WINDOWS
- To match existing (Budget Windows)
o Sliding window - aluminium 2 lite – Single Glaze – 5mm Clear - brick veneer / cladding or double brick / Masonry – Size to suit brick coursing (coursing chart available here) - U-Value: 6.3 (R-Value 0.158) - SHGC: 0.72 - Air Infiltration: 0.74 L/s m2 o East and West Facing Window Upgrade - tinting film - solar high performance window film – Low E (3M™ Thinsulate™ TCC 40 Window Film) – - U-Value (Glass upgrade only): Approx. 4.0 (R-Value 0.25) - SHGC (Glass upgrade only): Approx. 0.31 - Air Infiltration: 0.74 L/s m2
Windows can severely impact on the heating and cooling loads of a building. Up to 40% of a home’s heating energy can be lost and up to 87% of its heat gained through windows. Improving windows’ thermal performance reduces energy costs and greenhouse gas emissions.
Conduction: U-value U-value (expressed as Uw in windows) measures how readily a window system conducts heat. It is a measure of the rate of non-solar heat loss or gain through it. The rate of heat is indicated in the terms of the U-value of a window assembly which includes the effect of the frame, glass, seals and any spacers. The lower the U-value, the greater a window’s resistance to heat flow and the better its insulating value. A simple formula can help quantify the impact of improved U-value:• the amount of heat conducted through a glazed unit (in watts) equals the U-value (Uw)• multiplied by the number of degrees difference in air temperature on each side (T)• multiplied by the area of the glazing unit (A)Uw x T x A = watts (W) If your home has 70m2 of windows and glazed doors with aluminium frames and clear glass (i.e. U-value of 6.2), on a winter’s night when it’s 15°C colder outside, the heat loss would be about:6.2 x 15 x 70 = 6,510WThat’s equivalent to the total heat output of a large gas heater or a 2hp air conditioner running at full capacity. If you roughly halve the U-value of the window by selecting double glazing, you can halve the heat loss — in this example avoiding about 3,000W of heat loss, equivalent to the energy use of fifty 60W incandescent light bulbs. Solar heat gain coefficient The SHGC for windows (expressed as SHGCw) measures how readily heat from direct sunlight flows through a window system. The SHGC is the fraction of incident solar radiation admitted through a window, directly transmitted as well as absorbed and subsequently released inward. SHGC is expressed as a number between 0 and 1. The lower a window’s SHGC, the less solar heat it transmits.
Conduction: U-value U-value (expressed as Uw in windows) measures how readily a window system conducts heat. It is a measure of the rate of non-solar heat loss or gain through it. The rate of heat is indicated in the terms of the U-value of a window assembly which includes the effect of the frame, glass, seals and any spacers. The lower the U-value, the greater a window’s resistance to heat flow and the better its insulating value. A simple formula can help quantify the impact of improved U-value:• the amount of heat conducted through a glazed unit (in watts) equals the U-value (Uw)• multiplied by the number of degrees difference in air temperature on each side (T)• multiplied by the area of the glazing unit (A)Uw x T x A = watts (W) If your home has 70m2 of windows and glazed doors with aluminium frames and clear glass (i.e. U-value of 6.2), on a winter’s night when it’s 15°C colder outside, the heat loss would be about:6.2 x 15 x 70 = 6,510WThat’s equivalent to the total heat output of a large gas heater or a 2hp air conditioner running at full capacity. If you roughly halve the U-value of the window by selecting double glazing, you can halve the heat loss — in this example avoiding about 3,000W of heat loss, equivalent to the energy use of fifty 60W incandescent light bulbs. Solar heat gain coefficient The SHGC for windows (expressed as SHGCw) measures how readily heat from direct sunlight flows through a window system. The SHGC is the fraction of incident solar radiation admitted through a window, directly transmitted as well as absorbed and subsequently released inward. SHGC is expressed as a number between 0 and 1. The lower a window’s SHGC, the less solar heat it transmits.
Source: The Australian Window Association - Heat transfer mechanisms.
Glazing type and Orientation
In Perth’s climate, Northerly glazing should have a high SHGC.
Northerly windows are the home’s solar collectors. However, these windows should also have fixed shading designed to shade as little of the glass in winter as possible while shading as much as possible in summer (Eaves). Low-emissivity (low-e) double glazing with high solar transmission provides an even better annual result.
East and west-facing windows should have a low SHGC, particularly if they are large, because they present energy efficiency problems. It is better to use adjustable external shading if it is possible. The next best thing is a low SHGC window which dulls the overheating problem in summer at the expense of passive solar gain in winter. This is a trade-off where the summer benefit normally outweighs the winter issues.
It is always the case that the lower the U-value the better, because it is the U-value that measures the ability to retain heat in winter and cold in summer, regardless of orientation.
For all orientations a low U-value outperforms a high U-value, especially for north-facing windows.
South-facing windows can have any SHGC because there is little solar heat gain from that direction in winter or summer.
Information provided by: http://www.yourhome.gov.au/passive-design/glazing
Best Practice windows
North Facing – UPVC DG - Deceuninck uPVC Tilt and Turn Window - Double Glazed – 4mm clear float glass/14mm Argon filled Airspace/4mm Pilkington Energy Advantage™ Low-E Glass. - U-Value: 1.9 (R-Value 0.526) - SHGC: 0.40 - Air Infiltration: 0.27 L/s m2
East and West Facing - UPVC DG - Deceuninck uPVC Tilt and Turn Window - Double Glazed – 4mm Pilkington EverGreen™/14mm Argon filled Airspace/4mm Pilkington Energy Advantage™ Low-E Glass. - U-Value: 1.9 (R-Value 0.526) - SHGC: 0.23 - Air Infiltration: 0.27 L/s m2
South Facing - UPVC DG - Deceuninck uPVC Tilt and Turn Window - Double Glazed – 4mm clear float Glass/14mm Argon filled Airspace/4mm clear float Glass. - U-Value: 2.3 (R-Value 0.434) - SHGC: 0.43 - Air Infiltration: 0.27 L/s m2
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Note: As the above table shows, although the SHGC of the Budget window is 44% higher than the Best Practice glazing unit (North facing Orientation), the gain is greatly offset by poor performance in U value and Air tightness. The Best practice window is 2.3x more efficient than the Budget Window (Most common window assemblies in Perth) and 1.74x more air tight.
Single glazed 5mm clear float glass Aluminium Sliding Window 1210mm W x 1200mm H Supplied and Installed: $470.63 Plus GST (U value 6.3)
UPVC DG - Deceuninck uPVC Tilt and Turn Window - Double Glazed – 4mm clear float glass/14mm Argon filled Airspace/4mm Pilkington Energy Advantage™ Low-E Glass 1210mm W x 1200mm H Supplied and Installed: $1082.44 Plus GST (U Value 1.9)