solarthermal air vent

[watford 99]

The air vent at the high point in my solar thermal system, has what looks to be, a ball valve incorporated which seems to be in the closed position as the operating lever is horizontal. If the valve is closed does this mean it is only there to be opened when the system  is being filled? I had rather assumed that such a vent should be able to release air from the system all the time.

[greentangerine]

I think that's normal; when I installed mine the instructions said to close it once the air had been bled. 

[desperate]

I like the idea of using some kind of valve as an air vent, all my systems have  gate valves in them to enable me to drain and also  connect the garden sprayer pump in various places, this give me full control of air bleeding, flushing and filling the pipework.

Desperate

[watford 99]

Thank you greentangerine & Desperate for your interest and information. I would very much appreciate your experience Desperate when you flush and refill your installation as I need to do the same.

 I will purchase a garden spray type filling bottle but I would be very pleased if you could tell me how you go about draining down all your pipework if, as with mine, the hot water tank with heating coil is below the pump station draining point. If I connect the bottle to the filling outlet and pump it up will this force all the old antifreeze mix out of the system? Also, can the system be flushed with just water or is it really necessary to use Sentinal R200 or something similar?

My system was installed in 2006 or thereabouts but the heat transfer liquid, as the experts call the antifreeze mix,  has gone brown and the circulating pump keeps stalling. I may,of course, have a controlller and/or pump problem as the pump became very noisy when it started to play up. However, I think I must try a flush and refill first to see if this restores things to normal. I really am in need of advice as the cost of paying someone to do it all for me would, I fear, cause another banking crisis.

[desperate]

Hallo Watford99,

First of all you need to drain down the pipework anyway you can, ie loosen a connection on the hot water tank coil or something, a drain valve halfway up the system by the pump isn't much good. Then you need to consider where the low and high points of your system are, and tee into the pipework and fit a standard 15mm gate valve, bearing in mind where the air is naturally going to rise to, and where the fluid will want to drain to. Also it is well worth having an upstand of 22mm pipe above the pump, about say 30 cm long if you have room, to collect air. Fit a gate valve at the top of this upstand, this will make absolutely sure that no air is trapped in the pump, a sure fire cause of failed pump bearings resulting in the noise you hear. Just above the pump tee off this 22mm pipe and continue the pipework on its way to your panel, this then creates a natural trap for air which you have access to.

Now if you buy a garden pressure sprayer, get one that has a rigid plastic pipe with the sprayhead attached to, the Hozelock one has an 8mm fitting on the handle which is ideal. Then using standard plumbing fittings you will be able to connect the pressure bottle to your gate valves, I used a piece of 8mm microbore onto an 8*15mm reducer and a short length of 15mm pipe with a compression olive and nut on it, piece-a cake.

Now because the spray bottle has a dip tube inside by pressurising the bottle when nearly full of antifreeze solution you can force the fluid into the system, then by releasing the pressure from the bottle vent, fluid will flow from the system back down the dip tube flushing out and separating the air with it. Repeat this a few times at each of the gate valves you carefully positioned around your system, and no self respecting air bubble stands a chance. This will help your antifreeze and pump last for years.

I think if you flush the system a couple of times with clean water you will be fine, there is not going to be any real horrorbility in it that would need any chemical agents. Whilst flushing the system make a note of the capacity using the graduations on the sprayer bottle, this will help you work out how much antifreeze you need. Then finish off with a 20% solution of sentinel x500 antifreeze and your sorted.
The whole process is a lot easier to do than describe, once you have done it a couple of times it's no sweat.

Best of luck.

Desperate

[greentangerine]

Our hosts sell a suitable piece of kit to fill and pressurise your system; I have one.

http://www.navitron.org.uk/product_detail.php?proID=70&catID=122

Just buy the correct antifreeze and flush through slowly until it comes out clear, then close the output valve and pressurise; you won't waste much.  Not sure about using water.

Refilling every two years should be about right; if you stagnate too often then this will reduce the life of the fluid and turn it brown earlier.  The vapour produced during stagnation will escape through the auto air vent, hence why it needs to be closed.  If you don't do this, then it'll be lost rather than recondense so you'll have to keep repressurising / filling up.

I leave the top auto air vent open for a few weeks and then close; my pump station also has a device which catches the bubbles - about a month sees them disappear.

[ecogeorge]

Forgot to close my auto vent . Took ladders down. Seems to be ok left open-no loss of pressure!
rgds George

[Stuart]

I take the top off my vent to add antifreeze, if you leave it in the open position, and the plastic cover top unscrewed a bit this is what happens during stagnation.
http://www.youtube.com/watch?v=Dz43quDBPr4

[ecogeorge]

Thats why I fitted 12v pump and own pv panel with small 12v battery.No need to worry about power cuts or part P certification. Simples squeak.

[greentangerine]

Thats why I fitted 12v pump and own pv panel with small 12v battery.No need to worry about power cuts or part P certification. Simples squeak.

If your system is sized so that you get a decent amount of output for about two thirds of the year, then stagnation and/or a heat dump is part of the design.  A 12v pump/PV panel  is only useful if the heat can actually go somewhere.  A swimming pool is ideal.

[watford 99]

Thanks to all for passing on your knowledge and experience to me. I will bear it all in mind as I flush out and refill my solar thermal system. I would however add the following comments: The system was installed in 2006 or early 2007. It was already installed when my wife and I moved in. It has 20 glass tubes on the bungalow roof, one of which is broken and open at the bottom, a plastic end plug having come out. The firm that installed the system has gone out of business and when I made tentative enquiries to see what it would cost to replace the tube I was quoted £300. Needless to say I did not proceed.

The system is now in trouble again with the pump playing up and I have been given telephone quotes of £200-£300 plus vat to refill, all this within 5 years of installation. The pump has been running for about 9600 hours all told.

As the system was already here when I moved in I suppose it can be said that I paid for it in the price of the bungalow. I have my doubts however if it will prove cost effective unless I am able to do all the maintenance myself and disregard the cost of my own time.

Thanks again everyone. I will be pleased to hear anybody elses experience.

Watford 99

[Baz]

Are these vents normally out on the roof out of reach without a ladder? seems a bit awkward. I would want a relief valve joutside and up there ok but a refilling vent off the top joint but taken down to a point near a window for the tap.

If the brown stuff is gunky I should arrange your fill and drain points such that you can flush through with plain watter to remove the goop. I wouldn't trust a gate valve to be airtight and you vent off in stagnation you need to check the pressure is still positive at night. If it drops below atmosphere it will suck in air and that's what reacts with the antifreeze & any iron fitting it can find like a pump to produce the brown stuff.

[desperate]

You're right Baz gate valves sometimes do weep a little, but we always put a short piece of copper in the outlet with one of those John Guest push fit caps on it, the big advantage of a gate valve as a drain is being full bore you can drain really fast and actually flush out the debris. How many times have you come across one of those drain cocks that has been tightened too far and rammed the washer inside the seat, then it all drains at dribble speed.

I think it was Antman that invented the air vent using a piece of 15mm inside a piece of 22mm to allow you to bleed the air at the manifold from inside the loft, it really works a treat.

Desperate

[watford 99]

My air vent is in the loft, quite close to where the pipes come through the roof tiles presumably from the manifold.

Watford 99