Uponor discusses the UFH and cooling installation at TfL’s Old Oak Common depot

James Griffiths, Head of Specialist Projects at heating, cooling and plumbing specialist Uponor, discusses the underfloor heating and cooling installation at Transport for London’s Old Oak Common depot for the Elizabeth line.



esigned to accommodate up to 33 trains while routine maintenance is carried out, the Elizabeth line train depot at Old Oak Common in west London has been constructed with a clear focus on energy efficiency across all aspects of its specification.

Constructed for Bombardier Transportation UK by principal contractor Taylor Woodrow, the facility opened fully this summer but has already garnered two UK Rail Awards and a Green Apple environmental award. It has also been named as ‘Highly Commended’ in the NCE 100 Awards.

The reason for all these accolades is clear: to manage the demands of such a huge facility, renewable energy has been combined with technologies that require reduced thermal loading to drive down CO2 emissions and operational costs.

The underfloor heating and cooling system designed and installed for the project by Uponor has played a critical role in this energy strategy by optimising the maximum potential for heating and cooling outputs using the lowest possible water supply temperatures, powered by geothermal heat pumps and leveraging the thermal mass of the concrete structure.

Renewable energy

The Old Oak Common depot includes a covered shed with inspection pits, cranes and test facilities to enable maintenance teams to work on seven trains at any one time. There are two automatic train washing machines, along with a specialist cleaning area to provide graffiti removal and under-frame cleaning, and the depot also includes office accommodation and storage facilitates for parts, tools and cleaning supplies.

Uponor was originally involved in discussions about potential heating and cooling solutions for the depot at concept stage in 2012/2013, following similar large-scale transport sector projects it’s delivered in mainland Europe. Design of the underfloor heating and cooling system then began in earnest at RIBA Stage 2, when GI energy was engaged to design and specify the hybrid energy solution for the facility.

Old Oak Common’s energy is provided by a combination of sources, including a ground source heat pump, with peak heat of 900kW and peak cool of 560kW, energy piles and boreholes, a 530kWe/560kWth CHP unit, a 1500m² solar PV installation and a 220m² solar thermal installation. Around 54% of the depot’s heating and cooling will be provided by renewable energy sources, with 20% of electrical load generated by the CHP and solar PV installation.

Leveraging thermal mass

The Uponor underfloor heating and cooling system was identified as an ideal solution for the depot early in the design process for the facility thanks to its ability to optimise the thermal mass of the concrete structure, thereby reducing the amount of heating or cooling load required for a comfortable, ambient temperature. The ability to zone the system to provide different levels of heating and cooling also presented a distinct advantage as this has enabled a single solution to be specified across the offices, two workshops, the bogie and the platforms and tracks; a total area of 22,836m2 with varying heating and cooling needs in different locations.

The sheer size of the installation presented design challenges for Uponor; while the volume of concrete in the structure ensures that the efficiency of the system is optimised due to the structure’s ability to store and transfer heating and cooling, the installation involved finding an energy-efficient means of circulating the low temperature hot water (LTHW) within the structure.

The response was to specify 2000m of Uponor’s pre-insulated Ecoflex pipe to take the LTHW from large, bespoke manifold headers to the individual underfloor heating and cooling distribution circuits within the building, along with 76,000m of 20 and 25mm Uponor PE-Xa pipework, which was cast into the fabric of the building during construction. This provides a permanent and virtually maintenance-free heating and cooling infrastructure across all areas.

The Uponor team designed, specified and installed the system as a turnkey project, working in close collaboration with the design and construction partners, resulting in an installation that delivers water into the system within a temperature range of 15 to 20ºC for cooling and a range of 30 to 45ºC for heating. The completed installation requires a maximum energy load of just 600kW for cooling and 1150kW for heating and, thanks to a fully-integrated building management system, the temperature of the water in the system will automatically adjust to seasonal changes, aligned to the optimum temperature set for varying work areas.

Scale and savings

Fully opened in summer 2018, Old Oak Common is one of the largest rail depots in Europe. It demonstrates the benefits and flexibility of underfloor heating and cooling within multiple work environments in a single project.

The inspirational energy strategy for the Old Oak Common depot also offers proof of the financial viability of a low-carbon, low-energy approach. The renewable and low-carbon approach is estimated to have increased CAPEX for building services by 5%, but the net reduction in end-user costs is forecast to be around 33% of the building services’ CAPEX, providing a 1500% return on investment against that modest increase and payback within 10 years.

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