A refrigeration system control method and device based on dryness physical benchmark

Abstract

The application discloses a refrigeration system control method and device based on dryness physical benchmark. The method comprises the following steps: establishing a benchmark quantity of refrigerant, wherein the benchmark quantity Φ is only related to the physical property of the refrigerant and is irrelevant to system specific parameters such as pipeline length, charging quantity and heat exchanger area; acquiring the dryness of the condenser outlet in real time x ; taking the dryness x tending to 0 as a control target, and adjusting the total flow of the system so that the system approaches its inherent energy efficiency characteristic curve. The application also provides a float type device and an injection type device for realizing the method. The application promotes the dryness from a traditional measured quantity to an active physical benchmark, so that the refrigeration system automatically approaches the theoretical optimal state under various actual working conditions, and the energy efficiency is significantly improved, with an average COP improvement of 11.6% and a worst case improvement of 16.2%.

Description

Technical Field

[0001] This invention relates to the field of refrigeration and air conditioning technology, and in particular to a refrigeration system control method and apparatus based on a dryness physical standard. Background Technology

[0002] Vapor compression refrigeration is the most widely used form of refrigeration. Its control logic generally uses electronic expansion valves (EEV) or thermostatic expansion valves (TXV) to regulate the valve opening by detecting the superheat at the evaporator outlet. Theoretically, this control method attempts to maintain stable superheated vapor at the evaporator outlet, but it faces a series of inherent defects in practical applications: lack of a global physical reference, disconnect between control objectives and system load; "virtualized" data from the indoor unit thermostat; "fuzzy" refrigerant charge; inconsistent control effects due to differences in system parameters; and uncontrolled condenser outlet status, resulting in hidden energy losses.

[0003] The root cause is that the existing control logic lacks a global physical benchmark that is independent of the specific parameters of the system and can reflect the total load of the system. Summary of the Invention

[0004] Purpose of the invention This invention aims to provide a refrigeration system control method and device based on a dryness index physical reference. By using the dryness index at the condenser outlet as a global physical reference, dryness index is elevated from a measurable quantity to an active reference, enabling the system to automatically approach its theoretical optimal state under various actual operating conditions. To achieve the above objective, this invention provides the following technical solution:

[0005] In a first aspect, the present invention provides a refrigeration system control method based on a dryness physical reference, comprising: (1) Determine the baseline amount of refrigerant. ,in h g It is the enthalpy of saturated gas. h l The reference quantity is the enthalpy of a saturated liquid. Φ It depends only on the type of refrigerant and temperature, and is unrelated to specific system parameters such as pipe length, refrigerant charge, heat exchanger area, compressor displacement, and control method. (2) Real-time acquisition of the dryness of the condenser outlet x The dryness x Defined as the mass fraction of the gas phase in a gas-liquid two-phase mixture; (3) With the stated dryness x The control objective is to approach 0, and the total flow rate of the refrigeration system is adjusted to make the system approximate its inherent energy efficiency characteristic curve.

[0006] In a second aspect, the present invention provides a float-type dryness reference controller for implementing the above method, comprising: (1) Valve body, with refrigerant inlet and outlet; (2) A float, located within the valve body, has a density of ρ f satisfy ρ l > ρ f > ρ g ,in ρ l The density of a saturated liquid is... ρ g It is the density of the saturated gaseous state; (3) Valve core, which is linked to the float; Its working principle is based on Archimedes' principle: when the load increases, the dryness of point 3 increases, the average density decreases, the float sinks and drives the valve core to move down, the throttling orifice opens wider, and the flow rate increases; when the load decreases, the dryness decreases, the average density increases, the float rises and drives the valve core to move up, the throttling orifice closes smaller, and the flow rate decreases.

[0007] Thirdly, the present invention provides an ejector-type dryness reference controller for implementing the above method, comprising a gas-liquid separation chamber and an ejector. After the two-phase flow from the condenser outlet enters the gas-liquid separation chamber, the gas is separated and sent back to the condenser inlet via the ejector, while the saturated liquid is directly output. The liquid level is maintained stable by monitoring the opening of the liquid level control valve, thereby achieving dryness reference. x =0 output. Attached Figure Description

[0008] Figure 1 The pressure-enthalpy diagram of R410A refrigerant in this embodiment of the invention shows the key state points of the refrigeration cycle.

[0009] Figure 2 This is a graph showing the inherent energy efficiency characteristics of the R410A system in an embodiment of the present invention.

[0010] Figure 3 This is a schematic diagram of the float-type dryness reference controller of the present invention.

[0011] Figure 4 This is a schematic diagram of the ejector-type dryness reference controller of the present invention.

[0012] Figure 5 This is a comparison chart of COP distribution and dynamic response under frost conditions in Monte Carlo simulation of this invention. Detailed Implementation

[0013] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Example 1: Control method based on dryness physical reference

[0014] This embodiment provides a refrigeration system control method based on a dryness physical reference. First, the reference amount of refrigerant is determined. Taking R410A refrigerant as an example, under the operating conditions of evaporation at 5℃ and condensation at 45℃, Φ =210kJ / kg.

