TECHNOLOGY
CREDIT: STEPHEN PAAR the Croydon site offered a clear test case for retrofitting rather than rebuilding. The goal was to remove all fossil fuel gas use from the site, and achieving this relied on numerous strategies.
The retrofit works by cutting carbon at the point of intervention, instead of starting again with a high-carbon rebuild – new foundations, steel and concrete carry a heavy embodied carbon cost that can take years to offset.
The building was divided into two distinct environments. The office side, which is well sealed and insulated, was suited to heat pumps, upgraded ventilation and improved controls.
The maintenance shed required a different solution because heat in a large open space is quickly lost when trams move in and out.
“ We previously had big gas boilers which were blowing hot air into a big open space,” Dan explains.“ As soon as the doors open and the trams come in and out, all that hot air would escape. So, we went for infrared heaters – the key difference is we’ re heating the person, not the space.” Not only has this boosted the efficiency of the site, it has also made for a very happy – and warm – workforce, not least during colder months.
Swapping fossil fuels for solar The retrofit removed fossil fuel gas use by combining solar panels, heat pumps, infrared heaters and energyefficiency upgrades, resulting in lower operational carbon and a more comfortable workplace for staff maintaining the tram fleet.
“ Solar panels, heat pumps and infrared heaters have transformed the depot,” Dan says. The rooftop solar array is a key part of that equation. The installation has a capacity of 187kW peak that supports the depot’ s electrical demand and helps offset the building’ s new electric heating load. That balance matters in retrofit projects, where the aim is not simply to swap one fuel for another, but to reduce total energy use as well.
“ Retrofit usually gives a lower upfront carbon cost,” Dan says.
Transport for London assesses projects on a whole-life carbon basis, meaning
58 August 2026