26
Vision Magazine
Ongoing issues
There are always going to be a variety of ways to
interpret regulations because the design of buildings
is complex. But some issues keep repeating and this
warrants education of the industry to ensure they are
addressed.
The most common mistake is the assumption that
the values within that calculator are glazing values
only, and not whole window values. Designers
and architects were selecting glass from a glazing
manufacturer’s catalogue to meet the value in the
calculator. The lack of understanding resulted in
non-compliant designs. When the glass type selected
was fitted with a typical aluminium frame, the U-value
could be reduced in performance by up to 50%.
Before J was introduced, the architect would provide
a concept. The mechanical engineer would offer a
glass performance relative to the impact on their
mechanical air conditioning plant. With the advent of
Section J the mechanical consultant has somewhat
relinquished the control of this aspect of the design
and on many projects in the early days this small but
important role has been overlooked. Anomalies still
arise in terms of how the DTS calculator is used which
can impact the mechanical services.
For example the DTS calculator calls for a façade
height and length to be entered. Within this façade
area the window area is entered and an allowable
maximum thermal performance is calculated
depending on orientation and class of the building.
One common mistake still being made is the height
of the façade.
Designers misinterpret the calculator and do not
assess their design and the use of the calculator
using first principles. The objective of J (JO1) is to
reduce greenhouse gas emissions. The use of the
calculator should be coupled with the intent of the
buildings air conditioning services. Therefore the
calculator should reflect the mechanical zoning
designed to suit the intended space. Additionally
the façade height used in the calculator should
reflect the identified conditioned zone behind. For
example a standard office building typically uses the
ceiling void as a return air plenum with return air via
light troffers. As a result, the ceiling void effectively
Professional Development Series
becomes part of the conditioned zone and a floor
to slab height can be entered into the calculator.
However, if the building services design is to be a
ducted return and the intent for the use of space will
always be this type such as a hospital with infection
control, then the ceiling void will not be part of the
conditioned zone. The difference between these
two methods of measurement of the façade could
result in 20% difference in glazing performance or
more. What is presented now in the non-conditioned
ceiling void case above is the question of whether
the ceiling now requires insulation or not. This
example identifies an area within J that has a level of
ambiguity and yet to be resolved. It also emphasises
why it is so important to ensure the Section J
assessments on façade and glass are carried out in
conjunction with the mechanical services design
calculations to ensure that oversized equipment is
not installed. The result of oversized equipment is
that it will operate at lower than optimal efficiencies.
This error in design will result in an energy penalty
for the operating life of the plant.
What does need to improve drastically is the policing
of the final installations. It strikes me as ridiculous
that the developers and their team of designers can
go to great expense to develop higher performing
buildings when there is very little being done to
ensure J is being policed appropriately.
The Future
As understanding of construction materials and
occupant behaviour improves, so should the
performance of buildings. Among this glass plays
an important role. The main problem between
architects and energy efficiency designers is that
one wants high visible light transmission (VLT) and
the other requires low SHGC values. As glazing
technology improves, we can hope that there is an
uncoupling of these constraints and advancement
in the outcome from both perspectives. Lately there
has been an improvement on this front and we are
now seeing glass types with SHGC’s in the 0.30’s
and VLTs in the 0.55’s. Is triple glazing required in
Australia? Probably not all but for the most remote
regions of Tasmania or the mountains.