UNIVERSITY OF NAIROBI
DEPARTMENT OF MECHANICAL & MANUFACTURING
ENGINEERING
Project code: GO 01/2011
TITLE: REVIEW DESIGN OF UNIVERSITY OF NAIROBI MAIN
CAMPUS BOREHOLE WATER SUPPLY SYSTEM
MWANZA NYONGESA STEPHEN
F18/1836/2006
NYAGA JOHN FUNDI
F18/1837/2006
This project report is submitted in partial fulfilment of the requirements for the award of the
Degree of:
BACHELOR OF SCIENCE IN MECHANICAL AND MANUFACTURING ENGINEERING
2011
i
Review design of the University of Nairobi- Main campus borehole system
(NO.C-10497)
i
DECLARATION
We declare to the best of our knowledge that this final year project report to be submitted as a
partial fulfilment of the Bsc. Mechanical and Manufacturing Engineering degree, to be our own
original work and has not been presented in this or any other university for examination,
academic or any other purpose.
Nyaga john fundi
F18/1837/2006
Signature-----------Date---------------
Mwanza nyongesa Stephen
F18/1836/2006
Signature------------Date-----------------
Supervisor
This review design project has been submitted for examination with my approval as the
university supervisor.
Dr.G.O. Nyangasi
Signature------------Date------------------ii
DEDICATION
To our families and friends.
To Nyongesa’s daughter
Real Hope.
iii
ACKNOWLEDGEMENT
We would like to express our sincere gratitude’s to all the people who made this project
successful.
Firstly we thank our God for granting us the strength and wisdom to partake and complete this
project and also for gift of life.
In a special way we appreciate our dear parents who have continuously supported us in our
academics and endeavours.
We also appreciate Dr. G.O.Nyangasi who accepted to be the project supervisor, his continued
support and technical advice went a long way in bringing this project into reality.
We appreciate also the staff in ministry of water and irrigation (underground water department)
for the provision of data.
In addition we thank Eng.Roy Bwoma of Davis and Shirtliff for providing us with data required.
We express our gratitude to Maina, Limo and Edwin for their generosity in advice dispensing
and consultancy services.
Finally we thank our colleagues and lectures who were not hesitant to give constructive
criticism.
Thank you all and God bless
iv
SUMMARY
Review design of an existing system of university of Nairobi borehole involves looking at the
existing features of the system and analysing its performance; this is compared to the design
requirements and sees if the system is working as required by the design. The University of
Nairobi main campus borehole scheme review design was aimed at analysing the existing water
supply system and comparing to the design requirement and see if it can meet its intended
purpose of meeting water demand of the population in main campus at the time of review and
future. The design of the borehole system was done by estimation of the population by the time
of design, which was estimated at 2500 with a10 hrs peak demand total of 125 m3 of water a day.
This demand has risen to 10 hr peak demand of 217.5m3 a day due to increased population of
4350 persons.
The system comprised of the borehole, the pipeline, the pump and the reservoirs. According to
the driller’s report(Mburu Borehole Services)the borehole was drilled in 1993 with a depth of
251m and a capacity of 17.6m3/hr. The pipeline was considered as the drop pipeline from the
surface to the pump location of 195m, the rising pipeline from the surface to the reservoir of 9 m
and the surface pipeline of length132 m. Total pipeline length of 336m. The used pump is
grandfos sp17-27 supplied by Davis & Shirtliff. With power rating of 15kWh, designed to work
optimally at 16m3/h with total head of 225m. The reservoirs comprised of the main reservoir of
capacity of 16m3 and other subsidiary reservoirs totalling to a capacity of213.2m3, this gives a
total storage of 229.2m3.
This existing system’s performance was analysed first by calculating the frictional head loss in
the pipe which was found to be 19.55 mow at a flow rate of 16m3/hr.this was added to the static
head of 204mow to bring a total head of about 224 mow. From the pump characteristic curve it’s
v
found that the desired flow rate of 16m3/hr the total head to be overcome was 225mow which
justifies that the pump could perform as per the design.
Metre readings of the system when working without interruption was taken which showed that
the actual delivery was about 10m3/hr. From the pump characteristic curve at this flow rate the
pump was overcoming a total head of 280mow.this difference in total head might have been due
to the complex parallel reservoir arrangement and working.
Cost analysis carried out on the system if it was working under the designed conditions indicated
that it had an efficiency of 60.6% with unit cost of water at shs18/m3 of water.
The actual performance analysis showed that at 10m3/hr the efficiency was 55.2% and unit cost
of water was found to be shs26/m3.the actual performance was seen to be more costly and less
efficient compared to the design expected performance.
However if the system was to work as designed it was worthwhile compared to the council
scheme which delivers water at a unit cost of shs53/m3 of water. Actual performance is also
justified still due to reliability even though it’s at the same cost.
