How do exterior rolling shutters and screens save energy?
Saving Energy in Hot Climates
During the day, exterior shutters and shades block the heat from entering the home to prevent overheating. At night, you may raise your shutters and shades and use natural ventilation to cool your home. Both will limit the need for air conditional provides a more natural and comfortable indoor climate.
At night, close your shutters and shades to prevent heat loss through the window. Keep them open during the day to make use of the sun’s free heat. Both will limit the need for heating.
Energy efficiency terminology
The heat transfer coefficient: U
This relates to the window’s ability to maintain the indoor
temperature. It is represented by a heat transfer coefficient U,
which is expressed in W/m2.K.
The solar factor: g
The solar factor g expresses the fraction of the sun’s energy that is allowed to pass through a window.
Heat Transfer coefficient: U
The coefficient U becomes Uw when the thermal performance of the window frame is taken into account.
The coefficient Uw can therefore be used to calculate the heat
loss per m2 of window: heat loss per m2 of window equals
the temperature difference between the outside and the inside multiplied by the coefficient Uw.
Calculation example for a single-glazed window:
Outdoor temperature: 0°C
Indoor temperature: 20°C
Heat transfer coefficient for single glazind window Uw: 6
(20-0) X 6 = 120
So for 1m2 of single glazing, the heat loss is equivalent to
120 W, or the power of a television unit in operation.
Solar factor: g
In order to work out the solar factor for a complete window
(glass + frame), you also need to consider the frame’s thickness.
The solar factor for a complete window is expressed by
the coefficient g comprised between 0 and 1.
The higher g is, the more the solar heat goes through the
window .
This coefficient g changes with solar protection.
How to find the optimum level of thermal performance between insulation and heat capture?
Windows that use triple glazing and high-performance frames are sometimes seen as a solution for reducing heat loss, since the window’s coefficient Uw is generally below 1.
However, these windows are still very costly and are less effective at capturing the sun’s energy and allowing light to pass through them.
A window with a low solar factor (around 0.4) limits the sun’s heat in summer but is ineffective in winter.
The thermal performance of roller shutters in winter
Roller shutters offer genuine thermal performance in
addition to the initial properties of the window.
The performance of roller shutters is improved further when they are manufactured using an insulating material (especially PVC) and when they are designed and installed to provide excellent air tightness.
The keys to getting superb thermal performance from
your roller shutter:
• Choose a motorized shutter instead of a manual shutter
to avoid air escaping through the handle or strap (10% increase in insulation performance when a window is fitted with a roller shutter*).
• Use automatic locks to ensure perfect closure and optimal
air tightness.
• Choose new generation roller shutters, which eliminate
the risk of thermal bridges with specially designed frames.
(Frame coefficient U lower than 0.8).
* Source : Bauphysik, Fraunhofer Institut
When closed, the roller shutter traps a static layer of air in front of the window, increasing its insulation power.
The thermal performance of the window + solar protection
is represented by the coefficient ΔR.
The thermal performance of roller shutters in summer
There are other sun protection devices available to improve
summer comfort. The most common devices used in residential buildings are outdoor fabric awnings (vertical or drop arm) and adjustable exterior Venetian blinds.
In summer, the lower the solar factor, the less energy is allowed to pass into the room, keeping the indoor temperature cool.
Roller shutters have a solar factor g of 0.1, blocking 90%
of the sun’s energy.
Solar factor g of a double-glazed window in conjunction with a sun protection device
Reference window: double-glazed (solar factor 0.59)
Roller shutter
g = 0.05 to 0.1
External screen
g = 0.05 to 0.2
depending on the
color of the canvas
Indoor blind
g = 0.3 to 0.5
depending on the
color of the canvas