Vision TZ58/1800-10 Installation, Operation And Maintenance Manual page 8

Vision Solar Systems - 100 L Gravity Fed Type
The Collector
The collector consists of vacuum tubes that contain some of the thermal fluid (water) and are
connected into the tank via a silicon grommet type seal. The vacuum tubes are constructed from
two extremely strong Borosilicate glass tubes of different diameters and placed one inside the
other. At the one end the tubes are joined together and sealed and at the other end the inner tube
is supported. A vacuum is then drawn so that the space between them becomes a vacuum. The
vacuum prevents heat loss from the tubes (much like a thermos flask) and ensures that while the
inner tube can contain hot water the outer tube is cool to the touch.
In order to maintain the vacuum between the two glass layers a 'barium getter' is used (the same
as in television tubes). During manufacture of the vacuum tube the 'getter' is exposed to a high
temperature which causes the bottom of the tube to be coated with a layer of pure barium. The
barium layer actively absorbs any CO, CO², N², O², H²O and H² gasses from the vacuum tube
during storage and operation thus helping to maintain the vacuum. The barium layer also
provides a clear visual indicator of the vacuum status. It will turn white when the vacuum is lost.
The inner tube is coated with a special multi-layer coating forming a selective absorption layer
that assists with the collection of energy from the sun and transfers this energy into heat in the
water. The number of tubes used is chosen to cope with the volume of water in the tank which
needs to be heated on a standard solar day.
The Cistern or Reserve tank
The cistern or reserve tank is a small tank which feeds the main thermal tank. It contains a ball
valve which ensures that that the reserve tank is always filled to a certain level. If the level in the
main tank drops through the cooling (and reducing volume of the water) the ball valve will open
and top up the system. The ball valve is the only moving part in the complete system.
WARNING: Do not extend the pipe connecting the cistern tank to the main tank. This will
increase the pressure of the main tank which is designed to be vented to the atmosphere at a
height of less than 1m from the main tank.
The Backup Heating
In any heating system the time that hot water is not available must be limited. On cloudy days
the solar energy able to be harvested could be limited and, though there is a degree of energy
available, it may not be sufficient to heat the amount of water required. In this system a
thermostatically controlled backup electrical heating element is used to heat the water in the
tank.
NOTE: The element is supplied as an optional extra, and if required, should be included in your
order to your supplier.
Operation
Collecting the energy from the sun
As the sun's rays fall on the collector or collector tubes the irradiance is transformed from the
light energy to heat energy in the water in the tubes. The coating used on the inside assists in
transforming the ultraviolet light from the sun into heat inside the tubes. This aids in collecting
some solar (UV light energy) on cloudy days.
The heated water inside the tube expands and become more buoyant. It moves up the collector
tube and eventually enters the tank, and it is replaced by colder water from the tank which is, in
turn, heated by the sun's energy. This process, known as thermo-siphon, happens continuously
while the solar energy falls on the collector.
Copyright © 2013 - 2016 Enervision. All Rights Reserved.
8
Issue 2.0 Mar 2013