Among the recommendations made to increase the systems efficiency and cost effectiveness was
to address the probable causes of under delivery which includes: Wrong Rotation speed,
Clogged, worn out impeller and air Leaks
From this review it was established that the borehole scheme can effectively and efficiently
satisfy the current demand of main campus if its operating time is adjusted to 14 hrs delivering
16m3/hr. and at the actual performance of 10m3/hr it can satisfy the demand if it operates for 22.4
hrs about 23 hrs a day but not as cost effective as it does if it works as per the deign requirement.
vi
Hence strongly recommend for the need to Increase the operation hours of the existing system so
as to meet the current demand and also to minimize on water wastage and misuse.
vii
Table of Contents
DECLARATION .......................................................................................................................................................... ii
ACKNOWLEDGEMENT ............................................................................................................................................iv
SUMMARY .................................................................................................................................................................. v
1.0 INTRODUCTION ............................................................................................................................................... 1
1.1
PROBLEM STATEMENT .......................................................................................................................... 1
1.2
OBJECTIVE ................................................................................................................................................ 2
1.3 BACKGROUND ................................................................................................................................................. 2
1.3.1 University history ......................................................................................................................................... 2
1.3.2 Initial water demand ..................................................................................................................................... 2
1.4 GEOGRAPHICAL LOCATION ......................................................................................................................... 3
1.5 CURRENT WATER DEMAND ESTIMATION ................................................................................................ 4
CHAPTER TWO ........................................................................................................................................................... 5
2.1THE EXISTING SYSTEM .................................................................................................................................. 5
2.1.1The borehole specifications ........................................................................................................................... 6
2.1.2 Test results .................................................................................................................................................... 6
2.1.3 Surface pipeline route ................................................................................................................................... 7
2.1.4power supply.................................................................................................................................................. 8
2.1.5 The reservoir details ..................................................................................................................................... 9
2.1.5pump specification ....................................................................................................................................... 11
CHAPTER THREE ..................................................................................................................................................... 12
3.1 PERFORMANCE ANALYSIS OF THE EXISTING SYSTEM ...................................................................... 12
3.1.1 PIPELINE PERFORMANCE..................................................................................................................... 12
CHAPTER FOUR ....................................................................................................................................................... 19
4.1 ACTUAL PERFORMANCE OF THE EXISTING BOREHOLE SYSTEM. ................................................... 19
4.2Table2: Actual daily Metre reading .................................................................................................................... 20
4.3 Table 3: instantaneous readings at constant flow............................................................................................... 20
4.4 The actual performance general analysis ........................................................................................................... 22
CHAPTER FIVE ......................................................................................................................................................... 23
5.1COST ANALYSIS. ............................................................................................................................................ 23
5.1.1 ANNUAL COST METHOD ...................................................................................................................... 23
5.1.1b table 4cost analysis of the design features ................................................................................................ 24
5.1.1c table5: cost evaluation of the actual systems performance ....................................................................... 25
CHAPTER SIX ........................................................................................................................................................... 26
6.1 DISCUSSION OF THE RESULTS. .................................................................................................................. 26
Table 6.1.1: Summary of the actual performance and design features of the system .......................................... 26
6.1.2 Discussion of the results ............................................................................................................................. 27
CHAPTER SEVEN ..................................................................................................................................................... 30
7.1 RECOMMENDATIONS. .................................................................................................................................. 30
viii
7.1.1 Pump service............................................................................................................................................... 30
7.1.3 Reservoirs ................................................................................................................................................... 30
7.1.4Water usage ................................................................................................................................................. 30
7.1.5 Energy conservation ................................................................................................................................... 32
7.1.6. Redesigning ............................................................................................................................................... 32
CHAPTER EIGHT ...................................................................................................................................................... 33
8.1 CONCLUSION. ................................................................................................................................................ 33
ix
CHAPTER 0NE
1.0 INTRODUCTION
The continuously intensifying scarcity of water resources is crucial problem in almost all
contemporary societies. Even in areas where there are adequate quantities of water, the problem
of scarcity is usually confronted through the deterioration of water quality resulting in increasing
costs for certain water uses.
This problem of water scarcity has manifested itself in different ways in the past couple of years.
The most common ones being lack of water in the institution wash rooms which may lead to
break out of diseases. Water resources are finite and therefore eventually continuously increasing
number of potential users would be competing for this scarce resource, as a result the available
resources such as the borehole must be analysed to ensure that it is being used properly.
1.1 PROBLEM STATEMENT
The university of Nairobi main campus borehole system was set up in 1993, since then there
have been a lot of changes among them being climatic and ecological changes. Also there has
been increase in student intake in the university. As a result of these changes, review design is
necessary to ensure that the performance of the borehole system is as per the design specification
and may meet the demand requirement at time of review.
1
1.2 OBJECTIVE
A review design of the existing main campus borehole system involves water demand
estimation, the examination of the existing system, analysis of this system’s theoretical
performance, comparing to the actual performance and drawing conclusion on specific
performance aspects of the system.
1.3 BACKGROUND
1.3.1 University history
University of Nairobi was established in 1952 as Royal technical college of East Africa to
provide higher technical education in the region. The first intake of students was in April 1956,
since then the university was served by water from the Nairobi city water services until 1993
when the borehole was drilled and started serving as the major source of water to the university,
although the city water supply was still available to supplement in case of breakdown.
