A temperature control method for a central supply instant water heater

Abstract

The present invention discloses a temperature control method for a central supply rapid water heater, comprising the following steps: S1. The control device preset the target temperature Ts of domestic hot water and initialize the throttle valve and the heating water circulation pump; S2. The control device detects the flow rate Φ(t) of domestic hot water; and determines whether the flow rate Φ(t) reaches α L / min or more; S3. If so, the control device detects the actual temperature T9 of the heating water; and determines whether the difference ΔT between the actual temperature T9 and the target temperature Ts reaches m K or more and whether the flow rate change value ΔΦ reaches β L / min or more; S4. If so, the throttle valve is in the fully open state and the output power P of the heating water circulation pump is calculated by using the relationship P = f(Φ) between the output power P and the flow rate Φ(t); S5. The control device collects the actual temperature T10 of the domestic hot water and adjusts the opening degree of the throttle valve according to the comparison result between the actual temperature T10 and the target temperature Ts. The adjustment speed is improved and large fluctuations in the temperature of domestic hot water are avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of water heaters, and particularly to a temperature control method for a central supply fast water heater. Background Art

[0002] In existing central supply fast water heaters, the maximum hot water output flow rate of a single unit can reach 30 to 40 liters per minute (temperature rise of 35K), and the maximum hot water output flow rate can be further increased by cascading multiple units. It is heated by a plate heat exchanger which has two isolated sides. The primary side is connected to a boiler or one or more other heating devices (such as an air source heat pump, a solar collector, an electric heater, etc.) through a heating water buffer tank, and heating water flows therein; the secondary side is connected to the tap water pipe and the water usage point, and domestic hot water flows therein. Only when the user discharges water from the water usage point, the tap water source connected to the secondary side of the plate heat exchanger will deliver cold tap water to the heat exchanger, which is heated and then flows to the water usage point.

[0003] There is a circulation pump in the primary side circuit of this fast water heater. It drives the heat transfer medium (heating water) to circulate in the primary side circuit. Generally, a PI or PID controller is used to adjust the water temperature, but before the controller intervenes, the temperature of the domestic hot water must first deviate from the preset temperature. Due to the inertia of the thermal system, this results in a relatively long compensation process, especially when the tap water flow rate suddenly changes significantly, and the temperature of the domestic hot water will fluctuate greatly.

[0004] In summary, there is a need to design a temperature control method for a central supply fast water heater to solve the above problems in the prior art. Summary of the Invention

[0005] The present invention provides a temperature control method for a central supply fast water heater, which solves the problem of large temperature fluctuations of domestic hot water when its flow rate increases in the prior art.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A temperature control method for a central supply fast water heater includes the following steps:

[0008] S1. The control device presets the target temperature Ts of the domestic hot water and initializes the throttle valve and the heating water circulation pump;

[0009] S2. The control device detects the flow rate Φ(t) of the domestic hot water; and determines whether the flow rate Φ(t) reaches α L / min or more;

[0010] S3. If so, the control device detects the actual temperature T9 of the heating water; and determines whether the difference ΔT between the actual temperature T9 and the target temperature Ts reaches mK or more and whether the flow rate change value ΔΦ reaches β L / min or more;

[0011] S4. If so, the throttle valve is in the fully open state, and the output power P of the heating water circulation pump is calculated using the relationship P = f(Φ) between the output power P and the flow rate Φ(t);

[0012] wherein, the relationship is P = eΦ 2 + fΦ;

[0013] S5. The control device collects the actual temperature T10 of the domestic hot water and adjusts the opening of the throttle valve according to the comparison result between the actual temperature T10 and the target temperature Ts.

[0014] In some embodiments of the present invention, the step S2 specifically includes the following steps:

[0015] S21. The control device detects the flow rate Φ(t) of the domestic hot water and determines whether the flow rate Φ(t) reaches α L / min or more. If not, it returns to step S1. If so, the control device continues to determine whether the flow rate Φ(t) reaches α L / min or more for the first time;

[0016] S22. If the flow rate Φ(t) reaches α L / min or more for the first time, the opening of the throttle valve is adjusted to 50%, and the output power P of the heating water circulation pump is controlled to 100%, and then the actual temperature T9 of the heating water is detected;

[0017] S23. If the flow rate Φ(t) does not reach α L / min or more for the first time, the control device directly detects the actual temperature T9 of the heating water.

