16 CIRIAF National Congress

Assisi, Italy. April 7-9, 2016

16th CIRIAF National Congress Sustainable Development, Human Health and Environmental Protection

Natural and artificial lighting in glazed buildings: energy balance Cinzia Buratti 1, Domenico Palladino 1,* and Cristina Franceschini 1 1 CIRIAF - Interuniversity Centre of Research on Pollution by Physical Agents, University of Perugia, Via G. Duranti 67, Perugia 06125, Italy * Author to whom correspondence should be addressed. E-Mail: [email protected] Abstract: Due to energy consumption increasing and building internal comfort requirements, the application of design strategies is mandatory in order to improve lighting efficiency and to use daylighting techniques. For new and existing buildings, the challenge becomes the achievement of both maximum lighting efficacy and maximum energyefficiency, according to law’s specifications. In recent years, daylighting algorithms incorporated in building energy simulation programs have become increasingly sophisticated in their abilities to predict the illuminance, light power reductions, and associated thermal load interactions. The aim of this paper is to analyse simulated light levels of a non-residential building. An existing multifunctional building was investigated and in particular the offices placed at the second floor (with a large glazing system in the south façade); a model was implemented in DIALux. It was calibrated thanks to in-situ measurements: the daylight illuminance was monitored by illuminance meters in a typical office. After the model validation, illuminance was simulated with different glazings: standard double-glazing system, systems with granular silica aerogel in interspace, doubleglazing with sunlight control films and the influence of blind systems on the glazing facade was also evaluated. Furthermore different lighting plants were implemented, in order to compare a traditional solution and a LED lighting system, in terms of illuminance distribution and operating cost. Results showed that the best solution in terms of natural lighting is the standard glazing with blind systems: the shading device allows the entry of the natural light for many hours during the day, avoiding also glare problems. Considering the solar control films and the aerogel system, the turn-on periods of the lighting system during a day is too long. Concerning the lighting systems, LED lamps have a lower rated power and therefore a saving in terms of energy absorption. Despite the higher luminous flux turns out to be that of compact fluorescent lamps, LED lamps have more luminous efficiency and a longer service life. Keywords: Daylighting simulation; Glazing; Illuminance distribution; Operating Costs; DIALux. Cod_006_pp_1

16th CIRIAF National Congress

1. Introduction Building envelope has an important role in buildings for climate moderation between external and internal environments. As filter of air exchanges, sunlight and sound transmission for the occupants, it has a major impact not only on the energy consumption control but also on the quality of comfort. Glazing components are leading in carrying positive images such as transparency, natural brightness, modernity, freshness, and indoor/outdoor interactions. The de-materialization of solid envelope of the buildings by the use of glass has rattled the imagination of designers ever since: shape and function of the envelope have registered a substantial evolution from massive casing of historic buildings to the light ones of contemporary architectures. Highly glazed buildings have become a worldwide trend for whatever climate and fenestration technology is continuously evolving. Though innovations helped over the years to improve glazed components thermal performance, they do not yet allow to achieve results comparable to the one of building opaque areas. This led to much pressure on the global environmental issues like energy wastage and global warming deterioration, hence requirements in glass industry are growing bigger and more complex. To cope with sustainability and conservation needs, window glazing has been affected by a wide range of design options and experimentation of materials [1-2]. The presence of natural light in buildings guarantees appropriate lighting levels for human activities and reduces building electric energy consumption [3-6]. However, the potential for energy economy through daylighting does not only depend on its availability and rational use (Lamberts et al., 1997). The control of the artificial lighting system and the influence of gains from building openings and lighting equipment also affect the total building energy consumption [7]. For buildings and especially for commercial buildings, the artificial lighting could lead to excessive energy usage as it affects cooling and heating loads requirements of the buildings [8]. Daylighting algorithms incorporated in building energy simulation programs have become increasingly sophisticated in their abilities to predict the illuminance, light power reductions, and associated thermal load interactions [9]. The aim of this paper is to analyse simulated light levels of a non-residential building. An existing multifunctional building was investigated and in particular the offices placed at the second floor (with a large glazing system in the south façade); a model was implemented in DIALux, calibrated thanks to in-situ measurements and some scenarios with different glazing system were analyzed.

