CARBON REDUCTION AND NET ZERO
A diagram comparing open-loop and closed- loop systems.
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Open loop
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-12m
Sand and gravel -84m
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-105m Chalk water saturated
abstraction well rejection well Open-loop system
elements such as concrete floor slabs and internal walls to help stabilise internal temperatures.
n Natural ventilation: Designing operable windows and cross-ventilation strategies in non-clinical zones to reduce mechanical cooling needs.
n Solar control: Using fixed and operable shading (brise soleil, vertical fins) to prevent overheating while preserving daylight.
n High-Performance Envelope n A thermally efficient building fabric is fundamental. n Vacuum Insulated Glazing (VIG): Achieving U-values as low as 0.3 W/m²K, this lightweight glazing solution is especially valuable for retrofitting older façades, where weight or depth constraints preclude triple glazing.
n Airtightness: Designing to meet or exceed Passivhaus benchmarks reduces uncontrolled heat loss and improves system efficiency.
n Insulation and rainscreen systems: Aesthetically flexible and thermally robust, enabling performance uplift while respecting existing architectural identity.
Ground source heat pumps We are fans of solutions like ground source heat pumps (GSHPs), which offer compelling advantages. They use compact underground pipework to extract and deliver efficiently heat and even more cooling, with minimal maintenance requirements – an important distinction compared with air source heat pumps (ASHPs), which rely on large external fans and require more frequent servicing. Additionally, GSHPs demand less spatial allocation, a crucial benefit for constrained new-build sites, and have double the coefficient of performance of ASHPs. Mechanical ventilation with heat recovery (MVHR) systems further support energy conservation. By continuously supplying filtered fresh air while recovering heat from exhaust air, MVHR reduces the need for additional heating or cooling, and improves indoor air quality – key in both clinical and recovery environments. Advancements in solar PV technology have significantly increased efficiency, making it possible – particularly in low-consumption healthcare buildings – to approach or achieve near-grid independence, especially combined with other systems. This not only reduces operational carbon, but also enhances long-term energy resilience. Reducing overall energy consumption and decarbonising
46 Health Estate Journal September 2025 Closed-loop system
must be the primary focus, among wider sustainability measures. These components form the bedrock of any Net Zero
strategy, whether applied to a new hospital, or layered into a multi-phase retrofit masterplan. They allow the mechanical engineering side to be much more efficient, while tackling the subject from all sides opens up better solutions as the energy demand lowers. This is the reason why the collaboration between the architect and the specialist engineers needs to be very close from the project’s beginning. While new-builds are an ideal opportunity to embed
NZC strategies from the start, the bulk of the NHS estate is already in existence. In fact, over 80% of the NHS estate projected to be in use by 2040 is already standing. This means that achieving Net Zero Carbon targets will depend largely on how these existing buildings are retrofitted. Retrofitting is a powerful tool for improving the energy performance of existing healthcare facilities. The benefits of retrofitting are not just environmental, but also financial. By upgrading building insulation, replacing outdated HVAC systems, and installing renewable energy technologies, NHS Trusts can achieve significant energy savings. Architects play a key role in identifying which retrofit measures will deliver the most cost-effective results, taking into account the building’s age, energy use, and condition.
Priority criteria CWA’s approach to retrofitting involves prioritising projects based on energy consumption, patient volume, and structural integrity. By focusing on high-impact upgrades that deliver the greatest savings, architects can help NHS Trusts reduce their energy bills and maintenance costs, all while improving the environmental performance of the estate, which can include: n LED lighting upgrades. n Heating and ventilation refurbishments. n Solar photovoltaic (PV) installations. n BMS optimisations and insulation improvements. n GSHP systems. n Vacuum-insulated glazing.
Achieving Net Zero Carbon in NHS and other healthcare buildings goes beyond design alone; it also requires
Closed loop -121m London Clay
Consistent ground temparature of 10-12 °C
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