CN113446766B - Control method of water chilling unit - Google Patents
Control method of water chilling unit Download PDFInfo
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- CN113446766B CN113446766B CN202010218924.4A CN202010218924A CN113446766B CN 113446766 B CN113446766 B CN 113446766B CN 202010218924 A CN202010218924 A CN 202010218924A CN 113446766 B CN113446766 B CN 113446766B
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B49/00—Arrangement or mounting of control or safety devices
- F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
- F25B49/022—Compressor control arrangements
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
- F24F11/00—Control or safety arrangements
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B49/00—Arrangement or mounting of control or safety devices
- F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
- F25B2400/07—Details of compressors or related parts
- F25B2400/077—Compressor control units, e.g. terminal boxes, mounted on the compressor casing wall containing for example starter, protection switches or connector contacts
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2600/00—Control issues
- F25B2600/02—Compressor control
Abstract
The invention relates to a control method of a water chilling unit. The water chilling unit comprises a compressor unit with a plurality of machine heads, n is more than or equal to 2 under the condition that n machine heads in the plurality of machine heads are operated, and when the water chilling unit determines that load shedding is needed, the control method comprises the following steps: calculating the real-time load L of n operating machine headsnAnd calculating the maximum load L for running n-1 heads(n‑1)max(ii) a Comparing the real-time loads LnAnd a maximum load L(n‑1)max(ii) a If the maximum load L(n‑1)maxGreater than real time load LnCalculating a first energy efficiency ratio C of the water chilling unit when the n machine heads runnAnd a second energy efficiency ratio C of the water chilling unit when n-1 machine heads runn‑1(ii) a Comparing the first energy efficiency ratio C of the water chilling unitsnThe second energy efficiency ratio C of the water chilling unitn‑1(ii) a If the second energy efficiency ratio C of the water chilling unitn‑1Greater than the first energy efficiency ratio C of the water chilling unitnOne of the n handpieces is stopped. Under the condition that the water chilling unit needs to be unloaded, the number of the operation machine heads is reduced when the set conditions are met, and the high energy efficiency ratio COP of the water chilling unit can be kept under the condition of low load.
Description
Technical Field
The invention relates to a water chilling unit, in particular to a control method of the water chilling unit.
Background
Water chilling units generally include four main components: a compressor, a condenser, an expansion device, and an evaporator. With the development of technology and the diversity of load demands, prior art chiller units may include a plurality of compressor units (simply "heads") that can be operated independently of one another to meet large and varying cooling and/or heating load demands, the compressor units together comprising a compressor unit. Types of compressors include, but are not limited to, centrifugal compressors, scroll compressors, screw compressors, and the like. In particular, magnetic bearing technology has been applied to compressors (simply "magnetic levitation compressors") and, in turn, to chiller units. The chiller that uses the magnetic bearing technology is referred to as a magnetic levitation chiller for short. Magnetic levitation compressors typically use digital variable frequency control techniques so that they can operate at either full load or very low load (e.g., 20% part load). The magnetic suspension technology and the digital frequency conversion technology are combined for use, so that the magnetic suspension compressor has the outstanding advantages Of high efficiency and energy conservation, the energy efficiency ratio COP (coefficient Of performance) Of the water chilling unit can be greatly improved, and the purpose Of energy conservation is achieved. The energy efficiency ratio COP is the ratio of the refrigerating or heating capacity of the water chilling unit to the power.
For a chiller containing multiple compressors, when multiple compressors are operating simultaneously, the load on each compressor needs to be controlled. The prior art has developed a balanced load control technique, i.e., controlling multiple operating compressors to maintain the same load at all times. Controlling the load balance between the operating compressors can avoid large load deviation between the compressors, which can cause the compressors to excessively deviate from the optimal efficiency operating area. Therefore, the balanced load control logic can improve the safety of the compressor and the load balance of the water chilling unit. Further, such a balanced load control logic can ensure a high energy efficiency ratio COP of the chiller, e.g., at or near the highest energy efficiency ratio, under full load conditions.
