Banging solar system - pressure problem

mct1

Hi, I'm hoping someone will be able to advise me. We have 2 panels of evacuated tubes on the roof - been there happily working away heating our water for nearly 4 years. Then about 12 months ago we noticed the pressure had dropped. All was well until last month when on a hot day the panel started making an almighty clanking noise, like someone using a sledgehammer in the loft. It settled when I turned the electrics to the pump off.

So we called in a plumber who drained down and refilled the system, tightened some of the plumbing connections to the tank and charged us €150. The pressure dropped again within a few days and we found a tiny leak in the hot press, but the plumber was always "too busy" to come back.

So a few days ago we decided to call back the plumber who installed the system - he ran a few checks and tests, which were all normal, drained the system again, removed the air valve that he reckoned shouldn't have been part of the system to begin with, and said see how that goes.

Today the system started banging again - not as loud as the first time, but most definitely there. So once again I turned off the pump electrics.

Any bright ideas anyone? Our plumbers so far don't seem to be solving the problem, but they are costing us money we don't have in this economic downturn.

Thanks

heinbloed

Well, as long as the problem isn't solved by the plumbers then you shouldn't pay them.
From what you describe - and I'm only guessing here- there is air in the system. "Air" in this case means gas. This could be atmospherical air or as well evaporated water, steam. The pump isn't able to pump the steam and stagnation occurs.
The same problem can occure with a central heating system. Loss of pressure leads to a low boiling point (100 degrees Celsius) which leads to steam which leads to a spinning-but-not-pumping pump modus.

So find the leak and fix it.
The air remover (air valve) is a MUST. Your installer who said it should not be installed could be incompetent.
There are two different air valves with a closed(pressurised) ST system: automatic ones and manual ones. Since these valves should be installed at the highest point of a ST system the standard choice is the automatic air remover. Due to lack of easy acess to the roof , where usualy the highest point is to be found,the manual air remover is rather useless up there.
So an automatic one is used there.
Unless one want's to call the plumber every couple of weeks who climbs up and releases the air there manually.
You would need a special ST air valve for the ST system, the standard central heating system valves for €5.- won't do, they're useless for this type of stress and will fail very soon.
Note as well that PTFE tape (the white sealant tape) should not be used with ST installations containing glycol. The PTFE is not glycol resistant.
Only sealant material designed for the purpose should be used, otherwise you will have a permanent leakage problem with the installation.
Any plumbing shop will sort you out with the material.

And again: don't pay plumbers who are incompetent.

Good luck.

PeteHeat

There may be a problem with the pressure vessel causing the pressure to drop, using a process of elimination check all joints both inside and outside.

How is the system being filled manually or with a pumped filling station ?

There is a difference, manual pumping can leave air in the system, the professional filling station in the right hands does not.

Pressurised systems should not be drawing air into the system, being incompetant we don't use air vents.

I hope the above is of some help,

.

heinbloed

PeteHeat wrote:

Pressurised systems should not be drawing air into the system, being incompetant we don't use air vents.

Why than are radiators equipped with an air valve, why do boilers have them?
Sure, the rest of the plumbing world has no experience with pressurised systems...

PeteHeat

PeteHeat wrote: »

There is a difference, manual pumping can leave air in the system, the professional filling station in the right hands does not.


.

We don't use a filling station for central heating systems.

heinbloed

@ PeteHeat:
There is a physiological phenomena called "diffusion", a mixing of gases and liquids. This diffusion happens all the time in all water(liquid) containing plumbing systems.
Therefore automatic air release valves are included in all closed loop plumbing systems. State of the art in the heating industry, not to include air release valves is bad workmanship.
This diffusion can't be stopped by choice of material, only reduced. But not stopped.
Most plumbing material manufacturers give the diffusion rate of their pipes, sealants, joints, bits and pieces, it's part of the EN (European standard) and must be stated at the material data sheet.
Sooner or later there will get enough air in form of micro bubbles into a ST system, therefore a micro bubble seperator is a vital part of most solar stations. This air separator either works manually (one opens the valve by hand) or automatically.
The problem the OP seems to be confronted with is that in his ST system
large air bubbles are present in the system.
This can have several reasons: either the manual valve wasn't installed(!), not used or an automatic airvalve failed.

Whatever the micro bubble air valve on a ST station is doing: there must still be an air valve installed at the highest point. Which is to be found at the solar collector in many, most cases.
This second air valve is necessary because during stagnation - for example at night time - micro bubbles are doing what the laws of physics demand them to do: they travel upwards. To the highest point. And unite there to form a big bubble.
These big bubbles will then be pushed more or less in one unit through the system once the pump starts again, some air will stay in bends, some at the highest point.

Air bubbles work like CO2 in a champagne bottle, they get compressed and and they expanded. They pop.
This could cause the "banging" of the system observed by the OP.

The filling method you have described does not hinder diffusion to happen. No filling method does.
Not to install airvalves is an amateur's fault. Plumbers understand the laws of physics and know how to cope.
As long as air valves are installed in a closed loop heating system and the pressure is maintained and the system not overheated (steam!) no banging will occure.

Check the ST material suppliers lists, they all have these ST air valves available.

Now I would say you have a lot to do (smiley).
Contact your clients and make appointments to install the valves - at the highest point. They'll understand.....
With a faulty installed system, where parts are missing, the guarantee stays forever, so free of charge this job is. Including the refilling of course. Tell your clients that a loss of energy can be compensated as well, at least under EU consumer laws.

PeteHeat

Hi,

We don't use water, we don't over size systems, we don't have any outstanding complaints.

To OP

The fact that your system worked for four years without visible problems and was recently re-filled (eliminating air) and no leaks are visible is why the pressure vessel is high on my list.

Even with a faulty pressure vessel the plumber could have filled system achieving the correct pressure, however when the fluid heated and expanded the system could lose pressure again.

.