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
• Optimising insulation
• Space design for daylight optimisation
• 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

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

Background

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.

Figure 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. 

Conclusions

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

Quentin Jackson
Quentin is a Technical Director and leads Aurecon’s Sustainability team in Queensland. He is a Green Star Accredited Professional and a 2020 Green Star Champion. In 2020, Quentin was appointed President of the International Building Performance Simulation Association (IBPSA) Australasia where he looks forward to expanding the membership to other parts of the building value chain (architects, building owenrs etc) and continuing to use simulation to reduce our planetary impact. Quentin is also a Climate Leader for The Climate Change Reality Project, led by former US Vice President Al Gore.

Nicki Parker
Nicki is Senior Associate, Sustainability Manager at Norman Disney & Young.

Dr Paul Bannister
Dr Paul Bannister is Director of Innovation at DeltaQ. 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.