ASHRAE Standard 41.11 2020

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ASHRAE Standard 41.11-2020 – Standard Methods for Power Measurement (ANSI Approved)

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ASHRAE	2020	34

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Description

ASHRAE Standard 41.11 prescribes methods for power measurements under laboratory and field conditions when testing heating, ventilating, air-conditioning, and refrigerating systems and components.The 2020 revision of Standard 41.11 incorporates minor changes and complies with ASHRAE

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PDF Pages	PDF Title
1	ANSI/ASHRAE Standard 41.11-2020
3	CONTENTS
4	FOREWORD 1. PURPOSE 2. SCOPE 3. DEFINITIONS
6	4. CLASSIFICATIONS 4.1 Power Measurement Application. Power measurements that are within the scope of this standard are classified as one of the types in the following subsections. 4.2 Electrical Load Type. Electrical load configurations for electrical power measurement are classified as one of the types in the following subsections. 4.3 Electrical Power Analyzer Types. Electrical power analyzer types that are within the scope of this standard are the types listed in Tables 1 and 2. 4.4 Nonelectrical Power Measurements. Nonelectrical power measurements that are within the scope of this standard are as follows:
7	5. REQUIREMENTS 5.1 Test Plan. A test plan shall specify the power measurement system accuracy and the test points to be performed. The test plan shall be one of the following documents: 5.2 Values to Be Determined and Reported 5.3 Accuracy. A selected power measurement method must meet or exceed the required power measurement system accuracy specified in the test plan in Section 5.1 over the full range of operating conditions.
8	5.4 Uncertainty. The uncertainty in each power measurement shall be estimated using the method in Section 8 for each test point unless otherwise specified in the test plan. Alternatively, the worst-case uncertainty for all test points shall be estima… 5.5 Steady-State Test Criteria. Power test data shall be recorded at steady-state conditions unless otherwise specified in the test plan in Section 5.1. If the test plan requires power data points to be recorded at steady-state test conditions and pr…
10	5.6 Unsteady Power Measurements. If required by the test plan in Section 5.1, power test data shall be recorded 5.7 Current Transformer Restriction. An open circuit across the secondary winding of a current transformer is not permitted. 5.8 Potential Transformer Restriction. A short circuit across the secondary winding of a potential transformer is not permitted. 6. INSTRUMENTS 6.1 Instrument Requirements for All Measurements
11	6.2 Laboratory Electrical Measurements, Linear Loads. Electrical power measurement system accuracy for linear loads in laboratory applications shall be within ±1.0% of reading unless otherwise specified in the test plan. 6.3 Laboratory Electrical Measurements, Nonlinear Loads. Electrical power measurement system accuracy for nonlinear loads in laboratory applications shall be within ±1.0% of reading unless otherwise specified in the test plan. 6.4 Field Electrical Measurements, Linear Loads. Electrical power measurement system accuracy for linear loads in field applications shall be within ±3.0% of reading unless otherwise specified in the test plan. 6.5 Field Electrical Measurements, Nonlinear Loads. Electrical power measurement system accuracy for nonlinear loads in field applications shall be within ±3.0% of reading unless otherwise specified in the test plan. 6.6 Nonelectrical Power Measurements 7. TEST METHODS
12	7.1 Electrical Power Measurement Test Methods 7.2 Shaft Power Measurement Test Methods. The measurement of shaft power of rotating machines, in the absence of transients, using a dynamometer or a torque meter, shall be determined using Equation 7-1 for SI units or Equation 7-2 for I-P units.
13	7.3 Measurements of Power Derived from the First Law of Thermodynamics. This section provides an example of deriving power by applying the first law of thermodynamics.
