Solar operation queries

tipperary

Hi all

I'm just wondering if my solar system is operating correctly. Basically over the last few days, the cylinder is heating up well during the day - a 500 litre tank heating to about 60 celcius from 7.5m2 of flat panels. At about 6 pm both the top and bottom sensors in the tank are showing about 60 celcius, collector showing 20. However by 8 or 8.30 the bottom sensor has dropped to about 30 celcius and the collector has risen to 30! The hours pumped figure does not appear to have changed.

Effectively, it appears that the cylinder is heating the collector in the evening. I'm wondering is this a normal occurance due to the coil in the tank being hotter than the collector and the hot water rising?

Any help greatly appreciated.

quentingargan

tipperary wrote: »

Hi all

I'm just wondering if my solar system is operating correctly. Basically over the last few days, the cylinder is heating up well during the day - a 500 litre tank heating to about 60 celcius from 7.5m2 of flat panels. At about 6 pm both the top and bottom sensors in the tank are showing about 60 celcius, collector showing 20. However by 8 or 8.30 the bottom sensor has dropped to about 30 celcius and the collector has risen to 30! The hours pumped figure does not appear to have changed.

Effectively, it appears that the cylinder is heating the collector in the evening. I'm wondering is this a normal occurance due to the coil in the tank being hotter than the collector and the hot water rising?

Any help greatly appreciated.

Clearly you are leaking heat from your cylinder up to your panel. Normally a one-way valve should prevent this. It is possible that this isn't working, or is fitted the wrong way around.

The flow from the panel should be piped to the top of the coil on the cylinder. The bottom of the cylinder should then travel up, through the one-way valve and pump (usually all in a line in the pumpstation) back to the panel.

Another likely culprit is that someone has messed up the controller settings. There is a "recooling setting" which is used to dump surplus heat up to the panels when you go away on holidays. On the controller I normally work with, it is termed OREC, but you may have a different controller. Make sure this is set to off.

I have never used OREC (I prefer heat dumps) so I don't know if it has an effect on the hours pumped. Is the pump running after 6.00?
Q

tipperary

Hi Quentin

Thank you for your help. I have tried to investigate the theory about the one-way valve. I have a Resol Pump Station FlowCon B pumping station. I opened the front of the unit from where one can see the one-way valves on the inlet and outlet (Going by the arrows on the valves the inlet does seem to be connected to the top of the coil). The attached photo shows the position of the two valves. I tried looking at the documentation for the pump station system, but it is not clear what way the two valves should be. Do you know should they both be at 45 degrees?

Thanks again for your help. Unfortunately it seems I had a muppet of a solar installer! (this is not the first issue I have had).

quentingargan

tipperary wrote: »

Hi Quentin

Thank you for your help. I have tried to investigate the theory about the one-way valve. I have a Resol Pump Station FlowCon B pumping station. I opened the front of the unit from where one can see the one-way valves on the inlet and outlet (Going by the arrows on the valves the inlet does seem to be connected to the top of the coil). The attached photo shows the position of the two valves. I tried looking at the documentation for the pump station system, but it is not clear what way the two valves should be. Do you know should they both be at 45 degrees?

Thanks again for your help. Unfortunately it seems I had a muppet of a solar installer! (this is not the first issue I have had).

The valves will be right way around within a pump station as long as the pump station is connected to the cylinder properly.

The flow coming from the panel into the top of the cylinder should be connected to the left side of the pump station. Water returning from the cylinder to the panel should come from the bottom of the cylinder through the pump and on up to the panel.

But I don't think this is the problem. I would check the controller settings for the holiday setting... Q

tipperary

Hi Q

thanks for your input. I have gone through the various settings on the controller and everything seems to be in order. The flow coming from the panel is on the left and the return goes through the pump station on the right.

The one-way valves can be adjusted by turning a piece of the valve with a spanner. From looking at the manual I think this changes the valve from open - closed - one way. It's not clear what way the valve should be set so I guess I'll have to play around with it for a bit to see which setting gives the best results.

quentingargan

tipperary wrote: »

Hi Q

thanks for your input. I have gone through the various settings on the controller and everything seems to be in order. The flow coming from the panel is on the left and the return goes through the pump station on the right.

The one-way valves can be adjusted by turning a piece of the valve with a spanner. From looking at the manual I think this changes the valve from open - closed - one way. It's not clear what way the valve should be set so I guess I'll have to play around with it for a bit to see which setting gives the best results.

This is baffling... Hard to diagnose over the web to be honest.

Listen closely to see if the pump is running immediately after the sun has gone down (during the time when the cylinder appears to be losing heat to the panel). That would be down to the controller.

