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    1 s2.0-s036013230500257 x-main 1 s2.0-s036013230500257 x-main Document Transcript

    • ARTICLE IN PRESS Building and Environment 41 (2006) 1611–1621 www.elsevier.com/locate/buildenv Evaluating the potential for energy savings on lighting by integrating fibre optics in buildings Enedir Ghisia,Ã, John A. Tinkerb a Laboratory of Energy Efficiency in Buildings, Department of Civil Engineering, Federal University of Santa Catarina, ´polis-SC, Brazil 88040-900 Floriano b School of Civil Engineering, University of Leeds, Leeds LS2 9JT, UK Received 20 September 2004; received in revised form 7 June 2005; accepted 13 June 2005 Abstract The effective integration of an artificial lighting system and daylight in buildings occurs only when the artificial lighting system can be switched on or off as a function of daylight levels reaching the working surface of spaces. The paper considers fibre optics technology as a means of supplementing the daylight received at the rear of rooms and the subsequent integration of the total daylight received with a controlled artificial lighting system. Such an approach would contribute not only to energy savings but also to a reduction in environmental pollution. The evaluation took place using the climatic data from seven cities in Brazil and one in the UK. Results showed that by effectively integrating daylight from windows in buildings with the artificial lighting system, energy savings ranging from 17.7% to 92.0% could be achieved in the seven cities in Brazil and savings ranging from 10.8% to 44.0% could be achieved in the UK. By incorporating fibre optic technology into the system, the potential for energy savings on lighting was then found to range from 8.0% to 82.3% for the cities in Brazil and from 56.0% to 89.2% in the UK. For the city in the UK, it was further shown that there would be a reduction in carbon dioxide emission of 122 kg/m2 of built area per year if daylight from windows were integrated with the artificial lighting system, and that this would increase to 138 kg/m2 per year if fibre optics technology were to be installed. r 2005 Elsevier Ltd. All rights reserved. Keywords: Energy savings on lighting; Daylight integration; Fibre optics 1. Introduction In an attempt to reduce energy costs and greenhouse gas emissions and incorporate sustainability in the building process, innovations in daylighting technologies have been investigated worldwide. In Sydney, Australia, the installation of vertical and horizontal light pipes has been investigated [1]. The effectiveness of light pipes has also been studied in the UK [2], in Thailand [3], in Italy [4], to quote just a few examples. Other daylight systems, such as angle-selective glazing, light-guiding shades, vertical and horizontal light pipes, ÃCorresponding author. Tel.: +55 48 3315185; fax: +55 48 3315191. E-mail addresses: enedir@labeee.ufsc.br (E. Ghisi), j.a.tinker@leeds.ac.uk (J.A. Tinker). 0360-1323/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2005.06.013 switchable glazing and angle-selective skylights have been analysed by Edmonds and Greenup [5] in order to improve daylighting in buildings located in the tropics (latitude ranging from 10 to 23 ). Daylight-responsive lighting control systems have also been investigated in Turkey [6] and in Korea [7,8], amongst some examples. Energy savings in buildings not only lead to financial savings and a reduction in the demand for electricity, but also to environmental benefits. The generation of electricity involving fuel combustion is associated with the production and emission of carbon dioxide (CO2) and other gasses into the atmosphere, which in turn cause environmental pollution and global warming due to the greenhouse effect. Improved daylight penetration into a building to reduce the dependency on artificial lighting can be regarded as one of the easiest ways of
    • ARTICLE IN PRESS 1612 E. Ghisi, J.A. Tinker / Building and Environment 41 (2006) 1611–1621 improving energy efficiency and, as a consequence, of attaining energy savings and reducing environmental pollution. Since the early 1990s, fibre optic cables using an artificial light source have been used in remote-source lighting systems. Using this technology, light travels from its source to one or more remote points through fibre optic cables. The technology has been used in many applications such as museums and retail displays and in architectural applications to emphasise the features of a building or to outline its exterior contours; other applications have involved lighting exit signs and aisles in theatres and aeroplanes etc. to name but a few. Fibre optics is a new technology that is growing quickly. If it is possible to transport artificial light through a fibre optic cable, then it should be possible to transport daylight through a similar cable into a building. If this is economically possible, then the integration of daylight, both from the windows and the fibre optics installation, with artificial light would lead to greater reductions in the operating times of the artificial lighting system and hence save more energy and reduce environmental pollution. This paper presents a methodology to evaluate the energy savings likely to be obtained if fibre optics were used to transport daylight to the inner spaces in buildings, where it would then be integrated with the artificial lighting system. 