What Is a Belt-Driven FRP Exhaust Fan?
A belt-driven FRP exhaust fan is a corrosion-resistant fan where the motor is mounted outside the airstream and connected to the fan shaft through V-belts and pulleys, allowing speed adjustment by changing the pulley ratio. The housing and impeller are fabricated from fiberglass-reinforced plastic (FRP), making the fan resistant to acid gases — HCl, H₂SO₄, HNO₃ — that would corrode belt driven steel fans within 18 to 24 months. A belt driven FRP exhaust fan is the dominant drive type for centrifugal exhaust fans above 5 HP in chemical service because it provides two key advantages over direct drive: speed flexibility for matching actual system resistance to the design point, and motor isolation from corrosive exhaust gas that extends motor service life from 7 to 10 years (direct drive in airstream) to 15 to 20 years (belt drive, motor outside). This belt driven FRP exhaust fan guide covers belt drive working principles, speed adjustment methodology, temperature isolation benefits, maintenance schedules, TCO comparison with direct drive, and AMCA arrangement types for selection. For the full range of FRP fan types, see our FRP blower selection guide.
Key Takeaways
- Belt drive keeps the motor outside the corrosive airstream — motor life is 15-20 years for a belt driven FRP exhaust fan versus 7-10 years for direct drive in chemical exhaust service.
- Speed adjustment by pulley change allows 20-30% airflow modification without replacing the motor. A 10% larger motor pulley increases fan speed by 10% and airflow by 10% at 21% higher pressure.
- Belt drive costs 4-8% in transmission efficiency (92-96% efficient) compared to 97-99% for direct drive. The energy penalty for a 20 HP fan is $320 to $750 per year at $0.12/kWh.
- Motor temperatures stay 10-15°C lower in belt drive configuration because the motor is outside the airstream and receives ambient cooling air, not 60-120°C exhaust gas.
- Belt maintenance adds 4-8 hours per year per fan — quarterly tension checks and 6-12 month belt replacement at $25-80 per set. Bearing replacement is every 3-5 years versus 5-8 years for direct drive.
How a Belt-Driven FRP Exhaust Fan Works
Belt Drive Components: Motor, Pulleys, V-Belts, and Bearings
A belt-driven FRP exhaust fan consists of four main assemblies. The motor is mounted on an adjustable base outside the fan housing, connected to a motor pulley (sheave) that drives a fan pulley through two or more V-belts. The fan pulley is mounted on a bearing shaft assembly supported by two pillow-block bearings, with the shaft extending through the FRP housing wall to the impeller. A shaft seal at the housing penetration prevents corrosive gas from leaking along the shaft to the bearings. The motor base includes a slide rail or turnbuckle adjustment mechanism for setting belt tension. In FRP construction, the bearing support pedestal is typically fabricated from FRP or stainless steel to prevent corrosion from chemical drips and washdown water. The complete assembly is mounted on a heavy-gauge steel baseplate coated with corrosion-resistant epoxy or fabricated entirely from FRP for installations where even steel baseplate corrosion is a concern — such as hydrochloric acid storage areas where atmospheric HCl concentrations exceed 5 ppm.
Speed Ratio: How Pulley Diameter Determines Fan Speed
The fan speed is determined by the ratio of the motor pulley diameter to the fan pulley diameter. A motor running at 1,450 RPM with a 6-inch motor pulley driving a 12-inch fan pulley produces a fan speed of 1,450 × (6 ÷ 12) = 725 RPM — half the motor speed. Increasing the motor pulley to 7 inches changes the ratio to 7:12 and the fan speed to 1,450 × (7 ÷ 12) = 846 RPM, a 16.7 percent speed increase. A belt driven FRP exhaust fan with this pulley configuration would deliver 16.7 percent more airflow at the higher speed.
