Non-pressurised system

[erbus]

Having picked up the panel last year and fitted the solar tank with stove I'm ready to start the solar side of things.
I will be fitting the 20 tube panel  (indirect twin coil tank) soon and wonder can anyone help with a couple of queries:

Roof fixing - concrete tile over sarking board so cannot get s/s straps thru. Is the best way to fix simply to drill thru tile, sarking, joists and directly mount frame thru the lot with long s/s bolts?

I wish to fit the system non-pressurised (enough loft space for expansion tank). does anyone have a practical diagram showing the whole layout  including the best points for fill and vent etc.

any help would be most appreciated
thanks
david

[Antman]

Hi David - welcome to the fun!

Why would you opt for a gravity fed solar loop?  The pressurised loop is far simpler and removes the potential pitfalls of having a low-head gravity fed circuit.

You will need sufficient tank height above the height of the manifold to create a head pressure on the solar system - if not, removal of air (and possible airlocks on filling) will be a potential issue. Arguably, by the time you have installed a header tank, overflow pipe, mains feed, lagging jacket, built a platform for the tank to sit on etc, the £65 pressure kit will seem like a bargain   

Due to the low water content in the solar loop, unsuitable placement of conventional feed and expansion pipes could cause problems such as tank pump-over, sucking in air etc.

It would be interesting to hear other comments / opinions but:

I would use 15mm pipe to feed the solar loop from the tank, tee'd in below the pump and one-way anti-syphon valve in the Return pipe. Even if you use 10mm pipe for the solar loop itself, you must feed from 15mm otherwise filiing could be a problem with low head to the manifold. This will allow the loop to fill from the bottom up. Also ensure that the fill pipe from the tank has a general upward slope i.e. no horizontal runs to prevent airlocking.
Do not fit an isolating valve in the tank feed pipe.

I would not bother with an expansion pipe as per gravity CH systems - the tank feed pipe will perform both roles - but fit a pressure relief valve on the flow pipe near the manifold.That way if the tank f/e pipe should ever block or freeze, the PRV will operate. The PRV can also be used to vent the circuit at the manifold if placed on a short rising pipe from the highest part of the manifold flow pipe.

You can pour an appropriate quantity anti-freeze/inhibitor into the tank during final system filling (after leak testing and flushing).

Regards

Antman

[erbus]

thanks antman,

the main reason is i have very little room roundabout the tank for fittings also there is already an unused exp tank up high but as you point out maybe it is easier to go pressurised. I would still require an overflow (tundish) for the high pressure vent or are these 'normally' fitted outside by the panel?

also any ideas on the roof fixing as i cannot use the intended method due to the sarking.

another query, dumping excess heat. the indirect tank also contains a 28mm boiler coil (grav) for the stove. If the water went too high could i simply wire the ctrller to turn on the ch pump and circulate water around the cold stove and rad from the hw tank (reverse operation as it were).

thanks again
david

[Antman]

David

The only problem with fitting the PRV outside on the roof is future access. Better to have 'mechanical' devices where you don't need roof ladders/scaffold towers etc 
You still have to duct the PRV outlet vent pipe to the outside though. A tundish is used to act as a visual indication of outflow and, when placed near the point of exit from the wall, guards against freezing of the drop-pipe in winter should the valve develop a continuous flow/seep.

Paul Boats has just used a direct through tile fixing method on his installation see http://navitron.org.uk/forum/index.php?topic=1426.msg9818#msg9818. This seems to work perfectly OK. Just seal the fixing holes from both sides with good ol' silicone sealant.

As regards the dump, yes that is ideal. It's basically the same principle as I used except I have a gas boiler and coil instead of stove. And it is very effective. You only need 0.5 deg C differential between AHO and AHF on the BS controller.

Regards

Antrman

[erbus]

thank you for that, will check out the other thread.
 ref aho/ahf will uncover that stone when i open the ctrl box!

cheers
david

[lightfoot]

Hi erbus,

I assume you have connected your wood stove (by gravity) to a open vented hot water cylinder and not a unvented mains pressure one?  And that the wood stove & heating circuits are open vented too, it's just the mention of a unused expansion tank in the loft has made me a bit nervous.  Maybe I have just got the wrong end of the stick !

You mentioned running your central heating pump to circulate water around your gravity fed wood stove to act as a heat dump.  I don't know how you have connected it all up, but I'm not sure how effective that would be as your pump may just short circuit around the back boiler of the stove and not drag any heat from your cylinder.  Or in other words follow the least path of resistance.  If you have fitted a injector tee on the return from your heating circuit then this may help things a little.

Lightfoot.