2. Objectives The main objective of this paper is to present a methodology to evaluate the potential for energy savings in buildings when fibre optics are used to transport daylight to the rear side of rooms, where there is then integration of that daylight with artificial light. The analysis is performed considering the climatic conditions of seven cities in Brazil and one in the UK. 3. Methodology The first part of the study concentrates on assessing and quantifying the daylight provision likely to be obtained on the working surface of rooms having different dimensions and different window areas. Such an analysis, performed by calculating the Daylight Factors in the room, quantified the problem of lack of daylight supply at the rear side of spaces. The subsequent calculation of energy savings obtained through this analysis identified whether there was a potential for any energy saving to be made on lighting by applying fibre optics to transport daylight to the rear side of rooms. As such an analysis does not take into account the thermal effects related to glazed areas and orientation, simulation modelling using VisualDOE was used to identify the window area in which there is a balance between thermal load and daylight supply. Such a window area is referred to as the Ideal Window Area and is reported by Ghisi [9]. To verify the influence of the climatic and geographical location on daylight provision and thus on the Ideal Window Area, seven cities in Brazil and one in the UK were considered in the simulations. The methodology used in the first part of this work, using Daylight Factors, was then used again to predict the daylight supply and energy savings on lighting likely to be obtained when the Ideal Window Area is applied. Thus, the potential for energy savings on lighting due to the application of fibre optics was evaluated for each room size, room ratio and Ideal Window Area. Having predicted the potential for energy savings due to installing fibre optics, a physical model was built to evaluate the accuracy of the predictions. Fibre optics and an artificial lighting system were installed in the model to evaluate the potential for energy savings when there is integration of daylight coming into the model from a window and from the fibre optics, with the artificial lighting system. The final part of the work presents an economic analysis comparing the energy costs associated with providing adequate daylight in rooms using windows only, and secondly by using windows and an integrated fibre optics system. An environmental impact assessment is then presented, which quantifies the reduction in greenhouse gasses achieved due to the energy savings made by incorporating fibre optics. 3.1. Daylight provision Daylight provision was estimated based on Daylight Factors. These were calculated using the same procedure as presented in Hopkinson [10] and BRE [11,12]. The models in which the Daylight Factors were calculated comprised rooms whose ratios of width to depth were 2:1, 1.5:1, 1:1, 1:1.5, and 1:2 as shown in Fig. 1. In order to evaluate the influence of the size of the room on the supply of daylight, each room ratio was assessed over ten different sizes; each size being characterised by the room index ðKÞ ranging from 0.60 to 5.00. Each room was evaluated with four different glazed areas to one elevation, as seen in Fig. 2. The third window area (73.2%) is the one in which the window sill coincides with the height of the working surface. As the effect of urban air pollution on window daylight transmittance in buildings is not very significant as presented in Sharples et al. [13], this was not taken into account. To accurately evaluate the distribution of daylight in the rooms, the floor plan of each room was divided into hypothetical rectangles as close to squares of 50 cm Â
    • ARTICLE IN PRESS E. Ghisi, J.A. Tinker / Building and Environment 41 (2006) 1611–1621 1613 Fig. 1. Plan and isometric view of the five room ratios. 3.3. Fibre optics 25% 50% 73.2% 100% Fig. 2. Window area of the models. Table 1 Latitude and longitude of the eight cities City ´ Belem Natal Salvador Brası´ lia Rio de Janeiro Curitiba ´ Florianopolis Leeds Latitude  0 À01 27 À05 480 À12 580 À15 470 À22 540 À25 260 À27 360 53 480 Longitude À48 300 À35 130 À38 310 À47 560 À43 120 À49 160 À48 330 À 1 340 50 cm as possible. The Daylight Factor was calculated in the centre of each rectangle. 