How BIM computer modelling can help design buildings that are sustainable

BIM - the models used by architects and developers of buildings - has the potential to mould the design of buildings to save energy, says Colin Williams, managing director at BIM practitioner and consultancy Cadnet Ltd, part of the CADS Group

Using ‘building information modelling’, the energy performance of individual buildings or an entire estate can be evaluated against a standard benchmark or on an individual basis.

BIM provides a platform to rapidly create basic computer models that can be used to simulate the performance of the building envelope and proposed and installed systems.With a clear understanding of the relative performance of a property portfolio in terms of energy use and sustainability, new build, refurbishment and reassignment projects can be prioritised effectively, optimising limited budgets and returning the best value for money while maintaining a positive focus on the environment.

Alternatively, specific projects within a single building can be evaluated and multiple options can be considered before committing to significant expense. Individual technologies or combinations of technologies can be explored to identify the optimal economic and energy-efficient return. Regardless of the type of property in a portfolio, BIM offers a viable solution for delivering auditable, evidence-based results for predicted energy and sustainability performance.

Building construction and operation have a significant impact on the environment. Buildings use resources and raw materials, generate waste, and release harmful emissions. The UK government has set a legally binding target to reduce greenhouse gas emissions by at least 80 per cent from 1990s levels by 2050.

Building designers must respond by utilising the latest tools and processes, like BIM, to deliver new build and renovation projects with optimum energy efficiency and sustainability.

However, designers face a challenge in striking a balance between the ambition to produce green solutions and the expense of a project. Recent studies by the US Green Building Council revealed that energy efficient and sustainable building design increases the initial cost of a building between 2 and 7 per cent. Therefore, those of us planning and designing new buildings need this data to more clearly demonstrate the strong business case for selecting sustainable design options – measured throughout the lifetime of the building.

Beyond the design stages, BIM allows managers to analyse the operation of the building in use. For example, it allows project managers to measure how much energy is used once the building is completed and occupied, and comparing that against the targets set and predictions made while it was still being designed.

Energy analysis can provide feedback on elements such as energy usage, carbon dioxide emissions, whether a building will pass performance criteria (based on certain standards, such as LEED or BREEAM).

This analysis should be undertaken during all phases of the design process; at concept design to set targets; the schematic design stage to compare elements and components through optioneering (trial and review of design alternatives); and at the detail design stage to refine systems’ performance. All these create a design that will achieve or exceed the desired efficiency and sustainability targets for the building’s energy use and indoor environmental conditions.

At the end of the construction phase, an energy consumption target should be calculated for the future use of the building. Throughout construction, the main contractor should ensure that low energy features are assembled, installed and commissioned as designed, ensuring that construction details and specifications remain consistent.

Any changes occurring during construction should be captured as part of the field BIM process, where hand-held portal devices such as tablets capture information and incorporate the detail back into project models. At an agreed point, prior to practical completion, the project team should conduct a final energy review of the construction prototype BIM. This will confirm how the building will perform in respect to the original design targets.

During the commissioning and warranty period, the energy consumption target is updated for the normal operation of the building. By this time, the actual use of the building will be better understood and should be taken into account within the calculations. It is also now possible to capture field data from the equipment which has been installed. As a minimum requirement, the energy usage profiles along with any other assumptions that were used in the energy consumption target calculation for normal operation in the construction phase should be reviewed, and, if necessary, updated. Further continued analyses, where required will depend on individual projects and their specific details.

BIM offers a more comprehensive approach compared to traditional non-model based methods of assessing sustainability in the operational phases of a building, and hence reducing the costs of the building over its lifetime.

‘Post-occupancy evaluation’ is a way of providing feedback from initial concept through to occupation. This is especially important given the current emphasis on improving the ‘green’ aspects of an organisation’s estate portfolio, set against the need to reduce and control costs and the pro-active management of assets to continue to meet users’ needs. By establishing a clear POE and measurement strategy before a project commences, the client is able to provide a clear brief and specific performance targets that can be measured throughout the project. However, clients need to have data already available in order to know what target to set. This is usually achived by benchmarking their existing assets to establish optimal operation and energy use.

Again, BIM can play a key role in the recycling of information as part of this process. By taking the original model and the refined information gained in the commissioning stages, a client can compare the data collected during the POE with the original targets and see how the building is performing.