[0015] Real-time acquisition of dryness at condenser outlet (point 3) x 3 According to thermodynamic relationships, the total load Q of the system is related to the dryness fraction. x 3 There exists a definite mapping relationship:

[0016] in This is the refrigerant mass flow rate. h 1 This refers to the enthalpy value at the evaporator outlet. h l This is the enthalpy of saturated liquid.

[0017] In terms of dryness x 3 = 0 (saturated liquid) is the control target, and the total flow rate of the system is adjusted. When the load increases, if the flow rate remains constant, then x 3 When the load increases, the controller responds by increasing the flow rate; when the load decreases, the controller responds by decreasing the flow rate. x 3 It is always kept near 0. In this way, the system always operates on its inherent energy efficiency characteristic curve, achieving optimal energy efficiency. Example 2: Float-type dryness reference controller

[0018] As shown in Figure 3, this embodiment provides a float-type dryness reference controller. A float is installed inside the valve body, and the float density is designed to be between the densities of gaseous and liquid refrigerants. Taking an R410A, DN20 valve as an example, the float density is 300-500 kg / m³, and the float displacement corresponding to a load change from 10% to 100% is approximately 8-12 mm, located in the middle of the stroke, ensuring linear adjustment.

[0019] Engineering measures include: inertial filtering (time constant 0.2-0.5s), viscous damping (gap between float and guide sleeve 0.08-0.10mm), guiding constraints, temperature compensation (using Ni-Span-C constant elastic alloy springs), filter screen protection (100 mesh or higher), and straight pipe section requirements (5 times the pipe diameter before and 3 times the pipe diameter after). Example 3: Ejector-type dryness reference controller

[0020] As shown in Figure 4, this embodiment provides an ejector-type dryness reference controller, which consists of a gas-liquid separation chamber and an ejector. The workflow is as follows: (1) The two-phase flow (point 3') from the condenser outlet enters the gas-liquid separation chamber. Through cyclone or gravity separation, the gas rises to the top and the liquid sinks to the bottom. (2) The pure gas at the top enters the ejector's ejector inlet, and the ejector's driving flow is taken from the high-pressure gas at the condenser inlet; (3) The ejector pressurizes the gas and sends it back to the condenser inlet, where it mixes with the compressor exhaust and is condensed again. (4) Bottom saturated liquid (dryness) x = 0) Enters the main pipe through the level control valve and flows to the throttle valve.

[0021] This solution utilizes the system's own pressure difference for drive, requiring no additional energy consumption, and achieves a gas-liquid separation efficiency of over 96%. Example 4: Coordinated control with a thermostatic expansion valve

[0022] Provided that the refrigerant entering the TXV is saturated liquid, the temperature sensor of the TXV is located at the evaporator outlet. The valve core is adjusted according to the superheat to make the evaporator operate near the design conditions, thus achieving "strict adherence to the design capacity of the indoor unit".

[0023] To further meet users' needs for precise control of indoor temperature, a DC micro motor is installed on the TXV adjustment rod. Based on the comparison between the indoor temperature and the set value, the motor drives the valve core to fine-tune the valve core opening within a range of ±10%, and limit protection is provided. Example 5: Compressor Control Reconfiguration

[0024] Assuming that point 3 is saturated liquid under VQRC conditions, compressor control is simplified to single-variable regulation based on VQRC state variables.

[0025] For a float-type VQRC, the optimal operating point is when the float is at the midpoint of its stroke (50% opening); for an ejector-type VQRC, the optimal operating point is when the liquid level in the separation chamber is stable. The control law is a single-variable PID controller.

[0026] Where S is the VQRC state variable and S0 is the target value. Example 6: Upgrading of Existing Systems

[0027] For existing refrigeration systems, install an independent VQRC device. The installation steps are as follows: (1) Determine the installation location (straight pipe section at the condenser outlet); (2) Refrigerant recovery (optional); (3) Disconnect the original pipeline and connect the device; (4) Refill the liquid according to the VQRC design filling volume, so that point 3 is exactly saturated liquid; (5) Debugging and observation.

[0028] The cost of the equipment is controlled within 2,000 yuan. Based on an annual electricity saving of 3,440 kWh and an electricity cost of 0.8 yuan / kWh, the investment payback period is less than one year. Example 7: Monte Carlo Simulation Verification

[0029] To verify the robustness of this invention, nine key uncertainty parameters (charge volume deviation, sensor error, frosting, long piping, etc.) were selected, and 1000 sets of parameters were generated using Latin hypercube sampling for Monte Carlo simulation. The results are as follows: Figure 5 As shown in Table 1.

[0030] Table 1: Performance Comparison under Uncertainty Conditions index Traditional EEV VQRC Improvement range Average COP 3.042 3.395 +11.6% COP standard deviation 0.305 0.268 -12.1% 5th percentile (minimum 5% of operating conditions) 2.541 2.952 +16.2% Average COP during the frosting period 3.255 3.501 +7.6% Under the worst-case 5% operating conditions, the COP of the traditional EEV drops to 2.541, while the VQRC remains at 2.952, representing an improvement of 16.2%. This demonstrates that the present invention can maintain a good level of energy efficiency even under extreme operating conditions.

