About the thermal comfort

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 42°C, 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 14°C, 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 34°C, lightly clothed, in a room whose the sides are at 19 or 20°C, and calm air at 20 or 21°C, we feel good. A naked man, in inactivity, is in balance with an environment at 28°C.

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 30/35°C, 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 20°C heats better than air at 45°C.

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.