Method for calculating water conduction resistance of heat exchanger

Abstract

To provide a calculation method for accurately calculating water conduction resistance of a heat exchanger that performs heat exchange between water and air by flowing hot and cold water through an air conditioner.MEANS FOR SOLVING THE PROBLEM: The present calculation formula grasps a water conduction resistance characteristics of a heat exchanger from a result of actual measurement by flowing hot and cold water through an air conditioner; by applying unique correction of the present invention to part of the calculation formula that have a particularly large impact, can accurately calculate a water conduction resistance that is close to the actual measurement; and further uses the calculation result to calculate a heat quantity of the heat exchanger.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a calculation method for accurately calculating the flow resistance in a heat exchanger that performs water-air heat exchange by passing hot or cold water through an air conditioner. [Background technology]

[0002] Conventionally, as disclosed in Patent Document 1 (JP 2011-169588 A), when measuring the temperature, humidity, flow rate, and other physical quantities of working fluids such as water, air, and refrigerant required to operate an air conditioning system, various sensors are installed for each measurement, and the desired physical quantities are actually measured. Measuring these physical quantities is essential for optimal control of the air conditioning system. In this case, the flow meter used to measure the flow rate is a very expensive measuring instrument, and there is a problem in that it needs to be installed in advance on the air conditioning piping separately from the air conditioner. Furthermore, although the method for calculating the flow resistance required for flow rate calculations is publicly known as a theoretical value in the literature, it is limited to certain parts of a typical pipe (straight, bent, inlet change) and can be applied to piping with a simple structure, but it cannot be easily applied when calculating the flow resistance of a complex shape such as a heat exchanger, or when performing calculations that correspond to various sizes depending on the conditions. For this reason, calculation formulas were previously created by dividing the heat exchanger into two parts based on actual measurements, but this was not accurate enough to keep up with size variations, and there was often a problem of large discrepancies between the actual measurements and the calculations. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-169588 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides a calculation method for accurately calculating the flow resistance of a heat exchanger that performs water-air heat exchange by passing hot and cold water through an air conditioner. [Means for solving the problem]

[0005] The calculation formula of the present invention grasps the water flow resistance characteristics of the heat exchanger from the results of actual measurements, and by applying a unique correction to parts of the calculation formula that have a particularly large impact, it is possible to accurately and universally calculate water flow resistance that is close to the actual measurement. That is, in calculating the water flow resistance of a heat exchanger, the waterway is divided into parts (1) to (14) that have changes, and based on the known theoretical calculation formula for each part (1) to (14), corrections are made to the parts that deviate greatly from the theoretical calculation formula based on the results of actual measurements, and these calculation results are combined and added together to calculate the overall water flow resistance. The portions where the deviation is large and correction is necessary are as follows: (1) P1 = main pipe straight section, (2) P2 = header straight section, (3) P3 = extraction pipe straight section, (4) P4 = joint pipe section, (5) P5 = U-bend section, (9) P9 = pipeline inlet change section (from header to main pipe), (10) P10 = pipeline inlet change section (from header to extraction pipe), (11) P11 = sudden expansion section (from main pipe to header), (12) P12 = sudden expansion section (from extraction pipe to header), The parts that are not corrected are (6) P6 = header bend part (applies only to WT coils), (7) P7 = extraction pipe inlet bend part, (8) P8 = extraction pipe outlet bend part, (13) P13 = sudden contraction part (from header to main pipe), and (14) P14 = sudden contraction part (from header to extraction pipe). This is a method for calculating the water flow resistance of a heat exchanger by combining and adding up the values ​​of the parts of the heat exchanger that are the subject of the calculation from items (P1) to (P14) to calculate the total water flow resistance. This is a calculation method in which the water volume is calculated from the differential pressure measured by a differential pressure gauge installed between the outlet and inlet of the target heat exchanger and a graph of the water volume-water flow resistance characteristics, and the heat quantity of the heat exchanger is calculated from the temperature difference measured by a water thermometer installed at the inlet and outlet. [Effects of the Invention]

