By akademiotoelektronik, 04/11/2022

Net Zero Carbon Renovation: HQE-GBC lays the foundations Net Zero Carbon Renovation: HQE-GBC lays the foundations

Made by Bernard Reinteau, specialized journalist

The leading association in the field of low-carbon construction is delivering a new contribution as part of its research process begun in 2015. The finesse of the engineering work makes it possible both to identify new approaches to renovation and to develop a new vocabulary for stakeholders.

Major low-carbon renovation of 20,000 m2 according to the Cecina 2020 Climate roadmap

And the president of HQE-GBC, to lay the foundations for reflection

“Will we soon be talking about low-carbon renovation, just as we have gone through during the decade of from thermal regulations for new buildings to environmental regulations? This is the bet posed by Marjolaine Meynier-Millefert, deputy and president of HQE-GBC, at the opening of the webinar which was held on January 6 to present the first achievements of the work of this association on the theme of Net Zero Carbon renovation.

This initiative is intended to produce concepts useful to the construction sector so that they can be transcribed into methods and then written up in guides for daily application. Launched in 2015, practically in the wake of the publication of the energy transition law, this research project was actually launched in 2017. Funding for this work is provided by Redevco, a major real estate developer on a European scale, and the The execution of the studies was obtained by the AIA Environnement design office.

In 2018-2019, this work has already resulted in the publication of a methodology presenting a readjustment of the life cycle analysis method applicable to renovated buildings and, in the process, the publication of a file presenting the results of the renovations under the prism of the E+C- method.

Thus, the renovation LCA method used in 2018 differs from that applicable to new construction on a few key points. Like the original AVC method, it takes good account of construction and equipment products, energy, water and the site. However, renovation requires, the family of construction and equipment products (PCE) is the subject of a distinction between new, preserved and deposited products. And to go into detail, the products of the retained and deposited categories are subject to an original carbon amortization calculation: this is based on the estimation of their residual life in relation to their reference. A calculation whose logic we understand perfectly, but, we can guess, supposes an almost exhaustive inventory of the components of a construction before embarking on a renovation operation in accordance with the approach prescribed by HQE-GBC. (See the presentation made in 2018> link).

Tested on seven “low-carbon” renovation operations

Low-carbon renovation of 446 collective housing units (department 13)

The new phase of work presented during this digital conference concerns the experimentation of the methodology in the field. This heavy site analysis phase was carried out from January 2020 to September 2021 by the AIA Environnement design office.

In all, seven types of intervention – individual and collective housing, the tertiary sector – were selected, sites where areas ranging from 70 m² to nearly 32,000 m² were treated:

The examples taken for each of these families were the subject of a "carbodiversity" study, that is to say, an assessment of the carbon footprint of each of the contributors: energy, construction site, construction products… With the challenge of this assessment being the establishment of a specific renovation strategy.

What main lessons can be drawn from this work?

One of the most interesting is that all the examples studied are at a “carbon 2” level. Which, according to these few cases, allows Simon Davies, director of AIA Environnement, to affirm that in renovation, it is relatively common to reach such a level at a price lower than that of new.

Another lesson: due to the saving of materials, in particular those intended for the envelope, the share of construction products and equipment (PCE) – new materials and materials removed – is proportionally significant in terms of emissions overall costs of the project: from 25 to 75% of the overall assessment depending on the site.

In the same vein, renovation is clearly distinguished from new construction by the types of construction products that impact the site through carbon emissions. The dominant product families are climate engineering equipment (HVAC), electricity (high currents), plumbing and sanitation, and especially facades and interior finishes, these two families being less significant in new construction, "weight" structural materials require. The experiment therefore has the advantage of directing the monitoring of operations towards these specific positions.

The "carbon payback time", a renovation optimization index

That being said, which life cycle analysis optimization indicator should be used?

Maxime Havard, low-carbon pilot at AIA Environnement, presented the innovative concept of “carbon payback time”. Innovative, this concept is based on:

The goal is to minimize induced emissions, maximize avoided emissions and maximize sequestered emissions.

In the case of a renovation, how, on these bases, can you develop the calculation of a carbon payback time? Its operation is similar to that of financial investment.

Thus, we establish the principle of a “carbon debt” of the initial construction before its renovation. By undertaking the renovation, a new carbon debt is added to that of the construction products and equipment retained and deposited, the aim of the renovation being to reduce the overall volume of carbon emissions at the end of a given period - by l occurrence 50 years, to be consistent with RE 2020.

Like an investment to improve any existing installation, the interest of this concept of "carbon payback time" is to help retain products that will produce the least possible induced carbon emissions and which will help to avoid and sequester them. The goal is to find a “carbon neutral point” as soon as possible so that the renovation generates what could be called a “carbon benefit”. AIA environment calls it “gross carbon payback time”. It is obtained arithmetically by setting the ratio of 50 years of greenhouse gas emissions from new construction products and equipment on the difference between the greenhouse gas emissions linked to energy before renovation and those of GHG Energy total. Another formula for estimating the effect of renovation in terms of carbon: the ratio of the renovation effort to the gain in operation.

What is the translation of these new concepts on the low-carbon construction sites taken as a reference?

Taking into account their specificities, the projects monitored have been studied according to several variants of renovation:

Then the overall study of the seven projects looked at the construction products and equipment, the performance of the systems, as well as the different usable energies.

The report available today shows the impacts of each assumption. It shows reductions in greenhouse gas emissions of around -43% to -62%, with very different gross carbon payback times depending on whether the basic solutions are used – from 7 to 75 years – or optimized – from 7 to 27 years. A variability of the results which is explained, according to Simon Davies, by the constraints of carrying out the construction sites: heritage constraints, presence of asbestos on the facade...

Furthermore, a distinction can be made between residential construction sites, whose carbon payback time is rather around 10 to 20 years, and tertiary construction sites, which have much longer TRCs – 20 to 30 years. The message developed by AIA Environnement is of course to seek the shortest possible carbon payback time.

Other advantages of this analysis approach: it shows that heating energy remains the leading source of carbon emissions and, as such, it remains a priority for low-carbon renovation operations. In addition, it is necessary to ensure that summer comfort is taken into account, which concretely has the effect of increasing the carbon weight of operations...

Five new concepts: activity, circularity, materiality, technicality and externalities

The work carried out on the reference sites has also made it possible to better define the outlines of new concepts that should be taken into account by the project managers. works, designers and companies during renovations. They are called, in the order tacticity, circularity, materiality, technicality and externalities.

Definitions:

These five levers are intended to guide the management of the renovation project from its programming to its operation, each one intervening with more or less authority over time.

Furthermore, the promoters of this reading of worksites also attribute to them virtues in terms of defining “co-benefits”. No doubt…, but we must admit that the graphic representation provided to highlight all these positive aspects – economic, environmental and collective health – is perplexing. Things will certainly be clarified during future study phases.

Compiled by Bernard Reinteau, journalist specializing in construction and construction solutions, renovation with added environmental value

Sources

The book of low-carbon levers for renovation

Optimization and NZC scenarios of the generic cases retained

The webinar of January 6, 2022

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About the author

Bernard Reinteau

A journalist in the building press since the end of the 1980s, Bernard Reinteau is a freelance journalist. He has worked for the Public Works and Building Monitor, the Heating Journal, and Chaud Froid Performance. He is particularly interested in technical construction solutions, the environment, renewable energies, the energy and environmental performance of buildings. He mainly collaborates with the biggest construction press titles and in particular with Xpair.