An house is a closed volume where agreable temperature is wanted, mainly in winter, so that coats, gloves and fur boots are not needed, when outdoor temperature is very low. The heat contained in an object placed in a colder environment flees in it in the same way as the water in a mountain lake flees toward the sea.
The gap of altitude of the water is the gap of temperature for the objects regarding the environment. The water flow is like the amount of heat that the objects loses into the colder environment, which is the thermal energy flow. The lake empties, the object cools. The thermal energy flow that goes from the warm object into the colder environment depends on the gap of temperature, and of the ease with which the energy can travel from the object to the environment.
It can be said then that the heat loss of the house depends on the gap of temperature between the inside and the outside of a heat conduction coefficient , which will be noted "G". It also depends on the volume of the house, because the bigger the house is, the more surface is in contact with the environment. A shape factor should also be taken in consideration, because the less parallelepiped-shaped the house is, the more walls for the same volume. The shape whose the ratio volume/(wall surface) is the best is the shere. The cube isn't too far. Thus, this parameter will be ignored in what follows.
It can be written : Q = G × V × ΔT.
where Q euantity of energy lost (in Watt), G is the leakage coefficient (in Watt/°C/m3), V is the volume of the house (in m3) an ΔT is the gap of temperature between the inside and the outside (in Celsius degree).
Thermal energy travels by convection, radiation and conduction.
To understand the phenomenon of heat transfer (or thermal energy), it is necessary to admit a model of representation of the matter which says that this one is constituted of tiny invisible pieces which moves randomly.
- In the case of solid bodies - like metal, wood, glass or PVC - these pieces move while keeping an average position constant. They are said to viber.
- In the case of gas and liquids, these pieces move, while travelling globally according to a certain direction.
The vibrations of thes microscopic pieces of matter represent the thermal energy of the body in question. The higher the amplitude and the frequency of the vibrations, the more energy the body contains, the hotter it is.
Convection is the displacement of heat by the global displacement of an amount of a hot body. For instance, if you draw a bucket of 10 liter of water at 60øC from you water heater which is supplied with cold water at 10øC, to wash your floor and then you throw this water on your lawn, you lost by convection :
(60-10)×10×1.16=580 Wh, which is about 1/2 kWh of electricity.
Or if you aearte a 30 m3 room and you replace air at 25øC by air at 10øC, you lose by air displacement, thus by convection :(25-10)×0.3×30×1.16=157 Wh , which is about 1/6 kWh .
The coefficient 1.16 which we will meet in the calculations represents the value of the kilocalori in Wh, like 6.55957 reprensents the value of the Euro in frances. It allow to convert heat consumed per hour into paid kWh !!! It is worth : 1000cal×4.18/3600=1.16Wh.
But there is a very more harmful convection : it is the one that occurs on the whole surface of the house which is in contact with the ambient air outdoor, that is to say the whol surface of the outside walls plus the openings giving to the outside.
Thermodinamics courses call α in W/m2/øC the coefficient of transmission of the heat by convection, that is to say between a fixed body and moving matter. It depends on the nature of the surface, the orientation of it and the ambient conditions.
Indeed, heated and so dilated air in contact with some surface became lighter and goes up to be replaced by, say, new air, and hence colder. But that renewal depends on the orientation of the surface and on its state. It also depends on the global movement of the air, that is to say the wind. When there is wind, we take shelter to be less cold.
It is then necessary to bring two corrective coefficients, hence in first approximation :
α=2×(ΔT)1/4×σ×(1+V3/4)
σ is worth about 1.5 for a smooth surface, such as clean sheet metal, and 3 for a rought surface such as stone, concrete or roughcast.If we consider an average house having about 110 m2 of lateral surface and 110 m2 of ceiling, this gives, with a wall at 23øC and an outdoor ambiance at -7øC with no wind :
Q = α×S×(t2-t1) = 2×(30)0.25×3×30×220 = 93 kW
with a good wind, a breeze, of 10 m/s
Q = 614 kW
That is enormous. On the other hand if the surface of the wall is at -6øC we have respectively 1.32 kW and 8.74 kW.
That is still a lot. We observe that in order to avoid loss by convection, the thermal resistance of the wall must be very high so that the temperature of the surface of the wall is practically equal to the temperature of the outside air. Any calorie that arrives at the surface of the wall is irremediably condemnedt to fly off into the atmposhere.
We can realize it when we are shivering of cold with wet clothes. Wet clothes are good conductors of our heat, and the convection of the air grab every calorie. Before the rainstorm, the clothes being dry, we are not cold.
Clothes are like the insulation of the wall, the are the barrier to the loss of heat.
It exists also others loss by convection : these are the leak of air via the joint under the doors, around the doors and the windows, via the air intakes for the essential renewal of the air breathed in the house which must be about 25 m3 per hour and per person. We will come back on this point subsequently.
Loss by radiation are again more impalpable than the loss by convections, because contrarily to the draft under the aerator or close to the switchs, we do not feel them.
Losses by radiation of a body submerged in an ambiance, and small with regards to it, are given by the formula :
q (W/m2) = σ×[(T1/100)4-(T2/100)4] with T in øK
σ is a coefficient which characterizes the material. For stone or concrete, it is worth about 4.Q = S×q = 330×4×(296/100)4 = 101 kW
If we admit that the house is on Earth in an ambiance at -7øC with its walls not insulated at 23øC, we obtain, without taking the floor into account :Q = 220×4×[(296/100)4-(266/100)4] = 220×4×(81-53) = 20.8 kW
But the surface of the wall, we saw this, will go down to -6øC. The losses by radiation will then be :Q = 220×4×[(267/100)4-(266/100)4] = 220×4×[(1/100)4(4×2663)]
= 220×4×(1/100)×4×2,663 = 0.662 kW soit 2/3 kW.
(for the pernickety, I apply : a4-b4=(a-b).(a3+a2.b+a.b2+b3)).
Pizzas, bread, are cooked by thermal radiation of heat stored in the vault.....
The last sort of propagation of heat is conduction ou conductivity.
If we consider a rod of metal submerged by one end in ardent ember, the infrared radiation of the ember will excite the atoms of iron which will viber more strongly. The will hit the neighboring atoms which will be excited in turn and so on step by step until the other end. This one will warm up and you will burn yourselves when you will want to grab it.
The denser a body is, that is to say the heavier, the more conductive it is.
The less conductive body is vacuum : its conductance is null, its thermal resistance is infinite. That is why themos bottles from the last century, with double-partition filled with vacuum kept coffee hot for 24 hours, while today's thermos keep it for hardly 3 to 4 hours. This proves that polystyrene is clearly less insulating than vacuum.
Then comes the air, with the condition of being dry and still. What insulates with expanded polystyrene, it is not the polystyrene itself but the bubbles of air that are imprisoned inside. What insulates in a diving suit, it is not the rubber but the bubbles of air that are emprisoned inside. And this is why it is necessary to wear a lead belt to go down to the abyss.
This has been said previously, water is a good conductor of heat, wit a λ=0,65, 15 times more than polystyrene, and also it stores well the heat, that is why it can be used in accumulation water heat.
Any materials used for insulation insulates thanks to bubles of air that they contains.
When you touch polystyrene, it seems warm to you, while it is at ambient temperature, at -15øC if it is in you freezer, because it is a bad conductore and it takes no heat from you. If you touch a stone or a piece of metal in the shadow, it seems cold because, good conductor, it take you much more heat. The feeling of cold is the loss of heat.
