HABITAT-CTI ISSUE 4

Sustainable Architecture and Simulation Modelling


Ken Beattie
Dublin Institute of Technology
Dublin
Ireland
Tel: +353-1-402-3000
Tel: +353-1-402-3999
Email Kbeatie@DIT.ie

Overview

Sustainability

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Fig.1 The 4D computer simulation allows a range of dynamic performance software to be carried out.

Sustainability is part of a trend to once again consider the whole instead of specifics. Sustainability emphasises relationships rather than pieces in isolation. The ecological movement has focused attention during the last century on the degradation of natural systems. This brings to light the connections between natural and human communities and between nature and culture. Sustainability has come to mean that we are one species in a web and that we are dependent on the natural world for our survival.

There is a growing awareness and acceptance that population growth, resource consumption, and pollution are combining to weaken the ecology of the planet. There is evidence to suggest that we are altering the energy flows and material and nutrient cycles of the planet significantly enough to endanger and threaten a healthy future for humans and many other life forms.

As the built environment is the main consumer of resources (materials and energy), a society in pursuit of sustainability must now, and in the future, concentrate on sustainable architecture.

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Sustainable Architecture

Before the use of the term "sustainable architecture" became widespread, the term "solar architecture" expressed the architectural concept of a reduction in the consumption of natural resources and fuels via the capture of available solar energy through appropriate building design. The evolution of this design approach has brought us to the current and broader concept of "sustainable architecture". This term can be used to describe an energy and ecologically conscious approach to the design of the built environment.
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Simulation Modelling

The 4D computer simulation software from Integrated Environmental Solutions (IES) allows a range of dynamic performance assessments to be carried out on a building’s design using one computer model of the building. IES 4D applications which are suitable for use in this field include RADIANCE (Photo-realistic lighting simulation); SUNCAST (Solar mapping and insolation studies); MACROFLO (Simulation of infiltration and inter-zone bulk air flow); MICROFLO (Computional Fluid Dynamics simulation of air flow) and ESP (Simulation of building energy and occupant comfort).
The undergraduate students at Dublin Institute of Technology are introduced to IES simulation software in the third year of their course and use it in their fourth year design projects. Masters research students at the Institute are also using the software to provide information for their theses. The undergraduate students are encouraged to evaluate the interrelationship of the sun, wind and the building’s form and orientation so that its design can be optimised to achieve the maximum contribution to natural light, natural ventilation and solar heating. This significantly reduces the requirement for fossil fuels, limits carbon dioxide emissions to the atmosphere and contributes to sustainable building design.
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One Model of the Building

The use of one computer model of a building for all performance assessment evaluations is seen as having a great advantage in terms of time savings for the students as the building geometry need only be input once. The other advantage is that when the students are, for example, trying to optimise their building facade design in terms of thermal performance, natural ventilation and daylight, they are comparing results on the basis of the same window design, percentage glazing ratio, obstructions from adjacent buildings etc. The model of the building can be easily up-dated to allow evaluation of changes to important design parameters.
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Solar Mapping

The solar mapping program, SUNCAST, is used to analyse passive design features, the effects of surrounding buildings, and insolation "hot-spots". The output from this program can be used with the thermal analysis program ESP. The ESP program analyses the building’s performance dynamically over the whole year and the students are keen to make as much use as possible of available solar energy.
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Natural Ventilation versus Air Conditioning

The students carry out peak temperature checks on their design to see if air conditioning is required. Using the periodic steady state admittance method, the students found that this method substantially overestimated the peak temperatures in the building. This was particularly the case with office buildings, as it did not allow for the ability of the building structure to absorb the radiant element of the incidental gains (gains due to lights, people and equipment). As the incidental gains can be a significant percentage of the total gains, reliance on the admittance method would have shown that air conditioning was required in many instances, when in fact, natural ventilation would have provided satisfactory conditions.
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Building Facade Design

Design of the building facade is an important element in the final year thesis. This must be optimised so that adequate daylight is allowed in to the building to provide the occupants with a feeling of well-being. Thus the use of air conditioning will be avoided, solar gain will be maximised over the whole year and heating energy demand will be curtailed. The RADIANCE program is used to evaluate daylight possibilities. By avoiding the use of air conditioning, the ESP program assumes that the convective component of the incidental gains is experienced instantaneously. It is assumed that the radiant portion of the incidental gains behaves in a similar manner to short-wave radiation entering a building and is apportioned among the internal surfaces. The thermal capacity of the building facade available to absorb these radiant gains is governed by the materials used and the position of the insulation. The students input realistic values for the gains due to lights, people and equipment and specify their convective/radiant split. The database of materials in the program is used to design the facade so that peak load is reduced by storage in the building fabric, so avoiding the use of air conditioning. The ESP program can be used to give the dynamic temperature profile of the building fabric at each hour of the simulation run, in order that the students may see the contribution that surface temperatures make to room air temperature. When undertaking an evaluation of the contribution of solar energy to a reduction in auxiliary plant heating demand, it is important to know the contribution that is already being made by lights, people and equipment and the ability of the structure to store heating energy. An accurate hour by hour profile is set up for the incidental gains. This is used in ESP to evaluate the ability of the structure to store energy and calculate the auxiliary heating required.
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Student Performance

Final year student, Roger Cladingboel, started his thesis by considering the embodied energy of the building materials in his building design. The embodied energy for his building was obtained from the IDEAL program (its Sketch design feasibility application). In order to maximise his design he used ESP on the same model of the building to check its dynamic thermal performance and MACROFLO to ensure that his natural ventilation strategy worked. Some of the output from the 4D programs were used in a Powerpoint presentation which helped him win the CIBSE (Ireland) student competition this year.

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