Abstract
The scope of this study is a comprehensive analysis of the greenhouse gas emissions from the partial substitution of triple-glazing units with argon gas (U-value of 0.79 W/m2 K) with double-glazing units with either monolithic aerogel (U-value of 0.65 W/m2 K) or granular aerogel (U-value of 0.31 W/m2d K).
A residential building located near Oslo and fully upgraded with passive house solutions is used as a case study for this analysis. A cradle-to-site analysis is performed on the facade components. Two replacement schedules and three window-to-wall ratios are used to evaluate the differences in total emissions. Sensitivity analyses based on increasing the fraction of the aerogel glazing, varying the greenhouse gas emissions of the aerogel production, and changing the service life of the aerogel glazing are also performed.
Results show that both the options with windows with aerogel are effective in reducing the greenhouse gas emissions, regardless of the total window-to-wall ratio and the replacement schedule used. By increasing the share of the aerogel glazing, the savings in emissions increase from 5% to 9%. The sensitivity analysis shows that the greenhouse gas emissions from the production of aerogel should be at least 8 times higher than those currently reported to totally counterbalance the achieved energy savings.
Abstract
The current practice of building energy upgrade typically uses thick layers of insulation in order to comply with the energy codes. Similarly, the Norwegian national energy codes for residential buildings are moving towards very low U-values for the building envelope. New and more advanced materials, such as vacuum insulation panels (VIPs) and aerogel, have been presented as alternative solutions to commonly used insulation materials. Both aerogel and VIPs offer very high thermal resistance, which is a favourable characteristic in energy upgrading as the same insulation level can be achieved with thinner insulation layers.
This paper presents the results of energy use and lifecycle emissions calculations for three different insulation materials (mineral wool, aerogel, and vacuum insulation panels) used to achieve three different insulation levels (0.18 W/m2 K, 0.15 W/m2 K, and 0.10 W/m2 K) in the energy retrofitting of an apartment building with heat pump in Oslo, Norway. As advanced insulation materials (such as VIP and aerogel) have reported higher embodied emissions per unit of mass than those of mineral wool, a comparison of performances had to be based on equivalent wall U-values rather than same insulation thicknesses. Three different electricity-to-emissions conversion factors (European average value, a model developed at the Research Centre on Zero Emission Buildings – ZEB, and the Norwegian inland production of electricity) are used to evaluate the influence of the lifecycle embodied emissions of each insulation alternative. If the goal is greenhouse gas abatement, the appraisal of buildings based solely on their energy use does not provide a comprehensive picture of the performance of different retrofitting solutions.
Results show that the use of the conversion factor for Norwegian inland production of electricity has a strong influence on the choice of which of the three insulation alternatives gives the lowest lifecycle emissions.
Stricter energy regulations for energy use in buildings require new construction to be equipped with increasingly thicker insulation layers and minimal surfaces for glazing in cold climates. In recent years a new type of window has been proposed as a way to overcome the notoriously low thermal performance of transparent surfaces. In order to reach such performances, this glazing type has been equipped with monolithic aerogel as the glass-pane filling.
The scope of this study is a comprehensive analysis of greenhouse gas emissions from the partial substitution of typical triple-glazing-with-argon units with double-glazing-with-monolithic-aerogel units in residential building upgrades.
A social housing complex from the late 1960s, located in Oslo, is used as a test case. The building is fully upgraded using passive house solutions. The new facades have walls with a U-value of 0.10 Wm-2K-1 and triple-glazing-with-argon units with a U-value of 0.79 Wm-2K-1. In this study approximately 30% of the glazing area is substituted with double-glazing-with-aerogel units with a U-value of 0.50 Wm-2K-1. A cradle-to-grave analysis is performed on the facade components to determine the global warming potential of the two proposed glazing options. Differences in the share of the embodied emission over the building lifetime when increasing the total window-to-wall ratio from 24% to 33% and to 50% are also investigated. In addition, various maintenance schedules are used to evaluate the differences in emissions embedded in the façade components. Comparisons between the resulting energy demands and embodied emissions are presented.
Preliminary results show how the option with aerogel glazing is effective in reducing the annual heating demand by 7%. This increases to 18% for the façade design with a 50% window-to-wall ratio. The better insulation value of aerogel glazing effectively reduces the thermal losses while at the same time allowing passive solar gains. In addition, the mass of aerogel employed for glazing insulation does not significantly change the total embodied emissions of the façade. This suggests that the use of this window type is environmentally positive.
In the pursuit of stricter energy standards for buildings to reduce their share of energy use, the use of highly efficient insulation materials like aerogel and vacuum insulation has opened a path towards lighter construction in energy retrofitting, whereas commercially available materials, such as EPS and mineral wool, result in massive wall solutions. However, these new materials are notoriously energy intensive in production, resulting in high levels of embodied energy and emissions.
This work describes a comprehensive greenhouse gas analysis of the use of different insulation materials applied to residential building upgrades to passive house standard. It estimates the potential environmental disadvantages of using such materials in energy retrofitting.
A social housing complex from the late 1960s, located in Oslo, is used as test case. The building is upgraded to passive house standard. The facades are renovated by reducing the wall thermal conductivity to a U-value of 0.10 Wm-2K-1. This is achieved by applying correspondingly appropriate thicknesses of mineral wool, aerogel and vacuum insulation. A cradle-to-grave analysis is then performed on the facade components to determine the global warming potential of each proposed insulation option. Special attention is given to the share of the embodied emission over the building lifetime, by varying the electricity-CO2 conversion factor as well as the lifetime of the renovated building. Comparisons between the resulting energy demand and embodied emissions are presented.
Results show that the shares of embodied emissions of the options with mineral wool, aerogel and vacuum insulation are 13%, 29% and 49% of the total building lifecycle emissions, respectively. Despite the fact that aerogel and vacuum insulation have a global warming potential which is between four and eight times higher than that of mineral wool, the resulting effect is a minimal difference between the retrofitting alternatives. This is due to the limited amount of mass of vacuum insulation and aerogel needed to obtain a U-value equivalent to that of the wall equipped with mineral wool.