Sizing a Direct Drive Centrifugal Blower for AHU Systems

Building a Direct Drive Centrifugal Blower for AHU Systems

When an AHU builder scales up, making fans on the line slows things down. In this project, the customer needed a direct drive centrifugal blower. However, their first request split the parts up. First, they sent sizes for bare metal parts. They asked for sizes from 7×7 to 12×12. Next, they needed wall thicknesses between 0.7 mm and 1.25 mm. They planned to add their own AC motors. These motors ranged from 1/8 HP to 3/4 HP at 230V.

We saw their order volume reached 6,000 units for some sizes. So, building a full blower in our plant made more sense. Shipping bare metal wastes time. The setup faces an ambient range of -25°C to 50°C. Therefore, the gear must meet GB/T 13275 rules. Finally, they need airway tests to ISO 5801-1997. The units also need CE marks under the EN 60335-1 safety rule.

Choosing a Fully Built Fan Module

We had two choices for this large order. First, we could just stamp the metal and ship it. We rejected this path. It forces the buyer to balance the fan on their own floor. That step takes too much time. Instead, we offered a fully built fan. We matched their power needs with our own AC motors.

Matching Motors to Housing Sizes

For the small housings, we picked 4-pole AC motors to hit the target pressure. The DD9-9 unit uses a 550W motor. It runs at 1250 RPM. By contrast, the larger DD12-12 needs a 750W 6-pole motor. This motor runs at 900 RPM on 220V at 60Hz. Therefore, this slower speed keeps the noise between 58 and 67 dB(A). The DD12-12 setup pushes 6206 m3/h of air. It hits a peak static pressure of 336 Pa.

Every choice has a cost. Shipping built fans costs more up front than shipping bare metal. Furthermore, full fans take up more box space. This raises the freight cost. Even so, the buyer dropped their internal assembly step entirely. We promised a G5.6 balance grade. We also kept radial runout under 1.2 mm. Finally, this strict limit helps the TPI ball bearings reach a 40,000-hour life.

Technical Specifications

The electrical specs show a clear split in IP ratings. First, the IP20 rating on the 750W model helps shed heat in dry spaces. Meanwhile, the IP44 models block moisture. Therefore, engineers must pick the housing based on the exact wetness inside the unit.

Reference: IEC 60529 covers the test method behind these figures.

Technical Documentation

Review the DD12-12 750W 6-Pole Spec Sheet. It shows the P-Q air curve and ISO 5801 test data for system builders.

You can access the DD9-9 550W 4-Pole File here. Furthermore, control panel designers need this sheet to check the 1250 RPM electrical traits.

Buyers can check the DD9-9 375W 6-Pole Details to verify the 2.8A current draw. It also proves the IP44 rating.

Planning Your Fan Assembly

When you need a fan for a tight space, check your plant’s limits before buying bare parts.

• First, check if your line can balance a fan wheel after attaching it to a bought motor.
• Next, state your exact target in cubic meters per hour and Pascals.
• Do not just ask for a half-horsepower motor.
• Finally, since we make the metal wheels in-house, we control the early runout before final tests start.

Related: HVAC Systems.

Common Questions About Fan Integration

Q: Why limit radial and axial runout on the fan wheels? A: Too much wobble causes low-frequency shaking. For instance, parts measuring over 1.2 mm radially or 1.0 mm axially will vibrate. This shaking hits the unit frame and ruins the bearings.

Therefore, tight metal limits help the TPI bearings reach a 40,000-hour life. Q: How does the motor pole count change the airflow? A: The pole count sets the running speed. First, a 4-pole motor runs near 1250 RPM at 50Hz.

This builds high pressure inside small housings like the DD9-9. By contrast, a 6-pole motor runs slower at 900 RPM on 60Hz. Finally, this slower speed moves 6206 m3/h of air while keeping noise under 67 dB(A). Q: When should I pick IP20 over IP44 for a fan?

A: The fan’s exact spot inside the unit sets the needed rating. First, IP44 shields the motor from splashing water drops. So, it works well near wet cooling coils. Instead, IP20 lets more air flow over the hot motor coils. This makes it perfect for dry air paths where cooling the motor matters most.

Browse our centrifugal fans range, the backward-curved fans section, or forward-curved fans.