Smart approaches to perfecting Passivhaus

Improving the performance of new buildings relies on ensuring design achieves the best outcome for natural lighting, thermal performance, and energy efficiency. Passivhaus - with its emphasis on a fabric-first approach to attaining optimal energy efficiency and human comfort - is a highly effective design methodology. It benefits occupants, and it also has big picture benefits for the whole community, because when buildings use less energy, the overall strain on national energy supplies is also reduced.

However, the calculations involved in achieving the ideal outcome can be time-consuming. This also makes it difficult to present early design stage options and the effect of changing aspects of the design to clients or other members of a project team, such as Wall to Window Ratio (WTR) shading, or spatial planning in relation to orientation and passive solar performance.

This has also meant that we do not always get to take full advantage of the early design stage as the least-cost opportunity for testing different options and ideas. The Passivhaus early-stage optimisation tool I developed aims to resolve this challenge and give our designers a means of rapidly and effectively generating outcome-based design options that show how the building will perform when it is occupied.

The tool can deliver data on projected heating/cooling demand, hours of daylight and passive visual comfort, annual energy demand and embodied carbon. The use of parametric modelling gives the user control over the geometric elements of a 3D massing model so the impact of small design decisions and how they affect the energy performance of the final design can be seen in real-time.

When picturing Passivhaus, people often think of detached or low-rise buildings, but it is now an approach being used for many building types including medium-rise and high-rise multi-residential, hospitality, student accommodation and commercial offices. Where the clients or stakeholders have specific goals for energy consumption, knowing how the building will perform is critical. This is particularly the case if projects are targeting a sustainability rating based on operational data, or where the asset owner or stakeholders have committed to net zero carbon goals. It is the early design decisions that have the most influence on whether a building will achieve a specified benchmark.

The tool also gives insight into the experience those inhabiting a space will have, for example it incorporates daylight simulation to show how many hours a day treated floorspace will receive sufficient natural light above the desired illumination threshold. Changes to design geometry can be tested to see how the light levels change. It will also give data on how frequently a building is likely to overheat, which is a direct result of the interaction between mass, building shape and orientation.

Embodied carbon is also calculated, which allows us to see a part of a project emissions footprint that also needs to be where possible minimised for us to meet our collective net zero goals. We can also demonstrate how the balance between embodied carbon and expected operational carbon emissions change when we increase or decrease the amount of insulation in the building envelope.

This approach also supports a project team focusing clearly on operational performance. Implementing concentrates the attention of the project team. Implementing a Passivhaus Planning Package, simulation and embodied carbon into the early design stage brings energy analysis into the forefront of the project, to help the design team make energy conscious decisions through results. This early-stage analysis also assists the later stages of development when more detailed energy analysis is carried out.

Ultimately, reducing carbon emissions through optimising energy efficiency will always be a better option than relying on the purchase of carbon offsets to achieve net zero. Having the ability to rapidly calculate exactly how a building is likely to perform also means we can achieve higher quality buildings from an occupant experience perspective coupled with low ongoing energy costs.

Saving money, increasing comfort, and designing out carbon emissions to the greatest extent possible is a win for everyone - and puts us one step closer to achieving net zero carbon.