Real-time measurement method for inflow air volume under window of exhaust cabinet and application

Abstract

The invention discloses a real-time measurement method for the inflow air volume under an exhaust cabinet window and application, and relates to the field of intelligent exhaust cabinets. The measurement method comprises the following steps: acquiring a curve of static pressure values Ps at different opening heights and inflow air volume Q under an exhaust cabinet window, and establishing a measurement model; calling the measurement model according to the static pressure value Ps collected in real time and the current window opening height; and the real-time inflow air volume Q at the opening height is obtained in a table look-up or interpolation calculation mode. Through the established curve of the static pressure value Ps and the inflow air volume Q under the window of the exhaust cabinet, the inflow air volume at the micro-leakage structure is ingeniously eliminated, the inflow air volume Q under the window of the exhaust cabinet can be rapidly and accurately measured in real time, and a reliable data basis is provided for variable air volume adjustment of the exhaust cabinet.

Description

Technical Field

[0001] The present application relates to the field of variable air volume regulation of fume hoods, and particularly to a real-time measurement method and application of the inflow air volume under the fume hood window. Background Art

[0002] Fume hoods are mainly used in laboratories. By means of local exhaust, a negative pressure cavity is formed to prevent harmful substances such as chemicals and gases in the cavity from overflowing, thereby protecting the environment in the laboratory and the scientific research personnel.

[0003] Variable air volume (VAV) regulation of fume hoods realizes safe and energy-saving control by real-time controlling the exhaust air volume. When the fume hood is not in use or the pollution load is low, the VAV system can reduce the air volume to reduce energy consumption. When the demand increases, the VAV system can quickly increase the air volume. When the opening height of the fume hood changes, the VAV system maintains a constant face velocity (usually 0.3 - 0.5 m / s) under the fume hood window to prevent harmful gases from overflowing.

[0004] However, the VAV system needs to obtain accurate data of the inflow air volume of the fume hood under the window height to ensure the reliability of the variable air volume regulation of the fume hood.

[0005] In the prior art, the measurement of the inflow air volume under the fume hood window mainly relies on the following two methods: One is the direct measurement method (face velocity detection). According to the American Standard ASHRAE 110 and industry standards, the operation window of the fume hood is divided into equal-area grids. The wind speed is measured at the center point of each grid using an anemometer and the arithmetic mean is taken, and the inflow air volume is calculated by combining the window area. Although this method is the main means certified by the industry, it requires manual multi-point measurement, has high installation accuracy requirements, is complex, and has high costs.

[0006] The other is the indirect calculation method, the exhaust valve / pipeline flowmeter measurement method. By measuring the air volume of the fluid flowing through a throttling device (such as an orifice plate, nozzle, venturi valve), the air volume is calculated in combination with the calibration coefficient: Q = K·Q1, where Q is the inflow air volume of the fume hood; K is the device calibration coefficient, default 1; Q1 is the measured air volume flowing through the throttling device; Q1 can be obtained by measuring the wind speed flowing through the throttling device.

[0007] The inflow air volume of the fume hood measured by the indirect calculation method includes the inflow air volume at the micro-leakage structure and the inflow air volume under the fume hood window. However, the VAV system only needs to obtain the inflow air volume of the fume hood under the window height to achieve variable air volume regulation and realize energy conservation and low carbon. Summary of the Invention

[0008] In view of this, on the one hand, the present application provides a real-time measurement method for the inflow air volume under the fume hood window, including: Real-time measurement method for the inflow air volume under the fume hood window, including: S1. Obtain the opening height of the fume hood window. By adjusting the fan or air valve, obtain different static pressure values at the exhaust outlet at this opening height and the corresponding inflow air volume Q under the fume hood window; Fit to obtain the static pressure value and the curve of the inflow air volume Q under the fume hood window; S2. Adjust the opening height of the fume hood window. According to step S1, obtain the static pressure values and the curve of the inflow air volume Q under the fume hood window at different opening heights, and establish a measurement model; S3. According to the static pressure value collected in real time at the exhaust outlet and the current window opening height, call the measurement model; Obtain the real-time inflow air volume Q at this opening height by means of table lookup or interpolation calculation.

