How much solar fluid do I need?
The capacity of the solar circuit typically comprises the capacity of the collector manifolds, pipe runs and heat exchangers. Collector capacities are shown on the collector prices page (here), and typical pipe run volumes can be calculated by knowing that 15mm copper pipe contains about 0.14 litres per metre and 22mm copper pipe around 0.31 litres per metre. Heat exchanger capacities are usually stated by cylinder manufacturers. Average domestic installations with 15mm pipework are usually less than 10 litres.
General information about solar antifreeze.
Rule 1 is don't use vehicle antifreeze which is ethylene glycol and can cause kidney failure if ingested. In the event of a heat exchanger in a hot water cylinder failing, the solar fluid could find its way into domestic hot water.
It is generally thought that propylene glycol solutions will have a higher boiling point than water, because if neat it boils at around 180°C. However, when mixed as 40:60 PG/water, boiling occurs at 103°C. Pressure has a much greater effect on boiling point. Eco-nomical 40/60 solar fluid solution boils at 124°C at 1bar (gauge*) and 143°C at 2.5 bar.
Eco-nomical solar fluid
Eco-nomical solar fluid is ready to use, comprising 40% propylene glycol with high temperature corrosion inhibitor additives tailored to metals found in solar installations (primarily copper, brass and stainless steel), and approximately 60% demineralised water. It is non toxic and readily bio degradable if spilt. Freeze protection is provided to -20°C.
Temperatures above 170°C will cause the PG based solar fluids to age prematurely. and above 200°C will degrade the fluid and require its replacement. In normal operation it is generally recommended to replace the fluid at five yearly intervals.
1 bar approximately equals
14.5 psi (pounds per square inch)
0.1 MPa, (megaPascals)
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