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ASHRAE Standard 78 Method of Testing Flow Capacity of Suction Line Filters and Filter-Driers (ANSI/ASHRAE Approved) >
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ASHRAE Standard 78 Method of Testing Flow Capacity of Suction Line Filters and Filter-Driers (ANSI/ASHRAE Approved), 1985
- FOREWORD
- 1. Purpose
- 2. Scope
- 2.1 This test method is intended for use on both sealed and replaceable element type suction line filters and filter-driers of all types.
- 2.2 The test method is based on using air as the testing medium and calculating the results to refrigerant gas flow under various application conditions.
- 3. Definitions
- 4. Apparatus
- 4.1 A flowmeter is used to measure the airflow during the test. This flowmeter may be of any generally accepted design that is s...
- 4.2 Mercury manometers or other pressure-measuring devices with an accuracy and readability better than 0.1 psi (0.7 kPa) shall be used for measuring pressures and pressure drop across the filter being tested.
- 4.3 The temperature at the filter inlet and the flowmeter inlet shall be measured with a thermometer or thermocouple. An accuracy of ±0.5ËšF (0.3ËšC) is adequate.
- 4.4 The installation shall be made with line sizes that are convenient for the test being run and that are installed and arrange...
- 4.5 A receiver tank is generally part of the air supply system. This tank serves to store an adequate amount of air at a high enough pressure to permit running the test points desired without exhausting the air available at the filter inlet.
- 5. Test Procedure
- 5.1 Several different testing procedures have been found satisfactory. The preferred test setup is illustrated in Figure 1. Clea...
- 5.2 The test procedure is as follows:
- 6. Calculation of Results
- 6.1 Convert the flowmeter readings to lb/min (g/s) of airflow using the calculations appropriate for the meter involved. The pressure drop readings should be converted to psi (kPa) if the gage does not read in this unit.
- 6.2 Calculate the air density in lb/ft3 (kg/m3) at the filter inlet for each of the data points. Then calculate the product of this density and the pressure drop.
- 6.3 Prepare a graph on log-log paper (2 ° 3 cycle recommended) in which the air mass flow in lb/min (g/s) is plotted vs. the pro...
- 6.4 This air curve can be used to calculate refrigerant vapor flow for various conditions. To determine the refrigerant flow, ca...
- 6.5 For typical conditions, the information given in Table A1 can be used to calculate the refrigerant flow in lb/min (g/s) or in tons (kW) of refrigeration.
- Informative Appendix A- Theory of Flow Calculation
- A1. Well-known flow theory states that flow through an orifice is described by the following equation:2,3,4
- A2. Flow through a suction line filter is partly comparable to flow through an orifice and partly comparable to flow through a b...
- A3. It can be shown that for a given cross-sectional area, these two equations are the same. In both cases the mass flow is a function of
- A4. Detailed information and experimental verification for the above relationships using air at various pressures and various re...
- A5. Tests can be performed at inlet air pressure other than 50 psig (345 kPa gage) and calculated in a similar manner. These results are also satisfactory. Test results obtained at various inlet pressures should all fall on the same line.
- informative Appendix B- Sample Calculations
- B1. The following example shows a sample calculation required for a typical filter. Airflow was measured with an orifice-type meter.
- B2. Compute the test air density (entering the filter under test) by using the following equation:
- B3. Plot the DP vs. airflow values on log-log paper and fit a straight line (using the least squares method) through the data points, as shown in Figure B1.
- B4. To obtain refrigerant flow values, choose the desired refrigerant condition, calculate DP, and refer to the curve to obtain ...
- B5. For the conditions specified in Table B1, this flow rate in g/s can be converted to kW of refrigeration by dividing by the specific refrigerant flow rate from Table B1.
- B6. The same calculation can be made to obtain tons of refrigeration by using the I-P unit values.
- informative Appendix C- Bibliography [Go to Page]