1.3.2 Initial water demand
By the time of installation of the borehole system in 1993 the water demand was estimated at
12.5 m3/ hr for 10 hours day supply. This was to serve the total population of 2500 people. The
population has been steadily increasing with time and thus an increase in water demand. This
increase in water demand has led to periodic review of the pumping system to establish whether
it is meeting the design specifications as required. By time of installation of the borehole water
pumping system the population of two colleges was estimated at:
CAE population as 800 (4 departments and estimate of 200 persons in each department)
CHSS population as 1700.
2
Per capita water demand estimation is 50 litres per day (for 10 hrs a day).(source from the
ministry of water )
Overall water demand = total population * Per capita water demand.
= 50 * 2500 =125,000litres /10 hrs a day.
= 12.5m3/hr.
1.4 GEOGRAPHICAL LOCATION
Fig 1: sketch of the location of borehole (not drawn to scale)
3
The University of Nairobi, Main campus is situated in Nairobi city centre with elevation of 1660
m above the sea level. South of museum hill roundabout off Uhuru highway to the east and off
university way to the north and south of KBC as shown in the figure 1 above.
1.5 CURRENT WATER DEMAND ESTIMATION
Currently the borehole serves the university of Nairobi main campus which constitutes two
colleges; college of architecture and engineering (CAE), and college of humanity and social
science (CHSS)
The population estimate as by 2010/2011 academic year for the two colleges was:
CAE: 4 departments with an average estimate of 400 per department
Total population stands at 1600 persons
CHSS: This includes school of economics, school of arts, school of political science, school of
sociology and evening classes estimated at 550 people per school
The total estimated population was 2750
Per capita water consumption of 50 litres per day this gives an overall water demand of
=217.5 m3/day
For 10 hrs a day demand =21.75m3/hr
4
CHAPTER TWO
2.1THE EXISTING SYSTEM
The existing system consists of the:I.
II.
The borehole
Pipeline specifications
III.
pipeline route
IV.
Power supply
V.
VI.
Reservoir details
Pump specification
Fig 2: schematic diagram of a borehole system
5
2.1.1The borehole specifications
The borehole specifications include the total depth, which refers to the depth from the ground
surface to the bottom of the borehole as illustrated in fig3 below.
Static water level (SWL), this is the water level measured from the ground surface to the water
surface.
Pumping water level (PWL). This is the distance from the surface to the centre line position of
the pump location.
Casing diameter is the diameter of the column that is holding water.
Test yield is the recommended borehole capacity reached upon after pumping test.
From the drillers report (a copy in the appendix (2) :
Total depth =250m
Static water level (SWL) =114m
Pumping water level(PWL) =195m
Casing
= 152 mm
Test Yield = 17.6m3/h
With pump set at 226 m below surface
2.1.2 Test results
Quality of water Sample collected during the test showed that there were no sediment, no taste,
and no odour and clear in colour, temperatures were at 30 and it was within the spec for drinking
and domestic applications as per the standard : KS-05- 459 (1-7) :1996&1985 (confirmed 1999)
6
as indicated in appendix 4 for specifications for drinking water. This is reported in the test report
part of drillers report attached in the appendix.2
Fig 3: casing profile diagram
2.1.3 Surface pipeline route
The site survey gives the following data. Distance to the delivery point (reservoir), this is the
ground distance from the surface of the borehole to the point where the reservoir is located.
Elevation is the height above the ground to the location of the reservoir. (From the ground to
3rd floor of Hyslop building in Main campus of University Of Nairobi. Each floor is 3m
high).
From the physical examination on the ground the:
Distance to delivery = 132m (consists of 22 pieces of pipes each of length 6m) and
Elevation = 9 m
7
2.1.3.1 pipe specification
The pipe specifications in this case include the rising mains which are the pipes used from
the pump to the surface of the borehole. These specifications include the pipes internal
diameter, number of pipes used and the pipe material.
Rising mains from the borehole surface to the pump location(diameter) 63.5mm
No of pipes 32.5
Length of each pipe 6M
Drop pipe length 6*32.5=195M (from the ground).
Pipe material: galvanized iron.
Rising pipes from the surface to the reservoir 9 m
Surface pipe line 33 pipes(total of 138 m)
 Total pipe length = 138+ 195 + 9 =342m
(Data from Davis and Shirtliff borehole pump field test report attached in the appendix.2.)
2.1.4power supply
This is the location and type of the power supply available. It determines the length of the cable
the pump must have and the type of pump that can be used
From the physical examination of the site it was estimated that:Source: Mains
Three Phase
Distances of:
8

Power pt – Panel =5m

Borehole – Panel = 10m
This helps to determine the length of the power cable that is supposed to be used in the
installation of this pump.
2.1.5 The reservoir details
–
The main reservoir is located at the top of Hyslop building in main campus (UON).which
receives water for storage direct from borehole and redistributes to other reservoirs in the
colleges that have been installed booster pumps.
