阅读说明：本技术 内循环叠加热泵系统、控制方法及热泵烘干机 (Internal circulation superposition heat pump system, control method and heat pump dryer ) 是由 刘华 卓明胜 张龙爱 谷月明 胡乾龙 何建发 于 2019-11-25 设计创作，主要内容包括：本发明公开了一种内循环叠加热泵系统、控制方法及热泵烘干机。所述内循环叠加热泵系统包括串联的多级压缩循环,上一级压缩循环的节流阀与蒸发器之间设有分流器,所述分流器与下一级压缩循环的节流阀连通,上一级压缩循环中的蒸发器作为下一级压缩循环的冷凝器,上一级压缩循环中的四通换向阀与压缩机吸气端之间设有三通汇合阀,所述三通汇合阀与下一级压缩循环的四通换向阀连通。本发明提出的内循环叠加热泵系统及控制方法应用于热泵烘干机,不仅满足了烘干机持续高出风温度的需求,而且提高了热泵烘干机的使用可靠性和节能性。(The invention discloses an internal circulation superposition heat pump system, a control method and a heat pump dryer. The internal circulation superposition heat pump system comprises a plurality of stages of compression cycles which are connected in series, a flow divider is arranged between a throttling valve and an evaporator of the previous stage of compression cycle, the flow divider is communicated with a throttling valve of the next stage of compression cycle, the evaporator of the previous stage of compression cycle is used as a condenser of the next stage of compression cycle, a three-way converging valve is arranged between a four-way reversing valve of the previous stage of compression cycle and a suction end of a compressor, and the three-way converging valve is communicated with the four-way reversing valve of the next stage of compression cycle. The internal circulation superposition heat pump system and the control method provided by the invention are applied to the heat pump dryer, not only can the requirement of the dryer on the continuous high air outlet temperature be met, but also the use reliability and the energy saving performance of the heat pump dryer are improved.)

1. The internal circulation superposition heat pump system comprises a plurality of stages of compression cycles which are connected in series, and is characterized in that a flow divider is arranged between a throttling valve and an evaporator of the previous stage of compression cycle, the flow divider is communicated with a throttling valve of the next stage of compression cycle, the evaporator of the previous stage of compression cycle is used as a condenser of the next stage of compression cycle, a three-way converging valve is arranged between a four-way reversing valve of the previous stage of compression cycle and a suction end of a compressor, and the three-way converging valve is communicated with the four-way reversing valve of the next stage of compression cycle.

2. The system of claim 1, comprising a three-stage compression cycle in series, wherein a two-stage flow divider is used to correspondingly divide the refrigerant in the first stage of compression cycle.

3. The internal circulation summation system of claim 2 wherein check valves are provided between the four-way reversing valve and the three-way junction valve in the first and second stages of the compression cycle.

4. The system of claim 1, wherein the refrigerant in the multi-stage cycle is carbon dioxide.

5. A control method of an internal circulation superposition heat pump system is characterized in that compression cycles of all stages are synchronously controlled, flow distribution coefficients of all stages of shunts are calculated according to target exhaust superheat, exhaust superheat of all stages of compressors and intake superheat of throttle valves, and the opening of all stages of shunts is adjusted according to the flow distribution coefficients.

6. The control method of claim 5, wherein the opening of the primary splitter is calculated as V = α (V) for a compression cycle having three stages connected in series₁+ Toam1/ Toam2）；

Wherein α is the flow distribution coefficient of the primary splitter, V₁Is the initial opening, Toam1 is the superheat of the first stage throttle, and Toam2 is the superheat of the second stage throttle.

7. The control method of claim 6, wherein the flow distribution coefficient α of the primary splitter is calculated as:

in the formula, 0-t₀For the buffer period, Δ To1 is the difference between the target exhaust superheat and the superheat of the first-stage throttle valve, and Δ To2 is the difference between the target exhaust superheat and the superheat of the second-stage throttle valve; t1 is the data recovery period corresponding to the first and second level systems.

