Decarbonising a prime London commercial asset through advanced heat pump retrofit
Retrofitting low-carbon technologies into existing buildings is critical to achieving net zero, but doing so within constrained plant spaces and fully occupied environments requires a highly engineered approach.
At 45 Mortimer Street in central London, NG Bailey supported Great Portland Estates in transforming an ageing, fossil fuel-based system into a modern, low-carbon heating and cooling solution, aligned with the client’s wider decarbonisation strategy.
Faced with obsolete chillers and end-of-life gas boilers, the project moved beyond a like-for-like replacement. Instead, it redefined the building’s energy strategy, introducing a fully integrated heat pump system designed to reduce operational carbon while maintaining performance for tenants.
NG Bailey was initially appointed to validate and review the existing building services before developing the design through to construction, ensuring the final solution was both technically robust and deliverable within the constraints of an operational commercial building.
Reconfiguring building services for low-carbon performance
The scheme replaced two 650kW gas boilers and legacy chiller plant with a cascade system combining air source and water source heat pumps, delivering efficient heating and cooling to landlord systems and tenant areas.
Integrating this new infrastructure within the existing building presented significant spatial and structural challenges. The roof, already constrained, had to accommodate new plant, acoustic enclosures and associated pipework, all while maintaining safe access and egress.
To enable this, we undertook detailed modelling and coordination, supported by structural assessments to accommodate new loads. This included the installation of an 8,400-litre thermal store, requiring bespoke spreader steelwork to safely distribute weight across the existing structure.
The system was further enhanced through the integration of a dedicated Trane sequencer control strategy, enabling optimised operation of the heat pump systems and improving overall efficiency by staging plant in response to demand.
Delivering complex retrofit works in a live building
Maintaining uninterrupted service to tenants was a critical requirement throughout delivery. The building remained fully occupied, requiring all works to be carefully phased and coordinated.
Temporary systems and seasonal planning were used to ensure continuity of heating and cooling, including maintaining backup boiler provision during key stages of the installation.
Logistics added further complexity. Crane operations, plant positioning and access had to be precisely planned within a constrained central London site, while early procurement was essential to manage long lead-in times for specialist equipment.
Partway through delivery, the decision to integrate the new sequencer control system required elements of the scheme to be re-engineered, demonstrating the flexibility and technical capability of the project team to adapt without impacting overall progress.
Enabling decarbonisation through intelligent retrofit
This project demonstrates how existing commercial buildings can be successfully transitioned away from fossil fuels through carefully engineered retrofit solutions.
By replacing gas-fired systems with heat pump technology and integrating advanced controls, we have supported Great Portland Estates in taking a meaningful step towards reducing operational carbon, without compromising building performance or occupier comfort.
The scheme highlights the importance of early-stage technical validation, collaborative design and precise delivery planning in unlocking decarbonisation within complex, live environments, a challenge that will be central to the future of the built environment.