[0006] According to the calculation method of the present invention, the water flow resistance of a heat exchanger in an air conditioner that performs water-air heat exchange by passing cold and hot water through it can be calculated accurately without actual measurement. [Brief explanation of the drawings]

[0007] [Figure 1] Design variables for W coil and WT coil of heat exchanger [Figure 2] The coil water flow resistance portion of the present invention, [Figure 3] 1 is a graph showing the water flow rate-water flow resistance characteristic comparing the calculated values ​​and the measured values ​​of the water flow resistance and the water flow rate of the heat exchanger of Example 1; [Figure 4] 10 is a graph showing the water flow rate-water flow resistance characteristics comparing the calculated values ​​and the measured values ​​of the water flow resistance and the water flow rate of the heat exchanger of Example 2; [Figure 5] 10 is a graph showing the water flow rate-water flow resistance characteristic comparing the calculated values ​​and the measured values ​​of the water flow resistance and the water flow rate of the heat exchanger of Example 3; [Figure 6] 10 is a graph showing the water flow rate-water flow resistance characteristics comparing the calculated values ​​and the measured values ​​of the water flow resistance and the water flow rate of the heat exchanger of Example 4; [Figure 7] An explanatory diagram of how to obtain water volume from water flow resistance (differential pressure) using a heat exchanger water volume-water flow resistance characteristic graph. [Figure 8] An explanatory diagram of calculating the heat quantity of a heat exchanger using a conventional flow meter. [Figure 9] FIG. 10 is an explanatory diagram for calculating the heat quantity of a heat exchanger using the differential pressure gauge according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] A preferred method for calculating the water flow resistance of the heat exchanger of the present invention will be described in detail below. First, the heat exchangers that are the subject of the present invention are broadly divided into two types: W coil type and WT coil type. The design variables of the present invention are shown in Figure 1. In Figure 1, the WT coil (Water coil Thin) has a smaller outer diameter than the W coil, and the difference is whether the extraction pipe (the part coming out from the header) is "front extraction" or "top extraction." The W coil is only compatible with front extraction, while the WT coil is compatible with both front and top extraction. However, since the water pressure loss is affected by the position of the extraction pipe, they are divided into two types.

[0009] There are two conventional formulas for calculating water flow resistance: [Formula 1] [Formula 2] TIFF2025174104000002.tif61164The above (Equation 2) is the formula for calculating the water flow resistance (water side pressure loss) of a heat exchanger, but it varies depending on the size and water flow rate, and methods for calculating water flow resistance are publicly known as theoretical values ​​in the literature, but while the formula on the left above (Equation 1) is a rough calculation for the header section (WP2), the formula on the right calculates the water flow resistance WP depending on whether the header section (WP2) is outletted in a "front outlet" or "top outlet" manner, and at present this is closer to actual measurements.

[0010] Next, a suitable method for calculating the water flow resistance of the heat exchanger of the present invention will be described. As mentioned above, even if the water flow resistance WP is calculated by dividing the header section (WP2) outlet shape into "front outlet" and "top outlet," there is a discrepancy between the actual measured value and the value calculated using the formula. Therefore, by further understanding the water flow resistance characteristics of the heat exchanger from the results of the actual measurements and applying a unique correction to parts of the formula where the discrepancy is large, we are able to accurately calculate water flow resistance that is close to the actual measurement.

