Beyond Net Zero: The embodied carbon of MEP systems

Historically, operational efficiency has been the key objective for MEP systems, as their main carbon impacts were emitted during operation. To reduce the whole life carbon impacts of a system, however, we must look at both operational and embodied carbon. As heat pumps replace gas boilers, and as the National Grid decarbonises, the operational carbon impacts of MEP systems are reducing, while their embodied carbon contributions are coming into far sharper focus. 

We have collated our past project embodied carbon data to identify the MEP contributions towards total embodied carbon. In the table below, we have defined our results for upfront (A1-A5) and embodied carbon contributions (A1-C4) of all building services.
MEP contributions are reasonably consistent across building sectors, and mostly higher for refurbishment than new build. This is generally true across the industry, due to the lower architectural and structural impacts of refurbishments. Looking at the jump between upfront (A1-A5) and embodied carbon (A1-C4), we see MEP becomes a higher contributor over a building lifespan. Architectural and Structural impacts are largely upfront, while building services have in-use impacts – such as refrigerant leakage and replacement cycles – which become significant. 

The new version of BREEAM and the new UK Net Zero Carbon Building Standard (UKNZCBS) have defined targets for embodied carbon in both new builds and refurbishments across a range of building typologies. While these provide a useful whole building figure, there is little guidance on targets for specific design areas, such as MEP. Using our data, we have defined an MEP-specific upfront carbon (A1-A5) benchmark, compatible with an NZC future (overleaf). We hope that this will guide low embodied carbon MEP design, and set a reasonable target to work towards. 

While there is much still to learn about MEP embodied carbon, we believe there are certain things that the industry should adopt now:

• Heat pump selection: specify low GWP refrigerants and avoid over-sizing.
• Early-stage optioneering assessments in concept design: consider both embodied and operational carbon to inform design strategy, and minimise whole life carbon impacts.
• Improved modelling accuracy: expansion of an embodied carbon product database is needed to feed into MEP concept designs and specifications. We need to challenge manufacturers to publish their embodied carbon data on product ranges. Currently all models rely on ‘proxy products’ and have a large degree of uncertainty built in.  

In the future, there may be a limit to which we can reduce our impacts through ‘business as usual’ product specifications. As targets become stricter, projects will have to adopt refurbishment and circular economy principles to achieve accreditation. This is a rapidly developing business area, which may change how we approach procurement and specification in construction industry.

Above all, efforts to reduce embodied carbon must be a combined effort of multiple disciplines if they are to succeed. Design decisions are interconnected, and benefits in one area may have impacts on another. Decisions such as plant location and floor-to-ceiling height will have significant implications for MEP design, structure and architecture. Effort should be made to improve our understanding of these relationships, so we can implement low embodied carbon design principles at an early project stage.