerant gas flows back into the compressor 100, thereby realizing the recycling of the refrigerant. The pressure-enthalpy diagram of the refrigeration cycle is shown in fig. 3. The evaporator 300 of the present embodiment is further connected to the user side, and the chilled water in the evaporator 300 enters the user side after the temperature of the chilled water is lowered, and the chilled water in the evaporator 300 can be replenished from the user side.

The compressors 100 may be magnetic suspension centrifugal compressors or screw compressors, the number of the compressors may be adjusted according to the operation conditions, an inlet of each compressor is provided with an air suction temperature sensor and an air suction pressure sensor, an outlet of each compressor is provided with an exhaust pressure sensor and an exhaust temperature sensor, the evaporator 300 is provided with an evaporation pressure sensor, the condenser 200 is provided with a condensation pressure sensor, and the throttle valve 400 may be an electronic expansion valve.

The controller of the multi-head water chilling unit is configured to:

determining the theoretical specific enthalpy and suction density of suction gas of each running compressor according to the suction pressure and suction temperature of each running compressor;

determining the theoretical exhaust specific enthalpy of each operating compressor according to the exhaust pressure and the exhaust temperature of each operating compressor;

determining a total suction volume flow from the power of each of the operating compressors, the theoretical specific enthalpy of suction, the theoretical specific enthalpy of discharge, and the suction density;

and determining the target operation number of the compressor according to the total suction volume flow and a pressure ratio, wherein the pressure ratio is the ratio of the condensing pressure of the condenser to the evaporating pressure of the evaporator.

In this embodiment, the suction pressure, the suction temperature, the discharge pressure, the discharge temperature, the condensing pressure of the condenser and the evaporating pressure of the evaporator of each operating compressor are collected, the theoretical specific enthalpy and the suction density of the suction of each operating compressor are determined according to the suction pressure and the suction temperature, the theoretical specific enthalpy and the discharge density of the discharge of each operating compressor are determined according to the discharge pressure and the discharge temperature, the total suction volume flow is determined according to the power, the theoretical specific enthalpy and the suction density of each operating compressor, and the target operating number of the compressors is determined according to the total suction volume flow and the pressure ratio, wherein the pressure ratio is the ratio of the condensing pressure of the condenser to the evaporating pressure of the evaporator.

In order to determine the exact theoretical specific enthalpy of inspiration, in a preferred embodiment of the present application, the theoretical specific enthalpy of inspiration may be determined according to the first formula, which is specifically:

h1＝(a1+a2*x+a3*x1^2+a4*x1^3+a5*y1+a6*y1^2)/(1+a7*x1+a8*x1^2+a9*x1^3+a10*y1)

wherein h1 is the theoretical enthalpy of inspiration, a1, a2, a3, a4, a5, a6, a7, a8, a9 and a10 are a first group of preset constants, x1 is the pressure of inspiration, and y1 is the temperature of inspiration.

In order to determine the exact inspiratory density, in a preferred embodiment of the present application, the inspiratory density may be determined according to equation two, which is specifically:

ρ＝(b1+b2*ln(x1)+b3*(ln(x1))^2+b4*(ln(x1))^3+b5*y1)/(1+b6*ln(x1)+b7*(ln(x1))^2+b8*y1+b9*y1^2+b10*y1^3)

wherein ρ is the gettering density, b1, b2, b3, b4, b5, b6, b7, b8, b9, b10 are a second set of preset constants, x1 is the gettering pressure, and y1 is the gettering temperature.

In order to determine the accurate exhaust gas theoretical specific enthalpy, in a preferred embodiment of the present application, the exhaust gas theoretical specific enthalpy may be determined according to formula three, which is specifically:

h2＝(a1+a2*x+a3*x2^2+a4*x2^3+a5*y2+a6*y2^2)/(1+a7*x2+a8*x2^2+a9*x2^3+a10*y2)

h2 is the theoretical exhaust specific enthalpy, a1, a2, a3, a4, a5, a6, a7, a8, a9 and a10 are the first set of preset constants, x2 is the exhaust pressure, and y2 is the exhaust temperature.

To determine an accurate target operational number, in some embodiments of the present application, the controller is configured to:

determining the single compressor suction volume flow corresponding to each optional operation quantity according to the ratio of the total suction volume flow to each optional operation quantity;

determining compressor efficiencies corresponding to each of the selectable operating quantities based on the respective single compressor suction volume flows and the pressure ratios;

the target operation number is determined according to a highest efficiency among the respective compressor efficiencies and a current compressor efficiency at a current operation number.

In this embodiment, the number of optional operations is determined according to the number of the compressors, for example, if there are 4 compressors, the number of optional operations is 1,2,3, and 4. The method comprises the steps of firstly determining the suction volume flow of the single compressors corresponding to each optional operation quantity according to the ratio of the total suction volume flow to each optional operation quantity, then determining the compressor efficiency corresponding to each optional operation quantity according to the suction volume flow and the pressure ratio of each single compressor, selecting the highest one of the compressor efficiencies corresponding to each optional operation quantity as the highest efficiency, and determining the target operation quantity according to the highest efficiency and the current compressor efficiency under the current operation quantity.