Based on the balanced load control logic, for a multi-head compressor unit, the compressor can be stopped continuously only when the compressor reaches the minimum capacity and cannot be unloaded continuously, so that the load requirement of the whole machine is met. However, when the chiller operates at part or low load, the number of operating heads can significantly affect the energy efficiency ratio COP of the chiller. For example, fig. 1 shows exemplary COP curves for a magnetic levitation chiller having four heads for different number of heads. As shown in fig. 1, curves 1, 2, 3, and 4 represent COP curves for operating heads one (three other heads closed), two (two other heads closed), three (one other head closed), and four (inorganic head closed) in sequence. For example, running a head with refrigeration capacity less than 100RT (i.e., "cold ton") can achieve a high COP for the magnetically levitated chiller (curve 1). In the range of 100RT to 200RT, it is necessary to run two heads to achieve high COP for the magnetic levitation chiller (curve 2). In the range of 200RT to 300RT, three heads need to be operated to achieve high COP for the maglev chiller (curve 3). Above 300RT, four heads would need to be run to achieve a high COP for the chiller (e.g., curve 4). Therefore, under the condition of partial load of the water chilling unit, particularly low load, the water chilling unit is controlled only in a load balancing mode, so that the energy efficiency ratio COP of the water chilling unit deviates from the range of the highest energy efficiency ratio, and the energy saving of the water chilling unit is not facilitated.
Accordingly, there is a need in the art for a new solution to the above problems.
Disclosure of Invention
In order to solve the above problems in the prior art, that is, to solve the technical problem that the energy efficiency ratio of a water chilling unit deviates from the highest energy efficiency ratio under a low load, the present invention provides a control method of a water chilling unit, wherein the water chilling unit includes a compressor unit having a plurality of heads, n is greater than or equal to 2 under the condition that n heads of the plurality of heads are operated, and when the water chilling unit determines that load shedding is required, the control method includes: calculating the real-time load L of the n operating headsnAnd calculating the maximum load L for running n-1 heads(n-1)max(ii) a ComparisonThe real-time load LnAnd said maximum load L(n-1)max(ii) a If the maximum load L(n-1)maxGreater than the real-time load LnAnd calculating a first energy efficiency ratio C of the water chilling unit when the n machine heads runnAnd a second energy efficiency ratio C of the water chilling unit when the n-1 machine heads operaten-1(ii) a Comparing the first energy efficiency ratio C of the water chilling unitnThe second energy efficiency ratio C of the water chilling unitn-1(ii) a If the second energy efficiency ratio C of the water chilling unitn-1Is greater than the first energy efficiency ratio C of the water chilling unitnOne of the n handpieces is stopped.
In the preferable technical scheme of the control method of the water chilling unit, if the maximum load L is(n-1)maxLess than or equal to the real-time load LnThe control method controls the operation of the n handpieces in a load balancing manner.
In the preferable technical scheme of the control method of the water chilling unit, if the maximum load L is(n-1)maxLess than or equal to the real-time load LnThe control method controls the operation of the n handpieces in a load balancing manner.
In a preferred embodiment of the control method for a chiller, the control method calculates the real-time load L based on a real-time compression ratio Y of the chillernAnd the calculation formula used is as follows: l isn＝Kn＊Y+BnWherein, K isnAnd BnIs a polynomial coefficient and n is the number of operating handpieces.
In a preferred technical solution of the control method of the water chilling unit, the control method further calculates a maximum compression ratio Y when the n-1 machine heads are operatedmaxAnd based on the maximum compression ratio YmaxCalculating the maximum load L(n-1)max。
In a preferred embodiment of the control method for a water chiller described above, the control method calculates the maximum compression ratio Y based on the following formulamaxAnd said maximum load L(n-1)max：
Ymax＝Kmax＊n+BmaxWherein, K ismaxAnd BmaxIs a polynomial coefficient; and
L(n-1)max＝Kn-1＊Ymax+Bn-1wherein, K isn-1And Bn-1Is a polynomial coefficient and n-1 is the number of operating heads.
