Assessment of Operating Performance of Existing RE Systems

Assessment of Operating Performance of Existing RE Systems

Technical Assistance to Manufacturers of RE Equipment Subcontract

revised first interim report

Assessment of Operating Performance of Existing RE Systems

wIND PUMP

Prepared by:

International Resources Group – Philippines, Inc.

Unit 2303 Medical Plaza Ortigas Condo.

25 San Miguel Ave., OrtigasCenter

PasigCity 1600

ASSESSMENT OF OPERATING PERFORMANCE OF EXISTING RE SYSTEMS

1. Technology Area: WIND
2. Application: Wind Pump
3. Description of Wind Pump

Wind energy is an abundant source of renewable energy that can be exploitedfor pumping water in remote locations. Wind pumps are one of the oldest methods of harnessing the energy of thewind to pumpwater. A wind pump or windmill is a wind-driven machine that converts the kinetic energy of the wind into mechanical power which is then used to pump water.

Wind pumps are classified intodifferent categories:

1. Orientation of theaxis of rotation of the windmill rotor

1. Vertical-axis windpump - The axis of rotation of the rotor is perpendicular to the direction of the wind. These windmills can obtain power fromwind blowing in any direction. Vertical axis windmills has not led to practical applications due to their high cost per unit of water pumped (heavy machines combined with low efficiency), and poor reliability.

1. Horizontal-axiswind pump – The axis of rotation of the rotor parallel with the direction of the wind. These pumps must be oriented facing the wind toextract power. Most windmills for water-pumping applications are of the horizontal-axis type, and have multi-bladed rotors that can supply the high torque required to initiate operation of a mechanical pump.

1. Type of transmission between the wind rotor and the pumping device

1. Windmills driving piston pumps – This is the most common type of windmill wherein the wind rotor is coupled mechanically (directly, or through a gear box) to the piston pump.

1. Windmills with rotating transmission - The wind rotor transmit its energy through a (mechanical) rotating transmission to a rotating pump, for example a centrifugal pump or a screw pump. Both are used especially for low head/high volume applications.

1. Windmills with pneumatic transmission - Few manufacturers fabricate windmills driving air compressors. The compressed air is used for pumping water by means of an air lift pump (basically two concentric pipes), or a positive displacement pump (a cylinder with a few valves). This type of transmission allows the windmill to be installed at some distance from the well. Another advantage is the absence of pump rods and of any moving part inside the well.

1. Wind electric pumping systems - Wind electric generators are sometimes used to drive electric pumps directly (without being coupled to an electric grid). Again, this transmission provides the freedom to install the wind machine at a windy site at some distance from the well. Electric submersible pumps may be used to pump water from narrow boreholes, with flow rates far in excess of those attainable with piston pumps.

1. Windmills with hydraulic transmission -Several experiments have been performed on remote pumping by means of a hydraulic transmission. Mostly water is used as the operating fluid.

1. Level of technology

1. First generation – Classical, multi-bladed wind pumps incorporating a back-gearing transmission. These pumps are also called American wind pumps. They are highly reliable and last for more than 20 years with minimal maintenance. However, these wind pumps are heavy, difficult to install, and requires high investment cost.

1. Second generation – These are modern, lightweight wind pumps developed in the last 20 years. Gearboxes are omitted with new control systems developed. These are designed for specific applications, making them cost-effective. However, these are less reliable than the first generation wind pumps and applications are limited to low-head pumping.

1. Low-cost artisanal wind pumps – These wind pumps have simple designs which can be produced using locally-available materials. However, they have a short life span and require proper maintenance.

A windmill consists typically of the following components: the rotor, a tail vane, head, transmission, pump, and tower (Figure 1).

Figure 1. A typical wind pump system showing the major components

1.Rotor – The rotor captures the wind’s energy and converts it into mechanical power. It is composed of a shaft and spokes welded into a ring to support the blades. Usually the blades are curved steel plates, but sails are sometimes used. The number of blades varies depending on the rotor speed, i.e. 8 blades for fast-running rotors and 38 blades for slow-running rotors.

2.Tail vane - The tail vane directs the rotor to face perpendicular to the incoming wind. The top assembly pivots on top of the tower, allowing the rotor to face the direction of the wind. Most wind pumps are provided with mechanisms which turn the rotor away from strong winds to prevent damage.

3.Head – The head is where the rotor shaft seats and the tail vane are bolted. The head causes the yawning action of the rotor with the wind. It is designed to carry the weight of the rotor and the tail vane with adequate strength to overcome strong forces. Present wind pumps usually utilize angle bar braces and mild steel plates for the head.

