Energy and environmental life-cycle analysis of advanced windows

Energy and environmental life-cycle analysis of advanced windows

WREC 1996 Energy and Environmental Life-Cycle Analysis of Advanced Windows P W Griffiths, PC Eames, SNG Lo & B Norton PROBE: centre for Performance R...

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WREC 1996

Energy and Environmental Life-Cycle Analysis of Advanced Windows P W Griffiths, PC Eames, SNG Lo & B Norton PROBE: centre for Performance Research On the Built Environment School of the Built Environment University of Ulster Newtownabbey BT37 0QB N. Ireland

ABSTRACT The environmental consequences of options for the manufacture, application, disposal, reuse and recycling, applicable to the full range of currently conceived advanced window systems, are discussed. Advanced window systems may incorporate, singly and in various combinations: evacuated contiguously-sealed glazing, electrochromics, thermochromics, photochromics, aerogels, xerogels, inert gas filled double glazings, low infra-red emittance coatings, diffractive daylight deflectors, holographic daylight deflectors refractive daylight deflectors, toughened glass. The primary impetus for the development of such systems is that their use enables buildings to incur minimal energy use by reducing window heat losses and/or the displacement of electric lighting by enhanced daylighting. The energy savings associated with advanced glazings displace the combustion of fossil fuels directly and indirectly; environmental benefits thus ensue. However these benefits may be offset by the impact of energy embodied from manufacture and the negative impacts of the extraction and disposal of constituent materials. Over their total life-cycle the environmental impact for advanced glazing systems and their associated means of manufacture, system fabrication and the tenable reuse, recycling and disposal options are unknown. The usefulness of life cycle analyses during the research and development stage is discussed. KEYWORDS life-cycle analysis, advanced windows, sustainability INTRODUCTION The adoption of new window technologies has been estimated, by the year 2025, to provide the U.K. with an annual saving in primary energy equivalent to about 0.2m tonnes of coal with a CO2 saving of 5.2 million tonnes (Ruyssevelt et al, 1993). In the USA, the adoption of the "Green Seal" environmental standards for windows is estimated will save 350 million barrels of oil per year and reduce emissions of CO2, SO2 and NOx by 2.5% (Green Seal, 1993). However employing energysaving advanced windows does not lead to inevitable environmental soundness. Research into advanced glazing materials has concentrated so far on the need to achieve systems with acceptable visual transmittance with low thermal conductance and/or daylight deflection. So far this has resulted in the use of multiple sheets of clear float glass, or double glazing with low-emittance coatings and/or defractive/refractive media. Recent research has concentrated upon the application of thermo- and electrochromic films, aerogels and xerogels, transparent insulation materials manufactured from plastics and the use of a vacuum or inclusion of inert gases within purpose-made double glazed units. Information is only available currently on the embodied energy of traditional glazing systems (see e.g., Heijungs, 1992; Anderson et al, 1993). As new advanced glazing units are introduced, there is a pressing need to investigate their manufacturing methods and the materials involved to ascertain the extent of their environmental impact. Furthermore, with the use of materials such as tin, indium, tungsten, methanol, tetramethoxysilane and plastics, difficulties will arise when attempting to recover and recycle these materials at the end of their useful life. A finite world only has a finite set of material resources. Therefore a sustainable approach to these resources must be adopted by analyising the environemtnal consequences of a product or process in its totality. This can only be through the use of life-cycle analysis techniques. 219