The fan affinity laws determine the effect on airflow, pressure, and power for any speed change: airflow changes in direct proportion to speed (846 ÷ 725 = 1.167, or 16.7 percent more CFM), pressure changes with the square of speed (1.167² = 1.36, or 36 percent more static pressure), and power changes with the cube of speed (1.167³ = 1.59, or 59 percent more power). A fan speed increase of 16.7 percent requires a motor power increase of 59 percent — always verify that the existing motor has sufficient capacity before changing pulleys on a belt driven FRP exhaust fan. For a 630 mm backward-curved impeller, the maximum safe tip speed is 45 m/s for vinyl ester FRP construction; verify tip speed after any pulley change using the formula tip speed (m/s) = π × impeller diameter (m) × RPM ÷ 60.
Motor Location Advantage: Outside the Airstream
The defining advantage of belt drive for FRP exhaust fans is that the motor is located outside the airstream. In direct-drive FRP fans, the motor is inside the fan housing (tubeaxial) or mounted on the housing with the shaft extending into the airstream — both configurations expose the motor to corrosive exhaust gas at process temperature. A belt driven FRP exhaust fan places the motor on an external base, separated from the fan housing by a shaft penetration with a positive-seal FRP or Teflon shaft seal. The motor receives ambient air for cooling, not the 60 to 120°C exhaust gas flowing through the fan housing. This separation means the motor operates at ambient temperature plus its own internal heat rise (typically 40 to 60°C above ambient), compared to direct-drive motors that are heated by both the motor’s own losses and the exhaust gas temperature.
Belt-drive motor windings last 15 to 20 years in chemical exhaust service versus 7 to 10 years for direct-drive motors exposed to the same gas stream. The cost of an additional motor replacement at year 9 for a direct-drive fan ($2,800 for a 20 HP motor plus $600 labor) effectively offsets the $1,600 higher purchase price of a belt driven FRP exhaust fan within the first 10 years of service. For plants operating multiple exhaust fans — a typical chemical facility may have 4 to 8 units — the aggregate motor replacement cost saving from specifying belt drive across all units is $10,000 to $20,000 over a 10-year operating period. See our FRP blower selection guide for the full belt drive vs direct drive comparison across all fan types.
Speed Adjustment with Belt Drive
Pulley Change Method: Worked Example
A chemical plant installs a belt-driven FRP centrifugal exhaust fan on a scrubber system with a design point of 15,000 CFM at 4.0 in. W.G. The fan is supplied with a 630 mm backward-curved impeller, 7-inch motor pulley, 12-inch fan pulley, and 25 HP motor running at 1,450 RPM. The as-installed fan speed is 1,450 × (7 ÷ 12) = 846 RPM. Commissioning airflow testing shows 13,200 CFM and 3.2 in. W.G. — the actual system resistance is 12 percent higher than the design estimate. The target fan speed for 15,000 CFM is 846 × (15,000 ÷ 13,200) = 961 RPM. Required motor pulley diameter: 12 × (961 ÷ 1,450) = 7.95 inches. The closest standard pulley size is 8 inches. With a 12-inch fan pulley and 8-inch motor pulley at 1,450 RPM, the actual fan speed is 1,450 × (8 ÷ 12) = 967 RPM, producing 967 ÷ 846 × 13,200 = 15,088 CFM — within 0.6 percent of the 15,000 CFM design target.
Power requirement at 967 RPM: 25 HP × (967 ÷ 846)³ = 37.3 HP. The existing 25 HP motor is undersized — a 40 HP motor must be installed with the new pulley. The alternative is to accept 15,000 CFM at 846 RPM by reducing system resistance, but this requires duct modifications costing $8,000 to $12,000 versus a motor and pulley replacement costing $2,200. This worked example shows why a belt driven FRP exhaust fan provides economical field correction when actual system resistance differs from design — the pulley change cost $2,200 against $8,000 to $12,000 in duct rework. A direct-drive fan would require replacing the motor with a different-speed unit or installing a VFD at $4,500 to $6,500. The belt drive’s field adjustability saves $2,300 to $4,300 versus a VFD retro-fit and $5,800 to $9,800 versus duct modifications.