8. The control method of claim 5, wherein the opening of the two-stage splitter is calculated as V = β (V2 + Toam 2/Toam 3) for a compression cycle of three stages in series;

wherein β is the flow distribution coefficient of the two-stage splitter, V₂Is the initial opening, Toam2 is the superheat of the second stage throttle, and Toam3 is the superheat of the third stage throttle.

9. The control method of claim 8, wherein the flow distribution coefficient of the secondary flow splitter

in the formula, 0-t₀For the buffer period, Δ To2 is the difference between the target exhaust gas superheat and the superheat of the second-stage throttle valve, and Δ To3 is the difference between the target exhaust gas superheat and the superheat of the third-stage throttle valve; t2 is the data recovery period corresponding to the second and third stage systems.

10. A dryer characterized by using the control method of an internal circulation superposition heat pump system according to any one of claims 5 to 8.

Technical Field

The invention relates to the technical field of air conditioners, in particular to an internal circulation superposition heat pump system, a control method and a heat pump dryer.

Background

The heat pump dryer system is divided into three types of low temperature, medium temperature and high temperature, wherein the high temperature requires the air outlet temperature to reach 80-90 ℃, and the ultrahigh air outlet requires extremely high condensation temperature and sufficient compression ratio. The existing scheme mostly takes a cascade system as a main part and adopts a plurality of refrigerant systems to realize the purpose by superposition.

The problems of complex system and complex control exist in the adoption of a cascade system, the mechanical superposition of multiple systems can cause extremely high control delay between a demand end and an output end, and the control delay can be amplified by energy redundancy loss, random factors and human error, so that the operation evaluation index of a unit is reduced. On the other hand, the overlapping system also causes the development, manufacturing and use costs of the whole machine to increase sharply, and the evaluation of the user on the product is seriously influenced.

In the current heat pump market, a carbon dioxide technology is gradually developed, the excellent transcritical heat exchange property of a carbon dioxide refrigerant can provide an ultrahigh heat pump use value while reducing the power consumption of the whole machine, and the problem that the ultrahigh compression ratio cannot be applied can be solved if the scheme is applied to heat pump drying. Specifically, the temperature above and below the critical point floats, the ultrahigh air outlet temperature and the lower heat dissipation end circulation required by the actual dryer can enlarge the temperature floating range, and severe pressure is brought to the throttling section, namely, most of the current accessories and system schemes cannot achieve the purpose.

Disclosure of Invention

The invention provides an internal circulation superposition heat pump system, a control method and a heat pump dryer, which are used for solving the problems of throttling load caused by overhigh pressure ratio and continuous operation of high pressure load caused by overhigh air outlet temperature when a carbon dioxide system is applied to the heat pump dryer.

The invention provides an internal circulation superposition heat pump system, a control method and a dryer, which comprise a plurality of stages of compression cycles connected in series, wherein a flow divider is arranged between a throttling valve of a first stage of compression cycle and an evaporator, the flow divider is communicated with a throttling valve of a next stage of compression cycle, the evaporator in the previous stage of compression cycle is used as a condenser of the next stage of compression cycle, a three-way converging valve is arranged between a four-way reversing valve in the previous stage of compression cycle and an air suction end of a compressor, and the three-way converging valve is communicated with the four-way reversing valve of the next stage of compression cycle.

In one embodiment, the internal circulation superposition heat pump system comprises three stages of compression cycles connected in series, and two stages of flow dividers are adopted to correspondingly divide the refrigerant in the first stage of compression cycle.

Preferably, check valves are provided between the four-way reversing valve and the three-way converging valve in the first and second compression cycles.

Preferably, the refrigerant in the multistage cycle is carbon dioxide.

The invention also provides a control method of the internal circulation superposition system, wherein each stage of compression circulation is synchronously controlled, the flow distribution coefficient of each stage of flow divider is calculated according to the target exhaust superheat degree, the exhaust superheat degree of each stage of compressor and the intake superheat degree of the throttle valve, and the opening degree of each stage of flow divider is adjusted according to the flow distribution coefficient.