[0018] In some embodiments of the present invention, the step S3 specifically includes the following steps:

[0019] S31. The control device determines whether the difference ΔT between the actual temperature T9 and the target temperature Ts reaches mK or more. If not, it returns to step S2 after passing through the protection program;

[0020] S32. If the difference ΔT reaches mK or more, the control device continues to determine whether the flow rate change value ΔΦ reaches β L / min or more. If so, the throttle valve is in the fully open state and then it continues to determine whether the working condition coincides with any node of the grid. Otherwise, it directly determines whether the working condition coincides with any node of the grid; wherein, the calculation formula for the flow rate change value ΔΦ is: ΔΦ = Φ(t + 1) - Φ(t);

[0021] S33. If the working conditions coincide with any node of the grid, directly call the relational expression P = f(Φ) corresponding to the node to calculate the output power P of the heating water circulation pump; otherwise, fit the relational expression P = f(Φ) between the output power P and the flow rate Φ(t), and then calculate the output power P of the heating water circulation pump.

[0022] In some embodiments of the present invention, the working conditions include the target temperature Ts and the actual temperature T9 of the heating water; the control device is used to construct a grid according to the working conditions, the x-axis of the grid represents the target temperature Ts, and the y-axis represents the difference ΔT between the actual temperature T9 of the heating water and the target temperature Ts; a corresponding relational expression P = f(Φ) is stored on each node of the grid.

[0023] In some embodiments of the present invention, in step S33, if the working conditions do not coincide with the node, that is, when the working conditions fall within the surface area of the grid, use the nodes surrounding the surface area to form a boundary surface to calculate the relational expression P = f(Φ) under the current working conditions.

[0024] In some embodiments of the present invention, the boundary surface is analytically determined by the function w = auv + bu + cv + d; where u represents the target temperature Ts of the domestic hot water, v represents the difference ΔT between the actual temperature T9 of the heating water and Ts, and w represents the output power P of the heating water circulation pump corresponding to a certain flow rate Φ of the domestic hot water.

[0025] In some embodiments of the present invention, the throttle valve is controlled by a stepper motor, and the stepper motor adopts incremental proportional regulation.

[0026] In some embodiments of the present invention, the calculation formula for the target position Sd of the stepper motor is:

[0027] Sd = Sc + ΔS;

[0028] Where, Sc is the current position of the stepper motor, ΔS is the number of steps that the stepper motor needs to increase or decrease, and the expression of ΔS is:

[0029] ΔS = Kp×ΔT DHW = Kp×(T10 - Ts);

[0030] Kp is a constant; ΔT DHW is a differential signal, ΔT DHW = T10 - Ts, and Ts is the target temperature.

[0031] In some embodiments of the present invention, the protection program includes:

[0032] Judge whether the running time of the heating water circulation pump reaches more than t1 minutes. If so, after closing the heating water circulation pump and the throttle valve, lock the device for t2 minutes and then return to step S2; otherwise, directly return to step S2.

[0033] In some embodiments of the present invention, after initialization in step S1, the opening degree of the throttle valve is 0%, and the output power P of the heating water circulation pump is 0%.

[0034] The technical solution of the present invention has the following technical effects compared with the prior art:

[0035] By adjusting the output power P of the heating water circulation pump, first compensate the largest disturbance variable - the flow rate change of domestic hot water as fast as possible to ensure that the actual temperature of domestic hot water on the secondary side does not deviate significantly from the target temperature. Secondly, by finely adjusting the opening degree of the heating water throttle valve, make the actual temperature of domestic hot water reach the target temperature and remain constant. Different from the traditional control method, there is no need to first have a temperature deviation and then trigger the compensation process, that is, adjust the circulation flow rate of heating water. This temperature control method can adjust the circulation flow rate of primary-side heating water to an appropriate range before the temperature of domestic hot water changes. Brief Description of the Drawings

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0037] Figure 1 It is the working flow chart of the temperature control method.

[0038] Figure 2 It is the system structure schematic diagram of the central supply fast water heater.

[0039] Figure 3 It is the schematic diagram of the grid.

[0040] Figure 4 For Figure 3 The schematic diagram of the relationship between the output power P and the flow rate Φ(t) stored in any node in

[0041] Figure 5 It is the schematic diagram of the grid when the working conditions are within the region.

[0042] Figure 6 It is the structure schematic diagram of the throttle valve.

[0043] Figure 7 It is the control flow chart of the stepping motor.

[0044] Figure 8 It is the actual regulation effect diagram of the domestic hot water temperature.

[0045] Reference numerals: 1 - plate heat exchanger; 2 - control device; 3 - heating water buffer tank; 4 - boiler or other heating equipment; 5a, 5b, 5c - water using points; 6 - heating water circulation pump; 7 - throttle valve; 8 - Hall flowmeter; 9 - temperature measurement point of the actual temperature T9 of the primary side heating water; 10 - temperature measurement point of the actual temperature T10 of the secondary side domestic hot water; 11 - domestic hot water circulation pump; 12 - domestic hot water circulation temperature measurement point; 13 - heat loading circulation pump; 14 - safety relief valve; 15 - check valve; 16 - exhaust valve; 17 - ball valve; 18 - tap water source; 19 - primary side circuit; 20 - secondary side circuit; 21 - return water pipeline; 22 - heat loading circuit.