–
Storage tank capacity (reservoir) = 16m3.
–
material of the reservoir = steel tank
(Source of data physical examination)
Other reservoirs are located on different locations of the university buildings as follows:Jomo Kenyatta Memorial library 3 wings 3 tanks in each wing of capacity 4.6m3 =41.4m3
British wing(mechanical Building) 2 wings 4 tanks each wing of capacity 4.6m3=36.8m3
American wing 2 tanks each of capacity 4.6m3=9.2m3
Civil Engineering Block 1 tank of 16 m3 = 16m3
Education building 1 tank of 16 m3 =16m3
Central admission block 2 tanks each of 10m3 =20m3
Gandhi wing-finance 1 tank of 16m3 =16m3
Postgraduate 2 tanks each of 18m3 =36m3
Estates department 1 tank of 4.6 m3 =4.6m3
Nuclear Science department 2 tanks of 4m3 each =8m3
9
Workshop 2 tanks each 4.6m3 each =9.2m3
Total storage capacity available = 229.2m3
Figure 4: sample of 1 of the parallel reservoirs on 844 building
Fig 4b: Main reservoir in Hyslop building.
10
2.1.5pump specification
Product number:
12A01927
Type:
SP17-27
Flow
16.1m3/h
Head total:
225m
Model:
A
Valve:
pump with built in non return valves
Source: manufacture (Davis & Shirtliff) as indicated in appendix 3. (a)
2.1.5.1
The Pump Curve characteristic and power curves
Figure 5 pump characteristic curve
(Source of data pump manufacturer Davis and Shirtliff)
As attached in the appendix 3 (b)
11
CHAPTER THREE
3.1 PERFORMANCE ANALYSIS OF THE EXISTING SYSTEM
3.1.1 PIPELINE PERFORMANCE
3.1.1.1 Pipe friction loss
Applying the Darcy equation
Where
=pipe frictional head
λ = friction factor (from moody diagram at Re and relative)
Roughness = k/d
k= internal roughness and
d= internal pipe diameter
g=acceleration gravitational
From standard of (cast iron with d=63.5mm) k/d= 0.00315
Reynolds number Re =
Where:
V = flow velocity
d = pipe diameter
g = gravitational pull
v =kinematic viscosity
Sample calculation: given
d=63.5*10-3m; V=1m/s; v=µ/ρ =0.000001m2/s; g=9.81m2/s
12
At Q=11.4m3/hr V=1m/s
We get Re =
Thus Re
From the moody diagram at Re=63500 and k/d=0.00315 we read the value of λ =
0.038
From
Similarly other values of
were calculated and tabulated in the table 1 below.
3.1.1.1aTable1: The performance analysis of the existing pipeline system
characteristic data for the pipeline
external
wall
internal internal relative kinemati
diameter thickness diameter roughnes roughnes
c
D(mm)
t(mm)
d(mm)
s k(mm)
s k/d
viscosity
63.5
0.2
0.00315 0.000001
λ(from
Q
moody
Hf
M3/HOU d (metre)
Re
diagram
Mow/m
R
using k/d
and Re)
V m/sec
0
0.0635
0
0
0
0
11.4024
0.0635
1
63500
0.038
0.030501
12.54264
0.0635
1.1
69850
0.038
0.036906
13.68288
0.0635
1.2
76200
0.038
0.043921
14.82312
0.0635
1.3
82550
0.037
0.05019
15.96336
0.0635
1.4
88900
0.037
0.058208
17.10359
0.0635
1.5
95250
0.036
0.065015
18.24383
0.0635
1.6
101600
0.035
0.071918
pipeline
length
(m)
342
Hf Mow
o
10.43126
12.62183
15.02102
17.16492
19.90725
22.23506
24.59582
total
head
204
214.4313
216.6218
219.021
221.1649
223.9072
226.2351
228.5958
13
3.1.1.1b the graph of pipeline characteristic curve
230
total head(MoW)
225
220
215
210
205
200
0
5
flow rate10
Q (m3/hr)
15
20
3.1.1.2 PUMP SPECIFICATION AND PERFORMANCE
3.1.1.2.1 Dimensional Drawing of the pump (in mm)
Fig 7: dimensional drawing of the pump (in mm)
(The pump dimensions from the manufacturer are attached in the appendix 3(d)
14
3.1.1.2.2PUMP FEATURES
•
Stainless Steel
•
Octagonal bearings with high velocity sand flush canals reduce abrasive wear
•
Replaceable wear rings
•
Built in up thrust stop ring prevents damage during the critical start up
•
Inlet strainer limits passage of particles
Corrosion Resistance
long life of the impeller
3.1.1.2.3GRUNDFOS SP
•
Multistage submersible centrifugal pumps for installation with 4” & 6” diameters
•
Clean thin non-aggressive liquids without components or fibres like borehole water
•
Entire pump Stainless Steel with water lubricated rubber bearings
•
Handle sand content up to 50mg/l, where the pump efficiency will remain acceptable for
up to 35,000 duty hrs
•
•
Type Keys:
S P 17 – 27
•
17 : Nominal flow in m3/hr
•
27: Number of stages
Design Parameters
–
–
Total dynamic head, TDH in m
= 225.8m
Flow Q, in m3/hr
= 16 m3/hr
15
•
Components of Total dynamic head
–
Pumping Water Level (PWL)
=195mcurrently (drillers report 177.58 m)
–
Frictional head loss through drop pipes (Hf1)
=11.8m
–
Frictional loss through surface piping (Hf2)
=3.30
–
Elevation between borehole and delivery point (E)
=9m
•
TDH = PWL +
+E
=195+ 24.1+ 9
=228.1mow
(Source of data manufacturer grundfos (Davis and Shirtliff)
16
3.1.1.3a Super Imposed Pump characteristic curve and pipeline design performance curve
350
300
250
total
head 200
in Mow
150
pump…
pipeli…
100
50
0
0
10
Axis Title
20
30
flow rate Q
in M3/s
Figure 9 design pump characteristic and pipeline performance curve
The system performance specifications are obtained from the superimposed graphs of pipeline
specification curve and the curve of the pump which is obtained from the manufacturer.
