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Vacuum tube collectors – function, benefits and product range

Anyone investing in a new heating system today should design it to include a solar thermal system from the outset. By installing solar collectors, you are demonstrating your commitment to protecting the environment, by sustainably lowering CO₂ emissions. You can also save up to 60  percent of the annual energy consumption for domestic hot water heating. With Viessmann, you have a strong partner at your side. We can look back on 40  years of experience in the development and manufacture of solar thermal systems. You can rely on the highest of quality. With this technology, you can futureproof your system and rely on optimal interaction of all system components.

Structure and function of the Vitosol vacuum tubes

In contrast to Viessmann flat-plate collectors, the absorber in vacuum tube collectors on solar thermal systems is located directly on the tubes themselves. In the former, the tubes through which the solar medium flows are located between two flat absorber layers. Another special feature is the vacuum. In the tube collectors, there is a second tube surrounded by a vacuum. This ensures particularly effective thermal insulation. This helps to ensure that there is hardly any heat loss between the absorber and the internal glass tube. The absorber is inside the vacuum collector. This protects it from dirt and from the influences of weather. This in turn enables permanently high energy utilisation.

Another key element of Vitosol vacuum tube collectors from Viessmann is the heat exchanger. This transfers heat from the absorbers to the connected heating circuit. 

Vacuum tube collector for installation in any location

Vacuum tube collectors and their function: the heat pipe principle  

The core of Viessmann's technology for vacuum tube collectors is the "heat pipe principle". The most important feature of this principle is that the solar medium does not flow directly through the tubes. The heat pipes are dry-connected to the heat exchanger. But what exactly happens in the heat pipe, and how does the patented ThermProtect function work?  

The sun's rays hit the absorber. The solar heat evaporates the medium in the heat  pipe. When this then flows into the cooler regions of the collector, i.e.  farther away from direct solar radiation, the vapour turns to liquid again. This process releases energy –– heat that is transferred to the solar thermal system via the Duotec double pipe heat exchanger (Vitosol  300-TM) or via the copper heat exchanger (Vitosol  200-TM). In liquid state, the medium in the heat pipe flows back into the sunlit area and the process starts over again and continues for as long as the sun continues to shine.

This process is interrupted when the temperature limit of 150  degrees Celsius is exceeded. This happens when the medium no longer condenses or liquefies in the cooler regions of the tube. This principle helps to protect the system from excessive stagnation temperatures and thus prevents overheating. This makes the Vitosol  200-TM and Vitosol  300-TM suitable for buildings that are unoccupied for parts of the year, such as holiday homes. The circuit only restarts when low collector temperatures are reached.

Benefits of vacuum tube collectors

Both the Vitosol 300-TM and Vitosol 200-TM are characterised by the following:

Protection against overheating or excessive stagnation temperatures thanks to ThermProtect via self-regulating heat pipe
High efficiency through absorber with highly selective coating
Particularly effective thermal insulation due to a vacuum, virtually no heat loss between the glass tube and the absorber
Exceptionally long service life thanks to corrosion-resistant materials
Permanently high energy yields thanks to integration of the absorber into the vacuum tube and thus protection against dirt and weather effects
Particularly high operational reliability due to dry connection of the heat pipe to the heat exchanger and due to low liquid content
Straightforward installation thanks to modular design

In addition, Vitosol 300-TM is particularly suitable for areas of limited space, such as in detached houses and apartment buildings with a small roof area. The absorbers have flexibility of +/- 25 degrees in their alignment. This allows the collectors to be used in locations where the sun is less favourable.

The Vitosol 200-TM model is best used for horizontal installation in large systems on flat roofs and apartment buildings. Like the Vitosol 300-TM, it also position-independent, as the absorbers can be rotated by as much as +/- 45 degrees.

Product range – tube collectors

Effective use of the sun's heat – Viessmann tube collectors can convert even low levels of solar radiation into usable heat. Absorbers with highly selective coating ensure high efficiency. At the same time, the vacuum in the tubes provides very effective thermal insulation. This means there are almost no losses between the glass tubes and the absorber, enabling the collector to convert even low levels of insolation into useful heat. The vacuum tube collectors use the available insolation extremely efficiently, particularly in the spring and autumn, and in the winter when outside temperatures are low.

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