Aiming at the compression cycle of three-stage series connection, the opening degree of the first-stage flow divider is calculated according to the following formula:

V=α*（V₁+ Toam1/ Toam2）；

wherein α is the flow distribution coefficient of the primary splitter, V₁Is the initial opening, Toam1 is the superheat of the first stage throttle, and Toam2 is the superheat of the second stage throttle.

The flow distribution coefficient α of the primary splitter is calculated as follows:

in the formula, 0-t₀For the buffer period, Δ To1 is the difference between the target exhaust superheat and the superheat of the first stage throttle valve, and Δ To2 is the target exhaust superheat and the superheat of the second stage throttle valveA difference in degrees; t1 is the data recovery period corresponding to the first and second level systems.

The opening degree of the secondary splitter is calculated by the formula V = β (V2 + Toam 2/Toam 3);

wherein β is the flow distribution coefficient of the two-stage splitter, V₂Is the initial opening, Toam2 is the superheat of the second stage throttle, and Toam3 is the superheat of the third stage throttle.

Flow distribution coefficient of secondary flow divider

Calculated as follows:

in the formula, 0-t₀For the buffer period, Δ To2 is the difference between the target exhaust gas superheat and the superheat of the second-stage throttle valve, and Δ To3 is the difference between the target exhaust gas superheat and the superheat of the third-stage throttle valve; t2 is the data recovery period corresponding to the second and third stage systems.

The invention also provides a heat pump dryer which uses the internal circulation superposition heat pump system and a control method thereof.

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

1. the multistage compressor is arranged to operate and compress independently, so that the requirement of the dryer for continuously increasing the air outlet temperature is met;

2. by designing an internal circulation superposition system, operating according to actual operating conditions, throttling and reducing pressure in a gradient manner, and distributing shunt flow to realize high-load transcritical operation of carbon dioxide;

3. a corresponding control system is designed, the pressure conjunction operation of a multi-stage system is coordinated, and the energy saving performance of the whole machine is improved;

4. the system is coordinated again from the general direction, so that the system adapts to the characteristics of a carbon dioxide system, and the use reliability and the energy-saving performance of the heat pump dryer are improved.

Drawings

Fig. 1 is a schematic diagram of an internal circulation superimposed heat pump system according to the present invention;

fig. 2 is a pressure-enthalpy diagram of the internal circulation stacking system provided by the invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in detail with reference to the accompanying drawings and examples. It should be understood that the following specific examples are only for illustrating the present invention and are not to be construed as limiting the present invention.

The invention aims to provide a carbon dioxide transcritical system scheme for a heat pump dryer.

The refrigerant of the internal circulation superposition heat pump system provided by the invention adopts carbon dioxide. In general, the heating operation of the refrigerant (R410A, R32, etc.) is performed in a subcritical state, i.e., a state below the top of the saturation line, but such a circulation system is in a situation where the high pressure is insufficient when the circulation system needs to perform heating output at ultra-high temperature. But CO₂The system does not need, the temperature of the critical point of the system is low, and the state parameter of the system can easily go above the critical point under the compression of the compressor, namely CO₂Excellent transcritical properties.

In the embodiment shown in fig. 1, the internal circulation superimposed heat pump system includes three stages of compression cycles connected in series, a flow divider is used to correspondingly divide a main refrigerant flow, and throttling, evaporating and compressing processes are respectively performed in each stage of compression cycle. Through three-layer stage circulation, the temperature of the carbon dioxide can be directly increased to the required temperature, and meanwhile, the refrigerant is reduced to a two-phase area by adopting multi-stage flow division and throttling depressurization, so that the real transcritical operation of a carbon dioxide system is realized.

