A DESIGN APPROACH FOR THE SOLAR OPTIMIZATION OF BUILT VOLUMES Validation on a residential building’s project in a historical district in Milan, Italy
Massimiliano Giani1; Cristian Belfiore1; Gabriele Lobaccaro1; Gabriele Masera1; Marco Imperadori1; Francesco Frontini2 1: Politecnico di Milano, Department of Architecture, Built Environment and Construction Engineering, Campus Leonardo, 20133, Milano,
[email protected] Phone: 0223996017 2: University of Applied Sciences and Arts of Southern Switzerland (SUPSI) CH 6952 Canobbio, Switzerland
ABSTRACT
This paper presents a process of solar potential optimization for residential buildings in high density urban areas. The process is validated through its application to the project of a mixed use, net zero energy building including public facilities and four levels of apartments. The optimization process concerns three phases: energy, solar and panelling optimization. The design approach combines parametric volume transformations (Rhinoceros - Grasshopper), solar dynamic analysis (Daysim) and solar maps analysis (DIVA for Rhino). The energy optimization regards the reduction of the heated volume, compared with the allowable volume defined by the regulations of the city of Milan, to a smaller one with lower internal heights, minimizing the building’s energy demand. The solar optimization is focused on the transformation of the initial volume based on the local urban parameters (distance among buildings, allowable profile, building’s height, plot ratio), in order to improve the solar exposure and maximize the solar access. The façades are modified to reduce the overshadowing effect of the nearby buildings, maintaining the same volume. The optimized volume derives from parametric studies about solar availability tilting the vertical facades away from the vertical. Solar dynamic annual analyses were conducted using Daysim and DIVA for Rhino in order to compare the initial and the solar optimized scenarios. The first set of simulations was carried out on both the isolated initial and optimized volumes, while the second set was carried out on the latter volumes placed in the district, thus affected by the surroundings. The loss in floor area due to the slope of the south and east façades is balanced by the addition of living areas facing the inner court without losing any commercial floor area. This choice allows a comparison of the two buildings, which have different shapes but the same volume. The annual solar mapping analysis is performed to localize the most irradiated parts of the building envelope, giving the possibility to design both a photovoltaic or thermal solar system with variable density elements. The results show the increase of available solar radiation in solar optimized design, while the panelling study permitted to optimize both technology and energy design of the solar systems required and furthermore to justify the architectural choices that led the building’s design. The studies have demonstrated that through the optimization of the building shape, it is possible to obtain a huge improvement in the amount of solar radiation available on the façades, while keeping the same envelope surface. The next steps of the research will be focused on the analysis of both photovoltaic and solar thermal panels’ efficiency, as well as the related assessment of increased surface temperatures on the façades, due to the solar energy system integration. Keywords: Solar Potential, Energy optimization, Solar dynamic simulation, Panelling façade.
