Solar Water System problem

AlanD

Hi,

I have a 60 tube solar collector on the roof heating a 300 litre tank. The pump is a three speed pump and I can change the speeds manually using a screw driver.

Lately though it seems that a lot of air has enterered the system. The flow meter on the pipe returning to the roof barely registers some days and on other days there is too much flow and it can be full of bubbles. I wonder has the fluid in the system boiled at some stage causing some air in the system.

I could go a few days with some low pressure in the system and some days with lots of bubbles banging through the pump.

I think I need to replace the control panel anyway I think as on hot days with a full tank of hot water, the control panel doesn't know what to do and stops pumping and so the sensor on the roof goes off the chart. I manually have to turn on the pump if I'm around then. So maybe those really hot days have caused some issues.

Some controller suggestions would be appreciated by PM.

But to resolve the flow and bubble situation, do I need the system repumped?

Thanks,

Alan.

heinbloed

You propably need a real installer to check the entire system on-site. The manufacturer trained staff usually knows very little when it comes to a problem outside their brand.
I can't comment on the settings of your controll and pump station, no data.

So a few questions:
Is it a pressurised, closed system ?
Is an automatic air valve (micro bubble air seperator) installed/ is it functioning?
Is it an intelligent air valve, one which makes a difference between air and steam?

By "repumping" do you mean refilling or increasing the pressure by adding more brine? The brine ( or solar fluid) can be checked if it is still o.k.

Was the system checked for leaks? Were correct seals used ( no PTFE tape with glycol!)?

The temperature sensors should withstand higher temperatures than seen in a standard ST system. But they might be defect, test them with ice water and boiling water and see what the thermometer shows.


That the pump stops once the storage tank is heated up to demand saves on energy.
Some installers suggest to turn on an aditional pump to get rid of the surplus thermal energy, two electricity wasters running against each other ....the one filling the thermal storage tank whilest the other emptying it at the same moment.

PeteHeat

Hi,

I suggest you get the system checked for leaks and possibly re-pressurised using the proper equipment, bubbles are a sign of air in the system.

Depending on the product brand, supplier, installer your system may have been filled with water not glycol.

Also worth checking the safety valve there should be a pipe coming off it into a container or piped to where any hot glycol can be safely dumped or piped to where scalding water can be safely dumped in case of emergency.

Some controllers can be set to stop turning on the pump when the cylinder reaches the set temperature, 60 tubes can be a lot of collecting power even in a basic system especially with our sunny weather this summer, that is why a heat dump is recommended by some of us.

.

AlanD

heinbloed wrote: »

Is it a pressurised, closed system ?

The hot water system isn't a closed system. It feeds from an attic tank, if that is what you are asking.

heinbloed wrote: »

Is an automatic air valve (micro bubble air seperator) installed/ is it functioning?

I actually don't know what this is, but I would think there isn't one installed. Would this help get rid of tiny bubbles in the system?

heinbloed wrote: »

Is it an intelligent air valve, one which makes a difference between air and steam?

Again, not sure what this is, so doubt I have one. Should I?

heinbloed wrote: »

By "repumping" do you mean refilling or increasing the pressure by adding more brine? The brine ( or solar fluid) can be checked if it is still o.k.

Yeah I mean emptying it and repumping it to ensure that everything is ok. Checking the current stuff would work. But I was thinking that repumping it would allow the existing air to leave.

heinbloed wrote: »

Was the system checked for leaks? Were correct seals used ( no PTFE tape with glycol!)?

Yes, when installed, it was checked for leaks. We did have to empty and refill it shortly after for some other issue (can't remember what it was now) but it was checked for leaks then too.

Saying that though, I thought I smelled solar fluid in the attic a couple of times, but I figure if it leaked, it would continue to leak and I'd see some evidence of it up there.

heinbloed wrote: »

The temperature sensors should withstand higher temperatures than seen in a standard ST system. But they might be defect, test them with ice water and boiling water and see what the thermometer shows.

The sensors work fine, the problem is with the controller, it defaults out to 255 when the tank is full of hot water (not to the max temp set though), so the controller has a canary and doesn't know what to do. Controller goes back to reading good temps again after I manually turn on the pump a few times.

Unfortunately, my solar installer is out of business and the plumber contracted to actually install the plumbing part works for someone else now and is so busy, I can never get them. So if there is anyone who could come out to me to become my new solar guy, PM me. I am based in Annacotty, Co Limerick.

AlanD

PeteHeat wrote: »

Hi,

I suggest you get the system checked for leaks and possibly re-pressurised using the proper equipment, bubbles are a sign of air in the system.

