Solar Hot Water - mystery nocturnal activity

[Johntheo5]

No, don't know if the kick parameters can be set in the Vaillant controller. a 10C dT.on should be OK especially with evacuated tubes, if that doesn't cure the problem maybe consider changing dT.off to 6C. or maybe just extending the swimming pool circ pump to 1900hrs instead. Sensor trends would really tell a lot but all mine only display the preceding hour with 1min updates.


Cylinder priority
Two solar-charged cylinders can be connected to the
heating installation. You can use the PRIO cylinder priority
function to define which cylinder should be
charged as the highest priority.
This is normally the drinking water cylinder. The cylinders
can only be clearly identified via the cylinder sensors
(cylinder 1 = Sp 2; cylinder 2 = SP 3).
You can only change this setting at the installer level.
The cylinder that has been assigned the highest priority
will always be charged if the collector temperature is
greater than the sum of the actual temperature in the
cylinder and the activation difference specified. The
heating of the cylinder will stop once the maximum temperature
for the cylinder is reached, or if the collector
temperature is less than the actual cylinder temperature
plus the set deactivation difference.
The second cylinder can only be heated when the first
cylinder is not being heated. The charging of the second
cylinder is interrupted for at least 5 minutes every
15 minutes to check whether the cylinder can be
charged with the highest priority. The same activation
and deactivation conditions apply here as well.

 

[msd123]

Yes, its a pity I can't get a data dump off the controller. Best I can do is go in there and note the values every now and then.
The KOL1 sensor is (presumably) actually in the tube on the roof, but in the cupboard next to the pump/tank etc I have 2 analogue temperature gauges - one for each of the flow and return. At 1705 today (very sunny all day) the relevant readings are

SP2 43
SP3 21
KOL1 46
FLOW 40
RTN 32.

Two things stand out to me :
1) quite a high gap between the reported (KOL1) temperature (46) and the actual temperature (FLOW) near the point of use (40). You'd expect some loss in the pipe of course.
2) the pool reading (SP3) is lower at 5pm (21) than it was at 11pm (24) ! This is probably because the pool pump is active at 5pm so the applied heat is quickly removed into the pool rather than just hanging around as it does when the pool pump is off.

I think that kick function is probably off by default anyway, so I wont worry about it.

 

[Johntheo5]

My system ceased harvesting at 1730 hrs, the collector temperature was 40C and cylinder temperature 37C, ambient 14.5C, the collector is now 18C and cylinder temp 35C, ambient 12C so even if some one ran off the whole cylinder of hot water the cylinder temperature would only fall to the mains temp of ~ 15C just now, no chance of solar circ pump starting since my dT.on is 7C (dt.off is 3C). I can't see reverse convection being a factor in your high collector temp as the collector will have switched to the swimming pool Hx?.

 

[msd123]

As of 2200 :
Sp2 45
Sp3 24
KOL1 28
Ambient 14.4 (says Google)
No pump activity.

If reverse convection were going on I'd surely see a big drop in Sp1, and i don't.

 

[Johntheo5]

Don't think reverse convection is the problem, but surprising that Kol1 is 28C (same as later, last night). mine is currently 11C with ambient the same. You have a dT of 4C so if the solar circ pump starts again then the dT must reach 7C, if this, in fact, is the trigger.

If there is reverse convection taking place then its SP2 that will reduce as its located just at the top of the solar coil, you should see very little reduction in SP1 as its at the cylinder top.

0630 hrs: collector & ambient 7C. 0820 hrs. collector 24C, ambient 11C.

 

[Johntheo5]

Two responders on our website, boards.ie, indicate that 24C can be normal for evacuated tubes when off.

Just thinking that the swimming pool circ pump is/should be started/stopped from the controller, ie, 3 way valve changed to swimming pool+solar circ pump running or some logic like that, it would seem unlikely that it should run continuously during the timed period and probably shouldn't be linked to any timer. That leaves the legionella protection pump, LEG/Byp, which again probably only runs under certain conditions and you may be able to configure it differently or OFF if deemed not necessary.

 

[msd123]

I agree that, ideally, the pool pump should be integrated into the solar controller - but thats a whole can of worms that I'll leave for now.
Am now away from the house for a few weeks so will resume when I get back.

 

[OvertonPlumber]

In the early days of solar it was very easy to get the sensors mixed up. The two ntc sensors are almost identical the only difference is the resistance. The roof sensor has a range of say 5 - 130c whereas cylinder 10-60c but them mixed up and some wierd and wonderful things happen. My panels were at 46c at 11pm two weeks back. I hit 127c two days ago during day when I leaned up the flow rate too much.
Was at 98c at 3pm today when we had a slight malfunction.