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

Abstract

The present application discloses a real-time measurement method and application of the inflow air volume under the exhaust cabinet window, which relates to the field of intelligent exhaust cabinets. The measurement method includes obtaining a curve of the static pressure value P_s and the inflow air volume Q under the exhaust cabinet window at different opening heights, and establishing a measurement model; calling the measurement model according to the static pressure value P_s collected in real time and the current window opening height; and obtaining the real-time inflow air volume Q under the opening height by table lookup or interpolation calculation. The present application cleverly eliminates the inflow air volume at the micro-leakage structure by establishing a curve of the static pressure value P_s and the inflow air volume Q under the exhaust cabinet window, and can achieve rapid, real-time and accurate measurement of the inflow air volume Q under the exhaust cabinet window, providing a reliable data basis for the variable air volume adjustment of the exhaust cabinet.

Description

Technical Field

[0001] The present application relates to the field of variable air volume control of fume hoods, and in particular 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. They form a negative pressure cavity through local exhaust to prevent the escape of harmful substances such as chemicals and gases in the cavity, thereby protecting the environment and scientific researchers in the laboratory.

[0003] Fume hood variable air volume (VAV) control achieves safety and energy conservation through real-time exhaust air volume control. When the fume hood is not in use or the pollution load is low, the VAV system can reduce air volume to reduce energy consumption; when demand increases, the VAV system can quickly increase air volume. When the fume hood opening height changes, the VAV system maintains a constant air velocity below the fume hood window (typically 0.3-0.5 m / s) to prevent the escape of harmful gases.

[0004] However, the VAV system needs to obtain accurate data on the air volume flowing into the fume hood at the window height to ensure the reliability of the variable air volume adjustment of the fume hood.

[0005] In the prior art, the measurement of the inflow air volume under the exhaust cabinet window mainly relies on the following two methods:

[0006] One method is direct measurement (surface velocity testing). This method, based on ASHRAE 110 and other industry standards, divides the fume hood's operating window into a grid of equal area. An anemometer is used to measure the air velocity at the center of each grid point, taking the arithmetic mean. The inflow air volume is then calculated based on the window area. While this method is the primary method for industry certification, it requires manual multi-point measurement, requires high precision, is complex, and is costly.

[0007] The other is an indirect calculation method, the exhaust valve / duct flow meter measurement method, which measures the air volume of the fluid flowing through the throttling device (such as an orifice plate, nozzle, or Venturi valve) and calculates the air volume in combination with the calibration coefficient: Q=K·Q1, where Q is the air volume flowing into the exhaust cabinet; K is the device calibration coefficient, which defaults to 1; Q1 is the measured air volume flowing through the throttling device; Q1 can be calculated by measuring the wind speed flowing through the throttling device.

[0008] The inflow air volume of the exhaust hood measured by the indirect calculation method includes the inflow air volume at the micro-leakage structure and the inflow air volume under the exhaust hood window; while the VAV system only needs to obtain the inflow air volume of the exhaust hood at the window height, thereby realizing variable air volume adjustment and achieving energy saving and low carbon. Summary of the Invention

[0009] In view of this, the present application provides, on one hand, a method for real-time measurement of the inflow air volume under the exhaust cabinet window, comprising:

[0010] The real-time measurement method of the inflow air volume under the exhaust cabinet window includes:

[0011] S1. Obtain the opening height of the exhaust cabinet window and obtain different static pressure values ​​at the exhaust outlet at the opening height by adjusting the fan or air valve. And the corresponding inflow air volume Q under the exhaust cabinet window; the static pressure value is obtained by fitting and the curve of the inflow air volume Q under the exhaust cabinet window;

[0012] S2. Adjust the opening height of the exhaust cabinet window and obtain the static pressure value at different opening heights according to step S1. The measurement model is established by comparing the curve of the inflow air volume Q under the exhaust cabinet window;

[0013] S3, according to the static pressure value at the exhaust port collected in real time and the current window opening height, calling the measurement model; obtaining the real-time inflow air volume Q at the opening height by table lookup or interpolation calculation.

[0014] Preferably, the opening height of the exhaust cabinet window varies in an arithmetic progression, and the difference in the arithmetic progression can be any value of 10mm, 20mm, 30mm, 40mm, 50mm, 60mm, 70mm, 80mm, 90mm, 100mm, 110mm, 120mm, 130mm, 140mm, and 150mm.

[0015] Preferably, the difference in the arithmetic progression satisfies the static pressure value at adjacent heights. The Q curve of the inflow air volume shows an approximately linear change characteristic.

