Air collector
Air collectors are a type of solar collector in which air is used as a heat carrier instead of water . The structure is similar: As a rule, the heat collectors (so-called absorbers) are placed in a tub or box, which pass on the heat energy radiated by the sun to the air flowing below. The top is a glass cover that protects the collector from environmental influences (rain, hail, etc.). Modern air collectors achieve efficiencies of 50 to 70% in terms of heat transfer. The collector can be installed wherever it faces the sun during the day. It can be installed on the roof or on the facade. Since air itself can store almost no energy (over a long period of time), there are two methods of making the heat usable:
Type of use
- The air heated in the collector can be blown directly into the building with the help of a fan . This is a simple and uncomplicated variant for heating and ventilating with the sun for a wide variety of buildings (holiday homes, apartment buildings, hall buildings ...). A combination of air collectors with air heating systems is also possible. In areas with a moderate climate, air heating is very common in hall buildings, which is why the integration of air collectors is very interesting here.
- Alternatively, the strongly heated air initially transfers heat that is not required to a storage medium via a heat exchanger . Because of the high storage capacity , an insulated water storage tank is initially an option . Then the cooled air is blown into the rooms as in (a) .
Instead of a water storage tank, an insulated stone storage tank can also be used. Here too, after some of the heat has been released, the air is then blown into the building. Another possibility are so-called hypo- and murocaustes, which can offer a storage volume of one to three days if optimally designed.
Compared to water collectors, air collectors are currently not very common. However, air collectors are also becoming increasingly interesting in Germany, as they represent a simple and uncomplicated heating option without the consumption of fossil fuels. In addition, the collectors bring fresh, filtered air into the building and thus enable ventilation with energy gain.
Air collectors have been used successfully in agriculture and industry for several years to dry hay, grain, herbs or other biomass. With modern control devices it is also possible to use air collectors for cellar drying. The heating and ventilation effect of the system is also used here. The German Alpine Association (DAV), for example, uses solar air collectors for heating and ventilating mountain huts, but also for drying and composting residues from the hut operations. In the research project "Residue treatment in the high mountains", which was funded by the German Federal Environment Foundation (DBU), solar air collectors as solar sludge dryers and solar composters have been examined in detail.
Advantages disadvantages
The disadvantage is that thicker air ducts, rather than thin water pipes, have to be installed in the houses. In new buildings, this can already be taken into account during the construction phase, but old buildings require individual solutions. In addition, the heat is only available in direct sunlight and can only be stored with great effort.
The advantage is that air cannot boil and damage the collectors. In addition, air collectors and pipes cannot freeze. Leakage in the ventilation pipe system is less damaging than water damage. In winter, when less heat is captured by the sun , the air - as soon as it has room temperature - can be led directly into the rooms. Since air has a much lower specific heat capacity than water, air collectors are more responsive than water collectors.
Extended use through energy cascade
Another possibility is at very high temperatures (excess heat in summer, clear winter days with a lot of solar radiation). A second heat transfer medium (water, alcohol or other low-boiling liquids) can initially provide mechanical energy for generating electricity using the heated air from a steam engine or turbine. This so-called energy cascade first generates electricity and then supplies consumers with lower heat requirements. Furthermore, the strongly heated air can also be used to generate cold by operating an absorption chiller in the form of a refrigerator or air conditioning system . In the next few decades, weather-related increases in the need for cooling during the summer are expected. If the collector area is oversized and stored in a large stone storage tank, energy can still be obtained from the collector system at night.
Self-sufficient air collectors
There are models for arbors, huts, holiday homes and individual living rooms that consist of a normal air collector, but also have an integrated photovoltaic module. The electricity generated in the photovoltaic module drives a fan, which is also located in the collector. Warmed air is blown into the living rooms and temperature the interior. The regulation takes place via a simple thermostat control. Buildings that are only used from time to time can be used in buildings. The interior is ventilated (and thus kept dry) and tempered by the self-sufficient air collector system. Musty odor is prevented.
Solar balloon
Solar balloons are a very special way of using air collectors. A solar balloon is a hot air balloon with a black cover, usually made of plastic film, in which the air inside is heated by solar heat. Because the heated air inside the balloon is less dense than the colder ambient air, there is buoyancy and the balloon floats. Solar balloons are best known as children's toys.
Promotion of air collectors
In Germany, solar air collectors are subsidized by the Federal Office of Economics and Export Control (BAFA). According to the BAFA market incentive program or the KfW Renewable Energies program, the installation of a solar thermal system is funded; this can also be used for air collectors. Eligible or tested air collectors are listed on the BAFA website. This funding can be granted to private individuals, municipalities, local authorities, municipal special-purpose associations and non-profit organizations (e.g. registered associations), small or medium-sized enterprises (SMEs), SMEs in which a majority of municipalities are involved, freelancers, agriculture and forestry and Use horticultural companies for installation on existing buildings via the Bafa.
Since January 1, 2020, the funding rate of the basic funding has been 30% of the total investment costs in connection with the purchase, installation and commissioning of the system. Self-assembly is possible.
- requirement
- the intended collector must be listed with BAFA. This means that self-made collectors are ruled out.
- Minimum age
- Only systems in buildings in which another heating or cooling system had been installed for at least 2 years at the time the new system was put into operation (existing buildings) are funded.
- Time of application
- Private individuals, municipalities, local authorities, municipal special-purpose associations and non-profit organizations (associations, church institutions ...), companies, businesses and freelancers submit the application before the start of the project using the online form provided by BAFA.
literature
- Innovation warm air collector system , cellar drying (PDF; 206 kB) published by SONNENENERGIE: Journal for Renewable Energies and Energy Efficiency, the official specialist body of the German Society for Solar Energy e. V. (DGS)
- Topic Info II / 02 (PDF; 950 kB) published by Bine Information Service on solar air systems
- Book solar air heating systems, Ökobuch Verlag, ISBN 978-3-936896-04-6
Web links
- Project description - self-built air collector system for renovation of old buildings ... heating support for little money, air collector and heat pump
- Extensive, English-language website for do-it-yourselfers
- Architect Bruno Maurer: Air collector house
- DGS guidelines for solar thermal systems with chapter 9 "Solar air systems"
Individual evidence
- ↑ BAFA: Funding of solar collector systems
- ↑ KfW Renewable Energies Program
- ↑ BAFA funding application