Frequency control method of heat recovery system and heat recovery system

Abstract

The invention discloses a frequency control method of a heat recovery system and the heat recovery system. The heat recovery system comprises a compressor, two water heat exchangers and an outdoor heat exchanger driven by a fan to exchange heat. The frequency control method comprises the steps that the working state of the heat recovery system is obtained; when the compressor is connected with the outdoor heat exchanger and any water heat exchanger to form a refrigerant circulation loop, the frequency of the compressor and the frequency of the fan are cooperatively adjusted according to the heat load requirement; and / or when the compressor is connected with the outdoor heat exchanger and the two water heat exchangers to form a refrigerant circulation loop, the frequency of the fan and the frequency of the compressor are sequentially adjusted according to the heat recovery efficiency. The frequency change strategies of the compressor and the fan are intelligently distributed according to the working state of the heat recovery system, the adaptability of the heat recovery system is improved, and efficient operation of the heat recovery system is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of heat recovery systems, and in particular to a frequency control method for a heat recovery system and a heat recovery system. Background Art

[0002] With the rapid development of heat recovery technology, improving energy utilization efficiency by recovering waste heat in industrial processes or HVAC systems has become an important topic. In the prior art, there are significant limitations in the frequency control strategies of compressors and fans: traditional methods generally adopt fixed frequency settings or simple segmented control, which can neither achieve precise adjustment according to dynamic load changes nor have the ability to perform closed-loop optimization of heat recovery efficiency (η). Due to the lack of a real-time efficiency feedback mechanism, the actual heat transfer efficiency of the heat exchanger and the waste heat recovery potential have been mismatched for a long time, resulting in a large fluctuation range of heat recovery efficiency. This lack of refined control and efficiency optimization causes the system to deviate from the optimal operating point for a long time, resulting in large energy losses and difficulty in adapting to complex working conditions such as fluctuations in waste heat source temperature and fouling of the heat exchanger surface area.

[0003] More notably, the current technology lacks a deep coordination mechanism between compressors and fans: fans often only perform proportional speed regulation as auxiliary equipment of compressors, and no dynamic coupling relationship has been established between the two at the energy transfer level. This decoupled control causes a series of chain problems - when the air supply volume of the fan is insufficient under high load conditions, the exhaust pressure of the compressor quickly exceeds the limit and triggers protection shutdown, resulting in a significant increase in equipment failure rate; during partial load operation, the ineffective power consumption caused by redundant air volume reduces the overall energy efficiency ratio (COP) of the system below the theoretical value. Particularly seriously, when encountering sudden changes in waste heat sources (such as the start and stop of industrial equipment), the traditional PID control has a long response delay time, the system temperature fluctuates greatly, and it is extremely easy to induce the risk of compressor surge, which not only affects the user experience but also exacerbates mechanical wear and shortens the equipment life.

[0004] Therefore, how to design a frequency control method that is applicable to heat recovery systems and is more energy-efficient is a technical problem that the industry urgently needs to solve. Summary of the Invention

[0005] In order to solve the defects of poor adaptability and high system energy consumption of the existing frequency control scheme, the present invention proposes a frequency control method for a heat recovery system and a heat recovery system, which intelligently distributes the frequency change strategies of compressors and fans according to the working state of the heat recovery system, improves the adaptability of the heat recovery system, and realizes the efficient operation of the heat recovery system.

[0006] The technical solution adopted by the present invention is to design a frequency control method for a heat recovery system. The heat recovery system includes a compressor, two water heat exchangers, and an outdoor heat exchanger driven by a fan for heat exchange. The frequency control method includes:

[0007] Obtain the working state of the heat recovery system;

[0008] When the compressor is connected to the outdoor heat exchanger and any one of the water heat exchangers to form a refrigerant cycle loop, the frequency of the compressor and the frequency of the fan are coordinately adjusted according to the heat load demand;

[0009] And / or when the compressor is connected to the outdoor heat exchanger and two water heat exchangers to form a refrigerant cycle loop, the frequency of the fan and the frequency of the compressor are adjusted successively according to the heat recovery efficiency.

[0010] Further, coordinately adjusting the frequency of the compressor and the frequency of the fan according to the heat load demand includes:

[0011] Obtain the actual load parameters of the heat recovery system and calculate the current heat load demand L;

[0012] In the optimization stage, determine the target optimization frequency according to the current heat load demand L, the performance parameters of the compressor and the performance parameters of the fan, and adjust the compressor and the fan;

[0013] In the fine-tuning stage, perform dynamic ramp adjustment on the frequency of the compressor and the frequency of the fan according to the interval where the current heat load demand L is located.

[0014] Further, determining the target optimization frequency according to the current heat load demand L, the performance parameters of the compressor and the performance parameters of the fan includes: the first optimization strategy and / or the second optimization strategy;

[0015] The first optimization strategy includes: fitting based on a pre-established compressor performance curve database to determine the optimal operating frequency f of the compressor corresponding to the current heat load demand L compressor_opt , fitting based on a pre-established fan performance curve database to determine the optimal operating frequency f of the fan corresponding to the current heat load demand L fan_opt ;

[0016] The second optimization strategy includes: searching for the optimal frequency f of the compressor compressor_opt and the optimal frequency f of the fan fan_opt .

[0017] Further, in the optimization stage, after determining the target optimization frequency according to the current heat load demand L, the performance parameters of the compressor and the performance parameters of the fan and adjusting the compressor and the fan, detect the current operating parameters of the compressor, calculate the deviation e between the current operating parameters and the target parameters, and use the PID control algorithm to adjust the frequency of the compressor.