The value obtained for this particular design was found to be galvanized iron/class E * Grundfos
sp 17-27 = 16M3/hr / 224 MoW
3.1.1.4 General performance analysis of the theoretical design
Key:
P1= motor power
P2= pump power
Figure 10 the power curve of the pumping system (source manufacturer)
(Attached power curves in appendix 3(c)
17
Figure 1efficiency, current and rotation speed against power curves (source manufacturer) appendix 3(c)
From the pump performance characteristic curve if the system delivers 16m3/hr it overcomes a
head of 225m as shown in fig 9 above and further analysis from the power curves at the same
flow rate p1(motor power) = 16.2kW and p2(pump power) = 13.5kW.as illustrated in fig 10
above. At this values of p1 and p2 from the efficiency curve we obtain that the motor efficiency
=82.9 %
Pump efficiency=
=
Overall efficiency=
The pump efficiency =72.67% and the overall pump + motor efficiency = 60.6%.
18
CHAPTER FOUR
4.1 ACTUAL PERFORMANCE OF THE EXISTING BOREHOLE SYSTEM.
Fig 11: The flow rate meter
The actual delivery of the existing borehole can be obtained by taking daily meter reading or by
taking the periodic flow rate when the valve is fully opened and the system working constantly
uninterrupted. For instantaneous flow when the valve is fully opened, the time to deliver 1M3
was observed by timing using the stop watch and measuring the volume flow using the meter.
This actual performance was compared to the one taken on daily reading of the metre and it was
further compared to the pump manufacturer’s field test report.
19
4.2Table2: Actual daily Metre reading
performance test-case study(the daily meter reading)
flow rate
the actual running
hrs
per
delivery
hour(m3/hr
per
3
)
day(m
)
11-Jan-11 18:20
21190
22.5
0
12-Jan-11 18:12
21397
207
22.5
9.2
13-Jan-11 18:12
21598
201
22.5 8.93333333
14-Jan-11 18:12
21802
204
22.5 9.06666667
15-Jan-11 18:12
21998
196
22.5 8.71111111
16-Jan-11 18:12
22190
192
22.5 8.53333333
17-Jan-11 18:12
22393
203
22.5 9.02222222
18-Jan-11 18:12
22597
204
22.5 9.06666667
average flow rate
8.93333333
Date
time of value in M3
reading
(Source of data: daily metre readings)
The meter readings were taken for several days and the average delivery per day was calculated.
Also the average delivery per hour was calculated. These average values were calculated making
assumption that the borehole pump pumps nonstop.
4.3 Table 3: instantaneous readings at constant flow.
Time to deliver 1 M3
second
M3
365
365
366
365
367
366
366
1
1
1
1
1
1
1
M3/hr
9.863
9.863
9.863
9.863
9.863
9.863
9.863
(Source of data meter reading)
The actual average volumetric flow rate of the existing system taken at the instantaneous flow is
obtained by observing the time taken to deliver 1M3.
20
The time was recorded for eight readings and the volumetric flow rate was calculated whereby
the average volumetric flow rate was calculated as 9.863 M3/hr.
The test reports done by the pump manufacturer (Davis & Shirtliff attached in appendix 5.c)
carried out on February 2011 showed that the system delivers 10m3/hr, further inspection showed
that there was backflow when the pump was switched off as a result of worn out pipes in the
pipeline.
350
300
total 250
head
200
in Mow
150
100
50
0
0
5
10
15
20
25
Axis Title
flow rate Q
in M3/s
Figure 13 actual performance points on the pump characteristic curve
21
power in kW
20
18
16
14
12
10
8
6
4
2
0
p1
p2
p1(motor
power)
p2 pump
power
0
10
20
30
flow Rate in m3/hr
Figure 14: actual power points on the power curves
4.4 The actual performance general analysis
At the actual performance of around 10m3/hr from the pump characteristic this shows that the
pump overcomes a total head of around 280m. From the power curves at this flow rate p2 (pump
power) =11.5kw and p1 (motor power) =13.8 kW. At this p2 and p1 from the efficiency curves
we obtain the motor efficiency =81.5%, n (revolutions per minute) = 2900rpm and current I = 26
A.
