EcoSolar Energy Conscious Design Limited
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be confirmed and the valve replaced if there is any doubt over its operation and correct function.
The function of this valve shall be regularly checked and be appropriately maintained. The tempering
valve must be suitable for the high temperatures experienced in solar systems
•
damage to system components.
Some components installed in conventional hot water
systems are not compatible with the high temperatures experienced in solar hot water systems. Of
particular concern are;
•
mains pressure hot water cylinders which, unless manufactured specifically for use in high
temperature systems, have a recommended temperature limit. In many cases this will be between
70
O
C to 80
O
C. The specification of the installed cylinder should be checked and a temperature
limitation device installed to limit the temperature within the cylinder to within acceptable limits. The
solar controller has this function and should be programmed to suit.
•
Pipework. All hot water pipework upstream of the tempering valve should be completed in
copper. Please be aware that many other alternatives have unacceptable temperature limitations and
are not suitable for the high temperatures associated with solar hot water systems.
Frost Protection
Many areas of New Zealand are prone to collectors freezing and subsequent damage, including areas
which are not renowned for heavy frosts or pipes freezing. By their very nature solar collectors are
good at absorbing heat, they are also good at absorbing coolth. The collector temperature is raised
mainly by thermal radiation from the sun, in the same way its temperature is lowered at night by the
cold night sky. A night sky can, especially on a cold clear night, freeze the water within the solar
collector even if the ambient temperatures are above 0
O
C.
The water in the collector generally freezes within the pipe risers, the smaller copper tubes that run
the length of the collector, see Figure 2 below. Once the water in the collector freezes, it generally
results in the riser splitting and a subsequent leak once the ice has thawed. This split in the pipework
can generally be repaired by removing the absorber from the collector and brazing.
Antifreeze
A reliable system of frost protection, indirect systems circulate water with predetermined
concentrations of a suitable Propylene Glycol antifreeze through the collectors and through a heat
exchanger to transfer heat to the hot water cylinder.
Being a chemical, the handling and use of Propylene Glycol should be strictly in accordance with the
manufacturer’s recommendations. The Propylene Glycol should also contain:
•
a dye to help identify leaks and system failure. If a customer observes dye in the hot water
from the cylinder they should suspect a leak in the solar system and immediately contact their local
EcoSolar solar installer for guidance.
•
a corrosion inhibitor to prevent corrosion in systems containing dissimilar metals.
The PH of the Propylene Glycol mixture should be periodically tested and the mixture replaced as
necessary usually every year. The discharge of Propylene Glycol should be contained and not left to
enter the environment or rainwater tanks. If Propylene Glycol does enter a rainwater tank used for
drinking water, it will have an adverse effect upon the taste of the water and it may be necessary to
