|Simulation Based Design Tools for Energy
Efficient Buildings in Hong Kong
|Abstract: Building energy simulation is important
for the study of energy efficiency in buildings. This paper explains
the basic concept of energy simulation in building design and the properties
of simulation design tools. The range of applications and the limitations
of existing simulation tools are described. The relationship between
building design process and building energy simulation is examined from
the architect's point of view. Efficient simulation practice is discussed
in the context of integrated building design systems. Finally, this
paper discusses some of the current research in Hong Kong developing building
energy simulation techniques.
Keywords: building energy simulation; design tools; energy efficient buildings
2. Basic Concept of Building Energy Simulation
2.1 The Basic Theory3. Properties of Simulation Design Tools
3.1 Existing Tools in the Market4. Building Design and Simulation Environment
4.1 Building Design and Development Process5. Developing Simulation Techniques in Hong Kong
5.1 Analysis of Building Climatic Data6. Conclusions
Table an Figures:
|Energy efficiency of buildings is important from both an economic and
environmental point of view. The technology exists for sustaintial
energy savings in the building sector but the potential for such savings
has still to be fully exploited (Rosenfeld and Hafemeister 1988).
To achieve efficiency goals, building designers require effective design
tools for analysing and understanding the complex behaviour of building
energy use. In the past decade, computer simulation and modelling
has been used for providing an accurate and detailed appraisal of building
energy design. It is believed that building energy simulation is
a powerful, analytical method for building energy research and evaluation
of architectural design (Hensen, et al. 1993; Seth 1989; Newton, James
and Bartholomew 1988; Clarke 1985; Nall 1985).
However, the application of simulation in building design is problematic
because the simulation tools are complicated and many building designers
are not familiar with their properties and limitations. In real-life,
the nature of the building design process and the shortcomings of current
simulation tools have made it difficult for the architect to use such tools
efficiently (Holm 1993; Mathews and Richard 1993). There is a need
to develop a better understanding of energy simulation and to put into
practice the techniques for achieving energy efficient buildings.
It is hoped that the information in this paper can help increase an understanding
of energy simulation techniques and encourage building designers to have
the confidence to use the simulation based design tools.
|2. Basic Concept of Building Energy Simulation|
|The evolution of building energy simulation over the past few decades
has encouraged architects to apply this technology to building design (Clarke
and Maver 1991). From a traditional handbook approach to computer
simulation method, building designers are trying to extend the limits of
2.1 The Basic Theory
2.2 Major Elements
Fig. 1. Major elements of building energy simulation
The inputs to the simulation system are the building descriptions and design parameters; the boundary condition is the climatic context of the location. The outputs are the data for building energy consumption, peak demand and indoor environmental conditions. Usually, the modelling target is to provide comfortable indoor conditions while maintaining acceptable levels of fuel consumption; to optimise the system performance; or to compare different design options based on their life cycle costs. An additional module is required for the economic analysis.
To implement the simulation system on computer programs, different modelling
approaches and solution techniques can be used (Hensen 1995; Clarke 1985).
Although the method and level of detail may vary in different programs,
the general approach to the energy simulation task is similar. The
way energy modelling is expressed and carried out will determine the accuracy
and properties of the simulation tool.
|3. Properties of Simulation Design Tools|
|The variety and diversity of simulation tools give rise to a practical
need to distinguish the best applications and limitations of the existing
3.1 Existing Tools in the Market
Many simulation programs for building energy analysis are now available; they range from the simple and approximate to the detailed and sophisticated. It is difficult to categorise simulation programs since many of them have multiple features and the programs themselves are continuously evolving. Contemporary programs such as BESA, BLAST, BUNYIP, DOE-2, ESP-II, ESP-r, HVACSIM+ and TRNSYS are able to model a building in detail, but they also require great effort and heavy input from the user. Programs from commercial bodies such as Carrier HAP and TRACE 600 are more popular in design offices because they are easier to use and have better user interface and default features; but their independence sometimes may be questioned.
The selection of a simulation program for a given task depends on the project requirements, time and cost of the analysis, experience of the user and availability of suitable simulation tools and data (ASHRAE, 1995). Some selection guidelines are provided in ASHRAE (1995 & 1993), State Projects (1993) and Howard, Wager and Winterkorn (1994). The most important consideration is the capability of the program to deal with the application required.
3.2 Range of Applications
(a) Building energy simulation (whole building)
(b) Lighting and daylighting simulation
(c) Solar system simulation
Apart from energy analysis, many simulation programs also allow for
standard design load calculations to determine the design capacities of
equipment and plant. This is a feature often considered useful by
casual users. Table 1 shows a list of common simulation programs
for building energy design.
|4. Building Design and Simulation Environment|
|Energy efficient buildings are the result not of only a responsible
attitude towards energy but also of how successful the designer has been
in applying the technology and the energy analysis tools during the design
4.1 Building Design and Development Process
Fig. 2 Relationship between design and simulation
Architects usually develop their designs in drawing-based, graphical forms; prototypes are used to investigate the design concepts. What is important here is that building design is a creative process based on iteration: it consists of a continuous back-and-forth process as the designer selects from a universe of available components and controls options to synthesize the solution within given constraints. Fig. 3 illustrates the evaluation cycle of architectural design.