3.2. Computer simulations Computer simulations were then performed to determine the Ideal Window Area of each room, and these are presented in Ghisi and Tinker [14]. As daylight availability is affected by geographical location, the latitude and longitude of the seven cities located in Brazil and the one in the UK (Leeds) are shown in Table 1. The cities in Brazil selected for the analysis lie within the latitudes of À01 270 to À27 360 , in the southern hemisphere, and the city of Leeds is located at a latitude of 53 480 , in the northern hemisphere. Each one of the ten room sizes for each room ratio (as shown in Fig. 1) was simulated for eleven window areas (0–100% at increments of 10%) and four orientations, making a total of 2200 simulations for each city. In total, 17,600 simulations were performed to obtain the energy consumption of the models over the eight cities. The potential for energy savings on lighting was performed by the method presented by Ghisi [9] and Ghisi and Tinker [14]. This part of the research dealt with the possibility of using fibre optics as a technology to transport daylight to the rear side of rooms where the light supply from windows may be low. The assessment was performed using an experiment designed to evaluate the energy savings that could be obtained through the use of fibre optics to provide illumination coming from the ceiling as found in a regular lighting system. The energy savings obtained through this experiment were compared to the predictions obtained previously for a specific room index and a specific room ratio for a space located in the city of Leeds (UK). 3.3.1. Description of the model From the results obtained in the first part of the research, it was observed that rooms with a narrower width (smaller fac ade area) and larger size offer a higher potential for energy savings on lighting due to the use of fibre optics. Therefore, the room ratio selected for the experiment was 1:2 with a room index of 1.50. Hence, a room measuring 4:61 m  9:23 m with 2.80 m height was chosen. Due to the difficulties of building an experimental room to such dimensions, a 1/5 scale model was used measuring 92 cm  184 cm  56 cm high. The height of the working surface was taken to be 75 cm above floor level, which scaled to 15 cm in the model. In terms of window area, four different window areas were considered as used previously (Fig. 2). The floor and walls of the model were constructed using a 50 mm polystyrene sheet, and the ceiling using a thick sheet of cardboard. The Commission of the European Communities [15] acknowledges that materials which cannot be scaled easily are a limitation of scale modelling and may cause errors in the quantitative measurements. However, this is not a concern in this case as the internal surfaces of the model were white and represented the colour, if not the finish, of an actual space. Two incandescent light bulbs were installed on the ceiling of the model. To avoid errors due to the integration of artificial light in scale models, the illuminance level inside the model was controlled using a rheostat to produce an illuminance of 500 lux on the working
    • ARTICLE IN PRESS 1614 E. Ghisi, J.A. Tinker / Building and Environment 41 (2006) 1611–1621 surface. Two lux meters were installed in the model in order to measure the illuminance levels on the working surface. All the outside edges of the model were sealed to avoid unwanted light penetration. The energy consumption due to the artificial lighting was measured by installing a kWh meter between the electricity supply and the light bulbs. 3.3.2. The fibre optics system The purpose of the experiment was to evaluate the possibility of using fibre optics to transport daylight, but as this experiment was designed to confirm the energy savings on lighting that could be obtained in buildings, artificial lights were used in conjunction with fibre optics. The fibre optic system used in the experiment comprised a 150 W artificial light source and six 3-mlong fibre optic tails. The system was loaned from Schott Fibre Optics Ltd, UK, and can be seen in Fig. 3. The six fibre-optic tails were located in the ceiling of the model and symmetrically distributed around the light bulb located at the rear end, where daylight levels are known to be lower. An internal view of the model showing both light bulbs and fibre optics can be seen in Fig. 4. 3.3.3. The measurement period Measurements of lighting levels and energy consumption were performed over a 10-day period between the 2nd and the 18th of October 2000, between the hours of 10 am and 5 pm. The model was placed against a northeast-facing window on the third floor of a building located in Leeds, UK. 3.3.4. Procedure The first step was to measure the energy consumption of the two light bulbs necessary to provide an illuminance of 500 lux on the working surface with no integration of daylight or lighting from the fibre optics. Fig. 3. Fibre optic system used in the experiment. Fig. 4. The fibre optic system and the light bulbs installed in the model. This was measured using the kWh meter installed between the electricity supply and the light bulbs. Such a measurement was important as it would provide a reference value against which to compare other results. The next part of the experiment used different window areas, as shown in Fig. 2. The energy lighting consumption and the lighting levels achieved on the working surface were measured under three different situations: (1) The artificial lights were switched on to supplement the daylight coming