Optimising environmental performance using simulation

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15 October 2020 | 7 min | White paper

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.

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 opportunities for the use of simulation include:

Concept design

Establish environmental performance goals, align with project team
Perform modelling to inform early design decisions regarding: building siting and orientation, geometry, massing and program layout, passive strategies, glazing size and location, shading and daylight strategies
Preliminary compliance checks (NCC, NABERS, Green Star)

Design development

Space design for daylighting
Optimisation of natural or mechanical ventilation
Right-sizing of mechanical equipment, other mechanical system design decisions

Construction

Optimise operational and control strategies for mechanical systems, daylighting controls
Finalise performance calculations to text against project goals
Compliance calculations (NCC, NABERS, Green Star)

Post-construction

Establish post-construction targets for the building and its sub-systems
Calibrate model against actual post-construction use and use this to inform post-construction monitoring and tuning

Concept design – the biggest opportunity

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.

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

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

The South Australian Health & Medical Research Institute

Although still not commonplace, a performance-based approach to simulation in the early building design stage can have impressive results. The South Australian Health & Medical Research Institute (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 000m² 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.

Building performance simulation is an opportunity

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.

Co-authors: Nicki Parker, Dr Paul Bannister, Paul Stoller

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.