In a preferred embodiment of the control method for the water chilling unit, the control method is based on the real-time load LnCalculating a first energy efficiency ratio C of the water chilling unitnAnd the calculation formula used is as follows: cn＝Kn2＊Ln 2+Kn3＊Ln+Bn2Wherein, K isn2、Kn3、Bn2Is a polynomial coefficient and n is the number of operating handpieces.
In a preferred embodiment of the control method for the water chilling unit, the control method is based on the real-time load LnCalculating a second energy efficiency ratio C of the water chilling unitn-1And the calculation formula used is as follows: cn-1＝K(n-1)2＊Ln 2+K(n-1)3＊Ln+B(n-1)2Wherein, K is(n-1)2、K(n-1)3、B(n-1)2Is a polynomial coefficient and n-1 is the number of operating heads.
In a preferred technical scheme of the control method of the water chilling unit, the water chilling unit is a magnetic suspension water chilling unit.
In a preferred technical solution of the control method for a water chilling unit, before the load shedding, the control method controls the operation of the n heads in a load balancing manner.
It can be understood by those skilled in the art that in the technical solution of the control method of the water chilling unit of the present invention, in order to maintain the energy efficiency ratio of the water chilling unit under partial load (especially low load), when the water chilling unit determines that load shedding is required, the control method first calculates the real-time loads L of the n heads in operationnAnd calculating the maximum load L when n-1 heads are operated assuming that one head is stopped(n-1)max. The control method then comparesReal time loading LnAnd a maximum load L(n-1)max. If the maximum load L(n-1)maxGreater than real time load LnThe control method further calculates a first energy efficiency ratio C of the water chilling unit when the n machine heads runnAnd a second energy efficiency ratio C of the water chilling unit when n-1 machine heads runn-1And comparing the first energy efficiency ratio C of the water chilling unitnThe second energy efficiency ratio C of the water chilling unitn-1. If the second energy efficiency ratio C of the water chilling unitn-1Greater than the first energy efficiency ratio C of the water chilling unitnThe control method can stop one of the n handpieces, for example, the one that has the longest operation time. Under the condition that the load of the water chilling unit needs to be reduced, the number of the operating machine heads is actively reduced when the set conditions are met, the whole water chilling unit is favorably ensured to operate in the optimal energy-saving area, and therefore the energy efficiency ratio COP of the water chilling unit can be kept at the highest value or close to the highest value even under low load.
Preferably, the control method calculates the real-time load L based on the real-time compression ratio Y of the water chilling unitnAnd using the following calculation formula:
Ln＝Kn＊Y+Bn(formula 1)
Wherein, KnAnd BnThe number is a polynomial coefficient which can be determined according to the actual configuration of the water chilling unit, and n is the number of the operating heads. In the present invention, the load L is loaded in real timenAnd a polynomial function relation is established between the real-time compression ratio (abbreviated as 'pressure ratio') Y.
Preferably, the control method calculates the maximum compression ratio Y based on the following formulamaxAnd a maximum load L(n-1)max：
Ymax＝Kmax＊n+Bmax(formula 2)
L(n-1)max＝Kn-1＊Ymax+Bn-1(formula 3)
Wherein, Kmax、Bmax、Kn-1And Bn-1All are polynomial coefficients which can be determined according to the actual configuration of the water chilling unit, and n-1 is the number of operating machine heads. In the present invention, the compression is respectively at the maximumRatio YmaxBetween the number n of operating heads and at the maximum load L(n-1)maxWith maximum compression ratio YmaxA polynomial function relationship is established between the two.
Preferably, the control method calculates the first energy efficiency ratio C of the water chilling unit based on the following formulanAnd the second energy efficiency ratio C of the water chilling unitn-1：
Cn＝Kn2＊Ln 2+Kn3＊Ln+Bn2(formula 4)
Cn-1＝K(n-1)2＊Ln 2+K(n-1)3＊Ln+B(n-1)2(formula 5)
Wherein, Kn2、Kn3、Bn2、K(n-1)2、K(n-1)3、B(n-1)2The polynomial coefficient can be determined according to the actual configuration of the water chilling unit, and n-1 are the number of operating machine heads respectively. In the invention, the energy efficiency ratios C of the water chilling units are respectively set at the first energy efficiency ratio CnAnd real-time load LnThe second energy efficiency ratio C of the water chilling unitn-1And real-time load LnA polynomial function relationship is established between the two.
