Frequency control method of heat recovery system and heat recovery system

Abstract

The present invention discloses a frequency control method for a heat recovery system and 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: obtaining the operating status 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, collaboratively adjusting the frequency of the compressor and the frequency of the fan according to 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, sequentially adjusting the frequency of the fan and the frequency of the compressor according to heat recovery efficiency. The present invention intelligently allocates frequency change strategies for the compressor and the fan based on the operating status of the heat recovery system, thereby improving the adaptability of the heat recovery system and achieving efficient operation of the heat recovery system.

Description

Technical Field

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

[0002] With the rapid development of heat recovery technology, improving energy efficiency by recovering waste heat from industrial processes or HVAC systems has become an important issue. Existing technologies have significant limitations in frequency control strategies for compressors and fans: traditional methods generally use fixed frequency settings or simple segmented control, which cannot achieve precise adjustment based on dynamic load changes and lack the ability to optimize the heat recovery efficiency (η) in a closed loop. Due to the lack of a real-time efficiency feedback mechanism, the actual heat transfer performance of the heat exchanger and the waste heat recovery potential are mismatched for a long time, resulting in large fluctuations in the heat recovery efficiency. This extensive control and lack of efficiency optimization cause the system to deviate from the optimal operating point for a long time, resulting in significant energy efficiency losses and difficulty adapting to complex operating conditions such as temperature fluctuations of the waste heat source and dust accumulation on the heat exchanger surface.

[0003] More notably, current technology lacks a deep coordination mechanism between compressors and fans: fans are often only used as auxiliary equipment for proportional speed regulation of the compressor, failing to establish a dynamic coupling relationship between the two at the energy transfer level. This fragmented control leads to a series of chain reactions. When the fan air supply is insufficient under high-load conditions, the compressor exhaust pressure quickly exceeds the limit, triggering a protective shutdown, significantly increasing the equipment failure rate. During partial-load operation, the ineffective power consumption caused by redundant air volume causes the system's overall energy efficiency ratio (COP) to be lower than the theoretical value. More seriously, when encountering sudden changes in waste heat sources (such as starting and stopping industrial equipment), traditional PID control has a long response delay and large system temperature fluctuations, which can easily induce compressor surge risks. This not only affects the user experience, but also exacerbates mechanical wear and shortens equipment life.

[0004] Therefore, how to design a frequency control method that is more efficient and energy-saving and suitable for heat recovery systems 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 existing frequency control schemes, the present invention proposes a frequency control method and a heat recovery system for a heat recovery system, which intelligently allocates the frequency change strategy of the compressor and the fan according to the working status 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, which 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] Get the working status of the heat recovery system;

[0008] When the compressor is connected to 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 coordinated and adjusted according to the heat load demand;

[0009] And / or when the compressor is connected to 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 adjusted in sequence according to the heat recovery efficiency.

[0010] Furthermore, the frequency of the compressor and the frequency of the fan are adjusted in coordination according to the heat load demand, including:

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

[0012] In the optimization phase, the target optimization frequency is determined based on the current heat load demand L, the performance parameters of the compressor, and the performance parameters of the fan, and the compressor and fan are adjusted;

[0013] During the fine-tuning stage, dynamic ramp adjustment is performed on the compressor frequency and the fan frequency according to the range of the current heat load demand L.

[0014] Furthermore, 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;

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

[0016] 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 optimal frequency f of the fan fan_opt .

[0017] Furthermore, in the optimization stage, after determining the target optimization frequency and adjusting the compressor and fan based on the current heat load demand L, the performance parameters of the compressor and the performance parameters of 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 frequency of the compressor is adjusted using the PID control algorithm.

[0018] Furthermore, dynamically ramping the frequency of the compressor and the frequency of the fan according to the interval of the current heat load demand L includes:

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

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

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

[0022] In which, dynamic ramp regulation is performed on the compressor and fan until 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 base frequency, kf is the fan frequency adjustment coefficient, L base is the base load demand.

