Solar question

micky p · 12 Sep 2006

lcgs said:
The main problem with solar is stagnation. this is where the pump stops and the fluid turns to steam, by ensuring that the water in the cylinder is at low temps all the time your system will stagnate very quickly.Stagnation causes abreakdown of the glycol mix which you will have to change more frequently.

this is why it is very important to size your cyclinder and the amout of collectors you need. Even when sized correctly it still can be a problem tho i admit.

On mine once the panles have got to 120deg c you can divert the heat to another source via a second pump. You can either pump it to a swimming pool via a heat exchange or another cyclinder. Thing is i don't have a swimming pool or a second cyclinder. I'm thinking of adding a smaller single coil indirect cylinder to the system to heat up once the first cylinder is heated to try and stop this stagnation and link both cylinders together in series.

Biggles.. · 12 Sep 2006

What agile is suggesting with the stats is not uncommomn in solar system and by no means special. most modern systems have 3 stats,1 on the panel, 1 at the bootm of the cylinder one at the top plus your existing cylinder stat. The 6 degree diference(variable setting on solar controller) is to stop the pump cycling when the panel is hotter than the bottomof the cylinder.top stat is there to let you know water temp in cylinder to calculate solar gain.
if your spending the money on solar take the time to get it right, dont send preheated water to a boiler that wont accept it and in doing so invalidate any warrenty that maybe on the boiler. Go for a sealed system like Micky P suggests not just for his reason but also to save on instal time and space(you get enough bits with solar kits as they are without F&e tanks)

croydoncorgi · 12 Sep 2006

You need to differentiate 'drain-back' systems, which have NO fluid in the panels when 'idle', and 'pressurised' systems, which keep fluid under pressure to stop it boiling and keep the panel (or mainfold) full all the time.
I think I'm right that both types MUST include safety deviceto PREVENT circulation when the panel is ABOVE a preset max temperature.

Biggles.. · 12 Sep 2006

Flat panels have this feature, but evacyated tubes allow the heat to build up as long as water requires heating. Not unknown for tubes to hit 160degt and the pump still runs. Some manufacturers have had there tubes upto 300deg with the pump running during testing. This is why most manufacturers of tubes insist pipework is brazed to ensure solder joints dont melt.
PRVS are fitted to all panels and tubes and are generally the same as the type used on boilers being set at 3bar plus there is normally another PRV at the pump station should the one on the roof fail, but if this operates you really are in hot water.

ChrisRoberts · 12 Sep 2006

lcgs said:
Flat panels have this feature, but evacyated tubes allow the heat to build up as long as water requires heating. Not unknown for tubes to hit 160degt and the pump still runs. Some manufacturers have had there tubes upto 300deg with the pump running during testing. This is why most manufacturers of tubes insist pipework is brazed to ensure solder joints dont melt.
PRVS are fitted to all panels and tubes and are generally the same as the type used on boilers being set at 3bar plus there is normally another PRV at the pump station should the one on the roof fail, but if this operates you really are in hot water.

Or hot glycol.
When I was working for a solar company they ordered new pump stations with a sight glass in them. These were supposed to be made from Pyrex. But something got lost in the translation and the germans made them of perspex! PMSL. This resulted in quite a few, well all, of the systems that had been fitted bursting and spraying hot glycol all over peoples airing cupboards, lofts ect.....
Not nice. espesially when the panels were getting to 180C.

billy bob · 13 Sep 2006

The PRV that are fitted to solar systems are not the same as the ones on boilers, they should be made to a higher temperature rating, everything on solar systems should be designed for the purpose of solar and not every day heating equipment.
Chris Roberts, when you say a sight glass I assume you mean a flow setter or tachometer, again if these were bursting they were obviously not designed for solar temperature.

micky p · 13 Sep 2006

lcgs said:
Flat panels have this feature, but evacyated tubes allow the heat to build up as long as water requires heating. Not unknown for tubes to hit 160degt and the pump still runs. Some manufacturers have had there tubes upto 300deg with the pump running during testing. This is why most manufacturers of tubes insist pipework is brazed to ensure solder joints dont melt.
PRVS are fitted to all panels and tubes and are generally the same as the type used on boilers being set at 3bar plus there is normally another PRV at the pump station should the one on the roof fail, but if this operates you really are in hot water.

Viessmann send compression fittings for this reason but with copper liners to put inside copper tube

so you can really tighten the fittings up.

billy bob · 13 Sep 2006

The reason for the inserts is not so you can tighten the joint more, but to act as a support for the tube, with the high temps that can be reached the expansion and contraction of the tube is larger than on a heating system, the inserts support the tube wall to prevent it from distorting and causing leaks.
All solar systems should be either hard soldered, compression with inserts, or press fitting with Viton o-rings, soft solder should never be used because of the high temps.

micky p · 13 Sep 2006

billy bob said:
The reason for the inserts is not so you can tighten the joint more, but to act as a support for the tube, with the high temps that can be reached the expansion and contraction of the tube is larger than on a heating system, the inserts support the tube wall to prevent it from distorting and causing leaks.
All solar systems should be either hard soldered, compression with inserts, or press fitting with Viton o-rings, soft solder should never be used because of the high temps.

I was told by viessmann on there training course that the inserts were there so that you can really wind the compression fittings tight and not distort the copper.

But yeah never use solder fittings on solar.

Biggles.. · 13 Sep 2006

Worcester allow solder fittings with unleaded solder, vaillant only hard solder, Suhco allow unleaded. All state no soft solder. So varies between manufacturer. If using compression fittings dont use any boss white etc, it contaminates the glycol.Glycol should be checked every year for viscosity and using a refractometer.

micky p · 13 Sep 2006

lcgs said:
Worcester allow solder fittings with unleaded solder, vaillant only hard solder, Suhco allow unleaded. All state no soft solder. So varies between manufacturer. If using compression fittings dont use any boss white etc, it contaminates the glycol.Glycol should be checked every year for viscosity and using a refractometer.

i have just changed the glycol in mine as Viessmann reccommend every 2 years it should be changed.

billy bob · 13 Sep 2006

lcgs said:
Worcester allow solder fittings with unleaded solder, vaillant only hard solder, Suhco allow unleaded. All state no soft solder. So varies between manufacturer. If using compression fittings dont use any boss white etc, it contaminates the glycol.Glycol should be checked every year for viscosity and using a refractometer.

Unleaded solder IS soft solder

ChrisRoberts · 13 Sep 2006

billy bob said:
Chris Roberts, when you say a sight glass I assume you mean a flow setter or tachometer, again if these were bursting they were obviously not designed for solar temperature.

Well no they were made from perspex. Not Pyrex.

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