Hiding in Plain Sight: Embodied Carbon & MEP Systems

Mechanical, electrical, and plumbing systems are often left out of embodied carbon targets and benchmarks—but they have a huge impact on a building's footprint.

Most industry embodied carbon targets and benchmarks focus on architectural building materials, without considering the embodied carbon impact of mechanical, electrical, and plumbing (MEP) systems. But more and more studies are now revealing just how significant the embodied carbon impacts of our MEP systems can be.

Integral Group recently completed a study comparing different residential space heating options in the UK. The embodied carbon emissions associated with a Variable Refrigerant Flow (VRF) split system, with refrigerant for heating and/or cooling, was about 800 kgCO2e/m2 over 60 years—equivalent to a third of a typical home’s total operational energy use over that time. Additionally, in a study of an eight-storey office building, we found that the mechanical system design’s embodied carbon could be, to our own astonishment, equivalent to that of the building’s structure and envelope combined.

Until now, the industry hasn’t been considering the embodied carbon emissions from the MEP equipment that enable our buildings to operate efficiently. Clearly, that needs to change.

MEP systems have an embodied carbon footprint throughout the lifespan of a building.

Heavy Mass, All Metal, Frequent Replacement: A Perfect Recipe for High Embodied Carbon

Just how much do these MEP systems contribute to the overall mass in a building? One study by the Carbon Leadership Forum (CLF) estimates that the mass of MEP equipment in a typical office building in the U.S. Pacific Northwest can range from 14.6 to 22.7 kg/m2—roughly the weight of six four-litre water bottles stacked on each square metre. It would be far greater in labs, health care facilities or data centres.

MEP systems are made largely from high embodied carbon metals—for instance, aluminium for electric motors and heat exchangers; copper for internal pipework; rare earth metals for electric batteries and solar PVs; steel for enclosures, support rails, and ductwork; cast iron for pipework; and a combination of metals for boilers and chillers. Currently, due to the low recyclability of most of these equipment types, virgin metals need to be mined, treated, and processed—a highly energy intensive endeavour—to create new equipment. Moreover, since global mining is concentrated in a handful of countries, these metals must be transported over long distances to the manufacturing facilities where the final products are created. Ethical sourcing and forced labour issues are also a deep concern in the supply chain related to the mining, extraction, and manufacturing processes that create MEP systems.

These environmental impacts are compounded by how frequently equipment needs to be replaced. On average, HVAC equipment, including heat pumps and boilers, requires replacement every 20 years. Most lighting fixtures need to be replaced every three to seven years. This represents repeated carbon impacts during a building’s lifetime.

As more and more all-electric equipment is installed in buildings for cooling as well as heating, the use of refrigerants in such equipment skyrockets. Commonly used refrigerants, such as R410A or R134A, have very high global warming potential (GWP)—in the order of 1,000 times the impact of comparable volumes of CO2—and tend to leak into the atmosphere.

CIBSE TM65 enables consistent calculations at scale

In 2019, Integral decided to advance and share knowledge around embodied carbon in MEP designs, in order to make it a top priority for us and the building industry. One of the first things we realized was the need for an industry-wide methodology to assess the embodied carbon of MEP products. This would need to be developed in the absence of Environmental Product Declarations (EPDs)—as there were (and still are) a limited number of MEP EPDs.

We have been working with the Chartered Institute of Building Services Engineers (CIBSE) to develop this methodology, including addendums that show how to use this method globally. The methodology was published in early 2021 as Technical Memorandum (TM) 65. TM65 provides a consistent method to estimate the embodied carbon of MEP products when no EPDs are available. Our end goal is to create a knowledge bank and meaningful rules of thumb that can assist all engineers in making the right decisions early in the design, which is when we can have the most significant impact.

Today, many manufacturers that stepped up to provide information for TM65 calculations are asking us what next steps they can take to produce EPDs for their products. This is a huge win for the industry, and will escalate progress towards embodied carbon data transparency and accessibility for MEP systems.

A summary of some of the steps that can be taken to mitigate the carbon impact of refrigerants.

Case Studies: the numbers speak for themselves

As part of this research effort, we have explored the embodied carbon of MEP designs at different levels, from the product to the overall building. Here are some examples of these studies.

Rooftop solar PV installations

In this technical report, we explored the embodied carbon impact of different rooftop solar PV installations in the UK, and compared them against the operational carbon benefits. When including all equipment associated with the installation of PV—inverters, cables, optimizers, support, etc.—we found that the overall embodied carbon impact over the 25-year-lifespan of a system was around 100 kgCO2e/m2 of the building’s footprint. This impact was more than offset by the operational carbon benefits of the system. We calculated that 2000 m2 of PV could generate 87% of the energy required by a UK school, while representing 16% of the school’s embodied carbon impact.

Residential heating systems

In CIBSE TM65.1, we looked at the embodied carbon of typical space heating and hot water systems in highly insulated new-build homes. Our study tested 13 different strategies in a notional three-bedroom terraced home and a two-bedroom apartment. Depending on the heating design strategy, we found that space heating and hot water systems could represent between 1% and 9% of the upfront embodied carbon impact, and over 60 years, between 3% and 25% of the total embodied carbon impact. When refrigerant leakage is included in the calculations, the embodied carbon impact of the space heating and hot water systems can reach 832 kgCO2e/m2 in the case of VRF systems—exceeding the total embodied carbon impact of the building’s initial construction.

