EspañolAny surface except absolutely black body absorbs and reflects infrared (thermal) radiation partially. The closer to an absolutely black body the more radiation is absorbed and less is reflected. The heat energy itself does not disappear and will be reflected by other objects. This helps to achieve an even heat distribution all over the room.
Infrared radiation is emitted by any warm body. Wavelength of the radiation depends on the temperature of the body and density of the heat flow depends on the power of the heat source and its design (ability to create directional heat flow).
The choice of heater location influences its efficiency. Let’s take three options:
# Ceiling-mounted heater
# Wall-mounted heater
# Floor-mounted heater
Ceiling-mounted infrared heater can be compared to the sun at the equator of the planet where it is directly above the head; wall-mounted infrared heater can be compared to the same sun but closer to the poles (angle of the heat flow to the surface). Infrared heat-insulated floor can be compared to the core of the Earth. So we can see that at the equator it is hot and it is getting colder when we move to the poles. Internal heat of the Earth without sunlight cannot create comfortable temperature on the surface. Why is it so? If the sun is high, the heat flow is practically perpendicular and it is almost not scattered by the atmosphere, it has the greatest intensity and absorption of the earth surface from which the air has been already heated. When it is shifted to the poles the sun goes lower above the horizon, the angle of the directed heat stream decreases, the scattering by the atmosphere increases, and accordingly the intensity of the heat flow decreases. Everywhere we have the same sun but different results. The hot core of the Earth seems to be much closer than the sun but is significantly absorbed by the mantle and the crust with high heat capacity. A small part of it reaches the surface of the earth.
How does thermal (infrared) radiation affect living beings? It is not a secret that at the same temperature of the air the state of thermal comfort can be different. At temperature of +10C come from the shadow to the sunlight and very you will become much more comfortable after some time. You are getting solar energy directly.
As it has already been mentioned above, any warm body is a source of the infrared radiation.
Heat can be transmitted by three ways:
# direct heat exchange;
# convection;
# radiant heat exchange.
At direct heat exchange heat is transferred from a warmer object to a colder one. Effectiveness of the heat exchange depends on the physical proprieties of the objects, heat conductivity and heat capacity.
Convection implies heat transfer with warm and cold flows of the object.
Radiation heat exchange occurs as a result of the transformation process of the object internal energy into the thermal radiation energy, energy transfer and its absorption by the object. When the body absorbs radiation, its surface temperature rises.
All heating systems use all 3 methods of heat transfer but up to some extent. Traditional heating systems (central heating, convectors, fan heaters, boilers) use a convective heating method – they heat the air in the room directly.
It means that first as a result of direct heat exchange the air is warmed up near the heating element (convector, central heating battery), and then as a result of convection (natural or forced), warm air moves in the room.
It is clear that efficiency of convective heating systems is used somehow incorrectly. To get temperature in the human thermal comfort area (at the bottom of the room) equal to +23C it is necessary to warm up the air up to 35C and above (depending on the height of the room).
In case of forced convection some energy has to be spent on the built-in fans. Radiant heat exchange in such systems is minimal since the heat flow is not directed but it is scattered in all directions that reduces its density deliberately. During room ventilation the warm air will simply go away and you need to re-heat it.
Heat-insulated floor spends most of the energy in vein as significant amount of the heat is absorbed by the colder lower layers. Radiant heat exchange is also minimal because the heat flow is not directed but it is scattered in all directions.
Ceiling-mounted infrared heaters are designed mainly for radiant heat exchange. Due to design features of infrared heaters directed downward heat flow with a high density is created. It is partially absorbed, partially reflected by the surfaces. Reflected heat energy is consequently absorbed by other objects. Absorbed energy is accumulated in the objects due to heat capacity and colder air begins to warm up from them. In fact all the objects in the room become one big heater.
The main part of the objects is located in human thermal comfort area which is the lower part of the room, i.e. person receives heat both as a result of direct heat exchange (sits on a warm chair, lies in a warm bed, puts on warm clothes) and as a result of the contact with warm air that is warmed up evenly from below heated objects. In case of infrared heating the height of the room is not as important as convection as a result of the uniform heating of the air from all directions is decreased deliberately. In addition a person directly receives and absorbs thermal radiation which increases his or her thermal comfort. This allows you to maintain a lower air temperature in the room (at 2-3 degrees) than with traditional heating systems with the same thermal comfort for a person. Heated objects have a significantly higher ability to accumulate heat than air.
This allows infrared heaters to work cyclic. When infrared heaters are turned off heated surfaces continue to give off heat to the air. With heated walls the dew point moves closer to the outer wall which reduces the heat loss of the walls significantly. Thus the efficiency of infrared heating is much higher than of traditional heating systems as their thermal energy is used to the maximum.