[0011] In this invention, the water passage of the heat exchanger is divided into 14 sections (Fig. 2), and each section is (1) P1 = main pipe straight section, (2) P2 = header straight section, (3) P3 = extraction pipe straight section, (4) P4 = joint pipe section, (5) P5 = U-bend section, (9) P9 = pipe inlet change section (from header to main pipe), (10) P10 = pipe inlet change section (from header to extraction pipe), (11) P11 = sudden expansion section (from main pipe to The water flow resistance of the water pipes in the (12) P12 = sudden expansion section (from the extraction pipe to the header) is calculated after correction, and the sections that do not require correction are (6) P6 = header bend section (applies only to WT coils), (7) P7 = extraction pipe inlet bend section, (8) P8 = extraction pipe outlet bend section, (13) P13 = sudden contraction section (from the header to the main pipe), and (14) P14 = sudden contraction section (from the header to the extraction pipe). Therefore, P1 to P14 are the parts of the heat exchanger shown in Table 1 and Figure 2 below, and the water flow resistance of the entire coil is WP = P1 + P2 + P3 + P4 + P5 +P6+P7+P8+ P9 + P10 + P11 + P12 +P13+P14 (the underlined parts are the parts corrected in the present invention). [Table 1] [Formula 3] TIFF2025174104000003.tif108162In other words, the parts to be corrected are (1) P1 = main pipe straight section, (2) P2 = header straight section, (3) P3 = extraction pipe straight section, (4) P4 = joint pipe section, (5) P5 = U-bend section, (9) P9 = pipeline inlet change section (from header to main pipe), (10) P10 = pipeline inlet change section (from header to extraction pipe), (11) P11 = sudden expansion section (from main pipe to header), (12) P12 = sudden expansion section (from extraction pipe to header), The parts that are not corrected are (6) P6 = header bend part (applies only to WT coils), (7) P7 = bend part at the entrance of the extraction pipe, (8) P8 = bend part at the exit of the extraction pipe, (13) P13 = sudden contraction part (from the header to the main pipe), and (14) P14 = sudden contraction part (from the header to the extraction pipe).

[0012] Next, the calculation of the water flow resistance of each part will be explained, including corrections. (1) The calculation formula for the straight section of the main pipe P1 is as follows: TIFF2025174104000004.tif34161The correction points in this calculation formula are ε and C1 in the shaded areas.

[0013] (2) Calculation formula for the straight pipe section of P2 TIFF2025174104000005.tif34161Note, L h W:Hno is the coefficient of the coil size, and in the case of coil size W21, Hno =21. The correction part of this calculation formula is the shaded part L h , ε, C2.

[0014] (3) Calculation formula for the straight pipe section of P3 TIFF2025174104000006.tif38169The correction point in this calculation formula is the shaded area ε.

[0015] (4) Calculation formula for the joint pipe part of P4 TIFF2025174104000007.tif38169The correction point in this formula is the shaded area ε.

[0016] (5) Calculation formula for the U-bend portion of P5 and (6) Header bend portion of P6 (applies only to WT coils, no correction value) TIFF2025174104000008.tif61169In this calculation formula, there is no correction point for P6, and the correction point for P5 is C5, the shaded area. In the above figure, the small ellipse within the circle represents the movement of the vortex, and the small arrows on the wall represent the movement of the water vortex.

[0017] (7) Calculation formula for the bent part at the entrance of the extraction pipe (P7) and the bent part at the exit of the extraction pipe (P8) TIFF2025174104000009.tif48169There are no corrections in P7 and P8 of this calculation formula. The small arrows on the wall of the curved section indicate the movement of the vortex.

[0018] (9) Calculation formula for the change in the pipeline inlet (header → main pipe) of P9 and (10) Calculation formula for the change in the pipeline inlet (header → extraction pipe) of P10 TIFF2025174104000010.tif91155In this calculation formula, the correction area for P9 is the shaded area ζ i1 , P10 correction points are in the shaded area ζ i2 is.

[0019] (11) Calculation formula for the sudden expansion part of P11 (from the main pipe to the header) and (12) Calculation formula for the sudden expansion part of P12 (from the extraction pipe to the header) TIFF2025174104000011.tif75161In this calculation formula, the correction point for P11 is the shaded area ζ kk1 The correction points for ξ1 and P12 are the shaded areas ζ kk2 and ξ2.