[0016] Further preferably, the real-time inflow air volume Q at the opening height is obtained by difference calculation, including: when the window opening height is between two adjacent curves, the adjacent curves are interpolated by linear weighted average method to obtain the static pressure value at the height. The corresponding inflow air volume Q.

[0017] Preferably, pressure measuring holes are opened at at least two positions of the annular cross section of the straight pipe section of the exhaust outlet, and the static pressure value is measured after the pressure measuring holes are connected to each other. .

[0018] Preferably, the inflow air volume Q is measured by dividing the fume hood operating window at the window height into equal-area grids, measuring the wind speed at the center point of each grid using an anemometer and taking the arithmetic mean, and calculating the inflow air volume Q under the fume hood window in combination with the window area.

[0019] This application also provides a method for real-time measurement of the incoming air volume under a fume hood window, applied to a fume hood variable air volume control system. The fume hood variable air volume control system implements variable air volume control based on exhaust demand and the incoming air volume under the fume hood window obtained using the real-time measurement method described in this 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 demand increases, the air volume is rapidly increased, achieving dynamic response.

[0020] One or more technical solutions provided in this application have at least the following technical effects or advantages:

[0021] The existing technology divides the exhaust cabinet operating window into equal-area grids, uses an anemometer to measure the wind speed at the center point of each grid and takes the arithmetic mean, and calculates the inflow air volume based on the window area. The installation requires high precision, is complex, and expensive, and it is difficult to use it as a continuous monitoring method in batches at the product control end; however, the present application only monitors the static pressure in real time at the exhaust port, which is convenient and low-cost.

[0022] The existing technology measures the air volume at the exhaust outlet and calculates the inflow air volume under the exhaust cabinet window through a calibration coefficient. The inflow air volume of the exhaust cabinet measured by this indirect calculation method includes the inflow air volume at the micro-leakage structure and the inflow air volume of the exhaust cabinet at the window height, not just the inflow air volume at the window height, which results in a large error.

[0023] Moreover, the indirect calculation method uses a constant calibration coefficient to measure the air volume flowing into the exhaust cabinet, and does not take into account the influence of the window opening height on the resistance coefficient, resulting in a large error.

[0024] This application establishes a static pressure value The Q curve of the inflow air volume under the exhaust hood window cleverly eliminates the inflow air volume at the micro-leakage structure, and can achieve fast, real-time and accurate measurement of the inflow air volume Q under the exhaust hood window, providing a reliable data basis for the variable air volume adjustment of the exhaust hood. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0026] Figure 1 This is a schematic diagram of the fume hood cavity structure and internal airflow field under normal circumstances;

[0027] Figure 2 is the measured static pressure value described in this application Schematic diagram of;

[0028] Figure 3 is the static pressure value of the embodiment of this application Schematic diagram of the curve with the inflow air volume Q.

[0029] In the figure: 1. Static pressure ring; 2. Window. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described in this application are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0031] Example 1

[0032] The real-time measurement method of the inflow air volume under the exhaust cabinet window includes:

[0033] S1. Obtain the opening height of the exhaust cabinet window and obtain different static pressure values ​​at the exhaust outlet at the opening height by adjusting the fan or air valve. And the corresponding inflow air volume Q under the exhaust cabinet window; the static pressure value is obtained by fitting and the curve of the inflow air volume Q under the exhaust cabinet window;

[0034] S2. Adjust the opening height of the exhaust cabinet window and obtain the static pressure value at different opening heights according to step S1. The measurement model is established by comparing the curve of the inflow air volume Q under the exhaust cabinet window;

[0035] S3, according to the static pressure value at the exhaust port collected in real time and the current window opening height, calling the measurement model; obtaining the real-time inflow air volume Q at the opening height by table lookup or interpolation calculation.

[0036] The inflow air volume Q described in this application is the inflow air volume under the exhaust cabinet window, and does not include the inflow air volume at the micro-leakage structure.

[0037] The height of the window of a fume hood with variable air volume control can be adjusted automatically by electric motors, and the window opening height can be measured by a distance sensor to automatically obtain the opening height of the fume hood window. The window opening height of the fume hood can also be adjusted manually, but the automatic measurement method is preferably used to measure the window opening height to facilitate automatic adjustment of the variable air volume.

[0038] The opening height of the exhaust cabinet window varies in an arithmetical progression, and the difference in the arithmetical progression can be any value among 10mm, 20mm, 30mm, 40mm, 50mm, 60mm, 70mm, 80mm, 90mm, 100mm, 110mm, 120mm, 130mm, 140mm, and 150mm.