Depending on the product brand, supplier, installer your system may have been filled with water not glycol.

Also worth checking the safety valve there should be a pipe coming off it into a container or piped to where any hot glycol can be safely dumped or piped to where scalding water can be safely dumped in case of emergency.

Some controllers can be set to stop turning on the pump when the cylinder reaches the set temperature, 60 tubes can be a lot of collecting power even in a basic system especially with our sunny weather this summer, that is why a heat dump is recommended by some of us.

.

This controller is quite a cheap basic chinese no brand name thing. Cheapest they could get I'd imagine. No fancy holiday, anti freeze settings on it.

The 60 tubes work great for us I must say. So glad we got them, but I've a feeling the controller doesn't make the best of them. My tank would max out at maybe 60 on a hot day even though it's set for 70 I think. There is an overflow scald valve too. Overflow tank is empty.

heinbloed

Well, if the solar system is pressurised, a closed system, then there should be somewhere a manometer. A pressure meassure device which is usually placed next to the control unit or included in it.

What does the pressure show?

It should show around 1-2 bar of pressure, not more than 3 bar.

If the pressure has dropped repeatedly below the set pressure (when filling it) there is certainly a leak.
You have mentioned the solar fluid which you smelled. This could be either the fluid itself in it's liquid state or steam from the system escaping somewhere. I'm not sure how glycol/solar fluid smells, as far as I remember my school days in the lab glycol has no smell as such. There might be additives in your solar fluid to warn against internal consumption though.

The corrosion inhibitor used in central heating systems has a smell, could it be a seperate leak somewhere?

A small drop of pressure over a period of time is not to be worried about (0.1-0.2 bar over the year with standard household installations). This is due to diffusion and to air pressed out of the system at the valves. If you have a micro bubble vent installed....

There are usually two or three air valves (-traps) with a standard ST system. The first would be at the return, where the hot fluid comes from the collectors. These primary air traps come in two versions: a.) the manual valves which have to be bled like the old radiator air traps by hand. Either with a srew driver or with the little radiator key. Be very carefull with the steam, if the system is hot you better be carefull. Gloves, some sort of face protection ect.. Steam can shoot out and cause severe scalding.
And then there are b.) the automatic air valves at the return. Here you have to do nothing, they work on their own unless defect.
The standard cheap stations use manual valves, these MUST be bled regularly, most solar system owners never heard about this simple fact.And therefore risk the entire system whilest waiting for a proper harvest.....


The next air valve would be in the (solar) heating circuit AFTER the solar station, at the top of the storage tank where the heating tube (the heatexchanger) leaves the tank and goes back to the collectors.

And the third automatic air valve would be at the top of the collectors. Outside, at the highest point of the solar circuit. This is the coldest spot of the entire circuit, where it enters the collector.
The fluid will not only have there it's lowest density and therefore micro bubbles will form into macro bubbles. It also is there where in most installations the fluid's stream will be "split", the fluid loses pressure when coming from a small diameter tube into a larger diameter tube, ito the collector. With the combined effect that a.)
the pressure is reduced and
b.) the fluid has reached it's highest point.

The generation of macro air bubbles is guaranteed.

And since due to the laws of physics air bubbles rise upwards in in liquid water the macro bubbles won't come down on their own, back to the solar station where the bubble-trap is waiting for them. They stay up.

And this means the solar fluid has to pass by force through the air bubble. Air is not to be mixed-up with a vacuum, the fluid has to be forced through the bubble and along it. The air takes up space, and the smaller the left space is the less fluid will pass through, back down to the station.
The longer it takes the fluid to get through the collector the hotter it will get, the more steam bubbles will be created.
So with a hindered passing of the fluid the system will overheat and it's death bell, be made of air, will be heard.



Contact the company your plumber is working now for and ask them to come out to have a look and to recommend a solution.

It is absolut normal here in Ireland that closed loop plumbing is hardly understood by the plumbers resp. those who work in the thermal solar trade. Most ST installers work on a trial and error base. Ad to this Murphy's law and they are lost.

These air valves at the flow pipe (between the collector's inlet and pipe) are a MUST with intelligent plumbing, similar to the air valves in radiators.
The difference between them is the positioning: the one can be reached easily and the other not. So better go for an automatic air valve. So you don't have to climb onto the roof ever couple of weeks to let out the air manually, the term "bleeding" dosn't have to be taken seriously (smiley). The automatic solar air valves are of different brands and makes, one for a standard ST system around €100.- each.

Automatic air/bleeding valves for central heating radiators cost around € 5.-.

The difference between them is that a solar air valve has to withstand much higher pressure and temperatures and is exposed to glycol as well.

