Siting and building-massing considerations for the urban integration of active solar energy systems

Renewable Energy 135 (2019) 963e974

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Siting and building-massing considerations for the urban integration of active solar energy systems Andreas Savvides a, 1, Constantinos Vassiliades a, *, 2, Aimilios Michael a, 3, Soteris Kalogirou b, 4 a b

University of Cyprus, Department of Architecture, Cyprus Cyprus University of Technology, Department of Mechanical Engineering and Materials Science and Engineering, Cyprus

a r t i c l e i n f o

a b s t r a c t

Article history: Received 28 August 2018 Received in revised form 29 November 2018 Accepted 4 December 2018 Available online 5 December 2018

This paper aims to determine the optimum geometry of the building blocks in order to ensure the viable building integration of active solar energy systems in the urban fabric. Through literature review, similar research objectives are reported and analysed, whilst the building integration of active solar systems in urban areas is explored. The motivation for the proposed research emanates for a need for an analysis at the scale of urban blocks and of building massing configurations at the scale of a cluster of buildings rather than that of an individual building. These sets of physical characteristics are examined to arrive at simplified archetypes, while at the same time the habitation density is held constant. A set of twelve simplified building block configurations is created, whereby the geometrical parameters examined include the width of the streets separating the building blocks, the height of existing and proposed buildings and the massing configurations of the buildings that can be accommodated in the proposed building blocks. These parameters are manipulated to effect changes in collective building massing and siting decisions that result in the optimal integration of active solar energy systems that may be integrated on a building cluster’s facades and roofs. Subsequently, the energy production potential of the buildings’ integrated systems was calculated for each case so that the twelve simplified massing and siting configurations could be compared and contrasted, so as provide architectural designers as well as planning authorities a way of quantifying solar planning decisions at the neighbourhood scale. © 2018 Elsevier Ltd. All rights reserved.

Keywords: Solar planning Urban design Building massing Building insolation Sustainable development Building integration

1. Introduction In the last few years, society has become more aware of the negative externalities brought about by climate change [1e3]. The move away from conventional fuels and towards renewable energy

* Corresponding author. E-mail addresses: [email protected] (A. Savvides), [email protected] (C. Vassiliades), [email protected] (A. Michael), [email protected] (S. Kalogirou). 1 Present/permanent address. Department of Architecture, School of Engineering, University of Cyprus, P.O. Box 20537, 1678, Nicosia, Cyprus. 2 Present/permanent address. Department of Architecture, School of Engineering, University of Cyprus, P.O. Box 20537, 1678, Nicosia, Cyprus. 3 Present/permanent address. Department of Architecture, School of Engineering, University of Cyprus, P.O. Box 20537, 1678, Nicosia, Cyprus. 4 Present/permanent address. Department of Mechanical Engineering and Materials Science and Engineering, Cyprus University of Technology, 30 Arch. Kyprianos Str., 3036, Limassol, Cyprus. https://doi.org/10.1016/j.renene.2018.12.017 0960-1481/© 2018 Elsevier Ltd. All rights reserved.

production is one of the main challenges ensuring the protection of the environment and the promotion of sustainability. Noting that today about 50% of the world’s population lives in cities, with this figure reaching 80% by 2030 [4], the fact that cities use a significant part of energy resources and are responsible for over 70% of global carbon dioxide emissions [5e9], is of particular importance. Moreover, as the built environment accounts for over 40% of the total primary energy consumption in the world [10] and 24% of the greenhouse gas emissions [11], planning authorities need to contend with such requirements as the European Energy Performance of Buildings Directive (EPBD), which require all the new construction to amount to zero energy buildings by 2020 [12]. The approach for the design and construction of a nZEB (Nearly Zero Energy Building) starts with passive solar planning considerations [11e14], and it is based on two fundamental pillars, the reduction of its energy demands, and its potential to produce energy (e.g. electricity), in order to achieve the desired energy balance

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between consumption and production [15]. The use of solar energy is a crucial factor in renewable energy production that could cover a building’s energy needs in whole or in part. This means that the integration of active solar systems (photovoltaics, solar thermal systems and hybrid systems), see Fig. 1, will play a key role in the future design and operation of buildings and their systems [16]. All the above may be achieved by the implementation of two main design strategies. The first is the inclusion of passive solar design considerations for a building, which takes into account its location and the climatic conditions affecting the geometry of the building massing in relation to the sun, so as to minimize energy use and maximize the energy production potential of the building [15]. The second factor is the siting of the building in the urban fabric, wherein careful consideration of the orientation of the site in relation to a building’s passive strategies may result in 20e50% in energy savings [17] (Fig. 1). Thus, urban solar planning and design strategies can make a significant contribution to the sustainable design of the built environment, not only at the scale of individual buildings, but at the scale of building clusters. It is this shift in deciphering the potential differences in the methodology for the examination of optimal massing and siting configurations at the scale of the neighbourhood rather than the scale of the individual building and how these relates to good physical urban planning strategies that constitutes the main motivation for the research. The provision of solar energy has always been an important design factor for architecture and urban planning, as is shown by the design of the buildings and cities of various ancient civilizations [18]. However, the issue of solar urban planning is relatively modern, and is derived from current needs for increased solar potential to meet the energy requirements that can lead to smart cities, embedded with nZEBs [19,20]. One of the first attempts in this direction was made in 1855
developed the concept of the “compact city” when Ildefons Cerda and proposed the reorganization of the structure of a part of Barcelona, to exploit its solar potential [21]. However, the majority of contemporary initiatives that started to create some solar consciousness in building and neighbourhood design, took place mainly during the post-war period [22]. Bernhard Rudofsky’s “Architecture without Architects” exhibition at the Museum of Modern Art in New York in the 1960s, was one of these initiatives, and presented examples of bioclimatic design in traditional buildings that had been developed and tested by many generations and within different cultures [23]. In Europe, Le Corbusier, with his vision of the modern city, defined urban planning as the first field for the application of solar planning strategies [24]. Since the late 1970s, a series of planning initiatives for sustainable urban planning have been carried out, based on the wider aim of achieving a lifestyle that will ensure a sustainable built environment [22]. Today, the utilization of solar energy in conjunction with spatial