As shown in fig. 1, the first stage compression cycle includes a first-stage compressor 1, a four-way reversing valve 2, a condenser 3, a first-stage throttle valve 4, and a first-stage evaporator 6. The second stage compression cycle includes a second stage compressor 13, a four-way reversing valve 2, a first stage evaporator 6, a second stage throttle valve 8 and a second stage evaporator 10. The third stage compression cycle includes a three-stage compressor 14, a four-way reversing valve 2, a two-stage evaporator 10, a three-stage throttle valve 11, and a three-stage evaporator 12.

A primary flow divider 5 is arranged between the throttling valve 4 of the first stage compression cycle and the primary evaporator 6, and the primary flow divider is communicated with a throttling valve 8 of the second stage compression cycle. An evaporator 6 in the first-stage compression cycle is used as a condenser of the second-stage compression cycle, a three-way converging valve 7 is arranged between the four-way reversing valve 2 in the first-stage compression cycle and the air suction end of the compressor 1, and the three-way converging valve is communicated with the four-way reversing valve 2 of the lower second-stage compression cycle.

A second-stage flow divider 9 is provided between the throttle valve 8 of the second-stage compression cycle and the second-stage evaporator 10, and communicates with a throttle valve 11 of the third-stage compression cycle. The evaporator 10 in the second-stage compression cycle is used as a condenser of the third-stage compression cycle, a three-way converging valve 7 is arranged between the four-way reversing valve 2 in the second-stage compression cycle and the suction end of the compressor 13, and the three-way converging valve is communicated with the four-way reversing valve 2 in the third-stage compression cycle.

In the first-stage and second-stage compression cycles, a check valve is arranged between the four-way reversing valve 2 and the three-way converging valve 7.

During operation, the internal circulation superposition heat pump system independently operates and compresses through the multistage compressor, echelon throttling and pressure reduction are carried out, the shunt flow is distributed to realize high-load transcritical operation of carbon dioxide, the requirement of the dryer for continuous high air outlet temperature is met, meanwhile, the corresponding control system is designed, the multistage system is coordinated in pressure fit operation, and the energy saving performance of the whole machine is improved.

Fig. 2 is a three-level superimposed trans-critical pressure-enthalpy diagram using carbon dioxide as a refrigerant. In the figure, a is a liquid region, b is a two-phase region, and c is a vapor region. According to the pressure enthalpy flow, 1 → 2 is a three-stage compression process, 2 '→ 3 is a two-stage compression process, 3' → 4 is a three-stage compression process, 5 → 6 is a one-stage throttling process, 6 → 7 is a two-stage throttling process, and 7 → 8 is a three-stage throttling process.

The transcritical operation refers to a critical point state of carbon dioxide (the top of a saturation state line in the figure), and the temperature is 31.2 ℃. The first-stage throttling and the second-stage throttling shown in fig. 2 are all gaseous throttling processes, the third-stage throttling is a phase-change throttling process, and the three layers are superposed to realize the phase-change operation of the carbon dioxide system, namely a so-called transcritical carbon dioxide operation system.

The control mode of the internal circulation superposition heat pump system provided by the invention is as follows: and synchronously controlling the compression cycles of all stages, calculating the flow distribution coefficient of each stage of flow divider according to the target exhaust superheat degree, the exhaust superheat degree of each stage of compressor and the intake superheat degree of the throttle valve, and adjusting the opening degree of each stage of flow divider according to the flow distribution coefficient.

Wherein, the first, second and third stage compressors and the corresponding four-way valves and throttle valves adopt the same control action, so the control strategy can be designed to be a synchronous state; the first-stage flow divider and the second-stage flow divider dynamically control the opening degree by detecting overall parameters and working conditions of all stages, so that the optimal state of multi-stage throttling compression is realized.

