Ejector Refrigeration System

Abstract

To provide an ejector refrigeration device capable of performing superheat degree control for stably securing a superheat degree of a driving flow even when a heat source temperature is rapidly changed in a short time.SOLUTION: An ejector refrigeration device includes: a driving pressure sensor 21 for detecting a driving pressure Pg of a driving flow; a driving temperature sensor 22 for detecting a driving temperature Tg of the driving flow; a heat source temperature sensor 23 for detecting a heat source temperature Twh of a heat source; and a control unit C which calculates a saturation temperature Tsat on the basis of the driving pressure Pg, and performs feedback control for controlling a rotation speed of a pump 3 so that a superheat degree Ts which is a difference between a target driving temperature Tgo and the detected driving temperature Tg reaches a target superheat degree Tso, and performs feedforward control for correcting and controlling the rotation speed of the pump 3 when the heat source temperature Twh is less than a prescribed value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an ejector refrigeration device capable of performing superheat degree control that can stably ensure the superheat degree of a driving flow even when the heat source temperature rapidly changes in a short time.

Background Art

[0002] As an ejector refrigeration device, for example, the one described in Patent Document 1 has already been provided. In this ejector refrigeration device, an ejector is provided between a steam generator as a refrigerant heating means and a condenser in a circulation path through which a refrigerant circulates. While the refrigerant discharged from the steam generator is supplied to the ejector as a driving fluid, the refrigerant discharged from the ejector is supplied to the condenser. A branch path is provided in a portion located between the condenser and the pump in the circulation path. The branch path includes an expansion valve and an evaporator, and supplies the refrigerant after passing through the evaporator to the ejector as a suction fluid. In this ejector refrigeration device, if a heat source such as waste heat water from a steam utilization device or a production line in a factory is supplied to the steam generator and cooling water to be cooled is supplied to the evaporator, it becomes possible to obtain chilled water cooled in the evaporator.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, the steam generator evaporates a high - pressure refrigerant using waste heat water from a steam utilization device or a production line in a factory as a heat source to generate a driving flow of the ejector. This driving flow needs to ensure a sufficient superheat degree. When this superheat degree cannot be ensured and the driving flow to the ejector becomes a gas - liquid two - phase flow, the suction performance of the ejector significantly decreases, and the cooling capacity by the evaporator cannot be ensured.

[0005] Therefore, superheat control is generally performed by feedback control, such as detecting the degree of superheating of the drive flow and controlling the rotation speed of the pump. However, when the heat source temperature of the waste hot water changes rapidly in a short period of time, there is a time delay before the temperature change of the drive flow occurs. The superheat control cannot keep up with this change in heat source temperature, and the degree of superheating of the drive flow cannot be secured. This leads to a decrease in the suction performance of the ejector, and consequently, the cooling capacity of the evaporator cannot be secured.

[0006] The present invention has been made in view of the above, and aims to provide an ejector refrigeration device that can perform superheat control that can stably ensure the degree of superheating of the drive flow even when the heat source temperature changes rapidly in a short period of time. [Means for solving the problem]

[0007] To achieve the above objective, the present invention provides an ejector refrigeration system comprising: a pump for pressurizing a refrigerant; a steam generator for heating the refrigerant with a heat source to generate a drive flow; an expansion valve for reducing the pressure of the refrigerant; an evaporator for cooling a medium to be cooled with the refrigerant reduced in pressure by the expansion valve; an ejector for sucking the refrigerant evaporated by the evaporator with the drive flow of the refrigerant from the steam generator; and a condenser for cooling the refrigerant mixed with the drive flow after being sucked into the ejector, wherein the system includes a control unit that performs feedback control to control the degree of superheating of the drive flow based on the drive temperature of the drive flow, and a control unit that performs feedforward control to correct the control of the degree of superheating by the feedback control when the heat source temperature of the heat source falls below a predetermined value.

