Trial / Demo
Congratulations to Asmar for his exceptional submission to anticipate the operational energy yield of this complex project. It is a good example of the balancing act which today’s designers need to address in terms of the multitude of Building Regulations and Building Performance requirements.
Botanic Place highlights the pressure on the design to comply with Leti, UKGBC, BCO23 Well, BREEAM, Nabers -Design for Performance, and Part L England (UK), which presents a significant challenge for the Building Performance Modellers. It’s not as simple as just achieving a low energy and low carbon building but also involves subtle trade-offs to achieve the overall project’s goals.
Asmar also took advantage of the parametric capabilities within IESVE to look at opportunities on different facades of the buildings. With time being one of the major concerns of today’s modellers, the ability to be more productive is key. Using technology such as the parametric tool in IESVE allows for more simulation runs and more analysis, which is all key to maximising a building’s potential.
Botanic Place, Cambridge
Botanic Place is a large-scale office scheme in Cambridge which aimed to achieve WELL Core Platinum certification, BREEAM outstanding and a high NABERS ratings.
A unique heating, ventilation and air-conditioning (HVAC) approach was followed with perimeter-only trench heating and cooling with fresh air through pressurised floor plenums.
To illustrate the anticipated operational energy yield of the project, an energy model was fabricated using intricate ApacheHVAC networks within IESVE.
Comprehensive data provided by the MEP & Design team encompassed details pertaining to the HVAC systems, alongside industry benchmarked information for internal heat gains and expected profiles. Additionally, various supplementary end use scenarios were considered to ensure a comprehensive assessment of the overall energy consumption attributable to the base building.
Fabric Optimisation
Various iterations were carried out in the early stages to optimise the fabric and to provide a balance between heat gains versus heat loss. The glazing system was optimised with reduced ‘g’ values while retaining the ‘u’ values to prevent trapping additional heat within the building.
Off Axis Scenarios
The design was developed using various iterative measures on the DHW (domestic hot water), lighting, ventilation, heating, cooling, ICT and security, informing the team of valuable, strategic improvements to be implemented. This allowed the design to progress and achieve nearly a 41% reduction from the time of the baseline operational energy estimate until the end stage.
The design was also stress tested against any likely scenarios including CIBSE future weather files to estimate the likely impact of climate change, high air permeability caused by the disintegration of windows over time, failure of any mix mode strategy and any HVAC heat recovery failure
The office will have central air handling units (AHU) for mechanical ventilation, supplying fresh air to both the office and additional spaces. The airflow is calculated at 14 litres per second per person. Considering an occupant density of 1 person per 10 square metres, and following the BCO2023 guidance with an 80% diversity factor, the effective density becomes 1 person per 12.5 square metres. Consequently, the adjusted flow rate is 1.12 litres per second per square metre. The air handling system will feature heat recovery during colder external temperatures, with an 80% Sensible Efficiency for office AHUs and 75% for other AHUs.
Mix mode ventilation system to reduce cooling demand
A mix-mode ventilation strategy was developed with the help of the design team. The façade was developed to benefit from free area for cooling energy reduction in the summer and also to reduce the fresh air requirement, by letting the contaminants out through the actuated openable ventilation panels. IES scripted profiles were used to develop the optimum openable free area, internal and external temperature setpoints. The fresh air is provided through the pressurised floor plenums based on the CO2 control with a range of 800ppm to 400pmm.
Solar Gains Assessment
In line with the BCO 2023 guidance, perimeter peak solar gains were tested through IES VistaPro to benchmark against the 40-50 W/m2 target. A few parametric options were closely observed to identify opportunities on different facades of the building.
Industry Benchmarking
When evaluating the Botanic Place Office development against the Operational Energy targets set by UKGBC and LETI for offices, with the aim of showcasing a viable path to achieving Net Zero Carbon by 2050 in alignment with government objectives, the findings revealed positive performance in the landlord areas with respect to UKGBC targets.
