Air handling units Embodied
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MATERIAL WEIGHT BREAKDOWN
carbon in AHUs
Bruno Guedes, Airedale AHU product manager discusses the challenge of measuring embodied carbon in bespoke air handling units
a conservative estimate of the embodied carbon for any MEP product in the absence of an EPD. At Airedale we are now in a position to provide a mid-level embodied carbon calculation in line with the TM65 calculation method, along with the design data of each and every of our bespoke AHU products, from initial design stage.
What we’ve learned so far E
mbodied carbon refers to the emissions associated with the process of extracting and transforming materials used for the
manufacture of a product, as well as those associated with the assembly, transport, installation, maintenance, repair, disassembly, and disposal of the same product. On the other hand, operational carbon refers to emissions associated with the operation of the product throughout its lifecycle (e.g. its electricity usage when in operation). Environmental Product Declarations (EPDs)
are the most reliable method to assess the environmental impact of a product, including its embodied carbon, at every stage of its lifecycle. However, the development of EPDs requires the involvement of an EPD operator, as well as third- party certifi cation, which can be a lengthy and expensive process. Bespoke AHUs are designed from scratch, with
each product being unique in its confi guration, size, weight and material composition making it impractical and costly to provide an EPD for every AHU. Even if a bespoke AHU manufacturer committed
to provide an EPD for every product manufactured this would be likely be futile, because designers need access to embodied carbon information at the earliest design stages, with suffi cient time to make informed decisions. CIBSE’s recently released ‘TM65 – Embodied
carbon in building services: a calculation methodology’ was very welcome. The document succinctly introduces the product lifecycle stages and carbon related defi nitions, but more importantly it provides a clear calculation methodology to establish
16 September 2022
A traditional AHU product manufactured with a steel casework, might show that anywhere between 55- 75% of the product is manufactured from galvanized steel, 10-25% from aluminium, 5-10% mineral wool insulation and 5-10% copper, with the remainder being small quantities of plastics, rubbers, electronics and wiring boards. From an analysis of over 100 products so far,
we’ve also estimated that the embodied carbon associated with an AHU is in the order of 8 tonCO2e per m3.s-1 of air replaced, on a typical supply and extract (bidirectional) AHU including supply and extract fans, two stages of fi ltration, heat recovery device, chilled and hot water heat exchangers. However, AHUs can include much more or much less than this and deviations from this average fi gure are signifi cant when looking at smaller products where the weight of the internal components starts to outweigh that of the casework. One forthcoming conclusion from this initial
analysis is that using multiple smaller products rather than a single centralised system can very easily add up to a signifi cantly increased carbon footprint.
Reducing embodied carbon
Designing a product to be energy effi cient does not guarantee it will also be sustainable and environmentally friendly, since energy effi ciency only addresses those emissions related to the use phase of the equipment. While operational energy has been reduced
signifi cantly in recent years, the proportion of embodied energy has become more signifi cant to the point of now being one of the major contributors towards the total carbon footprint of the product. From our own research, we estimate that embodied carbon can account for up to 30% of the carbon emissions throughout the life span of an AHU.
In pursuit of operational effi ciency, it’s not unusual to see some manufacturers resorting to an increase on the size of the equipment in order to reduce pressure loss and energy consumption. It is important that designers communicate with manufacturers in order to get all the design alternatives laid out before them so they can opt for a solution that works best for both the operational and embodied energy of the product. Oversizing products due to lack of time to
correctly assess the building demands or for fear their performance will fall short, is a mindset that also needs to change. Oversizing results in bloated equipment which quite often comes with additional operational costs due to energy losses and a mismatch with actual demand from the building. The associated maintenance is also more expensive. Avoiding oversizing is fundamental to reduce embodied carbon. Finally we should consider refurbishment
as an alternative to new build. Airedale has a dedicated team of site engineers working on AHU refurbishment on a regular basis, and we often fi nd often that the framework of the products is still structurally safe, albeit sometimes in need of a good scrub and a lick of paint. Although the guts of the equipment might need to replaced or upgraded, it is often unnecessary to replace the existing structure with an entirely new product. To conclude, TM65 is a welcome tool that allows us to measure embodied carbon footprint of a bespoke air handling unit, and as this movement towards considering the full lifecycle carbon footprint of a product grows, Airedale is able to off er these measurements to AHU customers and deliver visibility to the balance of embodied carbon against operational carbon footprint.
MATERIAL A1 EMISSIONS BREAKDOWN
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