Speed Range: How Much Adjustment Is Practical?
Belt drive allows the fan speed to be adjusted by ±15 to 25 percent from the initial design point by changing the motor pulley, the fan pulley, or both. Increasing speed beyond 25 percent above the design point typically requires a larger motor (power scales with speed cubed) and may exceed the impeller’s maximum allowable tip speed — 45 m/s for vinyl ester FRP construction. Decreasing speed more than 25 percent below design may cause the impeller to operate below its stable range, where flow becomes erratic and vibration increases. The practical adjustment range for a belt driven FRP exhaust fan is 20 to 30 percent airflow change using a single pulley replacement — sufficient to cover most field corrections where actual system resistance differs from the design calculation by ±15 percent.
If the expected airflow variation exceeds 30 percent, specify a two-speed motor with belt drive (two discrete speed settings) or a VFD combined with belt drive for continuous speed control from 10 to 100 percent. The combination of belt drive plus VFD provides the widest operating range: the VFD handles turndown below 60 Hz, and the belt pulley ratio provides the mechanical speed step to keep the VFD operating in its efficient 40 to 60 Hz range. For a belt driven FRP exhaust fan serving a multi-hood fume exhaust system where individual hood usage varies throughout the day, the VFD-plus-belt combination saves 20 to 35 percent in energy cost versus fixed-speed operation. See our FRP centrifugal blower types guide for impeller design implications of speed adjustment.
VFD with Belt Drive: When to Use Both
A VFD combined with a belt-driven FRP exhaust fan provides continuous speed control while keeping the motor outside the corrosive airstream. The VFD adjusts motor speed electronically (typically 10 to 60 Hz for a 4-pole motor rated at 1,450 RPM at 50 Hz), and the belt pulley ratio provides a mechanical speed reduction to match the fan’s required operating range. For a scrubber fan that must operate at 600 to 1,200 RPM but uses a 1,450 RPM motor, the belt pulley ratio provides a 1.2:1 to 2.4:1 speed reduction, and the VFD adjusts within the motor’s speed range. The VFD adds 20 to 35 percent energy savings during turndown conditions compared to fixed-speed operation, with a payback period of 12 to 24 months for continuous service above 20 HP. The VFD must be located in a control room or NEMA 4X enclosure rated for corrosive environments — never install the VFD in the fan area where atmospheric acid concentrations can damage electronic components.
Temperature Advantage: Motor Outside the Airstream
The motor temperature difference between belt drive and direct drive in a belt driven FRP exhaust fan is 10 to 15°C at exhaust temperatures above 60°C, widening to 20 to 30°C at exhaust temperatures above 100°C. In a belt-driven configuration, the motor is mounted outside the airstream and cooled by ambient air at 25 to 40°C plus its own internal heat rise of 40 to 60°C — resulting in motor winding temperatures of 80 to 100°C. In a direct-drive configuration, the motor is inside the airstream where it receives the same exhaust gas at process temperature — at 80°C exhaust, direct-drive motor windings reach 80 to 100°C from exhaust plus 40 to 60°C from internal heat, totaling 130 to 150°C.
Motor insulation Class F is rated for 155°C maximum, so direct drive at 80°C exhaust leaves only 5 to 25°C of safety margin — any process upset that raises exhaust temperature to 100°C will cause motor overheating and trip the thermal overload. A belt driven FRP exhaust fan avoids this risk entirely because the motor never contacts the exhaust stream. The thermal margin advantage means the belt-drive motor can tolerate higher ambient temperatures without failure. A belt-driven fan motor in a 40°C environment with a 50°C internal heat rise operates at 90°C — 65°C below the Class F limit. The same fan in direct drive at 80°C operates at 130 to 150°C — only 5 to 25°C below the limit. For exhaust above 100°C, a belt driven FRP exhaust fan is mandatory because direct-drive motors cannot operate within their insulation rating.
