Can someone explain this 'problem' to a newbie please?

[inetdog]

I have turned the system off and will monitor the temps for a couple of days and report. But in the meantime let me ask another (possibly) daft question. The 'sufficient solar' symbol is coming on and the pump is cycling. So assuming no water is drawn off, can a situation exist whereby the action of the solar pumping would actually cool the tank temp, or does it work that if it kicks in then it should always contribute a positive temp?

Your controller should be set up with a temperature differential detector ( a "differential") which does not turn the pump on unless the exit temperature from the manifold is higher than the inlet temperature at the point where the system is drawing water from inside the tank. Assuming that the pipes from the panel back to the tank are well insulated, this should guarantee that you are getting a net increase of the heat inside the tank. But because it also will do some mixing of the tank contents, it could also result in the temperature at the top of the tank actually going down a bit.

You generally do not want to lock out the solar system from heating the cold water at the bottom of the tank just because the stratified temperature at the top of the tank is higher than the panel output. But this is why the solar is set up to return to the middle of the tank rather than the top unless it is the only heat source. Your situation, with a high temp heat source which is only sometimes available, is a difficult one to design for and I would like to see comments about this specific problem from those who have more design or use experience in this area.

The proper operation of the differential depends on the placement and accuracy of the two temperature sensors.

If the return pipe temperature at the heater is lower than the inlet temperature (the pipe at the heater going up to the panels) as measured by moving a single thermometer or with two calibrated/matched thermometers, then your controller should not be turning the pump on. If it does, then you need to look at your control system setup.

[nickbb]

Your controller should be set up with a temperature differential detector ( a "differential") which does not turn the pump on unless the exit temperature from the manifold is higher than the inlet temperature at the point where the system is drawing water from inside the tank. Assuming that the pipes from the panel back to the tank are well insulated, this should guarantee that you are getting a net increase of the heat inside the tank. But because it also will do some mixing of the tank contents, it could also result in the temperature at the top of the tank actually going down a bit.

You generally do not want to lock out the solar system from heating the cold water at the bottom of the tank just because the stratified temperature at the top of the tank is higher than the panel output. But this is why the solar is set up to return to the middle of the tank rather than the top unless it is the only heat source. Your situation, with a high temp heat source which is only sometimes available, is a difficult one to design for and I would like to see comments about this specific problem from those who have more design or use experience in this area.

The proper operation of the differential depends on the placement and accuracy of the two temperature sensors.

If the return pipe temperature at the heater is lower than the inlet temperature (the pipe at the heater going up to the panels) as measured by moving a single thermometer or with two calibrated/matched thermometers, then your controller should not be turning the pump on. If it does, then you need to look at your control system setup.

Thanks for that, i'm getting my head round this now. Although still not sure whether i'm getting what I should expect at this time of year. I turned off the solar last night and took a tank reading at 8:30 this morning which was as follows:

Bottom of tank 45.3 top of tank 54.2

Then again at 11:30 as follows:

Bottom of tank 39.6 top of tank 51
.
Should a brand new 250ltr very well insulated tank hold it's temp better than above or is that reasonable?

Also, just before pressing 'post' I have just checked the two tank temps and they are (as usual) on the way down, (50 and 38.8 after 15 mins) but I can't tell if that's down to the solar which I switched back on after taking the 11:30 reading or if it's just natural ambient loss?

I guess my big problem is that the installer is telling me that I "won't get much out of it at this time of year", but that he's going to be asking for the rest of his money long before I can prove whether that's right !

p.s. I will try and get hold of a thermometer and try the pipes as you say.

[Naptown]

How about posting the model numbers of the equipment and a few photo's these would be very helpful

[nickbb]

How about posting the model numbers of the equipment and a few photo's these would be very helpful

Thanks Naptown. I'll do that tomorrow.

[nickbb]

How about posting the model numbers of the equipment and a few photo's these would be very helpful

Ok, so equipment as follows:
20 x joule acapella tubes
Solarlogic temperature differential controller
Tristar 250 woodburner solar thermal store
dscf1456.jpgDSCF1459.JPG

If you want me to post any other pics etc let me know Naptown.

[Naptown]

Who made the tank and is the tank picture turned on its left side in the post?

[nickbb]

Who made the tank and is the tank picture turned on its left side in the post?

The tank was made by Telford Copper Cylinders, and yes (sorry) the picture is turned on to it's left hand side.

[nickbb]

Who made the tank and is the tank picture turned on its left side in the post?

Any more to add Naptown ?

[Naptown]

Not really at least at this time