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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
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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
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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
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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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[7] Choi AS, Sung MK. Development of a daylight responsive
dimming system and preliminary evaluation of system performance. Building and Environment 2000;35(7):663–76.
[8] Choi AS, Mistrick RG. Analysis of daylight responsive dimming
system performance. Building and Environment 1999;34(3):231–43.
[9] Ghisi E. The use of fibre optics on energy efficient lighting in
buildings. PhD thesis, School of Civil Engineering, University of
Leeds, 2002.
[10] Hopkinson RG, Petherbridge P, Longmore J. Daylighting.
London: Heinemann; 1966.
[11] BRE Building Research Establishment. BRE Digest 309—
Estimating daylight in buildings: Part 1. Building Research
Establishment Digest, Watford, England, 1986.
[12] BRE Building Research Establishment. BRE Digest 310—
Estimating daylight in buildings: Part 2. Building Research
Establishment Digest, Watford, England, 1986.

1621

[13] Sharples S, Stewart L, Tregenza PR. Glazing daylight transmittances: a field survey of windows in urban areas. Building and
Environment 2001;36(4):503–9.
[14] Ghisi E, Tinker JA. An Ideal Window Area concept for energy
efficient integration of daylight and artificial light in buildings.
Building and Environment 2005;40(1):51–61.
[15] Commission of the European Communities. In: Baker NV,
Fanchiotti A, Steemers KA, editors. Daylighting in architecture:
a European reference book. Directorate-General XII for Science,
Research and Development. London: James  James (Science
Publishers) Ltd; 1993.
[16] Carmody J, Selkowitz S, Heschong L. Residential windows: a
guide to new technologies and energy performance. New York,
USA: WW Norton  Company; 1996.
[17] Lancashire DS, Fox AE. Lighting: the way to building efficiency.
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1 s2.0-s036013230500257 x-main

  • 1. 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
  • 2. 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
  • 3. 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
  • 4. 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
  • 5. 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
  • 6. 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
  • 7. 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
  • 8. 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
  • 9. 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
  • 10. 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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