MULTI-PARALLEL CARBON DIOXIDE HEAT PUMP CONTROL METHOD BASED ON TARGET LOAD CONTROL

Abstract

A multi-parallel carbon dioxide heat pump control method based on target load control, wherein the multi-parallel carbon dioxide heat pump comprises a carbon dioxide circulation loop, a heat source pipeline and a hot water pipeline, and the control method comprises: adjusting the opening degree of an electronic expansion valve (3) according to the temperature of an inlet of the hot water pipeline, the temperature of an outlet of the hot water pipeline, the flow in the hot water pipeline and a target outlet temperature set by a user, such that the steady-state change of system pressure can be realized by adjusting the electronic expansion valve (3) on the basis of the fluctuation of parameters such as user side temperature and flow, thus a target outlet temperature change curve is rapidly and stably converged to a target value, and the outlet temperature can be rapidly stabilized.

Claims

1. A multi-parallel carbon dioxide heat pump control method based on target load control, wherein the multi-parallel carbon dioxide heat pump comprises a carbon dioxide circulation loop, a heat source pipeline and a hot water pipeline, wherein the carbon dioxide circulation loop comprises an evaporator evaporating pipe, a gas-liquid separator, a compressor unit, an oil-gas separator, a cooler condensing pipe and an electronic expansion valve which are arranged in series in the loop sequentially; the evaporator evaporating pipe and the heat source pipeline are arranged together to exchange heat with each other; the hot water pipeline and the cooler condensing pipe are arranged together to exchange heat with each other; the compressor unit comprises a plurality of variable-frequency carbon dioxide compressors arranged in parallel; the hot water pipeline is provided with a water pump and a flow meter, and an inlet end and an outlet end of the hot water pipeline are respectively provided with a temperature sensor, wherein the control method comprises adjusting opening degree of the electronic expansion valve according to inlet temperature of the hot water pipeline, outlet temperature of the hot water pipeline, flow in the hot water pipeline and a target outlet temperature set by a user.

2. The multi-parallel carbon dioxide heat pump control method based on target load control according to claim 1, wherein the control method comprises following steps: 1) obtaining the inlet temperature T.sub.hi of the hot water pipeline, the outlet temperature T.sub.ho of the hot water pipeline and the flow V of the hot water pipeline, and according to the target outlet temperature T.sub.obj set by a user, calculating a target heating capacity Q=1.163*(T.sub.obj−T.sub.hi)*V, and calculating a current heating capacity Q.sub.c=1.163*(T.sub.obj−T.sub.ho)*V; 2) when each carbon dioxide compressor is set to run at 50 Hz, the load of the carbon dioxide heat pump system is 100%, the number of the carbon dioxide compressors provided in the multi-parallel carbon dioxide heat pump is N, and according to the rated working conditions, the rated heating capacity of each carbon dioxide compressor is Q.sub.s, thus a target load L=Q/(N*Q.sub.s)*100%, and an actual load L.sub.r=Q.sub.c/(N*Q.sub.s)*100%; 3) according to the target load L, the actual load L.sub.r, the number n of variable-frequency carbon dioxide compressors, an upper limit F.sub.max and a lower limit F.sub.min of variable frequency of the variable-frequency carbon dioxide compressors, calculating a target opening degree of the electronic expansion valve $K_e=f\left(L,L_r,F_{\max },F_{\min },n\right);$ $f\left(L,L_r,F_{\max },F_{\min },n\right)=A*\frac{.Math.L_r-L.Math.}{L}+B*\frac{\left(F_{\min }-50\right)}{F_{\max }-F_{\min }}+C*\frac{n*\left(F_{\max }-F_{\min }\right)}{50N},$ wherein, A, B and C are respectively specific coefficients, and A, B and C obtained by different equipments are different, and N is total number of the carbon dioxide compressors included in the multi-parallel carbon dioxide heat pump; 4) adjusting the opening degree of the electronic expansion valve according to the target opening degree K.sub.e of the electronic expansion valve.