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

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

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

[0026] During the fan adjustment phase, 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;

[0027] During the compressor adjustment phase, the current heat recovery efficiency η is re-obtained, and the target heat recovery compressor frequency f is determined based on 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 adjust the fan including:

[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] Among them, f base_target The target air volume Q target Corresponding reference fan frequency, Q current is the current air volume, and kf is the fan frequency adjustment coefficient.

[0033] Furthermore, the target heat recovery compressor frequency f is determined based on the heat recovery efficiency deviation. compressor_target And adjust the compressor including:

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

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

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

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

[0038] After adjusting the compressor frequency and the fan frequency in coordination according to the heat load demand, or adjusting the fan frequency and the compressor frequency in sequence according to the heat recovery efficiency, the current frequency f of the compressor is detected. compressor ;

[0039] If the current frequency f compressor Below the set threshold f 喘振阈值 , then increase the frequency of the fan.

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

[0041] After adjusting the compressor frequency and the fan frequency in coordination according to the heat load demand, or adjusting the fan frequency and the compressor frequency in sequence according to the heat recovery efficiency, the exhaust temperature T of the compressor is detected. exhaust and / or suction pressure P inlet ;

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

[0043] If the suction pressure P inlet Below the set minimum value P min , then reduce the frequency of the fan.

[0044] The present invention also proposes a heat recovery system, comprising: a compressor, two water heat exchangers, and an outdoor heat exchanger driven by a fan for heat exchange. The heat recovery system adopts the above-mentioned 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 normal mode with the outdoor heat exchanger involved, by real-time detection of system load changes, the frequency of the compressor and fan are coordinated to adapt to different working conditions and user needs, achieving efficient operation of the heat recovery system;

[0047] 2. In the heat recovery mode with the outdoor heat exchanger involved, the system's heat recovery efficiency changes are detected in real time, and the fan frequency is adjusted first, followed by the compressor frequency, to improve heat recovery efficiency and reduce system energy consumption;

[0048] 3. Through frequency coordination logic and dynamic ramp function, the frequency of compressor and fan is optimized to avoid sudden frequency changes and improve system stability and energy efficiency;

[0049] 4. Combine multiple algorithms such as PID control and fuzzy control to improve the accuracy of frequency control methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The present invention is described in detail below with reference to the embodiments and accompanying drawings, in which:

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

[0052] Figure 2 This is a flow chart of the frequency control in a conventional mode with the participation of an outdoor heat exchanger of the present invention;

[0053] Figure 3 This is a flow chart of frequency control in a 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 in the hot water mode of the present invention;

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

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

[0057] Figure 7 Schematic diagram of the refrigerant flow in the cooling and heating water mode of the present invention;

[0058] Description of the drawings: 1. Compressor; 2. First water heat exchanger; 3. Second water heat exchanger; 4. Outdoor heat exchanger; 5. Liquid reservoir; 6. Control valve; 7. First one-way valve; 8. Second one-way valve; 9. Third one-way valve; 10. First throttle valve; 11. Second throttle valve; 12. Throttling element; 13. First four-way valve; 14. Second four-way valve. DETAILED DESCRIPTION

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

[0060] like Figure 1As shown, the frequency control method proposed in the present invention is applicable to a heat recovery system, which includes a compressor 1, two water heat exchangers, and an outdoor heat exchanger 4 driven by a fan for heat exchange. The two water heat exchangers are generally an air conditioning water heat exchanger and a hot water heat exchanger. In normal mode, compressor 1 is connected to any two heat exchangers (usually including outdoor heat exchanger 4) to form a refrigerant circulation loop. In heat recovery mode, when the heat load demand increases significantly (such as high 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, compressor 1 will be connected to all three heat exchangers to form a refrigerant loop. At this time, the outdoor heat exchanger 4 and the air conditioning water heat exchanger will work together to bear the heating load of the hot water heat exchanger.