[0046] 43 - valve flap; 44 - valve seat; 45 - valve stem; 46 - fluid inlet; 47 - fluid outlet; 48 - electric actuator (stepping motor); 49 - valve body. Specific embodiments

[0047] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0048] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations. In the description of the above embodiments, specific features, structures, materials, or characteristics can be combined in a suitable manner in any one or more embodiments or examples.

[0049] Embodiment 1: First, the temperature control method of the present invention is applied to a central supply fast water heater. Its maximum hot water output flow per single unit can reach 30 to 40 liters per minute (temperature rise of 35K), and the maximum hot water output flow can be further increased by cascading multiple units. It is heated by a plate heat exchanger which has two isolated sides. The primary side is connected to a boiler or one or more other heating devices (such as an air source heat pump, a solar collector, an electric heater, etc.) through a heating water buffer tank, and the heating water flows therein; the secondary side is connected to the tap water pipe and the water use points, and the domestic hot water flows therein. Only when the user discharges water from the water use point, the cold tap water source connected to the secondary side of the plate heat exchanger will deliver the cold tap water to the heat exchanger, and after being heated, it will flow to the water use point. The secondary side of the plate heat exchanger can also be connected to a loop, and the domestic hot water circulates in the loop under the action of a circulation pump, and one or more pipelines are led out from this loop to the water use points.

[0050] Refer to Figure 2 As shown, the control device 2 includes a program that can implement this temperature control method. This fast water heater includes a plate heat exchanger 1, and its primary side loop 19 and secondary side loop 20. In the primary side loop 19, there is a heating water buffer tank 3, a heating water circulation pump 6 that can accept pulse width modulation, a heating water throttle valve 7 driven by a stepper motor, and a temperature measurement point 9 (located at the inlet of the primary side of the plate heat exchanger). Three pipelines are led out from the secondary side loop 20 to the water use points (5a, 5b, 5c), and in the secondary side loop 20, there is a domestic hot water circulation pump 11, a temperature measurement point 10 (located at the outlet of the secondary side of the plate heat exchanger), and a Hall flowmeter 8 serving as a flow sensor for measuring the actual flow of the domestic hot water. In actual application, the return water pipeline 21 and its related components in the secondary side loop 20 can also be omitted: the domestic hot water circulation pump 11, the domestic hot water circulation temperature measurement point 12, and the one-way check valve 15. A boiler 4 (or one or more other devices capable of generating heat energy) is connected to the heating water buffer tank 3 through a heat loading loop 22, and there is a heat loading circulation pump 13 in the heat loading loop 22. The application of the heating water buffer tank 3 makes multi-source supply possible, for example: solar collectors, air source heat pumps, high calorific value boilers, etc. Geothermal energy and remote heating can also be selected as heat sources.

[0051] A temperature control method for a central supply fast water heater, including:

[0052] S1. After the device is powered on, the control device 2 preset the target temperature Ts of the domestic hot water and initialize the throttle valve 7 and the heating water circulation pump 6;

[0053] After initialization, the opening degree of the throttle valve 7 is 0%, that is, the throttle valve 7 is fully closed, and the position of the stepping motor is 100%. The output power P of the heating water circulation pump 6 is 0%, that is, the heating water circulation pump 6 stops running.

[0054] S2. The control device 2 detects the flow rate Φ(t) of domestic hot water; and determines whether the flow rate Φ(t) reaches α L / min or more; for example, the value of α is 3; specifically as follows:

[0055] S21. The control device 2 detects the flow rate Φ(t) of domestic hot water and determines whether the flow rate Φ(t) reaches 3 L / min or more. If not, it returns to step S1. If so, the control device 2 continues to determine whether the flow rate Φ(t) reaches 3 L / min or more for the first time;

[0056] S22. If the flow rate Φ(t) reaches 3 L / min or more for the first time, adjust the opening degree of the throttle valve 7 to 50%, that is, the throttle valve 7 is half open, the stepping motor is at 50% position, and control the output power P of the heating water circulation pump 6 to 100% and then detect the actual temperature T9 of the heating water;

[0057] S23. If the flow rate Φ(t) does not reach 3 L / min or more for the first time, the control device 2 directly detects the actual temperature T9 of the heating water.

[0058] S3. If so, the control device detects the actual temperature T9 of the heating water; and determines whether the difference ΔT between the actual temperature T9 and the target temperature Ts reaches m K or more and whether the flow rate change value ΔΦ reaches β L / min or more; for example: the value of m is 2, the value of β is 1, the specific steps are as follows:

[0059] S31. The control device 2 determines whether the difference ΔT between the actual temperature T9 of the heating water and the target temperature Ts reaches 2 K or more. If not, it returns to step S2 after passing through the protection program;

[0060] Among them, the protection program is to first determine whether the running time of the heating water circulation pump 7 reaches more than t1 minutes, for example, whether it reaches 5 minutes. If so, after closing the heating water circulation pump 6 and the throttle valve 7, lock the device for t2 minutes (for example, 10 minutes) and then return to step S2. Otherwise, directly return to step S2.