3. The multi-parallel carbon dioxide heat pump control method based on target load control according to claim 2, comprising: if the target load L≥the actual load L.sub.r and the target opening degree K.sub.e of the electronic expansion valve≥a current opening degree K.sub.c, adjusting the opening degree of the electronic expansion valve to the target opening degree K.sub.e; if the target load L<the actual load L.sub.r and the target opening degree K.sub.e of the electronic expansion valve≥a current opening degree K.sub.c, keeping the current opening degree K.sub.c of the electronic expansion valve unchanged; if the target load L≥the actual load L.sub.r and the target opening degree K.sub.e of the electronic expansion valve<a current opening degree K.sub.c, keeping the current opening degree K.sub.c of the electronic expansion valve unchanged; if the target load L<the actual load L.sub.r and the target opening degree K.sub.e of the electronic expansion valve<the current opening degree K.sub.c, adjusting the opening degree of the electronic expansion valve to the target opening degree K.sub.e.

4. The multi-parallel carbon dioxide heat pump control method based on target load control according to claim 3, comprising: after adjusting the opening degree of the electronic expansion valve, according to the target load L and the actual load L.sub.r, calculating the absolute value of the load difference L.sub.ab=|L−L.sub.r|, and calculating the number of the carbon dioxide compressors that need to be turned on or off N.sub.c=INT(L.sub.ab/100%/N); if the target load L≥the actual load L.sub.r, gradually turning on N.sub.c carbon dioxide compressors, and if the target load L<the actual load L.sub.r, gradually turning off N.sub.c carbon dioxide compressors.

5. The multi-parallel carbon dioxide heat pump control method based on target load control according to claim 4, wherein, when the N.sub.c carbon dioxide compressors need to be gradually turned on, the time interval for turning on each carbon dioxide compressor is 20 s; each time one carbon dioxide compressor is turned on, and it starts from the one with the shortest cumulative running time among the non-operating carbon dioxide compressors; when the N.sub.c carbon dioxide compressors need to be gradually turned off, the time interval for turning off each carbon dioxide compressor is 5 s; each time one carbon dioxide compressor is turned off, and it starts from the one with the longest cumulative running time among the operating carbon dioxide compressors.

6. The multi-parallel carbon dioxide heat pump control method based on target load control according to claim 4, comprising: after turning on or off the N.sub.c carbon dioxide compressors, recalculating the actual load L.sub.r, and the absolute value of the load difference L.sub.ab=|L−L.sub.r| between the actual load and the target load: if L.sub.ab≥100%/N, recalculating the number N.sub.c of the carbon dioxide compressors that need to be turned on or off, and turning on or off the carbon dioxide compressors; if L.sub.ab<100%/N and L<L.sub.r, adjusting the one with the longest running time among the variable-frequency carbon dioxide compressors in operation to reduce its working frequency, where its working frequency can be as low as F.sub.min until L=L.sub.r; if L.sub.ab<100%/N and L≥L.sub.r, adjusting the one with the shortest running time among the variable-frequency carbon dioxide compressors in operation to increase its working frequency, where its working frequency can be as high as F.sub.max until L=L.sub.r.

7. The multi-parallel carbon dioxide heat pump control method based on target load control according to claim 1, wherein an inlet and an outlet of each of the carbon dioxide compressors are respectively provided with a temperature sensor.

8. The multi-parallel carbon dioxide heat pump control method based on target load control according to claim 1, wherein a pressure sensor is provided between the gas-liquid separator and the compressor unit.

9. The multi-parallel carbon dioxide heat pump control method based on target load control according to claim 1, wherein the oil-gas separator is provided with a gas-liquid inlet connected to the outlets of the carbon dioxide compressors, a gas outlet connected to the inlets of the carbon dioxide compressors, and a liquid outlet connected to the cooler condensing pipe.