[0039] In the experiment, the height of the window from the table should be 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.

[0040] The static pressure value at any intermediate height is obtained by interpolating adjacent curves using the linear weighted average method. The corresponding relationship with the inflow air volume Q does not require intensive measurement.

[0041] The method of obtaining the real-time inflow air volume Q at the opening height by difference calculation includes: when the window opening height is between two adjacent curves, the adjacent curves are interpolated by the linear weighted average method to obtain the static pressure value at the height. The corresponding inflow air volume Q.

[0042] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the exhaust cabinet cavity structure and internal airflow field under normal circumstances. When the exhaust cabinet is in operation, the window opening height is A negative pressure gradient distribution is formed in the upper cavity structure. Analyzing along the longitudinal direction of the cavity space, the static pressure value The distribution of shows significant spatial variation: the static pressure in the area directly below window 2 approaches the laboratory's ambient pressure. As the spatial position moves toward the exhaust duct, the static pressure gradually decreases, and the negative pressure effect intensifies. The static pressure at the location of static pressure ring 1 reaches the peak negative pressure in the cavity, marking the maximum negative pressure measurement point in the entire measurement system.

[0043] The static pressure ring can be understood as an annular section of the straight pipe section of the exhaust port, with pressure measuring holes provided at at least two positions on the annular section. The straight pipe section of the exhaust duct can be understood as the exhaust port.

[0044] See also Figure 2 In this embodiment, pressure measuring holes are set at four positions of a circular cross section of the straight pipe section of the exhaust outlet. After the pressure measuring holes are connected to each other through the air pipe, a pressure sensor is connected. The other end of the pressure sensor is opened to communicate with the laboratory atmospheric pressure. The average static pressure at the 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.

[0045] The inflow air volume Q is measured by dividing the fume hood operating window at the window height into equal-area grids, measuring the wind speed at the center of each grid using an anemometer and taking the arithmetic mean as the average surface wind speed at window 2. , and by the formula Q= S is used to calculate the airflow Q under the fume hood window, where S is the operating window area.

[0046] Establish static pressure values ​​at different window opening heights The curve of the inflow air volume Q can be understood as the normalized local resistance system at different window opening heights. calibration.

[0047] The static pressure value obtained by fitting The curve of the inflow air volume Q; specifically including:

[0048] S101. Measure the current window opening height , calculate the operating window area S;

[0049] S102. Divide the window plane into equal-area grids, use an anemometer to measure the surface wind speed at the center of each grid, and take the arithmetic mean as the average surface wind speed at window 2. , and by the formula Q= S calculates the inflow air volume Q;

[0050] S103, synchronously record the current window opening height Static pressure value measured by lower static pressure ring 1 ;

[0051] S104: Adjust the window opening height to different gradients (such as 100mm, 200mm, 300mm, 400mm, 500mm) within the opening range of window 2, and repeat steps S101-S103 to obtain the window opening height at each height. -Q data group, through the processing unit -Q data group is fitted to generate static pressure values ​​at each window opening height The curve of the inflow air volume Q is stored in the database as a measurement model. Figure 3 , Figure 3 is the static pressure value of this embodiment Schematic diagram of the curve of the inflow air volume Q, Figure 3 The static pressure values ​​obtained by fitting are recorded when the window opening height is 100mm, 200mm, 300mm, 400mm and 500mm respectively. Curve of inflow air volume Q.

[0052] The static pressure value at the exhaust port collected in real time and the current window opening height, calling the measurement model; obtaining the real-time inflow air volume Q at the opening height by table lookup or interpolation calculation; the specific steps are as follows:

[0053] S301. Obtain the current static pressure value in real time through the pressure sensor , and get the current window opening height ;

[0054] S302. Call the current window opening height stored in the database The closest curve, e.g. Figure 3 Static pressure values ​​at heights of 100mm, 200mm, 300mm, 400mm, and 500mm The curve of the inflow air volume Q;

[0055] S303. If the current window opening height is between two adjacent calibration curves, for example, 250mm is between 200mm and 300mm, then calculate the number of intermediate heights by weighted average method. -Q relationship point, and then generate a smooth curve at the current height through function fitting;

[0056] S304. According to the real-time static pressure value The corresponding inflow air volume Q can be obtained by directly looking up the table or interpolating the fitted curve. =Q / S to calculate the inflow wind speed, where S is the operating window area at the current window opening height.

[0057] The table lookup described in this application can be understood as directly calling the existing curve in the measurement model.

