Greenheck Fan Mixed Flow Fans Belt and Direct Drive QEI-L - Manual (Page 11)

11
Belt Drive versus Direct Drive
Example of Annual Operating Cost Savings
For a system performance requirement of 25,000 cfm at 2.5 inches of static pressure (wg) the corresponding
operating power requirements are 13.97 Bhp with a QEI-I size 36 and 19.8 Bhp for a size 36 tubular centrifugal fan.
Formulas:
- Kilowatt-Hours = (Operating Power (Bhp) x 0.746 x Hours of Operation) / Motor Efficiency
- Operating Cost = Kilowatt-Hours x Power Cost per kW hour
Assumptions:
- Cost of electricity is $0.09 per kilowatt hour
- 3,120 annual hours of operation (12 hours per day, five days a week, 52 weeks a year)
- 93.0% motor efficiency (equal to NEMA Premium minimum efficiency for 15 and 20 hp, ODP, 1725 rpm motor)
Annual Operating Cost Savings = $4,460 - $3,147 = $1,313
High Efficiencies = Lower Operating Costs
Tubular Centrifugal Fan
kW-Hours = (19.8 Bhp x 0.746 x 3120) / 0.93 = 49,554
Operating Cost = 49,554 x $0.09 = $4,460
QEI-I - Mixed Flow Fan
kW-Hours = (13.97 Bhp x 0.746 x 3120) / 0.93 = 34,963
Operating Cost = 34,963 x $0.09 = $3,147
Belt Drive Advantages
• Lower sound levels
• Motor out of the airstream for easy access
• Motor size may be changed to accommodate
possible future air capacity requirements
• Final system balancing accomplished by
changing drives
Direct Drive Advantages
• Fewer wear components and less maintenance, no
shaft, bearings, pulleys, or belts
• More compact than equivalent belt drive size
• Motor in airstream for increased motor efficiency
and cooling
• Equal loading between mounting brackets
• Final system balancing accomplished by adjusting
the motor speed (ex. variable frequency drive use).