[0061] S32. If the difference ΔT reaches 2 K or more, the control device 2 continues to determine whether the flow rate change value ΔΦ reaches 1 L / min or more. If so, the state of the throttle valve 7 is fully open and then continue to determine whether the working condition coincides with any node of the grid. Otherwise, directly determine whether the working condition coincides with any node of the grid; among them, the calculation formula for the flow rate change value ΔΦ is: ΔΦ = Φ(t + 1) - Φ(t);

[0062] S33. If the working conditions coincide with any node of the grid, directly call the relational expression P = f(Φ) corresponding to the node to calculate the output power P of the heating water circulation pump 6; otherwise, fit the relational expression P = f(Φ) between the output power P and the flow rate Φ(t), and then calculate the output power P of the heating water circulation pump 6.

[0063] In some embodiments of the present invention, the working conditions include the target temperature Ts and the actual temperature T9 of the heating water; the control device 2 is used to construct a grid according to the working conditions and refer to Figure 3 As shown, the x-axis of the grid represents the target temperature Ts, and the y-axis represents the difference ΔT between the actual temperature T9 of the heating water and the target temperature Ts; the relational expression P = f(Φ) corresponding to each node of the grid is stored.

[0064] Specifically, in addition to the decisive interference variable - the flow rate change of domestic hot water, another significant interference variable is the temperature of the heating water stored in the heating water buffer tank 3. During the operation of the central supply instantaneous water heater, the actual temperature T9 of the heating water may change slowly, which will also have a certain impact on the stability of the domestic hot water temperature. Therefore, this interference variable must also be compensated. For this reason, in this temperature control method, a two-dimensional grid that can divide the working conditions of the central supply instantaneous water heater in detail is constructed.

[0065] Figure 3 As shown is a schematic diagram of the grid, which divides the working conditions of the central supply instantaneous water heater into several nodes. Among them, the x-axis represents the target temperature Ts of domestic hot water, in degrees Celsius, which can be preset by the user; the y-axis represents the difference ΔT between the actual temperature T9 of the heating water flowing into the plate heat exchanger 1 from the top of the heating water buffer tank 3 and Ts, in Kelvin, which is measured and calculated by the control device 2 in real time. Each node N in the grid i,j is a combination of Ts and ΔT. Each node can be uniquely named by its x-axis coordinate and y-axis coordinate. For example, for node N 45,10 , x = i = 45, y = j = 10, which represents a set of working conditions where the preset target temperature Ts of domestic hot water is 45°C, and the difference ΔT between the actual temperature T9 (55°C) of the heating water and Ts is 10K.

[0066] For the function P = f(Φ) stored in the node, its practical significance is: in order to make the actual temperature T10 of domestic hot water reach and maintain the target temperature Ts, the corresponding relationship between the actual flow rate Φ of domestic hot water and the required actual flow rate Φ HW of the heating water. When all components of the central supply instantaneous water heater have been completely determined, the actual flow rate Φ HWIt is only related to the output power P of the primary-side heating water circulation pump 6. That is to say, by controlling the output power P of the heating water circulation pump 6, the regulation of the primary-side heating water flow rate Φ can be achieved. This is the control variable of this control method. HW The abscissa shown in Figure 4 represents the actual flow rate Φ of domestic hot water, with the unit of liters per minute; the ordinate represents the output power P of the primary-side heating water circulation pump 6, which is expressed as a percentage. The meanings of the 3 points in the figure are as follows: When the actual temperature T9 of the heating water is 55 °C and the actual flow rates Φ of domestic hot water reach 5 L / min, 15 L / min, and 25 L / min respectively, in order to keep the actual temperature T10 of domestic hot water constant at 45 °C, the required output powers P of the primary-side heating water circulation pump 6 are 13%, 43%, and 81% respectively. With these 3 points, a polynomial in the form of P = eΦ 2 + fΦ can be fitted. This polynomial is the function P = f(Φ) = 0.010Φ 2 + 0.876Φ. These 3 points are the 3 fulcrums of this function. According to different differences ΔT, different functions P = f(Φ) can be fitted. For example, when ΔT = 5 K, the function P = 0.017Φ 2 + 1.022Φ; when ΔT = 15 K, the function P = 0.007Φ 2 + 0.748Φ.

[0067] It can be seen from the graph of the function P = f(Φ) that under the same node working conditions, the relationship between the actual flow rate Φ of domestic hot water and the actual flow rate Φ of heating water, HW or rather, the corresponding relationship with the output power P of the primary-side heating water circulation pump 6 is not linear but parabolic. This is because the fast water heater that this temperature control method needs to handle is a non-linear thermal system. When the domestic hot water load increases sharply, a larger flow rate of heating water is required to provide more heat to maintain the target temperature Ts constant. However, at the same time, the residence time of the heating water in the plate heat exchanger 1 also becomes shorter. The heating water flow rate Φ HW must increase at a super-proportional speed to provide sufficient heat.

