The « positive energy house » concept combines energy saving, e.g. applying the passive house approach, and electricity production using a renewable resource, leading to a positive primary energy balance on a yearly basis. Compared to a standard house, more materials and components are used (thicker insulation, triple glazing windows, renewable energy systems…), this is why the environmental relevance of this concept is often questioned.
In order to contribute to answer this question, a life cycle assessment (LCA) has been used to evaluate the environmental impacts of such buildings, including the fabrication of components, construction, operation, maintenance, dismantling and waste treatment. This paper presents results in the case of a positive energy building, showing also the influence of the choice of the heating system on various environmental impacts considered in this assessment (e.g. global warming potential, radioactive waste production, photochemical
oxidant formation potential, cumulative energy demand, abiotic depletion potential).
The case study concerns two attached passive houses built in Picardy, France, in which renewable energy systems are studied theoretically: the real houses include solar water heating but no renewable electricity production. The envelope has a high insulation, high airtightness and very low thermal bridges. The technical equipment includes a heat recovery ventilation and an earth-to-air heat exchanger. In this study, PV solar panels mounted on the roof have been added so as to obtain a positive primary energy assessment. For these houses,
three different heating solutions have been studied: an electric heat-pump, a wood pellet condensing boiler and a wood pellet micro-cogeneration unit.
The three alternatives have been modeled using the building thermal simulation tool COMFIE, in order to evaluate their heating load, possibly cooling load and thermal comfort level. Environmental impact indicators have been evaluated for these alternatives applying the LCA tool EQUER, linked to the building simulation tool COMFIE and using life cycle inventories from the Swiss Ecoinvent data base.