A series of indoor and outdoor tests for temperature and illuminance measurements were done on hourly and daily basis to evaluate the performance of each room. These tests enabled us to obtain an immediate evaluation of the efficiency of the system, to visualize the amount of daylighting redirection, to observe how direct sunrays penetrate the interior space, and to detect the presence of bright areas generated by the prismatic glazing panels. Temperature and illuminance measurements were taken at the height of 70cm~80cm for different interior reference zones

(Fig.3 & Fig.4). A Testo-435 Thermocouple Meter and Minolta T-10 illuminance meter with a data management Software T-A30 was used for data collection.

the maximum ambient temperature was 23.5oC whereas the temperature for reference case was 26.5oC and target case was 29.66 oC (Fig.5).The temperature of target room was 3oC higher than the reference room, and about approx 6oC than the ambient temperature. Prismatic panels directly transmit input solar thermal range radiations into the room, which causes to increase the temperature. This increase in temperature may, sometimes, produce local thermal discomfort in some parts of the room. In order to reduce this effect and for the ventilation purpose, an electric fan was used to circulate the hot air uniformly to produce better thermal

conditions inside the room. Fig.5. Temperature measurement results.

1.2. Illuminance Results

The measured results show that the reference room is full of glare due to direct sun patches (Fig.10). These sun patches changed their position throughout the day with respect to changes in altitude angles of the sun. The illuminance levels were measured over 150Lux~ 6kLux (Table.2) at a distance of 1m, 2m, 3m, and 3.5m from the window and the daylight factor (%) was calculated over 1~15.6 (for illuminance data collected) for ten different zones. Here the daylight factor means, ” The ratio of interior illuminance at a given point on a given plane (workplace) to the exterior illuminance (reference) under the same sky conditions”. i. e. Daylight Factor= Interior illuminance x100 / Exterior illuminance. The result comparison at morning, solar noon, and evening timing of the day, under clear sky conditions, shows that the distribution of work place illuminance along the centerline of the room (south facing wall) was not uniform (Fig.6, Fig.7 & Fig.8). The illuminance was varied up to 6kLux at a distance of 2m from the window, and daylight factor varies up to
15.6 (at solar noon Fig.9) which produced an uncomfortable glare. Moreover, there was no reasonable uniform drop-off in light levels with respect to distance increase from the window of the south-facing wall. Changes in azimuth and altitude angles of the sun throughout the day affect the depth of penetration and distribution of daylight in the room. The simple glass on the entrance of the reference room transmitted about 90% sunrays and was not able to control the directly penetrating sunrays into the room, which brightened some part of room while the rest of the room was in shadows.

Measured results of prismatic glazing system (target room) indicate that for solar azimuth angle у < +33°. The prismatic model achieved work place luminance level of over 400Lux near the south-facing wall. The illuminance levels were achieved > 100Lux at a distance of 3.5m from the window even in the evening times. The distribution of work place illumination along the centerline of the space from the window is fairly high and uniform through out the day, as expected (Figs.6, Fig.7 & Fig.8). Also the daylight factor ranged from 0.5 to 2.1 for ten different zones is fairly high and uniform (Fig.9).

There was no appearance of direct sun patches on work plan area in the target room (Fig.11.). The main reason for the uniform illuminance inside the target room is that the prismatic panels control the sunlight by reflecting, refracting, and diffracting the rays.

The transmittance of light rays through prismatic panels depends upon the incident angle. These panels accommodate a wide range of solar altitudes to produce uniform illuminance and to obtain maximum penetration without creating descending rays of sunlight that create glare.

Fig.11. The target room with PSHC (solar noon).

2. Conclusion

The results of illuminance measurement revealed that the target room showed uniform illuminance with respect to the position of sun while the reference room showed non­uniform high illumiance creating a glare inside the room. The daylight factor ranged from 0.5 to 2.1 also confirmed the illuminance uniformity for target room while the daylight factor ranged from 1 to 15.6 showed the nonuniformity in the illuminance levels for reference room. The prismatic solar hybrid collector unit was achieved better thermal conditions and significant redistribution of ambient sunlight within the target room, redirecting the incident light towards the ceiling where it was reflected onto the working area below. This drastically reduced the need for artificial light. The system with prismatic glazing unit has represented an efficient approach to exploit natural light for glarefree and uniform illumination of working spaces. Low luminance levels of back zones could be improved by improving the reflection properties of ceiling. According to the CIE guide on electric lighting of interior (CIE-1986), an illuminance of 20Lux is regarded as the minimum level for non working interiors and the recommended for normal working space is 200Lux, which validate the results of illuminance for target room (with PSHC). The overall results clearly proved that the prismatic solar hybrid collector could be successfully used to enhance the thermal and visual comforts preventing glare by solar radiation. For further optimization of

the light guiding properties, we plan to model the daylighting system with prismatic glazing unit with ray-tracing methods and Monte — Carlo simulation.