INTRODUCTION
Recent surveys show that 31% of the electrical energy and 44% of the thermal energy produced are consumed by houses, offices and commercial buildings causing 36% of CO2 emissions in Europe. Most of this energy is used for heating (78%) and air-conditioning (25%) [1]. These data show how important it is to design self-sustainable buildings in order to fulfil the energy needs taking advantage of renewable sources and reducing the impact on climate. In the recast of the Energy Building Performance Directive (2010/31/EU), the European Commission has established that by 2020 all new buildings within the European Union should reach the nearly zero energy buildings standards [2]. In this scenario it is necessary to develop an integrated design process taking into account the most important technical aspects since the early design phases. Therefore the right orientation, exposure and design of the building envelope, as well as its performance and the choice of the solar integrated systems, should be considered since the preliminary design steps [3] [4]. The design process should be carried out evaluating different shapes and observing their effects in terms of solar access and irradiation onto the building itself, as well as the effects over the surroundings and from the surroundings to the building [5] [6] [7]. This paper shows a process of design optimization of a new building located in via Palermo, North of the city centre of Milan (Italy). This is a high density area composed of 4 or 5 storey buildings. Currently the site of construction, constrained within an L shape rotated 12° clockwise from the North direction, is a big hole in the urban texture. Therefore, because of its localization, the area is strongly restricted in terms of footprint of the ground floor, building height, limits for elevations’ profile, plot ratio, and size of rooms. AIMS OF THE RESEARCH
The study presented in this paper is a validation of a new solar design approach based on the optimization of the built volume. The work proposes guidelines for the assessment of solar potential in urban areas through a process of parametric modelling of the relationships between buildings and districts. The new design approach is the result of a wider process started with a first optimization of volumes within an intervention of demolition and reconstruction, in search of the shape with the highest solar access [8]. The work continued with a second study [9], where a sensitivity analysis of the levels of total solar radiation on the external envelope has been carried out for several geometrical transformations of the building shape; finally, the same analyses were developed through parametric transformations of complex shapes [10]. As was shortly written above, the process of the solar design optimization here presented is organised into two different but logically consequent steps. The first part is related to the estimation of the increment of solar access of the new building through a comparison between the initial building's volume and the solar optimized shape, defined by a parametric study and maintaining the same volume (5,409 m3) and the same amount of the exposed surfaces (2,340 m2). The second part is focused on the localization of the most irradiated areas of the building envelope, suitable for the installation of solar systems in order to produce energy and reduce the building’s purchased energy demand. Therefore the aims of the study are: -
improve the solar access of the new building;
-
maintain or improve the solar access of the nearby buildings;
-
localize the best areas for the installation of solar systems.
THEORY AND METHODOLOGY
The approach starts from the maximum volume allowed by the city planning regulations, reducing the floor-to-floor height, from 3.80 m to 3.50 m changing the total height of the building from 19.20 m to 18.00 m. The preliminary transformation, which is permitted by the local regulations, allowed the reduction of the heated volume used for further parametric study for solar access optimization. This volume, called Vol.A-ref, is considered isolated and not inserted in any context.
Figure 1. Comparison of the maximum allowable volume (Vol.0), initial volume (Vol.A) (on the left) and solar optimized volume (Vol.B) (on the right). The approach is therefore based on the comparison, in different scenarios of analysis, between Vol.A and the Solar Optimized Volume, called Vol.B. The study started by fixing the urban parameters and modifying the shape of the building, varying them within the range indicated in the local urban planning regulations. All the transformations were conducted maintaining the volume of the building and the amount of surfaces exposed to the sky. Each transformation was applied taking into account parameters such as the orientation and inclination of the façades and the usability of the interior space. Figure 1 and Figure 2 summarize the different features considered for improving the solar exposure of the envelope surfaces. In particular the solar optimization process consists of an iterative parametric process that, for each façade, considers different slopes and orientations using generative modelling tools, such as Rhinoceros and Grasshopper [11]; the annual solar radiation analyses were run using a dynamic daylighting simulation tool, such as Daysim [12], considering all solar radiation components coming from sun (α), sky (β), reflections from the surroundings (λ) and from the ground (µ). After the shape modelling based on the solar optimization process described above, same volumes with different shapes were obtained. The data of total annual radiation were filtered in order to choose the best shape with the highest value of solar access, limiting the overshadowing effect from the surroundings. Table 1 shows the final parameters used for all Radiance-based simulations, validated previously [10]. ambient ambient ambient ambient ambient specular direct direct bounces division super-sample resolution accuracy threshold sampling relays 3 1000 20 300 0.1 0.15 0.20 2 Table 1. Set of “rtrace” parameters used for all radiance-based simulations. Table 2 reports the radiance material adopted for surrounding buildings. All external surfaces of neighbouring buildings were treated with the average colour (pink) of existing districts. All simulations used the EnergyPlus weather statistical data climate file recorded for MilanMalpensa Airport (latitude 45.27° N, longitude 9.11° E).
Radiance Number Description of values conc.plaster void plastic 005 Material
R (refl.) 0.713
G (refl.) 0.713
B (refl.) 0.713
Specularity Roughness 0.00
0.00
Table 2. list of radiance materials.
