Green heating of spaces using a solar thermal mass wall made of marble blisters and water
Not only does the Thermal Wall serve the heating needs of a building but also ensures the comfort if its tenants.
Improving the heat equilibrium in a space plays an important role in the feeling of euphoria. The aim of the product is to raise the solar annuity during winter using natural properties of materials (heat capacity, emission of infrared radiation, conduction, convection) and natural phenomena (greenhouse, natural ventilation) and also to increase the thermal inertia of the building so as to avoid large fluctuations in temperature (day to night).
Description and Function
The thermal storage wall is a system comprising a wall without insulation facing south (in the northern hemisphere), made of high heat capacity materials (marble, water) that operates as a depository and distributor of heat, and a glazing (element of the shell of the building) located at a distance of 12cm of the exterior, which serves to capture solar radiation (creation of greenhouse). The entire length of the wall has integrated ports for air circulation.
The solar radiation entering through the glazing is converted into heat in the space between the glazing and the wall and is stored as thermal energy within the wall. From there it is transmitted through conduction, emission and transported into the space. Simultaneously the glass pane acts as an insulation layer for reducing heat loss from the hot wall to the exterior cold environment. The exterior face of the wall exhibits high absorption of the solar radiation (dark colour of marble and rough surface), thus increasing the system’s performance since a temperature of up to 65oC is generated, while the internal face of the wall should be glossy and of light color in order to reflect the radiation in the space.
The gateways on the top and bottom parts of the compact segment help so that the transfer of heat toward the interior side of the space to be made apart from conductivity/infrared radiation through natural ventilation as well. The air, which is located between the glazing and the wall, is heated as it connects to the hot wall and enters the space through the gateways located at the top of the wall, while simultaneously cold air from the interior of the building enters through the bottom port into the gap and is thus heated. In this way additional heat is generated and transmitted in the space during periods of sunlight and heating of the space begins at the same time that the wall is heated and continues for 2-3 hours after the loss of sunlight. During the night hours of the winter period, the gateways must be closed (it is sufficient to close the top gateways), so as not to cause reverse circulation and thus cooling of the air.
The thickness of the wall is essential. The optimum value for maximizing performance is 20cm. The use of gateways plays a greater role in the rapid heating of the interior space. The thickness of the wall affects the fluctuation of the temperature in the heated space. The delay in heat transfer is estimated at 9-13 hours, in other words the wall blocks out the low temperatures prevailing at nighttime. For the heating of spaces not in direct contact with the thermal storage wall, pipes are used to carry the hot air from the ventilation gateways to the rear areas and capture and remove the cold air by recycling it.
Note that it is necessary to insulate the wall from all the elements with which it comes into contact so as to reduce thermal bridges. For thermal losses during the day the use of double glazing (glass thickness 4mm and 18mm gap in between) is sufficient. The night portable insulation (insulation panels) is essential during the winter and during the summer also for sun protection. Furthermore, the screens will have a reflective inner surface (anodized aluminum) so that during the day –when they remain open- they multiply the solar radiation towards the wall (increase 40% of solar radiation).Portions of the glazing will also open to allow the outflow of hot air from the space between the glazing and the wall to the external environment and to ensure discharge of heat and cooling of the wall during the summer, while allowing the cleaning of the internal surfaces of the wall – floor – glazing. It should be pointed out here that to minimize heat losses, a well insulated building shell is complementary to the wall and leads to a very high degree of system performance.
In Greece, despite the abundance of sunshine during the winter months which makes the system even more efficient, it is not widely used due to the lack of information and installation crews. This is what makes the proposal innovative. Informing (B2B, web promotion, fairs, flyers e.t.c.) about the product, and the undoubtedly great benefits (zero cost of operation and maintenance, low cost of purchase, performance, ecology, improvement of the Energy Performance of Buildings) and the construction and installation by specialized crews under the supervision of professional staff.
The second and most important innovation relates to the materials of construction, their structure within the system and the geometry of the wall. The innovative combination of water and marble – granite constitutes a choice of high performance, since all three are on the top list of materials with the highest heat capacity and low conductivity. This makes these materials more suitable than other such as concrete, bricks etc. because they have the ability to store large amounts of heat and to retransmit in to space with time delay (during the time that there is no sun to warm the building). So the marble casing participates in heat capacity, the inertia and therefore in the system performance.
It is also known that natural rocks have the propensity to emit infrared radiation when heated. It therefore follows that a further innovation derives from the use of marble in the system, the heating with an additional transmission which is radiation. Advantages of the infrared include the immediate production of heat for the users of the building (same as the sun that warms us), without having to first warm the air, the uniform distribution of the heat and preventing humidity due to the dewdrops in the walls. The light weight of the wall (due to materials and geometry) allows installation even in existing structures which is not the case today. As far as installation is concerned, the 3cm walls are transformed and special cells within them (all made of marble) filled with water promote rapid heat transfer into the bulk of the wall through convection during the day while at night time they “trap” heat in the internal cheek.
This mechanism is based on the inclined -width- of marble slabs that run the full length of the wall and set the limits of the cells. These slabs are inclined upward going from outside to inside facilitating the transfer of heat inwards during the day. On the contrary during the night they trap the currents and do not allow losses to the outside except with the long process of conduction-which due to the low heat transfer coefficient of the material is very slow (the water is isothermal). With this innovative technique the wall exploits all the advantages of its materials. The outer wall made of dark marble – granite while inside the aesthetic superiority of marble creates decorative surfaces according to the taste of the user, which makes the wall aesthetically rewarding as well.
The dimensions of the standard marble wall unit are: Height 1,20m, 0,20m Thickness and Length 1,50m. They may, however, be adapted to the requirements and needs of each space and of course will be combined in a row increasing the length of the system and under certain conditions will be combined to increase the height. The low height gives great flexibility in the installation of the wall, in utility, it reduces costs and keeps the heat low, thus increasing performance. The weight does not exceed 380 kg/m filled with water, while the bonding and the sealing are made with special cements in multiple layers and many levels of security.
Affordable & Efficient
Affordable & Efficient
The performance of this novel system is estimated (based on mathematical models and scientific data from experimental models and studies) at 5 to 6.1 KW / m². In a well-insulated home can be achieved autonomy if for every floorplan square meter 0.30 m² of wall is erected, without operating or maintenance costs. In cases that there is no room for so many square meters, the system will help in heating the space depending on the square meters of the floor and wall. The additional degree of energy saving of the thermal storage wall with marble and water compared with the conventional wall materials is calculated from 25% to 28% and is due to the combination of innovative techniques / technologies that optimize performance of the wall. The thermal mass wall belongs to the class of passive solar systems of indirect solar gain. Systems of the same category are the greenhouse (attached to the building with large glazing and favorable orientation), as well as the air collector and the direct gain systems (southern exposure and calculation of the building’s size of openings). The bioclimatic design often requires a combination of systems and so they work supporting one another. It is wrong make any comparison since one does not exclude the other, but complements and includes it. For example, the thermal mass wall includes greenhouse and vice versa, and the two combine good orientation and size of openings. However more often than not constructing a greenhouse and air collector is not feasible, especially in buildings within the city or existing ones.
Compared now to conventional heating methods, such as gas and oil (which also have an installation cost similar to that of the wall),the cogeneration of heat passively (as a primary or auxiliary source) of the thermal mass wall is cost efficient -even if users wish to install it. The cost of the wall is estimated at around 400 € / m². The wall will be recouped in a few years and will save energy and money. The potential price increase of fuel and maintenance costs of conventional systems were not calculated in the example which would further reduce the payback time.