Energy Efficient glazing

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					AdelAide City CounCil
Green BuildinG FACt SheetS

Energy Efficient glazing
Selecting Efficient Glazing
Glazing is used to allow natural daylight to enter buildings, this
improves occupant well being and productivity and reduces the
energy used for artificial lighting. It is important that the glazing
system enables daylight to enter without the associated heat
and glare that accompanies direct sunlight. There are many
ways that this can be achieved.
When properly selected and orientated, energy efficient
glazing can help provide year round comfort and reduce air-
conditioning energy consumption. The main factors are the size
and orientation of the windows, the amount of shading and
the type of glass that is used in the windows. Shading can be
applied either internally or externally.
Windows and other glazed external surfaces have a significant
impact on the energy efficiency of a building.
A distinct improvement in comfort levels can be achieved by
selecting a beyond-compliance solution to glazing for a new or
retrofitted residential, commercial or institutional development.
This Green Building Fact Sheet seeks to assist developers and
property owners in selecting glass types that meet requirements
and achieve high levels of occupant comfort.

ADelAIDe (CITY) DevelOpmeNT
The Objectives and principles of the Adelaide (City)
Development plan require new development to provide a
sustainable balance between comfort levels for occupants and
neighbours with minimized energy use for heating, cooling and
lighting, as follows:
   •   energy efficiency, (Objective 31; principles 104 to 113),
    • microclimate and Sunlight (Objectives 34 and 35;
       principles 117 to 124)
The Building Code of Australia has introduced new external
glazing requirements for commercial buildings (Classes 5 to 9).
A glazing calculator is provided at

energy efficient glazing systems can reduce carbon emissions,
provide insulation and enable cost savings for new and retro-fit
developments in the following ways:
   •   Reduce demand for cooling and heating
   •   Reduce size and cost of HvAC plant
   •   Reduce artificial lighting requirements
   •   provide acoustic insulation.
An energy efficient glazing system can also assist a building to      CASE STUDY 1
comply with:
   • Australian Building Greenhouse Rating scheme (ABGR),             40 Albert Road, South Melbourne
      Green Building Council Australia (Green Star), National
      Australian Built environment Rating System (NABeRS)             The building at 40 Albert Road, South
   • South Australian Government tenancy sustainability               melbourne has a NlA of 1200m2 and is
      requirements                                                    owned and occupied by Szencorp. In
   • Australian Building Code requirements                            refurbishing the building the company had
      (part J2 – external Glazing)                                    the vision of setting the benchmark for green
Glazing Types                                                         buildings in Australia.

There are many glazing types on the market, for the purposes          Among a host of environmentally sustainable
of this fact sheet the following four types are explored:             design features, the company installed floor
                                                                      to ceiling high performance double glazing to
   • Single Clear Glazing                                             maximise daylight penetration into the narrow
   • low e Single Glazing                                             east/west oriented building.

   • Double Clear Glazing                                             While allowing daylight deep into the building,
                                                                      the glazing qualities prevent excessive
   • low e Double Glazing                                             heat transfer, the windows can also be
Single Clear Glazing. Relative to all other glazing options,          opened allowing natural ventilation. These
single-glazed with clear glass allows the highest conductive          features reduce the need for lighting and air
transfer (i.e. heat loss or heat gain) while permitting the highest   conditioning.
solar heat gain and daylight transmission.                            Full length shading screens to the eastern
Low-E Single Glazing. low emissivity (low-e) glass has                façade along with operable internal blinds
a coating that minimises re-radiated heat. It has a clear             reduce glare and assist in reducing heat
appearance and good thermal properties and can be used                entering the building.
as single glazing or double glazing. low-e glazing sometimes          The ‘green’ qualities of the property have
called spectrally selective low-e glass helps to reduce the           been widely recognized with the Green
invisible, near infrared solar radiation that contributes to          Building Council of Australia awarding it the
unwanted heat gain while permitting daylight transmission.            first 6 star rating for a commercial office
Double Clear Glazing. This offers some thermal insulation. It         refurbishment, the highest standard available,
is made of two clear glass panes separated by an air gap. The         meriting world leadership status.
air gap acts as an insulating barrier between the window panes        Along with other energy saving features, the
and is an effective way of reduce conductive heat transfer.           glazing contributes to an overall energy saving
Compared to single glazing, it can cut heat loss in half due to       of 48% compared to typical office energy use
the insulating air space between the glass layers. In addition to     per square metre.
reducing the heat flow, a double-glazed unit with clear glass
 will allow the transmission of high visible light and high solar
heat gain.
Low E Double Glazing. This is made from coated glass panes
separated by argon/crypton gas. This type of low-e glazing,
sometimes called spectrally selective low-e glass, reduces heat
loss in winter but also reduces heat gain in summer. Compared
to most tinted and reflective glazing, this low-e glass provides
a higher level of visible light transmission for a given amount of
solar heat reduction.
Other features of glazing that can increase the energy efficiency
of glazing include:
   • Reflectivity, although neighbourhood amenity requires
     consideration, often reducing the reflectivity rate to 15 to
     20 percent.
   • Tints and tones act like sunglasses to absorb heat.
   • Spectrally selective glass which maximises visible light
     transmission while reflecting unwanted solar radiation
     (Uv) and heat. This can also have low emissivity.
   • polymers (plastic glazing) as alternatives to glass.
                                                                     CASE STUDY 2
                                                                     Ballarat University, Vic