Preferably, before the load of the water chilling unit is reduced, the control method controls the operation of the multiple machine heads in a load balancing mode, so that the high energy efficiency ratio of the water chilling unit can be maintained at all times.
Drawings
Preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which:
FIG. 1 is an exemplary graph of load-energy efficiency ratio COP for chiller units having different numbers of operating heads;
FIG. 2 is a flow chart of a method of controlling a chiller according to the present invention;
FIG. 3 is a flow chart of a first embodiment of a method of controlling a chiller according to the present invention;
FIG. 4 is a flow chart of a second embodiment of a method of controlling a chiller according to the present invention;
FIG. 5 is a flow chart of a third embodiment of a control method for a chiller according to the present invention;
fig. 6 is a graph showing the technical effect of the control method of the water chiller according to the present invention.
Detailed Description
Preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only for explaining the technical principle of the present invention, and are not intended to limit the scope of the present invention.
In order to solve the technical problem that the existing control method of the water chilling unit cannot maintain the high energy efficiency ratio of the water chilling unit under the condition of partial load (particularly low load), the invention provides a control method of the water chilling unit, wherein the water chilling unit comprises a compressor unit with a plurality of machine heads. Under the condition that n heads in the multiple heads are operated, n is more than or equal to 2, and when the water chilling unit determines that load shedding is required, the control method comprises the following steps: calculating the real-time load L of n operating machine headsnAnd calculating the maximum load L for running n-1 heads(n-1)max(ii) a Comparing the real-time loads LnAnd a maximum load L(n-1)max(ii) a If the maximum load L(n-1)maxGreater than real time load LnCalculating a first energy efficiency ratio C of the water chilling unit when the n machine heads runnAnd a second energy efficiency ratio C of the water chilling unit when n-1 machine heads runn-1(ii) a Comparing the first energy efficiency ratio C of the water chilling unitsnThe second energy efficiency ratio C of the water chilling unitn-1(ii) a If the second energy efficiency ratio C of the water chilling unitn-1Greater than the first energy efficiency ratio C of the water chilling unitnOne of the n handpieces is stopped.
In one or more embodiments, the chiller referred to herein includes, but is not limited to, a magnetic levitation chiller. The magnetically levitated chiller may include a magnetically levitated centrifugal compressor, a magnetically levitated scroll compressor, or a magnetically levitated screw compressor having a plurality of heads. The plurality of handpieces may include two, three, four, five, or more handpieces. In one or more embodiments, multiple handpieces can be housed in the same housing, or placed in different housings.
Fig. 2 is a flow chart of a control method of the water chilling unit according to the present invention. As shown in FIG. 2, the control method includes the steps ofSteps S1, S2, S3, S4, and S5. The water chilling unit has n (n is more than or equal to 2) machine heads in an operating state. In one or more embodiments, the operating heads may be controlled in a load balancing manner. Then, when the chiller determines that load shedding is required (i.e., cooling or heating amount is reduced), the control method calculates the real-time loads L of the n heads in operation from step S1nAnd calculating the maximum load L assuming n-1 operating heads after one operating head decrease(n-1)max。
In one or more embodiments, the real-time load L for n handpieces of operationnThe percentage of the refrigerating or heating load of the water chilling unit when the n units run and the refrigerating capacity or heating capacity of the water chilling unit when the water chilling unit is fully loaded is referred to, and the percentage can be determined based on the real-time compression ratio Y of the water chilling unit. The compression ratio is the ratio of the discharge pressure to the suction pressure of the compressor. The invention establishes a real-time load LnThe polynomial function relationship with the real-time compression ratio Y, i.e. the above equation 1: l isn＝Kn＊Y+Bn. Wherein, KnAnd BnIs a polynomial coefficient that can be determined experimentally based on the actual configuration of the chiller and n is the number of operating heads. Alternatively, the real-time compression ratio Y may be an average of the compression ratios of a plurality of operating compressors.
