account the outdoor environment, mechanical, electrical or structural systems, and traditional and ... By assessing equipment and system integration ideas, it can.
Hensen, J.L.M. (2001). Possibilities and challenges in using building simulation for sustainable building design. Proceedings of the 1st International Conference on Renewable Energy in Buildings "Sustainable Buildings and Solar Energy 2001", 15-16 November, pp. 115-117. Prague: Brno University of Technology/Czech Academy of Sciences.
POSSIBILITIES AND CHALLENGES IN USING BUILDING SIMULATION FOR SUSTAINABLE BUILDING DESIGN J L M Hensen Center for Building & Systems TNO-TU/e, Technische Universiteit Eindhoven, Netherlands Background Many buildings are still constructed or remodelled without consideration of energy conserving strategies or other sustainability aspects. To provide substantial improvements in energy consumption and comfort levels, there is a need to treat buildings as complete optimised entities (as indicated in Figure 1) not as the sum of a number of separately optimised components.
Figure 1 The building as an integration of energy systems
Figure 2 Main architecture of ESP-r
Integrated building performance simulation is ideal for this because it is not restricted to the building structure itself but can include the indoor environment, while simultaneously taking into account the outdoor environment, mechanical, electrical or structural systems, and traditional and renewable energy supply systems. By assessing equipment and system integration ideas, it can aid building analysis and design in order to achieve a good indoor environment in a sustainable manner, and in that sense to care for people now and in the future. For an overview of current building performance simulation software, see http://www.eren.doe.gov/buildings/tools_directory An example state-of-the-art building performance simulation environment The ESP-r system (Clarke 1985, http://www.esru.strath.ac.uk ) has been continuously developed since 1974. The main aim is to permit an emulation of building performance in a manner that a) corresponds to reality, b) supports early-through-detailed design stage application and c) enables integrated performance assessments in which no single issue is unduly prominent. ESP-r comprises a central Project Manager (PM) around which is arranged support databases, a simulator (consisting of specialised concurrent solvers for domains such as heat flow, fluid flow, power flow, control, etc.), performance assessment tools and a variety of third party applications for CAD, visualisation, report generation, etc. (Figure 2). The PM's function is to co-ordinate problem definition and give/receive the data model to/from the support applications. Most importantly, the PM supports an incremental evolution of designs as required by the nature of the design process. Case study: building embedded renewable energy systems The Lighthouse Building in Glasgow is a refurbished city centre building of major architectural significance. A specially configured portion of the building serves as a showcase for state-of-the-art
technologies that demonstrate the integration of complementary passive and active renewable energy components at the urban scale. Integrated building performance simulation was used to support the design process (Clarke et al. 1999). Implementation of renewable energy systems at the local level can be fraught with technical problems. When undertaking such tasks within an urban environment adds additional problems to a project such as impact on building aesthetics and most importantly, planning requirements which impair system performance. After careful consideration, the renewable energy systems chosen for this demonstration were categorised as passive, those that reduce energy demands (advanced glazings with light redirecting component and a variable transmission component; illuminance based luminaire control; and transparent insulation with integral shading) and active, those that generate electricity to meet some of the demands (facade-integrated photovoltaic (PV) cells with heat recovery; and roof mounted, ducted wind turbines with integral photovoltaic aerofoils). Lighthouse Viewing Gallery Version: Contact: Date:
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Figure 3: Integrated Performance Appraisal with Passive and Active RE Systems Applied
The design support was based on performance assessment method whereby computer simulation is used to determine the multivariate performance of an initial design of the building (e.g. corresponding to current best practice). The multivariate performance data are presented in the form of an integrated performance view as in Figure 3. The model is then modified by incorporating one of the renewable technologies and re-assessed. In this way, the contribution of the individual renewable technologies may be assessed and the different possible permutations compared. In comparison with the initial design hypothesis, the cumulative effect of advanced glazing, a fast response, critically controlled, convective heating system, high efficacy lamps and luminairs, lighting control and transparent insulation facade resulted in a 58% reduction in annual heating energy demand, a 67% reduction in heating plant capacity, an 80% reduction in lighting energy demand and a 68% reduction in overall energy demand. Figure 3 summarises the overall performance results. The combination of ducted wind turbines and PV components proved to be a successful matching of renewable energy systems to meet the seasonal energy demands. The wind turbines produce electricity predominately during the winter period when the PV components can contribute little. Conversely, the PV components supply power predominately during the summer period when the winds are light. The combination of the two systems gives rise to an embedded renewable energy approach that is well suited to the climate of Glasgow.
