FR2556454A1 - Method for storing solar energy by using accumulators and heavy weight concrete walls - Google Patents

Abstract

According to the invention, in order to store solar energy, the known solid elements, such as stones, burnt clay bricks, conventional concretes, are replaced by concretes or mortars formed using aggregates containing "heavy" metallurgical scoria and slags, which are rich in silicate of iron and whose density is at least equal to 3,000 kg/m<3>. Application to the formation of walls with high thermal inertia such as walls with parietodynamic insulation, the central body 5 of which, made of heavy weight concrete, is separated from the external facing 8, such as for example glazing, and from the internal insulating material 10 by cavity-like passages 7, 9 in which flows the air coming from the outside 11 and which, alternately, heats up the central body 5 or is heated up in contact therewith.

Description

The present invention relates to the field of solar energy and more especially of sor. storage by solid materials of improved thermal capacity. It relates very particularly to a method for storing energy from solar air collectors by the use of concrete or mortar parolis castings in solid blocks or similar elements.

Traditional solar heating systems consist of heating water or air in solar collectors and distributing the fluid in heaters. When the. amount of energy supplied by the sun is greater than immediate needs, the excess must be stored for use during periods of shortage, especially at night. In addition, long-term storage should also be considered because it is obvious that the advantage of being able to use during the winter period solar energy collected during sunny summer days.

Numerous storage systems have been devised, the most common being composed of accumula tower-exchanger installations for deferred supply. Depending on whether the heat transfer fluid is air or water, solar energy is stored in beds of stone, concrete or in water.

More sophisticated systems involve the latent heat of phase arrangement (solid <-> liquid) of mineral salts contained in spheres. These latter devices are expensive and difficult to make profitable in the case of single-family homes where only storage in simple accumulators may be feasible.

Apart from water accumulators, storage means are also known consisting of solid elements having appropriate geometric characteristics and assembled so as to promote heat exchange. In this regard, mention may be made of terracotta bricks and concrete elements obtained from common aggregates, which are placed in isolated enclosures located in the foundations of buildings.

The storage capacity depends on the specific heat of the material constituting the elements and on the mass of these elements making up the accumulator. For elements with the same geometric characteristics stacked in an identical manner, we can have different storage capacities. In addition, thermal exchanges (heating and cooling) are favored when the thermal conductivity of the constituent material of the blocks is higher. Thus for terracotta, the specific mass of the material is 1900 'kg / m3 on average and its specific heat of 0.16 kcal / kg C or 0.18 kt / TOC in the temperature range of 20 to 100 OC. Concrete full of common aggregates has an average dry density of 2300 kg / m3 and its specific heat is of the order of 0.21 kcal / kg C or 0.245 kwt / t C.

One of the aims of the invention is precisely to increase significantly the storage capacity of an arrangement of elements contained in a given volume available by using elements made of a material of high density.

To achieve this main goal, the method of the invention also calls for the construction of walls or walls made at least partially in concrete or mortar, but it is essentially characterized by the fact that one uses as aggregates for the preparation of these concretes and / or "heavy" metallurgical slag and slag mortar, with a density at least equal to 3,000 kg / m3 and rich in iron silicate, with contents of at least 20% (by weight) of SiO2 and of FeO.

Thus, for example, the Applicant was able to establish micro-concrete formulations from sands of 0 to 8 mm of granulated metallurgical slag which had the following chemical compositions Elements dosed in weight% slag 1 slag 2
SiO2 40 29
CaO 10 17
A1303 6 7
MgO 2 1
FeO 40 29
Zn - 8
S 0.8 3
These compositions characterize materials which are stable from a physicochemical point of view. This is the main difference with metallurgical slags, such as those of steelworks which have comparable specific masses but which can present a certain instability causing the slow or sudden deterioration of concretes and mortars, due to the presence of free lime.

Formulation 1. Granulate 0-8 mm slag 1: 100 kg
Cement CPJ 45: 40 kg
Mixing water: 15 liters
Water / cement ratio: 0.375
This composition makes it possible to obtain solid elements with a dry density of 2,600 kg / m 3.

Formulation 2: Granule 0-8 mm of slag 2: 86 kg
Crushed granulate: 14 kg
Cement CPJ 45: 20 kg
Mixing water: 10 liters
Water / cement ratio: 0.50
After drying in the open air, solid elements with a density of 2,670 kg / m 3 were obtained. The use of crushed granulate, by improving the workability of the concrete or the mortar, makes it possible to reduce the quantity of cement and the quantity of mixing water. In addition, the density of the mortar is further increased by replacing part of the cement having a specific gravity of 3100 kg / m 3 by slag fines having a specific gravity of 3600 kg / m 3.

