Environmental Engineering Reference
In-Depth Information
Pump and Tower
The most common type of pump being used with an American windmill is the
single-
action piston pump
, where water is lifted on the upward stroke. Cylinder diameter sizes
range from about 25 mm for deep wells to about 250 mm for shallow wells. Most towers are
of a truss design.
Recent Technical Developments in Water-Pumping Windmills
During the late 20th century, there were few fundamental changes in the design of the
American windmill or its water pump. One of the objectives in recent improved designs is
to reduce the required
starting torque
. This improvement would allow the machine to start
pumping water at lower wind speeds, as well as increase the flow rate at higher wind speeds.
The most direct approach is to balance most of the weight of the pump rod and the water
column using
counterweights
and/or
springs
. Another design approach is a
quick-return cam
mechanism
that directs more of the available energy during each cycle into the upward or
lifting stroke and less energy into the downward stroke.
The most promising new design is called an
automatic stroke controller
that can be at-
tached to a conventional windmill pump. This device varies the pump stroke proportionally
to the wind speed. At lower wind speeds the stroke is shorter, which results in a mechanical
advantage that decreases the rotor torque required to start pumping water. As the wind speed
increases, the stroke automatically increases at a predetermined rate. This design produces
a better match between the pump load and the available wind power. The highest known
windmill/pump system efficiency was obtained using this mechanism. With an automatic
stroke controller it should be possible to use high-speed, low-solidity rotors to achieve higher
efficiencies in pumping and lower rotor weights.
Improvements in the water pump designs include the use of
double-acting
rather than
single-acting pumps
,
long-life cylinders
,
larger flapper valves
, and
air lift pumps
. Many
different power transmission schemes are being tried. These include mechanical (direct or
indirect), electrical, pneumatic, and hydraulic.
Modern Wind Turbines for Water Pumping
Another approach for irrigation is to use conventional HAWTs or VAWTs to power an
electric deep-well pump [Clark
et al
. 98, Gaudiosi and Pirazzi 987]. This method allows
flexibility when the turbine is at a different location than the pump. In 987, the U.S. Depart-
ment of Energy sponsored a test of a wind-electric system utilizing a
Bergey Excel
0-kW
HAWT. In a trade-off study [Clark and Mulh 992] the calculated annual output of a modern
windmill (a 2.44-m-diam.
Aermotor
) and its mechanical pump was compared to that of a small-
scale wind turbine (a
Bergey 1500
.5 kW HAWT) powering a submersible electric motor and
pump. The basis for these calculations was short-term performance test data and long-term
wind data. For approximately the same installed cost, the wind-electric system was predicted
to pump about 68 percent more water per year for the same lift. However, a consideration of
the total system costs (
i.e.
, cost per cubic meter of water delivered with the same lift) may show
more balance between the two approaches [Moroz 993].
Most electrical configurations for water pumping will employ an
induction generator
connected to the grid for
excitation
. In an early study, however, USDA researchers dem-
onstrated that stand-alone wind turbines with alternators producing
variable-frequency
and
variable-voltage
electricity can also be used to drive well motors [Clark and Pinkerton 988].
This is an important consideration when designing pumping systems for remote applications
Search WWH ::
Custom Search