Calculations vapour permeability and transmittance
To evaluate the heat-insulating of walls made with Fiorditufo blocks is necessary to determine in advance the thermo-physical characteristics of the materials most commonly used in wall construction, as result from the following tables:
|Thermal Conducivity||w/m °k|
|Fiorditufo walls with mortar bed
from 1 cm every 12 cm
λ = (0, 37 • 11+0,90 • 1)/ 12
|Hollow bricks wall with mortar bed
from 1 cm every 26 cm
λ =(0,43 • 25+0,90 • 1)/26
|Thermal Strength||R m2 °K / W|
|Air gap > 5 cm||0,200|
|Fiorditufo wall:11 cm
|0,11/0,414 = 0,226
|Plaster: 2 cm||0,02/0,90 = 0,022|
|Board: 4 cm
|Brick wall: 8 cm||0,08/0,448=0,179|
The thermal conductivity is the amount of heat that passes through two opposite surfaces of 1,00 square meters of a 1,00 m thick material, which are at a temperature difference of 1°C.
Fundamental for a perfect insulation of walls and implants is that the material used has a low thermal conductivity (lambda). Therefore more the value of thermal conductivity is low, better is the insulating properties of the material itself or rather the material with the lowest value (lambda) has the highest resistance to the transmission of energy, then the best performance of thermal insulation.
The thermal conductivity is the main element used for the technical calculation of the thicknesses and also to avoid phenomena of condensation. The thermal conductivity values are definitely influenced by:
- chemical composition of the material.
- material density (kg/m3 o t/m3).
- molecular structure of the material.
The insulating property is also determined by the amount of air contained in the insulating material and the stability of this mass of air inside the structure itself.
CONTAINMENT OF ENERGY CONSUMPTION IN BUILDINGS
Each building consumes thermal, electric and of another sort energy for the winter heating and summer cooling.
If the energy is of the thermal type, or electric from thermal power stations, its consumption, in addition to increasing costs, bring in the environment heat and carbon dioxide which together increase the greenhouse effect.
In order to minimize energy expenditure and counteract the greenhouse effect, then for a better quality of life, becomes of primary importance contain the energy consumption of buildings, as well as in all other human activities, as well as, to this end, is been imposed by a specific legislation.
In a building, energy consumption depends on the location in which it is located, the exposure compared to the cardinal points, the shape and nature of the housing referring both to the glassy parts (windows) and opaque (walls and roofs). For the purpose of saving, the best walls are those that have a low thermal transmittance, which derives from the thermal conductivities of the layers that compose it, and high values of specific heat, from the unitary thermal capacity and vapour permeability and, consequently, the thermal inertia.
Qualities, these, that combine to create exterior walls that have low sensitivity to exterior climatic fluctuation and interior thermal regime, well as the onset of condensation phenomena on the humid walls of rooms like bathrooms and kitchens.
Thermal transmittance of walls made with Fiorditufo blocks
The rules on the reduction of energy consumption in buildings, occurring with Legislative Decree (D.Lgs) of 19 August 2005 No. 192 and of 29 October 2006 No. 311, are required to maintain the thermal transmittance of the opaque vertical structures under values (very low) for the different climatic zones, which new buildings must achieve progressively during the period from 1 January 2006 until 1 January 2010, as it is shown in the table below.
Thermal transmittance values allowed for the opaque vertical structures expressed in W/m °K:
|Climatic Area||from 06.01.06||from 01.01.08||from 01.01.10|
Climatic areas in Italy
|A||until a 600||Lampedusa, Linosa, Porto Empedocle.|
|B||from 600 to 900||Agrigento, Catania, Crotone, Messina, Palermo, Reggio Calabria, Siracusa, Trapani.|
|C||from 900 to 1400||Bari, Benevento, Brindisi, Cagliari, Caserta, Catanzaro, Cosenza, Imperia, Latina,
Lecce, Napoli, Oristano, Ragusa, Salerno, Sassari, Taranto.
|D||from 1400 to 2100||Ancona, Ascoli Piceno, Avellino, Caltanissetta, Chieti, Firenze, Foggia, Forlì, Genova, Grosseto, Isernia, La Spezia, Livorno, Lucca, Macerata, Massa Carrara,
Matera, Nuoro, Pesaro, Pescara, Pisa, Pistoia, Prato, Roma, Savona, Siena, Teramo, Terni, Verona, Vibo Valentia, Viterbo.