4.Transmission – The transmission of a windmill conveys the mechanical energy delivered by the rotor to the pump. An essential part of the transmission is some kind of eccentric that transforms the rotating movement of the rotor into a reciprocating movement of the pump rod. The pump rod transmits the power to the pump. A swivel joint prevents the pump rod from rotating when the windmill's head assembly is yawing due to a change of wind direction. Normally the pump rod is guided at several points in the tower. The swivel joint and the guides require regular lubrication by greasing. The efficiency of the transmission is somewhere between 70% and 90%.

5.Pump –The pump lifts the water from the well to the tank. Most water pumping windmills are equipped with single-acting piston pumps (Figure 2). When the piston movesdown, the foot valve closes and water passes through the open piston valve. On theupward stroke the valve in the piston closes, the foot valve opens, and water is pumped.

6.Tower – The rotor, tail vane, head, and transmission together form the head assembly. This assembly is supported by a tower, which raises it over any obstructions into a fair, unobstructed wind. The tower also serves as a rig when installing the pipes of deep well pumps. Typical height for towers in the Philippines is 20 to as high as 50 feet. Tower designs are three- or four-legged types, or a single pipe with guy wires.

Figure 2. Principle of operation of a windmill piston pump

Major applications of wind pumps in the Philippines are for domestic water supply and for agricultural irrigation. Other applications include water supply for large-scale poultry, piggery, and livestock farms; agricultural and industrial plants such as bottling companies and concrete hollow-block factories; beach and in-land resorts; salt pans; fish ponds.

1. Technical Evaluation of Wind Pumps

Evaluation of wind pumps starts with the system description where the system in its “as-found” condition is described. The next step is the Pumping Performance Test which provides technical performance information about the pumping system (i.e. the windmill, the transmission and the pump). Moreover it is a diagnosis of the technical condition of the system at the start of the evaluation that can be repeated during the testing period as often as desired, e.g. after repairs, overhauls or when the pumping system seems to fail.

1. Pumping Performance Test

The objective of the Pumping Performance Test of the wind pump system is toshow system water pumping rates, energy inputs and outputs, and efficiencies as afunction of ten-minute average windspeeds covering the normal range of wind speedexpected at the site.

Additional data are obtained on the performance of the windmill and of the pump.These include rotor speed characteristics as afunction of windspeed and load, and waterpumping rate as a function of rotor speed.

The Pumping Performance Test determines the pumping performance of a wind pump through a series of 10-minute measurements. A total of 100 sets of ten minute measurements are taken over a period of several days. If wind conditions warrant, the sets of measurements should cover periods when the wind speed is high as well as periods when the wind speed is low. If the rotor does not rotate at all during a 10-minute period, that period is omitted.

For the Pumping Performance Test, the following quantities to be measured and the equipment required are listed below:

1.Time – A digital watch or stopwatch is required for the timing of 10-minute periods during the test.

2.Head

1. Suction head – For surface water sources or dug wells, the suction head is measured directly with a measuring stick or tape. When the horizontal distance between water source and pump is long, a level is used to get a more accurate reading of the vertical distance. For example a U-shaped transparent hose partly filled with water can be used to indicate points of constant height, even at large distances apart. For bore holes where the water surface is not accessible, a well dipper is used to measure the suction head.

1. Discharge head – The discharge head is measured directly using a measuring stick or tape. During the test, particularly for systems with long or narrow discharge lines a pressure gauge at the pump discharge is used.

1. Pressure head – The pressure head should be measured at the boundary of the pumping system by means of a bourdon type pressure gauge.

3.Water volume pumped – Water flow is measured using an integrating flow meter that is able to measure irregular and pulsating flow. Proper cleaning and calibration is required to prevent errors.

4.Pump strokes or rotations – For reciprocating pumps, the number of strokes is obtained by visual inspection. If a more accurate measurement is desired, an LCD counter is used. For centrifugal pumps, a revolution counter is used (e.g. a car odometer attached to any shaft).

5.Wind speed – An integrating rotating cup anemometer (e.g. wind-run meter) is used. It is positioned at the height of the rotor shaft and at such a place that it is outside the wake of the wind pump most of the time. This is achieved by two different methods:

1. If the terrain is flat and without major obstacles (resulting in wind speeds not varying very much over larger distances), place the anemometer at a distance of about 20 times the rotor diameter away from the wind pump: then wake effects for all wind directions can be considered negligible.

1. If the terrain does not meet these conditions, place the anemometer at a distance between 2 and 8 times the rotor diameter away from the wind pump and at such a place with respect to the wind pump that it is outside the wake of the wind pump for the predominant wind directions.

To avoid disturbance of the wind speed measurements by the tower in which the anemometer is mounted, the tower height should be chosen such that the anemometer can be installed on top of it.

Procedure

Engage the rotor and pump early in the morning (just after sunrise) of a day with expected normal wind speed. After the wind speed has become so high that the rotor is turning steadily, take a series of ten-minute measurements as follows:

1.Time

Record the time, t (hour, minute, second) of the beginning and end of each ten-minute measurement period.