[0068] S4. If so, the throttle valve 7 is in the fully open state, and at the same time, the output power P of the heating water circulation pump is calculated using the relationship P = f(Φ) between the output power P and the flow rate Φ(t);

[0069] wherein, the said relationship is P = eΦ 2 + fΦ;

[0070] The relationship P = f(Φ) is obtained by measurement and fitting through an experimental device. Specifically, for each node, at least 3 fulcrums need to be measured. ​​

[0071] The cold water temperature is also an interfering variable for a fast water heater. The lower the cold water temperature, the higher the amount of heat required to reach and maintain the target temperature Ts of domestic hot water. The tap water temperature changes slowly throughout the year with the change of seasons. However, at the moment when the user uses domestic hot water each time, the tap water temperature can be regarded as constant, and its impact on the stability of domestic hot water temperature can be ignored under real-time working conditions. For the above reasons, the treatment of the interfering variable of tap water temperature in this control method follows the principle of the most unfavorable situation, that is, when measuring the function fulcrum under the working conditions of each node, the tap water temperature is always maintained at 10°C, which is the lowest temperature of tap water entering the household throughout the year. The function P = f(Φ) measured in this way can calculate the highest heat input.

[0072] During actual operation, the working process of the control device 2 is as follows:

[0073] 1. Receive the flow signal fed by the flow sensor 8, indicating that the user has a hot water demand;

[0074] 2. First, start the primary side heating water circulation pump 6 at the maximum power, and circulate the heating water to the plate heat exchanger 1;

[0075] 3. Measure the actual temperature T9 of the heating water through the primary side temperature measurement point 9;

[0076] 4. Calculate the temperature difference ΔT according to the target temperature Ts of domestic hot water input by the user;

[0077] 5. Find the corresponding node in the grid according to Ts and ΔT;

[0078] 6. Call the relational expression P = f(Φ) stored in the node;

[0079] 7. Measure the actual flow rate Φ(t) of domestic hot water through the secondary side flow sensor 8;

[0080] 8. Substitute Φ(t) into the function P = f(Φ) to find the power P that the primary side heating water circulation pump 6 should output at this time.

[0081] That is to say, under the current working conditions, the primary side heating water circulation pump 6 needs to operate at the power P calculated by the control device 2 to make the actual temperature T10 of domestic hot water reach Ts and remain constant. The above process is continuously and cyclically executed.

[0082] In some embodiments of the present invention, in step S33, if the working conditions do not coincide with the node, that is, when the working conditions fall within the surface area of the grid, the boundary surface formed by the nodes surrounding the surface area is used to calculate the relational expression P = f(Φ) under the current working conditions.

[0083] Specifically, in actual operation, there will also be such a situation where the actual working conditions do not exactly coincide with the nodes in the grid, but appear at any point within the region enclosed by any four nodes. For example, Figure 5 as shown;

[0084] The working conditions appear at a certain point within the region filled with diagonal lines. In this example, this point can be named N 48,13 , which represents the target temperature Ts of domestic hot water preset by the user = 48°C; the difference ΔT between the actual temperature T9 (61°C) of the heating water and Ts = 13K. In this case, it is necessary to jointly determine the corresponding relationship between the output power P of the primary-side heating water circulation pump 6 and the actual flow rate Φ of the secondary-side domestic hot water according to each of the functions stored in the 4 nodes enclosing this region. This will form a boundary surface, and the attributes of this surface will be stored in the node with the smallest grid coordinates among these 4 nodes, such as N 45,10 inside.

[0085] The above boundary surface can be analytically determined by the function w = auv + bu + cv + d; where u represents the target temperature Ts of domestic hot water, v represents the difference ΔT between the actual temperature T9 of the heating water and Ts, and w represents the output power P of the heating water circulation pump corresponding to a certain flow rate Φ of domestic hot water.

[0086] In this example, substituting the relevant parameters of the 4 nodes into the above function, we can get:

[0087] w1-1 = a1×45×10 + b1×45 + c1×10 + d1

[0088] w1-2 = a1×45×15 + b1×45 + c1×15 + d1

[0089] w1-3 = a1×50×10 + b1×50 + c1×10 + d1

[0090] w1-4 = a1×50×15 + b1×50 + c1×15 + d1

[0091] w1-1, w1-2, w1-3, w1-4 represent the 4 output powers of the heating water circulation pump 6 corresponding to the same domestic hot water flow rate Φ1 in the 4 nodes in the example, and they are known quantities. Combining these 4 equations into a linear equation system, the unknowns are the coefficients a, b, c, d in the original function. Using the Gauss-Jordan elimination method, this equation system can be solved to obtain a set of coefficients a1, b1, c1, d1.