Do not allow your installer to install any other air valves into your ST system but certified ones, certified for the purpose.
If you go for an 'intelligent' air valve less steam will be lost with the air. Standard ST air valves will not only let out air but steam as well. And this means frequent controlling, bleeding and topping-up of the fluid. What propably costs more primary energy than will be saved at all.....


One major weak point of the pressurised solar systems is their demand to expand into a expansion vessel. Which should be positioned somewhere at the flow pipe (leading back to the collector).

These pressure vessels must be correctly filled. Not only by using nitrogen at the gas side.They must be pressurised in a non-connected situation, when not connected to the system, to the correct pressure. Which would be the same as later in the wet system.
If employing solar installers ask for the nitrogen bottle. If they don't have one with them they can't do their job correctly and would have to call-out again. If they never heard about it you are talking to a cowboy of the trade.

Why nitrogen instead of the foot-driven tire pump? Because nitrogen won't diffuse through the membrane in the ST expansion vessel, into the pressurised solar fluid where it would dissolve and being carried up. At least not very fast. Plain air will. These membranes are of synthetic rubber and air (esp. the oxigene) will always get through rubber.


About the planned new solar station:

There are many different types for different purposed out there.
The major things to look for are the guarantee, the automatic (intelligent) air valve and an A-rated intelligent pump. One which sets it's speed accordingly to what is actually needed, incl. stagnation.

From your description of the pre-set limits of your existing station this station propably set for " heat-pipe" tubes. Direct flow tubes or flat collectors would need a different setting of the determinig parameters, these should be set accordingly to the overall system's demand.

Many manufacturers have reacted towards the low competence of solar installers and are now offering entire systems with a solar keymark. Plug-and-play, so to say.
Check the manufacturer of your solar system if the station was actually factory set for a certain lay-out (your system lay-out that is !)or if someone tried the trial and errror method.
You could rest it to it's original setting.

To get a suitable solar station one has to use math. Most solar installers are not competent enough for this, so they install something they think might work and hope for no come-back. A lack of solar harvest (kWh) wouldn't be realised by 99% of of the consumers. That is the idea behind some solar bussiness. The client doesn't know what he want's, cheap plunk in an expensive bottle sells as well....
For these consumers, confronted with no own knowledge and dubious installers, these complete sets are designed, check the ESTIF home page for a list.
If the come-backs become to many they close down.

So if you want your money back and compensation as well get a real heating engineer to write you a report what actually went wrong, what parts are missing and a calculation of the 'lost' energy. Which has a monetarian value.

Mod Edit: heinbloed, please stay on topic, padding out a post with incidental information tends to confuse and readers tend to ignore the post in full, thank you.

PeteHeat

Hi AlanD,

From your posts the system appears to require a general service, nothing too fancy.

If you get me the model number for your controller I should be able to send you a manual.

Surprising but some of the cheap Chinese controllers can have a lot of hidden extras, yes sometimes the installer has to calibrate the probes but nothing too difficult.

Sorry I don't cover the Limerick area purely because I could not expect a customer to pay for my travelling time and diesel.

Perhaps heinbloed could oblige ?????

.

saibhne

Hi Alan,
I've sent you a PM with a solar installer in Limerick I can recommend. Let me know if you need any more help.

S.

AlanD

Thanks Heinbloed for the detailed response.

There's a lot in there.

I guess the main points about the air valve could be most important here. With my basic knowledge of plumbing and being here with the plumber installed the system, I don't think any air valves were fitted on the system. Plus I was recently up at the panels replacing some insulation on the pipes since the birds had pecked it all off and I didn't notice any valves up there either.

The plumber who installed it all is very good, but I know on the day he installed what he was told to install. But he is pretty impossible to get in touch with and so I can't rely on him. The company he works for, has him all over the country doing installations. So I'd rather get someone close to me.

Thanks saihbne for the contact details. I'll give them a call to see.

You could be right that I just need a service.........and a new control panel, which I can fit myself. The day they installed my system, the electrician had a car accident and didn't make it down, so I wired up the panel myself. It was pretty easy. I have the user guide for the panel, it's pretty featureless.

Oh, the pressure in the system is currently 2.2 and has been for a while. Remember checking it before.

AlanD

Problem sorted. The contact I was PM'd came today and repumped the system to take the air out. It's possible it was in there since the last time I had someone here who replaced a flow meter. All working well now.

So in terms of control panel, is it worth installing a control panel that has holiday functions, anti-freeze functions?

PeteHeat

Hi,

If you are using water instead of glycol then you will need an anti frost setting, the problem with this setting is it works by activating the pump at 2 degress C to send warm water to heat the collector.

