Civil Engineering Reference
In-Depth Information
Regarding energy performance of the building in operation, parameters related
to local climate and building design and orientation are mostly fixed in refur-
bishment projects, and issues such as wind exposure and solar access can be
considered in detail before carrying out a refurbishment project. User behaviour
and preferences can also be addressed although uncertainty is quite high and they
can also largely influence the results. For example, a significant impact on the
reduction in household energy use could be achieved without any or little asso-
ciated embodied energy by assuming more conscious energy behaviour of the
occupants. This substantial reduction in energy use, in the case, for example, of
appliances and lighting, could also result in diminished internal gains, which
would mean that the heating energy demand could increase. On the contrary,
careful control of the heating, and flexible approach to thermal comfort by the
occupants could mean large savings in HVAC use. Uncertainty and sensitivity
analysis on building energy performance calculation methods have already been
analysed in detail in various studies (Hopfe
2009
), so it will not be discussed in
this section.
Regarding calculation of embodied energy for the products, as it has been
commented, data on factors such as service life or maintenance required for energy
systems of renewable energy present a high degree of uncertainty. While com-
mercial LCA software nowadays contains tools for a detailed sensitivity and
uncertainty analysis, including methods such as probabilistic Monte Carlo simu-
lations, many times the data necessary to perform a thorough sensitivity analysis of
embodied energy, such as the one performed in this chapter, are lacking. For this
reason, the use of a single value has been considered more appropriate in this
chapter for clarity and simplicity of the representation of results. However, some
comments can be made on the sensitivity of the results:
The choice of insulation material and its assumed lifetime has a large effect on
the results. For this study, it has been assumed a combination of an insulation
material with large embodied energy (88 MJ/kg), and a relatively long associated
service life (50 years). If service life would be diminished, as it could be con-
sidered in cases such as external insulation techniques or construction elements in
particularly harsh climates, the annualized embodied energy would be propor-
tionally increased, and therefore, life cycle energy savings and NER of the
refurbishments would be lower. On the other hand, if equal insulation levels would
be achieved with other insulation materials with a lower embodied energy than
polystyrene, life cycle energy performance would improve. Options using alter-
native products might include mineral wools (approximately four times less
associated embodied energy than polystyrene) and other natural or rapidly
renewable products with practically no associated embodied energy (Hammond
and Jones
2008
). These observations highlight the influence that the proposed
methodology would have on supporting the specification of materials with long
associated service life and low embodied energy in refurbishment projects. Ideally
in the near future, the application of this method would consider the value of
