C o s t – E f f e c t i v e n e s s M e a s u r e m e n t M o d e l
241
The sum of future worth values of the option selected can be calculated as follows:
n
FW
OPT X
=
∑
AC
OPT X
· (1 +
i)
n - k
k=0
(2)
Where,
FW
OPT X
= the sum of future worth value of the option selected
AC
OPT X
= annual energy cost of the option selected
i = interest rate
n = number of years
Moreover, in this study, a cost effectiveness measurement was modelled. In comparison
to the benchmark option (OPT 1), the cost-effectiveness of all other design options has
been calculated using the following formulae:
n
CE
OPT x
=
∑
CD
x
· (1 +
i)
n - k
k=0
(3)
CD
x
= AC
OPT 1
– AC
OPT x
(4)
Where,
CE
OPT x
= cost-effectiveness of annual energy cost difference
CD
x
= annual energy cost difference
AC
OPT 1
= annual energy cost of the benchmark option (OPT 1)
AC
OPT x
= annual energy cost of the option selected (OPT X)
i = interest rate
n = number of years
Accordingly, the future worth of the present design option (OPT 1) applied to ZEMCH109
can be estimated at £51.89 in profit after 10 years of the housing operation. In this
calculation, minus figures imply profits rather than costs. It is worthy of noting that in this
calculation, minus figures of future values imply profits rather than costs. Moreover, all
design options (i.e. combined design solutions) are compared to the benchmark design
option (Table 2). When the result shows a positive figure, the design option in question
can be considered as more beneficial than the original design. If it shows a negative
figure, it depicts that the design option chosen is financially inefficient.
The cost effectiveness analysis of this study suggests that investing in OPT 5 (which
contains most of the design features included in OPT 1 except for due south orientation)
is the most desirable approach as the figure exceeds 600%. It will save a great amount
of energy costs due to its profitable future worth in 10 years; however, the house needs
to be equipped with high thermal performance building envelopes as well as an air
source heat pump and PV and oriented due south. It is interesting to note that even
though options 2-8 use the same systems as OPT 1 (benchmark), they resulted in much
higher energy use, operational energy cost and CO
2
emissions. The results could be