[0009] Preferably, the opening height of the fume hood window changes in an arithmetic progression, and the difference of the arithmetic progression can be any value among 10mm, 20mm, 30mm, 40mm, 50mm, 60mm, 70mm, 80mm, 90mm, 100mm, 110mm, 120mm, 130mm, 140mm, 150mm.

[0010] Preferably, the difference of the arithmetic progression satisfies that the static pressure values and the curve of the inflow air volume Q show an approximately linear change characteristic at adjacent heights.

[0011] Further preferably, obtaining the real-time inflow air volume Q at this opening height by means of difference calculation includes: when the window opening height is between two adjacent curves, perform interpolation calculation on the adjacent curves by the linear weighted average method to obtain the inflow air volume Q corresponding to the static pressure value at this height.

[0012] Preferably, pressure measuring holes are opened at at least 2 positions on the annular cross-section of the straight pipe section of the exhaust outlet. After the pressure measuring holes communicate with each other, measure the static pressure value .

[0013] Preferably, for the measurement of the inflow air volume Q, adopt: divide the operation window of the fume hood at this window height into equal-area grids, measure the wind speed at the center point of each grid using an anemometer and take the arithmetic mean, and calculate the inflow air volume Q under the fume hood window in combination with the window area.

[0014] On the other hand, the present application also provides an application of a real-time measurement method for the inflow air volume under the fume hood window in a variable air volume regulation system of a fume hood. The variable air volume regulation system of the fume hood realizes variable air volume regulation according to the exhaust air demand and the inflow air volume under the fume hood window obtained by the real-time measurement method described in the present application. When the fume hood is not in use or the pollution load is low, the air volume is reduced to reduce energy consumption; when the demand increases, the air volume is quickly increased to achieve dynamic response.

[0015] One or more technical solutions provided in the present application have at least the following technical effects or advantages: In the prior art, the operation window of the fume hood is divided into equal-area grids, and an anemometer is used to measure the wind speed at the center point of each grid and the arithmetic mean value is taken, and the inflow air volume is calculated by combining the window area. The installation requirements are highly accurate, complex, and costly, and it is difficult to be applied as a continuous monitoring means in batches at the product control end; however, in the present application, it is only necessary to monitor the static pressure in real time at the exhaust port, and the measurement is convenient and the cost is low.

[0016] In the prior art, the inflow air volume under the fume hood window is calculated by measuring the air volume at the exhaust outlet through a calibration coefficient. The inflow air volume of the fume hood measured by this indirect calculation method includes the inflow air volume at the micro-leakage structure and the inflow air volume of the fume hood under the window height, not only the inflow air volume of the fume hood under the window height, and the error is large; Moreover, for the inflow air volume of the fume hood measured by this indirect calculation method, the calibration coefficient used is constant and does not consider the influence of the resistance coefficient on the window opening height, resulting in a large error.

[0017] In the present application, by establishing the static pressure value and the curve of the inflow air volume Q under the fume hood window, the inflow air volume at the micro-leakage structure is cleverly excluded, and the rapid, real-time and accurate measurement of the inflow air volume Q under the fume hood window can be realized, providing a reliable data basis for the variable air volume regulation of the fume hood. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present application, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0019] Figure 1 is a schematic diagram of the fume hood cavity structure and the internal air flow field under normal circumstances; Figure 2 is a schematic diagram of measuring the static pressure value described in the present application; Figure 3 is the static pressure value of the embodiment of the present application Schematic diagram of the curve of the inflow air volume Q.

[0020] In the figure: 1. Static pressure ring; 2. Window. Specific implementation mode

[0021] The following will clearly and completely describe the technical solutions in the embodiments of the present application in conjunction with the accompanying drawings of the present application. Obviously, the described embodiments of the present application are only some embodiments of the present application, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the scope of protection of the present application.

