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2.7 WINDOWS AND DOORS - Coggle Diagram
2.7 WINDOWS AND DOORS
1) WINDOWS
Most window manufacturers rate the thermal performance of windows not by the thermal resistance (RSI/R value), but by Heat Loss Coefficient (U-value)- the rate at which heat transfers. The greater the U-value, the greater the heat flow through a window.
Energy codes require the total U-value that takes into account the centre if glass, edge of glass and frame heat loss.
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Solar heat gains through a given widow are a function of the amount of available solar energy, the window's orientation, external shading, and the solar heat gain coefficient (SHGC). It is expressed as the fraction of solar energy striking the window that passes through the window.
SHGC is expressed as a number between 0 and 1. The ;lower the SHGC, the lower the amount of solar energy that will enter the living space.E.g. Window with SHGC 0.87= transmit approx .87% of available sunlight.
As a general rule, the performance of fixed windows will be better than other window types.
The measure or calculated performance of a specific window or sliding glass door is reported as the energy rating (ER).
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Most of heat loss through standard windows is via radiant heat, whereby the inside panel of the glass absorbs heat from inside and radiates it to cooler outside panel. This type of heat flow can be reduced with LOW-EMISSIVITY (low-E) Coatings, thin metallic coatings that decrease the rate of which glass radiates heat.
Gas-filled units----ARGON filled window, the inert gasses reduce convection within the space. KRYPTON is better performing but more expensive. Krypton is more commonly used in triple-glazed windows.
Insulating Spacers are used to reduce CONDUCTION in windows, Spacers are made of plastic,silicone foam, glass fibre, or composite materials. For Argon it is 12 mm (little more than 1/2 in) and for Krypton is 8mm (5/16 in.)
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To qualify for ENERGY STAR mark, products must meet strict technical requirements for both thermal and structural performance.
Products are qualified based on either U-value (rate of heat transfer from a warm area to cold area) or their energy rating(ER)
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3) WINDOW FLASHINGS
The key to flashings that must be considered are at window heads and sills. It should be well slopped ( a minimum of 2 in. in slope) and should extend a minimum of 25mm (1 in). Head flashing must be terminated at both ends in an end dam to direct any water that collects on the flashing to drain out and away from the wall.