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4.0 STAGNATION
Solar collectors should be sized based on the hot water usage by the end user and the amount of solar energy
available during the months of April to September. During this time the days are longer and solar radiation is at
its highest.
Trying to compensate for lower solar periods during the months of September to March by adding extra solar
panels, will lead to the hot water storage cylinders reaching the set maximum temperature earlier in the day
during the summer months. As a result the solar energy reaching the panels, continues to heat the fluid in the
panel, causing it to evaporate within the panel. This is referred to as stagnation. The Firebird solar fluid is
designed to cope with stagnation temperatures of up to 200˚C. However, repeated and frequent stagnation will
cause the glycol to disintegrate, thereby losing its frost protection and its recommended ph value, causing a
scale build up or corrosion in the pipes. This would reduce the overall efficiency of the solar collector and result
in potential damage to the collector and pipe work, especially in freezing conditions.
Stagnation can occur in a perfectly sized system where there has been no draw off of hot water from the
cylinder for a period of time, for instance the dwelling is unoccupied, or the householders are on vacation.
The Firebird solar system is supplied with safety features to cope with stagnation. These include a 6 bar
pressure release valve and a pressure vessel. These should be installed as per the instructions, on the return
line off the pump station. Also supplied is a solar fluid which is an anti-freeze and inhibitor, withstanding
temperatures of up to 200˚C and temperatures as low as -25˚C.
Additional options available to an installer with a Firebird solar system:
•
A holiday function in the controller. This function must be activated or “turned on” when the
householder is going on holidays. In the evening when the sun has gone, the controller will
register that the temperature of the collector is cooler than that of the tank and switch on the
circulating pump. The circulating pump will circulate the water through the coil in the cylinder
and back up to the solar collector, until such time as the temperature in the cylinder cools
down to the default cylinder maximum temperature, which is 60˚C, or specific temperature
inputted to controller.
WARNING
this function should not be activated unless a thermostatic mixing valve is installed
on the hot water supply to avoid the risk of scalding.
•
A heat dump radiator with its own circulating pump connected to the upper coil of the cylinder
can be used to dissipate excess heat from the cylinder. This circulating pump is connected to
the Second Relay (R2) of the solar controller (controller manual for AHO and AHF settings for
this function).
A temperature reducing vessel or intermediate vessel is available. Please refer to the solar system design
section of this guide for addition information on temperature reducing vessels.
STAGNATION