Optimising environmental performance using building performance simulation
It can be argued that industry’s use of computer simulation has not kept up with the potential contribution this technology can make to the design and construction of buildings.
We use the visionary South Australian Health and Medical Research Institute (SAHMRI) building as a case study of how dynamic thermal simulation (energy modelling) and daylight simulation methods can be optimally applied to enhance the environmental performance of a new building.
Computer simulation of a building’s environmental performance typically embraces three related but separate applications:
Dynamic thermal simulation of a building is the assessment of heat flows, internal thermal loads, and solar loads throughout a building to calculate achieved space temperatures and energy use
Daylight simulation refers to the calculation of daylight levels under typical conditions experienced at the site. Increasingly, the technique is being used to understand the risk of glare occurring for particular built-forms and facade properties
Computational fluid dynamics (CFD) calculates airflow and temperature patterns within individual spaces or in the surrounding external environment. While CFD is frequently used to demonstrate and improve building performance, the extensive wide-ranging capabilities of this tool are not discussed in this article.
How the potential of building performance simulation can be missed
Simulation is most commonly used for National Construction Code (NCC) and sustainable rating tool compliance.
In theory, simulations of this type can provide significant value to projects by freeing the designer from the constraints of Deemed-to-Satisfy (DtS) processes within codes and standards.
In practice, much of this potential value is lost because the analyses are undertaken well after the major design decisions have been made. The work becomes merely a validation of existing design rather than a tool for innovation or optimisation and fails to capture the full value of simulation.
Optimum use of simulation
The best value is obtained from simulation when it is used to inform all stages of building design and construction from concept through to post-construction.
The largest opportunity for built-environment designers is to use simulation to compare design decisions and opportunities during concept design. This requires buy-in from the whole design team, not just architects, in order to reach a common optimised goal.
Preliminary analyses can be used to inform key design decisions e.g:
Building siting, massing, layout and orientation for energy, daylight and external wind flows
Glazing size, shading and type for energy and daylight
Comparing different HVAC systems or central plant types for relative energy efficiency
Performance goal setting (e.g. NABERS, Green Star, Net Zero) or preliminary feasibility assessment
There are many software tools that can be used in early modelling.
Figure 1: Opportunities for the use of simulation throughout the design and construction process
Design Development – optimising systems
In design development, simulation has a myriad of uses informing the decisions of architects and engineers. Key opportunities include:
Detailed development and testing of glazing and shading design
Space design for daylight optimization
Right-sizing of mechanical plant
Design of more complex mechanical airflows
Natural ventilation through buildings
Testing efficiency options such as alternative mechanical systems and heat recovery
Optimising central plant sizing
There is extensive use of rule-of-thumb and spreadsheet calculations for preliminary equipment sizing. Such methods tend to routinely oversize plant items, causing unnecessary capital costs and poorer efficiency. The additional costs typically far outweigh the costs of simulation. Timely use of building simulation can also highlight other issues before design is finalised, saving time and money as well as optimising building performance.
Construction Documentation – optimising controls, documenting anticipated results
In construction documentation, the opportunities for changing design have largely passed, but simulation can still continue to add value through:
Testing and optimising control ‒ The energy efficiency and comfort of modern buildings is highly dependent upon control
Testing the full design against project goals ‒ The construction documentation phase is the last chance to simulate performance versus project goals. Late-stage design adjustments can be made
Testing compliance ‒ Many buildings will have NABERS, Green Star or NCC JV3 compliance requirements. Simulation models are needed to ensure that the final design delivers the required outcomes
Post-construction – verifying results
The use of simulation in post-construction performance verification is increasing, providing opportunities for improvement in control commissioning, tuning and modelling.
Case Study: SAHMRI
Figure 2: SAHMRI completed facade showing hood geometry
Although still not commonplace, a performance-based approach to simulation in the early building design stage can have impressive results. SAHMRI, and in particular its striking facade solution, is a product of performance-based design that balanced aesthetics, cost, and buildability, as well as environmental variables such as solar control, daylight availability, glare and thermal comfort.
SAHMRI is a 25 000 m2 research facility. Its design team included Woods Bagot, Atelier Ten, Cundall, NDY and Aurecon.
Key to the success of the design was developing quantifiable performance metrics upfront to allow robust testing of options between the environmental design consultant, Atelier Ten, and architect, Woods Bagot.
Fig 3 summarises the metrics and outcomes that could be impacted by the facade alone:
Figure 3: Impact of facade on building performance
Space versus energy planning
The first step of the facade optimisation process was to assess which space type required access to daylight and which spaces lent themselves to opaque elements. With the three-dimensionally curved form of the building and significant facade structural spans across multistorey atria, a triangular grid-shell solution was selected as the most appropriate facade system. Nine variations of exterior shading devices were simulated.
Regardless of the space type selected to sit behind a particular piece of facade, limiting direct solar gains was crucial in reducing HVAC plant size, energy consumption, risk of glare and improving thermal comfort.
However, the value of the simulation was in freeing the designers to select an external shading strategy optimised for cost and buildability rather than purely for energy savings.
Key comfort factor
With the facade significantly affecting thermal comfort, daylight and glare – the performance discussion focused on making an attractive, healthy workplace ‒ the Wellness factor for the occupants of this visionary building.
General comments on simulation
Quality assurance The phrase ‘garbage in, garbage out’ is as relevant to building simulation as to any other form of computing. The temptation is also ever present to accept results at face value leading to mistakes reticulating through to the final results without question.
Timing Time needed to create a simulation model varies widely. Some software tools, especially those designed for use during concept design, can provide peak load and energy consumption results instantaneously, once a 3D model has been created or imported; whereas a fully-detailed thermal simulation of a detailed design can take much longer. Once the base model is produced, design refinements and operational scenarios are typically quite easy and quick to produce.
Computer simulation gives design teams the opportunity to test building performance during the design process through to post construction. Correctly used, a simulation can return many times its cost to a project. However, often simulation is used purely for compliance with NCC JV3, Green Star or NABERS; this undervalues the simulation and wastes much of its value potential to a project.
Design teams should use simulation as an integral part of the design process to enable better design decisions to be made throughout the entire construction process.
This article is an abridged version of the original paper published in Environment Design Guide – EDG 91 NP October 2017. Reproduced with permission from The Australian Institute of Architects.
About the authors Nicki Parker Nicki has recently taken up the position of Norman Disney & Young’s Sustainability Manager for Brisbane after an 11 year career in building physics and sustainability.
Quentin Jackson Quentin is an Environmental Modelling and Sustainable Design specialist and leads Aurecon’s Sustainability team in Queensland.
Dr Paul Bannister Dr Paul Bannister is Director of Innovation and Sustainability at Energy Action. He is an internationally recognised authority on energy efficiency in commercial buildings and is the primary technical author of the NABERS Energy and Water ratings systems.
Paul Stoller Managing Director of Atelier Ten’s Australia offices, Paul Stoller is recognised for environmental planning and design consulting work on large-scale campus, community and urban building projects.