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ASHRAE 120 08:2008 Edition

ASHRAE 120 08:2008 Edition

$21.13

ASHRAE Standard 120 Method of Testing the Determine Flow Resistance of HVAC Ducts and Fittings (ANSI/ASHRAE Approved)

Published By Publication Date Number of Pages
ASHRAE 2008 68
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5 1. PURPOSE
2. SCOPE
2.1 This standard may be used to determine the change in total pressure resulting from airflow in HVAC ducts and fittings.
2.2 The test results can be used to determine duct flow losses in pressure loss per unit length. Fitting losses are reported as local loss coefficients.
2.3 This standard does not cover interpretation of test data.
3. DEFINITIONS, SYMBOLS, aND subscRIPts
3.1 Definitions. Refer to ASHRAE Terminology of HVAC&R1 for the definitions of terms not shown in this section.
3.2 Symbols and Subscripts
6 4. COMPLIANCE REQUIREMENTS
4.1 A duct or fitting test complies with this standard if the requirements of Section 6, “Instruments,” and Section 7, “Flow-Measuring Systems and Test Setups,” have been met.
4.2 A person or persons determining compliance shall state in writing that the test procedures and general test requirements of Section 8, “Observations and Conduct of Test,” have been met.
4.3 A person or persons determining compliance shall state in writing that the calculation requirements of Section 9, “Calculations,” and Section 10, “Test Results and Report,” have been met.
5. APPLICABILITY
5.1 Type of Ducts. This standard specifies test conditions for rigid and flexible ducts of rectangular, round, or other shapes constructed to contain airflow. Elastic materials that change size greater than 5% of any linear dimension with flow condit…
5.2 Type of Fittings. This standard specifies test conditions for fittings designed for use with the above ducts.
5.3 Sizes. This standard covers test conditions for ducts with an internal hydraulic diameter 50 mm or larger.
5.4 Test Air Velocities. This standard specifies test conditions for velocities in the range from 9 m/s to 36 m/s with a minimum of 6 m/s in a branch.
5.5 Measured Pressure Differential. The minimum pressure loss for a fitting (or the main of a fitting with a branch) shall be the smaller of 75 Pa or the pressure resulting from a mean velocity of 9 m/s. The minimum pressure loss for the branch of a …
6. INSTRUMENTS
6.1 Accuracy and Precision. The following specifications for instruments and methods of measurement include requirements for accuracy and precision. The specified accuracies correspond to two standard deviations and are based on an assumed normal dis…
7 6.2 Pressure
6.3 Pitot-Static and Total Pressure Tubes. Total pressure shall be sensed with a pitot-static tube of the proportions shown in Figure 3 or with a total pressure tube as shown in Figure 5. A pitot-static tube without the total pressure opening at the …
8 Figure 1 Static pressure wall tap.
Figure 2 Static pressure wall-tap disk.
Figure 3 Pitot-static tube.
9 Figure 4 Piezometer ring manifold.
6.4 Other Pressure-Measuring Systems. Pressure-measuring systems consisting of indicators and sensors other than those specifically allowed by this standard may be used if the combined error of the system, including any transducers, does not exceed t…
6.5 Flow Rate. The flow rate shall be calculated from measurements of pressure differential across a nozzle or an orifice as specified in Section 6.6 or 6.7, respectively. Nozzles and orifices are considered reference flow-measuring devices. Other fl…
6.6 Nozzles. The flow rate shall be calculated from the pressure differential measured across a nozzle or bank of nozzles provided the pressure differential is at least 75 Pa.
Figure 5 Total pressure tube.
10 Figure 6 Nozzles.
6.7 Orifices. Flow rate shall be calculated from the pressure differential measured across a sharp-edged orifice provided the pressure differential is 75 Pa or larger.
11 Figure 7 Orifice plates.
12 6.8 Special Flow-Measuring Methods. Special flow-measuring methods may be used if the error introduced by the method does not exceed that introduced by the nozzle or orifice flow-measuring systems. For any special flow-measuring method, the sensors a…
6.9 Thermometers. Both wet-bulb and dry-bulb temperatures shall be measured with thermometers or other instruments with accuracies of ±0.5°C, a precision of 0.5°C, and scale readabilities of 0.5°C or finer. Instruments used to measure the propert…