Case study: building reconstruction using a double-skin facade This project (Dunovska and Hensen 2001) was about reconstructing and converting an old factory hall in Prague into a modern office development (Figure 4). It includes a new two-floor superstructure on top of the original building. The superstructure is completely enclosed by a glass shell, thus forming a double skin facade (Figure 5).
Figure 4 View of the refurbished building
Figure 5 Double skin façade concept in summer
An extensive simulation study was carried out to predict the thermal behavior. It was proposed to control the double facade space so it would be closed in winter and serve as thermal buffer zone. In summer the controllable flaps would open to allow natural ventilation through the façade, and active shading would reduce the solar radiation gains (Figure 5). 55 E_SF=0 E_SF=0.5 E_SF=0.85 W_SF=0 W_SF=0.5 W_SF=0.85 Te
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Figure 6 shows the double facade outlet temperatures for different shading levels (SF). On a warm summer day, when the shading is closed (SF = 0.85), the façade air temperature can rise by 11°C on the eastern side and by 17°C on the western side of the building. Figure 7 shows the maximum cooling load for several levels of shading in two offices with different orientation. The cooling load reduces significantly with increased shading, even though the temperature in the double facade increases. Challenges Although most practitioners will be aware of the emerging building simulation technologies, few as yet are able to claim expertise in its application. This situation is poised to change with the advent of: performance based standards; societies dedicated to the effective deployment of simulation such as IBPSA1 ; appropriate training and continuing education; and the growth in small-to-medium sized practices offering simulation-based services. One thing is clear: as the technology becomes more widely applied (see e.g. Drkal et al. 2001, Bartak et al. 2001), the demands on simulation programs will grow. While this is welcome, in that demand fuels development, it is also problematic because the underlying issues are highly complex. Although contemporary programs are able to deliver an impressive array of performance assessments (see e.g. Hensen and 1 IBPSA: International Building Performance Simulation Association - http://www.ibpsa.org
Nakahara 2001), there are many barriers to their routine application in practice, mainly, in the areas of quality assurance, program interoperability, and task sharing in program development.
Figure 8 Expanding the scope of building performance simulation As indicated in Figure 8 there are many opportunities (and challenges) for expanding the scope (and thus the impact and usefulness) of building performance simulation. Conclusions This paper has elaborated and demonstrated the state-of-the-art in integrated building simulation and it’s value when used in (sustainable) building design. This paper has also argued the importance of this technology and how it will benefit in an economical and environmental context. Since many people in the field are not yet aware of this, there is a need for an organisation such as IBPSA. Its mission is to address the challenges above, and to promote and support moving the technology into the everyday practice of engineers and architects. REFERENCES Bartak M, F Drkal, J Hensen, M Lain, T Matuska, J Schwarzer and B Sourek 2001. “Simulation to support sustainable HVAC design for two historical buildings in Prague”, in Proc. PLEA 2001, Florianopolis, Brazil (in print). Clarke J A (1985) ‘Energy simulation in building design’ Adam Hilger, Bristol and Boston. Clarke J A, J Hensen, C M Johnstone and I Macdonald (1999). "On the use of simulation in the design of embedded energy systems," in Proc. Building Simulation '99 in Kyoto, pp. 113-119, International Building Performance Simulation Association. Drkal F, M Bartak, J Hensen, M Lain and J Schwarzer 2001. “Prispevek k vyvoji ve vetrani a klimatizaci”, in Proc. 50 year Environmental Engineering, Czech Technical University in Prague. (Contribution to the development of ventilation and air-conditioning) Dunovska T and J Hensen 2001. “Some experiences with building simulation in Czech construction industry”, in Proc. Building Simulation 2001 in Rio de Janeiro, pp. 837-840, International Building Performance Simulation Association. Hensen J and N Nakahara 2001. (Guest editors) Special issue on building performance simulation, Energy and Buildings, vol. 33, nr. 4.
