The Conceptual Design of High Pressure Reversible Axial Tunnel Ventilation Fans

Table 2

Relative merits of the three fan system concepts.

	Concept 1; (Counter rotating)	Concept 2; (High speed)	Concept 3; (Double ended motor)
Pressure	2.5	2.25	1.8
Peak efficiency	+8%	+2%	+5 %
Noise	15 dB noisier	10 dB noisier	8 dB noisier
Cost	2.0 a single fan	2.5 a single fan	2.0 a single fan
Size	2.0 the length of a single fan	1.1 the length of a single fan	1.3 the length of single fan
Technical risk	Low	High	Medium

Note 1: All comparisons are relative to that of a single-stage fan of the same diameter.
Note 2: Peak efficiency is relative to that of a current state of the art single-stage reversible fan with a peak efficiency of 70%.