The two summers of 2006 and 2007 reach external temperatures quite high for Lisbon, above 35°C achieving even 40 °C during day time. In these two summers the mean temperatures inside the building varies between 24°C and 25.4°C, for mean maximum temperatures from 26.4°C up to 28.1°C (see table 2). These temperatures correspond to the rooms in the south part of the building which are the hottest one, in the north part of the building, like in winter a difference in these location can achieve 2°C.

In figure 9, for the hottest month of summer 2006, the hourly temperatures are presented for outside air temperature (light blue) and for the three building levels. In the hottest days, with outside air temperatures above 35°C the air inside the building in the upper level reaches around 30 °C (mean maximum of 31.6°C). In particular in 6 of August for an outside air temperature of 40°C, the 3 level reached 30°C in the upper floor, 28 in the middle floor and 24 in the basement.

The basement is of course the one where the temperatures are the best (in green in figure 9). For the whole month a very smooth line between 23.2°C and 24.1°C has been measured.

The ground temperature during summer period varies between 17.5°C to 19.5°C which is a very interesting temperature for cooling purposes. Figure 10 presents the hourly temperatures for the hottest month in summer 2006 (August) in the system and boundary. External air temperatures reaching in August 6, 39.7°C (light blue), the ground temperature almost constant with a mean temperature of 19.1°C (dark red), and the temperatures in the pipes: red near the inlet tube (mean temperature of 21.1°C); green in the middle of the tube (mean temperature of 20.6°C) and blue near the enter of the building (mean temperature of 20.7°C).

Figure 11 presents the behaviour of the system when operated by the user in some particular days (from August 27 to September 8, 2007). There are two different modes of operation with circulation ON (4-9 Sept) and OFF. During the ON period, the temperatures incoming in the building (blue colour in the graph) can decrease up to 5°C when the circulation in the pipes are operating. In terms of air temperature in the room this can correspond to a decrease up to 3°C (red colour) see September 4.