factors affecting urban design, such as street orientation, building block geometry, and height and distance between buildings constitute a key set of design parameters that should define urban settlements. The development of the field of sustainable solar urban planning has triggered the current research, which combines the parametric side of urban planning with the need for solar energy exploitation, in a way that leads to the optimization of the energy performance of buildings as inspired by the concepts of Le Corbusier and Cerd
a [19]. Given the preceding contextual physical planning and siting analysis and the environmental concerns outlined in the motivation for undertaking this study, the rest of the paper is organized so as to include a broad literature review. This in turn examines and outlines related precedent case studies that help isolate the physical planning and design parameters that may lead to the optimization of massing and siting studies of buildings in parcelized urban blocks. Subsequently, these design parameters are synthesized in the proposed methodology of investigation so that relevant data may be collected and, analysed, evaluated and compared and contrasted amongst the selected archetypes to arrive at building massing geometries and urban block siting strategies that maintain constant habitation densities while examining building integration potential of active solar systems. 2. Literature review The need for a holistic environmental approach in architectural and urban design, dates back to the beginning of this millennium, as described in the work of Spiegelhalter [25] and Tombazis & Preuss [26], which state that the aim should be the design of buildings open to the sun, in urban environments that are organized in a way which maximizes access to natural resources required in the daily operation of buildings. Moreover, the bioclimatic design of buildings should take into account the negative externalities that may be inherent in the surrounding area. However, these challenges, may provide interesting starting points for architectural and urban design, and if they are comprehended from the beginning, they may lead to creative and innovative architectural and urban design proposals [27]. The observations and strategies presented above constitute the essence of environmental design and are applied in most of its aspects, starting with sustainable passive solar planning considerations [28,29]. Therefore, building orientation and building geometry together with the correct placement of a building in its site constitute a fundamental first design step [30,31]. This first design step determines solar access to the building and decisively influences several major design variables such as the need for openings and is related to the shading components, as well as the optimal placement and performance of photovoltaic and solar

Fig. 1. Left: Porter School of Environmental Studies in Tel Aviv, Israel, an example of a building integrated solar thermal system [www.archdaily.com (accessed 08/08/2018)]. Right: The BedZED development, an example of sustainable solar urban planning, with integrated solar systems in the urban scale [www.inhabitat.com (accessed 08/08/2018)].

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thermal systems [32e34]. All these decisions may lead to a reduction in the heating, cooling and lighting loads of the building, which may account for up to 62% of the total energy needs for a building the size of a conventional house [35]. All the above are crucial for defining the design principles that will meet the goals of the 20-20-20 program, that requires all new buildings to be nearly zero (nZEB), and to produce locally (as much as possible) renewable energy for their needs [36]. This requirement is difficult to achieve in densely built urban environments, because of the difficulty to access local renewable energy sources [37] and because the solar potential of buildings, depends mainly on the shading and reflection conditions from adjacent buildings [11]. Therefore, the design considerations must start from the urban scale, in order to strengthen the possibility of creating a sustainable environment at the building scale. This is vital, given that the research performed by Sauchelli et al. [38] shows that potentially reduced access to solar energy (which affects the optimal performance of solar systems, as well as natural lighting provision and the thermal performance of buildings), can be avoided by performing some preliminary siting analyses during the initial design phases. Building geometry, massing, density and siting are the basic urban design parameters that if implemented correctly, can help achieve net zero or nearly zero energy consumption in buildings [39]. This research also noted that buildings’ energy demand and solar potential can be greatly influenced by their orientation and location in relation to neighbouring buildings, as well as by town planning regulations and spatial characteristics of the neighbourhoods. In the same context, the research performed by Savvides et al. [27], recently aimed to determine the optimal geometry of building blocks in order to ensure the viability therein of particular building integrated solar systems (BISTS, BIPV). The creative complexity of Sustainable Solar Urban Planning lies in the quantity and complexity of the parameters that need to be taken into account during a study, as it is shown in the literature. Based on this, some researchers are engaged with the creation of design tools which will help urban planners and architects from the early stages of the design. Lobaccaro et al. [40] and Lobaccaro & Frontini [41], have tried to create design tools that optimize the volumes and the shape of buildings in existing urban areas, in order to harvest as much solar radiation as possible, and minimize their impact on the wider area, leading to an increase of energy production from building-integrated solar systems. The team of Lobaccaro et al. [11], deals with the estimation of the energy production potential of solar envelopes in urban environments. This research also aimed to the optimization of the building’s shape to maximize the solar incidence on it, in order to be exploited by building integrated solar systems. Compagnon’s 2004 research [42], is in the same field, as it presents a methodology for quantification of the facades and roofs’ potential in urban areas, for active and passive solar heating, photovoltaic electricity generation and natural lighting. In the same context, Savvides et al. [43] and Philokyprou et al. [44e46], investigated the insolation conditions and made an environmental assessment of the dense urban web of rural settlements in Cyprus. Further literature review includes a series of studies which investigate the broader theme above and analyse it into sub thematic areas. In particular, Kanters & Horvat [37], explored the geometric forms of the urban buildings and the potential of solar energy for local power generation and found that the impact of the geometric form on the solar energy potential is significant (up to 50%). Hachem et al. [39], also dealt with the calculation of the effect of the geometry and layout of buildings in space, on the solar potential and energy demand. In another research process, Kanters et al. [47], analysed the annual solar potential of a typical Swedish

