Understanding Energy Efficiency and Windows

The Window Energy Rating System (WERS) was developed by the Australian Window Association (AWA) in conjunction with the CSIRO and Unisearch Ltd. WERS brought Australia in line with international standards, in 2008. The ratings compare windows, based on performance. The ratings listed in the chart below combine several key performance criteria.

U – Value (Uw) represents heat transfer through a window, irrespective of direct sunlight. The U-value is specific to windows, though it is the inverse of R-value, commonly used to gauge wall or ceiling insulation and other building materials. For this reason, the lower the U-Value the better the insulation performance. Magnetite uses acrylic glazing rather than low-E glass to minimise the U-value. Acrylic glazing is up to six times more thermally efficient than glass.

Solar Heat Gain Coefficient (SHGC) measures the solar energy that travels through glazing. The lower the SHGC, the less solar heat is transmitted through the window. In hot weather climates, windows with a low SHGC are preferred, to minimise unwanted solar heat gain. In cold weather climates, windows with high SHGC are preferred to allow solar heat gain. In most climates the orientation of the window will determine the requirements for SHGC. Typically, West-facing windows should have a darker shade providing a lower SHGC compared to South windows, which should be clear. North or East facing windows have varying SHGC’s, based on building design and climate zone. Magnetite has a range of solar control films, (Solartite) to reduce the SHGC and minimise radiant heat before it enters the air cavity, delivering better results.

Visible transmittance (VT) measures the amount of light a window lets through. A higher VT means more light is transmitted. A higher VT can improve energy efficiency, as less artificial lighting is required (unless glare reduction is a consideration). Tinted glass, used to reduce solar heat gain, can also reduce the amount of visible light transmitted, which is not good for day lighting. A spectrally selective tint can help reduce the solar gain while providing as much visible light as clear glass.

Air infiltration (or leakage) measures the rate at which air passes through joints and seals in a window; the lower the air infiltration, the better a window’s energy performance. Magnetite’ has continuous magnetic seals, to limit the air infiltration from the existing window, virtually eliminating draughts. The addition of Magnetite panels will dramatically drop the air infiltration of an existing window from the standard 5.0L/m2 to 0.5L/m2, a tenfold reduction in air infiltration thanks to magnetic seals.

Glazing Type	Cooling Stars	Heating Stars	Cool%	Heat%	Uw	SHGC
Single glazed 3mm clear glass*					7.4	0.77
Single glazed 3mm clear glass & 4.5mm Magnetite			35%	59%	2.9	0.67

Glazing Type

Cooling Stars

Heating Stars

Cool%

Heat%

SHGC

Single glazed 3mm clear glass*

7.4

0.77

Single glazed 3mm clear glass &
4.5mm Magnetite

35%

59%

2.9

0.67

Glazing Type	Cool%	Heat%	Uw	SHGC
Single glazed 3mm clear glass*	20%	28%	5.5	0.69
Single glazed 3mm clear glass & 4.5mm Magnetite	37%	61%	2.6	0.66
Single glazed 3mm clear glass with Solartite** and 4.5mm Magnetite	76%	45%	1.8	0.20

Glazing Type

Cooling Stars

Heating Stars

Cool%

Heat%

SHGC

Single glazed 3mm clear glass*

20%

28%

5.5

0.69

Single glazed 3mm clear glass &
4.5mm Magnetite

37%

61%

2.6

0.66

Single glazed 3mm clear glass with
Solartite** and 4.5mm Magnetite

76%

45%

1.8

0.20

Glazing Type	Cooling Stars	Heating Stars	Cool%	Heat%	Uw	SHGC	AI
Double Glazed 3mm clear glass/12mm air gap/3mm clear glass IGU (Insulated Glass Unit)*			40%	55%	3.0	0.61	5.0
Single glazed 3mm clear glass & 4.5mm Magnetite			37%	61%	2.6	0.66	0.5

Glazing Type

Cooling Stars

Heating Stars

Cool%

Heat%

SHGC

Double Glazed 3mm clear glass/12mm air
gap/3mm clear glass IGU (Insulated Glass Unit)*

