Civil Engineering Reference
In-Depth Information
also generally represent a diminishing NER with the size of the installation, as the
annual solar input rate per square metre of installation decreases at constant heat
demand, once we have surpassed the summer base load with the summer solar
input. This frequently occurs with large solar installations, which are in practice
oversized for the summer, and progressive increases in collector sizes do increase
embodied energy but not proportionally increase the solar energy input. Tech-
nologies such as PV, however, will have a practically constant NER independent
of their size as the production of electricity will be proportional to the quantity of
materials used in their production and installation.
In the following section, a life cycle energy performance evaluation will be
performed as an example, using a typical house in Ireland as a case study.
4 Application of Life Cycle Energy Performance
Evaluation to a Case Study Building
To illustrate the method presented, a residential house in Ireland is used as a case
study. The house size and type were selected from an example in the Irish Building
Regulations Technical Guidance Document L (Minister for the Environment
Heritage and Local Government
2007
). The details of the case study house cor-
respond to a semi-detached two-storey house, (Fig.
4
), with a total floor area of
96 m
2
, distributed on two floors, and with east-west orientation. A picture of a
semi-detached house can be seen in Fig.
4
.
Table
2
shows some basic energy performance-related parameters related to the
existing house and different options that have been tested to represent refurbish-
ment options. The measures included in the analysis have the refurbishment of the
opaque envelope increasing insulation levels, refurbishment of the windows to
better efficient ones, installing a mechanical ventilation heat recovery system
(MVHR) and installing photovoltaic systems and solar thermal collectors.
The changes in insulation levels can be observed in the provided U-value of the
building envelope, reduced from 0.45 W/m2 K in the existing situation, which
represents approximately 30 mm of expanded polystyrene insulation in a cavity
wall, to values as low as 0.10 W/m2 K for the options with lower energy use,
which would represent construction solutions with up to 300 mm of expanded
polystyrene insulation. All refurbishment strategies include the substitution of
incandescent light energy bulbs for efficient compact fluorescent lamps. They also
include changing of the existing boiler of 75 % efficiency for a new one with 90 %
seasonal efficiency. Different window specifications can also be observed through
the display of U-values and solar transmittance, representing changes to double
low-E glazing or to triple glazing.
Solar water heating is included from Option 3 onwards, with 5 m
2
of flat-plate
collectors initially and doubling the size in options 8 onwards. The introduction of
MVHR systems is considered in options 7 onwards, and an efficiency of 85 % and