18	7.4 Measurements of Fluid Power Output from a Pump. The measurement of fluid power output from a pump, in the absence of transients, shall be determined using Equation 7-13 for SI units or Equation 7-14 for I-P units. 8. UNCERTAINTY CALCULATIONS 8.1 Uncertainty Estimate. An estimate of the measurement system uncertainty, performed in accordance with ASME PTC 19.1 3, shall accompany each power measurement. 8.2 Method to Express Uncertainty. All 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:
19	9. TEST REPORT 9.1 Electrical Power Measurements Described in Section 7.1 9.2 Shaft Power Measurements Described in Section 7.2 9.3 Fluid Output Power Measurement from a Pump Described in Section 7.4
20	10. REFERENCES
21	INFORMATIVE APPENDIX A: INFORMATIVE REFERENCES AND BIBLIOGRAPHY
22	INFORMATIVE APPENDIX B: POWER MEASUREMENT BASICS B1. POWER COMPARED TO ENERGY B2. ELECTRICAL VOLTAGE AND CURRENT MEASUREMENT BASICS B2.1 Instrumentation. Voltage and current instrumentation may be based on analog or digital technology. Digital instrumentation is the more modern of the two technologies and often has wider bandwidth, greater accuracy, and the capability to accurate… B2.2 Adequate Bandwidth. Bandwidth is defined at a gain of –3 dB, corresponding to a spectral density that is greater than half of the maximum. Therefore, with an adequate bandwidth, the gain at the frequency of what is being measured will be 0 dB…. B2.3 Range Extenders. The ranges of instrumentation may be extended through the use, for example, of resistive shunts, current transformers, Hall-effect transducers, potential transformers, or resistive dividers. The accuracy, bandwidth, and impedanc… B2.4 Harmonic-Related Losses. Harmonics is the name given to the condition where currents or voltages have frequencies that are integer multiples of the fundamental power frequency. In a normal alternating current (AC) power system, the voltage varie…
23	B3. ELECTRICAL POWER AND POWER FACTOR MEASUREMENT BASICS B3.1 Power. Power is the time average of the product of the instantaneous magnitude of voltage and current for both linear and nonlinear loads. The power associated with linear AC loads may be obtained if the root-mean-square (RMS) values of voltage … B3.2 Power Factor. Power factor is defined as the ratio of the true power in watts to the apparent power in volt-amperes. This is true for both linear and nonlinear loads. Power factor is a figure of merit, indicating how much of the apparent power i…
24	B3.3 Considerations for Nonlinear Units Under Test. Nonlinear units under test (UUTs) may require appropriate isolation and precautions to ensure that accurate power measurements are obtained. Nonlinear UUTs may require the use of instrumentation tha… B3.4 Connections and Loading Effects. The impedance of the voltage and current measuring elements and their loading effects may introduce errors in either the voltage or current reading, and thus the power reading. The connections required to measure… B4. NONELECTRICAL Power Measurements B4.1 Shaft Power Measurement. Shaft power is the product of the instantaneous shaft torque and the instantaneous shaft speed as prescribed in Section 7.2. Alternatives for measuring equipment include a noncontact speed sensor combined with an in-line… B4.2 Power Derived from the First Law of Thermodynamics. Power derived from the first law of thermodynamics is determined from combinations of temperature measurements, pressure measurements, flow rate measurements, and fluid properties—for example… B4.3 Fluid Power Output from a Pump. Fluid power output from a pump is the product of the volumetric flow at the pump outlet and the pressure differential across the pump as defined in the test plan.
25	INFORMATIVE APPENDIX C: AN UNCERTAINTY ANALYSIS EXAMPLE FOR THE INPUT AND OUTPUT POWER OF A VARIABLE FREQUENCY DRIVE C1. Review test objectives and test duration C2. List all independent measurement parameters and their nominal levels C3. List all calibrations and instrument setups that will affect each parameter
26	C4. Define the functional relationship between independent parameters and the test result

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Standard Title	ASHRAE Standard 41.11-2020 – Standard Methods for Power Measurement (ANSI Approved)
Published Code	ASHRAE
Publication Date	2020
Pages Count	34

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ASHRAE Standard 41.11 2020

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