A model retrofit
The integrated modelling workflow utilised for the retrofit building performance optimisation submission, which secured the prestigious Building Simulation Award 2023 for Yorgos Koronaios of Savills Earth, exemplifies the thorough modelling efforts undertaken for the refurbishment of Building 100, Bourne Business Park, a three-storey 2,600 m2 office building in Weybridge.
Savills Earth’s objective was to provide general design optimisation advice from early stages with a focus on façade and window optimisation, conducting feasibility studies and energy strategy optioneering. The scope included support for various modelling studies such as thermal comfort, daylight, and compliance modelling. Additionally, detailed TM54 modelling was carried out that was concluded with a formal NABERS Design for Performance (DfP) assessment that awarded the building with a 5.5-star rating, only one of the few in the UK.
The selection of the modelling tools was made with the aim to provide timely and robust feedback within a demanding timeframe. The tools were use for early fabric and operational performance analysis, complex scenario modelling, interoperability, parametrisation for ease of scenario testing and a single modelling platform for the Stage 3-4 analysis.
The tools selection included:
- Sketchup, designPH and PHPP for Stage 2 feasibility studies.
- Rhino, Grasshopper, Honeybee for Stage 3 daylight analysis.
- EDSL Tas for Stage 3-4 detailed loads, comfort, and energy modelling.
Early Stage 2 included modelling with Sketchup, designPH and PHPP to understand energy demands, test the feasibility of different options and set project specific targets. The combination of Sketchup, designPH and PHPP allowed for a quick feedback loop, where different fabric specifications were tested to understand their impact on heating and cooling demands.
Different ventilation options were also tested, including a fully mechanical option and two scenarios with a mixed-mode approach, which showed that significant reductions on cooling and ventilation demands could be achieved.
To evaluate the impact of these options on project targets, an early-stage TM54 model was built in PHPP with internal gains aligned with NABERS DfP and the available design input at the time. The study indicated that implementing mixed-mode ventilation had the capacity to elevate the performance from one UKGBC Net Zero bracket to another, prompting the decision to integrate it into the detailed design. The key findings and results at this stage played a pivotal role in guiding the client's decision to pursue an official NABERS rating for the building.
Ease of geometry manipulation in Sketchup allowed for quick updates in the model’s form in Stage 3, which was then transferred to Rhino, where it was progressed further to carry out a daylight study using Grasshopper and Honeybee. This model allowed for quick tests on materialities and glazing lighting performance. The results were not only used to inform the BREEAM certification, but also to gain insights into the daylight control conditions in the perimeter zones that were defined by reviewing the resulting lux levels.
Throughout Stages 3 and 4, EDSL Tas software was used to carry out modelling tasks that informed the design further such as load calculations, Part L, thermal comfort and to reinforce the overall design by verifying the performance on various fronts.
In Stage 3, Tas was also used to build a preliminary TM54 model that informed the potential NABERS rating. In Stage 4, more detail was incorporated into the model. This included actual ventilation rates, size, performance, and operation of each individual DX-coil unit, demand-control ventilation details, sizes of selected plant and product-specific parameters such as temperature correction factors and part-load ratios to inform the seasonal efficiencies of cooling and heating plant.
In addition, the proposed BMS weather prediction component was introduced into the model to regulate the operation of windows, AHU and DX-coil units. This was achieved by generating schedules of open/closed-window days through an analysis of simulation weather files and defined operating conditions including indoor temperature thresholds, outdoor temperature limits, wind speed and indoor CO2 levels.
For the DfP assessment, to guide the design process while safeguarding performance, certain risk scenarios were modelled, including one where mixed-mode ventilation was not utilised. This scenario validated the conclusions drawn from the Stage 2 feasibility study, demonstrating how a mixed-mode approach can significantly reduce the operational energy demands of the building.
After concluding our involvement, the design included a high-performing envelope with fixed shading elements in key locations, highly efficient all-electric air-conditioning, mixed-mode ventilation, full LED lighting with daylight control, maximised PV installation and sub-metering of all floors and plant equipment.
This highlights the value of an integrated modelling workflow, as it facilitates early and robust feedback, thereby shaping the decision-making process, fostering a commitment to high performance, and driving the design process from its initial stages all the way to completion.