[0020] (13) Calculation formula for the sudden reduction part of P13 (from the header to the main pipe) and (14) Calculation formula for the sudden reduction part of P14 (from the header to the extraction pipe) TIFF2025174104000012.tif98169There are no corrections on pages 13 and 14 of this formula.

[0021] When the above heat exchanger sizes were expanded according to the design variables shown in Figure 1, we verified how closely the calculations matched the actual measurements. The heat exchanger type in the graph of Example 1 in Figure 3 is W1227x500-HF (32A / 25A), where W: coil type, 12: header No., 2: number of rows, 7: fin pitch, 500: element size, and 32A / 25: header outlet pipe diameter (see Figure 1). The water flow resistance was measured by passing predetermined amounts of water through this coil (22.0 L / min, 32.6 L / min, 43.1 L / min, 64.7 L / min, 81.1 L / min), and the actual water flow resistance was calculated from the water flow resistance of Example 1 of the present invention, the water flow resistance of conventional calculation formula 1, and the water flow resistance of conventional calculation formula 2. As a result, it was confirmed that the values ​​of Example 1 of the present invention and the actual measurements were almost identical.

[0022] The heat exchanger type in the graph of Example 2 in FIG. 4 is W24 4 7×500-DF (80A / 80A), which has the same meaning as in FIG. The water flow resistance was measured by passing predetermined amounts of water through this coil (86.2 L / min, 172.6 L / min, 345.5 L / min, 518.5 L / min, 649.0 L / min), and the actual water flow resistance was calculated from the water flow resistance of Example 1 of the present invention, the water flow resistance of conventional calculation formula 1, and the water flow resistance of conventional calculation formula 2. As a result, it was confirmed that the values ​​of Example 2 of the present invention and the actual measurements were almost identical.

[0023] The heat exchanger type in the graph of Example 3 in FIG. 5 is W48 2 7×500-QF (50A / 50A), which has the same meaning as in FIG. The water flow resistance was measured by passing predetermined amounts of water through this coil (21.4 L / min, 43.1 L / min, 86.4 L / min, 129.8 L / min, 173.0 L / min), and the actual water flow resistance was calculated from the water flow resistance of Example 1 of the present invention, the water flow resistance of conventional calculation formula 1, and the water flow resistance of conventional calculation formula 2. As a result, it was confirmed that the values ​​of Example 3 of the present invention and the actual measurements were almost identical.

[0024] The heat exchanger type in the graph of Example 4 in FIG. 6 is W24 6 7×1000-HF (50A / 50A), which has the same meaning as in FIG. The resistance to water flow was measured by passing predetermined amounts of water through this coil (21.3 L / min, 43.0 L / min, 86.7 L / min, 130.2 L / min, 173.0 L / min), and the actual resistance to water flow was calculated from the resistance to water flow of Example 1 of the present invention, the resistance to water flow of Conventional Calculation Formula 1, and the resistance to water flow of Conventional Calculation Formula 2. As a result, it was confirmed that the values ​​of Example 4 of the present invention and the actual measurements were almost identical.

[0025] As explained above, the present invention accurately calculates the correlation between the water flow resistance and water volume of the target heat exchanger, so if the water flow resistance is known, the water volume can be calculated.As a result, we will explain a method for calculating the heat quantity of the target heat exchanger using only an inexpensive differential pressure gauge that can be installed in the extraction pipe, without using the expensive flow meter that is normally used. The formula for calculating the heat is: Heat quantity (calculation formula) = water volume x specific heat at constant pressure x density x inlet / outlet temperature difference Of these, the specific heat at constant pressure and density are physical properties of the water flowing through the heat exchanger, and are determined under certain conditions, for example, at a specific water temperature. The amount of water is generally measured by incorporating a flow meter into the piping of the air conditioner, as shown in Figure 8. However, in this invention, the flow resistance can be calculated with high accuracy using the above-mentioned formula for calculating water flow resistance, so there is no need to incorporate an expensive flow meter. Instead, a relatively inexpensive differential pressure gauge can be installed (Figure 9), and the amount of water can be calculated by finding the differential pressure between the inlet and outlet, i.e., the flow resistance, as shown in Figure 7.

