Copyright © 2014
Ikhwezi Solar (Pty) Ltd, Novatherm CC, Solar Assist (Pty) Ltd
4
5.
Frost, scaling and hail resistance, stagnation
5.1
Hail resistance
NovaSun collectors are hail resistant with 4mm toughened glass and have
passed SABS hail tests.
5.2
Freeze protection
Solar hot water systems can be classified as (i) direct: freeze resistant, (ii)
direct: non freeze resistant or (iii) indirect.
5.3
Direct systems – Freeze resistant
In direct systems the water to be used in the household circulates through
the collector, transferring solar energy into the solar geyser.
The Novasun panel contains a fully insulated heat exchanger that acts as a
freeze resistant mechanism, as declared by the manufacturer. The pipework
connecting to the solar geyser must be insulated with Insulflex insulation
material.
When installed with a PEX-lined Solartherm Cylinder it can be used in all SA
climate locations (i.e in areas where frost occurs and areas, where ambient
temperature may fall below 5°C). Contact Solar Assist to discuss water
quality matters.
5.3.1Direct systems: non-Freeze Resistant
In direct systems the water to be used in the household circulates through
the collector, transferring solar energy into the solar geyser.
Direct systems are used in
frost-free locations
, where ambient
temperature never falls below 5°C and where water quality is good (i.e. less
than 600ppm total dissolved solids/minerals).
5.3.2Indirect systems
In indirect systems the potable water used in the household does not
circulate through the collectors, but remains in the geyser and is heated
indirectly by a heat exchanger.
There are two basic types of heat exchanger, namely a jacketed system
where an inner cylinder is surrounded by a secondary outer layer and an
internal heat exchanger where the solar geyser contains an internal copper
pipe structure.
In both cases the solar loop (i.e. the pipe work to and from the collectors)
contains a heat transfer medium (i.e. propylene glycol/water solution) which
is physically separated from the potable water.
Propylene glycol has a lower freezing point and prevents the liquid in the
collectors from freezing and damaging the collector through expansion that
occurs when ice forms. Only food grade glycol should be used.
Indirect systems are used in locations where frost occurs and the
ambient temperature drops below 5°C
and/or where water quality is
poor (i.e. more than 600ppm total dissolved solids/minerals).
These collectors are resistant to freezing only when installed with an indirect
geyser and the solar loop filled with a solution of propylene glycol and
water. Water alone must not be used as a transfer fluid. The glycol / water
solution should be mixed in a glycol to water ratio of 1:3 (i.e. 33% glycol).
5.4
Scale resistance
Indirect systems containing a glycol solution also prevents scale build up
inside the collector in areas of poor water quality. It is important to note that
the geyser itself may still be affected by water quality as would be the case
with any conventional enamel-lined geyser unless a Solartherm PEX-lined
geyser is used.
If a direct system is used in areas of poor water quality the pipe work inside
the collector and solar loop may be subject to a build-up of scale. This may
be avoided through the use of a water softening system. This is good
practice regardless of type of system, as the water will affect other
household appliances in any event.
In the event collectors experience scale build-up the performance
of the system will decrease. Should this occur the system can be
flushed with a mildly acidic solution (e.g. vinegar solution) and in
the case of the Novasun collector, the Header Pipe should be
flushed. The pipe work should then be flushed with fresh water
after removal of scale prior to re-commissioning.
Ensure you are familiar with the relevant tank manufacturer’s warranty
terms and conditions in respect of water quality, particularly as it relates to
anode replacement in case of enamel-lined tanks.
6.
System placement and orientation
A number of basic fundamentals need to be observed when installing any
solar hot water system.
6.1
Collector orientation
Optimum system performance is achieved when the collectors face directly
North (i.e. true North) when installing in the Southern Hemisphere. The
closer the collector is to directly facing the equator the greater the amount
of solar radiation the collector will be exposed to and the greater the
potential for heating.
Angles up to 45° either side of North will not have a major effect on the
system performance given the state of the art technology used in the
construction of the NovaSun systems. Therefore, roofs that are orientated
away from North are also acceptable for installation.
Outside of the 45° range one could consider utilising more collector surface
area or using a mounting frame to adjust the orientation back to North.
6.2
Shading
With a system orientated to face North, the time period when the collector is
exposed to the most direct solar radiation is between 10h00 and 16h00.
Solar collectors with an East bias will achieve a greater gain in morning
hours and those with a West bias will do so in the afternoon.
Care should be taken to ensure that the collectors are not subjected to
excessive shading from trees or adjacent buildings, particularly between
09h00 and 16h00.
Also bear in mind that tree growth could lead to future shading issues.
If the installation takes place in summer, it is also important to take into
account the lower solar angles in winter, which result in longer shadows.