40%

55%

3.0

0.61

5.0

Single glazed 3mm clear glass &
4.5mm Magnetite

37%

61%

2.6

0.66

0.5

Glazing Type	Cooling Stars	Heating Stars	Cool%	Heat%	Uw	SHGC	AI
Double Glazed 5mm Supertoned glass/6mm air gap/5mm clear glass IGU (Insulated Glass Unit)*			54%	425%	3.30	0.461	5.0
Single glazed 3mm glass Solartite** and 4.5mm Magnetite			73%	38%	2.4	0.19	0.5

Glazing Type

Cooling Stars

Heating Stars

Cool%

Heat%

SHGC

Double Glazed 5mm Supertoned glass/6mm
air gap/5mm clear glass IGU (Insulated Glass Unit)*

54%

425%

3.30

0.461

5.0

Single glazed 3mm glass Solartite**
and 4.5mm Magnetite

73%

38%

2.4

0.19

0.5

Noise Reduction Technical Data and Results

Proven Results

Noise pollution is one the biggest problems faced in the cities today, particularly in a high-density living. Unwanted noise can be responsible for sleep loss and lack of concentration. This can lead to a deterioration of health through increased stress levels, headaches, high blood pressure and loss of hearing.

Noise penetrates windows through leaky seals or vibrations through the window structure. To reduce noise, a window should minimise air infiltration, hold enough weight to limit vibration and allow a large air cavity. This cavity, or air gap, is the key to secondary glazing.

Expert Advice:

CSIRO Research by John Davy shown an air cavity can effectively enhance sound insulation performance. The larger the air cavity the more noise the window system can reduce. Results show a wide air gap of 100-125mm will improve sound insulation by an average of 7dB(A) more than windows with a narrow gap of 8-13mm.

Window or Glass Door Type	Total Glass Thickness (mm)	Air Cavity Thickness (mm)	Sound Insulation (dB)
Single Glaze 3mm	3	0	23
Single Glaze 6mm	6	0	27
Double Glaze Narrow Gap	9-12	8-13	31
Double Glaze Wide Gap	9-12	100-125	38

Window or Glass Door Type

Total Glass Thickness (mm)

Air Cavity Thickness (mm)

Sound Insulation (dB)

Single Glaze 3mm

Single Glaze 6mm

Double Glaze Narrow Gap

9-12

8-13

Double Glaze Wide Gap

9-12

100-125

The human ear is less sensitive to low frequency sound. According to a study released by the CSIRO, the human ear needs a change of 3dB to detect a difference in noise levels and the human ear perceives a change of 10dB as a doubling or halving of the noise level.

If you double the thickness of glass in a window the noise level will decrease by 3dB the least amount possible to make a difference. If the glass is laminated there is no perceived difference in noise reduction.

National Acoustic Laboratory Testing:

Working with the principles of noise transfer, Magnetite® and Soundtite are designed for high performance, which is achieved by combining air tight seals with the ability to maximize an air cavity and the flexibility to vary glazing thickness to suit. Magnetite® is excellent at reducing general noise such as busy roads, commuter trains and noisy neighbours. Whereas, Soundtite works well to combat low frequencies noise such as garbage truck, freight trains or airplane during take-off and landing.

Test Code	Material Tested	Rw*	Improvement
ATF 707 (test window)	Aluminium sliding window, 3mm float glass with mohair seals	23	N/A
ATF 709	Test window, 100mm air gap and Magnetite System (4.5mm acrylic panel)	35	52%
ATF 1507	Test window, 100mm air gap and Magnetite System (10.0mm acrylic panel)	39	70%
ATF 817	Test window, 100mm air gap and Soundtite (6.38mm laminated glass)	41	78%

Test Code

Material Tested

Rw*

Improvement

ATF 707 (test window)

Aluminium sliding window, 3mm float glass with mohair seals

N/A

ATF 709

Test window, 100mm air gap and Magnetite System (4.5mm acrylic panel)

52%

ATF 1507

Test window, 100mm air gap and Magnetite System (10.0mm acrylic panel)

70%

ATF 817

Test window, 100mm air gap and Soundtite (6.38mm laminated glass)

78%

*The Weighted Sound Reduction Index (Rw) is a measure for sound insulation performance of a single building element such as windows. The higher the Rw rating, the better the sound insulation.

Understanding Energy Efficiency and Windows

The Window Energy Rating Scheme (WERS) Thermal Performance

Aluminium Frame Windows

Timber Frame Windows

Magnetite vs Traditional Double Glazing – What the experts says