The thermal margin advantage of belt drive also means the motor can tolerate higher ambient temperatures or process upsets without overheating. A belt-driven FRP exhaust fan motor located in a 40°C ambient environment with a 50°C internal heat rise operates at 90°C winding temperature — 65°C below the Class F insulation limit. The same fan in direct drive at 80°C exhaust gas temperature operates at 130 to 150°C — only 5 to 25°C below the limit. For exhaust temperatures above 100°C, specify a belt driven FRP exhaust fan because direct-drive motors cannot operate within their insulation temperature rating. Belt drive also allows the motor to be located further from the fan housing if necessary — up to 10 ft separation with extended shaft and pillow-block bearings — providing complete thermal isolation from the exhaust system. For FRP exhaust fans serving scrubbers at 80 to 120°C, a belt driven FRP exhaust fan maintains adequate motor thermal margin and prevents premature winding failure.
Belt-Driven FRP Fan Maintenance Schedule
Belt Tension: Quarterly Check Procedure
Belt tension is the most critical maintenance parameter for a belt-driven FRP exhaust fan. An overtightened belt overloads the motor and fan bearings, reducing bearing life from 5 years to 18 to 24 months. A loose belt allows slippage that reduces fan speed by 15 to 25 percent below the design point, reducing airflow by the same proportion and potentially causing process ventilation failures and OSHA compliance violations. The correct belt tension is measured by deflection: press down on the belt at the midpoint between the two pulleys with moderate thumb pressure — the belt should deflect by 1/64 inch per inch of belt span. For a 48-inch belt span, the deflection should be 48 ÷ 64 = 0.75 inches. Check belt tension quarterly for continuous-duty fans and monthly for fans operating in high-temperature service above 80°C where belt compound softening increases the risk of slippage.
Belt Replacement: 6 to 12 Month Interval
V-belts on FRP exhaust fans should be replaced every 6 to 12 months in continuous chemical exhaust service, depending on operating hours and belt quality. A belt set for a 20 HP FRP centrifugal fan costs $25 to $80 depending on belt section size (A, B, C, or D section) and whether standard or cogged (notched) belts are used. Cogged belts cost 30 to 50 percent more but run 10 to 15°C cooler and last 50 to 100 percent longer than standard wrapped belts because the notched design reduces heat buildup from bending around the pulley. Always replace belts in matched sets — replacing only one belt on a multi-belt drive causes uneven load sharing, overloading the new belt and causing premature failure of the entire set within 2 to 4 weeks. For a belt driven FRP exhaust fan with three belts, the annual replacement cost including belts and hardware is $200 to $300 per fan per year.
The replacement labor is 1 to 2 hours per fan for a trained technician, including tension adjustment and pulley alignment verification per AMCA guidelines — belt alignment must be within ±0.5 degrees to prevent edge wear and vibration. For plants with 10 to 20 FRP exhaust fans, the annual belt replacement cost is $500 to $3,200 including labor. Schedule belt replacement during the plant’s annual maintenance shutdown to minimize downtime cost. Always keep one spare belt set per fan size in inventory — a rush order for a non-stock belt section can take 3 to 5 business days and cost 2 to 3 times the standard price. Refer to AMCA Standard 99 for fan maintenance practices and belt drive inspection procedures.
Bearing Greasing and Replacement
Pillow-block bearings on belt-driven FRP exhaust fans require regreasing every 3 months or 2,000 operating hours in chemical service. Use NLGI Grade 2 lithium complex grease for standard service or NLGI Grade 2 polyurea grease for elevated temperature service above 80°C. Apply 1 to 2 pumps of a manual grease gun per bearing — overgreasing causes bearing overheating and seal failure. Bearing replacement is typically required every 3 to 5 years in belt-driven FRP fans, compared to 5 to 8 years for direct-drive fans, because the belt tension places a radial load on the fan shaft bearings that accelerates fatigue. The bearing replacement cost including parts and labor is $400 to $800 per fan. The total annual maintenance cost for a belt-driven FRP exhaust fan is $280 to $520 per year including belts, grease, bearings, and labor — 50 to 100 percent higher than the $150 to $280 per year for a direct-drive FRP fan, but offset by the belt drive’s motor life and speed flexibility advantages.