Figure 2. From the left side: site plan with the elevation of the analysed nearby buildings, the orientation of the building with respect to the sun path and section A-A’ with different solar radiation components (sun (α), sky (β), surroundings reflections (λ), ground reflections (µ)). The amount of solar radiation incident on the building envelope was calculated using the Daysim software. Daysim was developed by the National Research Council of Canada and the Fraunhofer Institute for Solar Energy Systems in Germany. It is one of the best software [13] to use for these kind of analysis. In a previous work [8], Daysim program was adopted and validated for a similar case of calculating solar radiation values on the external envelope of buildings. The calculations have been performed using the DDS (dynamic daylight simulation) model, allowing for a more detailed analysis of direct solar radiation [13]. A detailed solar maps analysis, aimed at locating the most suitable area to install the solar energy system, was conducted using DIVA for Rhino [14]. It is a highly optimized daylighting and energy modelling plug-in for Rhinoceros and Grasshopper, based on Radiance. RESULTS AND DISCUSSION
In the first part of the solar optimization process, regarding the improvement of the building’s solar access, two different sets of simulations were run: in the first set, the total annual radiation on the building envelopes has been calculated, in the condition of simple isolated volumes, in order to define the design with the largest solar irradiation; in the second set of simulations, the analysed volumes were considered together with the existing urban environment, in order to estimate the overshadowing effects by nearby buildings. Shape Vol.A-ref Vol.B Vol.A Vol.B
ab 3 3 3 3
gr. refl. 0 0 0.15 0.15
R [kWh/yr] 1,448,946.67 1,536,555.12 1,572,936.63 1,649,919.11
RA[kWh/m2yr] 620.53 652.7 673.63 700.85
Δref[%] Δrel[%] 6.0 6.0 8.6 13.9 4.9
Table 3. Isolated Scenario - Results of solar radiation analysis. R: total solar radiation impacting on the external envelope. RA: average solar radiation on the external envelope. Δref.: percentage of variation of solar radiation with respect to the initial reference volume (Vol.A-ref) and Δrel: with respect to the volume of the relative scenario analysed each time.
Shape Vol.A Vol.B Vol.A Vol.B
ab 3 3 3 3
gr. refl. 0 0 0.15 0.15
R [kWh/yr] 1,253,231.71 1,366,164.2 1,331,002.54 1,440,993.46
RA[kWh/m2yr] 536.71 580.32 570.01 612.11
Δref[%] Δrel[%] -13.5 -5.7 9.0 -8.1 -0.5 8.3
Table 4. Context Scenario - Results of solar radiation analysis. Legend: the same of Table 3.
Figure 3. Comparison of solar radiation maps analyses between Vol.A (on the left) and Vol.B (on the right) in a Context Scenario – Elaboration data by DIVA for Rhino. Each set of simulation includes two different scenarios: in the first, ambient bounces (ab) are set equal to 3 and ground reflectance (gr. refl.) equal to 0.0 in order to calculate only the solar reflection effect created by the surroundings, while in the second ab is considered equal to 3 and gr. refl. equal to 0.15, to calculate also the ground reflection contribution. The results are reported in Table 3 (Isolated scenario) and Table 4 (building inserted in a context – Context Scenario). The irradiation values obtained show that the solar optimization permits to increase the solar radiation on the building envelope up to 13.9% considering the isolated scenario. Moreover, the solar gains cover the reduction due to the surroundings (-0.5%) when the building is inserted in the context. It is important to underline that the ground reflectance affecting Vol.B, instead, does not provide the expected increment. The last column of Table 3 and Table 4 shows that the percentage of the scenario considering the ground reflection (ab=3, gr.refl.=0.15) is lower than the previous scenario (ab=3, gr.refl.=0.0). The increment of total solar radiation given by the ground reflected component is higher considering the Isolated Scenario (1.1%) and it is lower in the Context Scenario (0.7%). This is caused by the shape of the volume: the shape of the ground, visible in Figure 2, level has been designed in order to reduce the summer solar gains (both direct and reflected radiation) in the mediateca. More solar access analyses were carried out on the context, in order to estimate if the amount of solar radiation on the façades of the nearby buildings would remain the same or would instead increase because of the new building. Considering the Context Scenario (ab=3, gr.refl=0.15) and the presence of Vol.B, the North and East façades of the closest building, are affected by an increment of solar radiation of 8.2% for the East façade and 0.7% for the North façade compared to the Vol.A case. The purpose of the second part of the solar optimization process was to localize the most irradiated surfaces of the building envelope; these would be the most suitable locations for the installation of the solar systems. The optimized volume includes North and East elevations tilted 6° away from the vertical direction. Starting from the South façade of the initial building, a new elevation is created by slicing the volume for the best exposure of South façade, which is sloped 10°. The “solar shell” (Figure 4) composed by 27% of the overall surface is able to harvest up to 45% of the total radiation incident on the building envelope, as estimated in the Context Scenario (ab=3, gr.refl.=0.15).