In one or more embodiments, assume the maximum load L for n-1 operating heads after one operating head is stopped(n-1)maxMaximum compression ratio Y based on water chilling unitmaxAnd (4) determining. Alternatively, the maximum compression ratio YmaxRefers to the maximum compression ratio when n engines are running, and can be determined based on equation 2: y ismax＝Kmax＊n+BmaxWherein, K ismaxAnd BmaxIs a polynomial coefficient that can be determined experimentally based on the actual configuration of the chiller, and n is the number of operating heads. The invention establishes the maximum load L(n-1)maxWith maximum compression ratio YmaxThe polynomial functional relationship between them, i.e. formula 3: l is(n-1)max＝Kn-1＊Ymax+Bn-1Wherein, K isn-1And Bn-1Is a polynomial coefficient and can be based on a water chillerThe actual configuration of the stack is determined experimentally, with n-1 being the number of operating heads.
Calculating to obtain the real-time load LnAnd a maximum load L(n-1)maxThereafter, the control method of the present invention proceeds to step S2 to compare the real-time load LnAnd a maximum load L(n-1)max. If the real-time load LnNot less than the maximum load L(n-1)maxThe control method continues to maintain the current n operating heads and performs a balanced load control on the n operating heads. If the maximum load L(n-1)maxGreater than real time load LnThe control method proceeds to step S3.
In step S3, the control method calculates a first energy efficiency ratio C of the chiller when the n units are operatednAnd a second energy efficiency ratio C of the water chilling unit when n-1 machine heads operate after one operating machine head is supposed to stopn-1. In one or more embodiments, the chiller first energy efficiency ratio CnAnd the second energy efficiency ratio C of the water chilling unitn-1Are all based on the real-time load L mentioned abovenTo be determined. In one or more embodiments, in the case of n machine heads operating, the first energy efficiency ratio C of the chiller can be determined based on equation 4n：Cn＝Kn2＊Ln 2+Kn3＊Ln+Bn2(ii) a And under the condition that n-1 machine heads are operated, determining a second energy efficiency ratio C of the water chilling unit based on formula 5n-1：Cn-1＝K(n-1)2＊Ln 2+K(n-1)3＊Ln+B(n-1)2Wherein, K is(n-1)2、K(n-1)3、B(n-1)2Is a polynomial coefficient and n-1 is the number of operating heads. Aiming at the same water chilling unit, under the condition that the number of the operating machine heads is changed, the polynomial coefficients are correspondingly changed.
Determining a first energy efficiency ratio C of a water chilling unitnAnd the second energy efficiency ratio C of the water chilling unitn-1Thereafter, the control method of the present invention may proceed to step S4 to compare the chiller first energy efficiency ratio CnAnd the second energy efficiency ratio C of the water chilling unitn-1. If the chiller is first energy efficientRatio CnMore than or equal to the second energy efficiency ratio C of the water chilling unitn-1. The control method abandons the reduction of the number of the operated machine heads and continues to control the operation of the n machine heads in a load balancing mode. If the second energy efficiency ratio C of the water chilling unitn-1Greater than the first energy efficiency ratio C of the water chilling unitnThe control method proceeds to step S5 to select one of the n operating heads to be stopped, for example, the one having the longest operating time. The control method then ends. After one machine head is stopped, if no less than two machine heads are still in operation, the control system of the water chilling unit can continuously implement a load balancing strategy on the machine heads in operation. Further, after one machine head is stopped, if the water chilling unit still has the load shedding requirement, whether the water chilling unit needs to reduce the operation machine head or not can be continuously judged according to the control method. The active head reducing strategy is implemented on the basis of balanced load control, so that the water chilling unit can operate in the optimal energy-saving area, the highest or nearly highest energy efficiency ratio is realized, and the aim of saving energy is fulfilled.