It should be noted that the above solution of the preferred embodiment is only one specific implementation proposed in the present application, and other ways of determining the target operation number of the compressors according to the total suction volume flow and the pressure ratio are all within the protection scope of the present application.

In order to determine the accurate compressor efficiency corresponding to each optional operation quantity, in a preferred embodiment of the present application, the compressor efficiency corresponding to each optional operation quantity is determined according to a formula four, where the formula four specifically is:

η＝(c1+c3*ln(λ)+c5*ln(q)+c7*(ln(λ))^2+c9*(ln(q))^2+c11*ln(λ)*ln(q))/(1+c2*ln(λ)+c4*ln(q)+c6*(ln(λ))^2+c8*(ln(q))^2+c10*ln(λ)*ln(q))

wherein η is the compressor efficiency, c1, c2, c3, c4, c5, c6, c7, c8, c9, c10 and c11 are third group of preset constants, λ is the pressure ratio, and q is the suction volume flow of the single compressor.

To determine an accurate target operating quantity, in some embodiments of the present application, the controller is further specifically configured to:

if the difference value between the maximum efficiency and the current compressor efficiency is not smaller than a preset difference value, taking the selectable operation number under the maximum efficiency as the target operation number;

and if the difference is smaller than the preset difference, taking the current operation quantity as the target operation quantity.

In this embodiment, a difference between the maximum efficiency and the current compressor efficiency is determined, and if the difference is not smaller than a preset difference, it is indicated that the current operation number needs to be changed, and the selectable operation number at the maximum efficiency is taken as the target operation number, and enters the cutter switching program for smooth transition.

And if the difference value is smaller than the preset difference value, taking the current operation number as the target operation number to avoid frequent cutting of the compressor without changing the current operation number.

The preset difference value can be flexibly set by a person skilled in the art according to actual conditions, and different preset difference values all belong to the protection scope of the application.

To determine an accurate total inspiratory volume flow, in some embodiments of the present application, the control means is configured to:

determining the suction mass flow of each operating compressor according to the ratio of the power to the enthalpy difference value, wherein the enthalpy difference value is the difference between the exhaust theoretical specific enthalpy and the suction theoretical specific enthalpy;

determining a suction volume flow rate of each of the operating compressors according to a ratio of the suction mass flow rate to the suction density;

determining the total inspiratory volume flow from the sum of the inspiratory volume flows.

In this embodiment, the suction mass flow of each operating compressor is determined according to the ratio of the power of the compressor to the enthalpy difference value, which is the difference between the exhaust theoretical specific enthalpy and the suction theoretical specific enthalpy, then the suction volume flow is determined according to the ratio of the suction mass flow to the suction density, and finally the total suction volume flow is determined according to the sum of the suction volume flows.

In order to improve the accuracy of the target operation quantity, in some embodiments of the present application, the suction volume flow of the single compressor is a suction volume flow of the single compressor after a preset filtering process, and the pressure ratio is a pressure ratio after the preset filtering process.

In the embodiment, invalid data may exist in the original single-compressor air suction volume flow and pressure ratio, and the accuracy of the single-compressor air suction volume flow and pressure ratio is improved by filtering the single-compressor air suction volume flow and pressure ratio, so that the accuracy of the target operation quantity is improved.

By applying the technical scheme, in the multi-machine-head water chilling unit comprising a plurality of compressors, condensers, evaporators, throttling valves and controllers, the controllers are configured as follows: determining the theoretical specific enthalpy and suction density of suction gas of each running compressor according to the suction pressure and suction temperature of each running compressor; determining the theoretical exhaust specific enthalpy of each operating compressor according to the exhaust pressure and the exhaust temperature of each operating compressor; determining a total suction volume flow from the power of each of the operating compressors, the theoretical specific enthalpy of suction, the theoretical specific enthalpy of discharge, and the suction density; and determining the target operation number of the compressor according to the total suction volume flow and the pressure ratio, wherein the pressure ratio is the ratio of the condensing pressure of the condenser to the evaporating pressure of the evaporator, and the optimal load distribution scheme is determined according to the unit parameters, so that the operation reliability and efficiency of the compressor are improved.

In order to further illustrate the technical idea of the present invention, the technical solution of the present invention will now be described with reference to specific application scenarios.

The embodiment of the invention provides a control method of a multi-handpiece water chilling unit, which is applied to the 4 handpiece water chilling units comprising 4 compressors, a condenser, an evaporator, a throttle valve and a controller, wherein the 4 compressors are all in an operating state, and the method comprises the following steps:

in the first step of the method,collecting suction pressure (P) of an operating compressor₁₁、P₁₂、P₁₃、P₁₄) Intake air temperature (T)₁₁、T₁₂、T₁₃、T₁₄) Exhaust pressure (P)₂₁、P₂₂、P₂₃、P₂₄) Exhaust temperature (T)₂₁、T₂₂、T₂₃、T₂₄) Evaporation pressure Pe, condenser pressure Pc.

