Consulting-Specifying Engineer - January 2008 - (Page 53) Induced flow fan with nozzle and windband A Nozzle inlet area after blade discharge B Nozzle height C Nozzle discharge area Airflow D Windband inlet area E Windband height F Windband discharge area Fan Inlet G Overlap between nozzle and windband B Airf low AMCA 210/ASHRAE 51 airflow setup Variable supply system Temperature Settling Settling means means Induced flow fan G F Airflow D Airflow Temperature Airf low E AC Pressure P Temperature Pressure Figure 1: This example of a flow fan shows how a nozzle and windband on the outlet enhances induction. These fans are used as an alternative to centrifugal or axial fan exhaust systems. Source: AMCA International Inc. Figure 2: This example measures the inflow through the fan only, due to the setup on the inlet. Source: AMCA International Inc. The committee struggled to select performance parameters that adequately supply needed information for certified ratings. Without question, exhaust velocity or exhaust diameter is needed in addition to outlet airflow. Some committee members thought that thrust performance would be the only parameter that was needed, while others thought the influence of crosswinds was important. The committee could not conceive a test that could be performed under current lab conditions that is easily reproducible and practical. Crosswind performance, although not currently included in a standardized test—and not in a certified ratings program—was not completely abandoned by the committee. Testing and ratings for crosswind effects is a potential development in the future. The committee considered developing a method to quantify the exhaust velocity profile. The velocity profile would be useful to determine an effective area or diameter at the outlet, which is what was needed in the plume equations. The suggested velocity measuring device was a 16-hole probe. Manufacturers noted that the velocity profile would change for each operating point of the fan. Further investigation showed that the increase in velocity with an effective area, compared to the results from using the average velocity (gross airflow divided by outlet area) was less than 10%. The committee consensus was to use inlet airflow, outlet airflow (i.e., the induced airflow), and outlet area as the parameters of interest in the certified rating program. Inlet airflow already was being certified by AMCA using a multi-nozzle inlet chamber for measuring airflow. Measuring the outlet-induced airflow required a new test method. Several committee members operated laboratories from their own facilities and conducted various testing schemes to determine the outlet airflow. It already had been determined that the pressure at the outlet should be at atmospheric conditions, with the inlet at varying pressures. Several methods were discussed and researched. As a result, the committee finalized a method where an inlet cham- ber is attached to the fan and an outlet multi nozzle chamber is attached to the outlet (see Figure 3). The outlet chamber is kept at 0 in. water gauge pressure for each inlet pressure over the operating envelope of the fan. At least two labs performed the test using this method prior to completing the test procedure, and all questions were answered. In the end, this test method proved successful. AMCA Certified Ratings Program AMCA International is the trade association for fan manufacturers around the world and has developed many certified ratings programs covering the broad spectrum of products under its scope. In every case, these programs ensure catalog performance ratings are provided to the public based upon standardized testing and the development of ratings based upon sound engineering principles. The catalog ratings are then checked to ensure they are not misleading and the performance is, indeed, based upon standardized testing. Performance also is periodically rechecked and subject to challenge. These safeguards are in place to ensure the customer has the right information and that all products are compared on a level playing field. AMCA’s Certified Rating Programs include performance ratings for: • Acoustical duct silencers • Air curtain units • Airflow measurement stations • Blowers • Circulating fans • Dampers • Evaporative coolers • Fans • Louvers • Positive pressure ventilators • Shutters • Water penetration and air performance For more information about AMCA’s Certified Ratings Programs visit www.amca.org/crp. Consulting-Specifying Engineer • JANUARY 2008 53 http://www.amca.org/crp
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.