Life Cycle Energy Performance Evaluation - Nearly Zero Energy Building Refurbishment - page 208

an indicator to define optimal refurbishment strategies from a life cycle energy
perspective.
3.1 Calculating Annual Energy Savings (AES)
Methodologies for energy performance assessment of buildings at use stage are
well developed and used throughout the world. Energy use calculations have
evolved from steady-state heat loss and semi-static monthly energy demand cal-
culations to complex dynamic energy performance simulation tools which can
model annual energy use over very short intervals (hours, minutes, even to a
fraction of a second). Simulation programs have been compared in various papers
(Crawley et al. 2008 ; van der Veken et al. 2004 ), and detailed building energy
simulation practice is extensive not only within the research community but also in
the building industry. International standards such as EN ISO 13790 'Energy
performance of buildings—Calculation of energy use for space heating and
cooling' (CEN 2008a ), which include monthly calculation methodologies, are
considered of sufficient accuracy for application in energy certification. Although
ideally every energy use should be considered in a building energy calculation
method, factors such as plug-in loads and equipment are generally excluded in
some calculation methods, particularly in energy rating and certification methods.
In refurbishment projects, and particularly if the typology and pattern of use of the
building are not expected to change after refurbishment, it is generally good
practice to analyse historical energy use in the building to more accurately esti-
mate potential energy savings.
In the context of the present methodology for life cycle energy performance
evaluation, it is suggested that any validated building energy calculation method
could be upgraded to include a 'life cycle' perspective as proposed. The only
prerequisite for the application of the proposed methodology is the conversion of
the energy use results into 'primary energy' values. Some of the available meth-
odologies' software already provides results directly in the form of primary
energy, by using national average factors for the different fuels used. Where the
calculation tool does not directly offer this possibility, conversion factors for the
different fuels used need to be applied and implemented in accordance with
national guidelines. For countries that have no defined national primary energy
factors, definitions can be found, for example, in EN 15603 'Energy performance
of buildings—Overall energy use and definition of energy ratings' (CEN 2008b ).
However, it must be noted that there are multiple issues related to calculating
'primary energy', in particular when renewable energies are considered, which are
the subject of debate, as discussed by Segers ( 2008 ).
Once the assessment methodology for energy performance calculation during
use stage is selected, the expected annual energy use and corresponding energy
savings can be expressed, for example, in kilowatt-hour of primary energy, per
square metre and year (kWh/m 2 *year).