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FAQs - Utility, Centrifugal, and Radial Blowers

• Can a Series 21 (Permalock Seam) centrifugal fan be welded?
• Can a solid state speed control be used on a belt drive fan?
• Do spark resistant fans have any third party certification?
• For a two-speed fan, how is the low speed performance determined?
• Under what conditions will fan and isolation base combinations be shipped assembled from the factory?
• What determines the minimum horsepower requirement for Greenheck centrifugal and industrial fans?
• What factors prevent fans from not performing as specified?
• What information needs to be known in order to properly select a special coating?
• What is the maximum roof pitch that a fan can be mounted to without correcting the curb for the pitch?
• Which Greenheck centrifugal fans have a UL Listing?

• Q: Can a Series 21 (Permalock Seam) centrifugal fan be welded?

  A: In 1994, Greenheck developed the Series 21 scroll housing centrifugal fans. Series 21 fans were designed to meet more commercial applications. Series 41 fans are intended for both commercial and industrial applications. Physically, the only difference between a Series 21 and 41 fan is the method of fastening the side plates of the housing to the scroll wrap. Series 21 construction uses an Airtight Permalock design which crimp locks the two pieces together. Series 41 fans have side plates and scroll wraps which are welded together.

• Q: Can a solid state speed control be used on a belt drive fan?

  A: Greenheck does not offer solid state speed controls on belt drive fans because in order to use a solid state speed control, the motors have to be either a PSC (permanent split capacitor) or shaded pole type. These types of motors are not used on belt drive fans because they have very low starting and running torque. Belt drive fans have added torque requirements due to bearings, belts, and pulleys, all which hinder the ability of the motor to start the fan or even keep it running if the voltage is dialed down on the speed control.

• Q: Do spark resistant fans have any third party certification?

  A: Spark resistant fans do not have any third party certification. In other words, you will not see a sticker on the fan which states that the fan is spark resistant. The guidelines for spark resistant construction are noted in AMCA Standard 99-0401-86. If spark resistant construction is ordered, the fan manufacturer will build the fan to meet these requirements.

• Q: For a two-speed fan, how is the low speed performance determined?

  A: The fan laws should be used to determine how a fan would perform on low speed.
  CFM (low) = CFM (high) x [RPM (low) / RPM (high)]
  Ps (low) = Ps (high) x [RPM (low) / RPM (high)]2
  BHP (low) = BHP (high) x [RPM (low) / RPM (high)]3

• Q: Under what conditions will fan and isolation base combinations be shipped assembled from the factory?

  A: There are two main requirements for fans and structural steel isolation base packages to be shipped assembled from the factory. First, only centrifugal sizes up to 33 and industrial process sizes up to 23 can ship assembled. (Fan sizes larger than these are subject to additional freight charges.) Second, only Greenheck manufactured structural steel isolation bases apply. Inertia bases will ship separately.

• Q: What determines the minimum horsepower requirement for Greenheck centrifugal and industrial fans?

  A: Minimum horsepower for centrifugal and industrial fans is based on either the operating brake horsepower or the minimum starting horsepower of the fan. Operating brake horsepower is an obvious limit to the minimum motor horsepower, since the motor horsepower must exceed the operating brake horsepower for the fan to work. Minimum starting horsepower is based solely on the horsepower required to get the fan wheels rotating. Minimum starting horsepower begins to become a significant factor for single width wheels above size 49 and double width sizes above 44. For example, it is possible to have 49-BISW performance that requires less than one brake horsepower, but the minimum starting horsepower is 7.5 HP.

• Q: What factors prevent fans from not performing as specified?

  A: There are numerous reasons why fans may fail to perform as specified, but first it is important to understand what defines acceptable performance. According to AMCA Publication 200, a fan installed in a ventilation system should expect a tolerance of /- 7.5% for flow (cfm). In other words, a fan which produces 1,000 cfm in a lab environment should provide a volume flow rate of 925 to 1,075 cfm when installed in a properly designed ventilation system. Volume flow rates which fall below this range are typically the results of variances in system static pressure or mechanical problems with the fan. Common symptoms include:

  • Obstructions in the duct system - closed dampers, closed registers, dirty filters, clogged coils
  • Obstructions in the fan inlet - elbows to close to the inlet, walls too close to the inlet
  • Duct design - improperly designed turning vanes, leaks in supply or exhaust ducts
  • Fan related - impeller running backwards, fan speed too low, impeller dirty or clogged, clearances between inlet cone and wheel cone are incorrect.

• Q: What information needs to be known in order to properly select a special coating?

  A: To properly select a special coating for a fan, there are eight questions that should be answered.

  1. What specific chemicals are involved?
  2. What are the concentration levels of these chemicals?
  3. What will the airstream temperature be?
  4. What is relative humidity of airstream?
  5. What amount of time will the fan see this environment? (continuous or intermittent)
  6. What part of the country will the fan be located? (seaboard, snow country or desert)
  7. What are the specifications or requirements for this coating?
  8. What part of the fan is to be coated? (interior, exterior or entire)

• Q: What is the maximum roof pitch that a fan can be mounted to without correcting the curb for the pitch?

  A: As a general rule, the recommended maximum roof pitch is 2:12 or 10 degrees from horizontal. Steeper pitches will increase the possibility of moisture infiltration into the building as a result of water splashing off the roof and entering the fan. For roof pitches greater than 2:12, it is recommended to have a pitched curb, which will allow the fan to sit level and not at an angle.

• Q: Which Greenheck centrifugal fans have a UL Listing?

  A:

  Greenheck offers three UL listings: Power Ventilators (UL 705), Power Ventilators for Smoke Control, and Power Ventilators for Restaurant Exhaust (UL-762). UL-705 is concerned with mechanical and electrical construction that assures safe operation of the fan. UL-705 is offered on inline models AX, TBI-CA, TBI-FS, TDI, TCB, TCBRS, TCBRU, TCF, QEI(D) VAD(S), VAB(S), TAUB, TAUB-CA, TAUD, and scroll housing centrifugal models SFB, SFD, SWB, BISW, AFSW, BIDW, and AFDW (in Series 21 or 41).

  Power Ventilators for Smoke Control is concerned with the removal of smoke laden, and potentially high temperature vapors in the event of an emergency. This listing is available on inline models AX, TBI-FS, TCF, QEI(D), TAUB, and scroll housing centrifugal models SWB and BISW (in Series 21 or 41).

  UL-762 is concerned with fans designed for the removal of smoke and grease laden vapors with airstream temperatures up to 375º F. UL-762 is available on inline models TCB and QEI, lab exhaust fan model Vektor-H, and scroll housing centrifugal models SWB and BISW (in Series 21 or 41).