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Fuel eff ic iency andineff ic iency in pr ivatetubewell developmentGert Jan Bom

Solartec, PO Box 1130, Papendrecht, the Netherlands

Frank van Steenbergen

Arcadis Euroconsult, PO Box 441, Arnhem, the Nether-

lands

1. Introduction

In the last two decades there has been a proliferation of

private groundwater irrigation in India. Estimates put the

figure of diesel pumpsets in India at 6.5 million at present.

To this figure another 11 million pumps with electric mo-tors can be added, mainly operating in areas with deep

aquifers. Similar dramatic increases in private groundwa-

ter irrigation have taken place in Pakistan and Bangla-

desh.

This development has been driven by farmers’ invest-

ment, although a range of public subsidies has accelerated

the pace of groundwater exploitation.

The typical configuration in areas with shallow water

tables in India is that of a centrifugal pump operated with

a 2.5-10 horsepower (hp) (1 hp = 0.746 kW) engine. In

some areas diesel pumpsets have been common from the

beginning. In other areas the failing reliability of rural power supply has encouraged farmers to replace electric

pumps with diesel pumpsets. A striking feature is that

within this broad category each area has its own typical

irrigation tubewell configuration (size of the engine, ca-

pacity of the centrifugal pump, type of well), related to

the depth of the water table, prevailing land ownership,

soil condition and local tradition.

This is not to say that the tubewell configurations are

optimal in terms of fuel consumption or water-saving. In

fact, substantial improvements in well technology,

pumpset design and conveyance systems are possible at

modest cost. These improvements are indicative of the

technological vacuum in which private tubewell develop-ment has taken place. In this note evidence on fuel effi-

ciency improvements collected from three districts

(Cooch Behar, Jalpaiguri and Darjeeling) in the northern

part of West Bengal state (known as North Bengal) of

India is presented. After explaining improvements in tu-

bewell configuration, the note concludes with exploring

why the inefficiencies have persisted and have not been

self-corrected.

2. Inefficiencies in pump lift irrigation:

pumpsets, wells and conveyance systems in North

Bengal

Groundwater irrigation has only come to North Bengal

recently. For a long time the cultivation of kharif (the

term used in India for the crop using the south-west mon-

soon, the end-of-summer rainy season) rain-fed paddy on

monsoon-inundated land dominated the agricultural econ-

omy. In the last two decades the cultivation of wheat,

potatoes and vegetables in the dry winter season has

gained considerable popularity. This required the devel-

opment of groundwater irrigation facilities. A large num-

ber of government programmes set the trend, but

increasingly farmers have invested in shallow tubewells

from their own resources. Diesel pumpsets are most com-

mon, as elsewhere in the Terai belt [Shah, no date; Tyagi,

1995], the rich groundwater zone bordering the Himala-yan foothills, characterized by high recharge and shallow

water tables.

Investigations and field tests were undertaken under the

North Bengal Terai Development Project to review the

efficiency of the prevalent pumpset configurations in the

region. The investigations discovered that substantial im-

provements were possible in the configuration of diesel

pumpsets, wells and conveyance systems.

2.1. Improved diesel pumpsets

Most shallow tubewells in the region, but also open wells

and ponds, are operated with 5hp diesel pumpsets. During

field surveys it was found that these pumps were gener-ally oversized (only about 1.5 hp is effectively absorbed

by the pump), overcooled (the operating temperature is

generally only 35ºC instead of 80ºC) and that there was

excessive friction loss in the suction pipes due to the in-

Figure 1. A modified pumpset with drum cooling and priming pump on

the discharge.

Energy for Sustainable Development l Volume III No. 5 l January 1997

Letters

46



stallation of a poorly designed check valve.

Through a series of experiments on existing diesel

pumpsets, a set of modifications appropriate for North

Bengal was developed [Chakraborty et al., 1997]. It was

found that overcooling because of passing pump water

through the engine jacket was best corrected by fitting

thermosyphon drum-cooling. The drum-cooling increased

the engine operating temperature from a low 35ºC to a

normal level of 80ºC. This modification reduced the fuel

consumption of the standard pumpset by 13%. Next, re-

moving the check valve from the suction pipe reduced

the hydraulic friction losses, saving another 18% on the

fuel consumption. Finally, to mitigate the effects of the

engine being oversized, the engine speed was decreased

from 1500 to 1100 rpm. This resulted in a further reduc-

tion of the fuel consumption by 20%. Total fuel consump-

tion could in this way be reduced from 1 l/h to 0.5 l/h,

while the discharge of the pumpsets remained unchanged.The cost of these modifications on shallow tubewell

pumpsets is Rs. (rupees) 350 (US$ 8). During the irriga-

tion season, this cost can be recovered through fuel sav-

ings in 70 running hours, with the diesel fuel costing Rs.

