**4.2.3 Summer simulation of thermal comfort indexes**

In summer condition, a better situation is observed in the thermal comfort indexes. The numerical simulation is carried out assuming an external air temperature of 30 °C, with a relative humidity of 70 % and a wind velocity of 4 m/s. The internal vertical walls and floor are considered isothermal with a surface temperature of 15 °C, while the ceiling is considered adiabatic. In addition the external horizontal surface of the collector is superheated with respect to the air and its surface temperature is assumed equal to 36°C due to the effect of solar radiations. As evidenced in Figures 22 and 23, the indoor air temperature is included between about 25 and 27 °C, both on a horizontal plane 1,7 m high above the floor and in a vertical plane in the centre of the room.

Fig. 22. Indoor air temperature in summer condition on a horizontal plane 1,7 m above the floor

Fig. 23. Indoor air temperature in summer condition on a vertical plane in the centre of the room

Data about PMV and PPD indexes confirm that in the room a thermal comfort condition is obtained with the VDLPs in summer as shown by Figures 24 and 25, even though the internal relative humidity may not be satisfactory, ranging between 75 and 85 % all over the environment. It is an expected result since air is only refreshed without any dehumidification action, so the R. H. is increasing due to the decreasing temperature. Hence we can deduce that the internal air must be de-humidified in order to ensure complete satisfactory thermo-hygrometric indexes.

Fig. 24. PMV index on a horizontal plane 1,7 m above the floor

Fig. 23. Indoor air temperature in summer condition on a vertical plane in the centre of the

Data about PMV and PPD indexes confirm that in the room a thermal comfort condition is obtained with the VDLPs in summer as shown by Figures 24 and 25, even though the internal relative humidity may not be satisfactory, ranging between 75 and 85 % all over the environment. It is an expected result since air is only refreshed without any dehumidification action, so the R. H. is increasing due to the decreasing temperature. Hence we can deduce that the internal air must be de-humidified in order to ensure complete

room

satisfactory thermo-hygrometric indexes.

Fig. 24. PMV index on a horizontal plane 1,7 m above the floor

Fig. 25. PPD index on a horizontal plane 1,7 m above the floor

Regarding air velocity, we can say that the VDLPs seem to ensure good natural ventilation, since they are able to make available sufficient fresh air in the room and allow the necessary exchange of air for optimal hygienic condition. Figures 25-28 show the air speed spatial trend in the room on a horizontal plane and vertical plane, in the centre of the room and at the inlet and outlet devices. Being that in summer condition higher values of air velocity than in winter condition can be tolerated by the occupants of the environment, the air velocity is satisfactory both on a horizontal and vertical plane, and at the inlet, air flow-rate is able to sustain the necessary air exchange for hygienic comfort conditions. In fact the calculated inlet flow rate is about 540 m3/h, which correspond to 0,6 air exchange in an hour.

Fig. 26. Air velocity distribution on a horizontal plane 1,7 m above the floor

Fig. 27. Air velocity distribution on the vertical section at the inlet of VDLP

Fig. 28. Air velocity distribution on the vertical section at the centre of the room