onto the working surface of the model through the window in order to obtain 500 lux on the surface. This would determine the energy savings to be made on the artificial lighting due to the integration of daylight. Lighting from the fibre optic system was not used. (2) The artificial lights were switched on to supplement both the daylight falling onto the working surface of the model through the window and lighting from the fibre optic system. The fibre optic system had its power controlled in order to provide 50 lux on the working surface, while the artificial lights were controlled to provide a total illuminance level of 500 lux on the surface. (3) The final experiment was similar to situation (2), but the fibre optic system had its power controlled to provide an illuminance level of 300 lux on the working surface. For situations (2) and (3), the illuminance levels of 50 and 300 lux due to lighting from the fibre optics were selected at random. This was to represent a real-life scenario in which fibre optics are used to transport daylight into buildings and where illuminance levels cannot be guaranteed. An illuminance level of 500 lux was not considered for the fibre optics as this would lead
    • ARTICLE IN PRESS E. Ghisi, J.A. Tinker / Building and Environment 41 (2006) 1611–1621 to no artificial lighting being needed, and therefore to a 100% energy savings on lighting. Lighting levels on the working surface in the model under outside sky conditions were measured every 15 min and the rheostats were adjusted at the same time interval in order to maintain 500 lux on the working surface for the three situations described above. 3.4. Economic analysis Life cycle costs were evaluated for each of the ten room sizes and five room ratios, with each room having an Ideal Window Area for each of the eight cities. In order to verify whether fibre optics will be a costeffective technology to install in a building, two assessments were performed. The first is related to the integration of artificial lighting with daylight falling onto the working surface of a room through windows only. The second deals with the integration of artificial lighting not only with daylight supplied by windows, but also with light being transported onto a working surface by fibre optics. The economic analysis of the rooms was performed by calculating the corrected payback and also the internal rate of return as a function of the ratio of investment to benefits. The ratio investment/benefit, which gives the payback, was calculated for all room sizes and room ratios of all eight cities. The corrected payback and the internal rate of return were determined for all room sizes and room ratios only for the city having the highest payback period. For the other cities, the corrected payback and internal rate of return were calculated only for room indices of 0.60 and 5.00 to avoid repetition. 3.5. Environmental benefits Most people are unaware that the operation of buildings and particularly the electric lighting are associated with environmental costs. The energy used to operate the artificial lighting system in buildings in many countries comes from burning fossil fuels (coal, gas and oil), and this process contributes to environmental pollution through the production and emission of CO2 and other gasses into the atmosphere. This in turn contributes to global warming [16]. Hydropower is considered as a clean renewable energy source, because there is no CO2 or other greenhouse gas emissions associated with the generation as there is no fuel combustion involved. However, there are indications that the reservoirs associated with hydroelectric dams also emit CO2 and methane emanating from the decomposition of biomass. Consequently, irrespective of the energy source, energy savings in buildings will result in a decrease of environmental 1615 pollution independent of whether the electricity comes from hydropower or thermopower. As there are no published data to quantify such emissions, the environmental benefits of saving electricity in the cities located in Brazil could not be calculated. As for the environmental benefits of saving energy in Leeds, they were calculated using the indices determined by Lancashire and Fox [17], who reported that each kWh saved prevents the emission of 1.5 pounds (680.39 g) of CO2, 0.20 ounces (5.67 g) of sulphur dioxide, and 0.08 ounces (2.27 g) of nitrogen oxides. Therefore, it can be noticed that the more energyefficient a building is, the less the environmental pollution produced. Thus, considering the mentioned published data and the energy savings determined in this work, the amount of CO2, sulphur dioxide, and nitrogen oxides that can be prevented from emission in Leeds was calculated. 