Assessing Window Materials for Energy Ratings

Window Energy Ratings 1
ASSESS WINDOW MATERIALS FOR SUITABILITY OF ENERGY RATING
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Window Energy Ratings 2
Introduction
Research shows that windows contribute approximately 38% of heating energy use and
29% of cooling energy use (Brownlee & Wright, 2015). Hence, window design optimization and
material selection for thermal performance is important for occupants in achieving low energy
consumption and increasing the overall performance of the building. To achieve energy
efficiency in windows, manufactures have come up with ranking mechanism that label window
products on the basis of their energy efficiency through the Energy Rating System (ERS).
Energy rating system is an assessment method of comparing the energy performance of
windows. Its main purpose is to rank windows according to their energy performance in order to
enable customers to relate with the windows using particular numbers that is relative to their
energy efficiency. The energy rating formula is derived from the balance between heat loss
through conduction and air infiltration or leakage and heat gain via the window. It is
recommended to label each window with a separate energy rating (ER) for cooling and heating
conditions since heat gain and heat loss parameters have opposite effects on cooling and heating
energy. A number of countries have different variation of energy ratings on windows due to
different climatic condition throughout the year. An international standard method was
established by ISO to determine a similar method for calculating the energy rating (ER) for
windows in ISO 18292 (Sorgato, et al., 2016). Over the years, some challenges experienced in
energy performance of fenestrations have raised concern in the industry that could compromise
the validity of the energy ratings as a method of ranking the energy performance of windows in a
predominantly hot climate. This issues mainly deal with selection of a reference building, impact
of thermal comfort and the advancement in glazing technology.

Window Energy Ratings 3
Therefore, this paper will assess window materials of a builder in relation to their
suitability and energy ratings by comparing the builder’s choice of selection of the window
materials and comparing them with the energy rating report. The essay will go ahead to give
their material properties considering the thermal and durability property of each material. I will
then conclude by giving an alternative for window frame material will improve the energy
performance of the building.
On technical grounds, it was reported that the window energy rating scheme was
established in the year 1995 in cooperation with the University of New South Wales. The scheme
founders were Dr Peter Lyons and PC Thomas (Sorgato, et al., 2016). This enabled windows to
be labelled and rated for energy impact on the overall performance of the house in any climate of
Australia. Therefore, window makers must comply with the energy rating standards as stipulated
by the Australian Fenestration Rating Council in order to participate in Windows Energy Rating
System (WERS)
Suitability of materials
The builder’s choice of material was very simple. He opted to go with aluminum frames
with 3mm single glazing layer of glass material labelled window 1. Aluminum is a strong but
inexpensive material for home building given the advantage of its durability and the fact that it
can be painted (Kibert, 2016). Aluminum may not be the choice in regard to heat transfer
mechanisms since it is a good conductor of heat which translates to more heat gains and heat loss
through conduction process. The single pane glass has a low rating in terms of energy efficiency
since it provides only a thin barrier to heat transfer from daylight hence exhibiting very little

Window Energy Ratings 4
insulating value due to a high U- factor. This will definitely add up the hefty costs of heating and
air-conditioning. According to the star ratings table for generic windows created for the Window
Energy Rating Scheme (WERS) of Australia, it shows that window number 1, which is 3mm
single glazing clear glass with aluminum frame has zero cooling star and 1-star for heating
performance. Therefore, this means that when Post Occupancy Evaluation and thermal comfort
of the house is carried out, it will exhibit poor performance in terms of energy performance level
of the building.
Figure 1: single pane
Source: (Kibert, 2016)
Properties of materials
Windows are defined by sticker ratings that gives them their performance scores to
determine the best choice for building a home, if sustainability and thermal comfort is key to the
design implementation.