Flexibility in typology, technology, construction and performances: an innovative approach for an open construction kit

Transcription

1 Proceedings of the XVIII IAHS World Congress April 16 19, 2012, Istanbul, Turkey Flexibility in typology, technology, construction and performances: an innovative approach for an open construction kit Angelo Lucchini, Gabriele Masera, Enrico Sergio Mazzucchelli, Tiziana Poli BEST (Building Environment Science and Technology) Department, Politecnico di Milano, Milan, Italy Keywords: flexibility in construction, flexibility of performances, low environmental impact building. Abstract In recent years, the topic of flexibility has been widely investigated, but the prediction of performances for flexible construction systems was hardly addressed. Research works mainly focused on the issues related to typology, technology and construction, with the aims of rational use of resources and cost optimisation. The concept of flexible performances was limited to the possible variations of the energy transmission and reflection characteristics of the building envelope. In particular, the possibility of controlling and predicting the environmental and energy performances of a modular construction system has not yet been considered. The aim of this paper is to show how, using simplified assessment tools, it is possible to estimate the energy performance of a modular construction system in the preliminary design phase. First, the paper shortly describes the proposed construction system, which is modular, but with a large degree of adaptability as concerns: structural grid, envelope, internal partitions and building services. Then the paper presents the methodology for the estimation of the energy and environmental performances according to the basic design parameters (orientation, floor plan, window to wall ratio, U values and shading system) and to the boundary conditions around the building (obstructions). Finally, the simplified tools developed at Politecnico di Milano BEST Department for the preliminary design, the integration and the optimisation of the performances of both building fabric and services are presented. These tools have been developed in a research programme with TIS Innovation Park Cluster Edilizia, Bolzano, Italy. 1 Introduction Industrialisation of the building process has long been considered a way to increase productivity and cut production costs while guaranteeing high performance standards [1]. Although post war prefabrication techniques, mainly based on concrete, led to architectural uniformity and monotony and poor performances [2], the strategy of pre assembly is still identified as one of the tenets of improving construction in the 21st century [3] through the transfer of activities from the construction site to the

2 Angelo Lucchini, Gabriele Masera, Enrico Sergio Mazzucchelli, Tiziana Poli supply chain [4]. The original conflict between uniformity and variation, typical of industrialised, closed construction systems [5], can be overcome through more open concepts that can meet the individual requirements of users [2]. The current perspective for industrialised building technology is to allow a degree of customization in order to fulfil customer s needs and cultural, economical and environmental requirements [1] [5]. This is possible thanks to more adaptable construction techniques, based not only on concrete, but also on timber and steel and to computer assisted design and production allowing for customized prefabrication [2]. The concept of open building summarizes a multi disciplinary approach to the design, financing, construction and management of buildings allowing individual choices in a rationalised production and construction process [6]. This paper presents the systematised design process adopted to predict the energy and environmental performances of an industrialised construction system developed together with a group of construction companies within the Project 999 coordinated by TIS Innovation Park Cluster Edilizia, Bolzano, Italy. The aim of the work was to optimise the supply chain for residential buildings (design and production) thanks to a modular construction system adaptable to local conditions. As the final architectural outcome of the design process is, in principle, still unsettled, a pre engineering tool was developed to estimate the overall performances of the building in terms of energy efficiency, peak power requirements, and natural lighting. 2 The concept of an open construction kit The strategic vision guiding the development of the construction system was based on the identification of a set of needs that to date are not well met: on one hand, the customer and users, looking for low cost solutions with good architectural quality and low energy demand; on the other, building contractors that, while attempting to respond to the many needs of their clients, are not able to manage effectively the design and construction process in order to reconcile the limitation of construction costs with the aspects of quality and sustainability. Figure 1: The proposed modular construction system (plan). n, m are the dimensions of the functional module (functional units), N, M those of the structural module, x identifies variability of structural module, S is the dimension of the vertical connection system, and Balc identifies the module of balcony.

3 XVIII IAHS World Congress April 16 19, 2012, Istanbul, Turkey Figure 2: Catalogue of functional units. There is no connection between the functional module (or units) and the structural module to enable both standardization and customization of the building system. Filled in grey are the opaque envelope and partition walls, in black the service risers walls and outlined the portion of the envelope which can be made of various combinations of components. One of the main requirements of the new construction system is to allow a degree of variability and customization, while keeping the production and assembly cost very low through the process industrialization. This has led to the development of an optimized construction grid, governing the flexibility of the system in terms of use (adaptability and customization of internal and external finishing materials), lay out (serviceability), technology (maintainability, repair of parts, etc.) and performances of the building envelope components. The grid, and accordingly the whole construction kit, have been optimized combining the structural issues (static schemes and spans according to different materials) with the possible combinations of functional units (minimum size for each function) (see Figs. 1, 2 and 3), ancillary external spaces (loggias and balconies) and façade elements (modular envelope with different opaque to transparent ratios) (see Figs. 4 and 5). The control of the structural grid, building morphology (in term of obstructions and shading), typological variables (transparent surface to floor area ratio), technological variables (layers and details) and

4 Angelo Lucchini, Gabriele Masera, Enrico Sergio Mazzucchelli, Tiziana Poli performances (thermal resistance) allows to pre define, at the preliminary design stage, some of the major performances of the building, such as: the daylight factor (DF) for different window sizes, the heating energy demand according to window to wall ratio, U values and temperatures of surrounding thermal zones, and the peak heating power (which allows to determine the surface area to be allocated to radiant systems) (see Figs. 6 and 7). Balcony Balcony Balcony Figure 3: The modular construction system: possible aggregations of functional units (filled in grey are the building envelope portions that need to be opaque). The construction kit, based on the use of two different structural module, gives freedom in the aggregation of the functional units and the combination of the building envelope components. Figure 4: The opaque and transparent modules for the façade.