[0018] Further, performing dynamic ramp adjustment on the frequency of the compressor and the frequency of the fan according to the interval where the current heat load demand L is located includes:

[0019] When L < L Low At this time, according to ffan = f fan_base - kf×(L base - L) to reduce the frequency of the fan, according to f compressor = f compressor_base - kc×(L base - L) to reduce the frequency of the compressor;

[0020] When L Low ≤ L ≤ L high If L < L base , then according to f fan = f fan_base - kf×(L base - L) to reduce the frequency of the fan, according to f compressor = f compressor_base - kc×(L base - L) to reduce the frequency of the compressor, if L > L base , then according to f compressor = f compressor_base + kc×(L - L base ) to increase the frequency of the compressor, according to f fan = f fan_base + kf×(L - L base ) to increase the frequency of the fan;

[0021] When L > L high , according to f compressor = f compressor_base + kc×(L - L base ) to increase the frequency of the compressor, according to f fan = f fan_base + kf×(L - L base ) to increase the frequency of the fan;

[0022] Among them, perform dynamic ramp adjustment on the compressor and the fan until reaching f compressor and f fan , f compressor is the target compressor frequency, f compressor_base is the compressor reference frequency, kc is the compressor frequency adjustment coefficient, f fan is the target fan frequency, f fan_base is the fan reference frequency, kf is the fan frequency adjustment coefficient, L base is the reference load demand.

[0023] Furthermore, in the fine-tuning stage, during the process of performing dynamic ramp adjustment on the frequency of the compressor and the frequency of the fan, the difference between the frequency of the compressor and the frequency of the fan is maintained within a set range.

[0024] Furthermore, adjusting the frequency of the fan and the frequency of the compressor according to the heat recovery efficiency includes:

[0025] Obtain the current heat recovery efficiency η of the heat recovery system;

[0026] In the fan adjustment stage, according to the current heat recovery efficiency η and the target heat recovery efficiency η target Determine the target air volume Q target And adjust the fan;

[0027] In the compressor adjustment stage, re-obtain the current heat recovery efficiency η, and determine the target heat recovery compressor frequency f according to the heat recovery efficiency deviation compressor_target And adjust the compressor.

[0028] Furthermore, according to the current heat recovery efficiency η and the target heat recovery efficiency η target Determine the target air volume Q target And adjusting the fan includes:

[0029] According to the current heat recovery efficiency η and the target heat recovery efficiency η target Determine the target air volume Q target ;

[0030] Calculate the target heat recovery fan frequency f fan = f base_target + kf × (Q target - Q current ) ;

[0031] Perform dynamic ramp adjustment on the fan until the target heat recovery fan frequency f is reached fan ;

[0032] wherein, f base_target is the reference fan frequency corresponding to the target air volume Q target , Q current is the current air volume, and kf is the fan frequency adjustment coefficient.

[0033] Furthermore, determine the target heat recovery compressor frequency f according to the heat recovery efficiency deviation compressor_target And adjusting the compressor includes:

[0034] Calculate the target heat recovery compressor frequency f compressor_target = f compressor_current + kc × (η target - η) ;

[0035] Perform dynamic ramp adjustment on the compressor until the target heat recovery compressor frequency f is reached compressor_target ;

[0036] wherein, f compressor_current is the current compressor frequency, and kc is the compressor frequency adjustment coefficient.

[0037] Further, the frequency control method further includes:

[0038] After coordinately adjusting the frequency of the compressor and the frequency of the fan according to the heat load demand, or after sequentially adjusting the frequency of the fan and the frequency of the compressor according to the heat recovery efficiency, detect the current frequency f of the compressor compressor ;

[0039] If the current frequency f compressor is lower than the set threshold f 喘振阈值 , increase the frequency of the fan.

[0040] Further, the frequency control method further includes:

[0041] After coordinately adjusting the frequency of the compressor and the frequency of the fan according to the heat load demand, or after sequentially adjusting the frequency of the fan and the frequency of the compressor according to the heat recovery efficiency, detect the discharge temperature T of the compressor exhaust and / or the suction pressure P inlet ;

[0042] If the discharge temperature T exhaust exceeds the set maximum value T max , reduce the frequency of the compressor;

[0043] If the suction pressure P inlet is lower than the set minimum value P min , reduce the frequency of the fan.

[0044] The present invention also provides a heat recovery system, including: a compressor, two water heat exchangers, and an outdoor heat exchanger driven by a fan for heat exchange, and the heat recovery system adopts the above frequency control method.

[0045] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0046] 1. In the conventional mode with an outdoor heat exchanger involved, by detecting the change of the system load in real time and coordinately adjusting the frequencies of the compressor and the fan, it can adapt to different working conditions and user usage requirements, and achieve the efficient operation of the heat recovery system;

[0047] 2. In the heat recovery mode with an outdoor heat exchanger involved, by detecting the change of the system heat recovery efficiency in real time, first adjusting the frequency of the fan and then adjusting the frequency of the compressor, it can improve the heat recovery efficiency and reduce the system energy consumption;

[0048] 3. Through the frequency coordination logic and dynamic ramp function, etc., it realizes the optimized adjustment of the frequencies of the compressor and the fan, avoids the occurrence of frequency mutation, and improves the stability and energy efficiency of the system;

[0049] 4. By combining multiple algorithms such as PID control and fuzzy control, it improves the accuracy of the frequency control method. Brief Description of the Drawings

