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Author Topic: Endless multiple problems with solar thermal system  (Read 17719 times)
iank
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« on: March 17, 2015, 05:45:22 PM »

I would like to have  comments on out experiences, as I am beginning to think there is something seriously wrong with our system. We have had a Kingspan evacuated tube thermal panel installation for 3 years now, and it has been endless trouble, and has never worked properly for more than a few weeks at most. It was installed during some building work, and it is only subsequently I have become a bit more knowledgeable about these systems.

The system is way oversized for us, 3m2 panels for 250L tank, and we have low hot water usage. No-one asked us about our water usage or life style (often away for longish periods), and no heat dissipation system was considered.

Straight away there were continual problems with air in the system during the first summer, no cause was found, but multiple visits by the installer would effect a cure for a few days and then the problem would recur. They called a Kingspan technician for a site visit, found the pressure gauge and flow meter not working and these were replaced.  Whenever the panels did work in summer,  the tank would be at max temperature by about midday, and then the collectors sat at 160 degrees for the rest of the day.
Eventually, the installer got round to putting in a heat dump, but clearly had never installed one of these, and had made no calculation of the required size, turning up with a very small CH radiator. They eventually installed an appropriate size CH radiator (they assured me Kingspan had authorised this even though they are only rated to 80degrees) , but connected it up incorrectly. All this was sorted eventually by a live telephone link with Kingspan. This took all the first summer and into the next winter.

The following summer last year we were away 4 months, so there was minimal use last year, but all seemed well when it did work.

Now that spring has arrived and the panels started working, the system is again full of air and minimal flow. The pressure relief valve has been leaking and the pressure gauge is stuck again, the pump is very hot and noisy and no flow is registering in the flow meter (although there is a temperature difference between the 2 sides) so we are back with the same problem as initially. I have noticed in the Kingspan technical installation manual that the connection from the pump station to the cooling vessel and the expansion vessel should be level and at least 10cm below the level of the pressure gauge. Ours has a large uphill loop between the gauge and the cooling vessel.

 Could this be the reason that the pressure relief valve has been leaking fluid and the gauge is stuck again? My understanding is very hot fluid in the collectors forces fluid back into  the cooling and expansion vessel, this loop will cause fluid to overflow into the pressure gauge and into the PRV.

There has never been any explanation for the repeated episodes of air within the system, so any suggestions would be helpful, as I am beginning to think this is never going to be OK.

The installer has started to become very slow to respond. They were subcontractors to the builder, who knows nothing about thermal panels, but is clearly bothered that this may cause him legal problems if it comes to that.


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stannn
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« Reply #1 on: March 17, 2015, 06:14:51 PM »

Do you know where the bleed valves are, iank? Are they at the highest possible point.
Stan
« Last Edit: March 17, 2015, 06:56:39 PM by stannn » Logged

2.45 kWp PV (Navitron supply), 40 evacuated tubes (Navitron supply), Clearview 650 log burner with back-boiler heating cottage and water, 2 off 50W border collies, 1 off 35W cat, 1 off 25W cat.
todthedog
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« Reply #2 on: March 17, 2015, 06:50:02 PM »

Hello Lank,
You say you were away 4 months, where abouts are you?
Are you UK based?
The only probs that I have had was in high summer MrsT away low water usage and resulting stagnation in the system coupled with a local power cut.
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Kidwelly South Wales
iank
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« Reply #3 on: March 17, 2015, 08:06:01 PM »

Reply to Stann

there is an air separator on the pump station with a bleed valve. I have opened this a few times. A small amount of air comes out, the pump is slightly less noisy and gurgling, no obvious improvement in flow.
The collectors are inaccessible without a cherry picker, so I do not know if there an automatic vent there. I thought these were only needed if the system was filled with a manual pump. I will ask the installer if there is one if I ever see them again.

reply to todthedog

uk, sunny scarborough sometimes. We were away in Kyrgyzstan on a mountain bike tour.
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stannn
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« Reply #4 on: March 17, 2015, 09:09:19 PM »

Don't give up iank. It sounds as though it has never been fully bled of air. The air can only be completely removed at the top of the manifold on your roof. That will be by either an auto vent or by loosening a pipe connection up there before re-tightening.
The manifold (black box at the top of your evacuated tubes) will likely have an internal 22mm pipe which can be almost completely full of air. In that condition you will have no flow or very little flow.
My heat dump is the central heating radiator system which works very well in summer.
Stan
« Last Edit: March 17, 2015, 09:13:29 PM by stannn » Logged

