**4.2.2 Winter simulation on thermal comfort indexes**

A further numerical analysis was carried out with the aim of determining the indoor thermo-hygrometric comfort index such as the air temperature and velocity, the PMV and PPD index, the mean age of air in winter and summer condition.

In winter condition the VDLP is not able to guarantee thermo-hygrometric comfort condition as confirmed by the air temperature data and the PMV and PPD comfort indexes (cfr. Figures 15 and 16).

Fig. 15. Air temperature on a horizontal plan 1,7 m high on the floor

Fig. 16. PMV and PPD on a horizontal plane 1,7 m high above the floor

On the other hand, as underlined by graphs in Figures 14-17, the VDLP is able to guarantee a good natural air circulation. Figure 17 shows the air speed distribution on a horizontal plane 1,7 m above the floor in winter condition, with an external air temperature of 4 °C, in a two - level underground building, and a ground temperature of 15 °C. In the passage room the boundary walls and the floor are considered isotherm with a temperature of 15°C, while the ceiling is considered an adiabatic surface. The wind velocity corresponding to the inlet section of the collector is of 4 m/s. The wind direction is not considered because the device can vary its orientation in such a way that the inlet section is always normal to the wind direction.

Close to the inlet of the VDLPs, high values of air speed are observed (up to a maximum of about 0,5 m/s ) while all over the environment the air velocity is less than 0,2 m/s with quite a uniform spatial trend. In Figure 18 the vertical air velocity at the centre of the room,

Fig. 15. Air temperature on a horizontal plan 1,7 m high on the floor

Fig. 16. PMV and PPD on a horizontal plane 1,7 m high above the floor

direction.

On the other hand, as underlined by graphs in Figures 14-17, the VDLP is able to guarantee a good natural air circulation. Figure 17 shows the air speed distribution on a horizontal plane 1,7 m above the floor in winter condition, with an external air temperature of 4 °C, in a two - level underground building, and a ground temperature of 15 °C. In the passage room the boundary walls and the floor are considered isotherm with a temperature of 15°C, while the ceiling is considered an adiabatic surface. The wind velocity corresponding to the inlet section of the collector is of 4 m/s. The wind direction is not considered because the device can vary its orientation in such a way that the inlet section is always normal to the wind

Close to the inlet of the VDLPs, high values of air speed are observed (up to a maximum of about 0,5 m/s ) while all over the environment the air velocity is less than 0,2 m/s with quite a uniform spatial trend. In Figure 18 the vertical air velocity at the centre of the room, with the same boundary conditions is considered. It is evident that the vertical trend of air speed is quite uniform with very comfortable values, except for positions near the floor in which the suction action of the device causes high values of air speed. The vertical sections shown in Figures 19 and 20, corresponding to the inlet and outlet of the VDLPs, indicate that they are able to effect an efficient air change in the environment as confirmed by Figure 21 in which data about the mean age of air are reported. It is clear that the in flow of fresh air and the out flow of exhaust air is efficiently effected by the devices so that the mean age of air is satisfactory all over in the environment particularly near the inlet tubes. In fact the calculated inlet flow rate is about 720 m3/h which correspond to 0,8 air exchange in an hour.

Fig. 17. Air velocity on a horizontal plane 1,7 m above the floor

Fig. 18. Air velocity in the vertical plane at the centre of the room

Fig. 19. Air velocity in a vertical section of the inlet tubes

Fig. 20. Air velocity in the vertical section of the outlet tubes

Fig. 19. Air velocity in a vertical section of the inlet tubes

Fig. 20. Air velocity in the vertical section of the outlet tubes

Fig. 21. Mean age of air on a horizontal plan 1,7 m high on the floor