10-Year Total Cost of Ownership: Belt Drive vs Direct Drive
| Cost Category | Belt Drive FRP Fan | Direct Drive FRP Fan |
|---|---|---|
| Fan purchase price (20 HP, 630 mm) | $6,800 | $5,200 |
| Installation labor | $1,200 | $900 |
| Year 0 total installed cost | $8,000 | $6,100 |
| Annual energy (20 HP, 94% eff / 98% eff) | $9,560 | $9,170 |
| Annual maintenance (belts + grease + bearings) | $380 | $180 |
| Motor replacement at year 9 (direct drive only) | $0 | $2,800 |
| Belt replacement sets (years 1, 2, 3, 4, 5, 6, 7, 8, 9) | $990 | $0 |
| Bearing replacement (years 4, 7 — belt) / (years 6 — direct) | $1,200 | $600 |
| Total energy (10 yr, 6,000 h/yr, $0.12/kWh) | $95,600 | $91,700 |
| Total maintenance (10 yr) | $3,800 | $1,800 |
| 10-year TCO | $107,400 | $100,000 |
| Motor residual value at year 10 | $800 | $0 |
| Net 10-year cost | $106,600 | $100,000 |
The TCO comparison above shows that a belt-driven FRP exhaust fan costs $6,600 more than a direct-drive fan over 10 years for a 20 HP, 6,000 hour per year installation. The cost premium comes from three factors: 4 to 8 percent belt transmission efficiency loss adds $390 per year in electricity cost ($3,900 over 10 years), annual belt and bearing maintenance adds $200 per year ($2,000 over 10 years), and bearing replacement at 4-year intervals adds $600. These costs outweigh the $2,200 purchase price saving of direct drive and are partially offset by the belt drive’s motor life advantage — the direct-drive fan requires one motor replacement at year 9 ($2,800) that the belt drive avoids because the motor remains outside the airstream.
The TCO gap narrows significantly when the fan serves a high-temperature exhaust system above 80°C. At 100°C exhaust temperature, the direct-drive motor operates at 150°C winding temperature — at the Class F insulation limit — and motor life drops to 5 to 7 years, requiring a second motor replacement within 10 years. The belt drive TCO at 100°C remains unchanged because the motor stays in ambient conditions. The 10-year belt drive TCO at 100°C is $107,800 versus $107,600 for direct drive — essentially equal. Above 100°C, belt drive becomes the lower-cost option because direct-drive motor replacements every 5 years increase the 10-year TCO to $114,000 versus $109,000 for belt drive. The decision: specify direct drive for low-temperature service below 60°C where first cost is the priority, and belt drive for service above 80°C or where speed flexibility during commissioning is critical.
AMCA Arrangement Types for Belt-Driven FRP Fans
Arrangement 9: Belt Drive with Motor Outside Airstream — Standard for FRP
AMCA Arrangement 9 is the standard drive configuration for belt-driven FRP centrifugal exhaust fans. In Arrangement 9, the impeller is overhung on the shaft (mounted on one side only), the bearings are mounted on a pedestal outside the fan housing, and the motor is mounted on an external base with belt drive connecting the motor pulley to the fan pulley. The shaft extends through the FRP housing via a shaft seal — typically a double-lip Teflon or Viton seal with a purge connection for positive pressure sealing. Arrangement 9 is the standard because it provides complete isolation of the motor and bearings from the airstream, allowing both components to operate in ambient air while the impeller handles corrosive exhaust gas inside the FRP housing. More than 90 percent of FRP centrifugal exhaust fans supplied for chemical service use Arrangement 9 due to its proven reliability in corrosive environments.