Fig. 3 is a flowchart of a control method of a water chiller according to a first embodiment of the present invention. In this embodiment, the chiller may be a magnetic levitation chiller and its compressor has at least 4 heads. As shown in fig. 3, in step S11, it is determined that the chiller needs to be unloaded, for example, due to a change in ambient temperature. Then, the control method of the present invention determines in step S12 that the number of heads being operated is 4, and also determines the real-time compression ratio Y of the chiller, for example, the real-time compression ratio Y may be an average compression ratio of 4 heads. After the number of head operations and the real-time compression ratio Y are determined, the control method proceeds to step S13 to calculate the real-time load L for 4 head operations4＝K4＊Y+B4，K4And B4Determining based on the actual configuration of the water chilling unit; calculating the maximum compression ratio Y when 3 heads are operated assuming one head is stoppedmax＝Kmax＊4+BmaxAnd a maximum load L3max＝K3＊Ymax+B3Wherein, K ismax、Bmax、K3And B3Water chilling unit-based water chillerThe settings are configured, for example, by manual input. In step S14, L is compared3maxAnd L4. If L is4≥L3maxThe control method gives up subtracting the heads, continues to keep 4 heads running, and controls the operations of the 4 heads in a load balancing manner (step S15). If L is3max>L4The control method proceeds to step S16 to calculate a first energy efficiency ratio C of the chiller when 4 units are operated4＝K42＊L4 2+K43＊L4+B42，K42、K43、B42Based on the actual configuration settings of the chiller, such as by manual input; calculating a second energy efficiency ratio C of the water chilling unit when 3 machine heads run on the assumption that one machine head is stopped3＝K32＊L4 2+K33＊L4+B32，K32、K33、B32Based on the actual configuration settings of the chiller, for example, by manual input. Determining a first energy efficiency ratio C of a water chilling unit4And the second energy efficiency ratio C of the water chilling unit3Thereafter, the control method proceeds to step S17 to compare C4And C3. If C is present4≥C3The control method abandons the strategy of reducing the handpieces and proceeds to step S18 to continue to maintain the operation of the 4 handpieces and control the 4 handpieces in a load balancing manner. If C is present3>C4The control method proceeds to step S19 where one of the 4 operating handpieces, for example, the one having the longest operating time, is selected to be turned off. The control method then ends. After one head is stopped, the control system of the water chilling unit can continue to implement the load balancing strategy for the 3 heads which are running. After one machine head is stopped, if the water chilling unit still has the load shedding requirement, whether the water chilling unit needs to reduce the machine head or not can be continuously judged according to the control method.
Fig. 4 is a flowchart of a control method of a water chiller according to a second embodiment of the present invention. In this embodiment, the chiller may be a magnetic levitation chiller and its compressor has at least 3 heads. As shown in FIG. 4, in step S21, for example, due to ambient temperatureAnd changing to determine that the water chilling unit needs to be unloaded. Then, the control method of the present invention determines in step S22 that the number of heads being operated is 3, and also determines the real-time compression ratio Y of the chiller, which may be an average compression ratio of 3 heads, for example. After the number of head operations and the real-time compression ratio Y are determined, the control method proceeds to step S23 to calculate the real-time load L for 3 head operations3＝K3＊Y+B3，K3And B3Determining based on the actual configuration of the water chilling unit; calculating the maximum compression ratio Y when 2 heads are operated assuming one head is stoppedmax＝Kmax＊3+BmaxAnd a maximum load L2max＝K2＊Ymax+B2Wherein, K ismax、Bmax、K2And B2Based on the actual configuration settings of the chiller, for example, by manual input. In step S24, L is compared2maxAnd L3. If L is3≥L2maxThe control method gives up subtracting the heads, continues to keep 3 heads running, and controls the operations of the 3 heads in a load balancing manner (step S25). If L is2max>L3The control method proceeds to step S26 to calculate a first energy efficiency ratio C of the chiller when the 3 units are operated3＝K32＊L3 2+K33＊L3+B32，K32、K33、B32Based on the actual configuration settings of the chiller, such as by manual input; calculating a second energy efficiency ratio C of the water chilling unit when 2 machine heads run on the assumption that one machine head is stopped2＝K22＊L3 2+K23＊L3+B22，K22、K23、B22Based on the actual configuration settings of the chiller, for example, by manual input. Determining a first energy efficiency ratio C of a water chilling unit3And the second energy efficiency ratio C of the water chilling unit2Thereafter, the control method proceeds to step S27 to compare C3And C2. If C is present3≥C2The control method then abandons the strategy of reducing the handpieces, and proceeds to step S28 to continue to maintain the handpieces of 3The 3 heads are operated and controlled in a load balancing manner. If C is present2>C3The control method proceeds to step S29 where one of the 3 operating handpieces, for example, the one having the longest operating time, is selected to be turned off. The control method then ends. After one head is stopped, the control system of the water chilling unit can continue to implement the load balancing strategy for the 2 heads which are running. After one machine head is stopped, if the water chilling unit still has the load shedding requirement, whether the water chilling unit needs to reduce the machine head or not can be continuously judged according to the control method.
