CARBON AND ENERGY REDUCTION
reducing unwanted heat gains and glare that will reduce the building’s operational energy needs across the year. Taking a ‘fabric first’ approach for the hospital envelope design will reduce energy demand further through integrating PassivHaus principles such as a low form factor, a highly insulated and airtight façade, utilising heat exchangers, and avoiding thermal bridges to eliminate any heat losses through the building envelope. This early climate and thermal modelling analysis allows us to make design decisions based on data evidence in consultation with all stakeholders, and also provides cost and performance certainty to create the most efficient and low-energy hospital form. It is therefore important to allocate adequate design analysis time within the project at early briefing and concept stages, to ensure that critical themes and resource are included early on in the design process.
Research into passive design’s benefits
NBBJ and Hoare Lea are developing research into sustainable hospital design methodology and a digital tools palette that can help leverage the energy-saving benefits of good passive design. Simulation tools for early micro-climate simulation studies can determine the optimal built form best suited to the local site wind and solar orientation. Design studies prove that a building with a compact form factor and carefully placed façade shading is better for lowering energy footprint by reducing cooling loads. Our analysis shows that a window to wall ratio target of 30-35% can be achieved without risk of overheating, by finding the optimal limit for designing a highly insulated façade, without compromising on good daylighting and views. With daylighting and carbon analysis tools we can test the performance of different building morphologies in early concept stages to choose the one that achieves the biggest carbon and energy reductions.
kWh/m2 600 500 3% 7% 9% 400 10% 7% 300 13% 200 Operational carbon target
100
0 Base 1 2 3 4 Design interventions
Early design decisions on optimising façade and building engineering systems can substantially reduce energy use, and establish achievable Operational Energy Targets reductions from existing buildings’ actual energy use benchmarks.
1400 Embodied carbon target 1200 1000 800 600 400 200 0 Base 1 2 3 4 Design interventions
Early analysis supported by digital tools can help assess a building’s potential for reducing Embodied Carbon in construction materials that inform concept design decisions. Put together, these establish the achievable Embodied Carbon Targets.
3: Lower climate impact
A net zero carbon hospital design should track both operational and embodied carbon, with the aim of reducing its carbon emissions and impact on climate change as much as possible. After establishing clear performance benchmarks and an optimised building form, the next step is to design the most efficient energy systems
that minimise the hospital operational energy demand and reduce its carbon footprint. Early design analysis for optimising architectural form can be integrated further into detailed engineering energy models, and used to accurately measure performance, budget, and whole lifecycle assessments, over time. Hospital clinical functions have varying requirements for heating, ventilation, and cooling, occupancy patterns, and hi-tech equipment loads. So, a better operational zoning of services tailored to the varying energy intensity of departments is key to designing efficient building systems that meet specific energy demands.
Reducing energy bills
NBBJ and Hoare Lea have undertaken joint research into sustainable hospital design, using solar irradiance mapping and climate data digital simulations to arrive at the best building shape for maximising the potential for on-site solar PV renewable energy generation.
Designing smaller plant sizes that serve smaller energy zones tailored to sensing occupancy patterns can potentially achieve annual savings in energy bills by switching off when they are not needed, as well as saving embodied carbon in MEP services. Significant energy savings can be made by re-utilising waste heat generated from occupied spaces and
September 2021 Health Estate Journal 67 5 6 Target 14% 8% 11% 7% 15% 12% 5 6 Target
©Hoare Lea
kgCO2
e/m2
kWh/m2
.year1
Typical footprint >50% GGBS Recycled finishes Structural frame Façade materials Sequestration Glazing Good practice ©Hoare Lea ©Hoare Lea
Typical footprint Glazing ratio Adaptive set points U-values optimised Enhanced lighting Efficient fixtures Heat pumps Good practice
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