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HYDRAULIC COMPONENT SELECTION
A solar heating installation is made with two separate circuits:
ˇ Primary circuit:
this circuit conveys the heat captured by the collectors to the heat exchanger.
ˇ Secondary circuit:
this circuit conveys the water heated by the primary circuit to the tap for consumption
The primary circuit is the circuit which has the greatest differences with respect to a conventional heating or domestic hot water
installation.
Temperature:
the design of solar collectors is optimised to enable the greatest possible amount of energy to be conveyed to the
primary circuit, and they can therefore reach very hot temperatures.
As general criteria for component selection, the following may be taken into account:
a. Flow branch:
this is the branch that conveys the fluid heated at the panels to the heat exchanger. The elements installed in
this branch must be able to withstand a continuous temperature of at least 150ēC: ball valves, air separators, non-return valves,
zone valves, etc.
b. Return branch:
when the heat collected has been transferred inside the heat exchanger, the temperature of the fluid drops,
and the temperatures this branch needs to withstand are less extreme: continuous temperatures of 100ēC (pump, flow regulator,
ball valves, non-return valves, etc.).
Fluid:
The generator (collector) must be located outdoors in order to collect solar radiation. This means precautions must also be
taken to prevent the fluid in the circuit from freezing when the outdoor temperature drops below 0ēC. In regions where this could
happen, a mix of water and anti-freeze (ethylene glycol) is used as a fluid. The components installed in this circuit must therefore
be designed for working with these types of fluids.
Pressure:
the standard pressures these installations work at are similar to those of heating circuits (1.5-2 bar). However, in extreme
cases the temperature may cause the pressure to increase, and so the components should be able to withstand pressures of up to 8 bars.
SOLAR THERMAL CONTROLS
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