10/l.

A better solution in the long run for the North Bengal

region would be to introduce smaller engines instead of

modified 5 hp engines. In the shallow water tables of the

North Bengal Terai, 3.5 hp pumpsets fit the need much

better. Lower power engines have the additional advan-

tage that their weight is much less (90 kg instead of 220

kg). As a result, transport of pumpsets in the field will be considerably easier. First tests with a 3.5 hp diesel

engine driving a 3×63 mm pump (the same pump as is

normally driven by the 5 hp engine) have been positive.

Running at 1000 rpm, the discharge was measured to be

12 l/s at 4m water depth and a fuel consumption of 0.4

l/h, or 20% better than the 5 hp engine under the same

conditions. It is expected that optimisation of the pump

(adapting impeller vane angle) for 1000 rpm will further

reduce the fuel consumption to 0.3 l/h, or 30% of its origi-

nal level.

2.2. Improved well technology

A variety of well filters is in use in North Bengal. Shallow

76 mm tubewells may have 76 mm galvanized iron, brass,PVC or bamboo filters. The dynamic water levels vary

from 4 to 5m at extraction rates of 7-10 l/s and static

water levels of 2-3m. Measurements showed resistance of

the filter in general to be excessive (3-4m). As a result

about 40% of the total energy is required just for over-

coming the filter resistance. Because the well pipes in this

area also serve as the suction pipe for the pump (Figure

3), the dynamic water level is measured in an observation

well at 30 cm distance. For establishing the filter resis-

tance, a vacuum gauge is mounted on the well pipe where

it comes above ground and the difference between the

vacuum gauge reading (corrected for friction loss and ve-locity head) and the dynamic water level gives the filter

resistance.

The cause of the high filter resistance lies partly in a

faulty design (too small slot size of filter and insufficient

total open area) and partly in lack of development of the

well after construction. Most wells are made without agravel pack and have very small slot sizes (0.2 mm is

common) to avoid sand entering the well. The total filter

capacity (open area) however is usually insufficient. As

a result the velocity of the water entering the filter is too

high (exceeding the recommended maximum of 3 cm/s),

which propels small particles towards the well. This ulti-

mately clogs the filter. A second reason for the high filter

resistance is the inadequate development of the well after

construction. Cowdung is commonly used both as slurry

as well as to stabilize the borehole during drilling, but

after development the well is not properly flushed and the

cowdung partially blocks the filter slots, thus setting a process of further clogging in motion. Moreover, no gra-

dation of material around the screens takes place. Ideally

an outer layer of coarse material should evolve. This does

not happen, because the small slot size does not allow

Figure 2. Fuel consumption versus discharge for each modification on a

shallow tubewell pumpset, with static water level at 3m and dynamic water

level at 4.5m.

Figure 3. A typical well configuration in North Bengal with the well pipe

doubling as suction pipe.


Letters

47



the small particles to be pumped away.

Experiments in North Bengal with improved well de-

sign (mosquito net filter combined with PVC plain pipes)

plus post-construction development have already resulted

in wells with 70% less filter resistance (from 3m down

to 1m resistance), giving an additional fuel-saving (on top

of what is achieved by improving the pumpset) of about

30%. The cost of improved wells using bamboo filters

with mosquito netting is considerably less than for wells

with ‘‘modern’’ filters such as slotted PVC or brass.

While this would work for new wells, for existing wells

rehabilitation is an attractive, though still uncertain, op-tion [van Herwijnen and Ray, 1997]. By surging (moving

a piston up and down in the well pipe) and jetting (recir-

culating well water with a pump and directing a concen-

trated water jet at the filter inner surface) the well

discharge improves by about 20% (corresponding to 20%

decrease in fuel consumption). The cost of this operation

is Rs. 100. If this is done after modifying the pumpset,

the incremental fuel saving of 20% amounts to a saving

of Rs. 1.10/h. This investment is recovered in 90 running

hours.

Apart from the fuel saving, a second benefit of the well

improvements is that increased discharge will reduce the‘‘steady state’’ losses of the water conveyance channels

(discussed next).