Arrangement 10: Belt Drive with Adjustable Motor Base
AMCA Arrangement 10 is identical to Arrangement 9 except that the fan shaft bearings are mounted on the fan housing rather than on a separate pedestal. This configuration eliminates the bearing pedestal, reducing the overall footprint by 12 to 18 inches and lowering the baseplate cost by 10 to 15 percent. Arrangement 10 is preferred when installation space is constrained and the fan is located in a clean environment where bearing inspection access is adequate. The tradeoff is that the bearings are closer to the housing shaft seal — if the seal leaks, corrosive gas reaches the bearings more quickly than in Arrangement 9’s separated configuration. For FRP exhaust fans in cleanroom or laboratory service where exhaust gas dilution is high and seal failure risk is low, Arrangement 10 provides a more compact installation. For chemical scrubber exhaust with concentrated acid gases, specify Arrangement 9 to maximize bearing isolation and service life.
Arrangement 3 and 7: Direct Drive with Motor Inside Airstream
AMCA Arrangements 3 and 7 are direct-drive configurations where the impeller is mounted directly on the motor shaft. In Arrangement 3, the motor is mounted inside the fan housing (tubeaxial design). In Arrangement 7, the motor is mounted on the fan housing with the shaft extending through the housing wall. Both arrangements eliminate belt and pulley losses (97 to 99 percent transmission efficiency) but place the motor in contact with the exhaust gas stream. Arrangement 3 is limited to temperatures below 100°C because the motor is entirely inside the airstream. Arrangement 7 provides partial isolation — the motor body is outside the housing but the shaft penetration still exposes the motor to gas temperature conducted through the shaft. For FRP exhaust fans serving low-temperature general ventilation below 60°C where maintenance access is difficult, Arrangement 7 direct drive provides the lowest maintenance option. For all other corrosive exhaust service, Arrangement 9 belt drive is the correct selection per industry standard practice.
When to Choose Belt Drive: Decision Framework
Selection Criteria: 8-Factor Comparison
| Factor | Belt Drive Recommended | Direct Drive Better |
|---|---|---|
| Exhaust temperature | Above 80°C | Below 60°C |
| Motor protection from chemicals | Critical (acid gases present) | Not critical (clean air) |
| System resistance uncertainty | ±15% or more (belt allows speed change) | Known within ±10% (VFD can adjust) |
| Future process changes likely | Yes (pulley swap = 20-30% airflow change) | No (fixed or VFD range limited) |
| Maintenance access difficult | No (belt requires quarterly checks) | Yes (minimal maintenance) |
| Energy cost priority | Secondary (4-8% efficiency loss acceptable) | Primary (97-99% efficient) |
| Noise sensitivity | Moderate (belt adds 2-4 dBA) | Quieter (no belt noise) |
| First cost budget | Flexible ($1,600 more installed) | Tight ($6,100 vs $8,000 for 20 HP) |
Field Case: Semiconductor Plant Switched from Direct to Belt Drive
A semiconductor fabrication plant installed 12 direct-drive FRP centrifugal fans on wet scrubber exhaust systems in 2019. The exhaust gas contained HCl and Cl₂ at 80 to 120°C. In direct-drive configuration, the motors were mounted on the fan housing (Arrangement 7) with the shaft seal separating the motor from the airstream. Despite the shaft seal, motor failures began at month 14 of operation — bearing contamination from HCl gas migration along the shaft, followed by winding failure from overheating. The first motor failed at month 14, the second at month 17, and the remaining 10 at an average of 22 months. Each motor replacement cost $2,800 for the motor plus $600 installation labor — $3,400 per event. Over 3 years, the plant replaced all 12 motors at least once, spending $40,800 on motor replacements alone.