Those valves may control the flow rate. I would leave them fully open. There are debates about this, but my personal view is that I can see no benefit to slowing the flow rate. If the flow meter is showing an adequate flow rate at the lowest pump setting, I would leave those valves fully open (the flow rate should be at least 0.9litres per minute for every sq m of panel). Q

dathi

where the pipework is conected to the cylinder coil does it drop down 100mm before rising to the panel or does it just rise verticaly out of the coil to the panel if it rises verticaly then heat will travel up to the no return valve heat it and travel on its merry way to the panel

tipperary

Hi

Firstly thanks to Quentin for your help. One of the non-return valves was set incorrectly, which has improved things somewhat. I have been away for a bit over the last while so haven't really been able to monitor what's happening, but it does seem to be holding the temperature better. However it is still losing temperature a bit faster than I would have hoped.

Dathi, both the flow and return come out horizontally from the cylinder, before rising to the control panel and on up to the panels. The flow pipe does drop down about 50mm before starting to rise again, but the return does not drop at all. Do both the flow and return need to drop 100mm?

heinbloed

Quote:
" Do both the flow and return need to drop 100mm?"
Yes, and better more than that...
The pipes of a pressurised system are made from metal (copper/stainless steel?) and therefore conduct heat. As soon as a waterfilled pipe is warmer at it's bottom end compared to the temperature at it's top there will be a "stack effect". Similar to warm air rising in a chimney.
Meassure the temperatures to see if this is the case.
Therefore these pipes should not only drop when leaving the storage tank in a standard roof installation but they should also rise higher than the collector inlet and outlet. And then drop down towards the collector inlet or outlet.
So the warmest part of the piping (the top of it) won't be out in the cold. But within the insulation/attic.
Many installers haven't got the basics of the laws of physics. So better don't listen to theories but meassure. If the 'fault' can't be meassured it doesn't exist.

heinbloed

Does this installation look familiar? See

http://boards.ie/vbulletin/showthread.php?t=2055895817

The pipes going from the heated place (the tank storage within the house) straight in one line up and out ?

tipperary

All

I figured the easiest thing to do was to just take some photos of the setup. I have a 500 litre triple coil cylinder with stove back-boiler connected to the top, oil boiler connected in the middle and the solar panels at the bottom.

Of the two solar pipes, the one at the top is the flow from the cylinder. The pump is on the return side.

In the ceiling above the cylinder there is a horizontal section of pipework about 6m long before the pipes rise again to the panels.

Thanks all for your help.

quentingargan

tipperary wrote: »

Of the two solar pipes, the one at the top is the flow from the cylinder. The pump is on the return side.

I think this is the wrong way around on your system, though there is some debate about which way to do this. The flow from the panel ideally should go into the top of the coil, and the return from the cylinder then goes through the pump station.

Of more concern though is that I should imagine there is a lot of heat loss going on in here. You aren't meant to have a hotpress - it should be a cold press, not a hotpress. You really shouldn't see any copper on pipes coming out of the cylinder. I usually get a few lengths of 1.5" and 2" armaflex and put it on over both insulation and nuts and butt it right up against the cylinder.

Some of the pipes come out horizontally and then head uphill. If the heat is rising up those pipes, you will have further heat loss and this can be remedied. You would just have to feel those boiler pipes at a time when the boiler hasn't been running. If they are hot, they shouldn't be.

quentingargan

By the way, I recognise that controller. If it is the model I think it is, the instructions that come with this as standard are poorly translated. If you pm me your email address Tipperary, I can email you a revised instruction list I set out for this. Q

heinbloed

I agree with quentingargan, all pipes should be insulated, incl. the cold water pipes. The insulating foam should not be squeezed down with cable ties, use aluminia tape or similar material.
The expansion barrel should be 'fed' from upwards, so in no case hot water will get onto the membrane. The membrane should be touched only by cold water.At the moment as it looks like it could be o.k. but that is due to the flexible connection shaped into an U-bend, working as a knee or elbow.
I hope it is the cold part of the circuit it is connected to ?

If the space situation allows for it hang it downwards so the pipe is connected at it's top. Gravity forces will then cover the membrane with cold water, extending it's lifetime.
ST water in a pressurised system can get very hot, temperature plus pressurised steam will take their toll on it's lifetime. The rubber membrane being the weakest part in the chain would give in first, even if esp. designed for ST systems. And this will propably go unoticed (until the next inspection) causing further pressure stress onto system.

heinbloed

The grey pipe insulation is propably not suited for pressurised ST systems (check this out), it is designed is for temperatures below 100 degrees Celsius. At higher temperatures it will shrink and desintegrate.