Schlussbericht
(Englisch)
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The aim of this study was to examine the possibility of redirecting daylight deeper into tunnels by an innovative daylight system. The redirected daylight could either replace the electric lighting in the tunnel entrance to economise electricity or be used to increase security either in artificially lit tunnels with excess traffic or in unlit tunnels.The reasons for the project were three-fold: possible energy saving; the existence of a new Technology from building physics - the anidolic system - which redirects daylight further into spaces; increased security at tunnel entrances. If the exterior daylight and especially sunlight levels are of importance then high interior luminance levels are required for adequate eye adaptation. It is exactly in such circumstances that sufficient daylight is available to be redirected by an anidolic system into the tunnel to supplement electric lighting in the tunnel entrance. The anidolic system is composed of a scoop outside the tunnel and two facing reflectors inside which create a bundle of rays directed towards the tunnel depth. From a safety point of view, the eye can adapt more easily form high luminance levels to low ones if the transition is from daylight to daylight rather than from daylight to electric lighting. Redirecting daylight therefore helps the eye to adapt to lower light levels in the tunnel entrance.Scale models of an existing tunnel and an anidolic system were built. The daylight factors were measured inside the tunnel under the artificial skies in Lausanne for the cases with and without any anidolic system. The results of the comparisons of the measurements against the simulations (made with Radiance), were sufficiently good to proceed with the luminance simulations.Road lighting analysis generally is based on the road luminance. A particular luminance, which is a direct function of the area weighted luminance levels of the tunnel's immediate surroundings, as seen by an oncoming driver, is required inside the tunnel entrance. A maximum exterior luminance can be defined, which then establishes the maximum required interior luminance level for the whole tunnel entrance section. A lower level is acceptable further inside.Two tunnel, one in the mountains and the other without any mountains above it, but both with high solar incidence, were chosen for this study. For both tunnels, the following luminance values were calculated with Radiance for all daylit hours of a given day for five selected months: the hourly exterior luminance levels of the surroundings of each tunnel; the required interior threshold luminance; the interior road luminance due to the day daylighting without and with an anidolic system and the interior road luminance due to the necessary lamp scenarios required to produce the desired artificial lighting (which should exceed the required interior threshold luminance). Based on these calculations, the hourly electric lighting which could be saved due to an anidolic system was deduced for the chosen months. Yearly savings were calculated based on the hourly electricity savings and certain estimations. Two different methods were used: one depending on the frequency distribution of the exterior luminance of the tunnel surroundings "seen" by an oncoming driver, and the other, on the summation of the possible daily savings and on the monthly sunshine probability. The two extreme tunnel surroundings were such that from a safe stopping distance; in the first case which had high mountains, a driver could "see" no sky and in the second case, where there were no mountains, about 25_ of a driver's view consisted of sky.The first studied tunnel with an anidolic system, which is certainly not the optimal solution for saving electricity, indicates that the savings due to an anidolic system at the south facing portal are relatively small (about 500 kWh/a), which corresponds to about 15 % of the electricity required in the first section of the tunnel entrance. These savings are in addition to those possible due to daylight alone. The savings for a tunnel without mountains were higher (about 840 kWh/a) corresponding to about 23 % savings in the first tunnel section. Higher savings are possible if the catching area of the anidolic system is increased. Rough estimations for the total Swiss tunnel situation give possible yearly savings of about SFr. 24'000.00 if one assumes the current rate for electricity. Further investigations show that introducing an anidolic system at the tunnel mouth is economically more viable than using photo-voltaic cells for producing electricity. The anidolic system lies in a lower "electricity-cost" range than the photo-voltaic cells.In addition, if the lamps are not reduced in power, an anidolic system can provide extra security for visual adaptation. Firstly, the overall luminance level is raised in the tunnel entrance and secondly, the ratio of the a contribution toward the luminance due to daylight relative to that due to electric lighting is increased, which allows quicker adaptation of the eye for a given luminance level drop. The anidolic system can therefore decrease the eye adaptation time at tunnel entrances where regular traffic jams exist, and be useful in unlit tunnels in the mountains.
Auftragnehmer/Contractant/Contraente/Contractor:
Eidg. Technische Hochschule
Autorschaft/Auteurs/Autori/Authors:
Hopkirk,Nicole
Breer,Dieter
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