*4.4. Predicted Mean Vote (PMV)*

The Predicted Mean Vote (PMV) model uses six key factors to address thermal comfort: metabolic rate, clothing insulation, air temperature, radiant temperature, airspeed, and humidity. These factors may vary with time; however, in this article, the airspeed, metabolic rate, and clothing insulation are considered steady. Compliance with the ASHRAE-55 standard is tested using the CBE Thermal Comfort Tool. This tool, developed at the University of California at Berkeley, allows designers to calculate thermal comfort according to ASHRAE Standard 55-2017. The indoor air temperature and the MRT were taken from Figure 15 during operating hours. Clothing was set as 0.8 Clo (typical office indoor clothing); the metabolic rate was set as 1 Met (sedentary activity), the relative humidity was taken from Figure 14, and air velocity was set as 0.10 m/s (mean air velocity of the day). The ASHRAE-55 Comfort Zone, shaded in gray in Figure 16, represents the recommended predicted mean vote, between −0.5 and +0.5, for buildings where the occupants have metabolic rates of between 1.0 met and 1.3 met, and clothing provides between 0.5 clo and 1.0 clo of thermal insulation. Figure 16 illustrates the variations of the predicted mean vote (PMV), mean radiant temperature (MRT), indoor air temperature (*T\_int*), and operative temperature (*Top*) on four summer days. The PMV over the working hours ranged from −0.04 to −0.42 on 10/07/2019, while the MRT ranged from 23.0 to 19.3 ◦C, and the indoor air temperature ranged from 25.2 to 27.4 ◦C. During the working hours, the highest indoor temperature was on 11 July 2019 at 8:00 p.m., when the MRT was 20.1 ◦C and the predicted mean vote was 0.1, very close to the optimum value. Similar values are shown over the four days.

**Figure 16.** Operative temperature (*Top*) and Predicted Mean Vote (*PMV*) in summer—sample days 10 July 2019 to 11 July 2019 and 15 July 2019 to 16 July 2019.

The comfort zone is defined by the combinations of the six key factors for thermal comfort. The PMV model is calculated with the air temperature and mean radiant temperature in question along with the applicable metabolic rate, clothing insulation, airspeed, and humidity. If the resulting PMV value generated by the model is within the recommended range, the conditions are within the comfort zone. Table 15 defines the PMV range for the thermal sensation scale. For 1.1% of the working hours, the PMV was above +0.4; for 6.7%, the PMV was from 0 to +0.2; for 32.3%, the PMV was from 0 to −0.2; for 54.3%, the PMV was from −0.2 to −0.4; and for 5.6% of the time, the PMV was below −0.4. Despite the high indoor air temperature, the PMV showed that occupants would describe their comfort conditions as "Slightly Cool" and always within the recommended limits specified by ASHRAE-55 (−0.5 < PMV < +0.5). The transparent WFG provided the partition exposed to solar radiation with a temperature that prevented thermal asymmetry and a lack of comfort. Hence, the results in Figure 15 indicated that the system gave consistent performance and provided comfortable conditions.

**Table 15.** ASHRAE thermal comfort scale 1.


The same comfort analysis was carried out in February. Figure 17 illustrates the variations of the predicted mean vote (PMV), mean radiant temperature (MRT), indoor air temperature (*T\_int*) and operative temperature (*Top*), and relative humidity (RH) on four February days. As shown in Figure 9, the conditions on sunny winter days are required to operate the heat pump in cooling mode in the afternoon. The indoor air temperature dropped to 20.5 ◦C on 19 February 2020 at 8:00 a.m., and reached 27 ◦C on 24 February 2020 at 7:00 p.m. The relative humidity ranged from 35% to 40%. The PMV over the working hours ranged from −1 on 19 February 2020 to 0.8 on 24 February 2020. Both values are out of the comfort range. In the morning, the PMV on the four days was below −0.5, so the occupants

would describe their comfort conditions as "Slightly Cool" or "Cool". The heat pump was set to operate in heating mode when the indoor temperature was below 20 ◦C, and that condition was not met. On 24 February 2020, the PMV was above 0.5 from 5:00 p.m. to 8:00 p.m. Even though the heat pump was operating in cooling mode, the occupants would describe their comfort conditions as "Slightly Warm" or "Warm". For 45% of the working hours, the predicted mean vote was below −0.5, out of the shaded area representing the recommended comfort range. For 8% of the working hours, the predicted mean vote was above the comfort range when the indoor temperature surpassed 25.5 ◦C, and the WFG temperature was not low enough to bring down the mean radiant temperature.

**Figure 17.** Operative temperature (*Top*), Predicted Mean Vote (*PMV*), and indoor relative humidity (*RH*) in winter—sample days 19 February 2020 to 20 February 2020 and 24 February 2020 to 25 February 2020.
