The STS consists of 32 solar collectors with unit aperture area of 1.86 m2. The solar field is divided into 8 groups of 4 collectors oriented both at 27° (4 groups) and -63° (4 groups) azimuths, given architectural and space constrains. The tilt angle is 35°, optimized for the building latitude.

The effect of the decoupled orientation from south was studied on a daily basis and found never to exceed a 12% penalty (regarding an optimal south facing orientation) in monthly average (value for December, the less favourable month, being for example 8% in March, 1.35% in April, 0.87% in May and 0.16% in June).

The feeding of the collector batteries facing east and west is independent, thus using two separate lines starting in the pumping group (located in the basement, -1 floor).

After passing the two parallel collector fields, each one composed with 4 parallel groups of 4 collectors in series, the thermal fluid shares the same pipe which in turn feeds 5 vertical lines going to the independent building sectors feeding the individual storage tank located in each apartment.

Along its course, each line feeds 4 dwellings, until the technical room is reached. At the end of these lines there are flow meters and regulation valves to assure the hydraulic balance.

The heat exchange from the primary system to the secondary is done via a heat exchanger inside the storage tank located inside each dwelling. When the temperature inside the individual tanks, is higher than temperature of the primary water circuit, a three way valve was projected to avoid the heat transfer in the wrong direction.

The system has 4 pumps, 2 for each azimuthal group of collectors working in turns, so that the pumps can be repaired, if needed, without having to stop the system.

Upstream from the pumping group there is also the safety group, consisting in expansion vessel and a pressure safety valve, for each feeding line to the collectors.

The circuit includes also an energy count system, consisting of two temperature probes and a flow meter, that send information to the central which has a differential controller and calculates the energy delivered by the solar system. The "hot probe" is inserted in the totalizing pipe downstream after the two collector fields. The "cold probe" is placed just upstream of the pumping group.

Fig.1 is a schematic representation of the primary circuit.