We saw precedently that as soon as the surface of the wall exceeds by few degrees the ambient temperature, the kilowatts of heat flees away, by convection and radiation. Only the wall of the house can, due to its bad conductivity, resists the thermal pressure, like a dam resists water pressure.
Losses by radiation are in parrallel, simultaneous, with the losses by convection, and are thus negligible with respect to the latter, especially that, during the day, the flux is reversed : a stone in the sunshine seems hot, while at night it feels cold, though in both cases it is at ambient temperature, or very close.
The conductance of the convection, with an average wind, is : 8740/220=40 W/m2.°C, that is to say a thermal resistance of R=1/G=0.025 °C.m2/W, which will thus be neglicted in future calculations.
If we want to limit the losses of a 120 m2 house to, for instance, 4 kW with -7ÝC outside and 20ÝC inside, we need a volumic inside coefficient of : 4000/27/300 = 0.49 W/m3/°C, which gives an average surfacic coefficient of 4000/27/350 = 0.42 W/m2/°C.
The insulation of a house is the suppression of thermal losses in order to get a comfort at a good price.
In order to get a thermally resistant wall, it has to be made of light materials, but then it will not be mechanically resistant.
Thus two walls must be built : one which is mechanically resistant and one which is thermically resistant. Materials which have both properties at the same time do exist, but the thickness must be doubled. Furthermore they are often difficult to use : we did not got anything financially, and the problem of the thermal bridges and of the thermal comfort are still there.
A breeze block wall of 20cm thickness covered with 10cmm of polystyren has a coefficient of surfacic conductivity of k=0.33, for a cellular concrete wall of 40cm, k=0.50, for alveolar bricks of 40cm, k=0.70, for a sandwich wood-polystyrene-wood of 10cm, k=0.40.
Generally, nowadays, two walls are built or somehow.
Where the insulating wall should be place ? Inside or outside ? Nowadays, it is generally placed inside. But then, it is not a wall anymore, it is a juxtaposition of insulating panel, separated by load-bearing screeds and partition walls, that is to say separated by thermal bridges.
Let's go back to our hydraulic analogies.
Let's watch a calm river flowing. The flow is uniform, laminar, the twigs and the dead leaves (we are studying a theoric case without any plastic bottles and fatty papers) stream regularly. A bit further, some rocks limit the section of its bancks. We can see that, 2 meters way from the rocks, the floating objects speed up to rush into the trickle of current which dive between the rocks.
The section being reduced, in order to maintain the flow of the river constant, the current, that is to say the speed of the particles of water, increase : D = V×S = constant.
Just like the dam must resist water pressure, the wall of the house must resist the thermal pressure. As soon as there is a gap, the water in the first case, the flux of thermal energy in the other case, rush with speed and strength through the gap. Put your hand at the end of watering pipe. Of course, the strenght of the thermal flux, you do not feel it, it is the furnace which feels it.
Hot volumes under the screed are in common with cold volums, thus there is a direct transfer of energy hence the name of "thermal bridge", it could also be called "thermal rift".
As the sketch opposite shows, the leak lines of the calories withhold thermal energy at ground level and at the level of the ceiling of the house and spread this energy in the wall which plays the part of a radiator, like the radiators which are stuck on the microprocessors and other power components, completed most of the time by a fan, which in the case of the wall will be efficiently replaced by the wind.
The bottleneck, or ejection pipe, is the part of the floor tile which is inside the thickness of the insulating wall.
We will do the calculations for a slice of mur of L=1 meter, with a conductivity for the concrete of λ=1, e=10 cm d'isolation et h=15 cm d'épaisseur de dalle, 20 cm de distance de dispersion sur 50 cm de hauteur, 50 cm de zone de captage, 30°C between the inside and the outside, this gives
conductivity of the dispersion zone = 1×0,50/2/0,20 =1,25
conductivity of the bottleneck = 1×0,15/0,10 =1.5
conductivity of the reception zone = 1×0,50/0,25 =2
total resistance = 1/1,25+1/1,5+1/2 = 1,97,
This particularly harmful case is not utopian : sometimes, there is not even any insulation under the tile on the earth platform. Moreover, we did not take into account the partition walls if there is any, and we did not take into account the wind when there is any.
And if a balcony lenghten the tiling, imagine the radiator that this represents, it is the tongue of the dog which hangs outside its mouth to evacuate the calories that its coat can not evacuate.
Curves edited by the journal "Revue technique du bâtiment" NÝ 92 october 82 show that the coefficient of inside insulation is twice as bad as outside insulation, for the same thickness of insulating. The article of this magazine present so convicing arguments in favor of outside insulation that it is incomprehensible that some still build outside-insulated house ! It is the reading of this journal that drove me into build my house which is used as an example in this article.
Fortunatly, recent norms about house construction are stricter at the insulation level. We will analyze what it's all about.
The opposite sketch show that the bottom-floor tile, which is normally insulated from the ground either by a thickness of insulating, either by an enclosed crawl space (do not forget that the air is the best insulating after vacuum, with the condition of being stationary), bears a screed cast on a thickness of 4 to 5 cm of insulating, called floating tile.
The ground of the house is thus not in direct contact anymore with the thermal bridge of the floor tile. But the surface is big. Let's suppos that the house has a surface S=100 m2, this gives a conductivity of
G = 0,04/e×S = 0,04/0,04×100 = 100 Watt/°C, that is to say a loss of 3 kWatt for a cold of -7ÝC, only through the ground, if the tile was not insulated.
But the sketch show that only few leak lines are attracted by the thermal bridge, the others go toward the ground where they meet the insulating of the tile.
Let's call "reception zone" this strip of ground that border the outside walls and be 2x its width, x being then the distance to the thermal baricenter at the entrance of the thermal bridge. We make the calculations always considering a width of 1 meter of wall.
The conductivity of the reception strip is : Gc = 0,04/0,04×1×2×x = 2x soit Rc = 1/2x
The conductivity of the thermal bridge is: Gth = 1/(x+0,1)×1×h = 0,15/(x+0,1) soit Rpth = (x+0,1)/0,15
The conductivity of the dispersion sone is : Gd = 1/0,2×0,50/2 = 1,25 soit Rp = 0,8
thus Rtt = Rc + Rpth + Rp = 1/2x + (x+0,1)/0,15 + 0,8 = [1,5 + 2x(10x+1)]/3x + 0,8
Rtt = (20×x2+2×x+1,5)/3x + 0,8
By virtue of the principle of Fermat-Maupertuis, let's look for the point of maximum enthalpy, that is to say of maximum conductivity, by looking fo the zero of the derived of Rtt :
R' = [3x(40x+2)-3(20x2+2x+1,5)]9x2 = (60x2-4,5)/9x2
R' = 0 donne x2 = 1/13,33 et x = 0,27 , that is to say a reception strip of 54 cm.et Rtt = (1,5 + 0,54 + 1,5)/0,81 + 0,8 = 5,17 et G = 0,193 ≈0,2 that is to say Qpth = 0,2×30 = 6 Watt per linear meter of wall.
The thermal bridge of the floor is divide by 2,5, we passed from 15 W to 6 W, but in general the thermal bridge of the ceiling remains, which still makes 23,5 W of thermal bridge with regards to the 25 W of the 2,5 mètres of insulated wall. We are still on the CSTB's curves of 1982 which show that the inside insulation is twice less efficient than outside insulation.
