Engineered Systems - March 2008 - (Page 12)

Take the HVAC CHALLENGE ™ BY STEVEN G. LIESCHEIDT, P.E., CSI-CCS, CCPR ST STEVEN TE LIESCHEIDT, P.E., CSI-CCS, CCPR HEIDT, EIDT, CSI-CCS, C R 10. 11. 15. 5. Fans 17. fan fa fa , fan, with limited to low-pressure applicao nd prima ma m tions and a primary energy transfer by pressure. sure re. re. e velocity pressure. This type of axial ty ax type fan has good blade axial design that gives me at gives medium- to high-pressure t e capacity at good e apa y p o efficiency, and the blades capacity at good eff may have fixed, adj hav fixed, adjustable, or controllable ave have pitch. ch. ch h. h pitch. At this point in test n of a fan, the duct is t this point his testi testing completely blocked off. completely blocked o completely locked These calculated eff es a ul ed effect factors are only an s These calculated eff ap roxim tion, d fans supplied by differapproximation, and f p ox mation, oxima o approximation, ent manufacturers d not necessarily react ma an ers manufacturers do to this in the sam w sa ame same way. This association publishes Standard 210 “Laboratory Methods of Testing Fans for Aeordynamic Performance Rating.” To brush up on the facts behind this month’s clues, refer to Chapter 18 (“Fans”) in the 2004 ASHRAE Handbook – Systems and Equipment. Liescheidt is a sales engineer with Langendorf Supply Co., Inc. in St. Louis, MO. E-mail him at stevel@lsco-inc.com. Can't wait until next issue? Now, check out the answers for this month's "HVAC Challenge" on page 69 or check out answers from past puzzles on ACROSS 2. This data, as tabulated in the usual fan tables, is based on arbitrary increments of flow and pressure. 4. The operating speeds at which resonances tend to cause objectionable vibrations. 6. This type of fan has impellers that produce pressure principally by the change in air velocity as it passes through the impeller blades, with no pressure being produced by centrifugal force. 9. A fan type that is also referred to as backward-inclined. 12. All fans produce this by altering the airflow’s velocity vector. 13. This type of centrifugal fan is the highest efficiency of all centrifugal fans designs. 14. This is a function of the fan design, volume airflow rate, total pressure, and efficiency, and is reported by fan manufacturers as sound power levels in eight octave bands. 16. This type of specialized type fan design has a performance similar to a backwardcurved fan, except that the capacity and pressure are lower and the efficiency is lower than the backward-curved fan, and the performance may have a dip to the left of the peak pressure. 18. This type of fan has higher pressure characteristics than airfoil, backward-curved, and backward-inclined fans, and their curves may have a break to the left of the peak pressure and should not be operated in this area of the curve. www.esmagazine.com. Solution to February’s HVAC Challenge™ DOWN 1. This type of fan is somewhat more efficient and capable of developing more useful static pressure than a propeller fan and has a hub that is usually less than half the fan tip diameter. 3. This type of centrifugal type fan has a flatter pressure curve than airfoil, backward-curved, and backward-inclined type centrifugal fans. 5. To control air the characteristic curve of either this or the system must change. 7. This organization publishes Standard 51 “Laboratory Methods of Testing Fans for Aerodynamic Performance Ratings.” 8. This is historically a low-efficiency type 12 En gi neer ed S y stem s March 2008 http://www.esmagazine.com

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Engineered Systems - March 2008 Contents Editor’s Note Back2Basics HVAC Challenge Case In Point Commissioning Building Automation Energy Wiz HVACR Designer Tips Application Checklist Exemplary Design = Elementary Success The Modern Unit Ventilator On A Mission VAV Systems And Green Design – Part II Issues & Events Products Glossary Classifieds Advertiser Index Tomorrow’s Engineer

Engineered Systems - March 2008

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