[0061] Based on this, the frequency control method proposed in the present invention intelligently allocates the frequency change strategy of the compressor and the fan according to the working status of the heat recovery system, thereby improving the adaptability of the heat recovery system and achieving efficient operation of the heat recovery system.

[0062] Specifically, frequency control methods include:

[0063] Get the working status of the heat recovery system;

[0064] When the compressor is connected to 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 coordinated and adjusted 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, the frequency of the fan and the frequency of the compressor are adjusted in sequence according to the heat recovery efficiency.

[0066] In the normal mode with the participation of an outdoor heat exchanger, this design detects changes in system load in real time and coordinates the frequencies of the compressor and fan to quickly adapt to different working conditions and user needs, thereby achieving efficient operation of the heat recovery system. In the heat recovery mode with the participation of an outdoor heat exchanger, this design detects changes in the system's heat recovery efficiency in real time, prioritizes adjusting the fan frequency, and then the compressor frequency, significantly improving heat recovery efficiency and reducing system energy consumption.

[0067] like Figure 2 As shown, in some embodiments of the present invention, collaboratively adjusting the frequency of the compressor and the frequency of the fan 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 phase, the target optimization frequency is determined based on the current heat load demand L, the performance parameters of the compressor, and the performance parameters of the fan, and the compressor and fan are adjusted;

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

[0071] This design significantly adjusts the frequencies of the compressor and fan during the optimization phase, allowing their operating frequencies to quickly approach a state that meets the current heat load requirements. During the fine-tuning phase, the frequencies of the compressor and fan are fine-tuned according to different operating conditions, allowing their operating frequencies to accurately match the current heat load requirements, enabling the heat recovery system to operate efficiently.

[0072] There are many ways to calculate the heat load demand L, which are explained below with examples.

[0073] The first temperature difference method

[0074] Calculation formula:

[0075]

[0076] in:

[0077] : Heat load demand;

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

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

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

[0081] Application scenario: Applicable to systems that directly reflect heat load requirements through temperature changes.

[0082] The second pressure difference method

[0083] Calculation formula:

[0084]

[0085] in:

[0086] : constants related to system characteristics;

[0087] : The difference between the suction and exhaust pressures of the compressor;

[0088] : Compressor flow rate.

[0089] Application scenario: Suitable for systems that reflect heat load requirements through pressure changes.

[0090] The third comprehensive method

[0091] Calculation formula:

[0092]

[0093] in:

[0094] , , : weight 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.

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

[0100] In some embodiments of the present invention, determining the target optimization frequency based on 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, you can choose to determine the target optimization frequency with the first optimization strategy or the second optimization strategy, and only optimize and adjust the compressor and fan once during the optimization stage. You can also choose to determine the initial target optimization frequency with the first optimization strategy, and then determine the secondary target optimization frequency with the second optimization strategy, and optimize and adjust the compressor and fan twice in succession during the optimization stage. The advantage of this design is that the first optimization strategy is used to quickly respond to the current heat load demand, and the second optimization strategy is used for precise tuning to improve energy efficiency.

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

[0102] The logic of the first optimization strategy for compressors and fans is the same. Taking the compressor as an example, the compressor performance curve database usually includes the relationship between the compressor's exhaust temperature, suction pressure, flow rate and frequency. The performance parameters of the compressor at different frequencies are obtained from the pre-stored compressor performance curve database. 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 optimal frequency f of the fan fan_opt .

[0104] The second optimization strategy is to optimize system energy consumption, system stability, and equipment life. Genetic algorithms or particle swarm optimization algorithms can be used to find the optimal frequency adjustment solution and define a fitness function that comprehensively considers energy consumption, stability, and equipment life, as follows:

[0105]

[0106] in:

[0107] E: system energy consumption;

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

[0109] T: Equipment life indicator (such as number of starts and stops or operating time);

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

[0111] Constraints: 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 optimal frequency f of the fan fan_opt .

