High efficiency fans with low power consumption are used. Four different fan diameter available: 400 and 500 mm with three-phase motors (4/4 poles) 400V-50/60Hz, 560 and 630 mm with three-phase motors (4 poles) 230/400V-50/60Hz. The motors are with external rotor, constructed in accordance with VDE 0530/12.84. Protection class IP 54 according to DIN 40050. Integrated thermal protection by thermo contacts. This provides reliable protection against thermal overload. Fan diameter 630 mm with large bell mouth that optimizes the fan efficiency and ensures a lower noise level than a traditional short bell mouth.