So how do you convert a vast hospital complex, currently using steam or high-temperature water heating systems, to a low-carbon alternative? While there are numerous options available, many are unsuitable for hospitals due to high costs, space requirements or reliability issues.
Biomass boilers, for example, have high particulate and NOx emissions that make them unsuitable for most hospital sites. Biomethane boilers use anaerobic digestion to produce methane as a replacement for natural gas. But the size of anaerobic digesters required to supply enough methane for an entire hospital means they are economically – and practically – unviable.
Solar-powered water heating can be used to provide reliable hot water during the summer, but during UK winters there is insufficient sunlight to produce enough heat, meaning solar thermal alone is not a year-round solution.
Hydrogen is likely to have a role to play in decarbonisation for the UK, by reducing demand for gas. It is already used in some large-scale industrial processes, where combustion is required to generate high temperatures. Currently, these networks predominantly use ‘grey’ hydrogen, the production of which generates carbon emissions. Green hydrogen, which is produced using electrolysis with no associated carbon emissions, is unlikely to be widely available until around 2040 – too late to meet the NHS zero-carbon target.
One simple option is to convert existing gas boilers to electricity – heating the water with an electric coil. This could be used in combination with solar thermal, to provide a back-up when the sun isn’t shining, and to meet the requirement for water to be heated to above 80°C weekly to prevent Legionella. However, electric boilers are an extremely expensive way to provide heating.