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building block, in order to develop guidelines for urban planners and architects, while they found that the building block design has a significant effect on the overall annual - solar - energy production (up to 50%). In the framework of the geometric optimization of buildings other researchers [48,49] approach the issue of passive solar planning strategies and buildings’ solar access, by examining ways that reduce the buildings’ energy needs for heating, cooling and lighting. Both works are a review of previous studies of passive solar planning strategies and aim to improve the viability of new and existing urban developments, given that the maximization of the buildings’ solar access is desirable, either in a passive or in an active way. They also examine geometrical parameters such as the height of the buildings and the height and orientation of the roofs, but always with the limitation of a building factor [27]. In the context of the potential optimization of geometry, the research by Sanaieian et al. [4], studies the influence of the shape and location of the building blocks on thermal efficiency, solar access and ventilation. It examines how they affect not only the microclimate, but also the energy potential of each configuration. The discussion of this research in relation to the energy performance parameters of the structural elements under consideration, criticizes the existing methods and techniques for predicting thermal behaviour, solar access and ventilation in the urban scale. The geometry of the urban space is essentially concerned with two main elements, the volumes (building blocks) and the open spaces (roads and public spaces). The above researchers were mainly concerned with buildings, which have a very significant influence on the users. A different approach is presented in the work of van Esch et al. [50], which also examines the impact of the buildings and the urban design on solar access, but also takes into account the space between the building blocks and examines the possibilities for the utilization of passive solar heating strategies. It is also noted that the urban climate influences the bioclimatic and energy performance of the buildings, as well as the ways in which the city’s outdoor spaces can be used. Because of these differences, outdoor spaces between building blocks benefit from both sunny and shadowed areas, depending on the thermal needs of the users [27]. In the context of the analysis and parameterization of the complexity of the sustainable solar urban planning, Amado & Poggi [51], used the GUUD - Geographical Urban Units Delimitation model to present the solar energy integration in urban planning. The research suggests that the neighbourhoods of the city are transformed into solar power stations and provide functional support for the implementation of urban design practices for the solar energy integration in the urban scale. However, for the application of the above, it is assumed that the power supply from the large photovoltaic system installation and its management with the use of smart grids, must consider the spatial and functional characteristics of the urban model to which it is applied. It is also assumed that the energy that flows in the city has the dynamics which are associated with the production and consumption standards, which need to be analysed and controlled. The same research team, in another research process [52], promotes the energy transition to the utilization of solar energy in the urban environment, using the Geographical Urban Units Delimitation (GUUD) model that is related to the solar potential. The methodology of this research has five steps: the analysis of the urban systems, the parametrical urban modelling, the estimation of the solar potential, the forecast of electricity consumption and the application of an urban energy balance. The work flow of the process, consists of a combination of geographic information systems (GIS) with parametric modelling and analysis of solar potential. In the wider concept of the parametrization of solar urban

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planning, there are some other approaches, such as the one from Kanters et al. [53], which proposes the quantification of solar potential and the use of a solar map to increase the use of solar energy in urban environments. The research performed by Amado & Poggi [19], approaches this concept with the aim to develop a functional methodology in order to achieve better conditions for the development of ZEBs. This approach, though very interesting, results from the correlation between the use of solar energy, and economic, social, environmental and administrative factors. The methodology, based on the comparison of possible solar gains (assuming that the area is transformed with practices of the sustainable solar design) [54], with the solar potential in the given urban area, takes a different route from the methodology outlined here. Finally, looking at the wider environmental perspective of the subject, and that each building unit is a system interrelated to the environment, bound with it and subjected to the various seasonal and daily climate changes, it is realized that the introduction of an environmentally-responsible urban and building design practice, is necessary [1,2]. The ultimate aim of this particular body of work is to ensure that the solar potential at the urban scale which is affected by the early definition of the geometry and massing proportions of the building blocks and the layout of the city, should be the deciding factors encountered in the early stages of solar oriented urban design. 3. Methodology The proposed methodology, which is governed by the double design goal of the achievement of high densities and sufficient insolation of building shells, provides the opportunity to combine the principles of compact urban design with that of solar availability and natural lighting of urban areas, while minimizing the infringement of shadows cast by adjacent building masses [41]. Therefore, the quantification of these impacts can lead to the optimization of the buildings’ layout within a building block and it can significantly affect the natural light availability and thermal performance of buildings and its integration potential of solar active systems on the building. It is therefore suggested to use simulation tools to examine alternative configurations to discover the optimal layout of a settlement, so that they will operate in accordance to European planning and building regulations, which anticipate the development of a Net Zero Energy city. As part of subsequent investigation, it was deemed necessary to simplify and generalize basic geometrical and massing configurations of building blocks while keeping the usable area and by extension the floor area ratio constant. The three basic layouts settled upon (Fig. 2) were those provided by Martin and March [55] and these were applied to the Cypriot urban spatial and legal framework. Given that all configurations presented have the same allowable development parameters in terms of area and density, this is taken as the constant and comparison can then take place of the buildings’ shell insolation, affected only by their geometrical layout and massing. 3.1. Legal framework The urban development potential in Cyprus is based on codes, guidelines and directives defined by the Department of Urban Planning and Housing. The highest floor area ratio in the current legal framework today is 340% (that is, the allowable buildable area is 3.4 times the area of the development plot), while the highest lot coverage ratio is 70% (that is, 0.7 times the area of the development plot); additionally, the maximum height is 19.8 m, while the

maximum number of floors is six. At the same time, the minimum setback from the development plot boundaries is as follows: i. 3 m setback for a building up to three floors ii. 4 m setback for a building up to four floors iii. 5 m setback for a building exceeding four floors Within the framework of these regulations, the minimum width for a two-lane street is determined, depending on land use designation, as follows: i. 12,8 m right-of-way (Road 7,4 m, Pavements 2,7 m) ii. 11 m right-of-way (Road 7 m, Pavements 2 m) iii. 7.9 m right-of-way (Road 5.5 m, Pavements 1.2 m)

