Cagni Williams Energy supported the transformation of a Grade II-listed townhouse in Chelsea through the integration of a ground source heat pump system providing renewable heating, cooling and domestic hot water. Working within the constraints of a historic building and a dense urban setting, the project demonstrates how deep retrofit can be achieved where conventional low-carbon solutions may not be appropriate.
The client required year-round thermal comfort, including cooling during increasingly warm summers. The project therefore focused not only on replacing fossil fuel heating but also on introducing resilient low-carbon cooling in a discreet and architecturally sensitive way.
Ground Source Energy in a Dense Urban Environment
A key challenge was identifying sufficient space for ground-source infrastructure within a constrained central London site. Geological studies confirmed that deep vertical boreholes could provide the required energy capacity. Two boreholes were eventually installed within the narrow front lightwell, enabling the system to be delivered without compromising the garden or surrounding streetscape.
The boreholes serve a 22kW ground source heat pump located within the building's former coal vault, replacing the existing gas boiler and creating an all-electric heating solution.
Heating, Cooling and Ventilation Strategy
The heat pump supplies low-carbon heating to retained radiators and underfloor heating while also producing domestic hot water. During summer months, the same system provides cooling through ventilation units fitted with chilled-water coils. Rather than using visible fan-coil units, conditioned air is delivered through discreet linear diffusers with ducts integrated within the walls and ceiling voids. Mechanical and electrical equipment is concealed beneath the front entrance and within the attic space. Air is extracted cleverly via the existing chimney stacks.
This approach allows the building to maintain high standards of occupant comfort while preserving the character of the listed interiors.
Carbon Reduction and Future Resilience
At feasibility stage, the project team estimated annual carbon savings of approximately 4.7 tonnes of CO₂ compared with the previous gas-heated arrangement. Ground source heat pumps can typically reduce operational carbon emissions by 70-80% when replacing gas heating systems while significantly reducing reliance on fossil fuels.
Beyond carbon reduction, the project demonstrates a practical model for introducing renewable heating and cooling to heritage buildings and space-constrained urban sites. The lessons learned have informed wider studies into shared ground-source infrastructure in Chelsea, including the proposed Sydney Street Heat Network.
Consultant Team
- Cagni Williams: Architects and Lead Designer
- Cagni Williams Energy: Design Integration and Project Management of technical services
- Levrant: Heritage Consultant
- mstep: Building Services Engineer (MEP)
- Genius Energy Lab : Ground Source Heat Pump Specialist Consultant
- GSI Drilling: Groundworks and Drilling Contractor
- Elite Renewables: Ground-source heat pump installation
- Dominik: Main Contractor
