Critical analysis of the energy performance indicators for road lighting systems in historical towns of central Italy
Introduction
Energy demand represents a global issue that calls for innovative local energy solutions, such as the ones generally proposed in Sustainable Action Plans (SEAP) [1]. By the end of May 2016 more than 6700 cities around Europe (3100 in Italy), that involve 211,610,834 inhabitants, started to working on their SEAPs [2]. Public lighting (predominantly on roads) contributes for 2.3% to the global worldwide electricity consumption; thus, energy-efficient programs in this field are very welcome, since the possibilities for energy saving in road lighting are numerous and sometimes even enable reductions in electricity consumptions of more than 30% [3], [4]. In 2005, in Europe, road lighting consumed a notable amount of energy: approximately 35 TWh [5]. In 2010, in the Netherlands, about 0.8 TWh per year were used by municipalities for public lighting, accounting for 60% of the local government's energy consumption [6]. In the same year, in Italy, the national consumption for lighting was about 50.8 TWh per year and, of this amount, 6.1 TWh per year were used for public lighting [7].
Currently, towns throughout the world are engaged in road lighting refurbishment, carried out with the changeover to more efficient luminaires, in some cases at the end of the economic life of the existing ones, in others before the end. Several studies have shown that urban interventions on lighting can lead to positive results [8], [9], [10], [11], [12], since public lighting is an essential element of urban environments [13]. Public lighting should: provide good visibility conditions, reduce potential hazards by illuminating objects in and along the roadways [14], [15], [16], influence the emotions of the observers.
With increasing consideration of pollution and energy conservation, the needs to introduce new recommendations for energy efficient lighting and new indicators to evaluate the energy performance of lighting systems are arisen. At the beginning, the attention was paid to the indoor lighting systems [17], [18], [19], [20], [21], [22], nowadays new efforts are focused on the energy consumptions of public lighting systems [8], [11], [25] and some energy performance indicators have been proposed at international level to compare the performance of these systems [23].
In Europe, only few countries have provisions addressing the energy efficiency of the road lighting systems. In Ref. [8], useful suggestions for preparing such provisions were supplied, identifying a set of the most important recommendations regarding the influencing factors for energy savings in road lighting. However the suggestions were mainly qualitative and there was no systematic use of energy-based and lighting-based parameters for the comparison of different road lighting systems. In the Netherlands an energy efficiency A-G label were developed for road lighting systems, based on the Street Lighting Energy Efficiency Criterion (SLEEC), which is a whole system indicator taking into account efficiency of the lamp, ballast and luminaires [24]. In Ref. [25] a multi-objective evolutionary algorithms was presented with the aim to use it for planning efficient public lighting. The approach adopted in Ref. [25] was SLEEC-based, but no result about other performance indicators were shown, thus the work does not contribute to a critical comparison between the different performance indicators proposed at international level. In Italy, the legislative power in matter of light pollution, design and management of public lighting belongs to the Regions that can enact laws applicable in its territory [26], [27]. In Ref. [11] a new interesting methodology for the evaluation of the cost-benefit ratio, for energy saving interventions on the road lighting, was proposed by using the case study of the Comiso Municipality (Italy). In the case study, a comparison between 2 different scenarios (providing specific energy efficiency measures) was made, but also in this work the techno-economic analysis does not use the performance indicators proposed at international level. In this context, it is clear the importance to critically discuss and compare the energy performance indicators for road lighting systems, currently available at international and national (Italian) level.
In this paper the Authors propose a critical analysis of the most significant numeric indicators for the evaluation of lighting and energy performance of both new-designed and existing (whose refurbishment is to be planned) road lighting systems. The comparison of energy performance indicator takes into consideration the types of lighting systems (new-designed or existing under refurbishment) and it is aimed to:
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define strengths and weaknesses of each indicator,
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provide suggestions on the use of the appropriate indicators during the design stage of road lighting systems.
These aspects are not sufficiently clarified by the technical standards and nor by the scientific literature. To support the discussion, the use of the case study of the road lighting of the historical old town center of Pisa is proposed. In order to analyze the current state of the road lighting systems of the case study, the Authors have defined an investigation procedure that has been applied to a sample of 20 roads, representative of 80 similar roads. The use of the case study is not be intended as a limitation of the performed research, but as an application example of the investigation procedure defined by the Authors, useful in highlighting the critical issues about the evaluation of energy performance indicators, especially for existing public lighting systems. The same approach followed by the Authors, in fact, could be used in any other town. Moreover, being the state of the art of public lighting in the historical towns of central Italy (often characterized by similar lighting infrastructure, similar lamps and luminaires typologies), the use of Pisa as case study town can be considered representative for a large number of historical towns located in that geographical area.
Section snippets
Energy performance indicators for road lighting
Recently, with the aim to quantify the potential savings obtainable from the improvement of the energy performance of the road lighting systems, some numerical indicators have been introduced on European and Italian levels. The most important energy performance indicators for road lighting systems are summarized in Table 1, and briefly discussed in the Annex B.
In the European standard [23], the Power Density Indicator and the Annual Energy Consumption Indicator have been defined. The Power
Analysis of the energy performance of urban lighting systems: the case study of Pisa
The city of Pisa originated as an Etruscan river port around the middle of the sixth century, even though the presence of definite clusters of dwellings was documented around the ninth century [32], [33]. Pisa is located few kilometers from the Arno river mouth on the Tyrrhenian Sea and is considered to be one of the most important art cities in Europe [33]. The city covers an area of 185.2 km2; the oldest part of Pisa lies within its Medieval walls and is centrally located, whereas modern
Calculation and discussion of energy performance indicators
The energy performance indicators DP and DE specified in Ref. [23] and the energy performance indicators IPEA and IPEI specified in Ref. [31] have been calculated for the analyzed roads.
For calculating DP it has been necessary to identify the areas which make up the chosen typical span (sidewalk and carriageway) and to refer to the calculated average illuminance (see Table 5, Table 6). For calculating DE an operating time of 4000 h has been assumed with a single utilization profile in the
Conclusive remarks
From the detailed analysis conducted on the different performance indicators and from their application to the case study of the historical town of Pisa, the following considerations can be outlined for each studied indicator. Although deducted from the case study of Pisa, the following considerations are obtained with an investigation procedure of general validity and they can be extended to other towns, with particular reference to the historical towns of central Italy, whose road and
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