Civil Engineering Reference
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could be much more difficult to establish, as some components might last for
hundreds of years with little refurbishment, while others might experience various
major refurbishments or even be demolished within 50 years or less. Certain types
of buildings, such as speculative office developments, can often be refitted within
much shorter periods. ISO 15686 'Buildings and constructed assets—Service life
planning' (ISO
2008
) provides some guidance on how to predict the service life of
buildings and products. 50 years is frequently used as a typical value for the
service life of buildings before they undertake major renovations in many studies,
(Malmquist et al.
2010
) so this value is suggested here where no other data are
available.
The embodied energy data for each material, system or product, divided by the
expected service life, will be finally presented in kWh of primary energy per year
of service life. In this chapter, we will denominate this as AEE.
3.3 Calculating Life Cycle Energy Performance
From a life cycle energy perspective, the annual energy savings of a building
refurbishment project must only be taken into account after the embodied energy
of added building components and systems is subtracted. In the previous sections,
we have explained how the annual energy savings and embodied energy values can
be calculated and expressed in primary energy units per year. This now serves to
allow direct comparison of the results, so the impact of the building materials can
be discounted to the expected energy savings from the refurbishment project. The
life cycle energy performance of the refurbishment project will therefore consider
both the energy savings and the embodied energy of the products, as shown in
Fig.
2
.
An optimal refurbishment strategy would be one that would have the best life
cycle energy performance, that is, that would achieve high energy savings without
a high increase in the embodied energy of the products added to the building.
The life cycle energy performance can be also represented in an XY graph,
where the horizontal axis is the AEE and the vertical axis the annual energy use
(AEU) of the different refurbishment options.
The life cycle energy saving of a refurbishment strategy would be measured as
the distance to a 45 line, which would represent actuations that would have as
much embodied energy as the expected energy savings in the use phase, and
therefore would not represent any life cycle energy savings. Plotting different
refurbishment strategies in this graph, we can observe potential life cycle energy
savings for a particular refurbishment project, as it is described in Fig.
3
.
A refurbishment project that would be improved to a 'zero-energy' building
would always have an increase in embodied energy. If the building would produce
(export) enough energy to compensate the embodied energy increase, then only in
this case the refurbished building could be defined as a life cycle zero-energy
