EcoSolar Energy Conscious Design Limited
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Thermosyphon systems
Thermosyphon systems do not have pumps and operate on the principle of warm water rising from
the solar collector into the hot water cylinder. Thermosyphon solar heating systems can be either
direct or indirect systems depending upon site requirements. There are several forms of
thermosyphon system as follows;
Close coupled
The cylinder is mounted directly above the collectors on the roof. This system although generally
cheaper to install does have aesthetic and potential structural disadvantages. The cylinder is also
mounted horizontally, which increases mixing within the cylinder, which reduces the efficiency of the
system. See Figure below.
Remote Mounted Cylinder
These systems have the collectors on the roof and the cylinder located above and some distance
from the collectors. The greater the separation distances between the collectors and the cylinder, the
less efficient the system. Pipes should be installed inclined up to the cylinder at a grade greater than 1
in 7 and have minimal restriction to water flow by installing swept bends and no sharp changes in
direction such as elbows. As the separation distance increases so the resistance to flow also increases
and it is advantageous to increase the pipe size from ¾” as per many close coupled systems to 1” and
greater to increase the system performance.
Figure 13. Close coupled thermosyphon system