The use, as concrete aggregate, of a metallurgical slag based on iron silicate, therefore makes it possible to obtain mortars or micro-concretes the density of which is increased by more than 15% compared to a common aggregate concrete. Since the specific heat of these mortars is 0.21 kcal / kg C, therefore comparable to that of a normal aggregate concrete, the use of elements in granulated slag mortar based on iron silicate makes it possible to '' increase storage capacity by more than 15%.

In practice, metallurgical slags with a high iron silicate content and whose grain density is greater than 3000 kg / m 3 are used. It is known that, for certain slags, it is possible to have densities of the order of 3,300 to 3,600 kg / m 3. The invention thus makes it possible to develop slags of this type, rich in silicate and iron oxides.

According to the invention, the heavy concretes obtained from the aforementioned aggregates can be used to make walls or walls with high thermal inertia.

In the cold season, when the heating source is cut, a room with heavy walls insulated from the outside undergoes a slower cooling than a room with low thermal inertia.

In the sunny period, in spring and in autumn, the flow of solar energy entering a room through the windows can be greater than the losses; this results in a heating of the ambient air and consequently of the interior part of the wall which serves as a solar energy accumulator then returned. A damping of peaks of variations in the temperature of the ambient air inside the room is obtained.

We can therefore see the advantage of using heavy granulated or crystallized metallurgical slags for the production of walls with increased thermal inertia. These walls can be assembled from manufactured blocks or cast in poured concrete.

Among the many types of walls that can be produced according to the invention, two have been illustrated, without limitation, in the appended schematic drawings which represent
- figure 1: a simple wall with insulation by
outside
- figure 2 -: a more elaborate wall, with parietodynamic insulation.

The single wall in FIG. 1 is made up of a load-bearing element 1 made according to the invention in heavy concrete 11 and of an exterior facing 2 of small thickness. Between the two is a layer of insulation 3 of sufficient thickness. ensure that the assembly has a coefficient K allowing ze to meet the requirements of the legislation in force.

The number a corresponds to the interior finishing layer of wall 1. This type of wall only allows the storage of surplus solar energy entering a room through the glazing.

The parietodynamically insulated wall of Figure 2 is of another design. It consists of a central carrier body 5, made of heavy material according to the invention and having a high thermal inertia. At the upper part are arranged horizontal passages 6 joining the two faces. A first air space 7 is obtained using an exterior facing 8 of small thickness, of minimal thermal inertia but having a high thermal conductivity.

A second air space 9 is created by equipping the inner face by adding a flat insulator 10.

The outside air It introduced by low openings of the external facing 8 circulates in the first air space thanks to a controlled mechanical ventilation. It takes charge of part of the solar energy transmitted through the exterior facing, heats the face of the central body 4 which it passes through in the upper part and descends along the second air gap 9 while continuing heating the central body and recovering heat losses from inside the room and passing through the layer of insulation. The preheated air comes out in the lower part at 12 and is directed towards the heating body to be raised to the desired temperature.

The outer facing 8 may be glazing to allow direct transmission of solar energy 13 which heats the air circulating in the air space and also the face of the central body. Ur. Blackout system during hot summer hours limits solar gain and the outside air is only slightly heated during its passage through the air space between the exterior facing and the central body . However, this traps part of the solar energy, which improves indoor comfort during the summer period.

The use of mortars or heavy concretes according to the invention, based on slag or slag of high specific mass and rich in iron silicate is quite beneficial for the assembly of walls with insulation from the outside or with parietodynamic insulation. .

Claims (3)

1. A method of storing energy from solar air collectors by using accumulators composed of concrete elements or of insulating walls or walls made at least partially of concrete or mortar, characterized in that one implements , as aggregates for making said concrete or mortar, "heavy" metallurgical slag and slag with a density at least equal to 3,000 kg / m3, rich in iron silicate with contents of at least 20 8 'by weight of SiO2 and FeO. 2. Method according to claim 1, characterized in that said aggregates are used in raw form with a grain size of 0 to 8 mm, a part of these aggregates in the final concrete or mortar which can be replaced by fines obtained from the ground granulated slag. 3. Application of the method according to any one of claims 1 or .2 to the production of simple walls with load-bearing element (1) of heavy concrete, insulating material (3) and exterior facing, or to that of walls with parietodynamic insulation including the central body (5) in heavy concrete is separated from the exterior cladding (8), generally a glazing and the interior insulation (10) by louvers (7, 9) where air from the outside circulates