Fig. 5 is a flowchart of a control method of a water chiller according to a third embodiment of the present invention. In this embodiment, the chiller may be a magnetic levitation chiller and its compressor has at least 2 heads. As shown in fig. 5, in step S31, it is determined that the chiller needs to be unloaded, for example, due to a change in ambient temperature. Then, the control method of the present invention determines in step S32 that the number of heads being operated is 2, and also determines the real-time compression ratio Y of the chiller, for example, the real-time compression ratio Y may be an average compression ratio of 2 heads. After the number of head operations and the real-time compression ratio Y are determined, the control method proceeds to step S33 to calculate the real-time load L for 2 head operations2＝K2＊Y+B2，K2And B2Determining based on the actual configuration of the water chilling unit; calculating the maximum compression ratio Y when 1 machine head runs on the assumption that one machine head is stoppedmax＝Kmax＊2+BmaxAnd a maximum load L1max＝K1＊Ymax+B1Wherein, K ismax、Bmax、K1And B1Based on the actual configuration settings of the chiller, for example, by manual input. In step S34, L is compared1maxAnd L2. If L is2≥L1maxThe control method gives up subtracting the head, continues to keep 2 heads running, and controls the operations of the 2 heads in a load balancing manner (step S35). If L is1max>L2The control method proceeds to step S36 to calculate a first energy efficiency ratio C of the chiller when the 2 units are operated2＝K22＊L2 2+K23＊L2+B22，K22、K23、B22Based on the actual configuration settings of the chiller, such as by manual input; calculating the second energy efficiency ratio C of the water chilling unit when 1 machine head runs on the assumption that one machine head is stopped1＝K12＊L2 2+K13＊L2+B12，K12、K13、B12Based on the actual configuration settings of the chiller, for example, by manual input. Determining a first energy efficiency ratio C of a water chilling unit2And the second energy efficiency ratio C of the water chilling unit1Thereafter, the control method proceeds to step S27 to compare C2And C1. If C is present2≥C1The control method abandons the strategy of reducing the handpieces and proceeds to step S28 to continue to maintain the operation of 2 handpieces and control the 2 handpieces in a load balancing manner. If C is present1>C2The control method proceeds to step S39 where one of the 2 operating handpieces, for example, the one having the longest operating time, is selected to be turned off. The control method then ends.
Fig. 6 is a graph showing the technical effect of the control method of the water chiller according to the present invention. As shown in fig. 6, for example, for a magnetic suspension chiller having 4 heads, curve 1 with a dotted line represents a theoretically optimal energy efficiency ratio COP curve obtained by actively reducing the number of heads in operation under appropriate conditions using the control method of the present invention when the chiller needs to be unloaded, and the theoretical energy efficiency ratio COP is always maintained at the highest level in the range where the refrigeration capacity is greater than 50RT and less than 350 RT. Curve 2 represents the actual energy efficiency ratio COP curve obtained using the control method of the present invention to reduce the number of heads operating under the appropriate conditions when the chiller needs to be de-loaded, while curve 3 represents the actual energy efficiency ratio COP curve obtained using prior art balanced load control when the chiller needs to be de-loaded. As shown in fig. 6, curve 2 is closer to curve 1 than curve 3. This means that in the range that the refrigerating capacity is greater than 50RT and less than 300RT, when the water chilling unit is deloaded, compared with the prior art balanced load control method, the control method for actively implementing the head reduction strategy under the appropriate conditions can keep the energy efficiency ratio of the water chilling unit at the highest or close to the highest energy efficiency ratio under partial load (particularly low load), thereby enhancing the energy saving effect of the water chilling unit.
