2.4. Normalization of the data entries
The data entries for each indicator ix.y for a city Cj are normalized
based on the Min-Max method (OECD-JRC, 2008). The normalized
values have an identical range between 0 and 1. There are two
modes of the Min-Max method (Equations (1) and (2)). Both
equations are based on the difference of ix.y for a specific city Cj and
either the minimum (min) or maximum (max) value in the data set
divided by the range of the data set for the same indicator. The
range of the data set for ix.y considers the data inputs for all cities in
the sample Cj from j ¼ 1 to j ¼ 12.
Ix:y
Cj
¼
ix:y
Cj
max
ix:y
min
ix:y
max
ix:y
(1)
Ix:y
Cj
¼
ix:y
Cj
min
ix:y
max
ix:y
min
ix:y
(2)
Equation (1) normalizes the data inputs in a decreasing function
so that max (ix.y) receives the value of 0. Other data entries are
scaled between 0 and 1 accordingly. This mode applies to indicators
in which lower values are desirable, such as energy usage and CO2
emissions. Equation (2) normalizes the data set in an increasing
function so that min (ix.y) receives the value of 0. This mode applies
to indicators in which higher values are desirable, such as the
penetration of energy saving measures. Here, Ix.y is the normalized
value of the yth indicator in dimension x for a given city Cj. This
process is reiterated until all data entries are normalized.
2.5. Value aggregation for composite index
Equation (3) provides the means of aggregating all normalized
data values Ix.y into a composite index value per city Cj. The double
summation in Equation (3) sums the normalized values Ix.y of indicators
y ¼ 1 to y ¼ 5 (inner summation) in all dimensions x ¼ 1 to
x ¼ 7 in the Index.
SDEWES
Cj
¼
X7
x¼1
X5
y¼1
axIx:y where
X7
x¼1
ax ¼ 1 (3)
All dimensions have five indicators and may be weighted
equally. In this case, the dimension weights ax will be 0.14.Weights
ax may also be differentiated for each dimension. In practice, ax is
0.22 for D1 and D5 that directly involve energy and CO2 emissions
data from the SEAP. For the other dimensions that may indirectly
relate to SEAP data, the values of ax are 0.11. The output of the entire
process from data collection to aggregation is the SDEWES Index
value for each city in the sample Cj from j ¼ 1 to j ¼ 12. This output
is represented in Fig. 1 (right hand side) based on the summation of
all values Ix.y for each city Cj in the sample.