Thought experiment 1: The variable albedo tile.
This article is the first of a series dedicated to the realization of low-tech, low-cost and ecological devices, aimed at the production of renewable energy, the optimization of energy resources, the optimization of metal resources and the optimization and minimization of the impacts thereof on the environment.
Purpose of the device:
The device is aimed at thermal regulation of buildings, by using a brick or a slab-like element which has variable reflective properties depending on the temperature of the roof or the wall of the building.
The expected properties of the system are as follows:
- No power supply is required: the variation of the albedo of the tile (therefore of the roof) does not require any external energy to adjust itself automatically.
- Only an initial calibration of the tiles as a function of climate/location may be required. This could be carried out as factory settings or on site by a technician.
- It can be manufactured in a Low Tech manner in the factory of an average-size or small town, or alternatively by a craftsman in a village (which will be our working definition for the term Low Tech in practice).
- It does not require rare or expensive components or materials that need importing.
- The installation of the device can also be carried without requirement of high-tech means.
The basic idea is as follows:
The roof or wall we want to protect against overheating in the summer (or conversely in winter) is covered with elements which allow it to regulate the absorption of solar radiation (see figure 1).
Elements responsible for regulating the absorption of solar radiation:
These elements have a reflecting surface (light or metallic) on one side and an absorbing surface (dark) on the other. They can be made in the form of a cylinder or a rigid foil, rotating around its longitudinal axis (more or less like Venetian blinds).
Example using cylindrical elements:
Example using flat elements (blades-like):
These elements are preferably made of light materials, so that they can be moved effortlessly by a mere metallic spiral-shaped spring (made from a single metal or from two different, mutually secured, metallic strips with two different coefficients of thermal expansion).
The use of springs made of one or two metals (bimetallic springs) to rectify the operation of a clock, or to activate the operation of a thermostat, or to rotate the needle of an industrial thermometer has been known since the 18th century, when John Harrison thought about incorporated such a temperature-correcting spring in his “Chronometer”. This made navigation possible across the oceans from the 18th century onwards by the use of such a Chronometer in combination with a sextant (before this time navigation using the sextant was unreliable for voyages across the oceans because the watches and clocks used before Harrison’s invention were not reliable enough, as they did not compensate accurately for temperature changes).
References:
wikipedia.org/wiki/John_Harrison
Ressort bilame dans un thermostat
[Ressort bilame dans un thermomètre industriel(http://culturesciencesphysique.ens-lyon.fr/ressource/bilame.xml)]
Example of an element actuated by a metal spring which expands in response to temperature:
Illustration of a tile with variable albedo (reflectivity) equipped with rotating shutter elements actuated by the expansion of a spring (itself actuated by variations in ambient temperature).
Video illustration of the element rotation mechanism (video)
A protective pane of glass is provided to shield and seal the front part of the device. It can be manufactured from glass or Plexiglas, etc.
Illustration of a house, fitted with variable albedo tiles.
Tiles in action on a roof (video)
As initially proposed, the purpose of the device is to automatically switch from reflecting sunlight in summer to prevent overheating of the building under the effect of solar rays to allowing solar radiation to pass though in winter (automatically, depending on the temperature of the roof) in order to regulate the temperature of the building both passively (in terms of energy spending), and dynamically (in terms of the thermal management of the building) at zero energy costs.
