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Combi-boiler systems

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  • Combi-boiler systems

    I would like to hear from anyone who has a solar thermal system for a combi-boiler. I installed my own system last year (July 2013) and it has operated successfully since then. I used info. from the Internet and from the collector suppliers, etc. I fitted a new 210 liter insulated copper cylinder and insulated copper header tank, so it has been an expensive job, but I wanted good quality materials. The cylinder is about one metre higher than the evacuated tube collector which is on a flat roof facing south, and is about 4 square metres area. This is because there is a large building next door which blocks the sun until mid-day! The primary (solar) circuit heats the water in the cylinder through a coil made for that purpose. The cold feed to the combi goes through a second coil at the top of the cylinder, where it picks up heat, then feeds the combi, but first passes through a set of three thermostatic valves (designed for combis) which limit the temperature to 24 degrees C. If the water is hotter that 24 degrees, then the valves mix in cold water, since the combi cannot accept a higher feed temperature than this. If the water is hotter than 45 degrees, then it is diverted to the taps and bypasses the boiler altogether. This, rather complicated, system does work quite well, but the cylinder temperature needs to be above 65 degrees before the boiler stops firing up. An added benefit is that the boiler feed is preheated in winter which should save some fuel. The disadvantages are that heat is lost in the conversion process, and also, the water has to be drawn off slowly or else it passes through the coil too fast and does not gain enough heat. My partner wanted to keep the combi-boiler system, so that's why I have done it like this. As I said, I would like to hear about any other systems like this, or any tips to improve it. I would also be happy to answer any questions about the system, if I can.
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