[0113] In order to improve the accuracy and stability of frequency regulation, in the optimization stage, the target optimization frequency is determined according to the current heat load demand L, the performance parameters of the compressor and the performance parameters of the fan, and the compressor and fan are adjusted. Then, the current operating parameters of the compressor are detected, and the deviation e between the current operating parameters and the target parameters is calculated. 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 suction pressure P inlet ;

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

[0117]

[0118] PID control formula:

[0119] Calculating frequency adjustment :

[0120]

[0121] in:

[0122] : Deviation 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 in which the current heat load demand L is located includes:

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

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

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

[0131] In which, dynamic ramp regulation is performed on the compressor and fan until f compressor and f fan , using 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 base frequency, kf is the fan frequency adjustment coefficient, L base is the base load demand.

[0132] This design will be based on high and low load zoning, and the compressor and fan will be adjusted up and down according to different working conditions to achieve coordinated optimization of the compressor and fan frequencies, thereby improving the stability and energy efficiency of the heat recovery system.

[0133] It's important to note that during the fine-tuning phase, when dynamically ramping the compressor and fan frequencies, the preferred approach is to maintain the difference between the compressor and fan frequencies within a set range. This range can be customized to meet actual needs, for example, 5 Hz. This design improves the coordination between the compressor and fan frequencies and ensures the stability of the heat recovery system.

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

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

[0136] During the fan adjustment phase, 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;

[0137] During the compressor adjustment phase, the current heat recovery efficiency η is re-obtained, 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 fan frequency to increase the heat exchange capacity of the outdoor heat exchanger, so that the outdoor heat exchanger and the air conditioning water heat exchanger can jointly bear the heating load of the hot water heat exchanger, rapidly improving the current heat recovery efficiency of the heat recovery system. The heat recovery efficiency after the fan frequency change is then re-tested, and the compressor frequency is fine-tuned based on this to improve the heat recovery efficiency and achieve efficient operation of the heat recovery system.

[0139] In some embodiments of the present invention, 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 including:

[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 , the frequency is gradually adjusted using a time-continuous function, the function is:

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

[0144] Among them, f base_target The target air volume Q target Corresponding reference fan frequency, Q current is the current air volume, kf is the fan frequency adjustment coefficient, and k is the slope.

[0145] This design can achieve direct conversion of heat recovery efficiency η to physical air volume, solve the blindness problem of traditional open-loop control, greatly improve the air volume control accuracy, use ramp regulation to avoid frequency mutations, and improve 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 adjust the compressor including:

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

[0148] Perform dynamic ramp regulation on the compressor until the target heat recovery compressor frequency f is reached compressor_target , the frequency is gradually adjusted using a time-continuous function, the function is:

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

[0150] Among them, 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 efficiency deviation, achieving closed-loop control of heat recovery efficiency and refrigerant flow, solving the problem of hot and cold load mismatch, and using ramp regulation to avoid frequency mutations and improve system stability.

[0152] In order to improve the safety of the system, after adjusting the frequency of the compressor and fan, the frequency control method is also designed with anti-surge control and / or system protection control. After executing the protection control, it returns to regain the working status of the heat recovery system and enters the next cycle.

[0153] Specifically, the anti-surge control method is:

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

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

[0156] This design is suitable for centrifugal compressors and increases the fan frequency to avoid surge during low-frequency operation.

[0157] The system protection control mode is:

[0158] Detect the exhaust temperature T of the compressor exhaust and / or 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 Below the set minimum value P min, then reduce the frequency of the fan.

[0161] This design reduces the frequency of the compressor or fan when the system is overheating or operating at low pressure, allowing the system to return to normal operation and improve system reliability.

[0162] like 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, and the heat recovery system adopts the above-mentioned frequency control method.

[0163] For ease of understanding, the two water heat exchangers are 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 diagram of the heat recovery system, with the first end being "①" and the second end being "②".