So any gain harvested during a winters day goes to protect your collector, depending on the general weather conditions you could use more energy than collected to protect the system which is why I will not use water as the transfer medium, glycol does not need this feature.

Holiday settings can be useful however if you fit a heat dump you should not need a holiday setting.

.

saibhne

AlanD wrote: »

Problem sorted. The contact I was PM'd came today and repumped the system to take the air out. It's possible it was in there since the last time I had someone here who replaced a flow meter. All working well now.

Great stuff - glad it worked out.

quentingargan

PeteHeat wrote: »

Hi,

If you are using water instead of glycol then you will need an anti frost setting, the problem with this setting is it works by activating the pump at 2 degress C to send warm water to heat the collector.

So any gain harvested during a winters day goes to protect your collector, depending on the general weather conditions you could use more energy than collected to protect the system which is why I will not use water as the transfer medium, glycol does not need this feature.

Holiday settings can be useful however if you fit a heat dump you should not need a holiday setting.

.

Hi Pete,

I broadly agree, but as an add-on, I reckon both depend a bit on where the coil is. If it is right at the bottom of the cylinder, then by the time the panel is freezing, you will have used some hot water, and the water around the coil will be at ambient temperature, so the extent of the heat loss is negligible and will be brought back to ambient by heat coming from the bottom of a copper cylinder. I'd always recommend glycol for flatplates as they will freeze more frequently - also if you have a heat dump rad in the loft. But if you have vacuum tubes in the south of the country, probably just as well to use water. But boil it first to de-gas it.

Holiday settings are also somewhat useless if the coil is right at the bottom of the cylinder - it will only cool a small fraction of the cylinders contents, and once again the system will stagnate the following day.

Q

AlanD

Thanks for the advice guys.

My system has anti-freeze in it, or that's what he called it. It was something added to the water so it should be ok for freezing.

But in terms of stagnation, I think on subsequent sunny days we do get to stagnation quite quickly. So my tank is full of hot water, say it's at 60 degrees (max set to 80) and the next day it's sunny and it continues to heat. It might get to 65 or so and then the whole thing shuts down. The reading for T1 at the roof goes to 255 and the pump fails to come on. I have to manually turn on the pump to get things moving again and the T1 temp comes down. But it can hit 255 quite quickly again preventing the pump from coming on.

What is this?

quentingargan

AlanD wrote: »

Thanks for the advice guys.

My system has anti-freeze in it, or that's what he called it. It was something added to the water so it should be ok for freezing.

But in terms of stagnation, I think on subsequent sunny days we do get to stagnation quite quickly. So my tank is full of hot water, say it's at 60 degrees (max set to 80) and the next day it's sunny and it continues to heat. It might get to 65 or so and then the whole thing shuts down. The reading for T1 at the roof goes to 255 and the pump fails to come on. I have to manually turn on the pump to get things moving again and the T1 temp comes down. But it can hit 255 quite quickly again preventing the pump from coming on.

What is this?

PLEASE DON'T DO THAT!!!
You have no heat dump. If your cylinder is up to temperature, the system has to shut down (known as stagnation) to prevent overheating your cylinder. The pump stops and the water in the panel boils, turns to steam and is sent into your expansion vessel. You should never manually turn on the pump when the panel is above boiling point.

The problem with stagnation is that it rapidly degrades anti-freeze, makes insulation near the panel very brittle, puts undue pressure on fittings and shortens the life of many systems.

I prefer to see a heat dump - usually a high temperature 3 port valve on the solar circuit and a divert radiator. This can be managed by most controllers, but is seldom fitted because it adds a few hundred euro to the cost.

Retrofitting such a heat dump is a bit more work as you have to drain the system etc. There is another workaround sometimes used which runs a pump on the top coil in the cylinder to cool the cylinder. That way the heat is dumped into your boiler or into radiators, but if you later fit zone control valves on all this, you have to bear this in mind.

Q

AlanD

So, when the panel reads to 255 and the pump doesn't turn on, are you saying that that is ok?

If that is the case, why won't the tank reach the higher temp I have it set for?

quentingargan

AlanD wrote: »

So, when the panel reads to 255 and the pump doesn't turn on, are you saying that that is ok?

If that is the case, why won't the tank reach the higher temp I have it set for?

Well, I don't think it is OK, but most installers do. The panels are made to withstand these temperatures and have to do so in the event of a power cut, but I prefer to see heat dumps.

But there is something else wrong if the tank won't reach the higher temperature first. The shut down should only happen after your cylinder has reached the temperature you have set.