Then some builder, with the laudable goal of improving the situation, will partly neutralize, in the same way, the thermal bridge of the ceiling by sticking on its wall surface a thickness of alveolar placo.
But then goodbye to the vault effect, goodbye to the comfort of the cavemen!
Without forgetting the partition walls, and the walls of the garage ! Are the contiguous walls of the garage insulated, the ceiling when there is a room above, the gable wall, the junk romom : everywhere small walls either uselessly covered with insulation, either unfortunately not insulated ? It is impossible to eliminate all the thermal bridges of every nook in an house inside-insulated. To get convinced, go to the CSTB website and read the non-exhaustive list of thermal bridges.
Why should you outside-insulate ? Because you can non inside-insulate.
We know that the heat goes from hot bodies toward cold bodies, that hot bodies lose their heat and that cold bodies absorbs it. The same goes for our bodies which needs to lose its heat because it creates heat constantly because of its biological functionment and its physical activity. If it can't lose its heat, we feels hot, first we sweat because evaporation absorbs heat, and then this can become serious, after 42ÝC, it is the degradation of the brain and of the main organ, then death. If we lose too much heat, we are cold, we cover us in order to insulate us better and if we can not keep a vital minimum of heat, it is also death that watch for us. For instance, a man which fell in the see can not survive more than few minutes in water below 14ÝC, water being a good conductor of heat (15 times more than polystyrene) absorbs all his energy, the body cools down and the chemical reactions of the cells block.
We exchange our heat with environment essentialy by convection and radiation, sometimes in some areas of our planet, inhabitants sleep on marble or tiling floor to freshen up by convection. Some animals, the dogs, do this too.
When our body manages to dissipate exactly the heat that it produces, we feel good.
If our body, which, in calm conditions of activity, is at a superficial temperature of about 34ÝC, lightly clothed, in a room whose the sides are at 19 or 20ÝC, and calm air at 20 or 21ÝC, we feel good. A naked man, in inactivity, is in balance with an environment at 28ÝC.
Our body exchanges heat with the surfaces by radiation, and with air obviously by convection. If the surfaces are colder and the air is hotter, we have a feeling of shiver, we feel feverish, if it is the opposite, we find that it is hot, but that the bottom of the air is pleasant. In the case of reversible installations (we will come back on this later) the specialist of air conditioning rather install cold air convector high rather than refreshing by pipes in the floor, because cold air is more pleasant than a cold floor.
We are back to our celing and our cavern. Air heated by radiators, we can see trails along the walls, goes up to the ceiling and heat the ceiling. If this one is in concrete, it will absorbs the heat by convection at 30/35ÝC, event more, and will restitute it under the form of infrared radiation at very low frequency, a pleansant heat coming from the sky (see the advert on the electric "radiant" radiators, the heating system by radian ceiling). If the ceiling is covered with cardboard, the hot air will stagnate at the top until the thickness is sufficient to go down to the height of our face and will heat our cheeks, while leaving the feet cold.
The norm of the Commission du Chauffage et de la Ventilation say that the comfort temperature should be measured at 60 cm above the floor, it is certainly for that that the ambient thermostats are put at 1.40 meter about the floor !!!
In order to feel good, not having fever on the face and cold on the feet, being able to dissipate our own heat toward absorbant surfaces, the surfaces must be conductives, stable in temperature, and thus have thermal inertia, hence heavy surfaces, not covered with a thick layer of light matter not conductive of heat. The heavy materials are at the same times good conductor and good absorvant of heat. The heat stored is then restituted to the air by convection. Hence the walls must not be inside-insulated.
It is the bread oven, the pizza oven, the caveman cavern, the troglodyte house, the enormous stoves in ceramics from Central Europe, all this ancestral experience which is replace by oil, oil to heat, oil to freshen.
The cult of progress must not exclude the experience of our ancestors.
Hence, heating must not send heat, but avoid to lose too much to avoid the feeling of cold that comes from the fact that our body does not manage to profide heat sufficiently. A piece of evidence, one only has to makes few movements to get hotter. It is the temperature of the surfaces that limits the loss by radiation and brings the thermal comfort. Hot air is dry, the hotter the radiators, the drier the air. The drier the air, the worse conductor. This fetters the elimination of our own heat, hence the feeling of fever and the burning cheeks, because it is through the face, not covered, that we evacuates the most of our heat. Furthermore, when we breathe dry air, it absorbs more water in the lungs, and it dehydrates which increases the lack of comfort. We lose about 1 liter of water a day only by breath, in a tempered environment of course.
We find the same anologous problem with wall in compromis-material cited previously. They are, because of their function of insulating, bad conductors, and because inside insulation makes a discomfort by lack of absorption of our radiated energy.
Hot air heats also the surfaces if they are not covered with insulatin, that is what is called "heating by convection", or it does not heat anything because there is nothing to heat but the furniture. 50 years ago, heating installation by hot air where built with enormous sheath which comes to long grids at the bottom of the windows. At the time, there was no insulating on the walls.
They were quickly rejected because discomfortable. The central heating installationg by water are more comfortable thanks to the presence of radiatros, in melting if possible. We find again the presence of thermal inertia. Electric inertial radiators are more comfortable than metallic electric radiators.
In conclusion, the "cold" heat heats better, that is to say is more comfortable, than "hot" heat. Surfaces at 20ÝC heats better than air at 45ÝC.
The thermal comfort is air moderatly humid at a temperature 2 or 3 degrees above the one of the surfaces. This is what is obtain with outside insulation and the heating system that will be described further.
Windows are the main waster of heat, on the one hand because of the good conductivity of glass, on the other hand because of the leak around the frame. If you have old windows somewhere, just put the hand around it, particularly if there is wind.
The conductivity of a pane of 4 mm of thickness is 1/0,004=250. That is to say that 1 m2 of window wastes as much heat as 125 m2 of a breeze blocks wall, without any insulation. This windows protects only from the draughts and from the wind. That is why, in northern countries, has been invented the double-glazing window.
All this time before inventing it. It is true that coal was not expensive and the mine were the power of the nation.
The idea behind the double-glazing window, it is to enclose air inside it, because we said that the best insulating after vacuum is calm and dry air. The double window, which is expensive and bulky, has been replace by the double-glazing window which enclose a dry gas. Why is there no vacuum, the insulation power is much better ? Because, under the effect of atmospheric pressure, the two windows would implode one against each other (The same problem goes for cathodic screens). It is the space between both window that determines the quality of insulation of a double-glazed window.
For instance, with e=8mm, this leads to a conductivity g=λair/e=0,025/0,008=8,33, if e=16 this gives g=1,56.
Here is the miracle : we got from 250 to 1.56. As a piece of evidence, in the past, on single-glazed windows, there often was condensation. Now, with double-glazed window, you do not see condensation anymore, or very scarcely. Why ? It is the principle of the cold side : when the hot and humid air of the soup which is boiling comes close to a cold surface, it cools and the steam that it contains condense into fine drop, because the temperature of the air is under its dew point.
If the air (or nitrogen) of the double-glazed window is replaed by argon, rare gas that exist in the atmosphere, which has the advantage of having a λ smaller, but a price of useing higher, this leads to g=0,020/0,016=1,25.