Figure 4. Views of the “Solar shell”. CONCLUSION AND OUTCOMES
The results confirmed that a new solar design approach can significantly contribute to the definition of the building’s volume and the production of on-site renewable energy. Further studies are required to understand the consequences of the complex shapes deriving from the solar optimisation process, in terms of construction (panelling of surfaces) and cooling loads (increased surface temperatures due to solar panels). REFERENCE
1. Ecofys Germany GmbH, Danish Building Research Institute (SBi), Principles for nearly zeroenergy buildings - Paving the way for effective implementation of policy requirements, Buildings Performance Institute Europe (BPIE), 2011. 2. M. Hegger, M. Fuchs, T. Stark e M. Zeumer, Energy Manual. Sustainable architecture., Basel: Birkhäuser, Edition Detail, 2008. 3. M. Montavon, «Optimisation of Urban Form by the Evaluation of the Solar Potential,» École Politechnique Fèdèrale de Lausanne, Losanne, 2010. 4. V. Vannini, B. Turkienicz and A. Krenzinger, “Geometric optimization of building façades for BIPV,” in Proceedings of the Energy Forum 2012, Bressanone, Italy, 2011. 5. R. Compagnon, «Solar and daylight availability in the urban fabric,» Energy and Buildings, vol. 36, pp. 321 - 328, 2004. 6. R. Compagnon and D. Raydan, "Irradiance and illuminance distributions in urban areas," in In Proceedings of PLEA 2000, Cambridge UK, July 2000. 7. M. Montavon, J. Scartezzini and R. Compagnon, "Comparison of the solar energy utilisation potential of different urban environments," in In PLEA2004, Eindhoven, The Netherlands, 2004. 8. G. Lobaccaro, G. Masera and T. Poli, “Solar district: design strategies to exploit the solar potential of urban areas,” in Proceedings of the XVIII IAHS World Congress, Istanbul, Turkey, 2012. 9. G. Lobaccaro, F. Fiorito, G. Masera, Poli and T., “District Geometry Simulation: A Study for the Optimization of Solar Façades in Urban Canopy Layers,” Energy Procedia, vol. 30, pp. 1163-1172, 2012. 10. G. Lobaccaro, F. Fiorito, G. Masera and D. Prasad, “Urban solar district: a case study of geometric optimization of solar façades for a residential building in Milan,” in Solar 2012 Conference, Melbourne, 2012. 11. David Rutten and Robert McNeel & Associates., «Rhinoceros and Grasshopper software». 12. Harvard University, National Research Council Canada, Fraunhofer Institute for Solar Energy Systems, «Daysim version 3.1b,,» 2010. 13. D. Ibarra and C. Reinhart, “Solar availability: a comparison study of six irradiation distribution methods.,” in Proceedings of Building Simulation 2011: 12th Conference of International Building Performance Simulation Association., Sydney, 2011. 14. Graduate School of Design at Harvard University - Solemma LLC, «DIVA for Rhino,» 2013.