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2. The Case Study The case study analyzed is a multifunctional building built in 2008 in Perugia. The building is parallel aligned to a road of intense traffic and consist of a basement, two floors, and a roof garden. It has a modular structure, so that each floor is divided in ten zones. South elevation is characterized by a glass façade at ground floor that receives less solar radiation than offices at the first floor thanks to a cantilever structure. The south-oriented façade of the offices at the first floor is designed to receive maximum heat during the winter season. In order to avoid discomfort for the occupants, this large glazed area (21.50 m2) is equipped with venetian blinds, slat-type devices with a slat-angle control mechanism. The courtyards on the back side of the offices, near the entrances, allow the solar radiation to reach the north-facing rooms that are adequately ventilated (Fig.1). Each ground floor zone has a total area of 132 m2; the first floor zones have a ‘L’ shape and a total area of about 100 m2 each; the room height is 3 m. The thermal transmittance of the building opaque envelope is about 0.25 W/(m2K). The front side walls have a copper facing; the back side walls have a black plasterwork. Moreover, 0.04 m thickness of thermal and noise insulating material are provided in perimeter walls. The first and the ground floor are clay/cement mix with insulation board. The partition between zones is a gypsum plasterboard wall with a 0.20 m thickness layer of concrete block; its thermal transmittance is 0.70 W/(m2K). Figure 1. The Case Study: building and south oriented façade.

3. Methodology In order to analyse the simulated light levels of the non-residential building described in paragraph 2, a model of one office placed at the second floor of the building was created in DIALux. The simulation program was developed in three steps: STEP 0 – Calibration of DIALux model thanks to in situ measurements; STEP 1 – Illuminance analysis for different glazing systems implemented in DIALux; Cod_006_pp_3


STEP 2 – Illuminance distribution and operating cost analysis of different lighting plants. 3.1. DIALux Program DIALux is a German software that checks all the lighting parameters for indoor/outdoor spaces, roads, tunnels, providing results according to the latest regulations. Users can import drawings, apply "textures" and work with an extensive library of objects. Lamps and interior furniture can be easily placed. DIALux also meets the requirements of international laws on the design of lighting systems and allows to use simultaneously different workspaces, providing clear and accurate results [10]. In the program is easy to design an environment and to implement the necessary lighting features (walls, ceilings, floors, frames, etc.). Moreover by implementing lighting scenes, it is possible to display illuminance levels of one or more calculation surfaces, in daylighting conditions for different hours of the day. DIALux offers also the possibility of defining groups of lamps, various adjustment options for lights and switches, to calculate and display artificial light scenarios, and to analyze results of design implementation. The software has a wide library of lighting fixtures and lamps of many leading brand in lighting design. They can be imported into the program with their own characteristics of efficiency, power, color rendering, photometric solid. 3.2. Step 0 The analysis of the energy performance of the building was divided into the following phases: • collecting data about the building characteristics to be used as inputs; • realization of the model via software DIALux and calibration. The goal was to obtain a building description closer to reality and simultaneously simple enough to carry out all the steps of the analysis. The space under investigation is considered to have same shape, height and surface of the existing one. Glazed elements are also present: facing the courtyard there are three windows and one entrance door, while in the south there is a large glazed surface area of 21.5 m2 shaded by a sunscreen system programmable via mechanical adjustment. The DIALux input data related to the materials are reported in Table 1. Daylight illuminance was monitored for a week in April 2012 by illuminance meters in a typical office of the building. Five measurement points are considered for calibration. They are assumed to be located at 0.20 m from ground, at the same height of the ones during the experimental campaign (Fig. 2). The monitored data during April 17th are reported in Figure 3 [11]. A comparison is made between DIALux simulated illuminance values in the days 17th- 18th April (first and second day of the measurement campaign) at 10 a.m. and the measured ones. With a calibrated model, annual simulations of light scenes are carried out by considering a representative day for each month. The software returns the minimum, maximum and the average illuminance during the working period (9 a.m. – 5 p.m.) and the illuminance maps of the whole office on a surface at 0.80 m height from the ground (work plane in an office).

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Figure 2. Illuminance measurement points during the in situ campaign.