|E||from 2100 to 3000||Alessandria, Aosta, Arezzo, Asti, Bergamo, Biella, Bologna, Bolzano, Brescia, Campobasso, Como, Cremona, Enna, Ferrara, Cesena, Frosinone, Gorizia, L’Aquila,
Lecco, Lodi, Mantova, Milano, Modena, Novara, Padova, Parma, Pavia, Perugia, Piacenza, Pordenone, Potenza, Ravenna, Reggio Emilia, Rieti, Rimini, Rovigo,
Sondrio, Torino, Trento, Treviso, Trieste, Udine, Varese, Venezia, Vercelli, Vicenza.
VAPOUR PERMEABILITY μ (mu)
The index of vapour permeability allows detecting the resistance of the insulation material to water vapour diffusion.
It therefore is a coefficient that expresses the ability of the insulating material to create a barrier against the passage of water vapour.
- The index of vapour permeability is an essential parameter to determining the thickness of insulating material to be used in isolation, for example, refrigeration equipment and its components.
- The inability of an insulating material to act as a vapour barrier affects its same efficiency and limits its duration over time.
- In an elastomeric insulating the good resistance to water vapour is determined by the following requirements: :
- Molecular structure of closed cells
- Small cell size.
- Cohesion between the walls of the cells.
- Homogeneous resistance to vapour on the whole thickness.
- Here, therefore, that the coefficient of water vapour permeability and the thickness of insulating material, become important so that we have an excellent performance of the same material over time avoiding the onset of CONDENSATION between the pipe and the insulation, with consequent oxidation and corrosion of tube.
- To avoid the phenomenon of condensation is essential that the temperature of the surface of the insulating material is at least the same as that of the point of condensation, obtained from a calculation that takes into consideration also the value of thermal conductivity of the material, and it is for this reason that the material must absolutely remain unaltered and stable over time its own characteristics, in different conditions.
μ CONVERSION IN EQUIVALENT AIR THICKNESS
The resistance factor to water vapour diffusion, or μ, allows to obtain the air layer equivalent to the thickness of insulation used by the formula:
SA = m x s
where SA = Equivalent air layer in m
m = resistance coefficient to water vapour diffusion (dimensionless value).
s = thickness of chosen insulation express in m.
The energy consumption in buildings
The rules about the energy consumption reduction in buildings have been deeply innovate with Legislative Decrees (D.Lgs) of 19 August 2005 No. 192 and of 29 October 2006 No. 311 which provided for, among other things, the “energetic certification” of buildings and individual units that compose them, already built or to be built, the confirmation of the “climatic areas”, the “general classification of buildings by categories”, the “maximum ambient temperature” and “operating limits of thermal systems” provided in the Italian Presidential Decree (D.P.R.) 551.1999.
For the full implementation of the referred Legislative Decree (D.Lgs) you need to wait for the decrees, which were to be issued by 5 February 2006, which the Ministry of Economic Development has released, so far, only informal bills.
On the topic has worked an Italian interregional Working Group, “ITACA”, which dealt with the more general problem of clarifying what is meant by the term “sustainable building”, i.e. to determine the eco-friendliness limits of the building work.
The thermal inertia of Fiorditufo walls
The research carried out by the Giordano Institute of Bellaria (Forlì), listed in “Almanacco Termofisico”, showed that in walls made with Fiorditufo blocks, without plaster, the thermal attenuation, give by the ratio between the fluctuation amplitude of the exterior temperature Ae (between day and night, for the irradiation, etc.) and the interior Ai, μ = Ae/Ai is from 15, for those of 25 cm thick to 45 for those of 37 cm thick.
The fluctuation phase shift of the interior temperature compared the outside one, always varies, for referring walls without plaster, from 2,2 hours if 25cm to more than 3,3 hours if 37cm.
In all cases, the product thermal attenuation for the phase shift that is more than 20 to indicate that the wall is poorly sensitive to exterior climatic fluctuations and interior thermal regime. Poor sensitivity which is accentuated, of course, with the presence of layers of plaster, of coatings, also facing brick, of interspaces of air, etc..These factors all very favorable for the energy consumption reduction of air conditioning in both winter and summer, and maintain the performance of the building envelope.