3.2. Research procedure The simulations are carried out on a simplified hypothetical urban building block unit in Cyprus, which complies with the city planning standards and guidelines as proposed by the Department of Urban Planning and Housing. The simulated unit is a building block with lot area of 5000 sq.m. (with typical dimensions of 100 m
50 m), a floor area ratio/allowable building ratio of 150% and the lot coverage ratio of 50% (Fig. 3). The city block is initially placed with its long side to the south, and the building masses are sited according to the three main types of urban development (pavillion, street and patio) mentioned above, maximizing both the allowable building and lot coverage ratios (AIN, B1N, C1N). These geometries are then configured to allow for maximum insolation, thereby reducing the height of southern-facing volumes and increasing the height of the northern ones (A2N, B2N, C2N). The building block is then rotated by 90 , its short side to the south, with the building masses being sited yet again according to the main types of urban development (A1B, B1B, C1B). Finally, these geometries are configured again for maximum insolation, thereby reducing the height of southern-facing volumes and increasing the height of the northern ones (A2B, B2B, C2B). The first exercise in the research sequence was to investigate the influence of the width of the streets on the buildings’ insolation. The building masses are sited in fairly dense neighbourhoods where they are surrounded by other identical developments. The insolation on the building shell for all the twelve layouts (Fig. 3) will be simulated in this paper with road width of 12.8 m, 11 m and 7.9 m, respectively. Subsequently, the incident radiation on the buildings’ shell, is further analysed (per surface and shell), in order to understand which configuration receives the largest amount of solar energy. This may be an early sample of which geometries have good passive solar behaviour and the potential for active solar systems building integration. However, incident radiation cannot fully determine the viability of the buildings in relation to the integration of an active solar system. A building may exhibit a high value for average incident radiation, but a number of its constituent facades might exhibit comparatively lower incidence values, rendering the integration of an active solar system non-viable. Thus, based on current technological data (performance of PV ~15% and STS ~35%) and a depreciation of the investment in 7 years, it was estimated that in order for an active solar system to be considered viable as an integrated system on one of the building’s façade, the surface of said façade should receive at least 914,3 kWh/m2/yr for PV integration, while for STS this value is 688,8 kWh/m2/yr. These figures were calculated based on the following equation:

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Fig. 2. The three main urban development layouts. Floor area ratio and density are kept the same (constant) in all three layout types (a) pavillion, (b) street and (c) patio.

Fig. 3. The simulated building layouts.

!

Radiation

kWh m2

yr

to 783,7 kWh/m2/yr to render it viable according to the equation above, while the STS performance was increased to 40%, which reduced the minimum required radiation to 602,7 kWh/m2/yr. In the second scenario, the PV performance was increased to 20%, which reduced the minimum required radiation to 685,7 kWh/m2/ yr, while the STS performance was increased to 45%, which reduced the minimum required radiation to 535,7 kWh/m2/yr. All the energy production calculations which were made for all the scenarios, took into account only the building façade/shell surfaces that met these standards. At the conclusion of the calculations, the energy production potential of the buildings’ integrated systems was calculated for each case (the systems were integrated only on the buildings’ surfaces that received adequate insolation e as explained above). Their energy production potential was then compared with the total solar incidence for each case, thereby indicating which building type siting and massing geometries achieve a relatively high energy production potential given relatively low insolation levels. It should be noted that for all the surfaces with integrated solar active systems, 25% of each surface’s area was left uncovered, for the placement of openings in the case of buildings’ facades, and/ or other electromechanical equipment (tanks, piping, compressors, air conditioners etc.) in the case of buildings’ roofs. Once the above simulations were completed, the capability of these integrated technologies to meet the buildings’ energy needs was calculated. Based on the report of the Ministry of Energy, Commerce, Industry and Tourism of the Republic of Cyprus, entitled “Strategy for mobilizing investments in the buildings renovation sector” [56], the energy consumption for heating, cooling, domestic

  System Installation Cost mV2   ¼ V
Years for Repayment System Performance
Energy Cost kWh

Then, knowing that systems’ performance is constantly rising due to their technological development, two other future scenarios were also calculated. In the first scenario, the PV performance was increased to 17,5%, which reduced the minimum required radiation

(1)

hot water and lighting of the ‘90s conventional housing units in Cyprus, is outlined in Table 1: At this point, it should be noted that the values make no reference to primary energy, since the most economical solution is pursued.

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A. Savvides et al. / Renewable Energy 135 (2019) 963e974 Table 1 Energy consumption for heating, cooling, domestic hot water and lighting of the ‘90s conventional housing units in Cyprus. Type

Electricity kWh/m2/yr

Oil kWh/m2/yr1

Total kWh/m2/yr

Housing Unit Apartment Building Commercial Building

37,04 92,66 119,9

80,93 e e

117,97 92,66 119,9

Note: In the report the oil consumption is expressed in litres. In order to calculate the energy of the heating oil, its calorific value (CV), which is equal to 10500 kcal/kg, thus 43963,5 kJ/kg, was multiplied with its density of 0,851 kg/lt, and gave the result of 37412,9 kJ/lt. Therefore, 1 L of oil has 10,39 kWh of energy.

Table 2 Comparative simulation of the unimpeded insolation on surfaces of 0 , 30 and 90 tilt, between TRNSYS and Ecotect. Tilt

TRNSYS

Ecotect Analysis

Declination

Degrees

kWh/m2/yr

kWh/m2/yr

%

0 30 90

1690 1884 1214

1855 1960 1116

þ9 þ4 8

3.2.1. Software Computational simulations were also performed in order to obtain research results. Specifically, Autodesk Ecotect Analysis v5.2 software [57] was used to simulate the passive solar behaviour of the several geometries. This software focuses on architectural applications and is widely used in similar research studies. It provides reliability, both qualitative and quantitative in the comparative assessment of the passive design strategies. In addition, this software has a user-friendly interface and is compatible with other software. In order to confirm the validity of the results, some pilot simulations were performed in TRNSYS and the results were compared. In particular, the unimpeded insolation was simulated on surfaces of 0 , 30 and 90 tilt, and the results are shown in Table 2: Given that the fluctuation in the results obtained from the two software packages used is small, the use of Ecotect may be considered as reliable and secure.

