How calculations were made?

TEXTINERGIE calculations were made by the "Lucie" software package.

"Lucie" is a software package which enables to make a dynamic simulation of a building's thermal and lighting behaviour.

Calculations were made for an entire year with a time step of five minutes. They are in transient state, taking the inertia of interior surfaces into account. Temperatures within the entire area change according to the dynamic interaction of outside conditions (outside temperature, amount of sunlight, air temperature) and of the active control systems (heating, air-conditioning, lighting and positioning of the blind).

During sunny periods some of the incident radiation strikes the textile of the blind while the remainder is transmitted by the unprotected part of the glazed area depending on the incidence angle, which varies with the position of the sun.

The solar flux which enters the room is measured per time step by the radiosity method. The software continually adjusts the active control elements:

• - The heating and air-conditioning are engaged to maintain interior temperature according to predetermined levels of comfort requirements and planned occupancy of the room.
• - The positioning of the blind is adjusted in order to maintain the predetermined level of luminosity. Artificial lighting is switched on when the solar protection device is fully retracted and when there is not enough sunlight to meet the predetermined light levels during the hours of occupancy.

Operating principle of the "Lucie" software package
(click to enlarge)

The radiosity method allows the solar flux entering a building to be calculated taking account of multi-reflections.

When sunlight strikes a surface it can be at the same time:

• - reflected,
• - transmitted (if the surface is transparent),
• - absorbed.

In turn, the light which is reflected or transmitted will strike other surfaces in the room and will itself either be reflected, transmitted or absorbed. As multi-reflections take place simultaneously, the radiosity method evaluates them by determining a linear system of N equations with N unknowns, where N is the number of surfaces in question.

In this case there are 12 surfaces:

• - The opaque inner walls of the area (6 in number),
• - The interior and exterior glazed surfaces (4 in number as they are double glazed),
• - The interior and exterior surfaces of the blind's textile.

According to the radiosity method, for each wall we have the value of flux which is reflected, transmitted and absorbed. Absorbed flux will contribute to heating the walls and is at the heart of the thermal problem.

       Principle of the radiosity method