[0050] The present invention will be described in detail below in conjunction with embodiments and the drawings, where:

[0051] Figure 1 is a schematic diagram of the system connection of the present invention;

[0052] Figure 2 is a flowchart of the frequency control in the conventional mode with the participation of an outdoor heat exchanger according to the present invention;

[0053] Figure 3 is a flowchart of the frequency control in the heat recovery mode with the participation of an outdoor heat exchanger according to the present invention;

[0054] Figure 4 is a schematic diagram of the refrigerant flow direction in the hot water mode of the present invention;

[0055] Figure 5 is a schematic diagram of the refrigerant flow direction in the cooling mode of the present invention;

[0056] Figure 6 is a schematic diagram of the refrigerant flow direction in the heating mode of the present invention;

[0057] Figure 7 is a schematic diagram of the refrigerant flow direction in the cooling and heating water mode of the present invention;

[0058] Brief Description of the Drawings: 1. Compressor; 2. First water heat exchanger; 3. Second water heat exchanger; 4. Outdoor heat exchanger; 5. Liquid storage tank; 6. Control valve; 7. First check valve; 8. Second check valve; 9. Third check valve; 10. First throttle valve; 11. Second throttle valve; 12. Throttling element; 13. First four-way valve; 14. Second four-way valve. Detailed Embodiments

[0059] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention will be further described in detail below in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0060] As Figure 1As shown in the figure, the frequency control method proposed by the present invention is applicable to a heat recovery system. The heat recovery system includes a compressor 1, two water heat exchangers, and an outdoor heat exchanger 4 driven by a fan for heat exchange. These two water heat exchangers are generally an air-conditioning water heat exchanger and a hot water heat exchanger. In the normal mode, the compressor 1 is connected to any two heat exchangers (usually including the outdoor heat exchanger 4) to form a refrigerant circulation loop; in the heat recovery mode, when the heat load demand increases significantly (such as a large amount of hot water usage and high temperature requirements), causing the evaporation capacity of the air-conditioning water heat exchanger to be insufficient to support the heating demand of the hot water heat exchanger, the compressor 1 will be connected to all three heat exchangers to form a refrigerant loop. At this time, the outdoor heat exchanger 4 cooperates with the air-conditioning water heat exchanger to jointly bear the heating load of the hot water heat exchanger.

[0061] Based on this, the frequency control method proposed by the present invention intelligently distributes the frequency change strategies of the compressor and the fan according to the working state of the heat recovery system, improves the adaptability of the heat recovery system, and realizes the efficient operation of the heat recovery system.

[0062] Specifically, the frequency control method includes:

[0063] Obtain the working state of the heat recovery system;

[0064] When the compressor is connected to the outdoor heat exchanger and any one of the water heat exchangers to form a refrigerant circulation loop, adjust the frequency of the compressor and the frequency of the fan in coordination according to the heat load demand;

[0065] And / or when the compressor is connected to the outdoor heat exchanger and the two water heat exchangers to form a refrigerant circulation loop, adjust the frequency of the fan and the frequency of the compressor successively according to the heat recovery efficiency.

[0066] This design, in the normal mode with the participation of the outdoor heat exchanger, by detecting the change of the system load in real time and coordinating the adjustment of the frequency of the compressor and the fan, can quickly adapt to different working conditions and user usage requirements, and realize the efficient operation of the heat recovery system; in the heat recovery mode with the participation of the outdoor heat exchanger, by detecting the change of the system heat recovery efficiency in real time, adjusting the fan frequency first and then the compressor frequency can significantly improve the heat recovery efficiency and reduce the system energy consumption.

[0067] Such as Figure 2 As shown in the figure, in some embodiments of the present invention, adjusting the frequency of the compressor and the frequency of the fan in coordination according to the heat load demand includes:

[0068] Obtain the actual load parameters of the heat recovery system and calculate the current heat load demand L;

[0069] In the optimization stage, determine the target optimization frequency according to the current heat load demand L, the performance parameters of the compressor, and the performance parameters of the fan, and adjust the compressor and the fan;

[0070] In the fine-tuning stage, dynamic ramp adjustment is performed on the frequency of the compressor and the frequency of the fan according to the interval where the current heat load demand L is located.

[0071] In the optimization stage, this design greatly adjusts the frequencies of the compressor and the fan, so that the operating frequencies of the two quickly approach the state that meets the current heat load demand. In the fine-tuning stage, the frequencies of the compressor and the fan are fine-tuned according to different working conditions, so that the operating frequencies of the two accurately match the current heat load demand, enabling the heat recovery system to operate efficiently.

[0072] There are various calculation methods for the heat load demand L, which are illustrated below.

[0073] The first method is the temperature difference method

[0074] Calculation formula:

[0075]

[0076] Where:

[0077] : Heat load demand;

[0078] : Specific heat capacity of air or refrigerant;

[0079] : Mass flow rate of air or refrigerant;

[0080] : Temperature difference between the air inlet and the air outlet.

[0081] Application scenario: Applicable to systems where the heat load demand is directly reflected by temperature changes.

[0082] The second method is the pressure difference method

[0083] Calculation formula:

[0084]

[0085] Where:

[0086] : Constant related to system characteristics;

[0087] : Pressure difference between the compressor suction and discharge;

[0088] : Flow rate of the compressor.

[0089] Application scenario: Applicable to systems where the heat load demand is reflected by pressure changes.

[0090] The third method is the comprehensive method

[0091] Calculation formula:

[0092]

[0093] Wherein:

[0094] , , : weighting coefficient;

[0095] : heat load demand based on temperature;

[0096] : heat load demand based on pressure;

[0097] : heat load demand based on flow rate.

