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Capturing and transport system for natural light

Speech presented at the conference Lighting Technology: LightFocus 2002, Frankfurt
 
In 1988 iGuzzini started with photobiological studies and took part in a research project financed by the CNR (Italian National Research Council),
This research was especially oriented towards the study of a Variable Lighting System with Automatic Regulation for rooms without windows (called SIVRA).
With SIVRA we created a luminarie capable of producing “natural” lighting situations and of creating temporal rhythm by the light.
The second step of our investigation was how artificial light mixes with daylight for rooms without windows.
So started in the 1998 a new research “Teletransport System For Natural Light” financed by Italian Ministry of Scientific and Technological Research, and today i will show you a general overwiew of the first results.
We would therefore guarantee a deep transport of light with good levels of illuminance uniformity, without obstructing a view of the outside.
The results we wish to obtain are
- guaranteeing a suitable level of illumination for the visual tasks requested by the different types of applications,
- saving the maximum amount of energy in relation to a careful cost-benefit analysis and a maximum efficiency of the system.

This research was developed to improve the entrance of daylight in the buildings. In fact the quality of the lighting environment is of fundamental importance for the psycho-physiological well-being of man, especially when a person remains in rooms for a prolonged and compulsive amount of time (offices, hospitals, schools…).
Visual comfort is linked to the amount of light necessary to carry out specific activities, and to the overall quality of the lighting environment.
The result of this study would be a system capable of distributing daylight within those environments, where natural light is often screened (e.g. using venetian blinds) to avoid troublesome glares and thus replaced by artificial light.
With highly innovative integrated systems, we would obtain the following results:
1 – A deep transport of light with good levels of illumination uniformity, thanks to concentrated light, especially if these systems are adopted in sunny places. Then it would be possible the energy saving with the right control devices.
2 – An improvement in the illumination uniformity in the interior places, in fact natural light is driven deeply reducing the extreme contrasts between the front and the rear of the interior places.
3 – A control of direct irradiation, without screening the windows and obstructing a view of the outside.
4 – A control of direct glare.
 
The day lighting system is made up of three units: outside the building is located the collector and inside the diffuser.
In our case the conduction and transport unit correspond to the diffusion unit.
The focusing unit is an element connecting the collector to the diffuser, whose function is that of focusing and redirecting daylight within the transport unit;
The receiver, positioned outside: it collects and conveys daylight in its two components, direct and spill;
The interest was geared towards Fresnel lens linear concentration capturing systems, which, using the 3M-21X Fresnel lens film.
Our solution was the Active receiver with translation in the vertical plane. The receiver movement is due to a software program that calculate the exact solar height relative to the day, hour and season so that always focuses the sun radiation on the perfect focal line.
This reduces the number of the system components with positive benefits on the system management and maintenance.

This system traces the sun, following its path during the day only thanks to a translation in the vertical plane with a movement from 10° to 80° inclusive.
This solution has been chosen for the simple manufacture of the receiver and to verify the system efficiency in the maximum insolation hours, from 10 a.m. to 14 p.m.
A prototype of this active receiver has been built and established at iGuzzini Illuminazione sperimental Laboratory, in Recanati.
The focusing point is 40 cm far from the inferior lens surface (depth of the receiver), lined with high reflection material, consist of a box structure 180 cm width and 10 cm height, with changeable depth according to the wall depth in which it’s built in.
The diffuser, positioned inside the room, allows for the transport, emission and control of the flux.
The diffuser is a box structure with the same dimensions in width and height of the duct unit, while depth varies according to the dimensions of the room where the daylighting system is installed, in our prototype it is 6.60 meter.
The dimensional aspect, about 25 cm height in the section, is remarkably reduced if compared with similar system, It’s evident that the object with these reduced dimensions can be compared with built-in conventional lighting sources.
Inside the diffusion unit an optical film is curved from the transport duct till the diffuser, touching the inferior surface, the emission surface, made of a polycarbonate slab lined with 3M OLF.
The system is quit flexible, both in terms of the use of technologies and in terms of the integration between daylight and artificial light; as well as in terms of the size of the diffusers that can easily be adapted to different functions.
The innovative characteristics concern the use of specific sophisticated optical materials studied for the transport, control and diffusion of light in the three units.
Another innovation is represented by the integration, inside the system, (more precisely within the focusing unit), of artificial light sources, monitored by an electronic system of controlling both the starting and the intensity. This is how artificial light mixes with daylight thus making up for the low levels of natural lighting.
 
