Solar query.

[Steve001]

Last autumn I fitted a twin coil unvented cylinder 300litres, with solar panels, evacutated tube type. All working well, he's not used his oil boiler/immersion since March, that is until the scorching weather comes.

A few weeks ago I phoned him asking if all was ok, great he says but did have one day when the Temp/pressure relief valve (90 deg C) activated. Not good I told him. Temp at the collector was 125 C,

I turned down the solar Pump off temp to 60 C as it was 70C, and checked it with hot water at 60 deg C. It turned off ok.

How, with the pump stopped at 60C does the water in the cylynder still get above seventy deg C? it is a sealed system, with the glycol stuff in it, flow rate is at two litres (per min i think) two arrays of 18 evacuated tubes.

The system does not have a cooling function, the solar and its control panel was an Ebay special (dont go there, not my choice!) I read the MIs front to back, with not a clue how to stop this rise in temp, I'm going to reccomend a blending valve for the DHW, this was considered at the design stage but was deemed not necessary, but the cost of this won't please the client i'm sure, TMVs not the same thing are they? £30 as opposed to £200 - £300, cant be.

Look, just my second post and I'm causing problems already.

Another symptom that happens occasionaly, twice, is; even with a full tank of hot water on a few occasions its been cold by the next morning? I suggested they may have used it but the guy said he was on his own and hadn't used it, I've thought about it lots and can't come up with anything that makes sense or cures it, can anyone shed any light on this for me? Thanks.


Steve

 

[ecowarm]

Its sounds like its circulating on gravity, hence going cold over night and still heating up after pump stopped. Does the pump station have built in check valves?

Sounds like a cheap Chinese make not up to standard.

Solar mixing valves can be purchased for less than £100.

Eco

 

[Steve001]

Cheers for your answer, Eco, much appreciated, Gravity was a thought but I sort of ruled it out, it's been in the back of my mind but sure there is a built in check valve in the pump station - but, assumtion is the mother of all ---- ups I suppose, no paperwork with the pump station just the controller, could do without draining system down to check/put one in, gutted as it's works so well just too well on the three hot days we have each year.

Oh and I don't think it's cheap chinese tat. Middle east cheap tat!

Solar mixing valves and peace of mind for less than a ton, happy days! Will look at that. Especialy with a length of JG pipe inda house.

Thanks again Eco.

 

[Toddyplumb]

If you are measuring the tank temperature for your solar controller at the bottom coil (as you should) the top of the cylinder is going to be a lot hotter there is nothing wrong with this if the TMV is installed. A few manufacturers supply the solar TMV with the cylinder.
Turning down the solar off temp to 60 will actually make the panel temp worse as you will not be circulating through the panels/tubes and therefore will not be removing heat.
Are you on an East/ West with 2 banks of 18 ? 36 tubes on 300 litres sounds a lot

 

[Steve001]

Much appreciated Toddyplumb, Hope I'm gonna get to the bottom of this one soon

Yeah I'm using the lower sensor, and happy that it'll be hotter at the top, but from what the client says, even with the pump off it gets hotter, I'm going to wait for a scorcher and have a look at it. Might even put a coulple of data loggers on it and see what that'll come up with.

Will fit the TMV then will be happier to crank it up some, the highest temp seen so far on top of the arrays has been 121 deg C, two banks of 18 tubes, facing the SW direction (if i remember correctly) but with some shading at parts of the day, I think one bank wouldn't have been enough, I'm no expert as this was my first installation of solar panels but remember doing the survey and being happy that it would work and to be honest wasn't overly concerned with 300litres to heat up with Ebay specials.

I know temps are phenomenly high with some flat plat collectors but what sort of temps can you expect with evacuted tubes? Always possible to take off a couple of tubes I suppose.

 

[Toddyplumb]

Yeah your best bet is as you say go and look at it on a scorcher, keep us informed as to what you find.
As a comparison (sort of) we have just finished 30 tubes on 500litres, works fine (Baxi tubes) Due South

 

[ecowarm]

I'm starting one tomorrow, 12 x 100mm dia. tubes on 210l thermal store

 

[Steve001]

100mm dia. tubes

That's a fat one!

 

[Toddyplumb]

Which tubes you using Eco ?
I was gonna try Kingspan Heat pipe next . Baxi (our usual) dont seem to be able to deliver Heat pipe and I like the idea

 

[ecowarm]

The Ecotube solar hot water system

I think there the best

 

[lenny]

Hi,
Seems like the system is thermo-syphoning. A motorised valve will prevent this if you wire it to the pump so that when the the tank gets to the maximum temperature the pump stops the valve closes at the same time this will stop the flow of the glycol into the cylinder coil. A heat dump radiator in a cool place is also good practise. You could also try to improve on the flow rate, 2 litres per min is not good for long hot days.

thanks

 

[Steve001]

Right, been back on a scorcher, checked the wiring of the temp probes which seem all good and doing the job as intended, no sign of cooling in the morning again or further action past pump off temperatures, the pump off temperature is controlled by the max tank temperature which uses the top sensor, (that was me making assumptions, sorry) but it all ties in with the display in the right order. The bottom tank sensor controls the differential temperature pump on/off.

There is another sensor at the top, which is wired to the boiler etc, the solar controls were kept separate due to three boiler zones and five UFH zones and the spark pulling his hair out at that LOL.

Not sure entirely what has happened in the past but maybe somebody,possibly me, was playing with the controller panel too much and messed with the max temps. Now waiting for client to get back off holiday before I fit thermal blending valve and crank up max tank temp to 80 degs.

If the thermo syphoning happens again after that I'll stick a solar motorized valve on along with the pump.

lenny, eco, and Toddy, thank you for your valuable help, I'm gonna go away, beat myself up and learn more on this subject. Maybe find a better solar package to reccomend to my next client.

Thanks again.

 

[Gray0689]

Hi all I have found kingspan thermomax to be the best never had a problem with them
Used to use viessmann but they gave nothing but trouble on hot days blew off and always trouble with air in stainless coragated tubes