WREC 1996 It has been shown, to give a specific example, that evacuated and electrochromic glazings can be used to manipulate and optimise the flow of energy into and out of the building envelope, (Robinson and Collins, 1989; and Wittwer, 1994). For example, by utilising evacuated glazing as a standard glazing material, windows of larger area can be used thereby increasing the amount of solar energy entering the building, without increasing heat loss. Such improved thermal performance would allow evacuated glazings to overcome the thermal deficiencies associated with traditional glazed walls. In addition, glass curtain walls contain less embodied energy than traditional curtain walls which incorporate metal stanchions, transoms and panels. (The embodied energy in glass being 13 MJ/kg, while energy embodied in aluminium and steel is 180 and 36 MJ/kg respectively, (Lawson, 1994)). THE NEED FOR LIFE-CYCLE ANALYSIS Life cycle analyses have been undertaken on the building industry in general and on specific projects (Anderson et al, 1993). Research in the building products industry is undertaken usually with a specific aim, for example, producing a glazing system with a high thermal insulation value, with no regard to the energy and environmental consequences that may occur during the product's fabrication and use. Therefore, research may show that to continue particular current developments along their present tack may be futile in relation to the protection of the environment. In contrast, a datum analysis of traditional curtain walling and brick facades may highlight that certain forms of new glazing technologies in the context of specific life-cycles may be preferable environmentally than plain brick or metal curtain walling. To give a simple example, an advanced glazing may reduce the energy needed to heat and light a building by such an extent that the energy and environmental consequences of using advanced glazing materials is outweighed by the benefits of not using traditional materials. This may ensue because glass can be readily recycled, whereas brick and concrete cannot. The benefits of advanced glazing materials such as electrochromically coated or evacuated glazing, through reduced fabric losses and lighting loads, have been well documented. However, there is no rigorously-founded published information regarding the environmental and energy implications of their fabrication, use and disposal. The environmental impacts of building materials are probably greatest during their procurement and disposal. If it is clear which advanced glazing materials and production/disposal mechanisms are environmentally most benign, then life-cycle analyses would enable the glazing industry, building owners and operators to fully justify their use and enable new glazing product development, driven by market imperatives, to be fully cognisant of environmental implications. HOW THIS SHOULD BE APPROACHED Life-cycle analysis should determine the embodied energy and environmental costs resulting from the production, use and disposal of advanced glazing systems. Appropriate applications of these technologies can then be identified where the products will provide the greatest energy savings and improvements to the built environment, with the least environmental impact. Life-cycle analysis can be used to achieve a total cost of an asset over its operating life, including initial acquisition costs and subsequent running costs. Traditional life-cycle costing has involved the study of the costs arising from an investment decision, (Flanagan 1983, Flanagan et. al. 1989). Life-cycle analysis can also be applied to energy use and savings achieved from fabrication, through use to disposal of a material. The major direct environmental impacts of building materials are in their procurement and disposal, although some also have unintended effects on indoor air quality in use as well (Lawson, 1993). The full environmental implications of the manufacture, use, disposal and recycling of a range of advanced glazing materials can only be determined from the perspective of a 'cradle to reincarnation' life-cycle. This is achieved by defining and investigating the following: • define criteria for optimal advanced glazing system fabrication options and life-cycles which will be environmentally sustainable; • determine the overall energy savings that may occur through the use of these systems as compared to present-day materials; • determine the embodied energy that is in the materials used, as a result of the exploitation of the mineral resource and subsequent processing and fabrication of that material; • pin-point any environmental issues that may preclude production and/or disposal/recycling. DETERMINATION OF ENVIRONMENTAL COSTS Identification of all the materials used in the construction of advanced glazings is the starting point. The environmental costs of winning these materials from the earth including the energy costs must be quantified. The energy involved in producing window systems, and any environmental risks 220

WREC 1996 associated needs to be known. Indoor and outdoor testing equipment has been traditionally used to determine window thermal and optical properties. An understanding of the thermal performance of these 'smart' windows can be obtained using experimental and computer-based simulation modelling techniques and building thermal models. The investigation of the thermal performance of smart windows cannot ignore the energy needed to illuminate the rooms of a building, especially where a material reduces daylight so much that artificial lighting is needed. By using small-scale models and computer tools such as Radiance, data can be obtained on how much daylight is transmitted into the internal environment and how much artificial lighting is needed to supplement the natural light. From this understanding, the overall energy savings that may be achieved, using 'smart' windows, can be calculated. To complete the energy audit, a study of the energy embodied in these materials, during manufacture, and the energy expended during disposal or recycling can be undertaken. Figure 1 shows a theoretical methodology for predicting the balance between energy saved and that embodied.