[0092] The function P = f(Φ) stored in each node of the grid is determined by at least 3 pivot points. Therefore, it is also necessary to list the corresponding linear equations for the other two domestic hot water flow rates Φ2 and Φ3:

[0093] Domestic hot water flow rate Φ2:

[0094] w2-1 = a2×45×10 + b2×45 + c2×10 + d2

[0095] w2-2 = a2×45×15 + b2×45 + c2×15 + d2

[0096] w2-3 = a2×50×10 + b2×50 + c2×10 + d2

[0097] w2-4 = a2×50×15 + b2×50 + c2×15 + d2

[0098] Domestic hot water flow rate Φ3:

[0099] w3-1 = a3×45×10 + b3×45 + c3×10 + d3

[0100] w3-2 = a3×45×15 + b3×45 + c3×15 + d3

[0101] w3-3 = a3×50×10 + b3×50 + c3×10 + d3

[0102] w3-4 = a3×50×15 + b3×50 + c3×15 + d3

[0103] Solving these two systems of equations in the same way, we can obtain another two sets of coefficients a2, b2, c2, d2 and a3, b3, c3, d3. Substituting the three sets of coefficients obtained back into the original function, we get the system of equations:

[0104] w1 = a1uv + b1u + c1v + d1

[0105] w2 = a2uv + b2u + c2v + d2

[0106] w3 = a3uv + b3u + c3v + d3

[0107] Substitute the working conditions \(u = T_s = 48^{\circ}C\) and \(v=\Delta T = 13K\) represented by a point within the region in the example into this system of equations, and the corresponding three output powers \(P_1\), \(P_2\), and \(P_3\) of the heating water circulation pump 6 can be obtained for the domestic hot water flow rates \(\varPhi_1\), \(\varPhi_2\), and \(\varPhi_3\). In this way, three fulcrums \((P_1,\varPhi_1)\), \((P_2,\varPhi_2)\), and \((P_3,\varPhi_3)\) are found for point N 48,13 and the function \(P = f(\varPhi)\) of point N can be further fitted using these three fulcrums 48,13 .

[0108] To avoid recalculating the boundary surface by the above method each time, the above three sets of coefficients can be assembled in a \(3\times4\) matrix:

[0109]

[0110] and the matrix is stored inside the node with the smallest grid coordinates among the relevant four nodes. In actual operation, the control device 2 can quickly call the appropriate matrix according to the position where the working conditions occur, calculate and fit the function \(P = f(\varPhi)\) using the interpolation method, and then continue to execute steps 7 to 8 of the above work process to complete the power adjustment of the primary side domestic hot water circulation pump 6.

[0111] S5. The control device collects the actual temperature \(T_{10}\) of the domestic hot water and adjusts the opening of the throttle valve according to the comparison result between the actual temperature \(T_{10}\) and the target temperature \(T_s\).

[0112] Under actual working conditions, when the tap water temperature exceeds \(10^{\circ}C\), the problem of excessive input heat on the primary side of the fast water heater will occur, and this temperature control method is handled by the primary side heating water throttle valve 7.

[0113] The heating water throttle valve 7 located on the primary side of the fast water heater is itself a proportional regulating valve, and its internal structure is shown in Figure 6 . When the distance between the valve flap 43 and the valve seat 44 decreases, the resistance to the fluid increases, thereby reducing the fluid flow rate; conversely, when the distance between the valve flap 43 and the valve seat 44 increases, the fluid flow rate will also increase accordingly. In control technology, the control of the heating water throttle valve 7 is essentially the control of the position of the valve flap 43. For this purpose, an electric actuator 48 is connected to the valve stem 45 to drive the valve flap 43 to move up and down horizontally inside the valve body 49. In this temperature control method, a stepping motor is selected as the actuator of the heating water throttle valve 7. It is a DC brushless motor with the characteristics of simple structure, large thrust, and fast adjustment speed. It only takes 2 seconds to continuously travel a full stroke (600 steps), which can effectively shorten the adjustment time of the heating water throttle valve 7.