Pump efficiency=
=
Overall efficiency=
The pump efficiency =66.35% and the overall pump + motor efficiency = 55.29%.
22
CHAPTER FIVE
5.1COST ANALYSIS.
5.1.1 ANNUAL COST METHOD
The annual cost of each capital item is computed as the product of the capital cost of the asset,
and the capital recovery factor for the asset. The capital recovery factor in turn is a function of
the interest charged for capital and expected economic life of the asset. Capital recovery factor
for various asset lives and interest rates are shown in the appendix 6
The annual cost computed from the table below is the Equivalent Uniform Annual Cost (EUAC)
for this investment alternative. Any other investment alternative, which accomplish the same
purpose, but has unequal life, must be compared by the annual cost method. In this case, the
project’s purpose is to provide a specified quantity (82125m3) and quality (clean drinking) water
annually. The annual cost method assumes that each alternative will be replaced by an identical
twin at the end of its useful life (infinite renewal)
5.1.1aUnit cost of water
The total unit cost of water from the University of Nairobi Main campus borehole scheme is then
determined by dividing the total annual cost with the volume of the product supplied during the
year. This is then the indicator of the economic worthy-whileness of the project.
This annual cost method was used to get the unit cost of water for both theoretical design and the
actual systems performance as summarised in table 5.1 and 5.2 below respectively.
The installation price of electrical and mechanical appliances as obtained from the sale invoice
was kshs.1086433.00 as indicated in appendix 6
23
5.1.1b table 4 cost analysis of the design features
as s et
l i fe
years
Item No.
des cri pti on of capi tal As s et
mechani
1
cal and el ectri cal equi pments
2
GI water pi pel i ne
capi tal cos t
Shs
Di s coun
t Rate
1+i
(1+i
)n
i (1+i )n
(1+i )n1
i (1+i )n/(
1+i )n-1
Annual cost
15
1,086,433.00
0.12
1.12
5.5
0.6568
4.4736
0.1468
159514.7
20
210000
0.12
1.12
9.6
1.1576
8.6463
0.1339
28114.544
TOTAL ANNUAL COST OF CAPITAL
ANNUAL COST OF LABOUR
monthl y
cos t
Ks hs
Des
Item
criNo
pti on of l abour category
number
annual cost
Kshs
1
pl umber/operator
16000
1
192000
2
pi pe fi tter
0
0
0
3
l abour uns ki l l ed
0
0
ANNUAL LABOUR COST
0
192000
ANNUAL COST OF MAINTENANCE
Mai nt.
Capi tal
Ann.Mai nt Cos t
Factor% cos t Shs Ks hs
DESCRIPTION OF
Capi tal
CAPITAL ASSET
Item NO
1 Mechani cal and
0.05 ########
54321.65
cal pi
equi
2 El
GIectri
Water
pelpment
i nes
0.02 210000
4200
Total annual mai ntenance cos t
Equivalent Uniform Annual Cost(EUAC)Kshs
Annual Water demand-Supply(Cubic Metres )
Uni t cos t of water per cubi c metre(Ks hs /m3)
58521.65
1511250.893
81760
18.48398842
POW
ER
RATI
NG
OF
PUM
P IN
15
187629.24
ANNUAL COST OF ELECTRIC POWER
ope el ectri c el ectri c annual el ectri c power
rati energy
power
cos t Ks hs
ng
per year charge
duty Kwh
s s hs
hou
per
rs
kwh
per
14
76650
14
1073100
SUMMARY OF ANNUAL COSTS
187629.243
ANNUAL CAPITAL COST
ANNUAL LABOUR COST
192000
ANNUAL POWER COST
1073100
ANNUAL MAINTENCE COST
58521.65
Equi val ent Uni form Annual Cos t(EUAC) 1511250.893
COST STRUCTURE OF WATER SUPPLY SERVICES
UNIT CAPITAL COST
Shs /m3
2.2948782
UNIT LABOUR COST
Shs /m3
2.3483366
UNIT POWER COST
Shs /m3
13.125
UNIT MAINT.COST
Shs /m3
0.7157736
UNIT COST OF WATER
Shs /m3
18.483988
(Source of data estimation of wages, market value of power and GI pipe, water rates as per the Nairobi water company and
pump supplier’s appendix 6)
24
5.1.1c table5: cost evaluation of the actual systems performance
ACTUAL PERFORMANCE COST EVALUATION
TABLE: FEASIBILITY STUDY:ANNUAL COST-MAIN CAMPUS BOREHOLE SCHEM
ANNUAL COST OF CAPITAL BY CAPITAL RECOVERY METHOD
DAILY WATER DEMAND/SUPPLY = 16*24hrs = 384 CUBIC METRES
asset life capital cost
Item No.
