Buy a proprietary kit. Unless you are a solar designer/accredited installer. Anything else and you will be outside building regs and safety standards.

If you want to whisper me your design i shall be happy to take a look, but unfortunately neither I nor any other qualified solar installer can publicly suggest you use kit that is not certified and approved to standard. Otherwise you could say...'Well he said it would be fine...' And we would be hung, D & Q'd.

Posted By: an02ew: “3. Can someone recommend a reliable pump for a drain back system.”

I'm planning to try these first: http://www.solarproject.co.uk/page2.html

No idea of reliability, etc, but they seem to be plastic/ceramic so shouldn't have trouble with oxygenated water in a drainback system. Only 2 metre head though which could be a problem depending on your system set up (my panel manifolds will be just above the tanks) though I see he now does higher head ones.

“BS” stands for various things.

If DIY solar thermal has been banned in the UK then it's news to me.

Some fixed wiring needs to be signed off by a competent person. Pressurized systems of greater than a certain volume (forget what but more than most solar thermal systems & an02ew is planning on drainback which is typically not pressurised) needs a suitably qualified plumber. Roof loadings need some consideration.

None of this implies the need to use proprietary kit.

Crusoe, i am not totally mad, not yet anyway, i have the help of my old friend Mark a qualified plumber and ex solar thermal installer. The ex-bit stand for about 2 years out of the business. So a little rusty and he has no experience of drain back systems all previous were pressurized glycol.

Posted By: Ed DaviesOnly 2 metre head though which could be a problem depending on your system set up

Our head will be about 5M

Posted By: tonywhat is wrong with fully filled one?

We have decided to use drain back to save us money on coils as we are using 2 cylinders 1 dedicated DHW and 500l buffer should be a cheaper system all-round (see previous posts www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=9507&page=2#Item_5) where I think Crusoe was more than helpful in design my system (not so concerned about comeback)


Can we have a fully filled system that uses just the primary water and no glycol? Obviously inc an expansion vessel.

Drain back can mean that all the warm water drains out of the panel when the sun goes in and the PV-powered pump stops - then there's no standing warm water left in the panel to lose all its heat outwards, which then has to be re-heated when the sun comes out again. Not important when there's long periods of clear sky, but makes all the difference when the sun is coming and going.

It sounds to like you will have a heavy electric demand on the pump and should consider this in calculating the costs of running the system, again raise the drain back to just below the panels and again consider a fulled system?

it could if it didnt have to lift the water so high.

Posted By: fostertomThe pump can run on PV

Posted By: tonyit could if it didnt have to lift the water so high.

Eh?

Thanks Crusoe, glad to have you on board,

we have just install an 4x 20 tube array from "solar collect" say each bank is 3.5M gross or 1.89M aperture area.
I am planning say 210l DHW cylinder with back up 500L buffer and 1kw solar dump (a crude AGS) in the ground under our house. My good friend and old solar thermal installer Mark has express mild concern of overheat. But i have convinced him the AGS and buffer will deal with any overheat. Our system has to deal with all our DHW and have a good recharge, hence the oversize.

Posted By: crusoeA simple-but-effective, and last-forever S/S drainback ensemble is made by German firm PAW.

i have just seen the PAW drain back systems they look very good.

What do you think to mounting this PAW unit in the plant room (say 5M head) or under the panels in the roof? even if i do put the unit in the roof the pump still has to circulate to the plant room surly no great energy saving wherever I mount it.

Posted By: crusoeEd: Of course drainback is pressurised. Just because it is filled at atmospheric and there is no expansion vessel does not mean it is not pressurised.

Well, yes, in the silly sense that any plumbing full of water is pressurized; even 1 mm below the top of an open tank is above atmospheric pressure. But from the point of view of building regulations, etc, it's perfectly possible to have a drainback system (or pretty much any ST system, really) which is not pressurised in the same sense that a central heating system with an open fill/expansion tank is not considered pressurised (doesn't need special tickets and annual inspections, etc).

That's not commonly done with ST systems which are not drainback as it's often awkward to have the FE tank above the panels. Also, having a higher pressure allows the temperature to go above 100 °C (though I'm not convinced that's a good argument but let's not be distracted by that).

However, with a drainback system where the reservoir and the FE tank can be the same thing and needs to be below all the freeze-vulnerable parts it seems very sensible to me for it not to be a “pressurized” system in the regulatory sense.

The air volume above the fill-exit point in a drainback system will take up the slack as the fluid heats, but all drainback/flowback (pick your moniker) will have a PRV as standard...if supplied by an approved supplier.

I don't believe you. Central heating systems with an FE tank don't have a PRV; why should an ST system in the same circumstances?

If not approved - ie proprietary product it won't get signed off.

Really? What form of approval? It might make for more discussion with the BCO but I really doubt there's any specific rule which says you can't use any components which haven't been specifically approved by somebody.

What are you saying? Use non-approved product?

Yes, if you feel like it. E.g., I'd happily try the pump I linked to above even though there's nothing on the web page or in the video about it which says anything about any approvals. My guess would be that it might or might not have some sort of certification in China or wherever but not anywhere in the EC.

However, that wasn't your original assertion with which I took issue. Your wrote:

Posted By: crusoeBuy a proprietary kit. Unless you are a solar designer/accredited installer. Anything else and you will be outside building regs and safety standards.

Even if there was some “rule” that you had to use all “approved” components it wouldn't follow that you have to buy a proprietary kit as it could well be OK to source the components from multiple sources. Give or take issues with gas and pressurised systems a DIYer can self-install a central heating system without buying a kit, can't they? What's different about solar thermal?

Peter: Couldn't have put the DIY bit better myself - hence my caution in advising DIYers. There is no requirement for PRV in open vent in the UK, but in colder climates I do understand the precaution.