2.3. Improved conveyance

Typically, the water pumped from shallow tubewells

(drilled wells) or pump dug wells (91 cm diameter open

wells) is conveyed through makeshift earthen field chan-

nels. The water losses in these earthen channels are con-

siderable. Measurements in North Bengal show that,

depending on the quality of the channel, losses can be as

high as 53% per 100m [van Raalten, 1996]. Such high

losses are mainly attributed to overtopping of undersized

earthen channels. Yet even where the earthen channels

have sufficient freeboard, conveyance losses are signifi-

cant. They come in two categories. First are the ‘‘steady

state’’ losses that result from the seepage from the porous

earthen channels. In small-scale lift irrigation the flows

are usually 6-15 l/s. At these relatively established earthen

channels they were measured as 6% per 100m of the flow.

The second category are transient or ‘‘start-up’’ losses that

are related to the wetting of the dry perimeter of the

earthen channel. Each time the irrigation flow is started

it will take time and water before the water starts to flowin the channel. In small-scale lift irrigation water is usu-

ally started frequently, but for short durations. Obviously,

transient losses depend on the duration and number of

flows. Where water flows are started 30 times annually

and last 2.1h each, transient losses have been measured

at 8.4-10% of the flow per 100m. In intermittent ground-

water irrigation transient losses are therefore high, much

higher than in a constant flow situation, characteristic for

surface irrigation. The combined transient and steady state

losses are then at least 15% per 100m, but much higher

in the case of undersized channels.

As a remedy, farmers have adopted polyethylene tubes(‘‘leaflet hoses’’) as a superior alternative means of water

conveyance in various parts of North Bengal. Intriguingly,

areas where the leaflet hoses are widely accepted are

found right next to areas where they are unknown. The

usual length of the polyethylene tubes is 100-300m. They

weigh 15 kg for 100m length and are available for Rs.

7/m. Depending on the intensity of usage the tubes last

1 to 2 years. There is a thriving market for renting poly-

ethylene tubes. Whereas hire charges for a pump set (in-

cluding fuel) are typically Rs. 30/h in North Bengal, the

rent for a polyethylene pipe is usually Rs. 5/h. There are

significant advantages to using the polyethylene pipes.

Apart from the minimization of steady state and transientwater losses, the pipes allow the irrigation of higher areas

and do not require land, unlike field channels.

Attaching a polyethylene tube to the delivery pipe of

the pumpset (which has a diameter of 63 or 76 mm), how-

ever, increases the delivery head and results in a higher

consumption of diesel per unit volume of water lifted.

The attachment of 100m of polyethylene tube of 102 mm

diameter has been measured to require 11% more diesel

for a given quantity of water lifted. This is more than

compensated by a reduction in the hours of pumping, be-

cause water losses even in well-prepared channels are

15% per 100m. However, where 76 mm diameter tubesare used, as is more common in North Bengal, the in-

crease in delivery head is much more and diesel consump-

tion shoots up by 48% for a 100m tube [van Raalten,

1997].

Figure 4. Preparation of a mosquito net filter of 3.7m length and 76 mm

diameter.

Table 1. Comparison between netting filters and PVC or brass filters

Filter PVC Bamboo/netting

Diameter (mm) 76 76

Slot size (mm) 0.2 1

Filter length (m) 2 2

Static water level (m) 3 3

Yield with 5hp pump (l/s) 7.5 12

Total cost for 10m depth (Rs.) 2400 1500


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48



Apart from the polyethylene tubes a number of new

low-cost open-channel technologies have been tried in

North Bengal. The technology that got the most favorable

response from farmers was the soil cement channel. The

soil cement channel is made of a 1:1:4 mixture of sand,

cement and soil and has a thickness of 25 mm. The cost

per m for a channel carrying 15 l/s is Rs. 50. The advan-

tage over the concrete-lined channels, introduced in a

number of government programs, is the low cost (20% of

the costs of a brick-lined channel) and its adaptability to

skills of village masons.

2.4. Combined improvements

The combined improvements in well, pump and convey-

ance technology in North Bengal translate into a 70% sav-

ing in fuel required for a given volume of water (Table

2). Investigations in other parts of South Asia indicate

that savings of 40% are possible elsewhere too, using a

different, location-specific, package of modifications. Ina study in Gujarat state of India [Patel, 1988] a number

of changes to the electric pumps were introduced, result-

ing in 20-50% savings. Work by Enercon in Pakistan [Re-

inemann and Saqib, 1991] indicated that the overall

efficiencies of tubewells are only 30% of what is achiev-

able.

3. Introducing the improvements

The big question then is why, given the scope for signifi-

cant gains by low-cost modifications, fuel-inefficient

pump lift irrigation persists. There are a number of ex-

planations. The first is that the development of lift irri-gation has by and large taken place in a technological

vacuum. Unlike crop husbandry, water management and

well and pump technology choice has never been the sub-

ject of systematic agricultural extension, and technology

choices have been made by imitation rather than by in-

formed decisions.

