Environmental Engineering Reference
In-Depth Information
The results in Table 9.14 show the percentages of the nodes and corresponding ADF category
in which they will fall after the pipe failure causing the lowest available demand fraction,
ADF
min
. Clearly, the weakness of the layout nr.1727 is that the source has only one pipe
connection and obviously all nodes will fall in the first category because their
ADF
after the
failure of that pipe equals zero; thus, 100%. On contrary, the worst case failure in the layout
nr.3307 will cause only 2% of the nodes (one single node in this case) reduce their demand
for more than 90%, while the demand of 44% of the nodes (total 22 nodes) will be affected
less than 10% (and some maybe not at all).
The results in Table 9.15 show the percentages of original demand affected by the worst case
failure. Again, for the layout nr.3307, 3.28% of the original demand will be reduced between
90 and 100%, while 39.67% of the original demand will be affected between 0 and 10%.
Comparing these results with those in Table 9.14, it can be concluded if the extreme pipe
failure affects small/large number of nodes and/or small/large demand. In other words, an
assumption can be made to which extent the distribution area and major consumers have been
affected.
9.5.3 Economic Considerations
All cost calculations in this case study have been conducted applying the following default
values in the formula
a + bX
n
, as shown in Table 9.16.
Table 9.16
Input parameters used for cost calculations
D (mm) V (m
3
) Q (l/s)
Factor/X
O&M costs %
a
0
0
n/a
for pipes
0.5
b
1
222
n/a
for storage 0.8
n
1
1
n/a
for pumps
n/a
Loan repayment period
25 years
Annual interest rate
8%
Annual inflation rate
0%
Energy cost per pumped kWh
n/a
Due to relatively simple supplying (gravity) scheme, no sensitivity analyses have been done
by modifying these parameters. The pipe investment costs have been calculated taking into
considerations the pipe lengths calculated from nodal coordinates and the diameters as
determined in GA optimisation. The storage volume has been assumed at 10,000 m
3
.
As already indicated in Table 9.11, the most expensive amongst the three most reliable
layouts is nr.3307 with total annual cost of four million. Based on the input in Table 9.16,
more detailed costs for the six layouts from Tables 9.12 to 9.15 are given in Table 9.17.
As can be expected in case of gravity networks i.e. in the absence of pump energy costs, the
asset costs of the transmission part of the network become overwhelmingly dominant. This is
additionally amplified by relatively large lengths of the pipes.
Search WWH ::
Custom Search