Figure 3. In situ campaign results (17th April): illuminance (lux) in the measuring points and solar radiation (W/m2). Lux 1200 1100 1000 900

W/m2

Illuminance E (lux)

1200 Position 1 Position 2

800

Position 3

700

Position 4

600

Position 5

1000

800

600

500 400

Solar Radiation

400

300 200

200

100 0

04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17 04/17

00:00:00 00:50:00 01:40:00 02:30:00 03:20:00 04:10:00 05:00:00 05:50:00 06:40:00 07:30:00 08:20:00 09:10:00 10:00:00 10:50:00 11:40:00 12:30:00 13:20:00 14:10:00 15:00:00 15:50:00 16:40:00 17:30:00 18:20:00 19:10:00 20:00:00 20:50:00 21:40:00 22:30:00 23:20:00

0

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Table 1. DIALux input data. Gypsum plaster

Windows (Courtyard and South Area) 55.1mm | 15 mm air | 33.1mm; 100mm frame

Galvanized metal; blades 200mm height; 45° inclination

-

86% (typical glass)

-

78%

14%

70%

Walls Main Characteristics Visible light Transmission Visible Reflection

Sunscreen

3.3. Step 1 In this context, a focus on the influence of different glazing types on the natural light component in the office was considered useful. Three types of glazing were selected for the south oriented window: standard double-glazing system, systems with granular silica aerogel in interspace, doubleglazing with sunlight control films. Optical and thermal properties of the glazing systems are shown in table 2. In some simulations also the presence of blind systems on the glazing facade was taken into account. Simulations were performed for a typical day of each month, during the working period (9 a.m.-5 p.m.). The illuminance on the whole room surface at 0.80 m from the ground is given as output. Table 2. Glazing types and properties. Glazing Standard glazing Solar Control Granular Aerogel

Layers and thickness

Total thickness [m]

τv visible transmittance [-]

g solar factor [-]

U transmittance value [W/m2K]

55.1mm | 15mm air | 33.1mm

0.32

0.78

0.65

2.70

0.32

0.18

0.20

1.40

0.22

0.27

0.34

1.04

6mm sunlight control | 15mm air | 11mm low-e 4mm | 100% G-Aerogel 14mm | 4mm

3.4. Step 2 In the third step the availability of a calibrated model allowed the insertion of lighting plants inside the space, in order to analyze the new illuminance distribution and operating cost. Inside the office, it is assumed an internal distribution as follows: two work stations near southoriented glass surface and a work station in the reception area near the entrance (Fig. 4). As per the zones considered, visual tasks are identified: desks used as writing, data processing (Em = 500 lux); terminal of the reception (Em = 300 lux). Illuminance average project values are identified according to the UNI EN 12464/2004 [12]. Work surfaces are placed at 0.80 m from the ground and they have a total area of 2 m2 each. The plant is designed with the method of the total flow. A traditional solution and a LED lighting system are implemented and simulated in DIALux. Known the number and type of lamps (see Table 3), they must be rationally arranged within the room to ensure uniformity of illuminance and to avoid glare.

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Figure 4. Internal distribution of the office: zone 1 – reception, zone 2 – office.

Table 3. Type and number of lighting device Luminous flux [lumen] Lamp power [W] Lamp efficiency [lumen/W] Number of devices

Reception Office

Fluorescent Lamps 8900 120 74 3 6

LED System 7000 51 137 4 8

4. Results 4.1. Step 0 For calibration, 5 reference points at 0.20 m from floor level were considered and blinds slat angle is assumed to be 45°; these assumptions are in agreement with the measurement campaign of April 2012. Illuminance values are rated in the days 17th- 18th April (first and second day of the measurement campaign) at 10 a.m. (Fig.4 and 5). In Table 4 and 5 simulated illuminance values are compared to the measured ones and the percentage difference is shown for the two days. A small error was found (about 2-7% and 4-8% respectively for 17th and 18th April), except for point 5, due to his closer position to the south facade window. A detailed analysis of illuminance at reference point 1 during office occupancy hours (9 a.m.-5 p.m.) on 17th April highlights that the percentage differences are acceptable and still contained in the range 3-20%. Only at 5 p.m., the Cod_006_pp_7


measured values are higher than calculation results, mainly due to a greater contribution of light from the windows of the courtyard that in DIALux environment is not so high as in real situation. Generally illuminance simulated data is slightly higher than the measured ones during central hours while the opposite occurs when sun position is lower (9-10 a.m. and 4-5 p.m., see Tables 4 and 5). Figure 5. Measured and simulated illuminance values and percentage difference: 17 April.