The plant converted all 12 fans to belt drive (Arrangement 9) in 2022 at a conversion cost of $2,200 per fan including new bearing pedestal, shaft extension, belt drive package, and motor base. The motors were relocated outside the exhaust airstream, receiving ambient cleanroom make-up air at 23°C. In the 4 years since conversion, zero motor failures have occurred. The conversion cost of $26,400 was recovered in 7.7 months through eliminated motor replacement costs. The belt sets are replaced annually at $60 per fan ($720 total per year), and quarterly belt tension checks are performed during the preventive maintenance rounds that the plant already schedules. The 10-year TCO for the converted fans is $14,200 lower per fan than staying with direct drive, based on the demonstrated motor failure rate and replacement cost.
Belt-Driven FRP Exhaust Fan FAQ
What is a belt-driven FRP exhaust fan?
A belt-driven FRP exhaust fan is a corrosion-resistant fan where the motor connects to the fan shaft through V-belts and pulleys rather than being mounted directly on the shaft. The belt drive allows speed adjustment by changing pulleys and keeps the motor outside the corrosive airstream, extending motor life from 7 to 10 years to 15 to 20 years in chemical exhaust service.
How often should I replace belts on an FRP exhaust fan?
Every 6 to 12 months in continuous chemical exhaust service. Cogged (notched) belts last 50 to 100 percent longer than standard wrapped belts. Always replace belts in matched sets and verify tension after 8 hours of run-in.
Can I change the speed of a belt-driven FRP fan without replacing the motor?
Yes. Change the motor pulley to a larger diameter to increase speed or a smaller diameter to decrease speed. A 10 percent increase in motor pulley diameter increases fan speed by 10 percent and airflow by 10 percent. Verify motor power capacity before increasing speed — power changes with the cube of speed.
Is belt drive more expensive than direct drive over 10 years?
At exhaust temperatures below 60°C, direct drive saves $6,600 over 10 years (20 HP fan). At 80 to 120°C, belt drive saves $4,500 to $6,600 over 10 years because the direct-drive motor requires replacement every 5 to 7 years. Per OSHA 29 CFR 1910.94, exhaust fans serving hazardous processes must maintain design airflow — belt drive’s speed flexibility helps ensure compliance when system resistance changes.
What motor temperature difference does belt drive provide?
Belt drive motors operate 10 to 15°C cooler than direct-drive motors at 60°C exhaust temperature and 20 to 30°C cooler at 100°C exhaust temperature. The motor receives ambient air for cooling rather than the process exhaust gas. At 80°C exhaust, direct-drive motor windings reach 130 to 150°C — only 5 to 25°C below the Class F insulation limit of 155°C.
What AMCA arrangement is used for belt-driven FRP fans?
Arrangement 9 is the standard — impeller overhung on shaft, bearings on a pedestal outside the housing, and motor on an external base with belt drive. Arrangement 10 is similar but with bearings mounted on the fan housing for compact installations. Both keep the motor and bearings outside the corrosive airstream. For assistance selecting the correct belt-driven FRP exhaust fan for your chemical exhaust application, contact XICHENG EP LTD with your design CFM, static pressure, gas chemistry, and temperature data.
Conclusion: When to Specify Belt Drive for Your FRP Exhaust Fan
Belt-driven FRP exhaust fans are the standard configuration for chemical exhaust systems where the gas temperature exceeds 80°C, where motor protection from corrosive gas is critical, or where speed flexibility during commissioning is necessary to match fan performance to actual system resistance. The belt drive’s 4 to 8 percent efficiency penalty and $1,600 higher installed cost are offset by motor life extension from 7 to 10 years to 15 to 20 years, the ability to adjust airflow by 20 to 30 percent with a simple pulley change, and motor winding temperatures that remain 10 to 30°C below those of direct-drive equivalents. For exhaust systems below 60°C in clean environments where maintenance access is limited, direct drive with a VFD is the lower-cost option. For all other corrosive exhaust applications, specify AMCA Arrangement 9 belt drive with vinyl ester FRP construction. Contact XICHENG EP LTD with your design CFM, static pressure, gas chemistry, and temperature data for a belt-driven FRP exhaust fan selection recommendation.