2.Ulusal Yapı Fiziği ve Çevre Kontrolü Kongresi 04-06 Mayıs 2016 İTÜ Mimarlık Fakültesi, İstanbul USING DAYLIGHT SYSTEMS TO REDUCE ENERGY CONSUMPTION DUE TO LIGHTING: A CASE STUDY OF YAŞAR UNIVERSITY CAFETERIA Öğr.Gör.Arzu Cılasun a Yaşar Üniversitesi Mimarlık Fakültesi Bornova, İzmir ÖZET Yapılarda aydınlatma amacı ile harcanan elektrik enerjisi toplam enerjinin yaklaşık %40 ını oluşturmaktadır. Bu sebeple tasarıma günışığını dahil ederek enerji tasarrufu sağlamak ön plana çıkmaktadır. Aydınlatma tasarımcıları ve mimarlar günışığından daha fazla yararlanma görevini üstlenirken, geliştirecekleri tasarımların enerji verimliliği ile ilgili öngörülerde de bulunmalıdırlar. Günışığının içeriye daha fazla alınması ile planlandığı gibi aydınlatma açısından enerji tasarrufu yapılırken, CO 2 salınımı azaltılıp, görsel konfor koşulları iyileştirilebilir. Buna karşılık doğru yapılmayan bir günışığı tasarımında termal konforsuzluklara neden olunup, soğutma yükü arttırılabilir ve/veya kamaşmaya sebep olunabilir. Böyle sonuçlara yol açmamak için, hangi günışığı sisteminin kullanılacağı seçilirken dikkatlice karar verilmelidir. Bu çalışma kapsamında, seçilen Yaşar Üniversitesi Kafeterya binasında çatı penceresi kullanma önerisini DIALux ve DesignBuilder simulasyon programları ile test edilmiştir. Her iki programın özellikleri kullanılarak bu önerinin yapıdaki enerji tüketimine nasıl bir etkisi olduğu değerlendirilmiştir. Çalışma sonunda elde edilen sonuçlar incelenerek örnek yapıda önerilen çatı penceresinin kullanımının enerji tüketimi açısından yarattığı değişim tartışılmıştır. Anahtar sözcükler: Çatı penceresi, DesignBuilder, DIALux, Günışığı, Enerji Tüketimi ABSTRACT The share of electrical energy consumption for lighting in buildings is about 40% within the total consumption. Daylight integrated lighting solutions can significantly reduce energy consumptions. Lighting designers and architects are in charge of benefitting from daylight, so that they have to take some precautions and consider daylight in design period. Increasing daylight penetration may significantly save energy, reduce CO 2 emissions, improve visual comfort and enhance the quality of the indoor environment. On the other hand if not properly designed, this may turn the tides by increasing cooling loads, affect thermal comfort or causing glare. Therefore, deciding on which daylight system to use is a very important issue. In this study skylight s impact on a case study will be analyzed using two softwares; DesignBuilder and DIALux. These softwares are capable of simulating and evaluating skylights systems in energy savings both in terms of lighting and thermal comfort. In order to see how using skylight effects energy consumption, Yaşar University s cafeteria building has been evaluated as a case study. The gathered simulations (by using DesignBuilder and DIALux) have been analyzed. At the end of the study, the effectiveness of the proposed skylight system was discussed by looking at the energy consumption results. Key words: Skylight, DesignBuilder, DIALux, Daylight, Energy Consumption a e-posta adresi: arzu.cilasun@yasar.edu.tr
1.INTRODUCTION There has been a growing sense on global warming and climate change. Buildings happen to be a very big contributor to global warming with the high level of energy consumption. Buildings approximately consume 40% of the energy globally(1). Due to that reason, some precautions should be taken in building scale to reduce energy consumption and minimize negative impacts of climate change. At the end of the 19 th century initiated a new era for architecture, where electric lighting became a crucial component for spatial quality (2). Since the invention of electricity, lighting is one of the biggest energy consumption sources of buildings. Lighting energy consumption is around 20% of the total energy consumption in buildings, which is quite significant (3). Daylighting (defined as the planned use of daylight to offset electric lighting needs) has a vast potential to offset energy use in buildings (4). When one thinks, sunlight s average intensity is between 50000-100000 lux whereas humans require 200-1000lux to perform most visual tasks with accuracy; therefore, daylight is a very important issue. If one can redirect only %1 of outdoor flux to indoor, it will be sufficient for visual comfort (4). So integrating daylight design to building interiors has a potential to enhance visual quality while providing energy savings(5). The design objectives of the daylighting systems were to maximize daylight efficacy and redirection per unit glazing area and to increase the