Conduction
Heat moving through an object (i.e. heat will travel through an aluminium, or steel frame more easily than through a timber or PVC frame).
Radiant heat
Heat from the direct sun. It can pass through space until reflected or absorbed.
Convection
Heat flow resulting from air movement e.g. either 'natural' convection - warm air rises, or 'forced' convection - a breeze by a window, both can result in a draught by a window.
Infiltration
Air leaks around the frame, around the window sash and through the gaps in the movable window parts.
When evaluating your options to improve the thermal performance of your windows, the following double glazing key performance criteria should be considered:
U-Value (Uw)represents heat transfer through a window, irrespective of direct sunlight.The lower a window’s U-Value, the better the insulation performance.
Solar Heat Gain Coefficient (SHGC)measures the solar energy that passes through glazing.The lower the SHGC, the less solar heat is transmitted through a window.
Air Infiltrationor leakage measures the rate at which air passes through gaps in window joins and seals.The lower the air infiltration, the better a window’s energy performance.
The Window Energy Rating Scheme (WERS) Thermal Performance
Aluminium Frame Windows
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
Timber Frame Windows
Glazing Type
Cooling Stars
Heating Stars
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
*WERS standard typical industry window **Solartite is a range of high performance window film. The window tested above has Solartite’s low-e film.
Magnetite vs Traditional Double Glazing – What the experts says
Winter- the ideal situation is to let in as much of the sun's heat and then trap it inside to maintain a comfortable environment in your home or office. This will also significantly reduce heating costs and saves you money. The ideal window for winter will have ahigh SHGCto let the sun's heat in and alow U-Valueto prevent the heat from escaping. Clear windows without shading films are better suited for winter climates.
Compared with traditional double-glazing, Magnetite’s double-glazing solution can provide better results during winter or for cold climate areas such as Canberra, the Adelaide Hills and Blue Mountains.
Magnetite's clear acrylic window panels allow the direct heat from the sun's rays to enter the building and once inside, Magnetite's superior magnetic seals retain the heat, giving Magnetite an advantage over conventional operating windows.
Summer- the ideal situation is to minimize the heat coming in from outside and prevent the cool air inside from escaping through the window. This will make your home more comfortable and reduce your air-conditioning costs. The ideal window for summer, or for a large west-facing window, will have alow SHGCto limit the heat from the sun's direct rays, as well as, alow U-Valueto prevent the heat in the air outside from moving through the window and warming the cool conditioned air inside. It is better to have ashading filmon the first (outer) glass pane to limit the heat that enters the double glazed unit.
The combination of Magnetite retrofit double glazing and Solartite outperforms the traditional insulated glass unit for hot climate. Magnetite fit over an existing window with reflective film will give better summer heat control than a double-glazed window with supertoned glass.
The Magnetite system stops the conduction and convection of heat better than glass windows giving superior results for summer conditions. Combined with a film or a shading device, Magnetite is the ideal solution for the hot Australian conditions.
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
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%
*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.
