Tony
The expansion of the HTF is taken up by the "expansion vessel" in normal circumstances, the PRV does is not normally operate only in extreme stagnation i.e power or pump failure at peak radiation. The vaporisation of the HTF only takes place in the collectors and a small portion of the pipe work so it is only that volume that expands. A correctly sized expansion vessel can take the increased volume without increasing system pressure. The higher the system running pressure the higher the boiling point of the HTF so the less chance of vaporisation.
Hope this helps.
Eco
Eco,
I should apolagise to you as my previous post was really aimed at Agile who I didn't expect to reply as he never does when shown to be wrong (on any of the other forums we post on)
I have a few years real world experience of supplying and installing solar thermal systems so my views are at odds with the likes of Bpec and their qualified engineers such as Agile
😉
The very first mistake made in the solder can/cant be used arguement is to lump all systems types and sizes together. So just to clarify my remarks below will refer to the average domestic system installed in the UK, not commercial or swimming pool systems that will need carefull installation design consideration.
I agree that all solar collectors should be connected to the system pipework with some form of
Mechanical Fitting for a number of reasons. However, that does not mean you cannot use lead free solder on other joints in the system if using copper pipework.
If you were installling an heatpipe system I doubt there is a single collector out there that would lead to
System stagnation as opposed to
Collector stagnation temperatures that could melt lead free solder, if there is, then I've not come across it yet and doubt I ever will.
If you were installing a self limiting heatpipe system like the Thermomax HP200 or the Viessmann Vitosol 300-T or indeed the Narva heatpipe. All limited to around the 160c mark, why not use solder?
Direct flow systems are a different beast. the Thermomax DF100, AMK Solac or Ritter along with some of the better flatplate collector systems can and do stagnate at very high temperatures. If they vent they can produce large amounts of steam (they have to vent to produce large volumes) that can extend down as far as the cylinder coil where it will condense out. The steam zone when extending this far is likely to have passed into some of the system components none of which will be rated above 160c for brief periods. Many of the boiler manufactures re-baged kits come with Spirovent air scoops rated at 180c. On some systems they can allow a tremendous amounts of steam to escape, once that starts it will not stop until the system is vertually dry or the systems cools.
We repaired a Smart Energy AMK system last week that had around 1 litre left form a 12 litre fill. Having vented, it filled their airing cupboard and hallway with steam which scared the living daylights out of them. The only component changed was teh PRV fitted to teh collectors. Most of these types of systems are NOW installed using pre-insulated stainless flexi pipe the insulation is rated at 170c for brief periods. The insulation had not melted anywhere in that system.
I have said this before and it always causes a row. Solar thermal isn't new there has been a very small industry since the 70's when most systems were garage built flatplates or used the then NEW fangled Phillip's tubes and later the Thermomax tube systems. These were often installed using solder so whats changed? perhaps the noise
😉
Let the games begin(again)
😀
Tony Stone