6.10 Barometers. The barometric pressure shall be measured with a mercury column barometer or other instrument with a demonstrated accuracy of ±15 Pa and with a scale readable to 3 Pa or finer.
7. FLow-MEasuRING SYSTEMS AND TEST SETUPS
7.1 Flow-Measuring Systems. Flow-measuring systems using nozzles or orifices required by this standard are illustrated in Figures 8 and 9.
7.2 Test Setups. Approved test setups are illustrated in Figures 10 through 19. These figures specify the test setup arrangement including the pressure-measuring stations for each category of test fitting and duct. Two types of test systems are shown:
13 Figure 8 Flow-measuring system—inlet multiple nozzle chamber.
Figure 9 Flow-measuring system—ducted orifice/nozzle.
14 Figure 10 Test setup—duct-mounted entry fitting.
Figure 11 Flow-measuring nozzle chamber with an entry test fitting.
15 Figure 12 Test setup—plenum-mounted entry fitting.
Figure 13 Test setup—duct-mounted exit fitting.
16 Figure 14 Flow-measuring nozzle chamber with an exit test fitting.
Figure 15 Test setup—plenum-mounted exit fitting.
17 Figure 16 Test setup—straight duct.
Figure 17 Test-setup—duct-mounted fitting.
18 Figure 18 Test setup—diverging flow fitting.
Figure 19 Test setup—converging flow fitting.
19 7.3 Selection Guide. The test specimen and mounting method (duct or plenum) can be used with Table 1 to identify the appropriate test setup and the permissible airflow-measuring systems. Examples of the various combinations of test specimen setups an…
7.4 Chambers and Plenums
Table 1 Test Setup and Flow-Measuring System
20 7.5 Test Ducts
Figure 20 Transformation piece.
21 7.6 System Leakage. All joints in the test system shall be sealed. Measured leakage between the flow-measuring station(s) and the test specimen shall not exceed 0.5% of the minimum test flow rate at the maximum pressure expected during the test. A su…
7.7 Fan and Flow Control. A fan to move air through the test system and a means of varying the flow rate shall be provided for the test system. Fans used to obtain the desired test flow rate shall be selected to produce sufficient pressure at the des…
7.8 Flexible Duct. A flexible duct setup guide is given in Annex E.
8. OBSERVATIONS And CONDUCt OF TEST
8.1 General Test Requirements
8.2 Data to be Recorded
8.3 Test Procedures
22 9. Calculations
9.1 Calibration Correction. Calibration corrections, when required, shall be applied to individual readings before averaging or other calculations. Calibration corrections need not be made if the correction is smaller than one-half the maximum allowa…
9.2 Density and Viscosity of Air
9.3 Flow Rate at the Measurement Station
23 9.4 Flow Rate at the Test Specimen. The flow rate at the test specimen, Qx, shall be obtained by dividing the measured mass flow rate by the density at the test specimen, rx, where plane x at the test specimen is
24 9.5 Test Velocity. The test velocity shall be calculated from the volume flow rate at the test specimen divided by the area of the specimen:
9.6 Test Reynolds Number. The Reynolds number at the test specimen shall be calculated by
9.7 Test Velocity Pressure. The velocity pressure at any plane, x, in the test system shall be calculated by
9.8 Pressure Loss of the Test Specimen at Test Conditions. The total pressure loss of a test duct or fitting shall be the pressure measurement differential as shown on the test setups (Figures 10 through 19) corrected for (l) the duct pressure losses…
9.9 Test Specimen Pressure Loss Calculations
26 10. teST RESULTS And REPORT
10.1 Report. The report of a laboratory test of a duct or fitting shall include the purpose, scope, results, test data, and descriptions of the test specimen, test setup, and instruments as outlined in Section 8. The laboratory shall be identified by…
10.2 Data
10.3 Estimating Losses at Low Flow. Recommended estimating procedures to determine losses at velocities below the lowest test velocity are given in Annex I. These procedures may be reported in accordance with the Annex I guidelines.
11. REFERENCes
28 Figure C-1 Variable fluctuating with time.
Figure C-2 Time-weighted average.
29 Figure D-1 Setup to check pressure lines for leaks.
30 Figure D-2 Configuration to leak check flow-measuring system and device setup.
Figure D-3 Blower-flowmeter setup for measuring system leakage.
31 Figure D-4 Setup to measure nozzle plate leakage.
Figure D-5 Blower-flowmeter system to measure leakage in the nozzle chamber under negative pressure.
32 Figure E-1 Test setup for straight flexible duct.
Figure E-2 Test setup for flexible duct with 90° bend.
