EcoSolar Energy Conscious Design Limited
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operate as a direct (open loop) system, that is, the water contained within the cylinder that is drawn
off at the taps is also the water that circulates through the solar collector.
Most existing cylinders do not have an internal heat exchanger and therefore if a solar system is being
retrofitted on to an existing cylinder, the solar heating system will generally need to operate as a direct
system, that is unless an external or retrofit heat exchanger is installed.
If a new cylinder is being specified it is cost effective to manufacture it with a heat exchanger and
these cylinders are available from several manufacturers in New Zealand.
Cylinder capacity
Domestic solar heated cylinders are generally sized on the basis of 75litres of water storage per
occupant. This commonly results in the installed cylinder being of a greater capacity than would
otherwise be installed. This results in several issues;
•
Space allocation and structural loading for the cylinder, although many cylinder manufactures
can produce cylinders to suit the space available
•
Existing cylinder storage capacity is often only suitable for two to three people and therefore
retrofit solar systems, where the solar system utilises the existing hot water cylinder, are only suitable
for smaller households. Retrofit systems will be covered in more detail in a future article.
Horizontal versus vertical cylinders
Vertical cylinders are invariably more efficient than horizontal cylinders. However, site limitations
may dictate that a horizontal cylinder be installed.
Most thermosyphon systems are designed as a close coupled package of collector and storage
container with the storage container invariably horizontal for aesthetic reasons as it will be installed
on a roof where a horizontal cylinder blends in better than a vertical cylinder would.
Pumped / Thermosyphon systems
Solar systems can utilise two forms of circulation system;
Pumped systems
These rely upon a small circulating pump to circulate water between the collectors and the hot water
cylinder. These pumps are usually mains operated and are initiated by a controller that only turns the
pump on when the collector is warmer than the bottom of the hot water cylinder. These pumps are
very quiet offering no noise disturbance and only draw between 50 and 100 Watts.
We can also offer 12 volt pumps and controllers which are coupled to a photovoltaic cell of
approximately up to approximately 20 to 30 Watts depending upon system characteristics. These
systems offer increased reliability on sites susceptible to mains power failure. These systems are often
installed in remote sites where thermosyphon systems cannot be suitably installed.
