TP25-17 Direct Dry Cooling

The promise of direct drive cooling tower fans with Permanent Magnet (PM) motors is not new, but so far this approach has not seen significant adoption. This paper reviews the advantages of direct drive and the requirements for successful direct drive implementation, including performance and economic gaps that have impeded adoption. Efficient torque at the low speeds required for direct drive has been a critical constraint. Crossing this gap can be achieved by increasing motor pole count without increasing coil resistance. This combination has not been practical with PM Radial Flux (RF) motors, given their fundamental design and construction. An emerging motor type known as Transverse Flux (TF) offers promise to both increase pole count and simultaneously reduce coil resistance, a combination which is unique to this motor type. TF motors, originally invented in the 1980’s, have now been successfully commercialized in several markets including direct drive pumps and fans.