HarryUp Posted April 4, 2022 Share Posted April 4, 2022 Setup: a simple ten-year-old system solar thermal system consisting of a set of roof-mounted evacuated tubes serving a tank on the ground floor with a single pump station on the return line. Last year the system, which had been rather neglected in terms of maintenance, showed signs of erratic performance. I had someone in to service it, they recharged the circulating fluid and also turned the pump down from its highest setting to the medium one. Everything went back to working fine – regular triggering of circulation pump and transfer of heat. Fast forward a few months and I worked out from looking at the logged data that the system had started to lose heat to the collector at night – it was fine before the service but straight after the service this siphoning behaviour has started. Generally, not long after the panels lose the sun and the collector temp has dropped well below the tank temp, the circulation starts – the collector temp rises back up to a few degree below the tank temp and then they gradually both decline in parallel until the next day. The HW tank has recently been replaced to accomodate a heat pump and so the ST has been drained, cleaned well this time, and recharged. The installer wasn't able to offer any specific answers to the siphoning issue other than perhaps the clean would have dislodged some muck that was having an effect. Unfortunately the system does still seem to be siphoning heat. I have failed so far to find a local technician who can help or any relevant information on the internet that is aiding me in understanding how this problem might arise, what failure or lack might be the cause. Perhaps someone here can offer some knowledge to help! If drainback systems are designed to avoid thermal siphoning, what is it in a pumped, pressurised system that prevents unwanted circulation at all? Is it the pump mechanism itself that prevents flow when not operating? A check valve prevents flow in the reverse direction but that is not what is happening here. What it is that has changed in my system that resulted in night time circulation? I have tried adjusting the ball valve above the flow meter that restricts the flow rate to see if that would help, but it doesn't seem to have done so. Any suggestions that I can pass on to whoever I can find to work on the system will be gratefully received. Link to comment Share on other sites More sharing options...
SteamyTea Posted April 4, 2022 Share Posted April 4, 2022 Has the one way check valve that has failed? If there is one. Draw a sketch of the system, it usually helps. Link to comment Share on other sites More sharing options...
Dillsue Posted April 4, 2022 Share Posted April 4, 2022 Did they rework the pipework to the solar coil when the cylinder was replaced? There should be a non return valve in the pipework from the upper tapping on the solar coil to stop warm water rising from the coil to the collector. Maybe the NRV is faulty, fitted the wrong way round or missing altogether? Our controller has a store(cylinder) cooling function which circulates fluid through the coil to the collector in an attempt to cool the cylinder if the temp is too high. Its a long shot, but if youve got that feature could someone have tweaked the settings so the controller is cooling the cylinder? Link to comment Share on other sites More sharing options...
HarryUp Posted April 5, 2022 Author Share Posted April 5, 2022 I'd wondered initially whether the valve was at fault, but the circulation is in the same direction as it should be, i.e. it is the return pipe to the collector that is carrying the heat back up in the evening. I can turn the valve off and stop the flow entirely but then I have to remember to turn it back on first thing, and I've already forgotten once. As a check valve I think it is only going to stop reverse flow? I can't find much info that explains ST systems thoroughly enough to work it out. There are no additional functions enabled on the controller. Nothing so simple... Link to comment Share on other sites More sharing options...
Miek Posted April 5, 2022 Share Posted April 5, 2022 You might have ' one pipe circulation ' going on, but more likely the NRV is not working correctly The best solution to reverse circulation from the tank coil is to have the pipe from the top of the coil turn downwards to the bottom of the tank before heading back up to the roof. Effectively a Ubend so that the heat can't rise. This is better than a NVR as it can't fail and makes no noise ( sometimes an issue with the low flow rates on ST) Link to comment Share on other sites More sharing options...
Dillsue Posted April 6, 2022 Share Posted April 6, 2022 (edited) On 05/04/2022 at 16:11, HarryUp said: I can't find much info that explains ST systems thoroughly enough to work it out. Google "solamax manual" and you find a comprehensive manual on ST systems including schematic system drawings. No "r" in solamax! Edited April 6, 2022 by Dillsue Link to comment Share on other sites More sharing options...
scottishjohn Posted May 18, 2022 Share Posted May 18, 2022 I had this problem with my 40 tube array my solution was to put a motorised valve in system which opened when you neede flow -eg circulation pump turmed on heat is always going to rise so will start a themo syhpon system on its own and I found the one way valve not good enough to stop it totally it always bled a little - so fitted motorised valve problem cured Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now