[0008] Furthermore, the present invention relates to an ejector refrigeration system comprising: a pump for pressurizing a refrigerant; a steam generator for heating the refrigerant with a heat source to generate a drive flow; an expansion valve for reducing the pressure of the refrigerant; an evaporator for cooling a medium to be cooled with the refrigerant reduced in pressure by the expansion valve; an ejector for sucking the refrigerant evaporated by the evaporator with the drive flow of the refrigerant from the steam generator; and a condenser for cooling the refrigerant mixed with the drive flow after being sucked into the ejector, wherein the system comprises: a drive pressure sensor for detecting the drive pressure of the drive flow; a drive temperature sensor for detecting the drive temperature of the drive flow; a heat source temperature sensor for detecting the heat source temperature of the heat source; and a control unit that performs feedback control to calculate a saturation temperature based on the drive pressure and control the rotation speed of the pump so that the superheating degree, which is the difference between the target drive temperature and the detected drive temperature, becomes the target superheating degree, and performs feedforward control to correct the rotation speed of the pump when the heat source temperature falls below a predetermined value. [Effects of the Invention]

[0009] According to the present invention, it is possible to perform superheat control that can stably ensure the degree of superheating of the drive flow even when the heat source temperature changes rapidly in a short period of time. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a circuit diagram showing the configuration of an ejector refrigeration device according to an embodiment of the present invention. [Figure 2] Figure 2 is a block diagram showing the superheat control by the control unit. [Figure 3] Figure 3 is a flowchart showing the superheating control process procedure by the control unit shown in Figure 1. [Figure 4] Figure 4 is a time chart showing an example of superheat control according to this embodiment. [Figure 5] Figure 5 is a time chart showing an example of conventional superheat control. [Modes for carrying out the invention]

[0011] Hereinafter, embodiments for carrying out this invention will be described with reference to the attached drawings.

[0012] Figure 1 is a circuit diagram showing the configuration of an ejector refrigeration system 11, which is an embodiment of the present invention. The ejector refrigeration system 11 illustrated here recovers waste heat from waste hot water such as factory wastewater or used cooling water to cool the cooling medium, and has an ejector 1, a condenser 2, a pump 3, and a steam generator 4 connected sequentially on a circulation path L1. The ejector refrigeration system 11 is also provided with a branch path L2. The branch path L2 branches off from the portion upstream of the pump 3 at the branching point LS between the condenser 2 and the steam generator 4 of the circulation path L1, and supplies a portion of the refrigerant flowing through the circulation path L1 as a suction fluid to the ejector 1. The cooling medium can be water, oil, or other refrigerants. In this embodiment, in particular, an ejector refrigeration system that generates chilled water from the cooling water using waste heat recovered from waste hot water is illustrated.

[0013] Pump 3 circulates and supplies refrigerant in the circulation path L1. More specifically, pump 3 is, for example, a liquid-phase variable displacement pump that pressurizes the refrigerant and supplies it to ejector 1. In this embodiment, pump 3 is driven at a rotational speed according to a drive signal provided by control unit C, which will be described later. Steam generator 4 evaporates the refrigerant supplied from pump 3 by exchanging heat with a heat source such as waste hot water supplied to steam generator 4. Ejector 1 uses a driving flow, which is the gaseous refrigerant that has passed through steam generator 4, to draw in, mix, pressurize, and discharge the gaseous refrigerant supplied from evaporator 6. Condenser 2 condenses the refrigerant in the circulation path L1 by exchanging heat between the gaseous refrigerant discharged from ejector 1 and the cooling water supplied to condenser 2, thereby releasing heat.

[0014] The branch path L2 is equipped with an expansion valve 5 and an evaporator 6. The expansion valve 5 expands and reduces the pressure of the refrigerant that has passed through the condenser 2 and been supplied via the branch point LS. The evaporator 6 evaporates the refrigerant by exchanging heat between the liquid phase refrigerant after it has passed through the expansion valve 5 and the water to be cooled supplied to the evaporator 6. An electronic expansion valve is preferred as the expansion valve 5, but other types of expansion valves such as manual expansion valves, constant pressure expansion valves, and temperature expansion valves may be appropriately selected depending on the application and configuration.

[0015] Between the pump 3 and the ejector 1, there is a drive pressure sensor 21 that detects the drive pressure Pg, which is the pressure of the drive flow supplied from the outlet side of the pump 3, and a drive temperature sensor 22 that detects the drive temperature Tg, which is the temperature of the drive flow. In addition, there is a heat source temperature sensor 23 that detects the heat source temperature Twh of the heat source supplied to the steam generator 4.