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

[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 reservoir 5 is connected between the first throttle valve 10 and the second throttle valve 11. The refrigerant flowing out of the liquid reservoir 5 can enter the first water heat exchanger 2 through the first throttle valve 10, and the refrigerant flowing out of the main line 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 components mentioned above can be control valves with switchable switching states, or one-way valves. The one-way valve of the first water heat exchanger 2 is the second one-way valve 8, the one-way valve of the second water heat exchanger 3 is the first one-way valve 7, and the one-way valve of the outdoor heat exchanger 4 is the third one-way valve 9. The one-way conduction characteristics of the one-way valve are utilized 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 when switching between different modes, resulting in system pressure disorder or decreased efficiency. No additional electrical control signal is required, reducing the complexity of valve adjustment.

[0167] On this basis, to further optimize the heat recovery system, a defrost branch is designed between the second water heat exchanger 3 and the outdoor heat exchanger 4. Specifically, one end of the defrost 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 defrost branch is equipped with a throttling element 12 and a control valve 6, which switches the defrost branch on and off. The control valve 6 opens when the outdoor heat exchanger 4 functions as a condenser and the second water heat exchanger 3 functions as an evaporator (i.e., during the defrosting process of the outdoor heat exchanger 4, the second water heat exchanger 3 participates in the refrigerant circulation). The first throttle valve 10 and the second throttle valve 11 are both closed when the control valve 6 is open.

[0168] This design allows for the optional connection of the second water heat exchanger 3 and the outdoor heat exchanger 4 via a defrost branch when outdoor heat exchanger 4 requires defrosting. This provides greater flexibility and improved environmental adaptability for the heat recovery system. For example, in hot water mode (with the second water heat exchanger 3 acting as the condenser and the outdoor heat exchanger 4 acting as the evaporator), if outdoor heat exchanger 4 requires defrosting during hot water preparation, the refrigerant flow direction can be adjusted to connect the defrost branch, directing the high-temperature refrigerant discharged from compressor 1 to outdoor heat exchanger 4 for defrosting. The refrigerant then flows through the accumulator 5, the defrost branch, and the second water heat exchanger 3 before returning to compressor 1.

[0169] The working modes of the heat recovery system include at least one of hot water mode, cooling mode, heating mode, cooling water heating mode, and heating water heating mode. The following details the operating status of the three heat exchangers in different working modes.

[0170] like Figure 4 As shown, when the heat recovery system operates in hot water mode - normal 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 circulation, 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 flows as follows: compressor 1 → second water heat exchanger 3 → liquid accumulator 5 → second throttle valve 11 → outdoor heat exchanger 4 → returns to compressor 1.

[0171] like Figure 5 As shown, when the heat recovery system operates in the cooling mode - normal 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 circulation, the exhaust side of the compressor 1 is connected to the first end of the outdoor heat exchanger 4, and the refrigerant circulation loop flows as follows: compressor 1 → outdoor heat exchanger 4 → liquid accumulator 5 → first throttle valve 10 → first water heat exchanger 2 → returns to compressor 1.

[0172] like Figure 6As shown, when the heat recovery system operates in heating mode - normal 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 circulation, the exhaust side of the compressor 1 is connected to the first end of the first water heat exchanger 2, and the refrigerant circulation loop flows as follows: compressor 1 → first water heat exchanger 2 → liquid accumulator 5 → second throttle valve 11 → outdoor heat exchanger 4 → returns to compressor 1.

[0173] like Figure 7 As shown, when the heat recovery system operates in the cooling and heating water mode - heat recovery mode, the first water heat exchanger 2 serves as an evaporator and 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 circulation. The exhaust side of the compressor 1 is connected to the first end of the first water heat exchanger 2. The refrigerant circulation loop flows as follows: compressor 1 → second water heat exchanger 3 → liquid accumulator 5 → first throttle valve 10 → first water heat exchanger 2 → returns to compressor 1.