10. The multi-parallel carbon dioxide heat pump control method based on target load control according to claim 9, wherein a temperature sensor and a pressure sensor are provided between the compressor unit and the gas-liquid inlet of the oil-gas separator.

11. The multi-parallel carbon dioxide heat pump control method based on target load control according to claim 1, wherein the oil-gas separator is provided with a gas-liquid inlet connected to the outlets of the carbon dioxide compressors, a gas outlet connected to the inlets of the carbon dioxide compressors, and a liquid outlet connected to the cooler condensing pipe; the inlet and the outlet of each of the carbon dioxide compressors are respectively provided with a temperature sensor; a pressure sensor is provided between the gas-liquid separator and the compressor unit; the control method comprises following steps: 1) obtaining the inlet temperature T.sub.hi of the hot water pipeline, the outlet temperature T.sub.ho of the hot water pipeline and the flow V of the hot water pipeline, and according to the target outlet temperature T.sub.obj set by a user, calculating a target heating capacity Q=1.163*(T.sub.obj−T.sub.hi)*V, and calculating a current heating capacity Q.sub.c=1.163*(T.sub.obj−T.sub.ho)*V; 2) when each carbon dioxide compressor is set to run at 50 Hz, the load of the carbon dioxide heat pump system is 100%, the number of the carbon dioxide compressors provided in the multi-parallel carbon dioxide heat pump is N, and according to the rated working conditions, the rated heating capacity of each carbon dioxide compressor is Q.sub.s, thus a target load L=Q/(N*Q.sub.s)*100%, and an actual load L.sub.r=Q.sub.c/(N*Q.sub.s)*100%; 3) according to the target load L, the actual load L.sub.r, the number n of variable-frequency carbon dioxide compressors, an upper limit F.sub.max and a lower limit F.sub.min of variable frequency of the variable-frequency carbon dioxide compressors, calculating a target opening degree of the electronic expansion valve $K_e=f\left(L,L_r,F_{\max },F_{\min },n\right);$ $f\left(L,L_r,F_{\max },F_{\min },n\right)=A*\frac{.Math.L_r-L.Math.}{L}+B*\frac{\left(F_{\min }-50\right)}{F_{\max }-F_{\min }}+C*\frac{n*\left(F_{\max }-F_{\min }\right)}{50N},$ wherein, A, B and C are respectively specific coefficients, and A, B and C obtained by different equipments are different, and N is total number of the carbon dioxide compressors provided in the multi-parallel carbon dioxide heat pump; 4) adjusting the opening degree of the electronic expansion valve according to the target opening degree K.sub.e of the electronic expansion valve; if the target load L≥the actual load L.sub.r and the target opening degree K.sub.e of the electronic expansion valve≥a current opening degree K.sub.c, adjusting the opening degree of the electronic expansion valve to the target opening degree K.sub.e; if the target load L<the actual load L.sub.r and the target opening degree K.sub.e of the electronic expansion valve≥a current opening degree K.sub.c, keeping the current opening degree K.sub.c of the electronic expansion valve unchanged; if the target load L≥the actual load L.sub.r and the target opening degree K.sub.e of the electronic expansion valve <a current opening degree K.sub.c, keeping the current opening degree & of the electronic expansion valve unchanged; if the target load L<the actual load L.sub.r and the target opening degree K.sub.e of the electronic expansion valve <a current opening degree K.sub.c, adjusting the opening degree of the electronic expansion valve to the target opening degree K.sub.e; 5) after adjusting the opening degree of the electronic expansion valve, according to the target load L and the actual load L.sub.r, calculating the absolute value of the load difference L.sub.ab=|L−L.sub.r|, and calculating the number of the carbon dioxide compressors that need to be turned on or off N.sub.c=INT(L.sub.ab/100%/N); if the target load L≥the actual load L.sub.r, gradually turning on N.sub.c, carbon dioxide compressors, and if the target load L<the actual load L.sub.r, gradually turning off N.sub.c, carbon dioxide compressors; in step 5), when the N.sub.c, carbon dioxide compressors need to be gradually turned on, the time interval for turning on each carbon dioxide compressor is 20 s; each time one carbon dioxide compressor is turned on, and it starts from the one with the shortest cumulative running time among the non-operating carbon dioxide compressors; when the N.sub.c, carbon dioxide compressors need to be gradually turned off, the time interval for turning off each carbon dioxide compressor is 5 s; each time one carbon dioxide compressor is turned off, and it starts from the one with the longest cumulative running time among the operating carbon dioxide compressors; after turning on or off the N.sub.c carbon dioxide compressors, recalculating the actual load L.sub.r, and the absolute value of the difference L.sub.ab=|L−L.sub.r| between the actual load and the target load: if L.sub.ab≥100%/N, recalculating the number N.sub.c of the carbon dioxide compressors that need to be turned on or off, and turning on or off the carbon dioxide compressors; if L.sub.ab<100%/N and L<L.sub.r, adjusting the one with the longest running time among the variable-frequency carbon dioxide compressors in operation to reduce its working frequency, where its operating frequency can be as low as F.sub.min until L=L.sub.r; if L.sub.ab<100%/N and L≥L.sub.r, adjusting the one with the shortest running time among the variable-frequency carbon dioxide compressors in operation to increase its working frequency, where its operating frequency can be as high as F.sub.max until L=L.sub.r.