5 XVIII IAHS World Congress April 16 19, 2012, Istanbul, Turkey Figure 5: The modular construction system grid for the façade. 3 The simplified assessment tools The simplified assessment tools developed in this research allow to predict with a good accuracy, since the preliminary design phase, the energy demand, the peak power demand for the air conditioning and ventilation systems (for summer and winter seasons) and the daylight factor in the various rooms of a building made of an aggregation of the system s units, each one including a number of functional units (see Figs. 2 and 3). To this goal, each functional unit was provided with a specific technical data sheet. In addition to the set of functional units, the system includes the standard units of the vertical connections and the horizontal distribution as well. The functional units are to be grouped according to their intended use (living room, kitchen, bathroom, bedroom, etc.), their period of use (living and sleeping area) and size (single and double). The modelling of the non steady behaviour of each functional unit is carried out with TRNSYS software and Autodesk Ecotect Analysis 2010 v The following variables are considered in the modelling of individual units: orientation of the functional unit (steps of 45 ), ratio between transparent and opaque envelope areas (with the smallest opening satisfying the standard requirement of 1/8 ratio of window to floor surface areas, and the widest possible glazing taking into account the physical restraints of the façade), geometrical position of each functional unit with respect to the adjacent ones (protruding, aligned or recessed) and the dimension of heat losing surfaces (depending on the particular position of the functional unit, see Fig. 6). The design kit refers to a standard set of technical solutions (transparent and opaque vertical envelopes, roofs, etc.), with pre defined characteristics (U value, periodic thermal transmittance, effective mass, solar heat gain coefficient, etc.) the designers are allowed to choose from.

6 Angelo Lucchini, Gabriele Masera, Enrico Sergio Mazzucchelli, Tiziana Poli Figure 6: Possible configurations of heat losing surfaces and positions of functional units. In each functional unit, a mechanical ventilation with 75% efficiency heat recovery and 0.5 volumes per hour of air renewal are considered. Heat loss due to thermal bridges has been considered at a flat rate, computed using gross envelope dimensions and storey heights. In summer the use of adjustable solar protections is expected. This has been modelled with a shading factor of 0.70 and use time between 10:00 a.m. and 5:00 p.m. The internal loads for each functional unit depending on the specific intended use (living room, etc.). A data sheet is then drawn up for each functional unit. This technical support allows to characterize the unit, identifying its net energy need for heating (linked to the envelope of the functional unit) and the peak power demand for the air conditioning and ventilation systems, both in summer and winter, and showing in addition, by simple summary graphs, the variation of these quantities according to the orientation of the functional unit (see Fig. 7). As the peak power demand can be easily estimated at the preliminary design stage, designers working on this modular system have the possibility to avoid all those unfavourable configurations in which the power per unit area for heating or cooling should be too high: an obvious example for Italy are the units facing east and westward with full size glass cladding, critical with regard to the summer cooling loads. The combined use of these simple tables with the emission curves of the heating and cooling systems allows to immediately assess the fundamental characteristics of the various components, such as flow temperature at the terminals of heat emission in the room, coil steps, etc. The further development of the design tool will be the performance optimization (energy, etc.) of buildings as aggregation of multiple functional units with known performances, considering the change of orientation, the ratio of window to wall ratio, the geometrical relationship of each functional unit compared to the adjacent ones, and so on.

7 XVIII IAHS World Congress April 16 19, 2012, Istanbul, Turkey Figure 7: Example of a functional unit data sheet.

8 Angelo Lucchini, Gabriele Masera, Enrico Sergio Mazzucchelli, Tiziana Poli 4 Conclusions The development of an industrialised construction systems that allows some controlled variability and customization has required the implementation of a pre engineering tool to predict the major performances at the preliminary design steps. This paper showed that, through the control of some design aspects, it is possible to obtain initial indications about energy demand, peak power demand for air conditioning and ventilation systems (both in summer and winter) and daylight factor of the rooms of a building obtained as an aggregation of housing units. These units are in turn obtained as the aggregation of a number of functional units. For each functional unit specific technical data sheets are to be prepared to support and ease the work of designers. Moreover, this tool allows an easier industrialisation of the system, limiting the variability of the heating and cooling systems and easing its off site integration in the building components. The further development of this design tool will be the optimization of the supply chain for modular residential buildings (design and production) and the prediction of performances (energy efficiency, natural lighting, etc.) for buildings as larger aggregations of functional units with known performances. References The authors thank the Provincia Autonoma di Bolzano, Italy; TIS Innovation Park Cluster Edilizia in Bolzano and all the other industrial and scientific partners of Progetto 999 for the fruitful cooperation. References 1. Sarja, A. Open and industrialised building, E & FN Spon, London, Staib, G.; Dörrhöfer, A.; Rosenthal, M. Components and systems Modular construction: design, structure, new technologies, Institut für internationale Architektur Dokumentation, Munich, Gibb. A.; Isack, F. Re engineering through pre assembly: client expectations and drivers, Building Research & Information, 31:2 (2003), pp Vrijhoef, R.; Koskela, L. The four roles of supply chain management in construction, European Journal of Purchasing & Supply Management, 6 (2000), pp Gibb, A. Standardization and pre assembly: distinguishing myth from reality using case study research, Construction Management and Economics, 19:3 (2001), pp Kendall, S.; Teicher, J. Residential open building, E & FN Spon, New York, 2000.