A second explanation for the low fuel-efficiencies is the

fragmented nature of the relevant service industry. At

farmer level a farmer will typically go to different persons

for installing wells and selecting a pumpset, a practice

that does not encourage optimum fits. At the level of

pumpset suppliers, the pumps and engines/ motors are

manufactured by different enterprises, and subsequentlyassembled at local workshops, without taking into account

whether the combination of pump and engine is optimal.

Finally, the pumpset manufacturing sector is fragmented

in India and dominated by a large number of medium-

sized producers. None of these has the resources to invest

in substantial R&D. Besides, due to the fragmented nature

of the sector (different manufacturers for pumps and en-

gines, assembly by suppliers, sales by local dealers, all

independent from one another) feedback from the ultimate

customers does not reach the manufacturers. Moreover,

even manufacturers who are aware of the possibilities of

fuel savings are hesitant, because none of them dominatesthe market. Most of them generally prefer to produce a

product that is indistinguishable from that of the competi-

tors, rather than actively investing in a new type of pump.

A third explanation concerns the well technology and the

use of conveyance systems. Here, what is common in one

area is not known in another. One reason seems to be that

the well development sector is artisanal. In each area a

limited number of well-drillers operate, who are sole serv-

ice providers, accustomed to a certain technology. Among

farmers there is little awareness of well technologychoices. Moreover, water is an essential and critical input

in the irrigation of the dominant rabi (winter) crops in

North Bengal, i.e., vegetables and potatoes, but total water

requirements are not very high. In comparison with fer-

tilizer or pesticides, therefore, water is a far less costly

input. Though investments in better wells, pumpsets and

conveyance systems can be recouped within one irrigation

season, fuel-saving does not have the topmost place on

the farmers’ agenda.

Clearly, under these circumstances there is no such

thing as a self-correction in private sector service delivery.

It serves as a reminder of the limitations of technologyimprovement through the private sector. How then to pro-

mote fuel efficiency improvements in private groundwater

irrigation? One avenue that is being tried in the North

Bengal Terai Development Project consists of training of

farmers, mechanics, tubewell-drillers and dealers. This

has a positive result with one out of six farmers adopting

the pumpset modifications after demonstration and several

village mechanics and tubewell-drillers taking an active

interest in developing the pumpset modifications and well

rehabilitation as an additional line of business. The overall

impact of such a local training program is however lim-

ited, whereas the training resources required are substan-

tial. What is more important is to convert the entiretubewell service delivery sector. This is being done

through the dissemination of the improvements, but, more

important, through persuading some of the big tubewell

buyers in the public sector to adopt the changes and thus

set a new standard.

It could be useful if some kind of technological institute

developed appropriate standards for specific fuel con-

sumption expressed in l/m4 (litres of fuel per unit volume

of water per unit total head). This would define in a prac-

tical way the combined performance of a diesel engine

and pump. Standards could furthermore be developed for

well filter resistance as a percentage of the dynamic water level so as to define the well quality.

Acknowledgements

This note is essentially based on field studies implemented by a number of persons, who

Table 2. Combined fuel efficiency improvement in North Bengal

Improvement Fuel

savings

Remarks

Pumpset modifications 50% Comparing 100m of

102 mm polyethylenetube with established

earthen field channel

with 25% seepage loss

and corrected for

increased friction head.

Well technology improvements 30%

Conveyance improvements 15%

Total fuel saving 70%


Letters

49



are gratefully acknowledged: P.K. Biswas, Amer Dey, Aris van Herwijnen, Dhananjay Ray,

David van Raalten and P.K. Sen.

References

Chakraborty, K.K., Bom, G.J., and van Raalten, D., 1997. ‘‘Improved fuel efficiency of diesel

pumpsets in India’’, to appear inJournal of the Institution of Engineers.

Patel, S.M., 1988. ‘‘Low cost and quick yielding measures for energy consumption in agri-

cultural pumps’’, Pacific and Asian Journal of Energy, Vol. 2, No. 1, pp. 3-11.

Reinemann, D.J., and Saqib, S., 1991. ‘‘Tubewell audit and retrofit for improved energy

efficiency’’, TIDE, Vol. 1, No. 4.

Shah, T., (no date). Water Markets in North Bihar: Synthesis of Six Village Studies in Muzaf-

farpur District, The Policy School Foundation Studies, Anand.

Tyagi, B.N., 1995. Requirements for Electric Power for Agriculture in Uttar Pradesh, Centre

for Advanced Development Research, Lucknow.