[0022] Embodiment 1 A real-time measurement method for the inflow air volume under the exhaust cabinet window includes: S1. Obtain the opening height of the exhaust cabinet window, and obtain different static pressure values at the exhaust port at this opening height by adjusting the fan or the air valve and the corresponding inflow air volume Q under the exhaust cabinet window; Fit to obtain the static pressure value and the curve of the inflow air volume Q under the exhaust cabinet window; S2. Adjust the opening height of the exhaust cabinet window, and according to step S1, obtain the static pressure values and the curve of the inflow air volume Q under the exhaust cabinet window at different opening heights, and establish a measurement model; S3. According to the static pressure value collected in real time at the exhaust port and the current window opening height, call the measurement model; Obtain the real-time inflow air volume Q at this opening height by means of looking up a table or interpolation calculation.

[0023] The inflow air volume Q described in the present application is the inflow air volume under the exhaust cabinet window and does not include the inflow air volume at the micro-leakage structure.

[0024] For the adjustment of the window height of the exhaust cabinet with the variable air volume adjustment function of the exhaust cabinet, it can be adjusted automatically by electricity, and the opening height of the window can be measured by a distance sensor to automatically obtain the opening height of the exhaust cabinet window. The opening height of the window of the exhaust cabinet can also be adjusted manually, but the measurement of the opening height of the window is preferably measured by an automatic measurement method for the convenience of automatic adjustment of the variable air volume.

[0025] The opening height of the exhaust cabinet window changes in an arithmetic progression, and the difference of the arithmetic progression can be any value among 10mm, 20mm, 30mm, 40mm, 50mm, 60mm, 70mm, 80mm, 90mm, 100mm, 110mm, 120mm, 130mm, 140mm, 150mm.

[0026] In the experiment, the height of the window from the tabletop should be preferably 100 - 150 mm, and the maximum opening height should not exceed 600 mm; the difference of the arithmetic progression can be determined according to the experimental requirements, and the difference is preferably 50 mm or 100 mm; when the difference of the arithmetic progression is 100 mm, the different opening heights in step S2 can be 100 mm, 200 mm, 300 mm, 400 mm, and 500 mm respectively.

[0027] Interpolate and calculate adjacent curves by the linear weighted average method to obtain the static pressure value at any intermediate height The corresponding relationship with the inflow air volume Q does not require intensive measurement.

[0028] The real-time inflow air volume Q at the opening height is obtained by the difference calculation method, including: when the window opening height is between two adjacent curves, interpolate and calculate adjacent curves by the linear weighted average method to obtain the static pressure value at this height The corresponding inflow air volume Q.

[0029] Please refer to Figure 1 , Figure 1 is a schematic diagram of the exhaust hood cavity structure and the internal air flow field under normal circumstances. When the exhaust hood is in operation, a negative pressure gradient distribution is formed in the cavity structure above the window opening height In the longitudinal direction of the cavity space, the distribution of the static pressure value shows significant spatial differences: the static pressure value in the area directly below window 2 is close to the laboratory ambient atmospheric pressure. As the spatial position moves towards the exhaust duct direction, the static pressure value gradually decreases, and the negative pressure effect increases. Among them, the static pressure value at the position of static pressure ring 1 reaches the negative pressure peak value of the cavity and is the maximum negative pressure measurement point in the entire measurement system.

[0030] The static pressure ring can be understood as a circular cross-section of the straight pipe section of the exhaust port, and pressure measuring holes are provided at least at 2 positions on this circular cross-section. The straight pipe section of the exhaust duct can be understood as the exhaust port.

[0031] Please refer to Figure 2 , in this embodiment, pressure measuring holes are provided at 4 positions on a circular cross-section of the straight pipe section of the exhaust port. After the pressure measuring holes are connected and communicated through air pipes, they are connected to a pressure sensor. The other end of the pressure sensor is open to communicate with the laboratory atmospheric pressure, and the average static pressure at this position is measured, which is the static pressure value ; the axis of the pressure measuring hole is perpendicular to the axis of the exhaust duct.

