ASHRAE Standard 41.7 2021

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ASHRAE Standard 41.7-2021 — Standard Methods for Gas Flow Measurement (ANSI Approved)

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ASHRAE	2021	46

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Description

Standard 41.7 prescribes methods for gas flow measurement. The 2021 edition includes an update of the steady-state criteria for recording data

PDF Catalog

PDF Pages	PDF Title
1	ANSI/ASHRAE Standard 41.7-2021
3	CONTENTS
4	FOREWORD 1. PURPOSE 2. SCOPE 3. DEFINITIONS
5	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 gas flowmeter in the vapor-only state during data recording. Trace amounts of liquids shall be less t… 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 types in Sections 4.2.1 and 4.2.2. 4.3 Gas Flowmeters 4.4 Gas Flow Measurement Methods. Gas flow measurement methods that are within the scope of this standard are the methods listed below. Each of these gas flow measurement methods is described in Section 7.5. 5. REQUIREMENTS 5.1 Test Plan. A test plan shall specify the gaseous mass flow rate measurement system accuracy. The test plan shall also include the test points, targeted set points, and corresponding operating tolerances to be performed. The test plan shall be one…
6	5.2 Values to be Determined and Reported. The test values to be determined and reported shall be as shown in Table 1. Use the unit of measure in the Table 1 unless otherwise specified in the test plan in Section 5.1. 5.3 Test Requirements
13	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 Constraint on All Gas Flow Rate Measurement Methods. A selected gas flow measurement plane shall exceed 7.5 geometrically equivalent diameters downstream of an obstruction or any change in the airflow direction and shall exceed 3 geometrically eq…
14	7.2 Coriolis Flowmeters. Review Section 7.1. Coriolis gas flowmeters provide direct measurement of gas mass flow rates. In a Coriolis flowmeter, the gas flows through a vibrating sensor tube within the meter. An electromagnetic coil located on the se… 7.3 Thermal Flowmeters. Review Section 7.1. Thermal flowmeters provide direct measurement of gas mass flow rates. The basic elements of the constant heat input thermal mass flowmeters are two temperature sensors that are positioned on opposite sides … 7.4 Orifices, Flow Nozzles, and Venturi Tube Flowmeters. Review Section 7.1. Orifices, flow nozzles, and venturi tubes are mass flowmeters. ASME PTC 19.5 4 and ASME MFC-3M 5 describe measurement of fluid flow in pipes using orifices, flow nozzles, an…
19	7.5 Turbine Flowmeters. Review Section 7.1. Turbine flowmeters are volumetric flowmeters that have a turbine rotor suspended on low-friction bearings in the gas stream. The rotational speed of the turbine is a linear function of the average gas veloc… 7.6 Variable-Area Flowmeters. Review Section 7.1. Variable-area flowmeters are volumetric flowmeters. These flowmeters consist of a float that is free to move vertically inside a tapered transparent tube that has a graduated scale, as shown in Figure… 7.7 Ultrasonic Flowmeters. Review Section 7.1. Ultrasonic flowmeters measure gas flow velocity. Clamp-on ultrasonic flowmeters measure gas velocity within a pipe or tube without being inserted into the flow stream.
20	7.8 Pitot-Static-Tube Gas Flow Measurement Methods. Review Section 7.1. Figure 9 shows an example pitot-static tube construction and the connections to manometers or electronic pressure transducers. Sections 7.8.1, 7.8.2, and 7.8.3 describe three dif…
24	7.9 Vortex-Shedding Flowmeters. Review Section 7.1. Vortex-shedding flowmeters are used to determine gas velocities. Piezoelectric methods, strain-gage methods, or hot-film methods are used to sense dynamic pressure variations created by vortex shedd… 7.10 Drag-Force Velocity Flowmeters. Review Section 7.1. Drag-force flowmeters determine gas velocity. Piezoelectric or strain-gage methods are used to sense dynamic drag-force variations. Gas velocity shall be obtained from Equation 7-24 in SI units…