But warning, a breeze block wall of 20cm covered with 10cm of polystyren has a conductivity of 0,33, and 1 m2 of this excellent double-glazed window has the same deperdition as 4 m2 of insulated wall. That is to say that if you have large picture window that cover the 3/4 of your façade, then no need to insulate the wall !!!
It is pleansant to have large picture windows with a panoramic view on the landscape, this cost some calories in winter. But in summer, the sun penetrates and heat the tiled floor or the marble, the terrace reflects the infrared rays toward the ceiling and you living-room becomes an oven. It only remains for you to look for the shadow of big trees. If you are lucky enough to be close from a river, you will feel its coolness, because the water represents a cool face and good conductorof heat which absorbs your radiated energie., and furthermore, because of the evaporation, the air is more humid and hence better conductor and absorbs more easily you heat, and lastly the evaporation absorbs the energy and thus creates coolness : that is why one sweat when being too much hot.
At night, the heat accumulated spread in the house, and it is hot everywhere
If the large windows are suppressed, when it is cloudy, it is dark in every room. There is no ideal solution. Blinds in summer and glass wall in winter, no terrace on the south side, especially in hot areas.
The second cause of loss of the windows are the leak of air between the fix frame and the mobile leaves, leak which depends also on the wind pressure. Modern windows are very studied, with gasket, and absorption grooves and imprisonment of air to insulate according to the navy principles. The strenght of the water or of the wind is smashed, a volume is left to make the pressure decrease and then a joint which does not undergo any movements of the fluid look after watertightness.
Windows had also to ensure the renewal of the air in the rooms for breathing, extracting humidité from the kitchen and the breathing, the chink under the doors giving to outside brought the air for the stove or the chimney.
Now that the doors and windows are perfectly airtight, you are todl to add chinks in the chassis, or in the panes, in order to ensure this renewal of the air, which is cold air because it comes directly from outside. Then on one hand, you are sold airtights windows in order to make energy savings, and on the other and, they are made non-airtight by adding big chinks for the ventilation.
That's contradictory !!
The solution is to replace these chinks by a mechnical ventilation double-flux. Because the cold air that enters the house replace somehow hot air that goes out.
This installation consist of aspirate hot air from the technical room, the kitchen, the toilets and the bathroom and throw it outside after it be passed through a heat interchange in which new cold air from outside goes in opposite direction. This cold air, heated in the interchange, is then insufflated into the comfort rooms, such as the living room and the bedrooms.
60% of the air extracted is thus recuperated, which means that, because the extracted air is at about 25ÝC, if it is 0ÝC outside, the air which is insufflated is at 15ÝC, instead of being at 0ÝC when it comes in through the chinks of the windows.
This permanent renvewal, regular, of the air, allow also, by extracting hot air which is humid because it contains all the mist produced in the house, to maintain the house in a hygrometric state close to the one of the outer air and thus avoid the deposit of moistness in the house, particularly at the level of the thermal bridges.
Indeed at the level of the thermal bridges, the cold wall is in contact with the hot and humid air of the house. That air cooling, the mist which it contains set itself down under the form of tiny drops like dew or fog. The wall becoming humid, it becomes more heat conductor, and the thermal bridge effect is thus more accentuated, which accentuates the condensation and henceforth. Hence the tapestry which comes unstuck, the humidity spots, and even the water oozes at the bottom of the walls.
The house becoming more humid becomes more difficult to heat. Because humid air is more heat-conductore, it takes you more heat, and hence you feels colder.
And warning : when freeze falls on the walls impregnated with water, the water changes into ice and, the same way as the bottles which breaks under the volume increment of the ice, the wall fissures. It is the same phenomenon than the rocks which fall on the roads in mountain in winter.
With outside insulation, the wall are well wrapped, in the warmth, no thermal bridges, no condensation, no heat loss increase, no freeze, no fissure.
About the shutters : if they are relatively airtight, the create a volume of still air which ensures a complementary insulation between the windows and outside, thus reducing the loss by convection of the windows, especially when there is wind. One celsius degree can be won.
The air which allow us to live is a mixture of invisible and impalpable materials, which we call gas. This air, which constituted what we call our atmosphere, has nevertheless a weight which weighs on each piece of surface that surrounds us with a force of about one kilogramme and which we call atmospheric pressure. It is the weight of all this air that there is from where we are to where the satellites are up there in the sky. In his mixture, there is a fifth of oxygen, if it was aont, the atmosphere would be five times lighter, we said that there is a partial pressure of a fifth of atmosphere, which is about 0.2 kg.
It is it that ensures the combustions which free thermal energy : the heat. There are slow combustions, the one that occurs in the living cells, animal or vegetal, do not forget that the man is an animal, and everywhere around us : rust, verdigris, the silverware, the pewters, the paint which lose their sheen.
There are vivacious combustions which burn the fossil matter : oil, gas, coal, wood, which are actually only concentrated residues of living cells.
The other four fifth of the atmosphere is essentially constituted of nitrogen which is a relatively neutral gas. There is also the residues of combustion : carbon dioxide and carbonique gas which is guilty of the greenhouse effect. There are scarce gas but very useful, which we call rare gas : helium, neon, argon, krypton..., and the gaseous wastes of our activities which constitute the pollution.
And finally, there is the water vapour. Beware that mist is invisible : the white smoke from the nuclear power plants, the mist, the fog, the clouds, what you see above you saucepan of boiling water, this is not water vapour, this is very tiny drpos of water in suspension in the hot aire, which comes from the water vapour which escapes from the hot water, and which is already recondensed to water.
The quantity, the weight, of water vapour that can be in the air, that is to say the partial pressure, is very variable and also depends on the temperature of the air.
At a given temperature, say 20ÝC, the air can contains up to a certain maximum of water vapour, and then the supplement of water vapour recondenses immediatly into water, into very tiny drops, which are visible. This maximum partial pressure which water vapour can reach without recondensing is called the partial saturation pressure. We will say that the hygrometric degree of that air is 100%.
This partial saturation pressure decreases when the temperature of the air decreases, and increases when the temperature increases. Thus, if this air is at 20Ýc saturated, heats when passing through a radiator at 45ÝC, it is no more saturated without the amount of water vapour that it contains being changed. Its hygrometric degree will be for instance down to 50%, which means that it can contain twice more water vapour before being saturated, which means that it became dry and can again absorb water, this means also that it became less conductor of heat. The hygrometric degree of the air is the ratio between the amount of water vapour that it contains and the saturation amount.
60% is the hygrometric degree of comfort which gives to the air a suitable conductivity to absorb enought caloris and not too much, because the conductivity of the air depends on the amount of water that it contains, it is actually the water that absorbs the calories. Beyond 60%, the air is too humid, it cools too much, and below it is too dry and not enough conductive.
Let's take now the air of the kitchen at 25ÝC and 80% of humidity and let's cool it down for instance by passing it throught the interchange of the VMC, at a certain temperature, let's admit 18ÝC, it will reach its point of saturation and a part of the water vapour will recondense. We call this point : point of dew, like the dew. If now this air is only at 60% humidity, will the dew point be the same ? No, because due to the fact taht it does not containt the same amount of water vapour, the saturation temperature will be lower.
If the temperature is below 0ÝC, indeed very negative, the saturation pressure is very weak, the air is very dry, that is what happens in high mountain.