[0031] Beneficial effects

[0032] Compared with the prior art, the present invention has the following beneficial effects: (1) The dryness is elevated from a traditional "measured quantity" to an "active physical reference", providing a unified theoretical basis for the control of refrigeration systems; (2) The designed float-type and ejector-type VQRC controllers can achieve zero-delay physical feedback control, with an average COP improvement of 11.6% and a worst-case improvement of 16.2%; (3) Collaborate with TXV / EEV to form a dynamic-static decoupling architecture, simplifying the control algorithm; (4) The compressor control is simplified to single-variable regulation, which greatly reduces the algorithm complexity; (5) Applicable to absorption refrigeration, which can completely eliminate lithium bromide crystallization; applicable to centrifugal units, simplifying anti-surge control; (6) The existing system renovation plan is economically feasible, with an investment payback period of less than one year and an annual carbon reduction potential of 270 million tons of CO2.

[0033] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A refrigeration system control method based on a dryness index physical standard, characterized in that, Includes the following steps: (1) Determine the baseline amount of refrigerant. , where h g For saturated gaseous enthalpy, h l The specific enthalpy of saturated liquid is only related to the type and temperature of the refrigerant, and is independent of specific system parameters such as pipeline length, refrigerant charge, heat exchanger area, compressor displacement, and control method. (2) The dryness x of the condenser outlet is obtained in real time, wherein the dryness x is defined as the mass fraction of the gas phase in the gas-liquid two-phase mixture; (3) With the dryness x approaching 0 as the control target, adjust the total flow of the refrigeration system to make the system approach its inherent energy efficiency characteristic curve.

2. The method according to claim 1, characterized in that, The real-time dryness x at the condenser outlet is obtained directly by a float-type dryness sensing device installed at the condenser outlet. The float density of the float-type dryness sensing device is between the saturated liquid density and the saturated gas density of the refrigerant, and the float position corresponds one-to-one with the dryness x.

3. The method according to claim 2, characterized in that, The float-type dryness sensing device includes: (1) Valve body, with refrigerant inlet and outlet; (2) A float, located inside the valve body, has a density ρ f Satisfying ρ l > ρ f >ρ g , where ρ l ρ is the density of the saturated liquid. g It is the density of the saturated gaseous state; (3) Valve core, which is linked to the float; When the dryness of the condenser outlet increases, the average density of the refrigerant decreases, and the float sinks, causing the valve core to open the throttling orifice wider; when the dryness decreases, the float rises, causing the valve core to close the throttling orifice narrower.

4. The method according to claim 1, characterized in that, The real-time dryness x at the condenser outlet is obtained by a gas-liquid separation type dryness sensing device installed at the condenser outlet. The gas-liquid separation type dryness sensing device includes a gas-liquid separation chamber and an ejector. After the two-phase flow at the condenser outlet enters the gas-liquid separation chamber, the gas is separated and sent back to the condenser inlet through the ejector, while the saturated liquid is directly output. The liquid level is kept stable by monitoring the opening of the liquid level control valve, so that the dryness x = 0 is achieved.

5. The method according to claim 4, characterized in that, The ejector's drive flow is taken from the high-pressure gas at the condenser inlet, and is driven by the system's own pressure difference, requiring no additional energy consumption.

6. The method according to claim 1, characterized in that, It also includes a compressor control step: based on the deviation between the dryness fraction x and the target value 0, a single-variable PID control law is used to adjust the operating frequency of the compressor, wherein the control law is: ， Where S is the state variable of the dryness sensing device, and S0 is the target state.

7. The method according to claim 1, characterized in that, It also includes a step of coordinated control with the thermostatic expansion valve (TXV): under the premise of ensuring that the refrigerant entering the TXV is saturated liquid, the temperature sensing bulb of the TXV is located at the evaporator outlet, and the valve core is adjusted according to the superheat to make the evaporator operate near the design conditions.

8. The method according to claim 7, characterized in that, It also includes an intelligent fine-tuning step for the TXV: a DC micro motor is installed on the TXV adjustment rod, and the motor is driven to fine-tune the valve core opening based on the comparison between the indoor temperature and the set value, with the fine-tuning range controlled within ±10%.

9. The method according to claim 1, characterized in that, It also includes the following steps for upgrading existing systems: installing an independent VQRC device on the straight pipe section of the condenser outlet of the existing refrigeration system, and readjusting the refrigerant charge of the system according to the VQRC design charge amount so that the condenser outlet is exactly in a saturated liquid state.

10. The method according to claim 9, characterized in that, The readjustment of refrigerant charge includes: recovering the refrigerant in the original system and recharging it according to the VQRC design charge; or if the charge is too large, partially discharging it to a reasonable range, with the discharge process carried out in the recovery device.

Images