uniformity of the distributed daylight within the interior year round. The introduction of daylight to building interiors has the potential to enhance the quality of the indoor environment and also provide opportunities to save energy and reduce greenhouse gas production. However, improper usage of daylighting may cause visual and thermal comfort problems to overcome, thus negate the benefits of electric lighting energy reduction(5). For instance, direct solar penetration can be bothering for specific time of the day/year. Excessive heat may increase cooling energy consumption while ruining visual comfort as a result of glare. Therefore, energy consumption analysis has to be done and decisions have to be made in several counts. Another problem of daylight can be associated with the distribution of the admitted daylight flux. Generally sidelighting windows with low visible transmission glazing have been used. Though through sidelighting significant amount of daylight can be penetrate, visual discomfort may be caused as a result of bright window pane. direct sun and harsh luminance contrasts are the source of major complaints of occupants (4). Spreading daylight evenly through the space and obtain visual comfort through daylight is not easy. Therefore, additional daylight systems such as; skylight, light pipe systems, mirror sunlighting systems can be used to overcome this problem(6). However, to assure that the proposed system works good with the building, analysis and comparisons have to be done in advance. In order to analyze planned daylight interventions to reduce energy consumptions of buildings, existing simulation tools and energy modeling programs can be used. Advanced lighting simulation tools can be used to see how light behaves in a building. These tools play an effective role in daylighting projects thus contribute to create energy efficient buildings. They help to
overcome the challenges of sky modelling, time complexity of software towards real time control applications, validation and energy simulation. In the scope of this study, Yaşar University Cafeteria (YUC) was chosen to be improved in terms of lighting energy consumption. During 2013-2014 Fall semester, Yasar University INAR 350 Lighting Design course evaluated this case building for improving visual comfort. A skylight design was proposed to improve visual comfort while reducing energy consumption. The proposal was evaluated using two software. DesignBuilder was used for simulating internal gains, fuel breakdowns and CO2 emissions. Since lighting evaluation is not very comprehensive in DesignBuilder, illuminance levels were calculated in DIALux (which is one of the most outstanding lighting software in the market). This paper presents the results of the simulations and illustrates the change in energy consumptions due to the proposed skylight usage. 2. METHODOLOGY This study investigates a skylight strategy in Yasar University Cafeteria (YUC) building which is an unofficial workshop area for students. YUC building is located in Yaşar University Selçuk Yaşar Campus in İzmir, Turkey. It s a two storey steel constructed building with a mezzanine and flat roof (Image 1). Building has five west facing windows each having a dimension of (3*5 m) with metal frames (Table 1). Occupants of YUC were complaining about the low illuminance levels on the wall side of mezzanine during lunch time. In order to solve these problem, during the workhours all of the artificial luminaires are being actively used. YUC is occupied in weekdays from 08:30-18:00. Though it serves 9.5 hours a day, primarily heavy-occupied time interval is between 12:00-13:30. Therefore any dissatisfaction of visual/thermal comfort during those rush hours can be pretty disturbing. Table 1 Yaşar University's Cafeteria building properties YASAR UNIVERSITY CAFETERIA Length 13.5m Width 34.5m Window Height of the ground floor Height of the mezzanine Construction technique Length/ Width Alignment Frames Glazing Roof Artificial lighting 4m 3m steel 3X5m west metal Double glazing Flat roof 54x 32w pendant luminaire
Though window area is quite adequate for daylight penetration on the ground floor (Image 2), on the mezzanine, especially at the wall side of mezzanine, daylight penetration is not enough because conventional windows can provide daylight some 5 m into a building (7). Since daylight levels decrease asymptotically with distance from the window, in order to obtain visual comfort on wall side of mezzanine a modification was a must (Hata! Başvuru kaynağı bulunamadı.). To overcome this problem, the initial aim was to obtain visual comfort by means of passive daylight systems. Since the building has only one facade which is facing west, and during the rush hours, sun is on its highest position, using skylights was considered. Image 1 Exterior of YUC Image 2 Interior of YUC