Description

BRIEF DESCRIPTION

[0030] FIG. 1 is a principal diagram of a heat pump system of the present disclosure;

[0031] FIG. 2 is a schematic control flow chart of a heat pump system of the present disclosure;

[0032] In the figures, 1—gas-liquid separator; 2—oil-gas separator; 3—electronic expansion valve; 4—carbon dioxide evaporator; 5—gas cooler; 6—carbon dioxide compressor; 7—water pump; 8—flow meter.

DETAILED DESCRIPTION

[0033] In the following, the present disclosure is further described combining with specific embodiments shown in the accompanying drawings.

[0034] Referring to FIG. 1, a multi-parallel carbon dioxide heat pump comprises a carbon dioxide circulation loop, a heat source pipeline and a hot water pipeline.

[0035] The dioxide circulation loop comprises an evaporator evaporating pipe, a gas-liquid separator 1, a compressor unit, an oil-gas separator 2, a cooler condensing pipe and an electronic expansion valve 3 which are arranged in series in the loop sequentially. The evaporator evaporating pipe and the heat source pipeline are arranged together to exchange heat with each other to form a carbon dioxide evaporator 4, and the hot water pipeline and the cooler condensing pipe are arranged together to exchange heat with each other to form a gas cooler 5. The oil-gas separator 2 is provided with a gas-liquid inlet connected to the outlets of carbon dioxide compressors 6, a gas outlet connected to the inlets of the carbon dioxide compressors 6, and a liquid outlet connected to the cooler condensing pipe.

[0036] In this embodiment, the compressor unit comprises N carbon dioxide compressors 6 arranged in parallel, wherein the N carbon dioxide compressors 6 comprises n variable-frequency carbon dioxide compressors 6 arranged in parallel (only 4 compressors are shown in the figure), wherein n≤N, and in other embodiment, the appropriate number of carbon dioxide compressors 6 may be selected as required.