Fig. 4. Solar incidence.

4. Results - discussion The presentation of the results and relevant discussion based on the objectives of each sub-thematic research module, are included in this section. 4.1. Investigation of passive features 4.1.1. Investigation of street width influence The results of the simulations presented below investigate the influence of the width of the streets to levels of insolation for each of the different cases. Fig. 4 shows the solar incidence for each one of the 12 building massing configurations and perimeter streets. (A1N(1), A1N(2), A1N(3), etc. - where (1) e 7,9 m is the narrowest

Fig. 5. Total solar incidence analysis.

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width, (2) e 11 m is the medium width, and (3) e 12,8 m is the largest width). It is observed that the change of the street’s width parameter has a very little impact on the insolation of the building shells. Specifically, for the reduction of the street width from 12,8 m to 7,9 m, the maximum recorded solar incidence reduction comes from the A1B case, in which the solar incidence is reduced from 455,1 kWh/m2/yr to 448,9 kWh/m2/yr, which is a reduction of 1,35%. The minimum recorded reduction is 0,18% for the B2B case. The average reduction from all cases is 0,67%, which is deemed negligible, and hereto forth the simulations are carried out using 11 m as the average street width. 4.1.2. Total solar incidence analysis Subsequently, the total incident solar radiation is analysed per building massing, façade surface orientation (Fig. 5) and some early indications are given with regards to how viable building integration of active solar systems is (as defined above) for each building configuration presented. At the same time, the building massing configurations which result in the least likely propagation of interfering shadows are noted. For example, configurations that exhibit high insolation values, by extent have the least amount of interfering shadow propagation, as opposed to those that exhibit low insolation values. In particular, it is observed that B1B and C1B configurations are the only ones that exceed 1100 kWh/m2/yr, while comparably high levels of insolation are also observed in cases B1N, B2N, C1N and C2N with figures above 1000 kWh/m2/yr. A2B exhibits the worst performance, since the insolation received is just slightly above 750 kWh/m2/yr. In general, the worst performing geometry is that of the “pavilion” layout, a.k.a. the “A” cases. It is also observed that all the “B” cases (B1N, B2N, B1B, B2B) as well as C1N, C2N and C2B, exhibit high insolation of their southern facades (>900 kWh/m2/yr). This may be considered advantageous to their passive performance, since high southern insolation may reduce heating loads in winter, while in the summer it may be controlled with simple shading systems that limit the cooling loads. Additionally, another general observation is that east facing facades exhibit higher insolation compared to the western ones. This is because the weather file of Cyprus was used for the simulations, and it is observed that in Cyprus during the afternoon there is a higher possibility of cloudy conditions, something that explains these results [58]. 4.2. Investigation of passive features 4.2.1. Energy production potential The building integrated solar systems’ energy production potential of the twelve building block layouts is investigated in this section. 4.2.1.1. Solar thermal systems (STS). The investigation starts with the calculation of the building integrated solar thermal systems’ energy production potential. 1. Solar thermal systems with performance 35% As mentioned above, because the incident radiation cannot adequately meet the “viability” requirements of a building’s solar systems integration, the energy production potential for all the systems that can be viably integrated into the building massing configurations utilized is calculated. Specifically, for STSs with a performance output of 35%, it was calculated that in order to be viably integrated on a building’s façade surface, it should have a minimum insolation of 688,8 kWh/m2/yr. Fig. 6 shows the

Fig. 6. Energy production potential compared to the total insolation of the building (current situation - performance 35%).

maximum energy production potential of viably integrated STSs per square meter of installation, analysed per each different orientation. Concurrently, this value is compared with the total incident radiation on a building’s facades and roofs. The first conclusion drawn is that the A1N, A2N, A2B, B1B, B2N and C1N configurations exhibit the best performances, with an almost identical energy production potential close to 375 kWh/m2/ yr. However, A2B stands out, since it achieves this milestone with the lowest insolation value when compared to all the other cases. This fact does not necessarily render it as the optimal configuration, because low insolation translates into higher heating loads demand (given that all the necessary provisions for passive sun protection have been met). The worst performance is exhibited by B2B, with a potential output of 315 kWh/m2/yr. Finally, it is observed that the southern orientation is the most efficient for STS integration for all configurations examined (excluding their roof surfaces). 2. Solar thermal systems with performance 40% As mentioned above, knowing that the systems’ performance is constantly rising due to technological developments, STS performance output has been estimated to increase to 40%, which reduced the minimum total required insolation for a viable integration to 602,7 kWh/m2/yr. Fig. 7 shows the maximum energy production potential of the viably integrated STSs per square meter of installation, analysed per each different orientation. At the same time, this value is compared with the incident radiation on the building. The A1N, B1N and B2N geometries have the best performances, with an almost identical energy production potential close to 415 kWh/m2/yr. However, A1N stands out, since it achieves this milestone with the lowest insolation value when compared to all the other cases. As explained above, this fact does not necessarily render it as the optimal configuration. The worst performance is exhibited by C2B, with a potential output of 333 kWh/m2/yr. It is again observed, that the southern orientation is the most efficient for STS integration for all configurations examined (excluding their roof surfaces). Finally, it is also observed that the increase in performance, made some of the western facades viable to accommodate systems’ integration.

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Fig. 7. Energy production potential compared to the total insolation of the building (first scenario - performance 40%).

Fig. 9. Energy production potential compared to the total insolation of the building (current situation - performance 15%).

3. Solar thermal systems with performance 45%

configurations examined (excluding their roof surfaces).