[0016] The control unit C acquires detection values ​​from the drive pressure sensor 21, drive temperature sensor 22, and heat source temperature sensor 23, and controls the pump 3 and expansion valve 5, etc., based on these detection values. In particular, the control unit C has a feedback controller C1 and a feedforward controller C2, and controls the drive of the pump 3 based on the drive pressure Pg, drive temperature Tg, and heat source temperature Twh, thereby controlling the superheating degree of the drive flow. The superheating degree is the degree of temperature rise when the gas temperature is higher than the saturation temperature of the gas at a certain pressure.

[0017] Figure 2 is a block diagram showing the superheat control by the control unit C. As shown in Figure 2, the control unit C performs feedback control of the superheat of the drive flow via the feedback controller C1. Specifically, the drive temperature Tg of the system 12, which is the ejector refrigeration device 11, is fed back, and the difference temperature ΔTg, obtained by subtracting the current drive temperature Tg from the target drive temperature Tgo (which is the target superheat Tso) using the subtractor 31, is input to the feedback controller C1. The feedback controller C1 outputs a control command to the pump 3 for the pump rotation speed to make the difference temperature ΔTg zero. Controlling the difference temperature ΔTg to zero means bringing the current superheat (current drive temperature Tg - saturation temperature Tsat) closer to the target superheat (target drive temperature Tgo - saturation temperature Tsat). By performing this feedback control, the superheat of the drive flow can be brought closer to the target superheat Tso.

[0018] However, as described above, changes in the drive temperature Tg are detected with a time lag compared to changes in the heat source temperature Twh. Therefore, the heat source temperature Twh is input to the feedforward controller C2. If the heat source temperature Twh changes rapidly, for example, if it drops sharply below the saturation temperature Tsat, the feedforward controller C2 adds a control command to reduce the pump rotation speed to the control command from the feedback controller C1 via the adder 32, and inputs the added control command to the pump 3 to control the superheating of the drive flow. If the heat source temperature Twh is above the saturation temperature Tsat, the feedforward controller C2 does not output a control command to the adder 32, i.e., outputs a control value of 0, and does not perform feedforward control. Therefore, even if the heat source temperature Twh changes rapidly in a short period of time, feedforward control by this feedforward controller C2 is performed, and the superheating of the drive flow can be stably controlled by fast predictive control without a time lag.

[0019] <Superheating control process> Figure 3 is a flowchart showing the overheat degree control processing procedure by the control unit C shown in FIG. 1. As shown in FIG. 3, the control unit C first measures the drive pressure Pg (step S101). Then, the control unit C calculates the saturation temperature Tsat based on the drive pressure Pg (step S102). Then, feedback control and feedforward control are processed in parallel.

[0020] In the feedback control, first, the drive temperature Tg is measured (step S103), and the overheat degree Ts obtained by subtracting the drive temperature Tg from the saturation temperature Tsat is calculated (step S104). Then, it is determined whether or not the overheat degree Ts is different from the target overheat degree Tso (step S105). If the overheat degree Ts is different from the target overheat degree Tso (step S105: Yes), feedback control is performed to control the rotational speed of pump 3 so that the overheat degree Ts becomes the target overheat degree Tso (step S106), and this process ends. On the other hand, if the overheat degree Ts is not different from the target overheat degree Tso, that is, if they match (step S105: No), this process ends as it is.

[0021] On the other hand, in the feedforward control, first, the heat source temperature Twh is measured (step S107). Then, it is determined whether or not the heat source temperature Twh is less than the saturation temperature Tsat (step S108). If the heat source temperature Twh is less than the saturation temperature Tsat (step S108: Yes), feedforward control is performed to decelerate the rotational speed of pump 3 (step S109), and this process ends. On the other hand, if the heat source temperature Twh is not less than the saturation temperature Tsat (step S108: No), this process ends as it is. Note that the above processing is repeated at regular intervals.

[0022] <Comparison with the prior art> Figure 4 is a time chart showing an example of superheat control according to this embodiment. Figure 5 is a time chart showing an example of conventional superheat control. As shown in Figure 4, in this embodiment, when the heat source temperature Twh falls below the saturation temperature Tsat at time t1, feedforward control is added to the feedback control, and the pump rotation speed ω of pump 3 is reduced earlier, and the superheat control of the drive flow is stably maintained.