[0058] The above static pressure value The core function of the curve with the inflow air volume Q is to establish the static pressure value through experimental data. The dynamic mapping relationship with the inflow air volume Q breaks through the limitations of traditional fixed calibration coefficients. Window opening height Slight changes to normalize the local resistance system Window opening height Slight changes, direct reliance on theoretical models will lead to cumulative errors; among them, , is the friction coefficient Open height for the window, is the equivalent diameter, is the normalized local drag coefficient.

[0059] However, through the calibration curves at different heights (which can be understood as: static pressure value The experimental calibration curve can correct actual factors not covered by the theoretical model, such as cavity leakage and local turbulence, thereby improving accuracy. High-precision calculations at any height can be achieved through weighted averaging and interpolation, without the need for dense calibration points. Fitting parameters are pre-stored in the database and can be directly called by the processing unit for calculation, meeting continuous measurement requirements and providing real-time assurance.

[0060] If the curve resolution needs to be further improved, the density of calibration points can be refined by gradually adding accurate measurement data of denser window opening height gradients (such as 50mm intervals). Experimental verification shows that when the window opening height interval is 100mm, the static pressure values ​​at adjacent heights are The curve relationship with the inflow air volume Q shows an approximately linear change characteristic. Based on this characteristic, the adjacent calibration curves are interpolated by the linear weighted average method to accurately fit the -Q relationship, without the need for additional intensive calibration. This method significantly reduces the complexity of experimental data acquisition while ensuring measurement accuracy, meeting the needs of actual engineering applications.

[0061] Example 2

[0062] The real-time measurement method of the inflow air volume under the exhaust cabinet window is applied to the exhaust cabinet variable air volume adjustment system. The exhaust cabinet variable air volume adjustment system realizes variable air volume adjustment according to the exhaust demand and the real-time measurement method described in this application to obtain the inflow air volume under the exhaust cabinet window.

[0063] The measurement method selects the window opening height as 457mm (100% fully open), 228mm (50% half open), and 114mm (25%) to verify whether the design surface wind speed value of 0.5m / s is reached.

[0064] Testing was conducted according to the industry standard JG / T 222-2007, "Laboratory Variable Air Volume Fume Hoods." The fume hood window was set at various opening heights (100%, 50%, and 25%). The measurement grid points were calculated based on the operating window size at each opening height. The average surface velocity at these grid points was measured, and the arithmetic mean and deviation ratio of the surface velocity at the window were calculated. The results are shown in Table 1. The deviation ratios were all within 5.0%, meeting the test standard.

[0065] Table 1 Surface wind speed test results

[0066]

[0067] It should also be noted that, in this specification, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus comprising the element.

Claims

1. A real-time measurement method for the inflow air volume under the exhaust cabinet window, characterized in that: include: S1. Obtain the opening height of the exhaust cabinet window and obtain different static pressure values ​​at the exhaust outlet at the opening height by adjusting the fan or air valve. And the corresponding inflow air volume Q under the exhaust cabinet window; the static pressure value is obtained by fitting The curve of the inflow air volume Q under the exhaust cabinet window; the inflow air volume Q under the exhaust cabinet window and the static pressure value There is a positive correlation; S2. Adjust the opening height of the exhaust cabinet window and obtain the static pressure value at different opening heights according to step S1. The curve of the inflow air volume Q is used to establish a measurement model; S3, according to the static pressure value at the exhaust port collected in real time and the current window opening height, calling the measurement model; obtaining the real-time inflow air volume Q at the opening height by table lookup or interpolation calculation.

2. The method for real-time measurement of the inflow air volume under the exhaust cabinet window according to claim 1 is characterized in that: The opening heights of the exhaust cabinet windows vary in arithmetic progression.

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

4. The method for real-time measurement of the inflow air volume under the exhaust cabinet window according to claim 1 is characterized in that: Open pressure measuring holes at at least two locations on the annular cross section of the straight section of the exhaust outlet, connect the pressure measuring holes, and measure the static pressure value. .

5. The method for real-time measurement of the inflow air volume under the exhaust cabinet window according to claim 1 is characterized in that: The inflow air volume Q is measured by the following method: the fume hood operating window at the window height 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 as the average surface wind speed at the fume hood operating window. , and by the formula Q= S, calculate the inflow air volume Q under the exhaust hood window, S is the operating window area at the current window opening height.

6. The application of the real-time measurement method of the inflow air volume under the exhaust cabinet window in the exhaust cabinet variable air volume control system is characterized by: The fume hood variable air volume adjustment system realizes variable air volume adjustment according to the exhaust 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 to 5.

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