4. Results 4.1. Daylight provision Having calculated the Daylight Factors for all the room sizes, room ratios and window areas, it was then possible to calculate the energy savings on lighting likely to be obtained due to the integration of artificial lighting with daylight coming from the window. The figures presented here are probably underestimated as they are based on Daylight Factors calculated for the Commis´ sion Internationale de l’Eclairage (CIE) overcast sky condition. Fig. 5 illustrates the energy savings on lighting that can be expected in rooms of room ratios of 1:1 for the ten room indices and the four window areas, respectively. It can be seen that for lower Daylight Factors, or higher external illuminance, the energy savings on lighting are greater. The energy savings are also greater for lower room indices, which means smaller rooms. It can also be seen that by comparing the four charts, for window areas apparently larger than 50% of the wall area, the energy savings do not increase significantly, indicating that there might be a misconception in terms of window areas adopted in actual buildings. A similar behaviour was identified for the other room ratios. 4.2. Computer simulations The previous section assessed the provision of daylight in rooms of different dimensions, room ratios and window areas to quantify the potential for energy savings on artificial lighting. Such an analysis was carried out through the calculation of Daylight Factors, and results showed that integration of daylight from windows is likely to provide significant energy savings
    • ARTICLE IN PRESS E. Ghisi, J.A. Tinker / Building and Environment 41 (2006) 1611–1621 100.0 Energy savings on lighting (%) Energy savings on lighting (%) 1616 80.0 60.0 40.0 20.0 0.0 0.00 5.00 (a) K=0.80 K=1.50 K=3.00 K=5.00 15.00 20.00 60.0 40.0 20.0 0.0 0.00 K=1.00 K=2.00 K=4.00 5.00 K=0.60 K=1.25 K=2.50 10.00 DF (%) K=0.80 K=1.50 K=3.00 K=5.00 15.00 20.00 K=1.00 K=2.00 K=4.00 100.0 100.0 80.0 60.0 40.0 20.0 0.0 0.00 80.0 (b) Energy savings on lighting (%) Energy savings on lighting (%) K=0.60 K=1.25 K=2.50 10.00 DF (%) 100.0 5.00 (c) K=0.60 K=1.25 K=2.50 10.00 DF (%) K=0.80 K=1.50 K=3.00 K=5.00 15.00 80.0 60.0 40.0 20.0 0.0 0.00 20.00 5.00 (d) K=1.00 K=2.00 K=4.00 K=0.60 K=1.25 K=2.50 10.00 DF (%) K=0.80 K=1.50 K=3.00 K=5.00 15.00 20.00 K=1.00 K=2.00 K=4.00 Fig. 5. Energy savings on lighting in rooms having a room ratio of 1:1. (a) window area of 25%; (b) window area of 50%; (c) window area of 73.2%; (d) window area of 100%. on lighting in buildings. It was further observed that, depending on the room size, room ratio and window area, there is still a potential for greater energy savings to be made on lighting through the use of fibre optics if this technology could be proved to be effective to transport daylight into spaces. This potential grows as the window area of the room decreases. Therefore, the window area for rooms in which there is a balance between daylight supply and thermal load gains or losses was determined by using computer simulations. Fig. 6 shows a set of typical results obtained for the city ´ of Florianopolis, Brazil. As the Ideal Window Areas for rooms having a room ratio of 2:1 are relatively small, this may be an indication that there might be a potential to make more energy savings on artificial lighting if fibre optics were to be used for promoting the integration of daylight. Having obtained the Ideal Window Areas for the different room ratios and room sizes in each of the eight cities, it is important to identify the impact that such a window area will have on the supply of daylight. To assess the impact, the energy savings on lighting that could be achieved due to the availability of daylight on the working surface of each room were determined. Such an analysis would also identify the potential for energy savings on lighting likely to occur if fibre optics were used to transport daylight to the rear side of the rooms. Results indicated that there is a tendency for energy savings on lighting to be greater for smaller room indices ðKÞ and for room ratios whose room width is larger (room ratios of 2:1, 1.5:1 and 1:1). Therefore, the potential for energy savings on lighting due to the application of fibre optics is higher for rooms having a larger room index and a narrower width. Table 2 presents a summary of the potential for energy savings on lighting likely to be achieved in the eight cities when there is integration of artificial lighting with daylight entering the room through the Ideal Window Area, and also the potential for energy savings
    • ARTICLE IN PRESS 450 400 350 300 250 200 150 100 50 0 Energy consumption (kWh/m2.year) Energy consumption (kWh/m2.year) E. Ghisi, J.A. Tinker / Building and Environment 41 (2006) 1611–1621 0 10 20 30 40 50 60 70 Window area (%) 90 0 10 20 30 0 10 20 K=1.00 K=2.00 K=4.00 40 50 60 Window area (%) K=0.60 K=1.25 K=2.50 200 150 100 50 0 K=0.80 K=1.50 K=3.00 K=5.00 30 (b) 70 80 40 50 60 70 Window area (%) K=0.60 K=1.25 K=2.50 450 400 350 300 250 200 150 100 50 0 (c) 450 400 350 300 250 100 Energy consumption (kWh/m2.year) Energy consumption (kWh/m2.year) K=0.60 K=1.25 K=2.50 80 K=0.80 K=1.50 K=3.00 K=5.00 (a) 90 K=0.80 K=1.50 K=3.00 K=5.00 80 90 100 K=1.00 K=2.00 K=4.00 450 400 350 300 250 200 150 100 50 0 0 100 1617 10 20 (d) K=1.00 K=2.00 K=4.00 30 40 50 60 Window area (%) K=0.60 K=1.25 K=2.50 K=0.80 K=1.50 K=3.00 K=5.00 70 80 90 100 K=1.00 K=2.00 K=4.00 ´ Fig. 6. Energy consumption for a room in Florianopolis having a