[0098] Application scenario: applicable to systems that comprehensively consider changes in temperature, pressure, and flow rate.

[0099] In actual applications, the corresponding calculation method can be selected according to the specific type of the heat recovery system, and the present invention does not impose special restrictions on the calculation method of the heat load demand.

[0100] In some embodiments of the present invention, determining the target optimization frequency according to the current heat load demand L, the performance parameters of the compressor, and the performance parameters of the fan includes: a first optimization strategy (operating point optimization) and / or a second optimization strategy (multi-objective optimization). That is, the first optimization strategy or the second optimization strategy can be selected to determine the target optimization frequency, and only one optimization adjustment is made to the compressor and the fan during the optimization stage. It is also possible to select the first optimization strategy to determine the initial target optimization frequency, and then use the second optimization strategy to determine the secondary target optimization frequency, and two optimization adjustments are successively made to the compressor and the fan during the optimization stage. The advantage of this design is to quickly respond to the current heat load demand using the first optimization strategy and accurately optimize and improve energy efficiency using the second optimization strategy.

[0101] Specifically, the first optimization strategy includes: fitting based on a pre-established compressor performance curve database to determine the best operating frequency f of the compressor corresponding to the current heat load demand L compressor_opt , fitting based on a pre-established fan performance curve database to determine the best operating frequency f of the fan corresponding to the current heat load demand L fan_opt .

[0102] The first optimization strategy for the compressor and the fan has the same logic. Taking the compressor as an example, the compressor performance curve database usually includes the relationships between the exhaust temperature, suction pressure, flow rate and frequency of the compressor. The performance parameters of the compressor at different frequencies are obtained from the pre-stored compressor performance curve database, and curve fitting (such as polynomial fitting or spline interpolation) is used to determine the optimal operating frequency f of the compressor under different heat demand loads. compressor_opt 。

[0103] The second optimization strategy includes: finding the optimal frequency f of the compressor according to the pre-established multi-objective optimization model and constraint conditions compressor_opt and the optimal frequency f of the fan fan_opt 。

[0104] The optimization objectives of the second optimization strategy are system energy consumption, system stability and equipment life. Genetic algorithm or particle swarm optimization algorithm can be used to find the optimal frequency adjustment scheme and define the fitness function, taking into account energy consumption, stability and equipment life as follows:

[0105]

[0106] Among them:

[0107] E: System energy consumption;

[0108] S: System stability index (such as frequency change rate);

[0109] T: Equipment life index (such as start-stop times or running time);

[0110] : Weight coefficient, adjusted according to actual needs.

[0111] Constraint conditions: The frequency range is the maximum and minimum allowable values of the compressor frequency and the maximum and minimum allowable values of the fan frequency.

[0112] Repeat the iteration until the termination condition is met (such as reaching the maximum number of iterations or the fitness value converges), and output the optimal frequency f of the compressor compressor_opt and the optimal frequency f of the fan fan_opt 。

[0113] In order to improve the accuracy and stability of frequency regulation, during the optimization stage, after determining the target optimization frequency according to the current heat load demand L, the performance parameters of the compressor and the performance parameters of the fan and adjusting the compressor and the fan, the current operating parameters of the compressor are detected, the deviation e between the current operating parameters and the target parameters is calculated, and the PID control algorithm is used to adjust the frequency of the compressor.

[0114] Specifically, the calculation process of the PID control algorithm is as follows:

[0115] Detect the exhaust temperature T of the compressor exhaust and the suction pressure P inlet ;

[0116] Calculate the deviation between the current parameters and the target parameters :

[0117]

[0118] PID control formula:

[0119] Calculate the frequency adjustment amount :

[0120]

[0121] Where:

[0122] : Deviations of parameters such as temperature and pressure;

[0123] 、 、 : Proportional, integral, and differential coefficients.

[0124] Frequency adjustment:

[0125] Adjust the frequency of the compressor according to Δf:

[0126]

[0127] In some embodiments of the present invention, performing dynamic ramp adjustment on the frequency of the compressor and the frequency of the fan according to the interval where the current heat load demand L is located includes:

[0128] When L < L Low , reduce the frequency of the fan according to f fan = f fan_base - kf × (L base - L), and reduce the frequency of the compressor according to f compressor = f compressor_base - kc × (L base - L);

[0129] When L Low ≤ L ≤ L high , if L < L base , then reduce the frequency of the fan according to f fan = f fan_base - kf × (L base - L), and reduce the frequency of the compressor according to f compressor = f compressor_base - kc × (L base - L), if L > L base, then adjust the frequency of the compressor according to f compressor = f compressor_base + kc×(L - L base ) to increase the frequency of the compressor, and adjust the frequency of the fan according to f fan = f fan_base + kf×(L - L base );

[0130] When L > L high , adjust the frequency of the compressor according to f compressor = f compressor_base + kc×(L - L base ) to increase the frequency of the compressor, and adjust the frequency of the fan according to f fan = f fan_base + kf×(L - L base );

[0131] Among them, perform dynamic ramp adjustment on the compressor and the fan until reaching f compressor and f fan . Use a time - continuous function to gradually adjust the frequency. f compressor is the target compressor frequency, f compressor_base is the compressor reference frequency, kc is the compressor frequency adjustment coefficient, f fan is the target fan frequency, f fan_base is the fan reference frequency, kf is the fan frequency adjustment coefficient, and L base is the reference load demand.

