3.2.1. Standard Classroom

The analysis of the current daylight fruition in the standard classroom revealed, on the whole, good daylight availability, as pointed out by the *sDA* and useful *UDI* metrics amounting to 90.4% and 72.5%, respectively. On the other hand, daylight is unevenly distributed within the room (*UR* = 37%), with peak illuminance values being achieved close to the windows and rapidly declining if moving away from them. These issues are fairly typical for single-sided daylit spaces [28,29], and a range of design options can be implemented for reducing daylight levels close to the windows, while also improving those at the bottom of the room and thus increasing the overall uniformity. In particular, the refurbished scenario first aimed at reducing direct sunlight contribution by adding an external horizontal overhang at the top of the clerestory. Secondly, the bottom of the clerestory has been provided with a light shelf with internal and external protrusions, in order to bring daylight in and reflect it further inside through a highly reflective false ceiling.

Different geometrical solutions have been analyzed for the overhang and the light shelf (both internal and external sections) by varying their depth (more insights on this aspect can be found in parametric studies, such as ref. [30]), while in the case of the false ceiling, a planar and a double-curve configuration declining towards the bottom of the room have been investigated.

Various optical properties combinations for the glazing (namely the visible transmittance), the light shelf and the false ceiling (their diffuse and specular reflectance components in order) have been explored as well. The optimal combination resulted in:


Reflective glazing (visible transmittance = 0.65) has been used for the biggest panes below the clerestory (see Figure 5), while the light shelf exhibits a diffuse reflectance of 0.85 and a specular component of 0.5. The use of light shelves and ceilings with a specular component, aimed to enhance the amount of light re-directed towards the bottom of the room, has been described by other researchers [31,32] and it is actually observed in real products that are available on the market. In particular, a specular behaviour has been found to improve illuminance levels and their uniformity in winter and in the mid-seasons, while diffuse lightshelves perform better at high solar altitudes (in summer) [28].

**Figure 5.** Design solutions for the standard south-oriented classroom.

The use of these design solutions allowed for improving all of the metrics except for the *aDF*, which dropped from 1.8% to 0.8%, and for the *sDA* that dropped from 90.4% to 74.1%. These results sound reasonable, since the amount of light entering the room has been reduced by the combined action of the external overhang, the light shelf, and the reflective glazing. On the other hand, daylight is more evenly distributed thanks to the internal light shelf that re-directs the sunlight to the highly-reflective ceiling, which in turn conveys the light deep to the end of the room. This leads to a reduction in the *UDI* over 2000 lux metrics from the original value of 22.7% to the new one of 3.4%, and to an increase of the useful *UDI* (i.e., that in the range of 100 to 2000 lux) from 72.5% to 89.2%, respectively.

These improvements can be appreciated if looking at Table 5, where all of the values are summarized for both the existing and refurbished scenario, and where a column named 'effect' identifies if a metrics improves (better) or worsens (worse) the corresponding daylight performance if compared to its original value. In terms of annual *DGP* values, Figure 6 shows only minor improvements, meaning that glare is not an issue for the chosen observer's position.


**Table 5.** Daylight metrics for the standard classroom: existing and refurbished scenario.

**Figure 6.** Annual *DGPs* calculation for the standard classroom. Refurbished scenario.
