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Life Cycle Assessment of clear float glass for building applications

The European flat glass industry is fully committed to developing products with the smallest environmental burden and the greatest benefits. To do so, it continuously improves the energy efficiency and environmental performance of its manufacturing activities and of its products.

Life Cycle Assessment (LCA) provides the best framework to assess and determine the environmental impacts of products. As such it helps orientate improvements towards even greater sustainability. Complete LCA analysis take account of the environmental impact of manufacturing products but also the impacts and benefits of products in their use phase as well as their recyclability at their end-of-life.

In order to support the environmental assessment of final building products made of float glass such as windows, facades, etc. Glass for Europe carried out a "cradle-to-gate" life cycle study of clear float glass for building applications.

 

 

Scope of the work and deliverable

The work undertaken by Glass for Europe is a ‘cradle-to-gate' life cycle study of clear float glass for building applications. In simpler words, it assesses all environmental impacts of float glass manufacturing from the raw material extraction to the end of the float glass manufacturing plant.

The work however does not inform about further downstream treatments of glass products, the impact of products during their use-phase, nor their end-of-life aspects. This is simply due to the fact that additional data which would be required are not in the possession of Glass for Europe and/or because float glass can then be used in many different applications, each of them being extremely specific. In addition, this work does not inform about float glass for use in both automotive and photovoltaic applications, as different manufacturing constraints apply to these types of float glass.

The LCA study delivers a cradle-to-gate Life Cycle Inventory (LCI) and Environmental Impact Indicators of one kilogram of saleable float glass as a final product. It can serve as a basis for additional work on specific final products for use in buildings.

 

Study details

The LCA study includes the total inputs and outputs of energy and materials used in the upstream processing and production of raw materials and energies (upstream data) and from the float manufacturing process1 up to the factory gate (primary or "on-site" data).

1The main manufacturing processing activities taking place at the manufacturing site are the batch preparation, the melting of the raw materials in the furnace, the formation of a glass ribbon in the bath of molten tin, the conditioning in the annealing lehr, the quality control, automatic cutting and storage. Please click here for more information.

The LCA data represents European aggregated data collected by Glass for Europe (gate-to-gate data). It refers to the year 2005 and covers 25 sites in Europe, which account for about 50 % of the float glass production in Europe. It is therefore the most representative exercise ever done on flat glass production in Europe.

The ensuing analysis were modeled and calculated by two consultants, PE International (using the GaBi 4 database 2006) and Cabinet Ligeron (using the Ecoinvent database).

The study has been performed in accordance with ISO 14040 and 14044 methodologies, which harmonize the rules and methodologies to develop LCA studies. The PE International work has been proof-checked in the context of a German framework for environmental performance declaration performed according to the German IBU guideline for Type III EPDs. Data provided by Glass for Europe company members have been verified as part of the EU ETS and E-PRTR inspections.

 

Assessment of Environmental Impacts of glass manufacturing and benefits of glass products

As an energy-intensive manufacturing process, it is no surprise that the primary environmental impacts associated to float glass manufacturing are the Global Warming Potential (mainly due to CO2 emissions from raw materials and fuels use) and Primary Energy Demand (for which the upstream production of energy, in particular natural gas, is the main contribution).

That being said, it must be borne in mind thatend-products made of float glass provide tremendous benefits interms of CO2 emissions reduction in their different usages and in particular when used in energy-efficient windows and facades in buildings.Savings of more than 100 million tonnes of CO2 could be achieved annually if Europe's buildings were fitted with advanced energy saving glass(more information here).

For this reason, full life-cycle analyses which account for these energy-saving benefits are all the more important. Based on this LCI work and independent studies already available1, one can be confident that full LCA analysis would reveal that glass products are energy-saving products as savings realized by the products throughout their life largely offset the CO2 emitted during production.

1TNO Built Environment and Geosciences - Potential impact of low-Emissivity glazing on energy and CO2 savings in Europe - TNO Report 2008-D-R1240/B - November 2008
TNO Built Environment and Geosciences - Impact of solar control glazing on energy and CO2 savings in Europe - TNO Report 2007 - D-R0576/B - July 2007

To Glass for Europe's views, the full life-cycle analysis of products should be favored whenever possible as self-limiting analysis to manufacturing and carbon content would fail in providing a true picture of products' environmental performances. For instance, the production of a single glazing window will always require less energy than that of an energy-efficient double or triple glazed windows, whereas the latter are unquestionably more environmental-friendly.

For these reasons, Glass for Europe continues its work on life-cycle analysis and will make sure that flat glass is seen as what it is: an energy-saving product.

In particular, Glass for Europe is currently extending its work on life-cycle analysis to assess the additional impacts associated to the off-line coating of float glass used in building applications.

 

Results and data availability

The Life Cycle Assessment of float glass was conducted by two consultants, PE International and Cabinet Ligeron to support respectively the development of environmental performance declarations for building glass products in Germany and France.

Global Warming Potential (GWP) and Primary Energy Demand (PED) confirmed to be the principal Environmental Impact categories associated to float glass manufacturing:

  • GWP average value: 1,25±0,03 kg of CO2 equivalent per kg of float glass
  • PED average value: 17,2±2,2 MJ (net calorific value) per kg of float glass.

The below graphs taken from the PE International report illustrates the breakdown of these two indicators.

 
Summary report elaborated by both PE International and Cabinet Ligeron are available for download below. They provide different sets of results, which can be reasonably explained by the fact that different upstream data and softwares were used. Please, check the additional below recommendations for a proper understanding of variances.
 
The cradle-to-gate float Glass Life Cycle Inventories can be provided by the Glass for Europe secretariat upon request, for instance to serve as the basis for additional LCA analysis. Glass for Europe only requires that when use is made of its data, Glass for Europe's property rights are adequately mentioned. In addition, the user of this data will be asked to not disseminate or sell any parts or all of the data set to any third party, outside of the scope of the work for which the data was initially requested.

Should you be interested in receiving these, please send us an e-mail specifying your needs and the purpose of your request.

                                                                                                     

 

Additional remarks and recommendations

The outcomes delivered by both consultants in charge of the float glass life-cycle analysis resulted in two sets of data with inherent variances in the figures.

Gate-to-gate data provided by Glass for Europe to the consultants are the same, therefore variances are inherited from the use of different databases and subsequent choice of data sets, as well as the different modeling applied by the consultants. Along with LCA experts, Glass for Europe believes that variances up to 20% remain acceptable so long that they are justifiable for the reasons explained above. This illustrates that when publishing or comparing LCA figures, there is no unique absolute value as such. The figures have to be appreciated within the confidence levels of LCA works.

Within this Glass for Europe work on clear float glass, variances are generally low except for a few indicators/data of less relevance and limited impact in the case of glass manufacturing. Glass for Europe is comfortable with the overall convergence of the results and believes that it reinforces the validity of the work. This work is the most comprehensive, in-depth and accurate life-cycle assessment made on clear float glass at European level.

As expressed above, Glass for Europe would like to remind that environmental impacts of glass manufacturing processes and overall benefits of glass products and applications have to be accounted in a complete and balanced way. A full life cycle assessment of glass products, taking account of energy potential savings in the use phase and recyclability of glass products at the end-of-life is therefore preferable despite the inherent complexity. In any case, energy savings of glass products must always be kept in mind.