Life-eyrie Energy savings


Results Obtained

~ DataF r o m

Life-Cycle Net Energy


Figure1: ~

Methodology for prediction of balance between energy saved and that embodied

mbodied Energy

Once the energy audit is completed, an analysis to determine the optimum window size can be undertaken. This should involve deriving the annual energy consumption variation with the glazing ratio of the facade and then correlating how this changes with the embodied energy. This information can then be used to produce a graph as in fig. 2.

~. singleglazing Consumpfi~~,~ Annua. Energy



G~ l~a z i n~xg / F a_c a ~ e R e d atio


Figure2: Determinationof the optimalglazingratio, takinginto accountenergyconsumption andembodiedenergy

Alongside the energy audit, an environmental audit needs to take place. This audit will consider the socio-economic effects that arise from the extraction from the earth, of the raw materials, that are used for the manufacture of 'smart' windows . For example, there are a number of environmental 221

W R E C 1996 problems associated with the manufacture of evacuated glazing. At present, only 'hard' low-emissivity films are used, as these materials can withstand the baking process involved in the manufacture of evacuated glazing. The pyrolytic method used to attach the low-emissivity material to the glass involves the emission of environmentally harmful gases to the atmosphere. As a result for example, Scandinavian governments have refused licenses to Pilkingtons to produce "K-glass" in their countries. Therefore, environmental costs of these smart windows needs analyzing and new materials, or new methods of manufacturing evacuated glazing, should be proposed, where the glass does not have to be baked to over 450°C. Further investigations are needed, to determine how much carbon dioxide gas is given off during the manufacture of these films, and how much is saved by the use of such windows. Once a glazing unit is no longer serviceable and must be replaced, its components can be recycled, thereby reducing the amount of new raw materials needed to produce, for example, new glass. During recycling, any materials attached to the glass surface need to be removed, and as these materials are usually metals, they can be reused. The cost of recycling glass is known, the cost of recovering metal films such as tin oxides and tungsten is not. CONCLUSION

E~ro'nmental Impact l jlmpact~

nEvirdnmental I Ben~ l

Environmental Impact

re 3':B Basic ~ i ~ l ei e-cyc e o] of a Figure ~ ......... ........ ~~"'JJ material highlighting the 'cradle to ~ ' T ~ _ . reincarnation' which is a major root ~Environmental of sustainable development Impact Figure 3, shows the basic life-cycle of a material, including the energy inputs needed in processing along with the environmental costs that may occur, along with the environmental benefits and energy savings that may occur during its useful life. Energy and environmental costs occur even during use (for example, materials used may be leaching into the atmosphere and causing problems similar to those, say, that occurred through the use of asbestos). For the product to be of use, the energy saved over it's lifetime, compared with existing windows, must be greater than the energy embodied in the material during fabrication. Furthermore, the environmental consequences should be sustainable. If we are to avoid the mistakes which have occurred in the past in relation to the development of materials, products and processes, life-cycle analyses must be undertaken during the initial research stages. REFERENCES CITED Anderson, S. et al (1993) "Life-cycle-based building design, energy and environment, calculating tool and database" SBI Report224, Danish Building Research Institute, Copenhagen. Flanagan R (1983) "Life-cycle costing for construction" Surveyors Publications, London. Flanagan R, G Norman, J Meadows & G Robinson, (1989) "Life Cycle Costing, theory and practice", BSP, Oxford. Green Seal (1993) "Proposed Environmental Standards for Windows and Retrofittable Window Frames (GS-13, 14)" Heijungs, R (ed) (1993) "Environmental Life Cycle Assess of Products' Backgrounds" Centrum voor Milieukunde, Leiden. Netherlands, October. Lawson W, (1993) "The influence of Environmental Factors on the design of buildings". Proceedings DECA Conference, Centre for Appropriate Technology, Alice Springs. Lawson W, (1994) Private communication. Robinson S. J. and R. E . Collins, (1989) "Evacuated windows - theory and practice", ISES Solar World Congress, Kobe, Japan, 1079-1083, September. Ruyssevelt P.A. et al (1993) "Estimate of Saving and Potential for Advanced Glazing in the U.K." CLIMA2000, London. Wittwer V, (1994) "The use of transparent insulation materials and optical switching layers in window systems", Proceedings World Renewable Energy Congress, pp318-323, Reading. 222