2.45 kWp PV (Navitron supply), 40 evacuated tubes (Navitron supply), Clearview 650 log burner with back-boiler heating cottage and water, 2 off 50W border collies, 1 off 35W cat, 1 off 25W cat.
dhaslam
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« Reply #5 on: March 17, 2015, 09:58:38 PM »

The panel sizing is about right for  that size cylinder.   In the British Isles only about one day in six  has long sunny periods.  With a heat dump it should be fine.  It isn't good to have overheating because it can slightly loosen fittings and a tiny amount of liquid loss will  mean pressure is lost.  Lack of pressure  seems to cause more problems than  a little air in the system.   The flow meter is valuable because you can tell if circulation has slowed down or stopped.
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DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
oliver90owner
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« Reply #6 on: March 18, 2015, 12:29:03 AM »

Where to start?!

Pressurised systems do not get air in them - they leak liquid untl the positive  pressure is lost, then air can enter.

The system must be bled free of air at the highest point - as per Stannn.  If access is impossible without resorting to a cherrypicker, the installer should have made alternative provision for a bleed system inside the roof space.

Pressure guages shoud always be positioned such that solid particles cannot enter the guage.  Solid accumulation in the bellows will inevitably lead to the gauge not working properly.  Gravity is a simple method of avoidance, so they should always be installed at the top of a leg above, and away from, the liquid flow.

Your heat dump needs to be more than adequate for the maximum panel heat output in summer, in order to avoid stagnation.  Stagnation cannot be seen as good for a system, even if it appears to cause no ill effect.

Your pump will likely rely on flow to cool and lubricate.   A noisy pump spells trouble, either now or in the future.  The least is' that of air in the system.

What other faults may there be?  Seems like only a few other possibilities before the system could have been written off as a dead loss!

Sorry, but to me, it seems like a poor installation by a cowboy.  These systems are relatively simple and should run trouble-free for long periods if installed correctly in the first place.

RAB
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Ivan
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« Reply #7 on: March 18, 2015, 01:05:05 AM »

Also, it could be that the settings were never entered correctly into the controller (or maybe correct, but inappropriate) - for example, what is the controller set to do when the panel gets too hot? With the Navitron panels, the tubes/heatpipes will not be damaged by overheating, so you should set the controller to turn off the pump if the panel rises above 120C (for two reasons - 1)there may well be steam in the manifold, which will act like an airlock - pumps running dry or pumping against a resistance tend to overheat and fail and 2)the plastic impeller on the pump will melt if it gets very hot water flow through it). If your panel has been routinely overheating, and the controller is set to run above 120C, then this is likely to cause pump problems. Some manufacturers do advocate such settings - because their heatpipes fail under stagnation conditions, but I'm fairly confident that this doesn't apply to the Kingspan panel (but check with them!).

Air does tend to come out of solution as water heats up - so even if the air was all bled out initially, it can easily reappear, even though the system is still under pressure.

Rab is absolutely right that a pressurised system tends to leak rather than get air into it, but once the pressure has dropped to nothing, there is the potential for air to start entering the system. I saw a system recently that was pulling in air through an incorrectly-mounted spirovent - it was mounted 90degrees off it's intended position.
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oliver90owner
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« Reply #8 on: March 18, 2015, 07:05:01 AM »

Ivan is correct re the settings, of course, but now you have a heat dump those safety settings should be less relevant.  But heat dump diverters are known to fail.....

Initial degassing will occur within the system as there is some gas (mainly oxygen and carbon dioxide - think aquatic flora and fauna - in solution.  The other source at start-up and initial operation above about 85 C could be C02 released from temporary water hardness.  Assuming 15 litres system volume and 600ppm of temporary hardness (very hard water!), there would be approx 2 litres (at standard atmospheric pressure and temperature) of C02 expelled from the hardness alone.  Of course, this would be a somewhat reduced volume when pressurised and some CO2 would remain in solution, or slowly return to solution, as the system cools.

With a steel radiator as a heat dump, there should also be some inhibitor (may be incuded in the antifeeze) in the system to avoid rusting contamination (more solids to block every thing up!).  A leaky system will soon lose some antifreeze and inhibitor and any ingress of air to the system can cause sludge.  I'm no plumber or heating engineer, but I can easily understand your frustration with the continuing saga!

