Life Cycle Energy Performance: Exploring the limits of passive low energy buildings

There is an increasing trend in reducing energy demand of buildings by improving building envelope thermal
characteristics. Proven construction examples as used with the German PassivHaus standard achieve
substantial reductions on the heating demand compared to mainstream construction, generally by using high
levels of insulation together with ensuring excellent air tightness and minimizing of thermal bridges.
However, the limits to which levels of insulation in a building can be increased and still represent overall life
cycle energy savings are not clear. Particularly for temperate climates, adopting very-high insulation
standards can lead to a danger of over specifying construction elements: once we reach certain levels of
insulation, any extra material used can have larger energy costs or “embodied energy” than the energy it
saves in the life cycle of the building. This paper presents the heating energy use of sample houses in the
Irish maritime climate, and analyses the life cycle energy use including the embodied energy of the materials
used. A 50-year perspective is presented, and conclusions about the limits to which the heating energy
consumption can be lowered by “passive” means on a particular climate are drawn. This paper demonstrates
the life-cycle benefits of optimizing the building design ensuring a correct orientation and sizing of the
openings, but respecting certain limits when using energy intensive insulation materials.