Ed: Your points in order:

1. No. Different issue. We are not talking static head of water - a known pressure - in open-vented systems. We are talking sealed system, with designed-in air gap - see PAW or Filsol's Newark tapping positioning for self-evident air-gap, to take expansion. Having a joint blow because you don't understand the system isn't going to endear you to the customer.

2. Same point really, again you compare an F&E tank for some reason with a sealed solar system. The comparison is irrelevant, chalk and cheese. Whether you believe me or not is also irrelevant. But to solve the issue in everyone's mind, do list a UK approved product that doesn't recommend a PRV in a drainback (or flowback, same thing) sealed solar thermal system.

3. Simply put, unless the kit is approved to BS5918 or equivalent standards, it will not be signed off by the installer (if he values his licence) or the BCO who is looking for evidence of safety and hence needs mfrs to list their approval, BS or equivalent. The following also apply:

BS EN 12975-1:2006. Thermal solar systems and components. Solar collectors. General requirements
• BS EN 12975-2:2006. Thermal solar systems and components. Solar collectors. Test methods
• BS EN 12976-1:2001. Thermal solar systems and components. Factory made systems. General requirements
• BS EN 12976-2:2006. Thermal solar systems components. Factory made systems. Test methods
• DD ENV 12977-1:2001. Thermal solar systems and components. Custom built systems. General requirements
• DD ENV 12977-2:2001. Thermal solar systems and components. Custom built systems. Test methods
• DD ENV 12977-3:2001. Thermal solar systems and components. Custom built systems. Performance characterisation of stores for solar heating systems

3. Good luck with getting it past the BCO. This from a local council's BCO: Note the differentiation between factory and other!

1.
Factory made solar water heating systems to conform to BS EN 12976-1:2006 - Thermal solar systems and components. Factory made systems. General requirements.
2.
Other solar water heating systems to conform with pr/EN/TS 12977-1:2008 Thermal solar systems and components. Custom built systems. General requirements for solar water heaters and combi systems, or BS 5918:1989 BSCP Solar heating systems for domestic hot water (further guidance available from CIBSE Guide G).

Either way, pick-and-mix or factory, you need approval.

4. Answered by 3.

5. I have shown above that you DO have to use approved components. My advice to any DIYer is to get the kit from ONE source, as otherwise you will have multiple inputs from multiple experts, and no guarantee of compatability. 8m2 of Hi=per panel with a titchy coil in an unvented cylinder. And other snakes weddings. I have attended many such murine divorces after a few weeks of the customer desparately, belatedly, seeking good advice. Installed by one of Peter's plumber's plonkers, unconsciously dangerous.

In this context, of a specialist installation requiring specialist knowledge, advising any DIYer to get diverse bits of kit of unknown provenance or safety is not just reckless but highly irresponsible. You recommended this before an02ew even said he had a competent person to help! If you had ever seen the DIY/bad plumber nightmares most professionals come across on a regular basis, or have to carry the can for the advice you offer, you would never be offering the unqualified advice you do, such as no PRV in a drainback system.

Your analogy of CH is also not apposite, as gas needs a gas engineer to sign it off, oil ditto , solid fuel ditto. If they noted something wrong with the install, they would refuse to commission it. You would not believe the number of second calls for that very reason, once they have checked with BCo or their auntie's hamster that yes, they DO have to do what you say and put a PRV in a sealed system, etc etc.

Posted By: crusoeThere is no requirement for PRV in open vent in the UK, but in colder climates I do understand the precaution.

The wizened old plumber to whom I referred was in the UK and I have seen a couple F&E tanks frozen up in the UK, both caused by wild life destroying the tank insulation, there might be no regulatory requirement for PRV in an open system but I don't see that as reason not to fit them at what is a small additional cost for my peace of mind.

The main advantage of a drainback system is that you can turn it off when your tank is full of heat. The water drops out and the panel is left to get 'jolly hot' on its own. They are immune to stagnation. This is really useful on oversize systems designed to give heating system support (much more common on the continent than here, mostly for good reasons of latitude, but also convention.)

As to the requirements to buy everything from one place, all the listed standards and BCO requirements, I'm with Ed here: Crusoe is talking complete nonsense. There is nothing notifiable about a DIY solar thermal system (except often electrics), and you can make it out of whatever bits you choose. It's much _easier_ to get a designed system from one supplier but there is no regulatory requirement to do so. And people on the Navitron forum have been doing so for years without mishap, improving on some of the 'industry standard' system features in the process. (I did mine in 2009, and it's great: entirely free hot bath today, despite being nearly October).

Now it is true that if you are looking at RHI payments then you will almost certainly need everything to be 'MCS certified' which will indeed exclude both all sorts of perfectly good kit and anything you screw on yourself simply because you haven't sent yourself on a lot of expensive certification courses. That's the same nonsense that has made DIY PV a fairly pointless exercise in the UK, because screwing the _exact same kit_ the _exact same way_ to your roof simply doesn't count. However again, it isn't banned - you just don't get any payments (and there are regulations/requirements affecting the inverter and the electrics).

Posted By: davidfreeboroughDrainback systems often have two pumps; a high power one to lift the water into the solar thermal collectors initially & a lower power one to circulate the water once the collectors are charged.

For the low power pump to work a syphon would need to be held in the collectors. So how does the drainback work, then? I have various options in mind for this: either a motorised valve in the air-bleed path from the top of the collector or some sort of restriction in the flow out of the collector. Haven't decided yet and suspect that a bit of experimentation will be required.

I'd like to get that straight too, Ed.

Posted By: davidfreeboroughDrainback systems often have two pumps; a high power one to lift the water into the solar thermal collectors initially & a lower power one to circulate the water once the collectors are charged.

So why can't both be PV powered, as both are only reqd when the sun shines?