room ratio of 2:1. (a) north orientation; (b) east orientation; (c) south orientation; (d) west orientation. Table 2 Summary of potential for energy savings on lighting when using the IWA and potential for energy savings on lighting due to fibre optics City Potential for energy savings on lighting using the IWA (%) Potential for energy savings on lighting using fibre optics (%) ´ Belem Natal Salvador Brası´ lia Rio de Janeiro Curitiba ´ Florianopolis Leeds 24.8–70.6 17.7–62.1 20.3–80.5 22.4–92.0 17.7–82.2 20.6–87.7 20.6–86.2 10.8–44.0 29.4–75.2 37.9–82.3 19.5–79.7 8.0–77.6 17.8–82.3 12.3–79.4 13.8–79.4 56.0–89.2 on lighting if fibre optics are used to transport more daylight to the rear side of the rooms. The range observed covers the ten room indices considered in the analysis. 4.3. Fibre optics The previous sections have assessed the amount of daylight reaching the working surface of spaces through windows. Such an evaluation has shown that the integration of daylight and artificial lighting can provide significant energy savings. However, it should also be noted that there is still a high potential for energy savings on lighting that could be made if the supply of daylight to the rear side of rooms were higher. A comparison of the energy savings obtained from the model, which take into account the amount of light provided by fibre optics to the energy savings obtained by integrating the daylight coming from windows only, are presented in Fig. 7. It can be noted that the integration of daylight coming in from windows provides significant energy savings (71.8% on average), while the addition of fibre optics to bring in more light to the rear side of the model provides only a small increase on the energy savings (from 71.8% to 84.4% on
    • ARTICLE IN PRESS E. Ghisi, J.A. Tinker / Building and Environment 41 (2006) 1611–1621 1618 Table 3 ´ Simple payback (years) for Florianopolis, Brazil Energy savings (%) 100.0 80.0 K 60.0 Windows only Windows þ fibre optics 2:1 40.0 Window 20.0 Window + Fibre optics 0.0 25 50 75 Window area (%) 100 Fig. 7. Energy savings obtained by using fibre optics. average). This may be an indication that the application of fibre optics might not prove to be cost effective. By comparing the results obtained from this experiment with those presented in Ghisi and Tinker [14] for a space with a room index of 1.5 and room ratio of 1:2, located in Leeds, UK, it can be deemed to be a good approximation. The IWA for such a space ranges from 27% to 36% (for east and north orientations, respectively) and the potential for energy savings on lighting ranges from 24.3% to 33.0%; the results obtained from the experiment indicate energy savings ranging from 43.3% to 54.6% (for window area ranging from 27% to 36% as shown in Fig. 7). Taking fibre optics into account, the potential for energy savings would increase to between 67.0–75.7% [14], while results from the experiment indicated savings between 59.0% (for IWA of 27%) and 70.6% (for IWA of 36%). 4.4. Economic analysis The simple payback (ratio of investment to benefits) was calculated for each room size and each room ratio for all of the eight cities. The simple payback periods for ´ a typical city such as Florianopolis are shown in Table 3. The table presents two situations: simple payback periods for daylight supplied by windows only, and by windows and fibre optics. The values presented for each room ratio represent the average values for the four orientations. ´ From the results presented for Florianopolis, it is possible to note that investment in buildings to ensure the integration of artificial lighting with daylight coming onto the working surface from windows is more attractive than those with fibre optics and windows. It was observed for all eight cities that the ratio of investment to benefits is lower for smaller rooms (lower room index), and for rooms with a larger width and narrower depth. Such an analysis also shows that the integration of daylight from windows is more attractive as the ratio of investment to benefits is lower than those in which fibre optics are considered. 0.60 0.80 1.00 1.25 1.50 2.00 2.50 3.00 4.00 5.00 1.5:1 1:1 1:1.5 1:2 2:1 1.5:1 1:1 1:1.5 1:2 0.0 0.0 0.0 0.0 0.0 0.2 0.6 0.9 1.2 1.4 0.0 0.0 0.0 0.0 0.0 0.5 0.8 1.1 1.4 1.5 0.0 0.0 0.0 0.0 0.4 0.9 1.2 1.3 1.5 1.6 0.0 0.0 0.2 0.7 1.0 1.3 1.5 1.6 1.7 1.8 0.0 0.5 1.0 1.3 1.5 1.7 1.8 1.8 1.9 1.9 1.8 3.7 4.6 5.0 5.3 5.6 5.7 5.7 5.8 5.8 3.0 4.5 5.0 5.3 5.5 5.8 5.8 5.9 5.9 5.9 4.9 5.5 5.8 5.9 5.9 6.0 6.0 6.0 6.0 6.0 7.1 6.7 6.5 6.5 6.4 6.3 6.2 6.2 6.1 6.0 8.2 7.4 7.1 6.8 6.7 6.5 6.4 6.3 6.2 6.1 For the other cities located in Brazil, it was observed that the maximum simple payback when there is integration of daylight from windows ranges from 1.0 to 1.9 years; and when there is integration of fibre optics the maximum payback ranges from 4.4 to 8.2 years. As for Leeds, the maximum payback is 2.3 years when there is integration of daylight from windows only, and 8.5 years when fibre optics are used. Corrected payback and the internal rate of return (IRR) for the eight cities were calculated considering a life span of 30 years. The