[0032] The measurement of the inflow air volume Q adopts: dividing the operation window of the exhaust hood at this window height into equal-area grids, measuring the wind speed at the center point of each grid with an anemometer and taking the arithmetic mean as the average surface wind speed at window 2 , and through the formula Q = ·S calculates the inflow air volume Q under the fume hood window, where S is the area of the operation window.

[0033] Establish the static pressure values at different window opening heights and the curve of the inflow air volume Q, which can be understood as the calibration of the normalized local resistance system at different window opening heights of.

[0034] The static pressure value obtained by the fitting and the curve of the inflow air volume Q; specifically including: S101. Measure the current window opening height , and calculate the area S of the operation window; S102. Divide the window plane according to an equal-area grid, use an anemometer to measure the surface wind speed at the center point of each grid, and take the arithmetic mean as the average surface wind speed at window 2 , and calculate the inflow air volume Q through the formula Q = ·S; S103. Synchronously record the static pressure value measured by the static pressure ring 1 at the current window opening height ; ; S104. Within the allowable opening range of window 2, adjust the window opening height to different gradients (such as 100mm, 200mm, 300mm, 400mm, 500mm), repeat steps S101 - S103, and obtain the -Q data groups at each height. Through the processing unit, perform fitting on the -Q data groups to generate the curve of the static pressure value and the inflow air volume Q at each window opening height, and store it in the database as a measurement model. Please refer to Figure 3 , Figure 3 is the schematic diagram of the curve of the static pressure value and the inflow air volume Q in this embodiment, Figure 3 which records the curve of the static pressure value and the inflow air volume Q obtained by fitting when the window opening heights are 100mm, 200mm, 300mm, 400mm, and 500mm respectively.

[0035] According to the static pressure value at the exhaust port collected in real time and the current window opening height, call the measurement model; obtain the real-time inflow air volume Q at this opening height through the method of looking up a table or interpolation calculation; the specific steps are as follows: S301. Obtain the current static pressure value in real time through a pressure sensor , and obtain the current window opening height ; S302. Call the curve stored in the database that is closest to the current window opening height For example, Figure 3 the static pressure values at heights of 100mm, 200mm, 300mm, 400mm, and 500mm and the curve of the inflow air volume Q; S303. If the current window opening height is between two adjacent calibrated curves, for example, 250mm is between 200mm and 300mm, then calculate several -Q relationship points at the intermediate height through the weighted average method, and then generate a smooth curve at the current height through function fitting; S304. According to the real-time static pressure value and the fitted curve, directly look up the table or perform interpolation calculation to obtain the corresponding inflow air volume Q. It is also possible to calculate the inflow wind speed through the formula =Q / S, where S is the area of the operation window at the current window opening height.

[0036] The look-up table described in this application can be understood as directly calling the existing curves in the measurement model.

[0037] The above static pressure value and the core role of the curve of the inflow air volume Q is to establish a dynamic mapping relationship between the static pressure value and the inflow air volume Q through experimental data, breaking through the limitations of traditional fixed calibration coefficients. Since the friction coefficient varies slightly with the window opening height and the normalized local resistance system varies slightly with the window opening height direct reliance on the theoretical model will lead to cumulative errors; among them, is the friction coefficient is the window opening height, is the equivalent diameter, is the normalized local resistance coefficient.

[0038] However, the calibrated curves at different heights (which can be understood as: the curve of the static pressure value and the inflow air volume Q) can achieve the following advantages: The experimental calibrated curves can correct the actual factors not covered in the theoretical model, such as cavity air leakage and local turbulence, thereby improving the accuracy; high-precision calculations at any height can be achieved through weighted average and interpolation without dense calibration points; the fitting parameters are pre-stored in the database, and the processing unit directly calls for calculation to meet the continuous measurement requirements and provide real-time guarantee.