description of capital Asset
years
Shs
Discount Rate
1+i
mechanical
1
and electrical equipments
15 1,086,433.00
0.12
2
GI water pipeline
20
210000
0.12
CRF
i(1+i)n/(
(1+i)n
i(1+i)n (1+i)n-1 1+i)n-1 Annual cost
1.12 5.47356576 0.6568 4.473566 0.14682 159514.699
1.12 9.64629309 1.1576 8.646293 0.13388 28114.5438
TOTAL ANNUAL COST OF CAPITAL
ANNUAL COST OF LABOUR
monthl
y cost
annual cost
Kshs
Kshs
Item
Description
No
of labour category
number
1
plumber/operator
16000
1
192000
2
pipe fitter
0
0
0
3
labour unskilled
0
0
0
ANNUAL LABOUR COST
192000
ANNUAL COST OF MAINTENANCE
Maint. Capital
Ann.Maint
Factor cost Shs
Cost Kshs
DESCRIPTION OF CAPITAL %Capit
al
Item NO
ASSET
1 Mechanical and Electrical
0.05 ##########
54321.65
2 GI Water pipelines
0.02
210000
4200
Total annual maintenance cost
Equivalent Uniform Annual Cost(EUAC)Kshs
Annual Water demand-Supply(Cubic Metres)
Unit cost of water per cubic metre(Kshs/m3)
58521.65
2162775.893
82125
26.33517069
187629.243
ANNUAL COST OF ELECTRIC POWER
POWER operating electric electric annual electric power
RATING duty hours energy power
cost Kshs
OF PUMP per day
per
charges
IN Kw
year
shs per
Kwh
kwh
15
22.5 123188
14
1724625
SUMMARY OF ANNUAL COSTS
187629.243
ANNUAL CAPITAL COST
ANNUAL LABOUR COST
ANNUAL POWER COST
ANNUAL MAINTENCE COST
Equivalent Uniform Annual Cost(EUAC)
192000
1724625
58521.65
2162775.893
COST STRUCTURE OF WATER SUPPLY SERVICES
UNIT CAPITAL COST
Shs/m3
UNIT LABOUR COST
Shs/m3
UNIT POWER COST
Shs/m3
UNIT MAINT.COST
Shs/m3
UNIT COST OF WATER
Shs/m3
(Source of data estimation of wages, market value of power and GI pipe, water rates as per the Nairobi water company and pump
supplier’s appendix 6)
25
2.28467876
2.33789954
21
0.71259239
26.3351707
CHAPTER SIX
6.1 DISCUSSION OF THE RESULTS.
Table 6.1.1: Summary of the actual performance and design features of the system
comparison of the design parameters of the system against actual
performance
design parameters
actual performance
discharge in m3/hr
16
10
total head
225
280
pipeline size(diameter in inches)
2.5
2.5
pipeline route-length(m)
342
342
pump power-p2(kW)
13.5
11.5
motor power-p1(kW)
16.2
13.8
Pump efficiency (%)
72.67
66.35
Motor efficiency (%)
82.9
81.5
efficiency (%)
60.5
55.2
Current(A)
29.4
26
rotation speed(rpm)
2878
2900
Operating hours
14
22.4
Reservoir capacity (m3)
229
229
18.48
26.45
Overall (motor + pump)
Unit cost of water per
m3(shs/m3)
26
6.1.2 Discussion of the results
The estimated demand of water in university of Nairobi is found to be 21.75M3/hr for 10 hours.
Hence the daily peak demand for the two colleges is 217.5M3.
The design requirements of the system was initially to work for 10 hrs delivering 16m3/hr,this
would supply 160 m3 of water per day which would satisfy the demand of water in the
institution at the initial time of design which was estimated at 125m3 day.
If the system works at the design requirement but running hours increased to 14 hrs per day it
will deliver 224 m3 of water per day this will satisfactorily satisfy the demand of 217.5m3 day.
However the actual examination of the system indicates that its discharge rate is10m3/hr if it has
to operates for 22.4 hrs to deliver an equivalent of 224m3 a day.
With the total reservoir capacity at 229 m3 if the system is working under design conditions it
can hold water delivered past the peak demand time of 4 hrs which is 64 m3. During the peak
demand hr the deficit= 21.75 -16=5.75m3/hr a total of 57.5m3 which can be recovered from the
stored water in the reservoirs satisfactorily.
Similarly with the actual performance of 10m3/hr during off peak water stored is 124m3.and
during peak hrs the deficit 0f 117.5m3 can be satisfactorily be recovered from the stored water in
the reservoirs.
According to the republic of Kenya ministry of water and irrigation practice manual for water
supply services in Kenya balancing tanks shall be provided in order to reduce the peak flows in
the transmission and distribution lines. Generally the tank for the balancing of the daily peak
demands will have a capacity of 50% of the daily water demand of the area served by the tanks.
27
In this system the balancing tanks capacity is 229m3. This can hold for the system running at
least 14 hours without out flow from the tanks. This justifies that for constant operation pump
can run for 24 hrs without interruption the other 10 hrs are during daily peak demand.