In the second scenario, it was estimated that the STS performance output has been estimated to increase to 45%, which reduced the minimum total required insolation for a viable integration to 535,7 kWh/m2/yr. Fig. 8 shows the maximum energy production potential of the viably integrated STSs per square meter of installation, analysed per each different orientation. At the same time, this value is compared with the incident radiation on the building. The B1N and B2N geometries have the best performances, with an almost identical energy production potential close to 500 kWh/ m2/yr. The A2N, A2B, C1N and C2N geometries, have also good performances, with energy production potential close to 440 kWh/ m2/yr. The worst performance comes from B2B and C2B, with a potential output of 380 kWh/m2/yr. It is again observed, that the southern orientation is the most efficient for STS integration for all

4. Comments on solar thermal systems results The results of the simulations show that in all cases the most efficient geometry in terms of energy production potential for building integrated STSs is B2N. Also, A1N and B1N geometries indicate good performances. It is also noted that B2B and C2B geometries have the worst performances, which may render them non-viable for STS building integration. The results also confirm that geometries with large southern exposed surfaces have the best performance for STS integration. It is also indicated that a southern orientation is the most efficient for STS integration for all configurations examined (excluding roofs). Finally, it is observed that the increase of the systems’ performance, leads to an increase of the area of the building envelope on which the building integration of STS is viable.

4.2.1.2. Photovoltaics (PV). The calculation of the building integrated photovoltaics’ energy production potential is investigated in this section. 1. Photovoltaics with performance 15%

Fig. 8. Energy production potential compared to the total insolation of the building (second scenario - performance 45%).

For the PVs with a performance output of 15%, it was calculated that in order to be viably integrated on a building’s façade surface, it should have a minimum insolation of 914,3 kWh/m2/yr. Fig. 9 shows the maximum energy production potential of the viably integrated PVs per square meter of installation, analysed per each different orientation. Concurrently, this value is compared with the total incident radiation on a building’s facades and roofs. The first conclusion drawn, is that the A1B, B1B and C2N geometries have the best performances, with an almost identical energy production potential close to 200 kWh/m2/yr. However, A1B stands out, since it achieves this milestone with the lowest insolation value when compared to all the other cases. As explained above, this fact does not necessarily render it as the optimal configuration. The worst performance comes from B2B, with a potential output of 160 kWh/m2/yr. Finally, it is observed that southern is the only acceptable orientation for PV integration for all

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with a potential output of 170 kWh/m2/yr. It is again observed, that southern is the only acceptable orientation for PV integration for all configurations examined (excluding their roof surfaces). Finally, it is also observed that the increase in performance, made some of the eastern facades viable to accommodate systems’ integration. 3. Photovoltaics with performance 20%

configurations examined (excluding their roof surfaces).

In the second scenario, it was estimated that the PV performance output to increase to 20%, which reduced the minimum required insolation for the sustainable systems’ integration to 685,7 kWh/m2/yr. Fig. 11 shows the maximum energy production potential of the viably integrated STSs per square meter of installation, analysed per each different orientation. At the same time, this value is compared with the incident radiation on the building. In this scenario, the A1N, A2N, A2B, B1N, B2N and C1N geometries, have the best performances, with an almost identical energy production potential close to 214 kWh/m2/yr. It is observed that the maximum energy production potential is reduced compared to the first scenario, but the sum of the geometries’ performance has an upward trend. The worst performance is exhibited by B2B, with a potential output of 180 kWh/m2/yr. It is again observed, that southern is the only acceptable orientation for PV integration for all configurations examined (excluding their roof surfaces).

2. Photovoltaics with performance 17,5%

4. Comments on photovoltaics results

As mentioned above, knowing that the systems’ performance is constantly rising due to technological developments, PV performance output has been estimated to increase to 17,5%, which reduced the minimum total required insolation for a viable integration to 783,7 kWh/m2/yr. Fig. 10 shows the maximum energy production potential of the viably integrated PVs per square meter of installation, analysed per each different orientation. At the same time, this value is compared with the incident radiation on the building. The A1B geometry, has the best performance, with an energy production potential of 228 kWh/m2/yr, and achieves it with the lowest insolation compared to all the other cases. The A1N and B1B geometries, have also good performances, since they exceed the limit of 200 kWh/m2/yr. The worst performance comes from B2B,

The results of the simulations show that in all cases the most efficient geometry in terms of energy production potential for building integrated PVs, come mainly from geometry A. It is also observed that B2B geometry has the worst performance, which may render it non-viable for PV building integration. The results also confirm that geometries with large southern exposed surfaces do not have the best performance for PV integration, as it was observed in the STS cases. It is also noted that, there are more geometries that can have viably integrated PVs in their shell. However, it is confirmed that a southern orientation is the most efficient for PV integration for all configurations examined (excluding roofs). Finally, it is observed that the increase of the systems’ performance, leads to the increase of the area of the building envelope on which the building integration of PV is viable.

Fig. 11. Energy production potential compared to the total insolation of the building (second scenario - performance 20%).

4.2.2. Summary By looking comparatively at the passive and active characteristics of the configurations examined, it is concluded that no definitive comparison may be made between them, since the configurations with the highest passive insolation do not necessarily have the equivalent energy production potential. Specifically, configurations exhibiting very good passive performance (e.g. B1B and C1B - see Fig. 5) did not have an equivalent performance in terms of energy production potential, since in these cases, the potential production of both STS and PV was not one of the best. On the other hand, configurations with poor passive performance (e.g. A2B and C2B - see Fig. 5) do not exhibit the worst energy production potential. The explanation for the observation above is based on the fact that the total passive insolation of a building massing configuration, results from the combination of the insolation of all its surfaces, and therein a number of them may not meet the minimum required insolation value to be able to viably integrate an active solar system (see section 3.2). For example, there is a possibility that a particular geometry will have virtually zero sunshine on all of its surfaces except one that has sufficient insolation to viably integrate an active solar system. In this case, the geometry will have very low passive insolation performance, but it will be able to accommodate a viable active solar system.

Fig. 10. Energy production potential compared to the total insolation of the building (first scenario - performance 17,5%).