If some air comes close to a cold surface, locally it will cools down and reach its dew point, and some vapour will recondense on the surface and form water. But for that reason the amount of vapour of the air in the room will decrease and the air wille become drier. That is what we call the principle of the cold surface : the hygrometric degree of a room is established by the dew point of the coldest surface. It is the ratio between the saturation pressure at the temperature of the coldes surface and the saturation pressure at the temperature of the ambient air.
Furthermore the condensation yield energy which is absorbed by the surface, and get lost outside, when the surface is a window or a thermal bridge.
The inverse phenomenon, the evaporation absorbs energy, that is why you have to heat water to produce vapour, for instance to make the turbines which produces electricity spin, be in the power plants said "thermal" or in the nuclear power plant that are also thermal.
In a way summarize and general : air transports water, and water transports the calories. Vaporizing water absorbs calories, and restitutes it when recondensing, it is the coolant cycle.
Mankind did not invent anything, nature found it ages ago. The chrysalis or the cocoon of the silkworm and orther caterpillars of butterfly is the best example. The marmot which bury itself for the whole winter while outside is -25ÝC : snwo insulates as well as polystyrene and the marmot is outside-insulated by several meters of snow. And all the small mammals which live in the bottom of a burrow to protect thermselves from predators as well as to keep their brood warm.
Let's also mention the chalets in high mountains. Mountain men lived thery enclosed with their herd which they use as a low temperature heating, and they were outside-insulated by a layer of 2 meters of snow under which the chalets were completely shroud. Let's signal out the farm of our country, exposed full south, insulated est and west by the sties and the stables, and at the north by the lean-to for the wood, with a ceiling made of cob of straw (excellent insulating) and a granary with hay and cereals in inside.
Then outside insulating one's house, it means traditionnaly contruction like decades ago and wrap it up inside insulating.Remains the sole of the foundations, it is at least at 80 cm of depth, it never freezes, there is no wind, and if we want to be perfectionnist, we can cast the soles on 4 to 5 cm of styrodur or other compact insulating material which bears widely the same pressure than the soil of the basement.
Remains also the windows, or more exaclty the thresholds of the windows and above all the French doors and the doors. If we do not beware of it, we will get awesome thermal bridges, nevertheless localises to the openings and not on the whole periphery of the construction at the straight of each tile.
It is the only delicat point of the construction. We will get back to this.
Let's see the walls, they are hot, they are thus dry and less conductor of the heat than when they are humid. They radiate the heat they are brought. In summer, they are not in the sun thus keeping the coolness of the night. The house behaves like a cave : tepid in winter, cool in summer. It is the cave of the caveman, the burrow of the marmot, the cocoon of the silkworm.
A soft heat spreads in the walls which radiate in any directions which brings a thermal comfort unequalled.
Thermal bridges became our allies : the drive the heat from the tile into the walls. It can't be found better radiators : big, low temperature, conductor, big inertia. That is why the heating screed must not be too much insulated regarding the load-bearing tile, but the load-bearing tile must be well insulated regarding outside.
Inversing the technique inverses all the relations and must inverse the mentalities and the aprioris.
Only by suppressing the thermal bridges as we demonstrated precedently, and as the curves from the CSTP show, the insulation coeffeicient is twice better than for an inside insulation. By insulating seriously the screeds and by insulating the thresholds, we multiply, as we will see further, the coefficient per three, which allows, with a good security margin, to divided the power of the heating installation per two, thus to decrease significantly its price.
The fact that the house is particularly not greedy in heating energy allows also to fully profit of the outer contributions, for instance in winter when there is sun. The latter heats the tiling which then propagates this heat in the house, through the screed and the water which circulates in the heating circuit. During good days, we can retrieve up to about 5 kWh per m2, with 5 m2 of windows well exposed it suffices to heat the house.
A heating source that we often forget to mention are the beings. A marmot or a rabbit from the Groenland has not heating installation in his burrow. You certainly noticed that when there is a drink in your company, when coming in the meeting room, with cool weather, it is cold. Half an hour later, windows are wide open and some say : alcohol warms up. It is not the alcohol but those who consume it. Each of us dissipates about 2.5 kWh per day for a calm activity. When it is cold about 12ÝC, for persons, a bit of cooking and few lit light bulbs are sufficient to heat the house. Do not forget that the VMC double flux participates also to the conservation of the heat.
The bread oven, the pizza oven, thanks to their massive wrapping conserve and spread heat.
Outside insulated walls, thanks to their inertia and to their conductivity, conserve and spread a soft and isotropic heat, in summer they keep a comfortable freshness.
It is the opposite of inside insulation which does not have any inertia and any conductivity.
Air being heated at low temperature by the walls, conserves its hygrometric degree and thus its conductivity, which allow a small gap of temperature between the air and the walls, and to have a good balance of the thermal exchanges by radiation and convection. This equilibrium is the basis of thermal comfort.
There is no more thermal bridges, neither apparent or hidden, the only sources of important losses are the doors, the French doors and the windows.
For the doors, it exists good isotherm doors with peripheral joint, but dut to the thickness we can't find any coefficient better than 1.2 W/m2.°C, that is to say hardly better than a good double glazing. A good solutiong used in northern country, even in Northern France, is to create an entrance airlock, which permitted, decades ago, to put down umbrellas and coats..
For the windows, we saw this, we can get down to 1.25. Thus we only can play on the surfaces : but you have to see clearly.
The important point when we can act and win a lot, it is the assembly.
In the case of outside insulation, you have to enlarge the boards by 5cm at eachsides to foresee an insulation of 5cm at the peripheral of the boards. The windows will thus be mounted tunnel-like showing at the surafce, and the polystyrene of insulation weel be against the fixed chassis of the openings. Putting cord of joint well adapted, there won't be any cm2 of wall in contact with outside air, neither a trickle of air which won't slip in the house.
The sketch below try to be as precise as possible.
The last critical point, but not the least, is the assembling of the threshold : it must be prefab and wrapped in a caisson made of styrodur or sort of, the French door or the windows, or door is posed on top of it with the intermediary of a joint half-tough, then sealed in "good position". The seal paws are directly sealed in the wall, at the shortest, like it was made before the poorly justified inside insulation technology.
A word ... that is not true, because it is a problem.
The simplest is to build it beside, just against the house, but separated from it on the whole joint surface with 10cm of polystyrene, that is to say ensurethe continuity of the insulation without fault. I give opposite a possible realization (it is the one I practice). This gives the possibility to create an entrance airlock.
If we want to incrust the garage to the house, we have to include it in the insulation but with a garage door the most airtight and isotherm possible. This will be the comfort of the handyman. It will be good to also foresee an isotherm door between the garage and the house, possibly to insulate the adjoining wall with the house and the ceiling if there is a room upstaires.
In other cases, you'll have to vet the thermal briges, and there will be some !
The cellar garage would not pose too many problems if there were not the stairs. The garage as to be considered as outside the house and the walls and the ceilings have to be insulated like the outer walls of the house, put a wood stairs and an isotherm door upstairs. If it is in masonry, it should be wrapped in a box and with an isotherm door at the bottom. If the stairs is in a part of the cellar apart from the garage, there is nothing to add, it is enough to insulate the garage well, "internally", that's the last straw, from the rest of the cellar, the outside walls being insulated on about a meter deep.
