ASHRAE Standard 41.7 2015 RA2018
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ASHRAE Standard 41.7-2015 (RA 2018) – Standard Methods for Gas Flow Measurement (ANSI Approved)
| Published By | Publication Date | Number of Pages |
| ASHRAE | 2015 | 28 |
Standard 41.7 prescribes methods for gas flow measurement and applies to laboratory and field gas flow measurement for testing heating, ventilating, air-conditioning, and refrigerating systems and components.
PDF Catalog
| PDF Pages | PDF Title |
|---|---|
| 1 | ANSI/ASHRAE Standard 41.7-2015 (RA 2018) |
| 3 | CONTENTS |
| 4 | FOREWORD 1. PURPOSE 2. SCOPE 3. DEFINITIONS 4. CLASSIFICATIONS 4.1 Gas Flow Operating State. Gas flow measurement methods shall be restricted to applications where the entire gas flow stream enters and exits the flowmeter in the vapor-only state during data recording. Trace amounts of liquids shall be less than … 4.2 Gas Flow Measurement Applications. Gas flow measurement applications that are within the scope of this standard shall be classified as one of the following types. |
| 5 | 4.3 Gas Flowmeters 4.4 Gas Flow Measurement Methods. Gas flow measurement methods that are within the scope of this standard are shown in the following list. Each of these gas flow measurement methods is described in Section 7.5: 5. REQUIREMENTS 5.1 Test Plan. A test plan is a requirement. The test plan shall specify the test points and the required measurement system accuracy at each test point. A test plan is a document or other form of communication that specifies the tests to be performe… 5.2 Values to be Determined and Reported. The test values to be determined and reported shall be as shown in Table 5-1. Use the unit of measure in Table 5-1 unless otherwise specified in the test plan in Section 5.1. 5.3 Test Requirements TABLE 5-1 Measurement Values and Units of Measure |
| 6 | 6. INSTRUMENTS 6.1 Instrumentation Requirements for All Measurements 6.2 Temperature Measurements. If temperature measurements are required by the test plan in Section 5.1, the measurement system accuracy shall be within the following limits unless otherwise specified in the test plan: 6.3 Pressure Measurements 6.4 Time Measurements. Time measurement system accuracy shall be within ±0.5% of the elapsed time measured, including any uncertainty associated with starting and stopping the time measurement unless (a) otherwise specified in the test plan in Secti… 7. GAS FLOW RATE MEASUREMENT METHODS 7.1 Gas Properties. If not specified in the test plan in Section 5.1, the source of the gas property data shall be recorded in the test report. 7.2 Operating Limits. Operating conditions during gas flow rate data measurements shall not exceed limits for pressure, pressure differential, temperature, gas velocity, or pressure pulsations specified in the test plan or by the gas flowmeter manufa… 7.3 Leakage Requirement. Unless otherwise specified in the test plan in Section 5.1, measured gas leakage out of the test apparatus shall be not be greater than 0.25% of the gas flow at the greatest pressure tested under laboratory conditions, or not… 7.4 Gas Flowmeter Installation. The selected gas flowmeter shall be installed in accordance with instructions from the manufacturer, or the uncertainty calculations shall include estimated uncertainties for installations that are not in accordance wi… 7.5 Gas Flowmeter Descriptions |
| 7 | FIGURE 7-1 Orifice flowmeter geometric profile. (Reprinted with permission of ASME) |
| 8 | FIGURE 7-2 Long-radius nozzle geometric profile. (Reprinted with Permission of ASME) |
| 9 | FIGURE 7-3 Venturi tube flowmeter geometric profile. (Reprinted with Permission of ASME) |
| 10 | TABLE 7-1 References in ASME MFC-3M44,5 for ISA 1932 Nozzles, Venturi Nozzles, and Venturi Tubes |
| 11 | FIGURE 7-4 Variable-area flowmeter. FIGURE 7-5 Example of a Pitot-static tube. |
| 12 | FIGURE 7-6 Pitot-tube traverse measuring points for rectangular ducts and round ducts. |
| 14 | 8. UNCERTAINTY REQUIREMENTS 8.1 Uncertainty Estimate. An estimate of the measurement uncertainty performed in accordance with ASME PTC 19.16 shall accompany each gas flow measurement. 8.2 Method to Express Uncertainty. Assumptions, parameters, and calculations used in estimating uncertainty shall be clearly documented prior to expressing any uncertainty values. Uncertainty shall be expressed as shown in Equation 8-1. 9. TEST REPORT 9.1 Test Identification 9.2 Gas Flow Measurement Equipment Description 9.3 Ambient Test Conditions 9.4 Test Operating Conditions if Required by the Flowmeter 9.5 Test Results 10. NORMATIVE REFERENCES |
| 15 | INFORMATIVE ANNEX A—INFORMATIVE REFERENCES AND BIBLIOGRAPHY |
