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The first of these three scenarios seems less attractive, mainly due to the fact that the number of
customers that cover their space cooling loads via cold water supply is extremely low in islands,
at least in the residential sector, being most of these loads covered by small scale split air-
conditioners.
c. Coverage of connection cost: only indirect connection between the DH network and the
private users will be considered, thus having separate hydraulic circuits and avoiding any risk of
damages and leakages. Then, quite high cost of substations can be estimated, since they must
include one (or two) plate heat exchanger(s), controls and heat metering devices; according to a
recent survey carried out in Italy, costs in the order of 3-6 k€2011 and 15-40 k€2011 can be
estimated for “small scale”/residential and “medium-large scale”/centralized users, respectively
[30]. In the following of this paper, only voluntary connection of private customers will be
considered, assuming two distinct scenarios in terms of coverage of connection cost and share of
customers voluntarily requiring to be connected to the network:
 Cost of the substations totally covered by the district heating company, that is for
simplicity supposed coincident with the company currently supplying electricity, which
owns and operates the diesel engines to be converted in CHP operation mode. In this
scenario, obviously, the private customer requiring connection to the DH network would
have no initial costs, and the following high shares of customers voluntarily requiring
connection are supposed:
- 30% of residential users as concerns space heating loads (this low percentage is
influenced by the high share of residences not interested in hot water supply, being
served in winter by small heat pumps);
- 60% of residential users as concerns domestic hot water loads.
 Cost of the substations totally covered by private customer requiring connection to the DH
network. From the customer perspective, the initial investment obviously represents a
barrier that contributes to make connection to the DH network unattractive; then, in this
scenario lower shares of customers voluntarily requiring connection are supposed, as
follows:
- 10% of residential users as concerns space heating loads;
- 30% of residential users as concerns domestic hot water loads.

It may be observed that no differences have been supposed for the centralized users, since most
of them have usually hydronic systems for space heating and cooling and therefore such
customers are supposed to require connection to the DH network regardless of the assumption
made for the coverage of connection costs.
For each possible combination of the aforementioned scenarios, the procedure followed to
estimate the distribution costs and the most promising network geometry is now described. For
the sake of clarity, the analysis will be presented for one of the 6 examined islands, i.e.
Lampedusa, which probably represents the most complex but interesting case study. The
procedure consists of the following main steps:
1. Definition of a reasonable path for the main line (i.e. line with highest diameters and
flow rates) of a DH network connecting the power plant (where heat is made available from
engines) with all the identified built areas. All the main lines are consecutively numbered, as
shown in Figure 9 for the island of Lampedusa, and their length is calculated;

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