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Fig. 12. Energy production potential, compared to buildings’ energy needs.

4.2.3. Coverage of energy needs The results of the above simulations provided data in relation to the insolation and the energy production potential of each geometry. At this point, as described above, the sustainably building integrated systems were examined as to whether they can meet the energy needs of each building configuration examined. Knowing the typical energy consumptions for office buildings, houses and apartment buildings in Cyprus from the survey by the Ministry of Energy, Commerce, Industry and Tourism of the Republic of Cyprus [56], the maximum energy production potential per square meter of the useful area of each geometry was analysed, and the two are juxtaposed in Fig. 12. The results show that in all geometries, the energy production potential of STS far exceeds the average energy needs of each building use, making building integrated STS sustainable for all geometries. On the other hand, PVs’ energy production potential is not enough to cover the full energy needs of any of the aforementioned building uses. Only the B2N geometry can somehow cope, only if it is developed as apartment buildings (see Fig. 12). However, this does not make the building integration of PVs nonviable, since even in the worst case of the C2B geometry, it can cover up to the 46% of the total energy needs of an office building complex. 5. Discussion and conclusions The main aim of this research is to find out the extent to which the current urban fabric of Cyprus and of south-eastern Europe can accommodate buildings with building integrated active solar systems. The research is based on the work of Savvides et al. [27], in which a first attempt was made for the determination of the optimal building blocks geometry, in order to ensure the viability of building integrated active solar systems (BISTS, BIPV) in the current urban fabric. In order to achieve this, a methodological procedure was developed for this paper to deal with the analysis of solar incidence on a simplified geometric model. For the purposes of the research, a distinction between building integration and integration in the urban scale is made. In particular, the urban integration of active solar systems is based on the general urban planning and on a holistic design approach, rather than how the system’s unit is integrated on the building. Thus, the urban integration, implements all the necessary practices to ensure the systems’ adequate access to solar radiation, whether they are integrated in buildings or in public places. In this holistic way, it

ensures the viability of the building integration of active solar systems. Given that modern urban planning moves towards the implementation of dense urban environments that have lower energy consumption and a better ecological footprint per inhabitant, the arising problems have mainly to do with the shading and reflection conditions from adjacent buildings. Thus, the research presented in this paper tries to optimize the building blocks’ shape, through a solar access analysis and an assessment of the building integrated solar systems’ solar potential. The research results confirm and enrich the findings of other researchers of the subject [4,37e39,50,53], since they demonstrate the correlation between the building blocks and buildings’ massing and siting configurations, and the energy production potential of the building integrated active solar systems. Specifically, the analysis of the total insolation confirmed that the change in both the geometry of building blocks and buildings, affects their ability to receive insolation. It was observed that the best results came from the geometries that have the fewest possible infringing shadows created between the buildings’ massing. It was also observed that it is not necessary for a geometry to have large south exposed surfaces to achieve high insolation, since the best results were obtained from B1B and C1B geometries, which had their large exposed surfaces on the east and the west. The originality of the current research is the recognition of the two urban typological layouts, that are the optimal solution for a better passive insolation, the “street” and the “patio” typology (geometries B and C). However, although the relationship between geometry and solar access is confirmed, the results have shown that the change in the width of the roads between the building blocks, up to 4,9 m (from 7,9 to 12,8) has a negligible influence. This proves that the building integration of active solar systems is viable in the majority of urban fabrics with similar town planning regulations and meteorological conditions with Cyprus. This fact is a confirmation of the viability of the venture in new and existing building stock, irrespective of road width. Thus, the findings of Savvides et al. [43] and Philokyprou et al. [44] who proved that narrow street corridors in rural and urban settlements could allow unobstructed solar penetration of the building facades and streetscapes, are confirmed. An important part of the originality of this research process is based on the aspect that the study of the ability of the building integrated systems to produce energy, which was done to confirm or modify the findings of the first part, addressed the passive aspect of the subject. This part enriched the research conducted by Lobaccaro et al. [11] and Compagnon [42], which estimated and quantified the energy production potential of solar envelopes in urban environments. It was indicated that the adequate passive insolation of the building block and buildings’ geometries is not enough for the sustainable building integration of solar active systems. It was proved that each technology has a different behaviour on each geometry, without any clear rule that could determine an optimal geometry. At the same time, it became clear that geometries with large exposed southern surfaces are not necessarily ideal for the sustainable building integration of active systems. It was also proved that the change in the systems’ performance may affect their energy production potential, according to which geometry they are integrated. From the above it is concluded that the choice for either geometry or active system for building integration, should be done with the use of a multi-factor assessment as it depends on a number of parameters. Regarding the results of the investigation of whether the integrated active systems can cover the energy needs of the typical building stock of Cyprus, they have shown that the STS can cover them at 100% while the PVs are at the 65%. However, the building stock, following the European Energy Performance of Buildings