[0132] This design will be designed according to high and low load partitions, adjust the frequencies of the compressor and the fan according to different working conditions, realize the coordinated optimization of the frequencies of the compressor and the fan, and improve the stability and energy efficiency of the heat recovery system.

[0133] It should be noted that during the fine - tuning stage, when performing dynamic ramp adjustment on the frequency of the compressor and the frequency of the fan, the preferred solution is to keep the difference between the frequency of the compressor and the frequency of the fan within a set range. The set range can be determined according to actual needs, such as 5Hz. This design can improve the coordination of the frequencies of the compressor and the fan and ensure the stability of the heat recovery system.

[0134] As Figure 3 shown, in some embodiments of the present invention, adjusting the frequency of the fan and the frequency of the compressor according to the heat recovery efficiency successively includes:

[0135] Obtain the current heat recovery efficiency η of the heat recovery system;

[0136] During the fan adjustment stage, determine the target air volume Q target according to the current heat recovery efficiency η and the target heat recovery efficiency η target and adjust the fan;

[0137] During the compressor adjustment stage, the current heat recovery efficiency η is reacquired, and the target heat recovery compressor frequency f is determined based on the heat recovery efficiency deviation compressor_target And adjust the compressor

[0138] This design first adjusts the frequency of the fan to increase the heat exchange capacity of the outdoor heat exchanger, so as to enable the outdoor heat exchanger to cooperate with the air-conditioning water heat exchanger to jointly bear the heating load of the hot water heat exchanger, rapidly improve the current heat recovery efficiency of the heat recovery system, and then re-detect the heat recovery efficiency after the change of the fan frequency, and based on this, fine-tune the frequency of the compressor to improve the heat recovery efficiency and achieve the efficient operation of the heat recovery system

[0139] In some embodiments of the present invention, the target air volume Q is determined according to the current heat recovery efficiency η and the target heat recovery efficiency η target Determine the target air volume Q target And adjusting the fan includes

[0140] According to the current heat recovery efficiency η and the target heat recovery efficiency η target Determine the target air volume Q target , ;

[0141] Calculate the target heat recovery fan frequency f fan =f base_target +kf×(Q target -Q current );

[0142] Perform dynamic ramp adjustment on the fan until the target heat recovery fan frequency f is reached fan , and gradually adjust the frequency using a time continuous function. The function is

[0143] f fan(t) =f fan_current +k×(η target -η)×t

[0144] Where f base_target is the reference fan frequency corresponding to the target air volume Q target Q current is the current air volume, kf is the fan frequency adjustment coefficient, and k is the slope

[0145] This design can realize the direct conversion of the heat recovery efficiency η to the physical air volume, solve the blindness problem of traditional open-loop control, greatly improve the air volume control accuracy, and use ramp adjustment to avoid frequency mutation and improve the system stability

[0146] In some embodiments of the present invention, the target heat recovery compressor frequency f is determined according to the heat recovery efficiency deviation compressor_target And adjusting the compressor includes

[0147] Calculate the target heat recovery compressor frequency f compressor_target = f compressor_current + kc × (η target - η);

[0148] Perform dynamic ramp adjustment on the compressor until the target heat recovery compressor frequency f is reached compressor_target , and gradually adjust the frequency using a time - continuous function. The function is:

[0149] f compressor(t) = f compressor_current + k × (η target - η) × t

[0150] where f compressor_current is the current compressor frequency, kc is the compressor frequency adjustment coefficient, and k is the slope.

[0151] This design directly drives the compressor frequency adjustment through the efficiency deviation, realizes the closed - loop control of the heat recovery efficiency and the refrigerant flow rate, solves the problem of mismatch between the cooling and heating loads, and uses ramp adjustment to avoid sudden frequency changes and improve the system stability.

[0152] To improve the system safety, after adjusting the frequencies of the compressor and the fan, the frequency control method also designs surge prevention control and / or system protection control. After performing the protection control, it returns to re - obtain the working state of the heat recovery system and enters the next cycle.

[0153] Specifically, the surge prevention control method is:

[0154] Detect the current frequency f of the compressor compressor ;

[0155] If the current frequency f compressor is lower than the set threshold f 喘振阈值 , then increase the frequency of the fan, for example, increase the set fan frequency adjustment amount.

[0156] This design is applicable to centrifugal compressors. By increasing the fan frequency, surge during low - frequency operation can be avoided.

[0157] The system protection control method is:

[0158] Detect the exhaust temperature T of the compressor exhaust and / or the suction pressure P inlet ;

[0159] If the exhaust temperature T exhaust exceeds the set maximum value T max , then reduce the frequency of the compressor;

[0160] If the suction pressure P inlet is lower than the set minimum value P min, the frequency of the fan is reduced.

[0161] In this design, when the system operates at over-temperature or low pressure, the frequency of the compressor or the fan is reduced to enable the system to return to the normal operating state and improve the system reliability.

[0162] Such as Figure 1 As shown, the present invention also proposes a heat recovery system, including: a compressor, two water heat exchangers, and an outdoor heat exchanger driven by a fan for heat exchange. This heat recovery system adopts the above frequency control method.

[0163] For easy understanding, the two water heat exchangers are respectively the first water heat exchanger 2 and the second water heat exchanger 3. The first end and the second end of each heat exchanger have been marked on the connection schematic diagram of the heat recovery system. The first end is "①" and the second end is "②".