calculation of the corrected payback was based on an interest rate of 10% a year. Rooms that presented a nil ratio of investment to benefit have a nil corrected payback and an infinite IRR. For all eight cities, rooms integrating daylight from windows only presented more attractive corrected paybacks and IRRs than rooms with daylight from windows and fibre optics. Rooms with smaller room index and larger fac ade (from room ratio 2:1 to 1:2) are more attractive in terms of monetary investment as the corrected payback is lower and the IRR is higher for such rooms. Tables 4 and 5, respectively, present a summary of maximum corrected payback periods and minimum IRRs observed for the eight cities. It was observed that when only windows are considered for the supply of ´ daylight in Florianopolis, the maximum corrected payback likely to occur is 2.22 years (Table 4) and the minimum IRR is 52.63% per year (Table 5), which represents a very attractive investment. When fibre optics are used to supply daylight to the rear side of rooms, the investment is not so attractive as for the previous situation, but the maximum corrected payback of 17.99 years (Table 4) is still acceptable and the minimum IRR of 11.76% per year (Table 5) is still higher than the interest rate of 10% used in the calculations. Similar results can be identified for all the other cities in Brazil. As for Leeds, it was noted that the investment is not as attractive as for the cities located in Brazil. Even so, when only windows are
    • ARTICLE IN PRESS E. Ghisi, J.A. Tinker / Building and Environment 41 (2006) 1611–1621 1619 Table 4 Summary of maximum corrected payback period for each city and room ratio (years) City Windows only Windows þ fibre optics 2:1 ´ Belem Natal Salvador Brası´ lia Rio de Janeiro Curitiba ´ Florianopolis Leeds 1.5:1 1:1 1:1.5 1:2 2:1 1.5:1 1:1 1:1.5 1:2 1.35 1.35 0.88 0.99 1.11 0.77 1.59 1.96 1.47 1.35 0.88 1.11 1.23 0.88 1.72 2.09 1.59 1.59 0.99 1.23 1.47 1.11 1.84 2.35 1.84 1.72 1.11 1.35 1.72 1.35 2.09 2.62 1.96 1.72 1.11 1.47 1.84 1.47 2.22 2.75 7.28 7.07 4.37 5.37 6.67 5.90 9.11 16.39 7.50 7.07 4.37 5.37 6.87 5.90 9.37 16.89 7.50 7.28 4.53 5.55 6.87 6.09 9.63 18.60 7.71 7.50 4.85 5.55 7.28 6.28 12.99 19.24 9.63 8.15 6.09 6.09 14.56 6.28 17.99 19.91 Table 5 Summary of minimum IRR for each city and room ratio (% per year) City Windows only Windows þ fibre optics 2:1 ´ Belem Natal Salvador Brası´ lia Rio de Janeiro Curitiba ´ Florianopolis Leeds 1.5:1 1:1 1:1.5 1:2 2:1 1.5:1 1:1 1:1.5 1:2 83.33 83.33 125.00 111.06 99.98 142.84 71.40 58.82 76.87 83.33 125.00 99.98 90.90 125.00 66.65 55.55 71.40 71.40 111.06 90.90 76.87 99.98 62.49 49.98 62.49 66.65 99.98 83.33 66.65 83.33 55.55 45.45 58.82 66.65 99.98 76.87 62.49 76.87 52.63 43.47 19.91 20.33 29.40 24.96 21.21 23.21 17.09 12.26 19.51 20.33 29.40 24.96 20.76 23.21 16.79 12.09 19.51 19.91 28.56 24.35 20.76 22.68 16.50 11.60 19.13 19.51 27.01 24.35 19.91 22.17 13.79 11.44 16.50 18.40 22.68 22.68 12.99 22.17 11.76 11.29 considered for the supply of daylight, corrected paybacks for all the rooms analysed are lower than 2.75 years (Table 4) and IRRs are higher than 43.47% per year (Table 5). When fibre optics are taken into account to supply daylight to the rear side of rooms, corrected paybacks are lower than 19.91 years (Table 4) and the IRRs are higher than 11.29% per year (Table 5). also reduce the average emission of sulphur dioxide into the atmosphere by 1.02 kg/m2 per year, and this would increase to 1.15 kg/m2 per year if fibre optics were to be used. As for the reduction of nitrogen oxides, the values would be 0.41 and 0.46 kg/m2, respectively. 4.5. Environmental benefits The use of Daylight Factors to evaluate the energy savings likely to be achieved on lighting when there is integration of daylight and artificial light proved effective despite the fact that the calculations were based on the CIE overcast sky condition, which is acknowledged to underestimate internal illuminance levels. It was shown that such an integration would lead to significant energy savings on lighting not only due to high daylight levels near the window, but also due to the daylight that reaches the working surface at the rear side of rooms, a factor usually overlooked. From the computer simulations and Daylight Factor assessment, it was observed that there is a great potential for energy savings on lighting when using the Ideal Window Area concept. Such a potential is lower for larger rooms and rooms with a narrower width. Therefore, there was still a potential for energy savings Using the indices presented by Lancashire and Fox [17], the amount of CO2, sulphur dioxide, and nitrogen oxides that can be saved from emissions in Leeds, UK was calculated. Table 6 presents the results. The minimum, average and maximum values were obtained for each orientation and room ratio. Values are presented in kg per unit of floor area per year. Therefore, there would be an average reduction of about 122 kg of CO2 emission for each square metre of office floor area in Leeds per year if there were integration of daylight from windows with the artificial lighting. If the integration were complemented by fibre optics, the reduction of CO2 emission would, on average, increase to about 138 kg/m2 per year. The integration of daylight in office buildings in Leeds would 5. Conclusions