17th April - 10 a.m. E Measured

E DIALux

ΔE %

800 700 600 500 400 300 200 100 0 -100

1

2

3

4

5

E Measured

571

653

353

351

655

E DIALux

583

606

373

326

739

ΔE %

2.1

-7.2

5.7

-7.1

12.8

Figure 6. Measured and simulated illuminance values and percentage difference: 18 April.

18th April - 10 a.m. E Measured 800 700 600 500 400 300 200 100 0 -100

E DIALux

ΔE %

1

2

3

4

5

E Measured

561

667

373

354

624

E DIALux

587

607

371

325

739

ΔE %

4.6

-9.0

-0.5

-8.2

18.4

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Table 4. Measured and simulated illuminance values at reference point 1: 18 April - working period. hour 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00

E simulated lux 521 583 608 593 540 452 335 198 50

E measured lux 569 597.8 585.2 542 464.3 384.8 322.7 207.5 99.8

Error % -8.4 -2.5 3.9 9.4 16.3 17.5 3.8 -5.0 -49.9

A calculation surface equal to the office area was considered at 0.80 m height from the ground. Minimum, maximum and average illuminance are returned from the calibrated model for each month at two different hours (10 a.m. and 3p.m.). At 10 a.m. there is a slight percentage difference between the different months (14%), while at 15 the differences between July and December are about 70%. Table 5. Monthly average illuminance and radiation at 10 and 15 – office work plane.

January February March April May June July August September October November December

Eaverage 10 lux 428 463 496 491 490 482 481 488 487 467 443 420

Eaverage 15 lux 121 193 166 882 283 290 299 295 266 224 81 89

Emax 10 lux 1555 1681 1800 1782 1781 1752 1749 1772 1771 1698 1608 1524

Emax 15 lux 440 556 603 1026 1026 1053 1085 1070 965 815 294 324

Rad average 10 lux 73.8 596.3 557.3 495.3 361.0 676.5 611.3 494.3 448.3 169.3 308.8 379.5

Rad average 15 lux 117.0 828.0 628.0 736.0 555.7 741.0 841.7 803.7 723.5 145.2 319.3 229.3

4.2. Step 1 The simulations were performed for every representative day of the 12 months, for all the hours of the working period (9 a.m. – 5 p.m.). Average illuminance is rated on a surface corresponding to the entire room at 0.80 m from the ground. In Tables 6, 7, 8 and 9 are highlighted in yellow the hours in which it’s mandatory to turn on the system, since E < 500 lux (recommended value for offices); in orange values higher than 450 lux (the switching of the system is optional). Please note that solutions with films and areogel penalize Cod_006_pp_9


illuminance values because they do not exceed 300 lux (films) or 260 lux (areogel) and the plant must be turned on for many hours of the year (about 2000 work-hours), with a consequent increase of the electrical costs. The increasing of the hours of operation of the plant is about 12% for sunlight control solution and 23% for granular aerogel. The best solution is the one currently installed (standard glazing with sunscreens), that allows a good entry of daylight without glare in the central hours, thanks to the tilt adjustment of the blinds. Table 6. Average illuminance on reference surface for representative days of each month during the work period (9 a.m.-5 p.m.): Shading device.

9 a.m. 10 a.m. 11 a.m. 12 a.m. 1 p.m. 2 p.m. 3 p.m. 4 p.m. 5 p.m. dd work hours turn on hours switch off hours

Jan lux 406 431 424 387 322 232 125 22 2295 1766 529

Feb lux 428 456 452 416 350 259 149 27 20

Standard Glazing and Shading Device March April May June July Aug Sept lux lux lux lux lux lux lux 459 436 441 432 429 434 436 487 490 490 482 481 488 486 481 511 508 502 504 511 504 442 499 494 491 496 501 488 373 455 450 450 456 460 440 278 381 378 382 389 389 362 164 283 283 291 299 295 260 39 167 171 183 191 182 142 41 51 66 73 59 24 22 22 22 22 22 15 22

Oct lux 417 462 475 454 402 321 218 100 22

Nov lux 426 433 419 369 293 194 80 22

Dec lux 401 419 406 363 293 201 92 22

work dd 255

Table 7. Average illuminance on reference surface for representative day of each month during work hours (9.00-17.00): Standard Glazing.


