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

[Naptown]

Not really at least at this time

[nickbb]

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

Any more to add Naptown ?

[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.

[Naptown]

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

[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.

[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.

[Naptown]

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

[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.

[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]

A couple of questions:

1. What would the tank temperatures be for comparison if the panel system is turned off completely (valved off so no flow even without pumping)?
2. The tank top temperatures are looking OK, but the steady reduction in tank bottom temperatures suggest, as Naptown asked, that there was some cold water being added to the tank as hot water was used. Without having an idea how much, it is difficult to comment about what your panel output was compared to expected.

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?

[russ]

Right - a modern tank with good insulation should lose very, very little temp.

[inetdog]

Ok, pipes changed round and results as follows:

                     9:00am       10:55am      11:35am      12:05pm     1:20pm      2:35pm
Roof temp            21            48.5         48.3        47.3        46          45.8

Tank bottom temp     43.7          38.3         39.3        39.9        39.1        37.9

Tank Top temp        53.7          48.5         47.5        46.8        45.1        43.8

Now I know there are a lot of variables, but the day has been cloud free, the sun low in the sky with some tree obstruction. The first temp was just after the pellet boiler had switched off, and the last temp when the 'sufficient solar' symbol had gone off on the controller. My question is, given all of the above do you think the figures I have reported are reasonable for the time of year (in the south of England) or should I be getting more?

Thanx

A couple of questions:

1. What would the tank temperatures be for comparison if the panel system is turned off completely (valved off so no flow even without pumping)?
2. The tank top temperatures are looking OK, but the steady reduction in tank bottom temperatures suggest, as Naptown asked, that there was some cold water being added to the tank as hot water was used. Without having an idea how much, it is difficult to comment about what your panel output was compared to expected.

[Naptown]

Was there any water use during this time?

[nickbb]

Thanks, The solar is indeed connected to the coil in the bottom of the tank. The upper coil is fed by a pellet boiler, so hopefully things should improve when the solar is re-connected. I will post the results, but thanks for your help Naptown.

Ok, pipes changed round and results as follows:

9:00am 10:55am 11:35am 12:05pm 1:20pm 2:35pm
Roof temp 21 48.5 48.3 47.3 46 45.8

Tank bottom temp 43.7 38.3 39.3 39.9 39.1 37.9

Tank Top temp 53.7 48.5 47.5 46.8 45.1 43.8

Now I know there are a lot of variables, but the day has been cloud free, the sun low in the sky with some tree obstruction. The first temp was just after the pellet boiler had switched off, and the last temp when the 'sufficient solar' symbol had gone off on the controller. My question is, given all of the above do you think the figures I have reported are reasonable for the time of year (in the south of England) or should I be getting more?

Thanx

[nickbb]

That will certainly make a big difference! But you may still have problem with the capacity of the system. Best thing is to make more measurements once the flow direction is fixed.

One possible remaining problem is that if you have a separate boiler/heater to that tank, the solar should draw from the bottom of the tank and return to the middle of the tank so that it is not cooling the higher temperature water heated by the separate heater. Only if the solar heater output temperature is higher than the temperature produced by the heater should you connect the return to the top of the tank.
In your case, that would correspond to the stove coil being in the top half of the tank and the solar coil being in the bottom half.

Thanks, The solar is indeed connected to the coil in the bottom of the tank. The upper coil is fed by a pellet boiler, so hopefully things should improve when the solar is re-connected. I will post the results, but thanks for your help Naptown.