[0114] In some embodiments of the present invention, the throttle valve is controlled by a stepper motor, and the stepper motor adopts incremental proportional regulation. Its control process is as follows: Figure 7 as shown

[0115] The control device 2 continuously records the current position Sc of the stepper motor 48. It and the preset heating water temperature Ts by the user are jointly used as input quantities to enter the control process. The control device 2 also receives a feedback signal, that is, the actual temperature T10 of the domestic hot water, and compares T10 and Ts to obtain a differential signal ΔT DHW = T10 - Ts, and then multiplies it by the proportionality factor Kp to obtain the control quantity - the number of steps ΔS that the stepper motor needs to increase or decrease. Adding ΔS to the current position Sc of the stepper motor gives the output quantity - the target position Sd. The specific expression is:

[0116] ΔS = Kp×ΔT DHW = Kp×(T10 - Ts); Kp takes the value of 3;

[0117] Sd = Sc + ΔS

[0118] The 0% position of the stepper motor 48 corresponds to the fully open state of the heating water throttle valve 7; the 100% position corresponds to the fully closed state. When the differential signal ΔT DHW is positive (the actual temperature T10 of the domestic hot water is higher than the target temperature Ts), the calculated control quantity ΔS is also positive, and the stepper motor 48 increases the number of steps, driving the valve flap 43 to move downward, reducing the circulation flow rate Φ of the primary side heating water HW ; conversely, when the differential signal ΔT DHW is negative (the actual temperature T10 of the domestic hot water is lower than the target temperature Ts), the stepper motor 48 drives the valve flap 43 to move upward, increasing the circulation flow rate Φ of the primary side heating water HW . During actual operation, this process will be continuously looped until the differential signal is zero and the stepper motor stops operating.

[0119] In this temperature control method, first, by adjusting the output power P of the primary side heating water circulation pump 6, compensation is made for the two most important interference variables of the fast water heater - the flow rate change of the domestic hot water and the actual temperature change of the heating water, and the heat input to the primary side of the plate heat exchanger 1 is adjusted to an appropriate range; then, by adjusting the opening degree of the primary side heating water throttle valve 7, compensation is made for the secondary interference variable of the fast water heater - the over-temperature of the tap water, and the circulation flow rate Φ of the primary side heating water is finely adjusted HW, finally making the actual temperature T10 of the domestic hot water reach the target value Ts and remain constant. Since when the actual temperature of the tap water is higher than 10°C under the experimental conditions, the heat input to the primary side of the plate heat exchanger 1 is always excessive, the control device 2 mainly closes and adjusts the heating water throttle valve 7. Whenever the flow sensor 8 detects a change in the actual flow rate Φ of the domestic hot water (Φ(t + 1s) - Φ(t) > 1 L / min), the control device 2 will restore the heating water throttle valve 7 to the fully open state and then make fine adjustments. At the same time, the plate heat exchanger 1 itself also has a certain thermal inertia. Therefore, during the adjustment process, there will be a short-term water temperature fluctuation in the actual temperature T10 of the domestic hot water. After the adjustment process ends, the water temperature will return to the target value Ts.

[0120] Figure 8 As shown, it is the adjustment effect of this control method on the temperature of the domestic hot water under actual working conditions. During a period of time (preferably covering the period when the domestic hot water reaches the peak load), the actual temperature T9 of the heating water remains unchanged. The example is 71°C. If the heat output power of the heating equipment is equal to the heat exchange power of the instantaneous water heater, the actual temperature T9 of the heating water can remain unchanged for an infinite period of time. The actual flow rate Φ of the domestic hot water increases or decreases by 5 or 10 L / min. The actual temperature T10 of the domestic hot water fluctuates only at the moment when the flow rate Φ changes, and the amplitude and duration of the fluctuation are both controlled within a small range, greatly improving the stability of the domestic hot water temperature and enhancing the user experience.

[0121] The technical solution of the present invention has the following technical effects compared with the prior art:

[0122] In order to improve the control accuracy and shorten the response time, a control method is used. This method controls the output power of the heating water circulation pump located in the primary side loop by controlling variables, and at the same time controls the opening degree of the heating water throttle valve located in the primary side loop through incremental proportional regulation. This method constructs the operating conditions of a central supply rapid water heater as a grid, and each node in the grid is a combination of operating conditions and also a carrier of a function. Each function corresponds an output power P of the heating water circulation pump with a domestic hot water flow rate φ, and this flow rate φ is measured by a flow sensor located in the secondary side loop. During actual operation, it is necessary to input the target temperature Ts, and based on this, calculate the difference ΔT between the actual temperature T9 of the heating water at the inlet of the primary side of the plate heat exchanger and the target temperature Ts. By obtaining the combination of these two values Ts and ΔT, the corresponding node can be found in the grid, and thus the function stored in the node can be called. Therefore, once the flow rate of domestic hot water changes, it will directly change the output power P of the primary side heating water circulation pump by calling the function P = f(Φ), and at the same time finely adjust the opening degree of the heating water throttle valve so that the actual temperature T10 of the domestic hot water on the secondary side can reach the target value Ts as soon as possible and remain constant continuously, especially in the case of a sudden large change in the tap water flow rate.

[0123] In the description of the above embodiments, the specific features, structures, materials or characteristics may be combined in a suitable manner in any one or more embodiments or examples.