    • ARTICLE IN PRESS E. Ghisi, J.A. Tinker / Building and Environment 41 (2006) 1611–1621 1620 Table 6 Environmental benefits for Leeds, England K Windows only Min Average Windows þ Fibre optics Max Carbon dioxide (kg/m2 per year) 0.60 62 74 82 0.80 89 100 105 1.00 103 113 118 1.25 114 122 126 1.50 120 127 131 2.00 125 133 136 2.50 128 135 139 3.00 130 137 140 4.00 133 138 141 5.00 134 139 142 Average Min Average Max 97 117 126 134 138 142 145 146 148 149 104 122 132 138 142 146 148 149 151 151 111 128 136 141 145 148 150 151 152 153 122 138 2 Sulphur dioxide (kg/m per year) 0.60 0.52 0.62 0.68 0.80 0.74 0.83 0.88 1.00 0.86 0.94 0.98 1.25 0.95 1.02 1.05 1.50 1.00 1.06 1.09 2.00 1.04 1.11 1.13 2.50 1.07 1.13 1.16 3.00 1.08 1.14 1.17 4.00 1.11 1.15 1.18 5.00 1.12 1.16 1.18 Average 0.80 0.97 1.05 1.12 1.15 1.19 1.21 1.22 1.23 1.24 1.02 0.86 1.02 1.10 1.15 1.18 1.22 1.23 1.24 1.25 1.26 0.93 1.07 1.14 1.18 1.20 1.23 1.25 1.26 1.27 1.27 1.15 2 Nitrogen oxides (kg/m per year) 0.60 0.21 0.25 0.27 0.80 0.30 0.33 0.35 1.00 0.35 0.38 0.39 1.25 0.38 0.41 0.42 1.50 0.40 0.42 0.44 2.00 0.42 0.44 0.45 2.50 0.43 0.45 0.46 3.00 0.43 0.46 0.47 4.00 0.44 0.46 0.47 5.00 0.45 0.46 0.47 Average 0.41 0.32 0.39 0.42 0.45 0.46 0.48 0.48 0.49 0.49 0.50 0.35 0.41 0.44 0.46 0.47 0.49 0.49 0.50 0.50 0.50 0.37 0.43 0.46 0.47 0.48 0.49 0.50 0.50 0.51 0.51 0.46 on lighting if fibre optics were to be used to transport daylight to the rear side of such rooms. The research has shown that fibre optics can increase energy savings on lighting and therefore improve energy efficiency in buildings. However, the energy savings on lighting calculated by the integration of daylight with artificial lighting when the former comes onto the working surfaces through windows are significantly higher than the savings when fibre optics are used to transport daylight to the rear side of rooms. The economic analysis carried out in this work evaluated two scenarios. The first scenario considered the integration of artificial lighting with daylight coming in through windows only, when the window areas are properly assessed. The second scenario took into account not only the daylight coming in through windows, but also through fibre optics. Some assumptions had to be made and it was considered that the first scenario would lead to an increase of 5% in the total cost of a building, while for the second scenario an increase of 20% was considered. The latter cost was so high because the fibre optic system used to transport daylight around the building would require an adequate light collector system. Results showed that the use of fibre optics can increase the energy savings, but they represent an investment not as attractive as the integration of artificial lighting with daylight coming in through windows only. It was also shown that if buildings in the city of Leeds, UK, were to have integration of daylight with artificial lighting, there would be an average reduction in CO2 emission of 122 kg for each square metre of built area per year if daylight were supplied by windows only. If the integration took into account contributions from fibre optics, such a reduction would be about 138 kg/m2 per year. As for Brazil, where most of the electricity is produced by hydropower, successful integration of daylight with artificial lighting would avoid the construction of more dams which contribute to the emission of CO2 and methane due to decomposition of biomass. Energy savings and environmental benefits as presented in this paper are related to lighting only. Therefore, such savings and benefits will be even higher when considering the reduction in air-conditioning energy consumption as thermal load will be reduced due to daylight integration. Acknowledgements The authors would like to thank CAPES—Fundac a - ˜o ´ Coordenac a de Aperfeic oamento de Pessoal de Nıvel - ˜o Superior, an agency of the Brazilian Government for post-graduate education, for the financial support to undertake the project from which this paper is derived. References [1] West S. Improving the sustainable development of building stock by the implementation of energy efficient, climate control technologies. Building and Environment 2001;36(3):281–9. [2] Jenkins D, Muneer T. Modelling light-pipe performances—a natural daylighting solution. Building and Environment 2003; 38(7):965–72. [3] Chirarattananon S, Chedsiri S, Renshen L. Daylighting through light pipes in the tropics. Solar Energy 2000;69(4):331–41. [4] Canziani R, Peron F, Rossi G. Daylight and energy performances of a new type of light pipe. Energy and Buildings 2004;36(11): 1163–76. [5] Edmonds IR, Greenup PJ. Daylighting in the tropics. Solar Energy 2002;73(2):111–21. [6] Onaygil S, Guler O. Determination of the energy saving by ¨ daylight responsive lighting control systems with an example from Istanbul. Building and Environment 2003;38(7):973–7.
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