incalzitoare solare de aer
Almost all the energy we use both in industrial and domestic processes was generated by heating air with fossil fuels. Mechanical energy and electricity are produced through the transition of much larger quantities of heat from a heat source to a heat sink.
Heat is generated through the process of burning, that is the chemical reaction between the oxygen in the air and the combustible substance, resulting hot combustion gases. The thermal energy of these gases is used in the needed heating process and then the partially cooled gases are evacuated to the atmosphere.
By far the largest source of heat is the process of burning of fossil fuel (coal, oil, natural gas). Much less heat is produced by burning renewable fuels (bagasse, biogas, waste oils, wood, etc) or in the nuclear power plants. While the burning of renewable fuels has a smaller environmental impact, the burning of fossil fuels has important negative effects upon the natural environment.
Heating processes using electricity (both domestic and commercial) are the most inefficient and polluting way of producing heat because electricity itself was produced by burning large quantities of fossil fuels.
Solar energy would be suitable as a source of heat because it is a renewable and free source of energy. Air heated with solar energy is clean and contains the same quantity of oxygen (so it can subsequently be used for burning or as ventilation air).
Even if solar energy itself is free, the solar collectors that transform the solar radiation into a useful form of heat were expensive. Therefore until recently solar energy was not economical when compared with the traditional sources of heat.
Although one could initially think that heating air with solar energy would be simple, the actual practice has shown the opposite. This is mainly because air has small specific heat capacity and density and therefore small thermal conductivity. Therefore it is difficult to transfer efficiently the heat from the solar radiation absorber to the air to be heated. This is why it is somehow easier to build a solar water heater than a solar air heater.
Despite these difficulties that blocked the development of solar air heaters for decades, we succeeded to design and build a new generation of solar air heaters that can deliver hotter air for a given efficiency or that can deliver more air of a given temperature. As they are also less expensive than the previous solar air collectors, the heat they deliver is competitive with the fossil fuels.
Each solar air heater must be designed and precisely sized according to its use.