Van Herwijnen, A., and Ray, D., 1997. The Modification of the Shallow Tubewell: the Im-

provement and Cleaning of the Well, North Bengal Terai Development Project, Jalpaiguri.

Van Raalten, D., 1996. Crop Water Requirements and Irrigation Efficiencies in North Bengal,

North Bengal Terai Development Project, Jalpaiguri.

Van Raalten, D., 1997. Report on conveyance techniques, North Bengal Terai Development

Project, Jalpaiguri.

Indoor thermal comfort: thePakistan study

J. Fergus Nicol and Iftikhar A. Raja

School of Architecture, Oxford Brookes University, Ox-ford OX3 OBP, United Kingdom

1. Introduction

The existing indoor design temperatures in Pakistan are

based on ASHRAE standards. These are 26ºC in the cool-

ing seasons and 21ºC in the heating seasons irrespective

of where in Pakistan the building is to be built [ENER-

CON, 1990]. The evidence suggests that many air-condi-

tioning systems are designed to provide a constant 22ºC.

Analysis of field studies of thermal comfort has shown

that indoor comfort temperatures vary with the mean tem-

perature outdoors [Humphreys 1978, 1978a; Auliciem anddeDear, 1986].

Limited energy resources in Pakistan demand the pro-

motion of greater saving in energy and efficient use of

energy. The National Energy Conservation Centre (EN-

ERCON) of Pakistan is responsible for helping to frame

legislation for the government with a view to minimising

energy consumption. In the field of buildings it has pro-

duced a Building Energy Code for Pakistan [ENERCON,

1990]. In buildings, an increasingly important fraction of

the energy is used by air-conditioning systems. However,

the energy cost of air-conditioning is affected by indoor

air temperature standards. Realising these facts, ENER-

CON commissioned the School of Architecture, OxfordBrookes University, to advise on the setting of appropriate

indoor temperatures in the different climatic regions of

Pakistan. The operational thermal comfort standards are

based on non-flexible ASHRAE standards [ASHRAE,

1981]. On the other hand, the country, having a highly

variable climate from region to region at macro-scale and

within a region at micro-scale, needs variable indoor tem-

perature standards that take into account the outdoor cli-

mate.

To work out appropriate new indoor temperature stand-

ards for Pakistan, the two surveys were undertaken by a

team from Oxford Brookes University in co-operationwith ENERCON of Pakistan. The first survey was longi-

tudinal, undertaken during 1993-94 in five cities of Paki-

stan, using 25 subjects for a week in two seasons. The

results showed that there were big variations in tempera-

tures that people find comfortable in different climatic

zones and seasons. During 1995-96, following doubts

about the general applicability of results from so small a

sample, a second survey (transverse) was undertaken us-

ing 846 subjects at monthly intervals over a whole year.

The results of the survey confirmed the previous findings.

The aim of the research was to produce guidelines for providing comfortable indoor temperatures for buildings

in Pakistan. The objective of the surveys was to determine

the temperature found most comfortable (or the tempera-

ture found comfortable by the largest number of people)

in each climatic zone in each season and to:

l relate this to outdoor climate;

l suggest a method of setting indoor air temperature

standards for Pakistan;

l make recommendations for future work in the area in

Pakistan; and

l set a methodology for international work in this field.

The surveys showed that there was a definite relationship between indoor comfort and outdoor conditions. This pa-

per describes two thermal comfort surveys (longitudinal

and transverse) conducted in Pakistan. The variation of

comfort and discomfort with indoor temperatures and that

of comfort temperatures with indoor and outdoor tempera-

tures are analysed.

2. Climatic regions

Pakistan is a country of diverse climate. On the basis of

different schemes a number of climatic regions have been

identified. For example, Khan [1991] divided the country

into 8 zones, Shamshad [1988] presented 11 zones and

Raja [1996] 16 zones. However, on the basis of homoge-neity of climatic elements of interest, temperature and pre-

cipitation, the country may be divided into 5 major

climatic regions.

The climatic division of the country is given in Table

1 and the boundaries of different regions are marked in

Figure 1. Each region has its own cultural and architec-

tural traditions, reflecting its own particular climate. The

mean monthly average temperatures for a representative

city in each region are given in Table 2.

3. Thermal comfort survey

The aim of the survey was to establish the indoor temperature that the inhabitants of each climatic region of

Pakistan find most comfortable. There are five major cli-

matic regions. One city in each climatic zone was chosen.

These are indicated in Figure 1. The target group for de-


Letters

50

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