The monitoring of the system started during the first week of July 2000 and is expected to last for at least 6-8 months in order to test the system’s efficiency over a longer period.
Monitoring was carried out in a room with a 30 square meters surface.
We used fixed lux sensors connected by a computer to record the data:
15 sensors for the orizzontal illuminance on the floor at a distance of about 240 cm from the luminaire, and 6 sensors on the wall to check the vertical illuminance.
Two sky conditions were taken into consideration: clear and partially overcast sky.
The data are been checked every 5 minutes during the considered period of the day.
The charts included in the proseedings show the results under different sky conditions,
Obviously, the system is designed for application in sunny areas with clear sky conditions (the entire Mediterranean region), the best results are achieved in clear sky condition, with illuminance peaks higher than 500 lux (average on the work-plane).
The values checked on the floor of the room, where the system was applied, show that the system reaches its maximum efficiency between 10:00 a.m. and 1:00 p.m. with the average illuminance higher than the threshold value of 300 lux, average illuminance on the work plane (according to the objectives set for this research).
A first general evaluation of the energy saving that could be obtained with the aforementioned system can be made on the basis of the following considerations:

- The average illuminance value considered to be satisfactory in this research project is 300 lux.
- In a typical office as our reference setting, open from 9 a.m. until 5 p.m.: usually, the artificial lights stay on for then entire duration of the workday.
1st July 2000 was the reference day, based on the measurements taken.
To maintain a minimum illuminance of 300 lux, the system could exploit the artificial light sources for the first few hours in the morning at 100%, and then gradually decrease the artificial light supply and increase the natural light supply.
Then when the illuminance level guaranteed by natural light reaches 300 lux, the artificial light sources will be turned off, and then turned back on once the natural light is no longer enough to ensure the minimum threshold is respected.
As you can see from the graph, the artificial light sources stay off for approximately 3 hours, whereas they operate at 50% for approximately 40 minutes.
The energy evaluations for the prototype installed at the iGuzzini experimental laboratory in Recanati should be calculated and/or assessed in different situations.

1- energy saving during clear days with maximum sunshine;
2- energy saving during partially clear days (variable cloud cover);
3- use of artificial light sources (8 MASTERCOLOR 70W) to compensate for the drop in illuminance levels in conditions of variable cloud cover;
4- energy comparison with an “indirect” artificial lighting system featuring the same luminance to guarantee the minimum 300 lux.

The sum of these contributions leads to a saving of 1,867 kWh over the entire course of the day, which, in percentage form, means a net saving of 41.7 % in energy consumption.
 
If we want to analyse the global economical advantages deriving from the use of this system, we also need to consider the comfort levels that the system provides. The possible “indirect” advantages that could derive from an increase in the visual comfort are difficult to quantify economically: we would need a degree of analysis and detailed tests to perform on the many aspects of well-being.
In addition, for the correct energy evaluation of the costs/benefits, we need to consider the advantages in terms of savings energy for air conditioning, since the system has a low thermal transmission coefficient which, when combined with the correct insulation system of the vertical partitions of the windows, leads to an efficient drop in energy consumption levels.
This system is to be analysed and studied, so as to evaluate the possible implications on a wide variety of systems for building illumination. The result we wish to attain on this matter would be that of guaranteeing a suitable level of illumination for the visual tasks requested by the different types of applications in the lighting of buildings, reaching the objective of saving the maximum amount of energy in relation to a careful cost-benefit analysis and a maximum efficiency of the system.