[0037] In this embodiment, the hot water pipeline is provided with a water pump 7 and a flow meter 8, the flow meter 8 is used to obtain the flow V in the hot water pipeline, and an inlet end and an outlet end of the hot water pipeline are respectively provided with a temperature sensor to obtain the temperature T.sub.hi at the inlet of the hot water pipeline and the temperature T.sub.ho at the outlet of the hot water pipeline. The inlet and the outlet of each of the carbon dioxide compressors 6 are respectively provided with a temperature sensor to respectively obtain the temperature at the inlet of each of the carbon dioxide compressors 6 and the temperature at the outlet of each of the carbon dioxide compressors 6. A pressure sensor is provided between the gas-liquid separator 1 and the compressor unit to obtain the pressure between the gas-liquid separator 1 and the compressor unit. A temperature sensor and a pressure sensor are provided between the compressor unit and the gas-liquid inlet of the oil-gas separator 2 to obtain the temperature between the compressor unit and the gas-liquid inlet of the oil-gas separator 2.

[0038] Referring to FIG. 2, a method of controlling the multi-parallel carbon dioxide heat pump described above comprises following steps:

[0039] 1) obtaining the inlet temperature T.sub.hi of the hot water pipeline, the outlet temperature T.sub.ho of the hot water pipeline and the flow V in the hot water pipeline, and according to a target outlet temperature T.sub.obj set by a user, calculating a target heating capacity Q=1.163*(T.sub.obj−T.sub.hi)*V, and calculating a current heating capacity Q.sub.c=1.163*(T.sub.obj−T.sub.ho)*V;

[0040] 2) when each carbon dioxide compressor 6 is set to run at 50 Hz, the load of the carbon dioxide heat pump system is 100%, in this embodiment, the number of the carbon dioxide compressors 6 provided in the multi-parallel carbon dioxide heat pump is N, wherein the N carbon dioxide compressors 6 comprises n variable-frequency carbon dioxide compressors 6, and according to the rated working conditions, the rated heating capacity of each carbon dioxide compressor 6 is Q.sub.s, thus a target load L=Q/(N*Q.sub.s)*100%, and an actual load L.sub.r=Q/(N*Q.sub.s)*100%;

[0041] 3) according to the target load L, the actual load L.sub.r, the number n of variable-frequency carbon dioxide compressors 6, the upper limit F.sub.max and the lower limit F.sub.min of variable frequency of the variable-frequency carbon dioxide compressors 6, calculating a target opening degree of the electronic expansion valve 3:

[00002]$K_e=f\left(L,L_r,F_{\max },F_{\min },n\right)=A*\frac{.Math.L_r-L.Math.}{L}+B*\frac{\left(F_{\min }-50\right)}{F_{\max }-F_{\min }}+C*\frac{n*\left(F_{\max }-F_{\min }\right)}{50N},$

the formula f(L, L.sub.r, F.sub.max, F.sub.min, n) is obtained by experimental data fitting, wherein, A, B and C are respectively specific coefficients, and A, B and C obtained by different equipments are different, and N is the total number of the carbon dioxide compressors included in the multi-parallel carbon dioxide heat pump, and Nn.

[0042] 4) adjusting the opening degree of the electronic expansion valve 3 according to the target opening degree K.sub.e of the electronic expansion valve 3.

[0043] In this embodiment, A=¼, B=½, and C=½,

[0044] Assuming F.sub.max=70, F.sub.min=30, n=4, L.sub.r=60%, and L=80%, K.sub.e can be calculated as 51.3%, and then according to the calculated value, adjusting the opening degree of the electronic expansion valve 3 to 51.3%.

[0045] In the above step 4), the specific adjusting way is: if the target load L≥the actual load L.sub.r and the target opening degree K.sub.e of the electronic expansion valve 3≥the current opening degree K.sub.c, adjusting the opening degree of the electronic expansion valve 3 to the target opening degree K.sub.e;

[0046] if the target load L<the actual load L.sub.r and the target opening degree K.sub.e of the electronic expansion valve 3≥the current opening degree K.sub.c, keeping the current opening degree K.sub.c of the electronic expansion valve 3 unchanged;

[0047] if the target load L≥the actual load L.sub.r and the target opening degree K.sub.e of the electronic expansion valve 3<the current opening degree K.sub.c, keeping the current opening degree K.sub.c of the electronic expansion valve 3 unchanged;

[0048] if the target load L<the actual load L.sub.r and the target opening degree K.sub.e of the electronic expansion valve 3<the current opening degree K.sub.c, adjusting the opening degree of the electronic expansion valve 3 to the target opening degree K.sub.e.