33 Figure E-3 Forming a flexible duct bend.
Figure F-1 Ducted entry fitting—multiple nozzle chamber system.
34 Figure F-2 Plenum-mounted entry—ducted orifice system.
Figure F-3 Ducted exit fitting—multiple nozzle chamber system.
Figure F-4 Plenum-mounted exit fitting—ducted orifice/nozzle system.
35 Figure F-5 Straight duct—multiple nozzle chamber system.
Figure F-6 Ducted fitting—ducted orifice system.
Figure F-7 Diverging-flow fitting—flow measuring by ducted orifice (main and branch) system.
36 Figure F-8 Converging-flow fitting—flow measuring by chamber nozzle system and ducted orifice system.
Table G-1 Expansion Factors Yn for Nozzles
37 Table G-2 Discharge Coefficients Cn for Figure 6 Nozzles
40 H1. EXAMPLE 1: STRAIGHT DUCT
H1.1 General
H1.2 Data
Table H1 Dimensional Data
Table H2 Recorded Data
H1.3 Calculations. Tables H4 and H5 summarize the calculations for mass flow rate and the test specimen. Following these tables are the calculations for Test Point 1 and the coefficients for the equation Dpf, 1-2 = a Vb.
42 Table H6
Figure H1 Plot of test data and calculated friction rate.
44 Table H8 Summary of Test Specimen Error Analysis Calculations
45 H1.4 Error Analysis. Tables H7 and H8 summarize the error analysis calculations for mass flow rate, volumetric flow rate, and the uncertainty in the calculation of total pressure loss in straight duct.
49 H2. EXAMPLE 2: EQUAL INLET AND OUTLET AREA DUCTED FITTING
H2.1 General
H2.2 Data
Table H9 Dimensional Data
Table H10 Recorded Data
H2.3 Calculations. Tables H12 and H13 summarize the calculations for mass flow rate and the test specimen. These calculations are illustrated by Example H1. Following these tables are the loss coefficient calculation for Test Point 1 and the regressi…
50 Table H14 Summary of Pressure Loss and Local Loss Coefficient Calculations
51 Table H15 Regression Analysis to Determine Loss Coefficient
Table H16 Difference Between Test and Calculated Values
H2.4 Error Analysis. Tables H17, H18, and H19 summarize the error analysis calculations for mass flow rate and the fitting loss coefficient. The mass flow rate calculations are illustrated by Example H1. Following these tables are the error analysis …
53 Table H18 Summary of Test Specimen Error Analysis Calculations
54 Table H19 Summary of Fitting Loss Coefficient Error Analysis Calculations
55 H3. EXAMPLE 3: DIVERGING-FLOW JUNCTION FITTING
H3.1 General
H3.2 Data. Example is for one operating point (test point 3).
Table H20 Dimensional Data
Table H21 Area and FLow Rate Ratios
Table H22 Recorded Data
Table H23 Data for Test Point 3
H3.3 Calculations. Table H24 is a summary of the mass flow rate calculations. The method of calculating mass flow rate for the common section and branch of a junction is the same as Example 1. The mass flow rate of the downstream section is then calc…
Table H24 Summary of Mass Rate Calculations for Test Point 3
56 H3.4 Error Analysis. Table H25 summarizes the errors necessary to support the calculations that follow for Test Point 3. The calculation of the error values is based on the equations noted in Example 1 (Section H1).
Table H25 Partial Summary of Test Specimen Error Analysis
59 H3.5 Data Presentation. Only one test point was determined. Tests should be conducted so that the entire table can be completed. It is important that the end points of the table be included in the data reduction. Subscripts are as follows, with the e…
60 H4. EXAMPLE 4: CONVERGING-FLOW JUNCTION FITTING
H4.1 General
H4.2 Data
Table H26 Dimensional Data
Table H27 Area and Flow Rate Ratios
Table H28 Recorded Data
Table H29 Data for Test Point 3
H4.3 Calculations. Table H30 is a summary of the mass flow rate calculations. The method of calculating mass flow rates for the common and branch of a converging junction is the same as Example 1. The mass flow rate of the upstream section is then ca…
Table H30 Summary of Mass Rate Calculations for Test Point 3
61 H4.4 Error Analysis. Table H31 summarizes the errors necessary to support the calculations that follow for Test Point 3. The calculation of the error values is based on the equations noted in Example 1 (Section H1).
Table H31 Partial Summary of Test Specimen Error Analysis
64 H4.5 Data Presentation. Only one test point was determined. Tests should be conducted so that the entire table can be completed. It is important that the end points of the table be included in the data reduction. Subscripts are as follows, with the e…

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