The efficiency of the system working at design features was evaluated to be 60.5% and the unit
cost of water per m3 was calculated after considering the Equivalent Uniform Annual Cost
(EUAC) by Capital Recovery Method (CRM) and this was found to be shs. 18.48/m3 of water.
The actual overall efficiency was lower at 55.2% and the unit cost of water evaluated to be
higher at shs 26.09/m3 of water. This indicates that it’s more costly and less efficient to operate
the system at its actual performance features than the design requirements
The difference between the actual performance and the design performance might have been due
to:
Wrong Rotation speed
Clogged / Worn impeller
Air Leaks
Leaking mechanical joints
The aim of the borehole scheme was to replace a municipal supply scheme which offers water
services at a unit cost of shs53.8/m3 at the specified demand from the billing sheet appendix 6.
28
If the system works at the optimum conditions its worthwhile to run considering also the
reliability compared to the unpredictable interruptions of the council scheme.
At actual performance the borehole scheme is still reliable and cost effective compared to the
municipal scheme.
At the actual delivery the total head to be overcome is 280 m. this may be as a result of complex
parallel system of the reservoir arrangement that has different pipeline systems working at any
given time.
The summary of both design features and actual performance are tabulated as above (table 6.1.1)
29
CHAPTER SEVEN
7.1 RECOMMENDATIONS.
7.1.1 Pump service
• Impellers may be coated with deposits such as lime, rust, manganese or clay
Clean the
stainless steel parts with dilute acid (HCl)
•
Replace worn out rubber bearings and neck rings
•
When raising/lowering the pump with cable and drop pipes, avoid banging the motor
against the casing.
•
Protect the cable against sharp edges
Inspect to replace any worn-out pipes and joints
Replace worn out elbows and also tighten the loose parts.
In case when replacing the pipeline preferences should be given to pipes which are
manufactured in Kenya when there is no major difference between the performance and
cost as compared to when they are imported. UPVC and steel pipes are manufactured in
Kenya at present.
7.1.3 Reservoirs
The steel reservoirs should be painted on their outer surface to avoid corrosion.
Regular cleaning of the tanks.
7.1.4Water usage
Collection of the rain water to a common dam whereby it can be used to water the
flowers using a different piping since it does not require to be purified this will cut
down on the wastage of the clean drinking water that is coming at a cost.
30
Water usage for cleaning should be minimised through use of containers since when
using the hose pipe a lot of water is consumed, alternatively overhead rain collections
can also be collected and stored in tanks at each building to be used for cleaning and
car washing.
Running taps not in use are a common phenomenon in the college this should be
avoided to cut down wastage of water already pumped into the reservoir at a cost.
This can also be handled through replacing non self locking taps with self locking
taps with a moderated flow rate just enough to handle the purpose. Example of such a
tap is illustrated in fig 13 below
It was also part of the recommendations to minimise boreholes’ good quality water
wastage through getting an alternative source of water for watering the plants such as
the overhead collections or tap the borehole water in a collection tank before it
reaches the reservoir.
31
7.1.5 Energy conservation
It’s necessary to fix every individual electric appliance with an individual meter. The
borehole pump needs to be one of this appliances this will help the university know
the critical areas of energy consumption on which if energy is saved it has a huge
impact on the overall universities power cost. This will as well be eco friendly as
every unit of energy saved is crucial.
Energy consumption of the pump has to be monitored critically by fixing individual
power meter to the borehole pump to help analyse power consumption and
minimization plans or alternative power source might be put in place.
7.1.6. Redesigning
As part of the continuation of this project in order to improve the current systems
efficiency one can look at the option of redesigning the whole system and thus
coming up with the proper pipeline network that will enable proper head loses and
thus deliver almost according to design. However this might be important in future if
the demand goes higher than the current demand.
32
CHAPTER EIGHT
8.1 CONCLUSION.
From the review design of university of Nairobi main campus borehole it was found
that the actual borehole scheme delivery is 10m3/hr. The efficiency of the system was
55.5% and the cost evaluation on this system showed that it is delivering water at a
unit cost of shs 26/m3.
At this actual performance the system can satisfy the demand of main campus which
is 217.5m3/day by 2010/2011 academic year, by adjusting the running hours from
initial 10 hr to 22.5 hrs.
The unit cost of water is much lower than that of municipal supply which stands at
about shs.53
Alternatively from the analysis of the theoretical design if the efficiency of the system
is to be improved by redesigning to work optimally at 16m3/hr its efficiency will be
60% and the unit cost of water will be shs 18/m3.however this may take some time
and is also a costly exercise that if it has to be implemented preliminary design and
evaluation of cost implications has to be done properly.
The review also established that the borehole scheme satisfactorily replaced the city
water supply scheme which is costly at shs53/m3 and not always reliable in terms of
availability for such a big institution that needs almost constant supply of water.
The borehole scheme is a reliable and cost effective source of water supply to the
university but this can be made better use of by implementing some of the things
earlier discussed in the recommendations.
33