[0124] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A temperature control method for a central supply instant water heater, characterized in that, It includes the following steps: S1. The control device preset the target temperature Ts of domestic hot water and initialize the throttle valve and the heating water circulation pump; S2. The control device detects the flow rate Φ(t) of domestic hot water; and determines whether the flow rate Φ(t) reaches α L / min or more; S3. If so, the control device detects the actual temperature T9 of the heating water; and determines whether the difference ΔT between the actual temperature T9 and the target temperature Ts reaches mK or more and whether the flow rate change value ΔΦ reaches β L / min or more; S4. If so, the throttle valve is in the fully open state and the output power P of the heating water circulation pump is calculated using the relationship P = f(Φ) between the output power P and the flow rate Φ(t); wherein, the relational expression is P = eΦ 2 + fΦ; S5. The control device collects the actual temperature T10 of the domestic hot water and adjusts the opening of the throttle valve according to the comparison result between the actual temperature T10 and the target temperature Ts.

2. The temperature control method of a central supply fast water heater according to claim 1, characterized in that, The step S2 specifically includes the following steps: S21. The control device detects the flow rate Φ(t) of domestic hot water and determines whether the flow rate Φ(t) reaches α L / min or more. If not, it returns to step S1. If so, the control device continues to determine whether the flow rate Φ(t) reaches α L / min or more for the first time; S22. If the flow rate Φ(t) reaches α L / min or more for the first time, the opening of the throttle valve is adjusted to 50%, and the output power P of the heating water circulation pump is controlled to 100%, and then the actual temperature T9 of the heating water is detected; S23. If the flow rate Φ(t) does not reach α L / min or more for the first time, the control device directly detects the actual temperature T9 of the heating water.

3. The temperature control method of a central supply fast water heater according to claim 1, characterized in that, The step S3 specifically includes the following steps: S31. The control device determines whether the difference ΔT between the actual temperature T9 and the target temperature Ts reaches mK or more. If not, it returns to step S2 after passing through the protection program; S32. If the difference ΔT reaches mK or more, the control device continues to determine whether the flow rate change value ΔΦ reaches β L / min or more. If so, the throttle valve is in the fully open state and then it continues to determine whether the working condition coincides with any node of the grid. Otherwise, it directly determines whether the working condition coincides with any node of the grid; where the calculation formula for the flow rate change value ΔΦ is: ΔΦ = Φ(t + 1) - Φ(t); S33. If the working condition coincides with any node of the grid, the relationship P = f(Φ) corresponding to the node is directly called to calculate the output power P of the heating water circulation pump. Otherwise, after fitting the relationship P = f(Φ) between the output power P and the flow rate Φ(t), the output power P of the heating water circulation pump is calculated again.

4. The temperature control method of a central supply fast water heater according to claim 3, characterized in that, The working condition includes the target temperature Ts and the actual temperature T9 of the heating water; the control device is used to construct a grid according to the working condition. The x-axis of the grid represents the target temperature Ts, and the y-axis represents the difference ΔT between the actual temperature T9 of the heating water and the target temperature Ts; the corresponding relationship P = f(Φ) is stored on each node of the grid.

5. The temperature control method of a central supply fast water heater according to claim 3, characterized in that, In the step S33, if the working condition does not coincide with the node, that is, when the working condition falls within the surface area of the grid, the boundary surface formed by the nodes enclosing the surface area is used to calculate the relational expression P = f(Φ) under the current working condition.

6. The temperature control method of a central supply fast water heater according to claim 5, characterized in that The boundary surface is analytically determined by the function w = auv + bu + cv + d; where u represents the target temperature Ts of domestic hot water, v represents the difference ΔT between the actual temperature T9 of heating water and Ts, and w represents the output power P of the heating water circulation pump corresponding to a certain flow rate Φ of domestic hot water.

7. The temperature control method of a central supply fast water heater according to claim 1, characterized in that, The throttle valve is controlled by a stepping motor, and the stepping motor adopts incremental proportional regulation.

8. A temperature control method for a central supply fast water heater according to claim 7, characterized in that, The calculation formula for the target position Sd of the stepping motor is: Sd = Sc + ΔS; where Sc is the current position of the stepping motor, and ΔS is the number of steps that the stepping motor needs to increase or decrease. The expression of ΔS is: ΔS = Kp×ΔT DHW = Kp×(T10 - Ts); Kp is a constant; ΔT DHW is a differential signal, ΔT DHW = T10 - Ts, where Ts is the target temperature.

9. The temperature control method of a central supply fast water heater according to claim 3, characterized in that, The protection program includes: Judge whether the running time of the heating water circulation pump reaches more than t1 minutes. If so, after closing the heating water circulation pump and the throttle valve, lock the device for t2 minutes and then return to step S2; otherwise, directly return to step S2.

10. The temperature control method of a central supply fast water heater according to claim 1, characterized in that, After initialization in the step S1, the opening of the throttle valve is 0%, and the output power P of the heating water circulation pump is 0%.

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