So far, the technical solutions of the present invention have been described in connection with the preferred embodiments shown in the drawings, but it is easily understood by those skilled in the art that the scope of the present invention is obviously not limited to these specific embodiments. Equivalent changes or substitutions of related technical features can be made by those skilled in the art without departing from the principle of the invention, and the technical scheme after the changes or substitutions can fall into the protection scope of the invention.
Claims (10)
1. A control method of a water chilling unit is characterized in that the water chilling unit comprises a compressor unit with a plurality of machine heads, n is larger than or equal to 2 under the condition that n machine heads in the plurality of machine heads are operated, and when the water chilling unit determines that load shedding is needed, the control method comprises the following steps:
calculating the real-time load L of the n operating headsnAnd calculating the maximum load L for running n-1 heads(n-1)max；
Comparing the real-time load LnAnd said maximum load L(n-1)max；
If the maximum load L(n-1)maxGreater than the real-time load LnAnd calculating a first energy efficiency ratio C of the water chilling unit when the n machine heads runnAnd a second energy efficiency ratio C of the water chilling unit when the n-1 machine heads operaten-1；
Comparing the first energy efficiency ratio C of the water chilling unitnThe second energy efficiency ratio C of the water chilling unitn-1；
If the second energy efficiency ratio C of the water chilling unitn-1Is greater than the first energy efficiency ratio C of the water chilling unitnOne of the n handpieces is stopped.
2. The control method for a chiller according to claim 1 wherein if said maximum load L is exceeded, L(n-1)maxLess than or equal to the real-time load LnThe control method controls the operation of the n handpieces in a load balancing manner.
3. The chiller control method of claim 1, wherein if the chiller second energy efficiency ratio C is greater than Cn-1Less than or equal to the first energy efficiency ratio C of the water chilling unitnThe control method controls the operation of the n handpieces in a load balancing manner.
4. The chiller control method according to claim 1, wherein the control method calculates the real-time load L based on a real-time compression ratio Y of the chillernAnd the calculation formula used is as follows: l isn＝Kn*Y+BnWherein, K isnAnd BnIs a polynomial coefficient.
5. The control method for a chiller according to claim 1, wherein said control method further calculates a maximum compression ratio Y when said n-1 units are operatedmaxAnd based on the maximum compression ratio YmaxCalculating the maximum load L(n-1)max。
6. The control method of a water chilling unit according to claim 5, characterized in that the control method calculates the maximum compression ratio Y based on the following formula respectivelymaxAnd said maximum load L(n-1)max：
Ymax＝Kmax*n+BmaxWherein, K ismaxAnd BmaxIs a polynomial coefficient; and
L(n-1)max＝Kn-1*Ymax+Bn-1wherein, K isn-1And Bn-1Is a polynomial coefficient.
7. The chiller control method of claim 1, wherein the control method is based on the water chillerReal time load LnCalculating a first energy efficiency ratio C of the water chilling unitnAnd the calculation formula used is as follows: cn＝Kn2*Ln 2+Kn3*Ln+Bn2Wherein, K isn2、Kn3、Bn2Is a polynomial coefficient.
8. The chiller control method of claim 1, wherein the control method is based on the real-time load LnCalculating a second energy efficiency ratio C of the water chilling unitn-1And the calculation formula used is as follows: cn-1＝K(n-1)2*Ln 2+K(n-1)3*Ln+B(n-1)2Wherein, K is(n-1)2、K(n-1)3、B(n-1)2Is a polynomial coefficient.
9. The control method of the water chilling unit according to claim 1, wherein the water chilling unit is a magnetic levitation water chilling unit.
10. The control method for a chiller according to claim 1 wherein said control method controls the operation of said n heads in a load balancing manner prior to said load shedding.
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