[0174] When the heat recovery system operates in heating water mode—normal mode—either the first or second water heat exchanger 2 and 3 functions as a condenser, and the outdoor heat exchanger 4 functions as an evaporator. The heat recovery system typically prioritizes domestic hot water by default, but users can also customize the priority between air conditioning heating and domestic hot water. For example, in the domestic hot water priority mode, the system initially operates in hot water mode, with the second water heat exchanger 3 serving as the condenser and the outdoor heat exchanger 4 as the evaporator. The first water heat exchanger 2 is not involved in the refrigerant cycle. Once hot water has been supplied to meet customer demand, the system then operates in heating mode, with the first water heat exchanger 2 serving as the condenser, the outdoor heat exchanger 4 serving as the evaporator, and the second water heat exchanger 3 not participating in the refrigeration cycle. In heating water mode, if the current function meets the shutdown condition, the system determines whether another function meets the startup condition. If so, the system starts operating in that function. For example, if the domestic hot water function is prioritized by default, after the hot water function meets the shutdown condition, the system determines whether the heating function meets the startup condition. If so, the system starts operating in the heating function until the heating function's shutdown condition is met.

[0175] The heat recovery system utilizes three heat exchangers to work together, flexibly switching operating modes under different operating conditions to maximize waste heat recovery. For example, in cooling mode, the refrigerant absorbs heat in the first water heat exchanger to achieve cooling; in heating mode, the high-temperature refrigerant discharged from compressor 1 releases heat in the first water heat exchanger to achieve heating; in hot water mode, the high-temperature refrigerant discharged from compressor 1 is used to heat domestic water in the second water heat exchanger, improving the efficiency of hot water supply; in combined operating modes (cooling + hot water / heating + hot water), the recovered refrigerant heat is used to heat domestic hot water / heating, achieving cascaded energy utilization and improving the energy efficiency of the heat recovery system.

[0176] In the preferred embodiment, the heat recovery system operates in the five modes mentioned above. To achieve more accurate and reliable switching between different operating modes, compressor 1 is connected to the three heat exchangers via two four-way valves. Specifically, the D end of the first four-way valve 13 is connected to the exhaust side of 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 intake side of 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 intake side of compressor 1.

[0177] After adopting the above-mentioned frequency control method, the heat recovery system, in the normal mode with the participation of the outdoor heat exchanger, detects the changes in the system load in real time and coordinates the adjustment of the frequencies of the compressor and fan to quickly adapt to different working conditions and user needs, so as to achieve efficient operation of the heat recovery system; in the heat recovery mode with the participation of the outdoor heat exchanger, the system heat recovery efficiency changes are detected in real time, and the fan frequency is adjusted first, and then the compressor frequency 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 "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof. The order of execution of actions, steps, etc. in the devices and methods shown in the specification and the drawings can be implemented in any order as long as there is no special explicit limitation on the order and as long as the output of the previous processing is not used in the subsequent processing. Similar sequential terms used for the convenience of description do not mean that they must be implemented in such an order.

[0179] Techniques, methods, and apparatus known to those of ordinary skill in the relevant art may not be discussed in detail, but, where appropriate, such techniques, methods, and apparatus should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following figures, and therefore, once an item is defined in one figure, it does not need to be further discussed in subsequent figures.

[0180] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A frequency control method for a heat recovery system, wherein the heat recovery system comprises a compressor, two water heat exchangers, and an outdoor heat exchanger driven by a fan for heat exchange; characterized in that: The frequency control method comprises: Obtaining the working status 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, the actual load parameters of the heat recovery system are obtained and the current heat load demand L is calculated; in the optimization phase, the target optimization frequency is determined based on the current heat load demand L, the performance parameters of the compressor, and the performance parameters of the fan, and the compressor and the fan are adjusted; in the fine-tuning phase, the frequency of the compressor and the fan are dynamically ramped according to the range of the current heat load demand L; When the compressor is connected to the outdoor heat exchanger and the two water heat exchangers to form a refrigerant circulation loop, the current heat recovery efficiency η of the heat recovery system is obtained; in the fan adjustment stage, the current heat recovery efficiency η and the target heat recovery efficiency η are used. target Determine the target air volume Q target And adjust the fan; in the compressor adjustment stage, re-acquire 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 regulating the compressor.