Jan lux 640 680 670 611 507 366 197 22 2295 1574 721

Feb lux 675 720 713 656 552 408 235 43 20

March lux 725 768 759 697 588 438 259 61 22

April lux 689 772 806 787 717 601 446 263 65 22

Standard Glazing May June July lux lux lux 696 682 677 773 760 760 801 792 796 780 775 782 710 710 720 596 602 614 446 458 471 270 289 301 81 105 115 22 22 22

Aug lux 684 770 806 791 726 615 465 287 93 15

Sept lux 687 767 795 770 694 571 441 224 22 22

Oct lux 659 729 749 717 634 507 344 157 22

Nov lux 672 692 661 583 462 306 127 22

Dec lux 632 661 640 573 462 317 146 22

work dd 255

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Table 8. Average illuminance on reference surface for representative day of each month during work hours (9.00-17.00): Solar Control.


Jan lux

Feb lux

March lux

April lux

243 258 232 192 139 75 22

256 273 271 249 209 155 89 16 20

275 291 288 264 223 166 98 23 22

261 293 306 299 261 228 169 100 25 22

Solar Control May June July lux lux lux

Aug lux

Sept lux

Oct lux

Nov lux

Dec lux

264 293 304 296 269 226 169 103 31 22

260 261 292 291 306 302 275 292 233 263 176 217 109 156 35 85 8.53 15 22

250 277 284 272 241 192 131 60 22

255 262 251 221 175 116 48 22

240 251 243 217 175 120 55 work dd 22 255

259 288 300 294 269 228 174 110 40 22

257 288 302 297 273 233 179 114 44 22

2295 299 1996

Table 9. Average illuminance on reference surface for representative day of each month during work hours (9.00-17.00): Granular Aerogel.


Jan lux

Feb lux

March lux

209 222 219 200 166 120 64 22

221 236 233 215 181 134 77 14 20

237 251 248 228 192 143 85 20 22

Granular Aerogel April May June July lux lux lux lux

225 253 264 258 253 197 146 86 21 22

228 253 262 255 232 195 146 88 26 22

223 249 259 253 232 197 150 95 34 22

222 249 261 256 236 201 154 99 38 22

Aug lux

Sept lux

Oct lux

Nov lux

Dec lux

224 225 252 251 264 260 259 252 237 227 201 187 152 134 94 73 30 7.36 15 22

215 239 245 215 207 166 113 51 22

220 226 216 191 151 100 41 22

207 216 210 187 151 104 48 work dd 22 255

2295 117 2178

4.3. Step 2 Two alternatives were evaluated for the lighting of the office: the first consists in conventional fluorescent lamps, while the second in LED fixtures. For each case the new illuminance values and the operating costs are investigated. Illuminance maps given as output from DIALux showed that overall illuminance levels are in compliance to the recommended levels (500 lux and 300 lux respectively for the office area and reception) [12]. Peak values (Emax) are higher for LED plant (Fig. 7 and 8).

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Figure 7. Position of fluorescent lamps and output illuminance map (left: reception; right: office).

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Figure 8. Position of LED lamps and output illuminance map (left: reception; right: office).

A final analysis included the calculation of the electricity consumption for office areas, assuming an average annual turn-on time identified starting from average illuminance measured in DIALux in glazing configuration: standard glass and shading device. The annual cost for the operation of the type of lamp, designed to ensure the required illuminance, in the office and reception areas is: - FLUORESCENT: 381 €/year (monthly fee of about 32 €). Costs of lamps (no plant): 135€; - LED: 216 €/year (monthly fee of about 18 €). Costs of lamps: 480 €. A more careful analysis in which the consumption of the lamps according to nominal power and cost of energy are investigated, proves that LED technology is the most economical although at first impression seems to be the most expensive: a saving of about 43% is recorded compared to the design solution in which conventional devices are employed (see Table 11 and 12). Cod_006_pp_13


Considering the costs of the lamps (excluding that of the devices), the use of LED leads to an increase in costs of 345 € and to a saving in energy bills that amounts to approximately 165 €; the expected return period of the investment is therefore about 2 years. Table 11. Comparison of annual average electric energy consumption for plant analyzed. Zone

