Doorframes: the weak points of the shell of the buildings
The large flow of heat through the frames, from space to the environment in winter and vice versa in the summer, requires the search for the optimal solution.
Thermal permeability coefficient (U)
- Window surface 1 square meter
- Outdoor temperature: 19 degrees
- Indoor temperature: 20 degrees
- Thermal window permeability coefficient e.g. U = 3.0 W / (m².K)
Energy loss per second = Surface x Temperature difference x Thermal permeability coefficient (U) = 1m² x 1K x 3.0W / (m².K) = 3.0Watt
Thus, by multiplying the total surface area of the frames by the temperature difference and the U factor, we calculate the energy losses per second.
High thermal transmittance (U) means greater energy loss or vice versa
The lower the value of the thermal permeability coefficient (U), the more thermal insulation is a material or structural element.
Certified close low U values are achieved by modern double-glazed windows. They are usually filled with noble gases and have special coatings.
A double-sided balcony door of 1,40 x 2,20 has a surface area of 3,08 m²
This glass pane has a surface roughly (removing the frames in width and height):
(1,40-0,11-0,11-0,14) x (2,20-0,11-0,11) = 2,06 m²
The frame is about 33% of the surface and in a corresponding window it reaches 39%
Doors are the building’s “Achilles heel” in terms of energy losses.
The energy losses increase, the higher the coefficient of thermal permeability (U) of the frames (profiles) and the glass panes.
Synthetic frames are certified to be very low U = 1.3 W / (m².K) and make up more than 1/3 of the surface area of ordinary frames.
Combined with modern glazing with corresponding coefficients, an unbeatable product with a conventional price is created:
The synthetic frame with U = 1.3 W / (m².K) and energy losses 2 to 3 times smaller than the prescribed limits.