Note: if you have a burried and close cellar, it is sufficient to insulated the foundations on a meter deep like for a house without cellar. This would make an excellent insulation airlock. A slight ventilation should be planned.
It is like for the garage, there is a rigorous solution, then it is handiwork for each case.
If you have a four-slopes roof, the good solution is to build a caisson in the central part, as shown on the sketch opposite, with velux obviously. Do not forget that in same, it is better that air can flow between the caisson and the roof.
If you have gable walls, it is less neat. You have to insulate the gable walls on both side, for the inside part only on the surfaces which are not included in the converted permises. It would be a good thing to also insulate the wall slice. This seems wacko, but thermal bridges are so.
If you install a chimney, it is better to install it against a partition wall to benefit from its accumulation and of the spread of the heat thanks to its conductivity. If you install it against a peripheral wall, you will lose energy, because a wall, though insulated, lose three times more energy at 70ÝC than at 20ÝC, and it is 70ÝC or even more in the hood, when the chimney is on.
If on the other side of the wall, there is a bathroom, it is perfect. If it is a room, there are chances to be too hot, with too dry air. You may have a bad sleep. If there is no other solution, you rather install it agains a peripheral wall, mostly if you only use it at Christmas.
The water heater, if it is an electric ballon, it must be placed in the bathroom. It always lose some heat, just pass your hand around the bulb, and this soften the temperature of the bathroom. This can avoid, in mid-season, to use the heating. Furthermore, hot water comes faster, and thus you lose less water. Often, the kitchen is at the other end of the house, too bad, it is better to place it in the bathroom. Not lost energy is not paid energy.
We are going to determine the losses of a house of 15.40×8.40 = 129.36 m2 of floor surface intra-muros,
of (15.80+8,80)×2 = 49.20m of perimeter,
of 2.60m of ceiling height, that is to say 127,92m2 of lateral surface,
in an area where the average of the extremas of low temperature is of -7ÝC, with an inside temperature of 20ÝC.
The surface of the openings is
6×2.15×1.40+2.15×1.20+2.15×0.80+1.25×1.00+0.95×0.60 = 24.15 m2.
Hence, wall surface :
127.92-24.15 = 103.77m2.
The insulation coefficient is given by the curves of the CSTB for a wall with bay windows for 10cm of outside insulation and 0.07 for the residual thermal bridges, which gives a coefficient of 0.42.
For an inside insulation, with the same thickness of polystyrene, the thermal bridges are worth 0.52, that is to say cumulatively a coefficient of 0.87, more than the double!
The polystyrene being fixed by glue pins or on plastic rails, there is about 1.5 cm of stuffy aire which increases the insulation thickness, hence the coefficient 0.04/0.115=0.35 given by the CSTB. In our case, all the thermal bridges are eliminated, the losses through the threshold will be calculated separately, we can take this last coefficient for a calculation basis.
Losses through the walls are thus
103.77×27×0.35 = 980.63 Watt
Losses by the openings, with a current coefficient of 1.50, are :
24.15×27×1.5 = 978.07 Watts
We can notice incidentally that the losses through the openings are almost equal to the losses through the walls
Calculations of the losses through the thresholds :
Length of the thresholds
6×1.5+1.3+1+0.7 = 12 m
Width of the thershold vis-à-vis the tile and the wall
0.17+0.13 = 0.30 m
Average thickness of the thresholds : 0.06 m
Hevay concrete conductibility coefficient : 1.4 Watt/m;ÝC
Styrodur coefficient : 0.04 Watt/m.ÝC
Thermal resistance by m2: Rth = 0.06/1,4+0.03/0.04 = 0.79 °C.m2/W
Conductance: g = 1/Rth = 1.26 Watt/m2.°C
Surface: 12×0.30 = 3,60 m2
Tile temperature : 25 °C, gap = Text-Tint = 25+7 = 32 °C
Losses through the thresholds
3.60×32×1.26 = 145.15 Watts
The conductivity is then the one of the concrete hence the losses
3.60×32×1.4/0.06 = 2688 Watts
That is to say, 20 times more ! We will see at the end of the calculations that this represents 2/3 of the losses of the house for only 12 meters of thresholds!
Average perimeter of the foundations : (15.60+8.60)×2 = 48.40 m
Floor surface of the fondations : 48.40×0.20 = 9.68 m2
Conductibility coefficient of a wall of 0,20 m of height : 2 Watts/m2.°C, that is to say for 0,80 of foundation : 2/4 = 0.5
Floor temperature at 0,80 m deep : 4°C,
Tile temperature : 25 °C, thus a gap of 21°C
Losses through the sole of the foundations :
9.68×21×0.5 = 101.64 Watt
By -7 outside and +4 at 80 cm deep, this makes an average outside temperature of 4+(-7-+4)/2 = 4-5.5 = -1.5°C;
With +25 in the tile and +4 at 80 cm deep, this make an average inside temperature of 4+(25-4)2 = 14.5°C;
The lateral surface to take into account is the passage surface, that is to say the thickness of the wall thus 0,20cm, thus 49.20×0.2 = 9.84 m2;
The lateral losses of the foundations are thus of :
9.84×0.04/0.1×(14.5-(-1.5)) = 62.98 W.
Losses through the ceiling insulated by two layers of crossed glass wool :Ceiling temperature : 23°C, gap 23+7 = 30°C
Losses through the ceiling :
129.36×30×0.04/0.40 = 388.08 Watt
The thermal resistance is then: Rth = 0.17/0.04 + 0.6/0.8 = 5
hence the losses through the floor
129.36×21×1/5 = 543.31 Watts
The renewal must be about 25 m3 of aire per hour and per person, for an occupation of the house by four persons, this makes 100 m3 per hour.
The VMC has an effectiveness of 60%, the specific heat of the air is 0.3 kcal/m3.
The losses are thus of :
0.3×30×0.4×100×1.16 = 417.60 Watts
The total losses for a house with -7°C outside and +20°C inside are :
980.63+978.07+145.15+101.64+62.98+388.08+543.31+417.60 = 3617.46 Watt say 3600 Watts
The volume of the house is : 129.36×2.60 = 336.34 m3
The volumic coefficient of the losses is : G = 3617.46/(27×336.34) = 0.398 Watt/m3.°C, that is to say 0.40Watt/m3.°C
With regards to the traditional houses, nowadays built with inside insulation, we are three times better.
There is a free and renewable ad infinitum energy : it is the one that we do not consume.
The surface of the outside faces of the house is: 127.92+2×129.36 = 386.64 m2
The average surfacic conductivity coefficient is then : K = 3617.46/(27×386.64) = 0.347 Watts/m2.°C
In order to achieve the announced target, to divide the heating cost by ten, it lacks a factor 3 and something. The heating method will give this. You have to take a thermodynamic heating, a refrigerator, a freezer, an air-conditioner that works the in reverse manner : it takes cold calories from outside, change them into hot calorie by the mean of compression, and pour them into your heating pipes. Have you ever inflate a bycicle tire with a hand pump and didn't you let it go because it had become burning. : that's all the thermodynamic heating mystery, thermo because it heats, and dynamic because it moves.
When a gas is being compressed, it warms up, when it is decompressed, it is slackened, and it cools down. You can notice it each time you use an aerosol, particularly a deodorant.