[0164] The exhaust side of the compressor 1 can be switched to connect to the first end ① of any one of the heat exchangers, and the second end ② of each heat exchanger is respectively connected to the inlet pipe of the liquid storage tank 5 through a valve member. When the compressor 1 is connected to the first end ① of a certain heat exchanger, this heat exchanger serves as a condenser, and the second end ② of the heat exchanger is the condenser outlet side. The refrigerant flowing out of the second end ② can enter the liquid storage tank 5 through the valve member.

[0165] The second end ② of the first water heat exchanger 2 is connected to the second end ② of the outdoor heat exchanger 4 through a throttling pipeline. The throttling pipeline is connected in series with a first throttle valve 10 and a second throttle valve 11. The first throttle valve 10 is close to the first water heat exchanger 2, and the second throttle valve 11 is close to the outdoor heat exchanger 4. The outlet pipe of the liquid storage tank 5 is connected between the first throttle valve 10 and the second throttle valve 11. The refrigerant flowing out of the liquid storage tank 5 can enter the first water heat exchanger 2 through the first throttle valve 10, and the refrigerant flowing out of the main pipeline can also enter the outdoor heat exchanger 4 through the second throttle valve 11. The specific flow direction depends on the working mode of the heat recovery system.

[0166] The valve member in the above text can adopt a control valve that can switch the on-off state, or a check valve. The check valve of the first water heat exchanger 2 is the second check valve 8, the check valve of the second water heat exchanger 3 is the first check valve 7, and the check valve of the outdoor heat exchanger 4 is the third check valve 9. Utilizing the one-way conduction characteristic of the check valve to ensure that the refrigerant can only flow from the heat exchanger to the liquid storage tank 5, avoiding the reverse flow of the refrigerant during different mode switches, which may cause system pressure disorder or efficiency decline, without additional electric control signals, reducing the complexity of valve adjustment.

[0167] On this basis, in order to further optimize the heat recovery system, a defrosting branch is designed between the second water heat exchanger 3 and the outdoor heat exchanger 4. The specific connection method is that one end of the defrosting branch is connected to the second end of the second water heat exchanger 3, and the other end is connected between the first throttle valve 10 and the second throttle valve 11. The defrosting branch is provided with a throttling element 12 and a control valve 6, and the on-off state of the defrosting branch is switched through the control valve 6. The control valve 6 is opened when the outdoor heat exchanger 4 serves as a condenser and the second water heat exchanger 3 serves as an evaporator (that is, during the defrosting process of the outdoor heat exchanger 4, the second water heat exchanger 3 participates in the refrigerant cycle). The first throttle valve 10 and the second throttle valve 11 are both closed when the control valve 6 is opened.

[0168] The function of this design is that when the outdoor heat exchanger 4 has a defrosting requirement, it can be selected to connect the second water heat exchanger 3 and the outdoor heat exchanger 4 through the defrosting branch, and the heat recovery system has higher flexibility and better environmental adaptability. For example, in the hot water mode (the second water heat exchanger 3 serves as a condenser and the outdoor heat exchanger 4 serves as an evaporator), if the outdoor heat exchanger 4 has a defrosting requirement during the preparation of hot water, the refrigerant flow direction can be adjusted, the defrosting branch can be connected, and the high-temperature refrigerant discharged from the compressor 1 is sent to the outdoor heat exchanger 4 for defrosting. The refrigerant flowing out of the outdoor heat exchanger 4 passes through the liquid storage tank 5, the defrosting branch and the second water heat exchanger 3 in sequence, and finally returns to the compressor 1.

[0169] The working modes of the heat recovery system include at least one of the hot water mode, the cooling mode, the heating mode, the cooling and heating water mode, and the heating and heating water mode. The operating states of the three heat exchangers in different working modes are introduced in detail below.

[0170] As Figure 4 shown, when the heat recovery system operates in the hot water mode - the conventional mode, the second water heat exchanger 3 serves as a condenser, the outdoor heat exchanger 4 serves as an evaporator, the first water heat exchanger 2 does not participate in the refrigerant cycle, the exhaust side of the compressor 1 is connected to the first end of the second water heat exchanger 3, and the refrigerant circulation loop flow direction is compressor 1 → second water heat exchanger 3 → liquid storage tank 5 → second throttle valve 11 → outdoor heat exchanger 4 → return to compressor 1.

[0171] As Figure 5 shown, when the heat recovery system operates in the cooling mode - the conventional mode, the first water heat exchanger 2 serves as an evaporator, the outdoor heat exchanger 4 serves as a condenser, the second water heat exchanger 3 does not participate in the refrigerant cycle, the exhaust side of the compressor 1 is connected to the first end of the outdoor heat exchanger 4, and the refrigerant circulation loop flow direction is compressor 1 → outdoor heat exchanger 4 → liquid storage tank 5 → first throttle valve 10 → first water heat exchanger 2 → return to compressor 1.

[0172] As Figure 6As shown, when the heat recovery system operates in the heating mode - the conventional mode, the first water heat exchanger 2 serves as a condenser, the outdoor heat exchanger 4 serves as an evaporator, the second water heat exchanger 3 does not participate in the refrigerant cycle. The exhaust side of the compressor 1 is connected to the first end of the first water heat exchanger 2, and the refrigerant circulation path is Compressor 1 → First water heat exchanger 2 → Liquid receiver 5 → Second throttle valve 11 → Outdoor heat exchanger 4 → Back to Compressor 1.

