Frequently Asked Questions About Centrifugals

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: Can inline fans be used for kitchen grease exhaust applications?

A: Yes, inline fans (GFC models TCB and QEI) are UL Listed for use in grease exhaust applications. Additionally, these units are designed to meet the requirements of NFPA 96 - Ventilation Control and Fire Protection of Commercial Cooking Operations. Greenheck is the only manufacturer that meets both UL and NFPA for inline grease exhaust applications. Our "Easy Access Door" makes routine service and cleaning fast and easy. All service work can be accomplished without removing the fan from the ductwork.

Q: Can inline centrifugal fans be used for continuous high temperature exhaust applications?

A: Inline centrifugal fans (GFC models TCB or TCF) are not recommended for use in high temperature continuous exhaust applications. The reason is based solely on inline centrifugal fan design, which has the impeller at the inlet of the housing. As seen on the following diagram, the fan housing becomes pressurized and heated to the temperature of the incoming air. Leakage of heated air and heat transfer through the bearing cover and belt tube reduce the life of the bearings and motor. Our recommendation is not to exceed 200° F with inline centrifugal fans.

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 and scroll housing centrifugal models SWB and BISW (in Series 21 or 41).

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: 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 require less than one brake horsepower, but the minimum starting horsepower is 7.5 HP.

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.