By recording operational energy and sustainability targets in a model, BIM can be used to address a number of post-occupancy evaluation questions:

• How effective was the process from inception to completion?
• Does the building perform as intended?
• What problems need to be tackled quickly?
• Have the user’s needs changed?
• What can be learned for future projects?

BIM can:

• Continue maintaining and improving energy efficiency through the analysis and comparisons of current and potential systems.
• Hold data on building systems and equipment to help streamline preventive maintenance scheduling.
• Simulate system and component failures and alternative strategies devised for repair or renewal.
• Improve space management by integrating building data with human resources data (such as changes to staffing levels, departments expanding or contracting and needing extra or less space, etc), reducing empty space and predicting future needs.

Evaluations also provide useful benchmark data with which other projects can be compared. The greater the amount of data captured from different projects, the more accurate and useful benchmarking can be achieved. The BIM process can facilitate sharing information from projects from different organisations by creating data so structured that institutions can easily compare their own buildings with those of others.

The owner or operator should aim to ensure that the building operates according to the targets set during design, by monitoring indoor conditions and energy consumption. BIM is dependent on the information available, so the more information is comprehensively and consistenty collected and put into the model, the more accurate the model will be. Energy analyses carried out at this point in the project lifecycle can be used to compare the effects of changes during operation to the original targets that were set during design. Generally data should be collected for a full seasonal cycle so that information on how the building’s systems perform under different seasonal conditions can be captured. Also, it gives users and building managers time to get used to the building and identify any chronic problems.

During this time the client, owner or operator will normally implement and employ the energy monitoring protocol, as well as undertaking energy analyses and simulations. If the necessary money to pay for this is not available, then a specialist energy consultant should be employed to undertake analyses under an appropriately structured annual energy review or audit contract. In the future, monitoring will become increasingly automated as buildings become more intelligent. For example, the use of passive systems and lights out technologies, like remotely monitored/controlled movement sensors, will be used to link feedback from actual use with baseline figures determined during design.

Occupiers need to implement a systematic and consistent methodology to monitor how a building behaves in real life and to make critical decisions to ensure the building meets the energy criteria set in the design. As the generation and storage of building information data is done by different teams, for different purposes and held in different systems, it is difficult to integrate this information into a flexible and interrogable system. BIM can do this, producing useable data for visualisations and simulations.

Unfortunately, one issue is disturbingly clear: currently energy and post occupancy analyses are rarely undertaken, despite the benefits, due largely to the limits of programme, scope and cost. With appropriate adjustments to programmes and contracts to reflect the workload, project teams can be encouraged to deliver accurate models that can support the management of an asset from inception to disposal.

Lack of feedback from post-occupancy evaluations to BIM systems has had a similarly negative impact on life-cycle assessments. An LCA is a technique to assess environmental impacts associated with all the stages of a product’s life from cradle-to-grave. BIM can help facilitate this process by storing data related to each element of the building which can be updated, interrogated and considered in relation to the building as a whole. BIM models can embed data on embodied carbon, running costs, life expectancy and replacement costs, thereby helping an owner understand benefits of investing in materials and systems that may cost more initially but have a better payback over the life of the building. However, key decision makers within projects are currently rarely able to make use of life cycle cost analysis tools due to the lack of meaningful data returned to design teams from post occupancy analysis of previously completed projects. Many organisations carry out POEs. But few use BIM to support their POEs. So there is limited information fed back to BIM models on how an element, e.g. an airconditioning system, performs throughout its life. BIM can hold life cycle data on every element in a building, and in a format that can be used, interrogated and shared.

BIM can support, and even lead, sustainability throughout the design process and beyond, by providing a valuable and useful tool to constantly measure, review and adapt a building to its current and future needs. Developing a sustainable BIM strategy can be challenging. To be successful, facility owners and managers, designers and contractors need a focused and cost-effective way to analyse building performance and prioritise refurbishment and reallocation. Clients often find it difficult to move beyond the design and build stage and consider the benefits of using BIM techniques through the whole life of the building. This is perhaps because so few exemplar projects exist.

Detailed energy analyses and sustainable design take longer - and as a result cost more at the start of a project - but the additional cost will be dwarfed by the potential savings in terms of reduced energy costs, improved environmental conditions and pro-active use management over the lifecycle of the asset. Even with the emphasis on making savings today, clients must consider the broader picture and take a long-term view of their estate.