Solar cylinder trouble?

mad m

Recently got a solar package, cylinder is dual coil etc. Had a couple of leaks from cylinder on solar pipe. Lads came back and fixed it. But then noticed my pressure gauge was at zero. Got them back and they replaced expansion vessel. Re-pressurized cylinder at 2bar. They said it might go up and down according to heat from pipes etc. Noticed other night the pressure gauge was at zero but during the day this might go up to over 5bar then as the night comes it drops to zero again..

Is this normal or should it be at 2bar all the time. I rang them and told them this but they were onto manufacturers of the cylinder and they said this is normal..

I just thought because a system like this should be pressurized?

bertie1

The pressure is dropping down at night because the system is cold ( especially the last few nights ) , it is rising back up to normal during the day when the weather outside is ok & when the sun is shining & the system is getting hot the pressure increases again . You see the same thing happening with the pressure guage on a gas heating system ( low when the system is off & high when its on ) . The expansion vessel is put into the system to cope with the changes in pressure.
The system I have in my house is set to 1 bar & it increases to just over 3 when the sun is shining & the solar panels are working full belt.
It sounds to me like it it is working ok

mad m

But does yours ever drop to zero?

bertie1

I have them put into 2 houses. The one at home doen't go all the ways back to zero when its freezing but does go down betwen 0 and 1 bar when it is. When the system is stable & cold ( panels not yet working early morning )it is at 1 bar. In the second house we own ( a holiday home) it does go to zero,and usuallyfluctuates between 0 and 1 bar but I have also noticed that there is a small bit of air still in the system ( it hasn't worked its way out yet) , you notice it when the system starts up first and before anybody asks yes there is an automatic airvent on the highest point of the both systems. The solar panels are in the second house since September 2008 and perhaps haven't got a lot of use since installed.

rayh

A solar system is an enclosed fliud circuit with and expansion cylinder (kinda like a ballon) into which excess fliud enters when the system fluid heats or expands.

The size on the expanion cylinder should match the range of expansion that the circuit is likely to experience. Therefore, capacity of the circuit, working temperature range or rate of expansion and capacity of expansion cylinder are all related.

If you are having large pressure variations, you are likely to have too small an expansion cylinder or extreme temperatures and my guess is too small an expansion cylinder

copper12

i
If the system pressure increases to 5 bar at this time of year; what will happen during the summer?
5 bar seems way too high for a solar system
Your expansion vessel is to small if the system pressure goes above this 3 bar
There should be a safety valve that releases the pressure if it reaches 3 bar
What are the specifications of your system

mad m

300 litre stainless steel dual coil cylinder, 3 solar panels...All windhager.

copper12

http://www.ribaproductselector.com/Docs/3/24323/external/COL724323.pdf?ac=

operating pressure can be as high as 10 bar according to the above
With a recently fill system I would expect the pressure to drop as the air is expelled
Might need a top up there should be a filling loop fill to one bar and Waite and see

SolarHome

The pressure difference that you are recording seems irregular! Have you got a long run between panels and tank and with gauge is the pipework? This could be the cause of your problems. In my experience a .2bar change in pressure is what should be recorded during cold night time temps and around 3.5bar at 150C during summer stagnation. If you are seeing 5bar now your pressure release vave will blow off during the summer for sure (its usually 6 bar)

mad m

I think the distance from cylinder to panels is around 18-20ft. At moment I haven't seen any 5bar,at present its at 2bar, but tonight it will probably drop to 0....Obviously I'm getting pressure build up from sun and at night it drops. But I think I may have a slight leak somewhere...agh!

MickLimk

mad m wrote: »

I think the distance from cylinder to panels is around 18-20ft. At moment I haven't seen any 5bar,at present its at 2bar, but tonight it will probably drop to 0....Obviously I'm getting pressure build up from sun and at night it drops. But I think I may have a slight leak somewhere...agh!

2 bar pressure variation at this time of the year really sounds like a problem with the expansion vessel. I'm going with rayh on this one - what size is the expansion vessel?

Seeing as it is a recent install, have you verified that you are getting some heating contribution from the system? Is there any chance that there's no circulation in your system? What controller have you in there?

nmacc

A pressure range of 0-5 Bar is too great for any normal mode of operation. The most likely explanation is that at the time of the first problem the diaphragm in the expansion vessel failed and the vessel filled with fluid, causing the pressure to drop to zero.

If the system was then presurised to 2 Bar when cold it would be completely full with no possibility of absorbing thermal expansion. Thus when the sun shone and the system heated up, the pressure would rise until, if it rose enough, it would trip the safety valve (opv). This would bleed off the excess fluid and when it cooled down the pressure would drop to around zero.

Obviously for that to happen there would be a discharge from the safety valve. If your system is filled with antifreeze there should be a collection vessel under the safety; if there is and it's empty and dry, then I'm wrong. Either way your expansion vessel is definitely not doing it's job.

It's fairly easy to diagnose unseen as it's a common problem with central heating systems.

mad m

The expansion vessel has a capacity of 25litres if thats any useful information for you. The expansion vessel has been changed to a new one when I started to get problems with pressure at start.

I felt under the solar pipe thats at the cylinder and my finger would be very very slightly wet. Looks like a leak again. I've a pain in my you know whats...

The pressure is at 1bar at present. The pressure release pipe is connected to a collector if the pressure gets to much, so the glycol can go somewhere other than my hotpress floor. Terrible oily stuff it is....

nmacc

25 litres is a good-sized vessel Des, and if it's been changed it should be fine. There are a couple of things:

The vessel should be charged when installed to the final required system pressure. 2 Bar is fine, but a 25 litre vessel may have been delivered at 3 or more. Even so, that shouldn't cause those symptoms.

It is not unknown for expansion vessels to not expand. That is, when new the membrane sometimes sticks to the casing and the vessel will not work until it's been pressurised to 5 or 6 Bar to force it away.

A third possibibility is that the system has been overheated, but that could only have happened with a decent period of sunny weather. If there is no heat dump and the system stagnates, then boiling steam can run back down the pipes. If the expansion vessel is too close to the collector the steam can reach it and melt the membrane, but this usually only happens if the vessel is within 2m of the panels.