Step two, calculating the suction theoretical specific enthalpy (h) of the running compressor in real time by the formula I₁₁、h₁₂、h₁₃、h₁₄Calculating the theoretical specific enthalpy (h) of exhaust gas of the running compressor in real time according to the formula III₂₁、h₂₂、h₂₃、h₂₄)。

Step three, calculating the suction density (rho) of the running compressor in real time according to the formula II₁₁、ρ₁₂、ρ₁₃、ρ₁₄) And calculating the system pressure ratio lambda, wherein lambda is Pc/Pe in real time.

Step four, respectively calculating the mass flow (q) of the refrigerant of the running compressor according to the collected power (W1, W2, W3 and W4) of the running compressor_m1、q_m2、q_m3、q_m4) Mass flow q of refrigerant_mW/(h2-h 1). Calculated q_mRho calculating the volume flow (q) of the refrigerant in the running compressor respectively_v1、q_v2、q_v3、q_v4) Volume flow rate q_v＝q_m/ρ, q_v1、q_v2、q_v3、q_v4Adding the obtained flow rates to obtain the total air suction volume flow q of the unit_{v total}。

Step five, calculating the suction volume flow (q ') of the compressor under the optional operation quantity'_v1、q’_v2、q’_v3、q’_v4)，q’_v＝q_{v total}/N＝(q_v1+q_v2+q_v3+q_v4) N, N is different optional operation numbers (1, 2,3 and 4 respectively).

Step six, finally obtaining the compressor suction volume flow q 'through measurement and calculation'_vAnd system pressure ratio λ, inspiratory volumetric flow q'_vSum system pressure ratio lambda is filteredAfter treatment, the efficiency eta of the compressor under different optional operation quantities is obtained according to a formula IV, and the efficiency of the compressor under each formula is compared to determine the highest efficiency.

Step seven, if the difference value between the highest efficiency and the current compressor efficiency is not less than the preset difference value, the selectable operation number under the highest efficiency is taken as the target operation number, and the target operation number enters a cutter cutting program for smooth transition;

and if the difference value is smaller than the preset difference value, maintaining the current operation quantity.

The energy-saving control effect of the control method of the multi-head water chilling unit in the embodiment is shown in fig. 4.

Corresponding to the multi-faucet water chilling unit in the embodiment of the present application, an embodiment of the present application further provides a control method for a multi-faucet water chilling unit, which is applied to a multi-faucet water chilling unit including a plurality of compressors, a condenser, an evaporator, a throttle valve, and a controller, and as shown in fig. 5, the method includes:

step S501, determining theoretical specific enthalpy and suction density of suction gas of each running compressor according to suction pressure and suction temperature of each running compressor;

step S502, determining the theoretical exhaust specific enthalpy of each operating compressor according to the exhaust pressure and the exhaust temperature of each operating compressor;

step S503, determining total suction volume flow according to the power of each running compressor, the suction theoretical specific enthalpy, the exhaust theoretical specific enthalpy and the suction density;

in order to determine an accurate total suction volume flow, in some embodiments of the present application, the total suction volume flow is determined from the power of each of the operating compressors, the theoretical specific suction enthalpy, the theoretical specific discharge enthalpy, and the suction density, in particular:

determining the suction mass flow of each operating compressor according to the ratio of the power to the enthalpy difference value, wherein the enthalpy difference value is the difference between the exhaust theoretical specific enthalpy and the suction theoretical specific enthalpy;

determining a suction volume flow rate of each of the operating compressors according to a ratio of the suction mass flow rate to the suction density;

determining the total inspiratory volume flow from the sum of the inspiratory volume flows.

Step S504, determining the target operation quantity of the compressor according to the total suction volume flow and a pressure ratio, wherein the pressure ratio is the ratio of the condensing pressure of the condenser to the evaporating pressure of the evaporator.

In order to determine an accurate target operating number, in some embodiments of the present application, a target operating number of the compressor is determined according to the total suction volume flow and the pressure ratio, specifically:

determining the single compressor suction volume flow corresponding to each optional operation quantity according to the ratio of the total suction volume flow to each optional operation quantity;

determining compressor efficiencies corresponding to each of the selectable operating quantities based on the respective single compressor suction volume flows and the pressure ratios;

the target operation number is determined according to a highest efficiency among the respective compressor efficiencies and a current compressor efficiency at a current operation number.

In order to determine an accurate target operation number, in some embodiments of the present application, the target operation number is determined according to a highest efficiency of the compressor efficiencies and a current compressor efficiency of the current operation number, specifically:

if the difference value between the maximum efficiency and the current compressor efficiency is not smaller than a preset difference value, taking the selectable operation number under the maximum efficiency as the target operation number;

and if the difference is smaller than the preset difference, taking the current operation quantity as the target operation quantity.

In order to improve the accuracy of the target operation quantity, in some embodiments of the present application, the suction volume flow of the single compressor is a suction volume flow of the single compressor after a preset filtering process, and the pressure ratio is a pressure ratio after the preset filtering process.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not necessarily depart from the spirit and scope of the corresponding technical solutions in the embodiments of the present application.