Already a subscriber? 
MADCAD.com Free Trial
Sign up for a 3 day free trial to explore the MADCAD.com interface, PLUS access the
2009 International Building Code to see how it all works.
If you like to setup a quick demo, let us know at support@madcad.com
or +1 800.798.9296 and we will be happy to schedule a webinar for you.
Security check
Please login to your personal account to use this feature.
Please login to your authorized staff account to use this feature.
Are you sure you want to empty the cart?
ASHRAE Standard 41.7-2025 -- Standard Methods for Gas Flow Measurement (ANSI/ASHRAE Approved), 2025
- ASHRAE Online Bookstore
- Addenda
- Errata
- Return to Previous Page
- ANSI/ASHRAE Standard 41.7-2025 [Go to Page]
- Contents
- Foreword
- 1. Purpose
- 2. Scope
- 3. Definitions
- 4. Classifications [Go to Page]
- 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. The following gas flow measurement methods are within the scope of this standard. Each of these gas flow measurement methods is described in Section 7.
- 5. Requirements [Go to Page]
- 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...
- 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
- 6. Instruments [Go to Page]
- 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 [Go to Page]
- 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 gas flow direction and shall exceed 3 geometrically e...
- 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 8 and ASME MFC-3M 9 describe measurement of fluid flow in pipes using orifices, flow nozzles, an...
- 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.
- 7.8 Pitot-Static Tube Gas Flow Measurement Methods. Review Section 7.1. Figure 7-5 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 d...
- 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...
- 8. Uncertainty Requirements [Go to Page]
- 8.1 Post-Test Uncertainty Analysis. A post-test analysis of the measurement system uncertainty, performed in accordance with ANSI/ASME PTC 19.1,4 shall accompany each gas mass flow rate measurement if specified in the test plan in Section 5.1. Instal...
- 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 [Go to Page]
- 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
- 10. References
- Informative Appendix A: Informative References and Bibliography
- Informative Appendix B: An Uncertainty Analysis Example for a Differential Pressure Flowmeter [Go to Page]
- B1. Calculate the Random and Systematic Standard Uncertainties for Each Parameter [Go to Page]
- B1.1 SI Units. Using Equation B-1, Equation B-2, and Table B-3, the following random and systematic standard uncertainties are calculated for each parameter:
- B1.2 I-P Units. Using Equation B-1, Equation B-2, and Table B-3, the following random and systematic standard uncertainties are calculated for each parameter:
- B2. Calculate the Random and Systematic Standard Uncertainties of the Working Fluid Properties [Go to Page]
- B2.1 SI Units. Assuming a large degree of freedom and using the previously calculated random and systematic standard uncertainties of t1 and p1, the expanded uncertainties are as follows:
- B2.2 I-P Units. Assuming a large degree of freedom and using the previously calculated random and systematic standard uncertainties of t1 and p1, the expanded uncertainties are as follows:
- B3. Calculate and Evaluate the Partial Derivative of the Mass Flow Rate for Each Parameter [Go to Page]
- B3.1 Derivations of the Partial Derivatives in SI Units. Due to the derivation complexity of most of the partial derivatives of Table B-1, this section does not provide a step-by-step procedure with partial results; only the final partial derivatives...
- B3.2 Evaluation of Partial Derivatives in SI Units
- B3.3 Evaluation of Partial Derivatives in I-P Units. The calculated partial derivatives in I-P units are the same as in SI units; however, each partial derivative must be multiplied by a factor of 0.47268 for the correct unit conversion.
- B4. Calculate the Random and Systematic Standard Uncertainties Of the Mass Flow Rate [Go to Page]
- B4.1 SI Units
- B4.2 I-P Units
- B5. Calculate the Combined and Expanded Uncertainties of the Mass Flow Rate [Go to Page]
- B5.1 SI Units
- B5.2 I-P Units
- Informative Appendix C: Flowmeter Accuracy Comparisons [Go to Page]
