The purpose of this article is to clarify the relative
importance of operating and embodied energy in a building’s
life cycle, especially in low-energy buildings. Design of lowenergy
buildings directly addresses the target of reducing the
operating energy. This is done by means of both passive and
active technologies. Passive technologies include, for example,
increased insulation, better performing windows, reduction of
infiltration losses and heat recovery from ventilation air and/or
waste water. Active technologies include, for example, heat
pumps coupled with air or ground/water heat sources, solar
thermal collectors, solar photovoltaic panels and biomass
burners. There has been, and there is, a variety of approaches to
designing low-energy building, and it is not in the scope of this
paper to analyze their peculiarities. However, a common aspect
is that a reduced demand for operating energy is achieved by
increased use of materials, and especially of energy intensive
materials, both in the building envelope and in the technical
installations. It has even been argued for a substitution effect
[3], for which the benefit of reducing operating energy is, to a
large extent or completely, counterbalanced by similar
increases in the embodied energy.