Image 3 Interior of mezzanine floor As a design suggestion, skylight usage was proposed to increase the illuminance levels in the deeper parts of the space. Skylights are frequently used in underroof spaces where windows in vertical walls are not sufficient for daylighting. The skylight does not require difficult improvements and complicated constructions in a load-bearing structure of a roof and it does not change significantly architectural view of buildings, which is important for renovation and reconstruction of historical buildings (8). Since YUC building is a renovated historic building, proposing skylights to improve daylight penetration was found to be proper for this specific case study. Proposal consists of adding three skylights (1x3m) to the existing cafeteria. The general rule of thumb for distances between the skylights is to place skylights at 1.0 to 1.5 times ceiling height (center- to-center in both directions)(image 4). Therefore, in order to have uniformly distributed daylight inside, this general rule was obeyed and skylights were placed with 4.5 m distance (9). Image 4 General rule of thumb for skylight spacing (9)
This study involves comparison of the illuminance levels, internal gains, fuel breakdown and CO2 emissions of the YUC before and after the skylight implementation. As a result of these calculations and evaluations, this study will underline the proposed skylights effect to buildings energy consumption. YUC was modelled in DesignBuilder and results gathered for lighting, internal gains, fuel breakdown and CO2 emissions. Simulations were done for a year period, for overcast sky, using Design Builder s default schedule for non-residential education buildings- Eat/drink facilities which is parallel to the YUC. For lighting calculations, daylight scenes for each month were constituted in DIALux. In both of the programs calculation hour was fixed as 13:00 since it is the most occupied time of the day for YUC. 3. RESULTS 3.1. Illuminance levels from DIALux Table 2 Illuminance values gathered from DIALux When the output results of DesignBuilder and DIALux are analyzed, it is seen that using the proposed skylights has increased illuminance levels of YUC. Illuminance levels on the workplane show significant increase (average 58%) in deeper parts of the mezzanine (Table 2).
3.2. Internal gains of without and with skylight Image 5 Internal gains without skylight Image 6 Internal gains with skylight As it is seen on Image 5 and 6, adding skylight to YUC, solved illuminance problem but in the meantime, increased heat gains due to the increased glazing area. 3.3. Fuel breakdown of without and with skylight Image 7 Fuel breakdown without skylight Image 8 Fuel breakdown with skylight Additional heat gains resulted with increase of cooling loads of the YUC with skylight. Though fuel breakdown increase is not big, yet it is more significant on summer times compared to other seasons.
3.4. CO2 production of without and with skylight Image 9 CO2 production without skylight Image 10 CO2 production without skylight CO2 emission of the model with skylight is greater on June, July and August compared to the one without (Image 9&10). It s again related with the increase of cooling loads due to the heat gains. 4. DISCUSSION When proposed skylights added to YUC, illuminance levels on the workplane increased significantly. European Standard EN 15193-4 suggests that for cafeterias, 300 lux have to obtain, and after the modification this level can be obtained and even exceeds for some months (10). Though using the proposed skylight might reduce energy consumption due to lighting, since energy consumption is not only limited with lighting loads, total energy consumption of the space has to be considered. As it is seen on the Table 3 below, after implementation of skylight, total energy consumption of the building had increased. Table 3 Total energy consumption of the YUC Total Energy [kwh] Energy Per Total Building Area [kwh/m2] Energy Per Conditioned Building Area [kwh/m2] Without skylight 163458.61 218.16 With Skylight 166932.25 222.80 As it is seen on Table 4, increase of total energy consumption is approximately %1 which can be neglected in order to obtain visual comfort. Besides this increase can actually be prevented when artificial lighting system is dimmed or turned off whenever daylight penetration is enough.