[0023] On the other hand, as shown in Figure 5, conventionally, superheat control is performed based only on the drive temperature Tg before the inlet of the drive flow ejector 1. Therefore, even if the heat source temperature Twh falls below the saturation temperature Tsat at time t1, the temperature change of the drive temperature Tg corresponding to the temperature change of the heat source temperature Twh is detected at time t2 with a time delay, and feedback control of the superheat is performed from this time t2. However, it is too late to start superheat control at time t2, so at time t3, the superheat becomes 0 and the system becomes uncontrollable. In other words, the drive flow becomes a two-phase gas-liquid flow.

[0024] In this embodiment, when the heat source temperature Twh changes rapidly in a short period of time, the rapid temperature change of the heat source temperature Twh, for example, a temperature drop, is detected, and feedforward control for superheat control is performed at this point. Therefore, even when the heat source temperature Twh changes rapidly in a short period of time, the superheat control of the drive flow does not become uncontrollable, and stable superheat control can be performed.

[0025] Feedforward control is performed when the heat source temperature Twh is below the saturation temperature Tsat, but this threshold is not limited to the saturation temperature Tsat; it may also be performed at temperatures near the saturation temperature Tsat. Furthermore, feedforward control may be performed considering the temperature gradient of the heat source temperature Twh. For example, if the temperature gradient is below a predetermined value, feedforward control may be not performed. In other words, if the temperature change is not rapid, it may be assumed that the feedback control is following the temperature change, and this can be added as a condition for deciding whether or not to perform feedforward control.

[0026] Furthermore, it is preferable to install the heat source temperature sensor 23, which detects the heat source temperature Twh, in a location close to the heat source. This is because it allows for earlier detection of changes in the heat source temperature Twh.

[0027] Furthermore, in the above embodiment, the feedforward control was turned on and off by detecting the heat source temperature Twh using the heat source temperature sensor 23. However, the system is not limited to this, and the feedforward control may also be turned on and off based on the detection of the heat flow rate of the heat source and the change in this heat flow rate.

[0028] Furthermore, the feedforward control may either change the control variable according to the magnitude of the change in the heat source temperature Twh when it detects a temperature below the saturation temperature Tsat, or it may output the same control variable in all cases where the temperature is below the saturation temperature Tsat.

[0029] It should be noted that the configurations illustrated in the above embodiments are functional schematics and do not necessarily have to be physically represented as shown. In other words, the forms of distribution and integration of each device and component are not limited to those shown, and all or part of them can be functionally or physically distributed and integrated in any unit according to various usage situations. [Explanation of symbols]

[0030] 1 Ejector 2. Condenser 3 pumps 4. Steam generator 5. Expansion valve 6. Evaporator 11 Ejector Refrigeration System 12 Systems 21 Drive pressure sensor 22 Drive temperature sensor 23 Heat source temperature sensor 31 Subtractor 32 Adder C control section C1 Feedback Controller C2 Feedforward Controller L1 Circulation Route L2 Branch Route LS branching point Pg drive pressure Tg operating temperature Tgo target operating temperature Ts superheat degree Tsat saturation temperature Tso target superheat degree Twh Heat source temperature ΔTg differential temperature ω Pump rotation speed

Claims

[Claim 1] An ejector refrigeration system comprising: a pump for pressurizing a refrigerant; a steam generator for heating the refrigerant with a heat source to generate a drive flow; an expansion valve for reducing the pressure of the refrigerant; an evaporator for cooling a medium to be cooled with the refrigerant reduced in pressure by the expansion valve; an ejector for drawing in the refrigerant evaporated by the evaporator by the drive flow of the refrigerant from the steam generator; and a condenser for cooling the refrigerant mixed with the drive flow after being drawn into the ejector, A drive pressure sensor for detecting the drive pressure of the drive flow, A drive temperature sensor for detecting the drive temperature of the drive flow, A heat source temperature sensor for detecting the heat source temperature of the heat source, A control unit calculates the saturation temperature based on the drive pressure and performs feedback control to control the rotation speed of the pump so that the superheating degree, which is the difference between the target drive temperature and the detected drive temperature, becomes the target superheating degree. Furthermore, if the heat source temperature falls below a predetermined value, a control unit performs feedforward control to correct the rotation speed of the pump. An ejector refrigeration system characterized by being equipped with the following features.

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