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
There are numerous reasons why fans 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 too 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.
There are eight questions you need answered to accurately select a special coating for a fan.
- What specific chemicals are involved?
- What are the concentration levels of these chemicals?
- What will the airstream temperature be?
- What is relative humidity of airstream?
- What amount of time will the fan see this environment? (continuous or intermittent)
- What part of the country will the fan be located? (seaboard, snow country or desert)
- What are the specifications or requirements for this coating?
- What part of the fan is to be coated? (interior, exterior or entire)
Greenheck offers centrifugal fans meeting UL Listing criteria that align under three UL Standards: 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, QEI(D) VAD(S), VAB(S), TAUB, TAUB-CA and TAUD; lab exhaust fan models Vektor-H, HS, MD, MH, MS, CD, CH and CS; and scroll housing centrifugal models SFB, SFD, USF, CSW, FJC, FJI, BIDW, and AFDW.
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, QEI(D), TAUB; and scroll housing centrifugal model CSW.
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 USF and CSW.