Several simulations were performed for the different buildings situated in Lisbon. For the office building, the best results occur for a collector area and a storage volume between 120-180 m2 and

0. 05-0.13 m3/m2, respectively; that represents a storage capacity between 1-5.5 hours. For the hotel, the best results occur for a collector area and a storage volume between 200-300 m2 and 0.01-0.07 m3/m2, respectively; that represents a storage capacity between 0.3-3.1 hours. For the single-family house, the best results occur for a collector area and a storage volume between 15-30 m2 and 0.05-0.13 m3/m2, respectively; that represents a storage capacity between 2.5-13 hours.

4.2 Energy, economics and emission savings

Considering a solar thermal system size that provides an annual solar fraction of 60%, for the office building and hotel, the solar fraction is higher for March and December; for the single­family house, the solar fraction is higher for April, May and October. The higher solar fraction is related to the lower energy need that occurs in those months.

4.4.1 Office building

Table 4 presents the energetic, economic and emission analysis for the system configuration with lower total cost of produced energy for a solar fraction of 60%.

For the office building there is no economic viability in any of the locations considered — see Figure 3.

In situations where an electric backup is not possible (only gas backup), the solar system installed in Rome with a solar fraction of 60% is economically more profitable.

A gas boiler as backup solution, instead of an electric compression chiller, allows a reduction in solar collector area between 3-9%, for the same solar fraction.

In the Mediterranean cities, the flat-plate collector compared to the vacuum tube collector, allows a reduction in the total cost of produced energy between 0-1.6 c€/kWh — see Figure 3. In Berlin, both collector technologies show similar results. Vacuum tube technology has the advantage of allowing a reduction of collector area between 30-50% — see Figure 4.

4.4.2 Hotel

For the hotel, in Rome it is possible to achieve economic viability for a solar system with gas backup and solar fractions between 20-40% — see Figure 3. Comparing with a conventional electric air-conditioning, this system leads to a reduction of 5 c€/kWh of produced energy. In situations where an electric backup is not possible (only gas backup), solar systems installed in Rome and Lisbon with solar fractions between 20-60% are economically interesting. A gas boiler as backup solution, instead of an electric compression chiller, allows a reduction in solar collector area between 0-20% for the same solar fraction.

In the Mediterranean cities, the flat-plate collector compared to the vacuum tube collector, allows a reduction in the total cost of produced energy between 0-2.8 c€/kWh — see Figure 3. In Berlin, both

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collector technologies show similar results. Vacuum tube technology has the advantage of allowing a reduction of collector area between 20-50% — see Figure 4.