Solar thermal panel is exporting my tank heat!

TheSaint_2

Hi everyone,

I have a solar hot water panel on the roof. When I use my boiler or immersion heater to heat my water tank the solar panel will turn on and heat up from my tank. It's driving me mad because it's a waste of energy.

For example my panel temp this morning was 8.9 degrees. My tank temp was 44 (bottom the tank 22 degrees) and it turned on. Within a few seconds the panel was up at 15 degrees, so I manually turned off the water panel. 
I can't do that myself every day, other than calling the company that installed it (years before we moved in) does anyone know of any resources I can use to reprogramme the panel? I tried looking at the manual for the controller online but it was no help.
The panel controller is a deltasol bs.

Thanks in advance.. It's been doing this since we moved in so its wasting a lot of energy

paul991

can you  not  get  a  local plumbing  company to  fit a solenoid valve  on the heating circuit

TheSaint_2

Not sure what you mean, but the problem is the controller of the panel not the gas system. The temperatures are set wrong on the controller I'm guessing, it doesn't seem to know the difference between the tank being hotter than the panel (collector) and the panel being hotter than the tank. It just turns on when there is a temperature difference between the two that is over about 25 degrees. That means in winter I lose more and more energy as the days get darker and colder.

YBR

Our solar thermal is set up only to run the pump when the panel temperature is higher than the tank temperature. This is what you need. It could be that the thermocouples are failed, or that the controller is not set correctly.

I suggest that you get a company in to service the system if that's not been done recently and ask them to fix this symptom. It may not have to he the company that originally installed it.

70sbudgie

Which model do you have? A quick search of deltasol bs shows a few options.

The high level description includes a heat dump function, which sounds like what's happening. So I wonder if it is a setting that has been accidentally turned on?

TheSaint_2

It’s a Deltasol bs
I'm leaning  towards it being broken. I've emailed delta sol for their opinion, and may just order a new controller. The menu is not responding in the way that the manual says it should so I think it's faulty.
Cheers all.

zeupater

Hi

.. Can you describe the cylinder setup? (no of coils etc) ...

.. What pump setup is installed? .. (Simple pump or solar pump unit)

.. When maximum water temperature is reached does the system stagnate & if so what panel temperatures are registered? ... (ours was ~170C when I looked this afternoon)   

.. When your cylinder is fully heated, (i) do both of the sensors show the same(ish) temperature & (ii) the panel temperature sensor shows at the deltaT above this as set within the controller?

.. When your described issue happens does the solar pump turn on or is the heat siphoning?

.. If the solar pump turns on, does it do so as soon as the boiler kicks in .

.. Could you note the current controller settings? (DeltaT etc as per manual)

HTH - Z

TheSaint_2

zeupater said:

Hi

.. Can you describe the cylinder setup? (no of coils etc) ... 
1 coil, top and bottom temp sensors

.. What pump setup is installed? .. (Simple pump or solar pump unit)
simple I think, it’s in the loft and looks the same as my central heating pump

.. When maximum water temperature is reached does the system stagnate & if so what panel temperatures are registered? ... (ours was ~170C when I looked this afternoon)   
it seems to get to about 60 degrees ish and stop. The panel temp can get into the 70’s

.. When your cylinder is fully heated, (i) do both of the sensors show the same(ish) temperature & (ii) the panel temperature sensor shows at the deltaT above this as set within the controller?
both tank sensors do show about the same temp when fully heated, but I don’t really think it often gets to that point, even with a very sunny day

.. When your described issue happens does the solar pump turn on or is the heat siphoning?
 The pump turns on every time. 

.. If the solar pump turns on, does it do so as soon as the boiler kicks in .
 Yes

.. Could you note the current controller settings? (DeltaT etc as per manual)
 no, the controller seems to be broken, I can’t get into the menu to look at the settings. I have emailed the manufacturer and am waiting for them to get back to me

HTH - Z

thank you for your detailed question set. it is interesting that your panel has reached 170 degrees, the most I have ever seen on mine is about 130 but that was when I had to turn the power off on a hot day to do some electrical work. When I turn it back on the panel was very hot. I only have two panels, and it might just be that as a result I don’t get much heat from the system.