25	8. UNCERTAINTY REQUIREMENTS 8.1 Uncertainty Estimate. An estimate of the measurement uncertainty performed in accordance with ASME PTC 19.1 6 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 uncertainty values. Uncertainty shall be expressed as shown in Equation 8-1. 9. TEST REPORT 9.1 Test Identification 9.2 Unit Under Test (UUT) Description 9.3 Instrument Description 9.4 Measurement System Description 9.5 Test Conditions 9.6 Test Results
26	10. REFERENCES
27	INFORMATIVE APPENDIX A: INFORMATIVE REFERENCES AND BIBLIOGRAPHY
28	INFORMATIVE APPENDIX B: AN UNCERTAINTY ANALYSIS EXAMPLE FOR A CORIOLIS FLOWMETER B1. Estimate Uncertainty in SI Units B1.1 Define the Measurement Process B1.2 List Elemental Error Sources
29	B1.3 Calculate Systematic and Random Uncertainty of Parameters B1.4 Calibration Error Estimate. The manufacturer stated that the flowmeter test facility calibration error was 0.05%. On further investigation of their calibration uncertainty analysis, the error appears to consist mainly of a bias error that can be… B1.5 Data Acquisition Error Estimate. The frequency meter that will be used was specified by the manufacturer to be ±0.010% of the reading for readings greater than 40 Hz. Because the inaccuracy in determining frequency was only specified as a perce…
30	B1.6 Data Reduction Error Estimate. The mass flow will be a function related to the measured frequency as shown in the first two columns of Table B-3. Various linear curve fits were reviewed to determine which had the smallest error over the entire o… B1.7 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-4. The summing of the terms is by the root-sum-square method bec… B1.8 Propagate the Bias and Precision Errors
31	B1.9 Calculate Uncertainty. Select UADD or URSS as models for combining the bias and precision errors of the test result, and obtain the uncertainty. URSS will be used because a 95% confidence level is desired. The value of t for the Student’s t-fu… B1.10 Report B2. Estimate Uncertainty in I-P Units B2.1 Define the Measurement Process
33	B2.2 List Elemental Error Sources B2.3 Calculate Systematic and Random Uncertainty of Parameters B2.4 Calibration Error Estimate. The manufacturer stated that the flowmeter test facility calibration error was 0.05%. Upon further investigation of their calibration uncertainty analysis, the error appears to be mainly consisting of a bias error tha… B2.5 Data Acquisition Error Estimate. The frequency meter that will be used was specified by the manufacturer to be ±0.010% of the reading for readings greater than 40 Hz. Because the inaccuracy in determining frequency was only specified as a perce… B2.6 Data Reduction Error Estimate. The mass flow will be a function related to the measured frequency, as shown in the first two columns of Table B-8. Various linear curve fits were reviewed to determine which had the smallest error over the entire …
34	B2.7 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-9. The summing of the terms is by the root-sum-square method bec… B2.8 Propagate the Bias and Precision Errors
35	B2.9 Calculate Uncertainty. Select UADD or URSS as models for combining the bias and precision errors of the test result, and obtain the uncertainty. URSS will be used because a 95% confidence level is desired. The value of t for the Student’s t-fu… B2.10 Report
36	INFORMATIVE APPENDIX 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
37	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 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…
40	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:
42	C7. Study uncertainty results and reassess the ability of the measurement methods and instrumentation to meet acceptable accuracy C8. Install selected instrumentation in accord with relevant standards or best practices C9. Perform initial verification of data quality
43	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.
44	INFORMATIVE APPENDIX D: FLOWMETER ACCURACY COMPARISONS

Additional information

Standard Title	ASHRAE Standard 41.7-2021 — Standard Methods for Gas Flow Measurement (ANSI Approved)
Published Code	ASHRAE
Publication Date	2021
Pages Count	46

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ASHRAE Standard 41.7 2021

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