MEP as share of an office building’s overall embodied carbon

In an early study, we found that, over 30 years, the impact of MEP can represent between 15%-49% of a commercial building’s total embodied carbon (including PV systems and refrigerant leakage). In the case of a retrofit, it can be up to 76%.

Key steps to mitigate the embodied carbon of MEP systems.

Key actions for architects

How can architects reduce the impact of the embodied carbon of MEP systems in their designs? Here are the key strategies that have emerged from our research so far.

1. Prioritize passive design. Take a “fabric first” approach and incorporate passive design strategies like good daylighting, natural ventilation, and sensible window-to-wall ratio to “design out” building services as much as possible. In CIBSE TM65.1, our research showed that upgrading the envelope performance from business-as-usual (30 W/m2 load) to Passive House design standard (10 W/m2) leads to a 40% embodied carbon reduction of the mechanical equipment alone.

2. Incorporate the philosophy of “less is more.” Assess the project program to determine where mechanical systems can be eliminated altogether. When they do need to be designed, collaborate with the project engineers to specify equipment with a lower weight. Look for efficiencies of scale, too. Our research has shown that having one, larger-capacity piece of equipment has a lower embodied carbon impact compared to multiple pieces of equipment providing the same total capacity. In another study, we found that by downsizing equipment and integrating it with architectural design (in this case, choosing a concrete slab with radiant cooling over a typical steel structure with VRF cooling) reduced the whole-life carbon emissions by at least 40% over a business-as-usual all-electric building.

3. Adopt circular thinking. Ensure easy access for equipment inspection, maintenance, and replacement. Specify products and components that can be easily demounted, disassembled, reused, or recycled at the end of their useful life. Give preference to manufacturers that offer take-back programs and promote Extended Product Responsibility. Additionally, explore Products as a Service (PaaS) models for leasing equipment, instead of owning it outright. Most MEP products are materials-intensive but have short lifespans. It’s important to work towards using those materials longer.

4. Mitigate refrigerant leakage. Increasing air pollution and warmer temperatures are requiring more mechanical cooling. Moreover, as electricity grids decarbonize, the use of heat pumps and variable refrigerant flow (VRF) systems is becoming more widespread. When designed correctly, these systems can deliver significant reductions in energy demand. However, their operational carbon savings can be negated when the embodied carbon impact of refrigerant leakage is factored into the whole-life carbon emissions.

Refrigerant leakage varies by equipment type, and the GWP of different refrigerants also varies. Specify low-GWP refrigerants that have low leakage rates. Reduce the overall refrigerant charge by right-sizing equipment and, where possible, specify factory-sealed equipment to minimize leakage during transportation and installation. At the end of the product life, take the necessary steps to capture and recover 100% of the refrigerant during decommissioning.

To help engineers and other designers make informed decisions on selecting systems and refrigerants with the least environmental impact, we authored Refrigerants & Environmental Impacts: A Best Practice Guide.

5. Conduct Life Cycle Assessment early. Work with the engineer and LCA consultants to start developing and analyzing LCA models as early as possible in design. Iterate and refine the results to inform better design decisions. Think holistically about operational and embodied carbon impacts, as these are highly interconnected when it comes to MEP systems.

6. Ask for EPDs. Advocate for data transparency by requiring product-specific EPDs during bidding and procurement. When EPDs are unavailable, methodologies such as CIBSE TM65 can be used to calculate the embodied carbon impacts associated with MEP systems.

7. Support the MEP 2040 Challenge. Working with the Carbon Leadership Forum, Integral Group is one of the founding signatories of the MEP 2040 Challenge. This initiative calls for MEP engineering firms to work towards total lifecycle decarbonization, including embodied and operational carbon. As an architect, your support of this challenge is valuable, as it contributes to helping raise awareness of this issue throughout the industry.

8. Don’t forget operational carbon along the way—it’s all about Whole Life Carbon thinking. Shifting our focus away from operational carbon and solely onto embodied carbon would be a mistake. Instead, we must adopt a Whole Life Carbon approach to designing our buildings, which considers both operational and embodied carbon. We are involved in different industry working groups, such as ASHRAE and CIBSE, to create more knowledge on this next frontier.

Energy efficiency should remain a top priority, but we also need to broaden our thinking to ensure that we also select the lowest embodied carbon options available with the lowest GWP refrigerant. The time for action is now!

Louise Hamot (M. Arch, MSc Eng,) is the Global Lead of Sustainable Innovation at Integral Group and has been instrumental in creating industry knowledge about MEP embodied carbon. She is the primary author of CIBSE TM65 – Embodied Carbon Calculation for Building Services Equipment, and several studies on the subject.

Kanika Arora Sharma is an Associate Principal and the Sustainability team lead for Integral’s USW offices. She spearheads Whole Life Carbon work in the US, working closely with clients to deliver high-value, high-quality analysis, starting early in design through construction and procurement, for better decision-making on embodied carbon emissions reductions.

Jeremy Field is a Senior Sustainability Officer based in Integral’s Vancouver office.