ACHRNEWS

Explaining Synchronous Drives: Are They Intended for HVAC Applications?

August 9, 2010

While synchronous drives do have many industrial applications, they are generally not accepted as the best option for HVAC equipment. Virtually no HVAC original equipment manufacturer (OEM) uses or recommends synchronous drive designs due to cost, unacceptable noise and vibration, structural design concerns, and reliable availability of replacement components. For those applications that are suitable or require synchronous drives, Browning, for example, offers a full synchronous product offering and can assist with proper design.

Synchronous drives (often called timing belt drives) differ from V-belt drives in that they have a tooth profile and require sprockets with teeth that create a direct engagement with the synchronous belt. Product is categorized by trapezoidal or curvilinear design.

SYNCHRONOUS DISADVANTAGES FOR HVAC EQUIPMENT

1. Significantly higher component cost.

2. Increased noise can be severe and transfer/amplify through entire system including ductwork.

3. More susceptible to increasing vibration.

4. Replacement part availability can be an issue.

5. Will not correct unsatisfactory drive conditions.

6. Higher start-up loads that can cause the belt to jump sprocket teeth and damage the sprocket, destroy a belt, motor, or even fan blower.

7. Alignment and tension is absolutely critical. Not as forgiving and far more sensitive to misalignment than V-belt designs.

EFFICIENCY

Recently some customers have asked if synchronous drives are suitable for HVAC retrofits because of their efficiency. While synchronous drives do offer stable efficiency in the 98 percent range, V-belts are much more economical and can mirror synchronous efficiency if properly designed and periodically tensioned. The U.S. Department of Energy publishes that V-belts also have efficiency up to 98 percent when installed (DOE/GO-102005-2060). Cogged V-belts are 2-3 percent more efficient than standard wrapped style V-belts. Wrapped belt drive designs have a peak efficiency of about 95 percent compared to cogged designs at 98 percent. If periodic re-tensioning is performed on a cogged V-belt drive and sheaves are in good condition, virtually no advantage or return on investment (ROI) exists by retrofitting with synchronous belts.

SUMMARY

Without question V-belt drive designs are used almost exclusively in commercial and industrial HVAC equipment because the disadvantages listed above for synchronous drives are minimized when using V-belts. As a leader in belt drives, Browning has collaborated with many HVAC OEMs on drive design. Given today’s lighter framework trend, it would be extremely challenging to maintain the necessary alignment and structural rigidity for a synchronous drive to be effective in these applications. Given the mirroring efficiency potential using cogged V-belts, retrofitting an existing HVAC drive with a synchronous product is unnecessary and can easily create performance and noise issues. A far more effective ROI would be to implement a preventive maintenance program that encompasses periodic belt tensioning, inspection of sheave grooves for wear, and usage of cogged V-belts when possible.

Reprinted with permission from the Browning Belt Drive Monthly published by Emerson Industrial Automation. For more information, visit www.emerson-ept.com.

Publication date: 08/09/2010