There is more to a system than just fitting the parts and filling with liquid, but a well arranged one should not give trouble like yours.   I might be worried about freeze damage in the future, if your installer is as (in)competent as you seem to suggest!  Seems to me that your system needs some repair/modification and a good service by someone who knows what needs doing.  Repressurising, alone, is simply a poor patch by 'treatiing the symptoms and not the disease'.

RAB
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iank
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« Reply #9 on: March 18, 2015, 12:26:05 PM »

Thank you all for these useful comments.

The controller is set to turn the pump off when the collectors are at 130C, which is the default setting by Kingspan. According to the Kingspan technical manuals and advice I have received by email and phone is that this system is oversized by 50%. I have noticed many times the cooling vessel and expansion vessel have been too hot to touch, and there must have been very hot fluid in the system for long periods of time. This has expanded into the pressure gauge and pressure relief valve, so the gauge is now stuck and I do not know what the pressure is, and air may have been entrained at the pressure relief valve. The plastic cap has dried encrusted fluid around it.

The installer was a sub-contractor, not accredited by Kingspan,  as part of a larger building project, and I am reluctant to resort to legal action against the main contractor as he is a genuine bloke, but it seems that is the law.
 I will probably get an independent report, service and repair, and then assess what to do in the long term. I would like to keep the system, so I am wondering if I need some arrangement whereby I could get onto the roof to cover part of the panels in mid summer and when we are away as a solution to avoid stagnation rather than take out 10 of the 30 tubes.
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todthedog
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« Reply #10 on: March 18, 2015, 12:40:07 PM »

Rather clutching at straws, but I have a friend who is now on their 3rd autovent.
I was just thinking you might be somewhere seriously sunny so lack of a heat dump might have been a big prob.
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dhaslam
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« Reply #11 on: March 18, 2015, 01:02:34 PM »

Covering panels when you are going away is not very advisable because it a bit like taking down the family flag.    A heat store would be a better option.   Most companies seem to advertise systems that are too small  because it keeps cost down and causes less problems  but  a system that produces excess in  sunny weather  is better.   I have  a two separate stores, the one in the attic  takes the surplus on sunny days in summer and returns the heat on dull days.   The other, lower temperature, store uses separate panels for winter heat.
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DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
iank
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« Reply #12 on: March 18, 2015, 03:46:26 PM »

 Thank you for that. I read somewhere that if there will be a prolonged period without power that it was recommended to cover up the panels, so that is where I got the idea.
I think the installer will suggest reducing the tubes down from 30 to 20, and I thought that being able to cover and uncover the 30 tubes as required would get the benefit of 30 tubes in spring and autumn and reduce the available heat in summer. I will have a think about an additional heat store.

I have looked at the Kingspan installation manual, and there should be manual vent at the manifold, so I will get some method of getting up there to look at this.
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Iain
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« Reply #13 on: March 18, 2015, 04:04:09 PM »

Hi
Might be worth putting a manual air vent in the loft. The pump will push air through the collector if there is a air collector/vent before the pipe starts going down again.
I just put a "T" in my 12mm pipe in the loft, on the collector outlet (HOT) pipe at the highest part of the system. The "T" has a 22mm up stand about 30 cm high with a manual vent at the top, closed end. The 22mm pipe acts as a collector for the air and is so easy to vent out. I also fitted a bypass valve across the non return valve which is a great help in filling and venting. No problems in 8 years with air in the system.

Also worth checking the EV has the correct precharge pressure. Normally about 0.2 bar below system working pressure. Tested with no pressure in the system.

Iain
« Last Edit: March 18, 2015, 04:07:29 PM by Iain » Logged

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DonL
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« Reply #14 on: March 18, 2015, 09:56:51 PM »

I've been reading this thread with interest and really hope you get it sorted out. If properly designed and installed this should be really reliable technology. My system has been running for nearly 10 years without a problem.

Oversizing the system is generally a good thing as you get more hot water in marginal conditions. In your first post you say that you now have a working heat dump so that should prevent stagnation when you're away.

It just occurs to me that the expansion vessel may be too small for the "oversize" system and that, particularly if the system has not been perfectly bled, you go over pressure when it is very hot, lifting the relief valve. Which means, of course, that the system has lost fluid and the pressure will drop when cold, perhaps allowing air ingress.

It would be quite straightforward to replace the pressure vessel with a bigger one or double up.

Just thoughts to add tothe debate. Without a proper survey of what's there by a competent person it's not possible to fully understand what's happening.
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