[0026] Next, a method for obtaining the water volume from the value of the differential pressure gauge will be explained. FIG. 7 is a graph obtained from the calculation formula of the present invention obtained in Example 1. If the value of the differential pressure gauge is 13 kPa, the amount of water flowing through the target heat exchanger is 100 [L / min].

[0027] In addition, the temperature difference between the inlet and outlet can be determined from the water thermometers installed at the inlet and outlet. The heat quantity of the heat exchanger of Example 1 can be calculated by applying the water volume calculated in this manner, the inlet / outlet water temperature difference, and the physical properties of water, namely the specific heat at constant pressure and density, to the heat quantity (calculation formula).

[0028] As described above, according to the method for calculating the water flow resistance of a heat exchanger of an embodiment of the present invention, the water flow resistance of a heat exchanger that performs water-air heat exchange by passing cold and hot water through it in an air conditioner can be calculated accurately without actual measurement.

Claims

1. In calculating the water flow resistance of a heat exchanger, the water channel is divided into sections (1) to (14) where there are changes in the waterway. Based on the theoretical calculation formulas for each of the following items (1) to (14), corrections are made to the parts that deviate greatly from the theoretical calculation formulas based on the results of actual measurements, and these calculation results are combined and added together to calculate the overall water flow resistance. The portions where the deviation is large and correction is necessary are as follows: (1) P1 = main pipe straight section, (2) P2 = header straight section, (3) P3 = extraction pipe straight section, (4) P4 = joint pipe section, (5) P5 = U-bend section, (9) P9 = pipeline inlet change section (from header to main pipe), (10) P10 = pipeline inlet change section (from header to extraction pipe), (11) P11 = sudden expansion section (from main pipe to header), (12) P12 = sudden expansion section (from extraction pipe to header), The portions that are not corrected are: (6) P6 = header bend portion (applicable only to WT coils), (7) P7 = extraction pipe inlet bend portion, (8) P8 = extraction pipe outlet bend portion, (13) P13 = sudden contraction portion (from header to main pipe), and (14) P14 = sudden contraction portion (from header to extraction pipe). A method for calculating the water flow resistance of a heat exchanger, characterized in that the water flow resistance of the parts to be calculated is calculated by combining and adding up the values ​​of the parts (P1) to (P14) to calculate the overall water flow resistance.

2. The method for calculating the water flow resistance of a heat exchanger according to claim 1, wherein the specific calculation formulas for the parts (1) to (14) of the heat exchanger are as follows, and the shaded parts are the correction parts of this case. (1) Main straight pipe section of P1 (2) P2 header straight pipe section (3) P3 straight pipe section (4) P4 joint pipe part (5) U-bend portion of P5, and (6) Header bend portion of P6 (applies only to WT coil, no correction value) (7) The bent portion of the inlet of the extraction pipe P7, and (8) The bent portion of the outlet of the extraction pipe P8 (9) P9 pipeline inlet transition part (from header to main pipe) and (10) P10 pipeline inlet transition part (from header to extraction pipe) (11) The sudden expansion part of P11 (from the main pipe to the header), and (12) The sudden expansion part of P12 (from the extraction pipe to the header) (13) The sudden contraction portion of P13 (from the header to the main pipe), and (14) The sudden contraction portion of P14 (from the header to the extraction pipe)

3. In the method for calculating the water flow resistance of a heat exchanger described in claim 2, the water volume is determined from a graph of the differential pressure measured by a differential pressure gauge installed between the outlet and inlet of the target heat exchanger and the water volume-water flow resistance characteristics, and the heat quantity of the heat exchanger is calculated from the temperature difference measured by a water thermometer installed at the inlet and outlet.

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