                                                                     Some advanced glazing products not only
                                                                     offer reductions in heat transfer and solar
                                                                     radiation but can incorporate solar energy
                                                                     generation through Building Integrated
                                                                     photovoltaic (BIpv) systems.
                                                                     Such technology has been adopted in
                                                                     a number of properties, one example is
                                                                     the University of Ballarat’s new Building &
                                                                     Construction Training Centre which has
                                                                     recently (December 2006) incorporated a
                                                                     200m2 north facing glazed façade.
                                                                     This project uses Schott Solar’s ASI glass
                                                                     product which is double glazed and blocks
                                                                     solar radiation. This reduces the heat transfer
                                                                     into the building in the summer and prevents
                                                                     heart loss in the winter.
                                                                     The glass still allow for excellent visibility as
                                                                     it allows light through but at the same time
                                                                     allowing a reduction in the capacity of the air
                                                                     conditioning plant of 40%.
                                                                     The BIpv façade generates 7.300KWh of
                                                                     renewable energy each year and saves 9,500
                                                                     kg of CO2-e.

Glazing performance – Definitions
When considering the properties of different glazing options,
various measurements can be used to compare the
performance of products against the cost.
The following definitions are the most commonly used in
assessing the performance of windows.
U-value (U factor) measures the rate that heat transfers
through glazing and window assemblies. The lower the U value
the better the window’s insulation value and its ability to resist
heat flow.
Solar Heat Gain Co-efficient (SHGC) The SHGC measures
how well a product blocks heat from the sun. The co-efficient                  FIND OUT mORe
is the fraction of incident solar radiation admitted through
a window, both directly transmitted, and absorbed and      
subsequently re-released inward and the lower the co-efficient       (A Glazing Calculator has been launched by
the less solar heat it transmits. (                     the Australian Building Codes Board (ABCB).
Visible transmittance (VT) measures how much light comes   
in through a product. It is an optical property that indicates the   The Window energy Rating Scheme
amount of visible light transmitted. vT is expressed as a number
between 0 and 1. The higher the number, the more light is            Factsheets for home design
transmitted. (
Spectrally selective glass maximises visible light transmission      Green Building Council of Australia
while reflecting unwanted solar radiation (Uv) and heat. This
can also have low emissivity. Glass properties that affect the       The Australian Building Greenhouse Rating
amount of sunlight penetrates a building are known as the
shading factor (SF) and the light transmission (lT) rate.

 Glass Type                     U Value        SHGC           VT       Glazing Cost/m2           Daily Electricity         Payback
                                                                                                     Savings                Period
 Single Clear Glazing              5.8           0.81        0.87              $50                        -

 low e Single Glazing              3.7           0.7         0.82             $125                 $ 0.09 / 10m2            7.8 yrs

 Double Clear Glazing              2.7           0.7         0.78             $130                 $ 0.16 / 10m2            4.7 yrs

 low e Double Glazing              1.9           0.66        0.73             $180                 $ 0.20 / 10m2            6.1 yrs

*Cost savings based on computer simulation test results based on a hypothetical1000m2 building with glazing facing N, E, S and W and air
conditioning operating 12 hours per day. Based on 15c/kWhr of electricity.

                                                                                             CASE STUDY 3
                                                                                              Air Apartments, Greenhill Road, SA

                                                                                              In designing these prominent apartments,
                                                                                              created from the shells of two former
                                                                                              eTSA towers, it was vital to maintain the
                                                                                              panoramic views. The project required a high
                                                                                              performance glazing which would enable
                                                                                              great clarity and but offer energy savings
                                                                                              as well.
                                                                                              The architects selected pilkingtons Clear Solar
                                                                                              e Glass which is designed to offer
                                                                                              high visual transmittance and good
                                                                                              thermal performance.
Adelaide City Council is committed to promoting ecologically
sustainable building practices.                                                               This project gained extra energy efficiency
                                                                                              dividends from the use of passive design in
This Green Sheet is provided for introductory reference.                                      deep balconies which act as shading and
Before proceeding with an glazing system, property owners                                     complement the qualities of the glazing.
and builders are advised to engage specialists and to comply                                  The company claims that this combination
with statutory requirements including the Adelaide (City)                                     means that in all but the warmest weather,
Development plan and Building Code of Australia.                                              natural ventilation is sufficient for comfortable
                                                                                              climate control.

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