solar DHW system - repressurising?


Postby Ian G » Mon Jun 08, 2009 7:16 pm

I'm after a few pointers on how to refill / re-pressurise our solar powered hot water system

It's pretty standard, with a dual core hot water tank, an expansion vessel in the loft with evacuated collector tubes on the roof.

A year ago, it had conked out (collectors boiling away at over at 130 degrees) with no heat geting in the tank.

the company who fitted them diagnosed it was out of solar transfer fluid, so they refilled it with basically ethlyene glycol, using a pump.

But they've since gone bust, so we can't get them round to do this again.

But having watched the bloke do it last year, it seems pretty straight forward: the filling point is isolated with a ball valve, and has a simple compression join.

So, does anyone have any tips, or pointers about how to do this?

Is there anything I should watch out for? Or should I just steer clear and get a solar specialist round to have a look?

Having said that, it's not actually cost effective to repair the system - we'll probably just leave the damn thing switched off, given how poor savings it returns. The £155 the company wanted to charge us last year massively outweighed any possible savings!!

thanks

Ian
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Postby cmhicks » Tue Aug 11, 2009 3:31 pm

Ian,

did you get anywhere with this? I have just bought a house which has a 25-year-old solar water heating system installed, about which I have very little information.

I have reverse-engineered most of how I think it is supposed to work, but it almost certainly needs refilling/repressurising - there's a pressure gauge on the (sealed) solar circuit which reads well under 1 bar - and certainly needs anti-freeze of some sort in it.

Thanks in advance,

Christopher Hicks
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Postby Ian G » Thu Aug 13, 2009 6:11 pm

Hi there

yes, I did get somewhere with it.

The fluid: what I needed was propolyene glycol. However, for convenience (and cost) I used distilled water from a car parts shop. Nearer winter I'll track down some proper anti freeze.

How to pressurise the system:

my system is 15mm copper tubing. I had a T-junction plumbed in, with a ball valve isolating a short capped off piece of tubing. So I had a way of getting into the circuit.

I then dug out a garden sprayer I had. I got it from Lidl for £10. The hose of this connected to 8mm brass piping. What I did was go to a plumber shop and get a 8mm - 15mm connector. I soldered a short tube onto the 15mm end.

I then soldered this onto the end of my garden spray. the garden spray hose would now fit into the system with a compression joint.

I filled up the garden spray with distilled water, and pressurised it to 2 bar. I made sure the water was right to the end to get rid of any air,

Then, I fitted this end of the garden spray to the solar circuit, tightened it up, and opening the ball valve

Pressing the trigger pushed the water through the hose, and into the solar circult. I could hear it filling up, and saw the pressure gauge move.

As the system got fuller, the gauge increased. I had to keep the pressure on my garden spray up. Eventially I reached the 2 bar mark, which indicated the system was full of water.

I have a bleed valve cap, so I made sure any air was out, and topped it up.

then, I just closed the ball valve, and disconnected the hose.



the system did work well for a few weeks, holding at 2 bar, but gradually lost pressure again down to one.

I had previously made sure the expansion vessel was at 1.5 bar - it had dropped to 0.7 bar.



I hope this helps - it confirmed that filling some copper tube full of water is not fundametnaly difficult. like most DIY, you just need the right tools.


It all depends how your system fitter approached this and how they left capacity for the system to be filled.

Ian
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Postby cmhicks » Mon Aug 17, 2009 3:59 pm

Thanks. Very helpful.

CH
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Postby plumbbob » Mon Aug 17, 2009 8:38 pm

Are you sure they used Ethylene Glycol as the antifreeze? Ethylene Glycol is good for protecting car engines, but does have the downside of being rather toxic. Given that hot water cylinder coils can fail, there must be a potential for the DHW becoming contaminated with it thus resulting in a possible health risk.
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Postby cmhicks » Tue Aug 18, 2009 10:14 am

Seems to me it's no worse than having Furnox in the radiator circuit, which also has the potential to leak into the DHW if the heat exchanger coil fails. In fact, I found that Furnox makes a combined antifreeze and corrosion inhibitor which looks ideal.

CH
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Postby chris_on_tour2002 » Wed Aug 19, 2009 8:33 am

"Seems to me it's no worse than having Furnox in the radiator circuit" - the point is that Fernox is non-toxic as there is a risk of cross contamination with your domestic supply.

antifreeze isn't non-toxic.
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Postby Fixter » Mon Aug 31, 2009 8:44 am

Use can try using 'Tyfocor L'. Its an inhibitor, anti-freeze and enhances heat transfer. Obtainable from Barilla Solar ( on the web ). If your pressure is reducing, clearly there is a leak. I am running my solar system a 1.5bar.
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