[0049] Due to that this embodiment can realize the steady-state change of system pressure by adjusting the electronic expansion valve 3 on the basis of the fluctuation of parameters such as temperature and flow at the user side, so as to realize a stable adjustment of system energy, to realize a rapid and stable convergence of the target outlet temperature change curve to a target value, and to ensure to rapidly stabilize the outlet temperature.

[0050] In this embodiment, after adjusting the opening degree of the electronic expansion valve 3, according to the target load L and the actual load L.sub.r, calculate the absolute value of the load difference L.sub.ab=|L−L.sub.r|, and calculate the number of the carbon dioxide compressors 6 that need to be turned on or off N.sub.c=INT(L.sub.ab/100%/N); if the target load L≥the actual load L.sub.r, gradually turn on NI, carbon dioxide compressors 6, and if the target load L<the actual load L.sub.r, gradually turn off N.sub.c, carbon dioxide compressors 6. Compared with reducing the frequency, turning off unnecessary compressors can further save energy, thereby improving the working efficiency of the unit.

[0051] The specific method of controlling the carbon dioxide compressors 6 is: when the N.sub.c carbon dioxide compressors 6 need to be gradually turned on, the time interval for turning on each carbon dioxide compressor 6 is 20 s; each time one carbon dioxide compressor 6 is turned on, and it starts from the one with the shortest cumulative running time among the non-operating carbon dioxide compressors 6;

[0052] when the N.sub.c carbon dioxide compressors 6 need to be gradually turned off, the time interval for turning off each carbon dioxide compressor 6 is 5 s; each time one carbon dioxide compressor 6 is turned off, and it starts from the one with the longest cumulative running time among the operating carbon dioxide compressors 6. Setting the interval time can prevent the carbon dioxide compressors 6 from being started or shut down frequently, and can extend the service life of the carbon dioxide compressors 6 to a greater extent.

[0053] In order to further improve the working efficiency, after turning on or off the N.sub.c carbon dioxide compressors 6, recalculate the actual load L.sub.r, and the absolute value of the load difference L.sub.ab=|L−L.sub.r| between the actual load and the target load:

[0054] if L.sub.ab≥100%/N, recalculate the number N.sub.c of the carbon dioxide compressors 6 that need to be turned on or off, and turn on or off the carbon dioxide compressors 6;

[0055] if L.sub.ab<100%/N and L<L.sub.r, adjust the one with the longest running time among the variable-frequency carbon dioxide compressors 6 in operation to reduce its working frequency, where its working frequency can be as low as F.sub.min until L=L.sub.r;

[0056] if L.sub.ab<100%/N and L≥L.sub.r, adjust the one with the shortest running time among the variable-frequency carbon dioxide compressors 6 in operation to increase its working frequency, where its working frequency can be as high as F.sub.max until L=L.sub.r.

[0057] Based on the target load control, this embodiment adjusts the system energy in real time, calculates the deviation between the current load and the target load, and quickly reduces the deviation by loading and unloading of the carbon dioxide compressors 6; when the system deviation is less than the variable-frequency adjustable range, variable-frequency adjustment is performed, after coarse adjustment, fine adjustment is performed to meet the current energy compensation, and finally achieves the target load, to ensure the efficient, safe and stable operation of the unit.

[0058] The embodiments described above are only for illustrating the technical concepts and features of the present disclosure, and are intended to make those skilled in the art being able to understand the present disclosure and thereby implement it, and should not be concluded to limit the protective scope of the present disclosure. Any equivalent variations or modifications according to the spirit of the present disclosure should be covered by the protective scope of the present disclosure.