[0039] ​If it is necessary to further improve the curve resolution, precise measurement data of the opening height gradient of a denser window (such as at 50 mm intervals) can be gradually supplemented to refine the density of the calibration points. Experimental verification shows that when the opening height interval of the window is 100 mm, the static pressure values and the curve relationship with the inflow air volume Q show an approximately linear variation characteristic. Based on this characteristic, by using the linear weighted average method to perform interpolation calculations on adjacent calibration curves, the -Q relationship at any intermediate height can be accurately fitted without additional dense calibration. This method significantly reduces the complexity of experimental data acquisition while ensuring the measurement accuracy, meeting the requirements of practical engineering applications.

[0040] Embodiment 2 Application of the real-time measurement method for the inflow air volume under the fume hood window in the variable air volume regulation system of the fume hood. The variable air volume regulation system of the fume hood realizes variable air volume regulation according to the exhaust demand and the inflow air volume under the fume hood window obtained by the real-time measurement method described in this application.

[0041] The measurement method selects the window opening heights of 457 mm (100% fully open), 228 mm (50% half open), and 114 mm (25%) to verify whether the designed face velocity value of 0.5 m / s is achieved.

[0042] The test is carried out according to the test standard of JG / T 222-2007 "Laboratory Variable Air Volume Fume Hood". The fume hood window is set at the opening heights (100%, 50%, 25%). The measurement grid points are calculated according to the operation window size at the window opening height, the average face velocity value of the measurement grid points is measured, and the arithmetic mean and deviation ratio of the face velocity under the window are calculated. The results are shown in Table 1, and the deviation ratios are all within 5.0%, meeting the test standard.

[0043] Table 1 Face Velocity Test Results

[0044] It should also be noted that in this specification, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

Claims

1. A real-time measurement method for the inflow air volume under the fume hood window, characterized in that, Including: S1. Obtain the opening height of the fume hood window. By adjusting the fan or the air valve, obtain different static pressure values at the air outlet at this opening height and the inflow air volume Q under the fume hood window corresponding thereto; Fit to obtain the curve of the static pressure value and the inflow air volume Q under the fume hood window; S2. Adjust the opening height of the fume hood window, and according to step S1, obtain the static pressure values at different opening heights and the curve of the inflow air volume Q to establish a measurement model; S3. According to the static pressure value collected in real time at the exhaust port and the current window opening height, call the measurement model; obtain the real-time inflow air volume Q at this opening height by means of looking up a table or interpolation calculation.

2. The real-time measurement method of the inflow air volume under the fume hood window according to claim 1, characterized in that The opening height of the fume hood window changes in an arithmetic progression.

3. The real-time measurement method of the inflow air volume under the fume hood window according to claim 2, characterized in that, The real-time inflow air volume Q at the opening height is obtained by interpolation calculation, including: when the opening height of the window is between two adjacent curves, interpolation calculation is performed on the adjacent curves by the linear weighted average method to obtain the inflow air volume Q corresponding to the static pressure value at this height.

4. The real-time measurement method for the inflow air volume under the fume hood window according to claim 1, characterized in that, Open pressure measurement holes at least at two positions on the annular cross-section of the straight pipe section of the exhaust outlet. After the pressure measurement holes communicate with each other, measure the static pressure value .

5. The real-time measurement method of the inflow air volume under the fume hood window according to claim 1, characterized in that The measurement of the inflow air volume Q is carried out by the following method: divide the operating window of the fume hood at this window height into equal-area grids, use an anemometer to measure the wind speed at the center point of each grid and take the arithmetic mean, which is used as the average surface wind speed at the operating window of the fume hood. , and through the formula Q = ·S, the inflow air volume Q under the window of the fume hood is calculated, where S is the area of the operating window at the current window opening height.

6. Application of the real-time measurement method for the inflow air volume under the fume hood window in the variable air volume regulation system of the fume hood, characterized in that: The variable air volume adjustment system of the fume hood realizes variable air volume adjustment according to the exhaust air demand and the inflow air volume under the fume hood window obtained by the real-time measurement method according to any one of claims 1-5.

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