Sustainable Construction

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What do we mean by 'net zero carbon buildings'?

Although the construction industry has seen many targets on building energy efficiency introduced through legislation such as Part L of the Building Regulations, or Minimum Energy Efficiency Standards, there is currently no agreed definition of a ‘net zero carbon’ building.

However, many leading organisations such as CIBSE, BRE, and Better Buildings Partnership (BBP). London Energy Transformation Initiative (LETI) and others are working on a Net Zero Carbon Standard for buildings. The work will bring together several reports and guidance documents to provide a single, agreed definition and approach to delivering net zero carbon.

The Net Zero Carbon Standard proposal defines a net zero carbon (whole life) built asset as:

“One where the sum total of all its asset related greenhouse gas emissions, both operational and embodied, over an asset’s life cycle are minimised, meet local carbon, energy and water targets and with residual ‘offsets’, equals zero.”

Net zero carbon and energy efficiency – an important link

While a net zero building and an energy efficient building are not necessarily the same, designers and building owners targeting net zero carbon emissions must also have energy efficiency as a key consideration.

CIBSE and LETI define net zero carbon – operational energy in a building as:

“A Net Zero Carbon – Operational Energy asset is one where no fossil fuels are used, all energy use has been minimised, meets the local energy use target (e.g. kWh/m2/a) and all energy use are generated on- or off-site using renewables that demonstrate additionality. Direct emissions from renewables and any upstream emissions are ‘offset’"

Since HVAC equipment in a commercial building can use up to 40% of its energy, it’s vital to focus on the specification of energy efficient systems and their long-term efficient operation.

Why net zero buildings? Avoiding stranded assets

Legislation aimed at reducing energy consumption and delivering decarbonisation of heat in our commercial building stock is putting some buildings in danger of becoming stranded assets.

Building owners can face significant costs to meet higher standards for Energy Performance Certificates (EPCs). Or they must remove gas boilers to decarbonise space heating and hot water. Every year, as targets on energy use and emissions tighten, these buildings fall further behind environmental requirements, leaving them un-lettable, with shrinking sales values – stranded assets.

Many corporations are setting their own public net-zero carbon emissions targets and want low-carbon buildings to align with these strategies. Financial investors are also showing an increased preference for sustainable/environmental instruments.

Moreover, there are buildings currently in the design or early construction phases that are also in danger of being stranded assets even before they open their doors to potential buyers or tenants. While these buildings may meet the current requirements of Part L of the Building Regulations, for instance, the buildings are not necessarily ‘net zero’.

The Mitsubishi Electric Net Zero Carbon Design Team is here to advise on net zero buildings and where current proposed legislation and guidance on this issue are heading.

We are here to help clients look at their HVAC systems – whether new designs or refurbishment – and spot where they can reduce energy and move to low-carbon heating and hot water production smoothly and with minimal disruption.

View and download our new 'Stranded Assets' White Paper

Embodied carbon, whole life carbon and energy use intensity

In achieving net zero carbon buildings, it’s essential to understand the terminology. This makes it easier to agree on the goal and how to get there.

Currently, legislation such as Part L offers no formal definition of a ‘net zero carbon’ building. However, several organisations such as CIBSE, BRE and LETI are working on a Net Zero Carbon Standard to address this issue. We use their definitions below: 

Net zero (whole life) carbon building:

“One where the sum total of all its asset related greenhouse gas emissions, both operational and embodied, over an asset’s life cycle are minimised, meet local carbon, energy and water targets and with residual ‘offsets’, equals zero.”

Net zero carbon (operational energy) building:

“A Net Zero Carbon – Operational Energy asset is one where no fossil fuels are used, all energy use has been minimised, meets the local energy use target (e.g. kWh/m2/a) and all energy use is generated on- or off-site using renewables that demonstrate additionality. Direct emissions from renewables and any upstream emissions are ‘offset’”

Net zero embodied carbon building:

“ Net Zero Embodied Carbon asset is one where the sum total of greenhouse gas (GHG) emissions and removals over an asset’s life cycle are minimised, meets local carbon targets (e.g. kgCO2/e/m2) and with additional offsets equals zero.”

Source: CIBSE and LETI document

Useful information:

The London Energy Transformation Initiative has created a helpful information resource around whole life carbon and embedded carbon. This includes further insights into basic definitions and one-page explainers. To find out more, see: https://www.leti.london/carbonalignment

Energy use intensity (EUI)

EUI refers to the energy use of a building related to its size. EUI is measured as kWh/m2/yr.

CIBSE has called on the UK government* to set actual energy consumption requirements for buildings based on EUI. This contrasts with current legislation, which suggests a reduction relative to a prescribed ‘notional building’.

*view more

More on Embodied Carbon

Download our embodied carbon brochure today

Decarbonisation – heating, hot water, cooling and net zero

Reducing the UK’s reliance on fossil fuels (particularly natural gas) for heating and hot water is one of our biggest challenges. Around 86% of buildings in the UK rely on gas boilers (this includes our homes) so the extent of the change required is explicit.

Tapping into our green grid

One of the main proposals for decarbonisation is to encourage building owners to switch to electric heating and hot water production. Heat pumps provide a highly energy efficient solution, and they’re suitable for almost every building type, from homes to hotels, retail and office blocks.

Mitsubishi Electric leads the sector in heat pump development and can now offer realistic alternatives to the gas boiler, even in buildings with high hot water demand. For example, the Mitsubishi Electric QAHV heat pump can produce water up to 90oC.

Most recently, Mitsubishi Electric has launched the Ecodan Hydrodan, which can be applied in ambient temperature heat loops known as Fifth Generation Heat Networks.

Low-carbon cooling – the future of low GWP refrigerants

The F Gas Regulations impact the refrigerants used in air conditioning systems (read our CPD Guide on this topic).

The regulations aim to cut the use of refrigerants which have the potential to damage the earth’s ozone layer and contribute to global warming if released from cooling systems. Every refrigerant is allocated a GWP number – the lower the number, the less damaging it is.

We are moving toward refrigerants with a low Global Warming Potential (GWP) in air conditioning systems. This includes R32, which is used in a growing range of Mitsubishi Electric systems, including our Mr City Multi VRF products.

However, with our eye on the future, Mitsubishi Electric has also introduced a range of chillers that use Hyrdofluoro Olefins (HFOs) with very low GWP.