| 16 | INFORMATIVE ANNEX B—AN UNCERTAINTY ANALYSIS EXAMPLE FOR A CORIOLIS FLOWMETER B1. Define the Measurement Process B1.1 Review the test objectives and duration. The test objectives were clearly stated in the above description. B1.2 List all independent measurement parameters and their nominal levels. The only independent measurement is the frequency output from the Coriolis flowmeter. The full-scale output of the flowmeter was set by the manufacturer to 4.0 kg/s (8.82 lbm/… B1.3 List all calibrations and instrumentation setups that will affect each parameter. The manufacturer verified basic flowmeter operation on their test facility that has a stated uncertainty, URSS, of ±0.05% per ISO 5168A10. The calibration data pr… B1.4 Define the functional relationship between the independent measurement parameters and the test results. Since the mass flow is a direct measurement, there is no functional relationship between multiple measurements and the final test result. B2. List Elemental Error Sources B2.1 Make a complete list of all possible measurement error sources. The number of possible error sources for this system is small due to the simplicity of the overall system. Measurement error sources may include the manufacturer’s calibration res… B2.2 Group the error sources according to the following categories: B3. Estimate Elemental Errors B3.1 Obtain an estimate of each error identified in B2.2(b). B3.2 If data are available to estimate the precision index, tentatively classify the error as a precision error. Otherwise, classify it as a bias error. |
| 17 | FIGURE B-1 Flow error vs. flow rate. TABLE B-1 Manufacturer’s Initial Gas Flowmeter Calibration Data TABLE B-2 Error Estimates as a Function of Flow Rates |
| 18 | B3.3 Calculate the Bias and Precision Errors for Each Parameter. The results from the previously defined elements are now summarized at each of the four calibrated flow rates in Table B-3. The summing of the terms is by the root-sum- square method, a… B4. Propagate the Bias and Precision Errors B4.1 The bias and precision errors of the independent parameters are propagated separately all the way to the final test result. The individual terms are now summed together again by the root-sum-square method, as a 95% confidence level is desired, a… B4.2 Error propagation is performed according to the functional relationship of B1.4 via a Taylor series. This requires a calculation of the sensitivity factors, either by differentiation or by computer perturbation. Because the mass flow rate is the… B5. Calculate Uncertainty B6. Report B6.1 The report summary shall contain the nominal level of the test result, bias limit, precision index, degrees of freedom, and uncertainty of the test result, stating the model used. B6.2 The report shall include a table of the elemental errors included in the uncertainty analysis along with the bias limit, precision index, and degrees of freedom of each parameter. The report for this analysis would include the average value dete… TABLE B-3 Data Reduction Curve Fit Error Comparison |
| 19 | TABLE B-4 Bias and Precision Error Summary TABLE B-5 Propagation and Final Uncertainty Estimate |
| 20 | INFORMATIVE ANNEX C—AN UNCERTAINTY ANALYSIS EXAMPLE FOR A DIFFERENTIAL PRESSURE FLOWMETER C1. Identify experimental goals and acceptable accuracy C2. Identify the important variables and appropriate relationships C3. Establish the quantities that must be measured and their expected range of variation C4. Tentatively select sensors/ instrumentation appropriate for the task C5. Document uncertainty of each measured variable C6. Perform a preliminary uncertainty analysis |
| 21 | C6.1 Calculate the Bias and Precision Errors for Each Parameter. The estimates from the previously defined elements in Table C-3 are now summarized for each elemental term using the root-sum-square method, as 95% confidence is desired. The degrees of… C6.2 Propagate the Bias and Precision Errors. The individual parameter errors are propagated into the flow rate according to a Taylor series expansion. The relative bias limit for the mass flow equation is as follows: |
| 22 | C7. Study uncertainty results and reassess the ability of the measurement methods and instrumentation to meet acceptable accuracy |
| 23 | C8. Install selected instrumentation in accord with relevant standards or best practices C9. Perform initial verification of data quality C10. Collect experimental data subject to ongoing quality control criteria C11. Accomplish data reduction and analysis C12. Perform final uncertainty analysis C13. Report experimental results |
| 24 | TABLE C-1 Independent Parameters Descriptions TABLE C-2 Relationships of the Calculated Parameters |
| 25 | TABLE C-3 Uncertainty of Each Measured Parameter TABLE C-4 Calculated Density at Minimum, Nominal, and Maximum TABLE C-5 Minimum, Nominal, and Maximum Values of e |
| 26 | TABLE C-6 Summary of Calculations |