Type of plant and lamp

Reception and Office

FLUORESCENT BEG. 29-023/254/CB Lyra LED IGUZZINI MR71 Galaxy T16 51W

Number of devices

p kW

t h

E kWh/year

cost €/kWh

cost €/year

9

1,08

1766

1907

0.2

381

12

0,612

1766

1081

0.2

216

Table 12. Annual energy consumption and saving. €/year Fluorescent LED 381 216

Saving % 43

5. Conclusions In recent years, daylighting algorithms incorporated in building energy simulation programs have become increasingly sophisticated in their abilities to predict the illuminance, light power reductions, and associated thermal load interactions. The aim of this paper is to analyse simulated light levels of a non-residential building. Results showed that the best solution in terms of natural lighting is the standard glazing with blind systems. Considering the amount of 2295 work hours, for this solution the plant must be switched on for 1766 hours while for solutions with films and areogel the increasing of the hours of operation of the plant is about 12% for sunlight control and 23% for granular aerogel. The shading device allows the entry of the natural light for many hours during the day avoiding also glare problems; films and areogel penalize illuminance values that do not exceed respectively 300 lux and 260 lux with a consequent increase of the operation hours (about 2000 work-hours) and electrical costs. Conventional fluorescent lamps and LED fixtures are considered as alternatives lighting plant of the office that is assumed to be divided in two zones: office and reception. For each case and for each area illuminance values and the operating costs are investigated. Illuminance maps given as output from DIALux showed that overall illuminance levels are in compliance to the recommended levels (500 lux and 300 lux respectively for the office area and reception). Peak values (Emax) are higher for LED plant: 658 lux and 784 lux respectively for reception and office area against 533 lux (reception) and 682 lux (office) for fluorescent devices. Concerning the lighting systems, LED lamps have a lower rated power and therefore a saving in terms of energy absorption. Despite the higher luminous flux turns out to be that of compact fluorescent lamps (8900 lumen versus 7000 lumen for LED), LED lamps have more luminous efficiency and a longer service life. The annual cost for the operation of the type of lamp in the office and reception areas amounts to 381 € for fluorescent plant and to 216 € for the LED one.

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Considering the price of the lamps, if on one hand the use of LED leads to an increase in initial investment costs, on the other brings to saving in energy bills of about 165 € so the return period of the investment is expected to be 2 years. References 1.

Erdem Cuce, Saffa B. Riffat, A state-of-the-art review on innovative glazing technologies, Renewable and Sustainable Energy Reviews, 2015, 41, 695–714. 2. Cinzia Buratti, Elisa Moretti, Nanogel Windows. In Nearly Zero Energy Building Refurbishment: A Multidisciplinary Approach, 2013 edition; Fernando Pacheco Torgal, Marina Mistretta, Artūras Kaklauskas, Claes G. Granqvist, Springer-Verlag: London, UK, 2013, pp.555-582. 3. Moncef Krarti, Paul M. Erickson, Timothy C. Hillman, A simplified method to estimate energy savings of artificial lighting use from daylighting, Building and Environment, 2005, 40, 747–754. 4. I. Pyonchan, N. Abderrezek, K. Moncef, Estimation of lighting energy savings from daylighting, Building and Environment, 2009, 44, 509–514. 5. K. Konis, Evaluating daylighting effectiveness and occupant visual comfort in a side-lit open-plan office building in San Francisco, California, Building and Environment, 2013, 59, 662–677. 6. M.C. Singh, S.N. Garg, Illuminance estimation and daylighting energy savings for Indian regions, Renewable Energy, 2010, 35, 703–711. 7. Rogério Versage, Ana Paula Melo, Roberto Lamberts ,Impact of different daylighting simulation results on the prediction of the total energy consumption, Simbuilding 2010, Fourth National Conference of IBPSA, New York City, USA, August 11 – 13, 2010. 8. D.H.W. Li, T.N.T. Lam, S.L. Wong, A.H.L. Mak, Lighting and cooling energy consumption in an open plan office using solar film coating, Energy International Journal, 2008, 33, 1288–1297. 9. P.G. Loutzenhiser, G.M. Maxwell, H. Manz, An Empirical validation of the daylighting algorithms and associated interactions in building energy simulation programs using various shading device and windows, Energy, 2007, 32, 1855-1870. 10. DIALux Documentation. Version 4.9,March 2011. 11. Cristina Franceschini, Architettura Eco-Logica. Progetto di Miglioramento Bioclimatico del Centro Cortonese a Perugia. Master’s Degree Thesis, University of Perugia, Perugia, 26 July 2012. 12. UNI EN 12464 -1: 2011 Lighting of work places.

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