 Thanks

zeupater

Hi

So you have a single heat exchange coil in the cylinder which is shared between the GCH DHW and the solar system? ... if so is there a motorised valve to switch heating flow between GCH & solar thermal? ... is this stuck so that it doesn't fully open/close, resulting in thermal syphoning on the open solar circuit ? ...

... Alternatively, when the cylinder reaches maximum temperature do you have a heat-dump circuit to a towel-rail/radiator?

... Is there a separate thermostat on the cylinder for GCH DHW? ... what's it set to? ... is it on timer or always on?

Regarding solar heating the cylinder to "about 60 degrees ish and stop" tends to suggest that the solar max temperature is set to 60C, however with the panel not going above 70C would tend to suggest that there is some form of designed cooling or the panels reach a state of equilibrium (gain=loss) at around this temperature, however, if you've seen ~130C after the power's been off then that can't be the case (thought) ... unless it's designed as a drainback system - so is there a drainback cylinder somewhere or is it a pressurised design (i.e. with expansion vessel)?  

From looking at the manual it seems that you can only display one temperature sensor reading at a time, so as you've detailed different sensors, I don't follow the "the controller seems to be broken" comment as it would be necessary to scroll through the settings using the same buttons required to access the parameters (manual: Version BS4 2.00) ... do all 3 buttons on the controller work (+/-/OK) as per Resol DeltaSol BS manual page 7, section "2.1 Buttons for adjustment" ?

Anyway, regarding our panel stagnation temperatures ... 170C is pretty standard for a bright day, but I've seen it higher in really sunny & hot conditions .... we have a vacuum tube setup therefore heat gain/loss equilibrium depends more on the manifold than the insulated collector area, that's why tubes tend to provide heat in less bright/cooler conditions ... today's bright with a milky white/blue sky & when I last looked (just before starting this post) we were close to reaching cylinder thermostat setting ... just checked again & the panel temperature just indexed from 161 to 162C ..      

HTH - Z

#Edit : 16:33 - Panels (stagnated) 179C - Ambient 26C - Sunny with light blue hazy sky.

TheSaint_2

zeupater said:

Hi

So you have a single heat exchange coil in the cylinder which is shared between the GCH DHW and the solar system?

-Sorry I misunderstood, the central heating has its own coil.

... if so is there a motorised valve to switch heating flow between GCH & solar thermal? ... is this stuck so that it doesn't fully open/close, resulting in thermal syphoning on the open solar circuit ? ...

... Alternatively, when the cylinder reaches maximum temperature do you have a heat-dump circuit to a towel-rail/radiator?

-I don't think so, but I can't be sure. I have seen the towel radiator get hot once.

... Is there a separate thermostat on the cylinder for GCH DHW? ... what's it set to? ... is it on timer or always on?
-yes, it's set to 60 degrees, but that stat is no way connected to the solar heater.

Regarding solar heating the cylinder to "about 60 degrees ish and stop" tends to suggest that the solar max temperature is set to 60C, however with the panel not going above 70C would tend to suggest that there is some form of designed cooling or the panels reach a state of equilibrium (gain=loss) at around this temperature, however, if you've seen ~130C after the power's been off then that can't be the case (thought) ... unless it's designed as a drainback system - so is there a drainback cylinder somewhere or is it a pressurised design (i.e. with expansion vessel)?  
- I think it is pressurised, there is a pressure gauge next to the tank connected to the solar pipes. There is also a small round tank in the loft about the size of a big basketball.

From looking at the manual it seems that you can only display one temperature sensor reading at a time, so as you've detailed different sensors, I don't follow the "the controller seems to be broken" comment as it would be necessary to scroll through the settings using the same buttons required to access the parameters (manual: Version BS4 2.00) ... do all 3 buttons on the controller work (+/-/OK) as per Resol DeltaSol BS manual page 7, section "2.1 Buttons for adjustment" ?

