Velux GGU INTEGRA Uživatelský manuál stáhnout pdf (Strana 103)

Building physics

VELUX 103

Thermal insulation – U-value

Basically, thermal insulation of constructions is made to delay the

inevitable equalisation of the temperature between warm and cold

air and between warm and cold building components. This means

that somewhere in the construction there must be a layer of insula-

tion material.

The heat conducting capacity of a material is called the lambda-

value (λ) and is measured in W/(mK). The lower the lambda-value

of a material the poorer the heat conducting capacity and thus the

better insulating capacity.

When dierent materials are combined in the same component, the

lambda-value of each material contributes with a certain share to

the total heat conducting capacity. This capacity of components

is called the U-value, or the thermal transmittance coecient and

is measured in W/(m²K). Also in this case the insulating capacity is

better the lower the U-value.

In a VELUX roof window two components speciﬁcally have an

inﬂuence on the total U-value of the window.

The insulating glass unit accounts for the largest share of the

total thermal loss through the window. The insulating capacity of

the insulating glass unit has a great impact on the comfort in the

area close to the window as a poorly insulated insulating glass unit

will cool the air. The cold air will ﬂow from the insulating glass unit

as a downdraught.

The frame and its connection to the roof construction cover a

smaller area. Appropriate insulation around the frame is, however,

essential as insucient frame insulation results in lower surface

temperatures and thus a risk of condensation on the interior sur-

faces. The stated U-value of a VELUX roof window applies only if

the frame is insulated carefully up to the upper side of battens. The

required level of insulation can be achieved using the VELUX frame

insulation collar from installation set BDX 2000.

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Velux GGU INTEGRA Uživatelský manuál Strana 103