2.Windrun

Record the readings (kilometers) of the integrating anemometer (windrun meter), Rw, at the beginning and at the end of each ten-minute measuring period.

3.Water volume pumped

Record the readings (cubic meters) of the integrating flow meter, QB, at the beginning and at the end of each ten-minute measuring period.

4.Rotor rotations

Record the readings (revolutions) of the integrating rotation counter attached to the rotor, Nr, at the beginning and the end of each ten-minute measuring period.

5.Pump strokes

For reciprocating pumps, record the readings (number of strokes) of the integrating stroke counter, Ns, at the beginning and the end of each ten-minute measuring period.

6.Suction head

Record the reading (meters) of the suction head, Hin, at the beginning of each ten-minute period.

Note: If the pump is below the water surface in the well the suction head should be recorded as a negative number.

7.Discharge head

Record the reading (meters) of the pressure gauge at the pump discharge, Hdis, at the beginning of each ten-minute period. During pumping performance tests, the discharge head is defined as the head the pump "sees", including pipeline friction losses.

Calculations

Length of Period (T), in seconds

T simply equals the difference in time between the start and end of the measuring period.

Average wind speed (VT), in meters/second

VT =1000 * (Rw,e – Rw,b)

T

where Rw,b = integrating anemometer reading (in kilometers) at the beginning of the measuring period

Rw,e = integrating anemometer reading (in kilometers) at the end of the measuring period

T = length of the measuring period

Average water flow rate (qPT), in liters/second

qPT = 1000 * (QP,e – QP,b)

T

where QP,b = integrating flow meter reading (cubic meters) at the beginning of each ten-minute period

QP,e = integrating flow meter reading at the end of each ten-minute period

T = length of the measuring period

Average rotational rotor speed (nRT), in revolutions/second

nRT = NR,e – NR,b

T

where NR,b = integrating rotation counter reading at the beginning of the measuring period

NR,e = integrating rotation counter reading at the end of the measuring period

T = length of the measuring period

Average stroke rate (nST), in strokes/second (optional)

nST = NS,e – NS,b

T

where NS,b = integrating stroke counter reading at the beginning of the measuring period

NS,e = integrating stroke counter reading at the end of the measuring period

T = length of the measuring period

Average effective plunger capacity (PC), in liters/stroke (optional)

PC = qPT / nST

Hydraulic power output (Ph,T), in Watts

Ph,T = 9.81 * qPT * (Hin + Hdis)

where qPT = average water flow rate

Hin = reading of the suction head

Hdis = reading of the pressure gauge at the pump discharge

9.81 = the acceleration due to gravity

Power input (Pi,T), in Watts

Pi,T = 0.393 * a * D2 * VT3

where 0.393 = conversion factor equaling /8

D = rotor diameter, in meters

VT = average wind speed

a = density of air, obtained from the table below:

Overall Wind Pump Performance Factor (CP)

CP = Ph,T

Pi,T

Results of the above calculations are then used to generate curves/graphs to arrive at estimates of the overall performance of the windmill system. The following curves are generated:

1.Water Output Curve

For each of the ten-minute measurement sets, plot the average water flow rate, qBT, along the vertical axis versus the average wind speed, VT, along the horizontal axis.

2.Rotor Rotational Speed Curve

For each of the 10-minute measurement sets taken with the rotor engaged, plot the average rotational speed, nRT, of the windmill rotor along the vertical axis versus the average wind speed, VT, along the horizontal axis.

3.Hydraulic Power Output Curve

Plot the hydraulic power output, Ph,T, as calculated for each ten-minute measurement along the vertical axis versus the average wind speed, VT, along the horizontal axis.

4.Overall Windpump Performance Factor Curve

Plot the wind pump performance factor, CP, for each ten-minute measurement set along the vertical axis versus the average wind speed, VT, along the horizontal axis.

1. Sample Results of Short-Term Test

The following curves were generated for a wind pump with an 8-meter diameter rotor:

Water Output Curve:

Rotor Rotational Speed Curve:

Overall Wind Pump Performance Factor:

1. Analysis of Results for Pumping Performance Test

As can be seen from the water output curve, average flow rate increased with increasing wind speed. As wind speed increased, an increase in water output was observed. This is expected of a fully-functioning wind pump.

Also, the rotor rotational speed curve indicated an increase in rotor rotational speed with an increase in wind speed. This suggests that the rotor is performing as expected and no defects on the rotor were detected.

The graph of the overall wind pump performance factor showed a large scatter in the region with average wind speeds between 1.2 and 2.8 m/s. This is due to the hysteresis effect. Within this range of wind speeds, a running wind pump will continue to run and a not-running wind pump will not start.