Fig. 3. Evaluation cycle of architectural design
A full range of architectural issues and criteria have to be considered simultaneously. The goal of design in architecture is to achieve the best balance of performances in a complete set of application criteria (Gero, D'Cruz and Radford 1983). Understanding the design and performance relationships is essential and this can be facilitated through simulation.
In real-life, however, building design often happens in a disorganised fashion and frequently jumps from concept to concept. Energy design is only one consideration amongst many and often not as important and prominent as the others. Since energy performance has usually been invisible, the most that could be hoped for in the past was that the architect would follow some general guidelines for energy efficiency and make sure the design fell within certain constraints (Nall 1985). Since architectural design decisions have a significant impact on building energy performance, it is desirable to improve this area by an efficient simulation environment.
4.2 Efficient Simulation Practice
Fig. 4. Energy analysis in the building design process
To solve a design problem using simulation, care should be taken to consider, inter alia, the nature of the problem and the approach of the investigation. Explicit knowledge on how to translate the problem into proper input and how to use the tool for evaluation is currently lacking. Newton, James and Bartholomew (1988) have suggested seven major steps as a good framework for a successful analysis:
Integration of simulation into the building design process can ensure that important data and information for each major design decision is provided in a timely fashion. By establishing design links and exchange between architecture and engineering, an integrated building design system (IBDS) can be developed. Some researchers have taken the initiative to develop future IBDS for efficient and flexible use of simulation tools. The COMBINE (Computer Models for the Building Industry in Eurpoe, http://erg.ucd.ie/combine.html ) project in Europe (Clarke, et al. 1995; Kennington and Monaghan 1993) and the AEDOT (Advanced Energy Design and Operation Technologies, http://apc.pnl.gov:2080/0projects_and_capabilities/aedot/html/aedot.html )project in USA (Brambley and Bailey 1991) are typical examples.
With the development of computer-aided design, building energy simulation and analysis is an important component in an integrated building design methodology (Augenbroe and Winkelmann 1991). Program development for future simulation tools consists of some of the following features:
|5. Developing Simulation Techniques in Hong Kong|
|To realise the benefit and potential of simulation technology in Hong
Kong, it is necessary to develop more information, experience and skills
about building energy simulation and analysis (Lam and Hui 1993).
Research work is now being conducted in the Department of Architecture
of The University of Hong Kong to provide support to architects and building
designers on the application of building energy simulation tools (BEST)
(Further information about BEST can be found at:http://arch.hku.hk/research/BEER/
). Current research activities focus on the analysis of building
climatic data (ABCD), building up of simulation experience and development
of simulation know-how.
5.1 Analysis of Building Climatic Data
5.2 The Hong Kong Experience
Architects and building designers in Hong Kong often use overseas technology and software for energy design. The aspects in local climatic data and design conditions are based on approximations since well-collated research in this area is lacking. Initial research by Chow, et al. (1994) indicates that the difficulties include not only the shortcomings of the simulation tools but also some unique problems in Hong Kong, such as the time constraint in commercial projects and lack of real building performance data. Analysis of office building energy performance by Lam and Hui (1996) shows that sensitivity technique when integrated into building energy simulation can be a powerful tool for building thermal design and energy analysis. It is believed that technology transfer combined with development of understanding of local conditions and characteristics is the key to simulation technology in Hong Kong.
5.3 Developing simulation know-how
|As computer simulation tools are constantly changing and evolving,
it is useful at this time to outline the current and future development
of building energy simulation. Knowledge about the properties, applications
and limitations of simulation tools is of practical importance because
both current and potential users of the tools are, to some extent, frustrated
and puzzled by the existing programs. To apply simulation tools and
techniques successfully, a clear understanding of the building design process
and its relationship with the simulation environment is advisable since
humans (in other words architects) and not computers dictate the creative
and evaluation process. For maximum efficiency, the integrated building
design systems such as COMBINE and AEDOT currently being developed in other
parts of the world will be an important step for the next generation of
Mathews and Richards (1993) pointed out that the success of a
design tool is only proven when many people in the building industry apply
the tool successfully in practice. To evaluate building performance
and achieve energy efficiency goals, architects and building designers
should take full advantage of computer simulation tools that are readily
available. With a better understanding of building energy simulation
through education and training, it is possible for us to establish confidence
and efficiency in the use of simulation based design tools.