It is cool down to colder than outside temperature, as the calories go always from the hot body into the cold body, it will take the calories from outside, from the air, from the water, from the ground depending on the case, and then it is compressed to hotter than the inside temperature of the floor of the house, and it will yield the calories to the floor. We will finally have transferred thermal energy from a cold outside into a hot inside, increasing the temperature of the caloreis. It is like we increase the level of water with a pump, the amount of water didn't change, but the pressure changed. That is why this system is called "heating pump". The compressor functions like a pump, excepted that it pumps a gas instead of pumping a liquid.
Two main systems exist, either calories are taken from air, it is the aerothermodynamic system, either they are taken from the ground or from a phreatic table, it is the geothermodynamic or (badly said) geothermic system.
The big advantage with these system, it is that they supply more thermal energy than they consume electric energy, because a big part of the energy is withold from the outside environment. We call the ratio between these two quantities the efficiency coefficient.
Aerothermodynamic systems have a freezing problem when the air is humid and close to 0ÝC, which lower their efficiency coefficient by about 3.
Geothermodynamic systems have a efficiency coefficient close to 4. They are more constricting, hence more expensive, to put in place because it is necessary to either to drill a boring, either to burry few hundreds meters of collecting pipes at 80 cm of deepness in an area where it is no more possible to make holes or to plant big trees.
In the case of the house calculated previously it as been chosen the geothermic system.
3*4=12, heating electric consumption has been divied per 12
3500 divided by 4 makes 875 Watt, a compressor of 1 kW is sufficient to heat the whole house, to be compared with a 20 kW oil-fired boiler.
With these systems, low temperature heat is obtain, 25 to 30ÝC, it is necessary to have a big surface for diffusing the heat. It is all the opposite to the boilers which burn a fuel and gives water at 65/70ÝC which is made circulating in small radiators. That is why it is all indicated and without any drawbacks to use the floor to diffuse the heat.
It is now very important to insist on the role played by the outside insulation. As the heat dissipating pipes are drowned inside the screed which rests on the load-bearing tile, with a small thickness of insulating to favor slightly the dissipation toward the florr, the load-bearing tile take a part of the heat.
And like all the walls are on the load-bearing tile, the heat goes up in these walls. The floor, the walls, the ceiling which is heated by convection, all this form a huge low temperature radiator. Air is never heated, it is pratically at the same temperature than the surfaces, it keeps its hygrometric degree and hence its conductibility, it is never dried like the air that goes through radiators at 65ÝC where it is necessary to put small water pot to give it back a little humidity..
There is a perfect equilibrium between our energy dissipated by radiation and our energy dissipated by convection with the air. These are the perfect conditions for thermal comfort.
The heating installation is provided with a flowmetter, a thermometer on the hot water arrival and on the tepid water return and an electricity meter.
With a min/max thermometer, I noted the temperature mornings and evenings:
Measurement summary:
| Date | Tmin | Tmax | m3 | kWH |
|---|---|---|---|---|
| 1276.4 | 44 | |||
| 30/11/1995 | 5.0 | 8.0 | 1286.8 | 72 |
| 01/12/1995 | 5.0 | 11.0 | 1294.5 | 93 |
| 02/12/1995 | 8.0 | 13.0 | 1298.3 | 103 |
| 03/12/1995 | 10.0 | 13.0 | 1298.3 | 103 |
| 04/12/1995 | 7.5 | 9.0 | 1302.4 | 114 |
| 05/12/1995 | -4.5 | 3.0 | 1310.4 | 136 |
| 06/12/1995 | -6.0 | -2.0 | 1314.0 | 146 |
| 07/12/1995 | -8.0 | 0.0 | 1321.5 | 166 |
| 08/12/1995 | -8.0 | 0.0 | 1328.2 | 186 |
| 09/12/1995 | -3.0 | 4.0 | 1335.8 | 211 |
| 10/12/1995 | 3.0 | 5.0 | 1346.3 | 230 |
| 11/12/1995 | 0.0 | 2.0 | 1352.4 | 246 |
| 12/12/1995 | -1.0 | 2.0 | 1354.3 | 251 |
| 13/12/1995 | 0.0 | 4.0 | 1366.3 | 282 |
| 14/12/1995 | -1.0 | 2.0 | 1377.1 | 310 |
| 15/12/1995 | -2.0 | 2.0 | 1383.6 | 327 |
| 16/12/1995 | -3.0 | 4.0 | 1391.3 | 349 |
| 17/12/1995 | 0.0 | 8.0 | 1394.3 | 355 |
| 18/12/1995 | 1.0 | 5.0 | 1398.2 | 367 |
| 19/12/1995 | 1.0 | 6.0 | 1402.4 | 376 |
| 20/12/1995 | 2.0 | 6.0 | 1407.8 | 390 |
| 21/12/1995 | 3.0 | 6.0 | 1411.9 | 401 |
| 22/12/1995 | 6.0 | 12.0 | 1416.8 | 414 |
Sum of minimal temperatures : 15
Sum of maximal temperature : 123
Average temperature :(15+123)/23/2 = 3,00
Gap between hot water and tepid water temperature : 8 to 9, that is to say Δ = 8,5
Amount of m3 of water : 140,40
Amount of kWH : 370
Amount of heat brought into the house : Qa = m3×Δ×1,16 = 1384,34 kWH
Compressor efficienty coefficient : Cp = Qa/kWH = 3,74
Amount of degree.day :Dn = N×(21-Tmoy) = 414
Volume of the house : 146×2,6 = 379,60 m3
Volumic coefficient of losses : G = Qa×1000/(24×Dn×vol) = 0,367
Average heating power = 676,29 Watt (in december with several freezing days)
Consumed power on the coldest day (Second day at -8°C): 1041,67 Watt
(The compressor has a power of 1,5 kW)
Yield of the compressor without the pump: Qa/KWH×(1-5%) = 3,94
The consumption of the heating installation is, to within few kWh from one year to another, of 2500 kWh.
hence a total resistance of 12.75 and a conductivity λ= 0,0784 W/m2.°C
If we calculate the losses through the florr of hour second house in these conditions,
we obtain p = 129,36×21×0,0784 = 213,06 Watt
if we apply this corrective term on G this gives : (3617,46-543,31+213,06)/(27×336,34) = 0,362
we are 5/1000 under the measured coefficient, which is normal considreing the losses which are not taken into account, such as for instance the small wall of the timbers wrapped in 20cm of glass wool.
If we take this second corrective term into account, we obtain
p = 49,20×0,20×0,04/0,2×30 = 59,04 Watt, thus Gcor = (3617,46-543,31+213,06+59,04)/(27×336,34) = 0,368
Equals the value measured to within a 1/1000, on a house with a different size and a different disposition
We didn't use this options on the second house because, apparently, norms forbid not ventilated crawl space, it is better worth refreshing in winter and humidify in summer, it is good for oil seller. Once filled with polystyrene, it is no more a crawl space, polystyrene sellers unerdstood it rather well !!
It has been mathematically and experimentaly proved that the combination outside insulation plus geothermic heating allows :
to divid the heating bill by 3×3.74 = about 11
to obtain an excellent thermal comfort and to live in tee-shirt in the house with -7ÝC outside
to emit no CO2 which is a greenhouse effect gas
and even to be completely ecological
and energetically autonomous because due to the small powerd of 1 kW needed by the compressor, this one can be provided thanks to a windmill (for 25000€, you can get a 5 kW one) or a solar sensor of 1 kW, about 6 m2(6000€). Notice that the windmill kW and the solar kW are about the same price.
to keep freshness in summer,
or even to function in reversible mode, that is to say in refreshing mode.