Table 4 Detailed energy consumption comparison of YUC WITHOUT SKYLIGHT WITH SKYLIGHT Total [kwh] Energy Energy Per Total Building Area [kwh/m2] Energy Per Conditioned Building Area [kwh/m2] Energy Per Total Building Area [kwh/m2] Energy Per Conditioned Building Area [kwh/m2] Total Site Energy 163458.61 218.16 166932.25 222.80 Net Site Energy 163458.61 218.16 166932.25 222.80 Total Energy Net Energy Source Source 373661.49 498.71 376690.06 502.75 373661.49 498.71 376690.06 502.75 As a conclusion, to solve lighting related problems with daylighting systems, analyzing only lighting consumption or visual comfort of the building may be misleading. Though lighting is one of the biggest contributors to energy consumption of buildings, cooling/ventilation loads are also important contributors. Achieving indoor environmental comfort should be taken as a whole design approach. With regard to these results, skylight proposal in the given dimensions and conditions do not ensure energy savings, instead there is a slight increase in terms of total energy consumption. The main aim of this study was to show students that, though the intention of some interventions are sustainable result may not be that sustainable. Unfortunately there is no rule of thumb for all buildings to provide energy savings while increasing indoor environmental comfort. Every intervention to the building should be well analyzed in terms of all building physics issues, and total energy consumption must be considered before taking an action. REFERENCES 1. Yun GY, Kong HJ, Kim H, Kim JT. A field survey of visual comfort and lighting energy consumption in open plan offices. Energy Build [Internet]. Elsevier B.V.; 2012 Mar [cited 2013 Oct 20];46:146 51. Available from: http://linkinghub.elsevier.com/retrieve/pii/s0378778811004981 2. Kutlu GH. AN EVALUATION METHODOLOGY FOR ASSESSING ARTIFICIAL LIGHTING QUALITY IN ARCHITECTURE : THE CASE OF APIKAM A Thesis Submitted to in Architecture by. Izmir Institute of Technology; 2007. 3. Shen E, Hu J, Patel M. Energy and visual comfort analysis of lighting and daylight control strategies. Build Environ [Internet]. Elsevier Ltd; 2014;78:155 70. Available from: http://dx.doi.org/10.1016/j.buildenv.2014.04.028 4. Selkowitz SE, Berkeley L, Lau H, Ander GD, Edison SC. Demonstration of a Light-Redirecting Skylight System at the Palm Springs Chamber of Commerce. In: Palm Springs Chamber of Commerce. 1995. p. 229 40. 5. Yoon YJ, Moeck M, Mistrick RG, Bahnfleth WP. How Much Energy Do Different Toplighting Strategies Save? J Archit Eng. 2008;(December):101 11. 6. Kim JT, Kim G. Overview and new developments in optical daylighting systems for building a healthy indoor environment. Build Environ [Internet]. Elsevier Ltd; 2010 Feb [cited 2013 Oct 20];45(2):256 69. Available from: http://linkinghub.elsevier.com/retrieve/pii/s0360132309002315 7. Mayhoub MS, Carter DJ. The costs and benefits of using daylight guidance to light office buildings. Build Environ [Internet]. Elsevier Ltd; 2011 Mar [cited 2013 May 26];46(3):698 710. Available from: http://linkinghub.elsevier.com/retrieve/pii/s0360132310002921
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