If there is a problem with your flow rate, then there is a possibilty that the panel will reach its max temperature (usually a default of 140) because the circulation isn't good enough to dissipate the heat. That may be your problem. Q

AlanD

quentingargan wrote: »

If there is a problem with your flow rate, then there is a possibilty that the panel will reach its max temperature (usually a default of 140) because the circulation isn't good enough to dissipate the heat. That may be your problem. Q

This could be the problem. I did have a problem with my flow rate as the system had a load of air in it, which I sorted out this week and have the system flushed out of air and replaced with more fluid. The pump and flow have been working perfectly since. So I'll wait for a run of hot days to see how it works out.

Actually, now that I think of it, I got the 255 readout last weekend when the tank was only 47 degrees or so. The flow was not good that day. But we're good now, so hopefully that sorts out the problem.

Thanks for your advice.

Kevinjh

AlanD wrote: »

Problem sorted. The contact I was PM'd came today and repumped the system to take the air out. It's possible it was in there since the last time I had someone here who replaced a flow meter. All working well now.

So in terms of control panel, is it worth installing a control panel that has holiday functions, anti-freeze functions?

Hi Alan D, I think I have air in my solar hot water system, was the plumber you got to pump the air out expensive?

Kevinjh

AlanD

Kevinjh wrote: »

AlanD wrote: »

Problem sorted. The contact I was PM'd came today and repumped the system to take the air out. It's possible it was in there since the last time I had someone here who replaced a flow meter. All working well now.

So in terms of control panel, is it worth installing a control panel that has holiday functions, anti-freeze functions?

Hi Alan D, I think I have air in my solar hot water system, was the plumber you got to pump the air out expensive?

Kevinjh

Hi there,

I don't think it cost a lot if I recall. Had to pay for some fluid and then he pumped all the air out. Been fine since.

No more than 100/200 but that's a guess.

Kevinjh

Hi Pete Heat,

I have a solar tube system about four years old, the roof temperature can sometimes be about 16'C higher than the temperature on the dials in the hot press, ie. temperature drop of about 16'C from roof to entering hot press cylinder, would that indicate air in the system and if so is there an easy way to remedy it?

Kevinjh

quentingargan

Kevinjh wrote: »

Hi Pete Heat,

I have a solar tube system about four years old, the roof temperature can sometimes be about 16'C higher than the temperature on the dials in the hot press, ie. temperature drop of about 16'C from roof to entering hot press cylinder, would that indicate air in the system and if so is there an easy way to remedy it?

Kevinjh

If you have a pump station, there is usually a glass flow gauge so that you can see what the flow rate is. Could be a small amount of air, but there are other possible causes.

Sometimes a wide temperature gap like that is because of either a poor quality coil in the cylinder, and/or wrong settings on the controller.

If you have a large array of panels, and the coil is a standard coil, it can be hard for the coil to dissipate the heat. Also, I wonder if you have a lot of lime in your water? It is possible if the system has been running at high temperatures that the coil has limed up a bit. In areas with lime in the water, it is better not to let the system go above 60C. Some installers let the cylinder go up to 75 or 80 without taking a peep at the kettle to see if the area has a lot of limescale.

Have a look at the flow meter and check the temperature difference at which the pump is switching on and off.

Has this problem come into the system more recently, or always been there?

One other thing - if the system regularly goes into stagnation, the antifreeze can become a bit sludgy. The normal time to change out antifreeze is five years, but if there is no heat dump (and usually there isn't) and the system regularly gets to max temperature, the antifreeze may degrade.

Kevinjh

Thanks Alan D,
I contacted a solar plumber and he is to come over and replace the fluid in the system and as you advised he said it will be about €150,

Kevinjh

Kevinjh

Thanks Quintengargen,

A plumber looked at my system and advised that the fluid needs replacing as after a few years the fluid looses its ability to bring the heat down from the roof efficiently,

Kevinjh

PeteHeat

Kevinjh wrote: »

Hi Pete Heat,

I have a solar tube system about four years old, the roof temperature can sometimes be about 16'C higher than the temperature on the dials in the hot press, ie. temperature drop of about 16'C from roof to entering hot press cylinder, would that indicate air in the system and if so is there an easy way to remedy it?

Kevinjh

Hi Kevinjh,

Sorry for the delay getting back to you unfortunately I was not available to go online as a family member was ill and subsequently died.

Hopefully everything back to normal on Monday.

I see you have some very good replies.

.

Kevinjh

Hi Pete Heat,
Sorry to hear your news, my plumber is due to call over on Monday, it is still working meantime, but probably not as efficiently as it should be, a bit like boiling a kettle with the lid off.
Kevin