These are my and my Blower Balancing and Repair divisional manager's opinions from our combined 72 years of experience in the field. We are against installing direct drive fans on the Type 1 grease exhaust systems as we think they have limited longevity and more expensive and time consuming repair issues compared to belt driven fans. On the direct drive fans, all of the fan stress, vibration, wear, and tear are completely on the smaller motor bearings. The belt driven fans have the larger pillow block bearings with fan belts that not only absorb much of the stress, but allow easier changes in fan speeds and parts when needed in the future. On the maintenance side, the motors are far easier to source and replace on a belt driven fan when they fail. The same with the bearings. On the direct drive fans, the blades have to be removed from the fan motor shaft to replace the motor which involves completely disassembling the fan. That is not always an easy proposition and sometimes the motors have to be cut off and the shaft pieces driven off the blade housing. The is not an issue with belt driven fans. The only positive I see on direct drive fans is that they do not require normal PM service. I also have recommended to some that stores with the direct drive fans carry a spare fan motor to avoid any sourcing issues.
One of the reasons this can up again is that a concept is currently going through excessive shutdown time at several different locations from direct drive fan motor failures. These fans are several years old now and the wear and tear failures are starting to show up. 2 were from bearings and the others were from electrical issues (storms or brown outs). None of the repairs have been less than $500 each so far plus the down time and attempts to get the specialty motors out to them. On another different concept, the direct drive fans actually had to be completely replaced the next day as it was faster than waiting 3 days for the motors to be sourced. We just want restaurants and installers to be proactive on this to avoid loss of business and expensive repairs.