[0173] As Figure 7 shown, when the heat recovery system operates in the cooling and heating water mode - the heat recovery mode, the first water heat exchanger 2 serves as an evaporator, the second water heat exchanger 3 serves as a condenser. If the heat load demand is low, the outdoor heat exchanger 4 does not participate in the refrigerant cycle. The exhaust side of the compressor 1 is connected to the first end of the first water heat exchanger 2, and the refrigerant circulation path is Compressor 1 → Second water heat exchanger 3 → Liquid receiver 5 → First throttle valve 10 → First water heat exchanger 2 → Back to Compressor 1.

[0174] When the heat recovery system operates in the heating and heating water mode - the conventional mode, either the first water heat exchanger 2 or the second water heat exchanger 3 serves as a condenser, and the outdoor heat exchanger 4 serves as an evaporator. The heat recovery system usually defaults to giving priority to domestic hot water, and users can also independently set the priority of air conditioning heating and domestic hot water. Taking domestic hot water priority as an example, it first operates in the hot water mode, with the second water heat exchanger 3 serving as a condenser and the outdoor heat exchanger 4 serving as an evaporator, and the first water heat exchanger 2 does not participate in the refrigerant cycle; after the hot water has met the customer's needs, it operates in the heating mode, with the first water heat exchanger 2 serving as a condenser and the outdoor heat exchanger 4 serving as an evaporator, and the second water heat exchanger 3 does not participate in the refrigeration cycle. In the heating and heating water mode, after the current function reaches the shutdown condition, it is judged whether the other function meets the startup condition. If so, the system starts and runs with that function. For example, with domestic hot water priority default, after the hot water function reaches the shutdown condition, it is judged whether the heating function meets the startup condition. If so, the system starts and runs with the heating function until the shutdown condition of the heating function is reached.

[0175] The heat recovery system can flexibly switch operating modes under different working conditions through the coordinated operation of three heat exchangers to maximize the recovery of waste heat. For example, in the cooling mode, the refrigerant absorbs heat in the first water heat exchanger to achieve refrigeration; in the heating mode, the high-temperature refrigerant discharged from the compressor 1 releases heat in the first water heat exchanger to achieve heating; in the hot water mode, the high-temperature refrigerant discharged from the compressor 1 is used to heat domestic water in the second water heat exchanger to improve the hot water supply efficiency; in the composite working mode (cooling + hot water / heating + hot water), the heat of the refrigerant is recovered to heat domestic water / achieve heating, realizing cascaded utilization of energy and improving the energy efficiency of the heat recovery system.

[0176] In a preferred embodiment, the operating modes of the heat recovery system include the five operating modes mentioned above. To achieve a more accurate and reliable switch to different operating modes, the compressor 1 is connected to three heat exchangers through two four-way valves. Specifically, the D end of the first four-way valve 13 is connected to the exhaust side of the compressor 1, the E end is connected to the first end of the first water heat exchanger 2, the S end is connected to the suction side of the compressor 1, and the C end is connected to the D end of the second four-way valve 14; the C end of the second four-way valve 14 is connected to the first end of the outdoor heat exchanger 4, the E end is connected to the first end of the second water heat exchanger 3, and the S end is connected to the suction side of the compressor 1.

[0177] After the heat recovery system adopts the above frequency control method, in the conventional mode with the participation of the outdoor heat exchanger, by real-time detecting the change of the system load, the frequencies of the compressor and the fan are coordinated to adjust, so as to quickly adapt to different working conditions and the usage requirements of users, and realize the efficient operation of the heat recovery system; in the heat recovery mode with the participation of the outdoor heat exchanger, by real-time detecting the change of the heat recovery efficiency of the system, the frequency of the fan is preferentially adjusted, and then the frequency of the compressor is adjusted, which significantly improves the heat recovery efficiency and reduces the system energy consumption.

[0178] It should be noted that the terms used above are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. When the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations. For the actions, steps, etc. in the devices and methods shown in the specification and drawings, as long as there is no specific limitation on the execution order, and as long as the output of the previous process is not used in the subsequent process, they can be implemented in any order. The similar sequential terms used for convenience of description do not mean that they must be implemented in such an order.

[0179] Technologies, methods and devices known to those of ordinary skill in the relevant fields may not be discussed in detail, but in appropriate cases, the said technologies, methods and devices should be regarded as part of the specification. In all the examples shown and discussed here, any specific value should be interpreted as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further discussed in the subsequent drawings.

[0180] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. Frequency control method for a heat recovery system, the heat recovery system comprising a compressor, two water heat exchangers, and an outdoor heat exchanger that is heat-exchanged by a fan; characterized in that, The described frequency control method includes: Obtaining the operating state of the heat recovery system; When the compressor is connected to the outdoor heat exchanger and any one of the water heat exchangers to form a refrigerant circulation loop, coordinately adjusting the frequency of the compressor and the frequency of the fan according to the heat load demand; And / or when the compressor is connected to the outdoor heat exchanger and the two water heat exchangers to form a refrigerant circulation loop, adjusting the frequency of the fan and the frequency of the compressor successively according to the heat recovery efficiency.

2. The frequency control method according to claim 1, wherein Coordinately adjusting the frequency of the compressor and the frequency of the fan according to the heat load demand includes: Obtaining the actual load parameters of the heat recovery system and calculating the current heat load demand L; In the optimization stage, determining the target optimization frequency according to the current heat load demand L, the performance parameters of the compressor and the performance parameters of the fan, and adjusting the compressor and the fan; In the fine-tuning stage, performing a dynamic ramp adjustment on the frequency of the compressor and the frequency of the fan according to the interval where the current heat load demand L is located.

