Abstract
This paper presents an analysis of how the design of a photovoltaic (PV) system influences the greenhouse gas emission balance in a net zero emission building (nZEB). In a zero emission building, the emissions associated both with the energy required in the operation of the building (operational emissions) and the energy used to produce the building materials (embodied emissions) are offset by renewable energy generated on-site (avoided emissions). The analysis is applied to a nZEB concept for a single-family building, developed by the Norwegian Research Centre on Zero Emission Buildings. Previous analyses have shown that the installation of a PV system accounts for a significant share of the embodied emissions of a nZEB. The objective of this paper is to assess how the PV system design choices influence the embodied and avoided emissions, in order to determine how the environmental impact can be minimised. Four different PV technologies (Si-mono, poly-Si and CIS, and high-efficiency Si-mono) in four different system designs for flat roofs are evaluated using two different grid emission factors. The installations are compared by means of net avoided emissions, greenhouse gas payback time (GPBT), greenhouse gas return on investment (GROI), and finally the net emission balance of the building. The results show that the system with the largest area of high-efficiency Si-mono modules achieves the best lifetime emission balance, but that the greenhouse gas return on investment is highest for the optimally oriented CIS modules.
Abstract
In a net zero energy building (nZEB), the energy demand from the operation of the building is met by renewable energy generated on site. Buildings require energy both in the form of heat and electricity, and solar energy utilization is important in order to reach a net zero energy balance. In projects with ambitious energy targets or limited available areas for local energy generation, solar thermal and photovoltaic (PV) installations will eventually compete for space on roofs and facades. Hybrid photovoltaic–thermal (PV/T) modules, in which heat and electricity is generated simultaneously, are therefore an interesting technology for building applications, which can potentially lead to a higher total efficiency and lower use of space. This paper describes a comparative simulation study of different solar energy solutions for a Norwegian residential building concept aiming for a net zero energy balance. Separate PV and solar thermal systems are compared to PV/T systems, and the resulting energy balances analyzed. The results show that the building with only high-efficiency PV modules comes closest to reaching a zero energy balance, but that the results depend greatly on the nZEB definition, the boundary conditions and the design of the building’s energy system.
Abstract
This paper presents a review of projects where hybrid photovoltaic-thermal (PV/T) systems are used in buildings. PV/T systems convert solar radiation to electricity and heat simultaneously, in one module. The output of both electricity and heat suggests that the technology can be suited for use in buildings, especially when the available area for installation is limited. The market and research activities related to PV/T technology has increased in recent years. This article adds to existing reviews on PV/T technology by focusing on the building perspective. Different strategies for the use of PV/T in buildings are discussed, and examples of building projects are presented. An attempt is also made to assess to suitability of different PV/T technologies for use in buildings. Finally, the regional variations in market and applications are discussed.
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.