When it comes to carbon emissions in building services, attention is often drawn to operational energy, and how efficiently a building performs when it is being used. Another significant piece of the puzzle, though, is embodied carbon. This term relates to the greenhouse gas emissions associated with a product’s entire life cycle, which includes pre-use elements such as manufacture, transport, installation, as well as maintenance, and eventual disposal.
Embodied carbon can be a significant consideration in building services systems, particularly within large MEP equipment. The challenge, though, is that a lot of MEP products don’t carry Environmental Product Declarations (EPDs), which means accurate carbon calculations are difficult to carry out.
In a forward-thinking bid to address this gap, the Chartered Institution of Building Services Engineers (CIBSE) has developed TM65, which provides a practical methodology, enabling engineers and designers to estimate embodied carbon even when detailed data is unavailable. There are two calculations within this methodology:
1. Basic Method – This method utilises basic data like product weight and material composition, allowing a quick estimate of embodied carbon. This can be useful when only limited product data is available.
2. Mid-Level Method – This requires more detailed information, which includes the energy used during manufacturing and transport distances. Whilst this data takes more effort to source, it provides a more accurate carbon estimate, increasing its value when the priority is accurate data.
A practical example can really provide context in these situations.
If we look at specifying an Air Handling Unit (AHU) for a large office in Scotland, this AHU might weigh 1,200kg with a composition mostly of steel and aluminium, transported 800km to site.
With the Basic Method, calculating the embodied carbon may result in an estimate of about 20 tonnes CO₂e. The weight and material type are the only considerations in this calculation, resulting in a broad approximation.
If you happen to have more data available, for instance the manufacturing energy consumption and transportation carbon intensity, the Mid-Level Method may provide a figure closer to reality, perhaps around 25 tonnes CO₂e. Across a large project of AHUs, an additional 5 tonnes CO₂e can quickly add up.
If TM65 is adopted, engineers can make informed decisions as they specify equipment. Examples of this include choosing lighter materials, if possible, to reduce embodied carbon, reducing replacement frequency by specifying longer-lasting products, Specifying low-GWP refrigerants in equipment to reduce indirect emissions and focusing on modular, reusable systems.
As we cement embodied carbon as a key metric in sustainable design, TM65 provides a practical framework to assist in moving the industry towards net zero. Not only is it about how efficiently we operate buildings, but how sustainably they’re constructed and maintained from day one.
CIBSE TM65 has game-changing potential for MEP professionals. It equips us with the tools to estimate embodied carbon even with very little data, which can lead to smarter, more sustainable design decisions. The TM65 methodology provides encouragement to the industry to try to look beyond operational energy and take the entire lifecycle impact into account when specifying MEP equipment.
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