The specific logic of the primary shunt control strategy is as follows:

monitoring the exhaust temperature To1 of the primary compressor in real time, corresponding To the high pressure P1, and calculating the exhaust superheat Toa1 of the primary compressor;

monitoring the air inlet temperature Tom1 of the primary throttle valve in real time, corresponding to the pre-throttle pressure Pm1, and calculating the air inlet superheat degree Toam1 of the primary throttle valve;

monitoring the exhaust temperature To2 of the secondary compressor in real time, corresponding To the high pressure P2, and calculating the exhaust superheat Toa2 of the secondary compressor;

monitoring the air inlet temperature Tom2 of the secondary throttle valve in real time, corresponding to the pre-throttle pressure Pm2, and calculating the air inlet superheat degree Toam2 of the secondary throttle valve;

setting the opening degree V of the primary flow dividing valve to be 0-100%, setting V =0% to indicate that all the refrigerant flows into the primary evaporator, setting V =100% to indicate that all the refrigerant flows into the secondary throttle valve, and setting the initial opening degree to be V1;

setting a target exhaust superheat degree Toao, and calculating delta To1= Toao-Toa 1, and delta To2= Toao-Toa 2;

the opening of the primary splitter V = α (V1 + Toam1/Toam 2);

wherein α is the flow distribution coefficient of the primary splitter, and is calculated according to the following formula:

in the formula, 0-t₀For buffering period, buffering period0-t₀And n is the cycle number, and can be adjusted according to the proportional relation of actual parameters. Δ To1 is the difference between the target exhaust gas superheat and the superheat of the first-stage throttle valve, and Δ To2 is the difference between the target exhaust gas superheat and the superheat of the second-stage throttle valve; t1 is the data recovery period corresponding to the first and second level systems; t1 is the data recovery period corresponding to the first and second level systems.

In the above expression, the target adjustment value (exhaust superheat) and the actual throttling capacity expression (superheat before throttling) are mixed to construct, and the flow distribution coefficient is calculated to adjust the opening degree of the flow divider.

The secondary shunt control strategy is as follows:

monitoring the exhaust temperature To2 of the secondary stage compressor in real time, corresponding To the high pressure P2, and calculating the exhaust superheat Toa2 of the secondary stage compressor;

monitoring the air inlet temperature Tom2 of the secondary throttle valve in real time, corresponding to the pre-throttle pressure Pm2, and calculating the air inlet superheat degree Toam2 of the secondary throttle valve;

monitoring the exhaust temperature To3 of the three-stage compressor in real time, corresponding To the high pressure P3, and calculating the exhaust superheat Toa3 of the three-stage compressor;

monitoring the air inlet temperature Tom3 of the three-level throttle valve in real time, corresponding to the pre-throttle pressure Pm3, and calculating the air inlet superheat degree Toam3 of the three-level throttle valve;

the opening V of the secondary flow divider is 50% -100%, V =50% indicates that half of the refrigerant flows into the secondary evaporator, V =100% indicates that all the refrigerant flows into the three-stage throttle valve, and an initial opening V2 is set;

setting a target exhaust superheat degree Toao, and calculating delta To2= Toao-Toa2, and delta To2= Toao-Toa 3;

the opening of the secondary splitter V = β (V2 + Toam 2/Toam 3);

β is the flow distribution coefficient of the opening of the secondary flow divider, and is calculated according to the following formula:

in the formula, 0-t₀For the buffering period, the specific relationship is 0-t₀= m t2, m isThe cycle times can be adjusted according to the proportional relation of the actual parameters. Δ To2 is the difference between the target exhaust gas superheat and the superheat of the upper second-stage throttle valve, and Δ To3 is the difference between the target exhaust gas superheat and the superheat of the third-stage throttle valve; t2 is the data recovery period corresponding to the two-stage and three-stage system.

For systems with more than three compression cycles, the control method is analogized.

The control strategy of the flow divider is summarized through a large amount of experimental data, and the practice proves that the effect is good.

The internal circulation superposition heat pump system provided by the invention is applied to the dryer, not only meets the requirement of the dryer on the continuous high air outlet temperature, but also improves the use reliability and the energy saving performance of the heat pump dryer.

The foregoing is considered as illustrative only of the embodiments of the invention. It should be understood that any modifications, equivalents and changes made within the spirit and framework of the inventive concept are intended to be included within the scope of the present invention.