- you can only scroll through the sensors and then to the code option. When you hold the button down to go into programming menu nothing happens. 

Anyway, regarding our panel stagnation temperatures ... 170C is pretty standard for a bright day, but I've seen it higher in really sunny & hot conditions .... we have a vacuum tube setup therefore heat gain/loss equilibrium depends more on the manifold than the insulated collector area, that's why tubes tend to provide heat in less bright/cooler conditions ... today's bright with a milky white/blue sky & when I last looked (just before starting this post) we were close to reaching cylinder thermostat setting ... just checked again & the panel temperature just indexed from 161 to 162C ..      

HTH - Z

#Edit : 16:33 - Panels (stagnated) 179C - Ambient 26C - Sunny with light blue hazy sky.

Thanks for your help 

zeupater

Hi

Regarding the question/answer ...

"... Is there a separate thermostat on the cylinder for GCH DHW? ... what's it set to? ... is it on timer or always on?
-yes, it's set to 60 degrees, but that stat is no way connected to the solar heater."

This is very important for the following reasons ...

.. With a twin coil cylinder you may have a situation where both heating systems switch in at the same time due to thermostatic settings and the mode you're running the GCH DHW provision.

.. The lower of your two coils should be for the solar thermal and there should be a sensor reading the bottom of the cylinder ... the top coil will be the GCH and will have it's own GCH thermostat. If the GCH DHW is set to always on as opposed to off or timer, then as soon as the stored water at the level of that thermostat falls below the set temperature the GCH provision will fire up, even if the solar is already trying to heat the water as well ... let's look at an example ...

---

It's early morning & you have a full cylinder of hot water and neither the solar thermal or GCH are called upon to provide heat ... someone washes their hands & uses enough HW to cause the solar thermostat at the bottom of the cylinder to fall below it's set point, however the panels on the roof are not yet warm enough for the controller to switch the pump on, so no heat is provided immediately ... the panels gradually heat up and when the preset deltaT between the panel sensor and the one at the bottom of the cylinder is reached, the solar pump switches on and starts heating the water at the bottom of the cylinder.

At this point it's important to note that a vertical DHW cylinder is designed to stratify multiple layers of water temperatures so that you still have hot water at the top whilst the bottom is receiving water at mains supply temperature ... the layers at this point will be (from bottom up) ... cold / cold+solar thermal heated / hot with no heating required ... the ST system is providing heat and the GCH is not.

Next, the household uses a considerable amount of water (shower/bath) ... the ST cuts in first and starts to heat using the bottom coil, but the amount of water used moves the cool layer to the DHW coil thermostat, which (if set to always on) turns the DHW boiler on ... if this is the case then at this point both GCH & ST are providing heat - which may be what you're observing ...

If this is the case, then the GCH will heat the upper part of the cylinder to it's thermostatic set point and switch off, however, the ST (lower heat provision) will continue to run and heat the lower part of the cylinder until it reaches it's own thermostat's set point .... now, it's really important to understand that with the ST coil being lower than the GCH coil, the ST system will not have an effect on the water heated by the GCH unless it reaches a temperature which is higher than that achieved by the layer achieved by GCH DHW provision & therefore will not 'export' any of the GCH provided energy.       

--       

If the above scenario is what you're seeing, then the solution at this time of year would simply to be to switch the GCH DHW provision to manual (off) (if that works for you) and then play around with creating a timer schedule that works for your level of consumption / cylinder capacity / average solar provision, but take care to recognise that in using the GCH for DHW you're actually limiting the heating capacity of the solar thermal system .... if you've already heated the water at the top of the cylinder, then the solar thermal only has the volume of water between the bottom of the cylinder and the GCH coil to heat before it cuts out and probably stagnates for the rest of the day ...

Our GCH hot water provision at this time of year is set to off & will not normally be needed to support the ST until some time in late October/November, but even then only being used as a random top-up measure depending on weather conditions .... only in deep winter do we heat the DHW on a timed basis.

HTH - Z