Submitted to: Windpower
Publication Type: Proceedings
Publication Acceptance Date: 3/27/1995
Publication Date: N/A
Interpretive Summary: Increased maintenance costs of old windmills and high costs of extending electric grids to remote areas have spurred a resurgence of manufacturing of mechanical windmills. These newly manufactured units are designed for remote water pumping, mainly for livestock, and are designed without gearboxes. Two multibladed, mechanical water-pumping windmills were compared in side-by-side tests by the USDA-ARS, Bushland, TX. The two units were quite different in rotor design and the method of transferring the shaft power to reciprocating motion. The Dempster windmill was of the traditional design with a rotor diameter of 2.44 m (8 ft) containing 15 vanes and a gearbox for transferring the power to the pump rod. The Dutch Delta used a delta wing design which had 32 small vanes around a 4.88 m (16 ft) diameter circle and had a counter-balanced pump jack style arrangement to change the rotary motion into reciprocating motion. The Dutch Delta with a rotor diameter twice as large as the Dempster started pumping in a wind speed of 2.5 m/s (5.6 mph) as compared to the 3.5 m/s (7.8 mph) required for the Dempster. At a pumping head of 45 m (150 ft), the Dutch Delta pumped about 35% more water than the Dempster. The peak overall efficiency of the Dempster was measured at 10.5% as compared to 6.5% for the Dutch Delta. The peak efficiency occurred at wind speeds of 4 to 6 m/s (8-14 mph) when the windmills were turning slowly and the torque was high. The efficiency was low for the Dutch Delta because the delta wing design has a large open space in the center of the rotor that does not contribute power to the rotor. It is believed that the maintenance of the Dutch Delta will be high because of the large number of small bolts on the rotor and the number of bearings to keep greased.
Technical Abstract: A comparison of two mechanical wind pumping systems was carried out to determine windmill performance at different water depths. A 2.44 m (8 ft) rotor diameter windmill with 18 vanes, and a 4.88 m (16 ft) rotor diameter windmill with 32 delta wind vanes, were compared. The smaller windmill had vanes that filled 90% of the rotor area while the vanes on the larger one filled 41% of the rotor area. The smaller unit used a gearbox and the larger one used a pump jack style with a counter weighted shaft. Results from this study showed that both windmills started pumping at about the same wind speed, but the larger rotor operated at 4 to 6 strokes per minute faster than the smaller system when wind speeds were between 4 and 10 m/s. Although both windmills were fitted with the same size and style of pump, the larger rotor pumped more water because it had more strokes per unit of time. The delta wind rotor averaged 14,874 L/day compared to 10,974 L/day for the traditionally designed rotor. However, one must consider the difference in rotor diameters, total weight, cost and the efficiency of the two units. The larger rotor had a peak efficiency of 6.5% compared to 10.5% for the smaller rotor. The 25% more water pumped required twice as much rotor diameter and weight which usually means twice the cost.