2. The frequency control method according to claim 1, wherein: 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 operating frequency f of the compressor 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 optimal fan 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 optimal frequency f of the fan fan_opt .

3. The frequency control method according to claim 1, wherein: In the optimization stage, after determining the target optimization frequency based on 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 frequency of the compressor is adjusted using a PID control algorithm.

4. The frequency control method according to claim 1, wherein: Performing dynamic ramp adjustment on the frequency of the compressor and the frequency of the fan according to the interval in which the current heat load demand L is located includes: When L<L Low When, according to f fan =f fan_base -kf×( L base -L) reduce the frequency of the fan, according to f compressor =f compressor_base -kc×( L base -L) reducing the frequency of the compressor; When L Low ≤L≤L high When L<L base , then according to f fan =f fan_base -kf×( L base -L) reduce the frequency of the fan, according to f compressor =f compressor_base -kc×( L base -L) reduce the frequency of the compressor, if L>L base , then according to f compressor =f compressor_base +kc×(L-L base ) Increase the frequency of the compressor according to f fan =f fan_base +kf×(L-L base ) increasing the frequency of the fan; When L>L high When, according to f compressor =f compressor_base +kc×(L-L base ) Increase the frequency of the compressor according to f fan =f fan_base +kf×(L-L base ) increasing the frequency of the fan; The compressor and the fan are dynamically ramped until the 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 base frequency, kf is the fan frequency adjustment coefficient, L base is the base load demand.

5. The frequency control method according to claim 1, wherein: During the fine-tuning stage, the frequency of the compressor and the frequency of the fan are dynamically ramped, and the difference between the frequency of the compressor and the frequency of the fan is maintained within a set range.

6. The frequency control method according to claim 1, wherein: 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: According to the current heat recovery efficiency η and the target heat recovery efficiency η target Determine the target air volume Q target ; Calculate the target heat recovery fan frequency f fan =f base_target +kf×( Q target -Q current ); The fan is dynamically ramped until the target heat recovery fan frequency f is reached. fan ; Among them, f base_target The target air volume Q target Corresponding reference fan frequency, Q current is the current air volume, and kf is the fan frequency adjustment coefficient.

7. The frequency control method according to claim 1, wherein: Determine the target heat recovery compressor frequency f based on the heat recovery efficiency deviation compressor_target And regulating the compressor includes: Calculate the target heat recovery compressor frequency f compressor_target =f compressor_current +kc×(η target -η); Dynamically ramp 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.

8. The frequency control method according to any one of claims 1 to 7, characterized in that: The frequency control method further includes: After cooperatively adjusting the frequency of the compressor and the frequency of the fan according to the heat load demand, or adjusting the frequency of the fan and the frequency of the compressor in sequence according to the heat recovery efficiency, the current frequency f of the compressor is detected. compressor ; If the current frequency f compressor Below the set threshold f 喘振阈值 , then increase the frequency of the fan.

9. The frequency control method according to any one of claims 1 to 7, characterized in that: The frequency control method further includes: After cooperatively adjusting the frequency of the compressor and the frequency of the fan according to the heat load demand, or adjusting the frequency of the fan and the frequency of the compressor in sequence according to the heat recovery efficiency, the exhaust temperature T of the compressor is detected. exhaust and / or 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 suction pressure P inlet Below the set minimum value P min , then reduce the frequency of the fan.

10. Heat recovery system, including: 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 described in any one of claims 1 to 9.

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