Note that there is no maintenance needed, or maybe a review every decade.
(Mine has been running for twelve years, I opened the lid only to show the system to visitors)
The refreshing via the ground is terrible because, on the one hand, cold air stay at ground level (it is heavier than hot air) thus cold at the feet and hot at the head. On the hother and, hot and humid air ( in summer, hot air is humid due to the evaporation of all the water surfaces, it is not the same than hot air from the radiators) produces condensation when cooling off, hence humidity at the foot of the wall and with the years delamination of the tapestry among other things. It is better worth addin convectors high, for instance upstairs. This complicates the heating installation which becomes an air-conditionning installation.
We can also convert the VMC into an air-conditionner.
We add on the circuit some insuflatted air, at the end of the interchange, a supplementary caisson which contiains a radiator water-air, sort of car radiator. We plug this radiator on the (supplementary) circuit of the heating dispenser of the room (like if there were a room more).
So in summer, when the installation is in refreshing mode, this refresh the insufflated air, in winter, this brings to the air the few degrees that it lacked (see before).
The water flow must be well adjusted so that not to change the VMC into "blizzard".
it must then be brought : 0.3×100×5 = 150 kilocalories per hour.
there thus must be a flow of 150/10 = 15 dm3/Hour, with a yield of 70%, this makes about 40 dm3/Hour, which represents about 10% of the debit of the installation.
We must thus take 300kcal, if the temperature of the water increases by 5ÝC, this gives a flow of 300/5=60 dm3 per hour, that is to say, with a yield of 70%, about 85 dm3 per hour.
To refreshing, we may make a direct interchange between inside water, and water of the outside circuit, sort of "canadian well"
How much is it ?
Builder would instantly answer you, without any survey in support : "It's expensive".
The outside surface is a bit larger than the inside surface because of the foundations, apart from that, placing polystyrene inside or outside is the same work. I would even say that it is faster outside, because there is less cut-out and adjustment.
With outside insulation, the roughcast is included, about 30€ per m2, but with inside insulation, you do not have the plaster, about 15€ per m2, as there is about twice more surface inside, these make up each other at the cost level, but on the other hand, at the aesthetic level, after one or two year (appartitions of the joint lines and undulations of the plasterboards).
By following the norms, the insulation under the flagstone and the insulation of the roof timbers should be of the same price.
If there is a slight overcost for outside insulation, do not forget that you consume three times less heating energy, whatever is your heating system, and you win in comfort in your house.
Though a heating pump compressor is just a fridge compressor five times more powerful, and is not more complex than a oil-fired boiler (which handle explosives and must respect drastic security norms, it turns out that, because the market is not important, a 8 kW heat pump, that is to say 2 electric kW, cost three times the cost of a very good oil-fired boiler of 20 kW, that is to say about 6000€.
In total, compressor, sensors (burried pipes or air radiator), diffuser (pipes in the ground), a thermodynamic heating system cost between 15000 and 20000€, that is to say 30% to 50% more than a not renewable fossil energy heating system. But do not forget that you consume three to four times less billed energy.
Insulation and heating represents about 20% of the cost of a house, if the outside insulation and the heating are worked out 50% more expensive, it is largely estimated, this makes 10% of the cost of a house, that is to say 20000€ for a house of 200000€.
If a traditional house consume 4000 l of oil per yeat, that is to say with current price 2800€, you would save 2500€ per year, hence a return on investment of 8 years, with the current cost of the oils, with the comfort and the security into the bargain. But these hypothesis are willingly very pessimistic.
Durability
See opposite pictures of my house built in 1995, and now in 2006 under at the end of the work.
Some claim that you can not lean a bike against the wall, other claim that children can not play the ball against the wall : obviously, Mr Zidane must not come and train making penaltys against the walls. Of course, you should'nt attack the wall with pickaxe or a hammer. Anyhow, this can be easily repaired with some foam, some glass fabric and some coating. It is easier to repair than a ship hull.
In return, no harmful toxic emations from the polystyrene and the glue in the house, no problem for hanging pieces of furniture in the kitchen or curtains, and no appearances of glue strips.
Other talk about the mice : every precaution are taken for the glass fabric, which the mice do not like, and which wrap the polystyren, ensures a perfect airtightness. Some metallic protection canvas are planned at the top and at the bottom. There is no more risk than in inside-insulated house, maybe even less considering the dispositions taken.
Beware of the ants, like in any house, ant roads can cross through any passage of pipe, even between the bricks. I had some once, along my bathtub, at the thrid floor of a brand new construction, in the middle of a big city, and I had great difficulties to get rid of them because they were resistant to most of the insecticides. It is wise to spread an insecticide powder every year when it is hot at the bottom of the wall around the house and mainly on the southern side. There is no survey which say that ants eat polystyrene. But all the houses have polystyrene. I think that, because the ant feed themselves with insects corpses, they must not appreciate polystyrene.
Have you ever heard about the red micro-fungus which develop themselves under the traditional roughcast and that can be seen under the form of long red trails on the walls of the gable, well they do not survive the synthetic coats used with outside insulation. It is nevertheless recommanded to make every decades a pulverization of water repellant.
The heating screed, under the influence of the heating, expands by 5 to 10 mm, depending on its size. With inside insulation, the load-bearing screed, and particularlty the walls are in the cold and thus do not follow this dilatation, that is why a dilatation joint must be put placed all around the heating screed, so as to prevent this one from not pushing the walls which would crack, because the dilatation pressure is huge.
With outside insulation, this problem does not existe because the walls are almost at the same temperature than the heating screed. The joint is nevertheless placed, but there is no risk if its thickness would have been badly estimated, or in case it would have been badly set up.
I did not talk about energy savings about the water heater.
For the heating of the water with an electric water-heater, a household of four persons spend about 250€ each year.
An electric balloon of 300 litres costs 450€.
A thermodynamic water heat independant of 300 litres cost between 2500 and 3000€, let's take the most favorable case, this makes 2050€ more to save 50% on the hot water bill, that is to say 125€, because there is always a heating resistance to bring the water to 65ÝC because of the legionellosis :
2050 divided by 125 makes 16,4 years that is to say about 17 years to earn back its cost (with the current cost of energy).
Obiously, it is not placed in the bathroom, it is too much noisy
It exists also ballons, still with the additional resistance, anti-legionellosis, connected to the compressor of the heating system, the compressor is more expensive and it must be in permanence running, it is not very advantageous. The ballon costs about 2000€ and the compressor 500€ more, and it seems that it has some break down risks.
There is the solar water heater : 6000 to 7000€, there is also an additional resistance, not for the legionellosis but for the no-sun periods, the yield is estimated, depending on the areas, to 70% for the case that we are interested in (Pays de Loire). Let's take the favorable case, this makes 5550€ more to save 175€:
5550 divided by 175 makes 31,7 years, that is to say about 32 years to earn back the investment (still with the current energy currency), if you did'nt have to change it before!!
Of course, if the state pay you half of it, this is brought back to 16 years.
You can amortize it faster by taking many showers, mainly in summer days, because it gives hot water directly, but water cost increaser as faster as oil or almost !!!
It is an intimate conviction question : be ecological, or be thrifty.