3. The frequency control method according to claim 2, characterized in that, Determining the target optimization frequency according to the current heat load demand L, the performance parameters of the compressor and the performance parameters of the fan includes: a first optimization strategy and / or a second optimization strategy; The first optimization strategy includes: determining the optimal compressor operating frequency f corresponding to the current heat load demand L based on a pre-established compressor performance curve database. compressor_opt , based on the pre-established fan performance curve database, the fan optimal operating frequency f corresponding to the current heat load demand L is determined by fitting fan_opt ; The second optimization strategy includes: finding the optimal frequency f of the compressor according to the pre-established multi-objective optimization model and constraint conditions compressor_opt and the optimal frequency f of the fan fan_opt .

4. The frequency control method according to claim 2, wherein In the optimization stage, after determining the target optimization frequency according to the current heat load demand L, the performance parameters of the compressor and the performance parameters of the fan and adjusting the compressor and the fan, detecting the current operating parameters of the compressor, calculating the deviation e between the current operating parameters and the target parameters, and adjusting the frequency of the compressor using a PID control algorithm.

5. The frequency control method according to claim 2, wherein Performing a dynamic ramp adjustment on the frequency of the compressor and the frequency of the fan according to the interval where the current heat load demand L is located includes: When L < L Low , reduce the frequency of the fan according to f fan = f fan_base - kf×(L base - L), and reduce the frequency of the compressor according to f compressor = f compressor_base - kc×(L base - L); When L Low ≤L≤L high If L < L base , then according to f fan = f fan_base − kf×(L base − L) to reduce the frequency of the fan, and according to f compressor = f compressor_base − kc×(L base − L) to reduce the frequency of the compressor. If L > L base , then according to f compressor = f compressor_base + kc×(L − L base ) to increase the frequency of the compressor, and according to f fan = f fan_base + kf×(L − L base ) to increase the frequency of the fan; When L > L high , increase the frequency of the compressor according to f compressor = f compressor_base + kc × (L - L base ), and increase the frequency of the blower according to f fan = f fan_base + kf × (L - L base ); Among them, dynamic ramp regulation is performed on the compressor and the fan until reaching f compressor and f fan , f compressor is the target compressor frequency, f compressor_base is the compressor reference frequency, kc is the compressor frequency adjustment coefficient, f fan is the target fan frequency, f fan_base is the fan reference frequency, kf is the fan frequency adjustment coefficient, L base is the reference load demand.

6. The frequency control method according to claim 2, wherein In the fine-tuning stage, during the process of performing a dynamic ramp adjustment on the frequency of the compressor and the frequency of the fan, the difference between the frequency of the compressor and the frequency of the fan is kept within a set range.

7. The frequency control method according to claim 1, characterized in that Adjusting the frequency of the fan and the frequency of the compressor successively according to the heat recovery efficiency includes: Obtaining the current heat recovery efficiency η of the heat recovery system; During the fan adjustment stage, based on the current heat recovery efficiency η and the target heat recovery efficiency η target determine the target air volume Q target and adjust the fan; During the compressor regulation stage, the current heat recovery efficiency η is retrieved again, and the target heat recovery compressor frequency f is determined based on the heat recovery efficiency deviation compressor_target and the compressor is regulated.

8. The frequency control method according to claim 7, wherein Based on the current heat recovery efficiency η and the target heat recovery efficiency η target Determine the target air volume Q target And adjusting the fan includes: Based on the current heat recovery efficiency η and the target heat recovery efficiency η target determine the target air volume Q target ; Calculate the frequency f of the target heat recovery fan fan = f base_target + kf × (Q target - Q current ); Perform dynamic ramp regulation on the fan until the target heat recovery fan frequency f is reached fan ; Among them, f base_target is the reference fan frequency corresponding to the target air volume Q target , Q current is the current air volume, and kf is the fan frequency adjustment coefficient.

9. The frequency control method according to claim 7, characterized in that Determine the target heat recovery compressor frequency f based on the deviation of the heat recovery efficiency compressor_target And adjusting the compressor includes: Calculate the target heat recovery compressor frequency f compressor_target = f compressor_current + kc × (η target - η); Perform dynamic ramp regulation on the compressor until the target heat recovery compressor frequency f is reached compressor_target ; Among them, f compressor_current is the current compressor frequency, and kc is the compressor frequency adjustment coefficient.

10. The frequency control method according to any one of claims 1 to 9, characterized in that, The frequency control method further includes: After coordinately adjusting the frequency of the compressor and the frequency of the blower according to the heat load demand, or after adjusting the frequency of the blower and the frequency of the compressor successively according to the heat recovery efficiency, detect the current frequency f of the compressor compressor ; If the current frequency f compressor is lower than the set threshold f 喘振阈值 , increase the frequency of the fan.

11. The frequency control method according to any one of claims 1 to 9, characterized in that The frequency control method further includes: After coordinately adjusting the frequency of the compressor and the frequency of the blower according to the heat load demand, or after sequentially adjusting the frequency of the blower and the frequency of the compressor according to the heat recovery efficiency, detect the exhaust temperature T of the compressor exhaust and / or the suction pressure P inlet ; If the exhaust temperature T exhaust exceeds the set maximum value T max , then reduce the frequency of the compressor; If the intake pressure P inlet is lower than the set minimum value P min , then reduce the frequency of the fan.

12. Heat recovery system, comprising: A compressor, two water heat exchangers, and an outdoor heat exchanger driven by a fan for heat exchange; characterized in that the heat recovery system adopts the frequency control method according to any one of claims 1 to 11.

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