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Directive (EPBD) and the requirement for all the new buildings to be nearly energy zero (nZEB) by 2020, is on a continuous improvement process, which will significantly reduce their energy needs. This, in connection with the continuous increase of the systems’ performance, will make them soon able to meet the energy needs of the building blocks into which they are integrated, regardless of their geometry. It was also noticed that regardless of which system/geometry combinations have better performance in terms of energy production or needs, the wider performance of the combinations is able to play an important role in the improvement of the energy performance of the building stock. This was noticed since no combination was considered completely unsustainable, but every combination is able to contribute in energy, each one on a different scale. Thus, it is proven that building integration of active solar systems is achievable, since it contributes significantly to the achievement of the objectives set under the 20-20-20 program. In summing up the key findings may be enumerated as follows: - There is a clear association between the massing, configuration and parcel siting of building blocks building blocks and the energy production potential of building integrated active solar systems. - Building massing geometries with extensive exposed surfaces to the south, do not necessarily achieve optimal insolation values. - The optimal massing configuration for better passive insolation comes from the use of “street” and “patio” typologies. - Realistic road width changes between building blocks, given the physical planning scenario presented in this paper has negligible influence on their insolation potential, indicating that building integration of active solar systems is viable in the majority of planning regulatory frameworks and meteorological conditions resembling those of Cyprus. - Building integrated active systems can cover most of the energy needs of the typical building stock in Cyprus, as indicated by the fact that solar thermal systems can cover 100% of operational needs, while photovoltaics can account for 65% of stock requirements. Future research looks to the examination of further building massing archetypes as a precursor for studies coupling aspects of urban density e with respect to number of users in a building e their thermal and electrical needs and the ability of a building’s shell to optimally accommodate building integrated active solar systems as part of architectural and urban design processes. Subsequent research would also look at the creation of automated simulation methods pertaining to the goal set above that culd be used by architectural design teams and the respective monitoring authorities that would enable them to evaluate and come up with a set of physical planning indicators that lead to optimal building block massing and siting solutions. 5.1. Summary of general design guidelines On the design process on the urban/urban scale, the designer should fundamentally know that the geometry of the building blocks and buildings is directly related with their insolation and the energy production potential of the integrated active solar systems. Because of that, geometries with the fewest possible interrelation of shadows created between the buildings’ surfaces must be selected. However, it is clear that a geometry does not have to have large exposed south surfaces to achieve high insolation (the best results were obtained from the B1B and C1B geometries, which had their large surfaces exposed to the east to west). At the same time, due to the fact that the variation in the width of the roads between

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the building blocks up to 4,9 m, has a negligible influence on their insolation, it is not necessary to be taken into account in the design. When the design aims on the efficient operation of the integrated active solar systems, the designer should know that the high passive insolation of a building block, and the building geometries with large exposed southern surfaces, are not enough for the viable building integration of an active solar system. At the same time, each technology has a different behaviour on each building geometry, without any clear rule, which means that each study must have a different approach, but always be based on the same methodology. Finally, the designer must know that STS can cover the 100% of the energy needs of the current building stock, while the PVs can cover the 65%. Funding It is clearly stated that the funding source had no involvement in the preparation of this manuscript; in the study design; in the analysis and interpretation of data; in the writing of the paper; or in the decision to submit the article for publication. Acknowledgments The research described in this paper was carried out in the framework of Doctoral Studies in Architecture partially funded by University of Cyprus, as well as in the framework of the multidisciplinary research program Building Integration of Solar Thermal Systems (Cost Action TU1205 BIST) supported by EU Framework Programme Horizon 2020. References [1] M. Phocas, A. Michael, P. Fokaides, Integrated interdisciplinary design: the environment as part of architectural education, Renew. Energy Power Qual. J. 9 (2011) 501. [2] A. Michael, M. Phocas, Construction design and sustainability in architecture: integrating environmental education into architectural studies, J. Renew. Energy Power Qual. 10 (2012). [3] A.N. Tombazis, Architectural design: a multifaceted approach, Renew. Energy 5 (1994) 893e899. [4] H. Sanaieian, M. Tenpierik, K. Van Den Linden, F. Mehdizadeh Seraj, S.M. Mofidi Shemrani, Review of the impact of urban block form on thermal performance, solar access and ventilation, Renew. Sustain. Energy Rev. 38 (2014) 551e560, https://doi.org/10.1016/j.rser.2014.06.007. ^t-Regamey, Collaborative urban modelling platform– [5] U. Wissen Hayek, A. Gre facilitating incorporating of ecosystem services into planning for sustainable urban patterns, in: TEEB Conf. Leipzig, Ger., 2012. [6] C. Luederitz, D.J. Lang, H. Von Wehrden, A systematic review of guiding principles for sustainable urban neighborhood development, Landsc. Urban Plann. 118 (2013) 40e52, https://doi.org/10.1016/j.landurbplan.2013.06.002. pez, [7] R.E. Vega-Azamar, M. Glaus, R. Hausler, N.A. Oropeza-García, R. Romero-Lo An emergy analysis for urban environmental sustainability assessment, the Island of Montreal, Canada, Landsc. Urban Plann. 118 (2013) 18e28, https:// doi.org/10.1016/j.landurbplan.2013.06.001. [8] M. Cheung, J. Fan, Carbon reduction in a high-density city: a case study of Langham Place Hotel Mongkok Hong Kong, Renew. Energy 50 (2013) 433e440, https://doi.org/10.1016/J.RENENE.2012.06.060. [9] M.-A. Knudstrup, H.T. Ring Hansen, C. Brunsgaard, Approaches to the design of sustainable housing with low CO2 emission in Denmark, Renew. Energy 34 (2009) 2007e2015, https://doi.org/10.1016/J.RENENE.2009.02.002. [10] C. Vassiliades, A. Savvides, A. Michael, Investigation of sun protection issues of building envelopes via active energy production systems, in: L. Bragança, A.N. Yuba, C. Engel de Alvarez (Eds.), Euro Elecs 2015, EURO ELECS 2015, ~es, 2015, pp. 697e706. Guimara [11] G. Lobaccaro, F. Fiorito, G. Masera, T. Poli, District geometry simulation: a study for the optimization of solar facades in urban canopy layers, Energy Proced. 30 (2012) 1163e1172, https://doi.org/10.1016/j.egypro.2012.11.129. [12] The 2020 Climate and Energy Package, Eur. Comm. Clim. Action, 2009. http:// ec.europa.eu/clima/policies/package/index_en.htm. (Accessed 1 June 2015). [13] S. Paiho, H. Hoang, M. Hukkalainen, Energy and emission analyses of solar assisted local energy solutions with seasonal heat storage in a Finnish case district, Renew. Energy 107 (2017) 147e155, https://doi.org/10.1016/ J.RENENE.2017.02.003. [14] M.J.N. Oliveira Panao, H.J.P. Gonçalves, Solar XXI building: proof of concept or a concept to be proved? Renew. Energy 36 (2011) 2703e2710, https://doi.org/

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