New installation design

[JohnS]

Hi,

I am finalising my plans for solar thermal panels.  This is my present thinking, which I should be grateful for any comments, criticism or ideas.  It will be installed in conjunction with a loft conversion whilst there is access to the outside of the roof and before the inside is insulated etc.  There will be underfloor heating in the loft and eventually I shall retrofit it in about 50% of the house.  We are 4 but with 2 young teenage daughters whose demand for hot water is increasing.

2 * 20 * 47mm tubes, roof mounted facing about 10o west of south.  I note that the width of 20 tubes is 1500mm.  Is this the manifold width or the flow and return width?

Pipe work in 16mm stainless Naviflex for ease of installation.  Total flow and return length will be around 15m.  Standard EV, PRV, NRV, pump, filling loop, drain etc.

New 300 litre vented thermal store with solar coil and boiler coil and probably a second top solar coil.  This will be ‘made to measure’ and probably 2000mm * 450mm with triple insulation.  I could go higher or wider, but is there any real benefit?  Second solar coil is to give a small amount of hot water quickly before the whole cylinder is heated up.  3 way valve as per TDC3 schematic 7.1.5.  What are the differences between Resol VA300 and Resol VA32? Are either/both suitable?  Could I use two pumps as pumps are cheaper than three way valves?

Note, I prefer a separate high efficiency boiler coil rather than having the boiler directly heating the store.  The boiler circuit can be pressurised and is totally independent and isolated from any possible future radiator sludge etc.  Boiler circuit and radiator circuit will be protected with Magnacleans.  Radiator circuit can act as a heat dump without interfering with boiler pump overrun etc.

Tappings for central heating radiators and underfloor heating – can they be combined or are they better separate to aid stratification?  Return above the bottom solar coil and flow somewhere between the boiler coil and the DHW and top solar coils.

The header/expansion tank will be about 1400mm above the loft floor – is this enough?

Manifold will be fitted with a radiator style air vent, which will be accessible via a ‘velux’ window.

Anything else that I should consider?

Thanks in advance.

JohnS

PS what (free) software do people use to draw nice diagrams with pumps, NRVs etc?

[dimengineer]

If you can afford it, go for more panel area (or a smaller tank). 40 tubes will only just be enough for a 300 litre tank. I've got a 30 tube Kloben panel, with a 250 litre tank, and its only marginal. I have 3 kids (2 teenage daughters) and 250 litres is OK. The habit of the youngest of standing under the (mains pressure) shower for 25 minutes does not help

Tim

[guydewdney]

It appears to be the considered opinion of the professionals on here that thermal stores are a bit carp for this application. Having 300 litres of 60-80 degree water overnight looses a lot of energy, compared to an unvented cylinder.

16mm pipe is too big for such a short run - go for 10mm if you can.

I have a 300 litre tank, and incredilby long runs, and 2 x 30 x 47 panels. Its only just enough, but Im probably loosing a fair bit along the pipework

[David]

Having 300 litres of 60-80 degree water overnight looses a lot of energy, compared to an unvented cylinder.

Why?

Assuming apples are being compared with apples, 300 litres in both cases with the same amount of insulation, then both should lose much the same amount of energy. A thermal store will have a few more connections, which need to be insulated properly, but otherwise they are very similar for heat loss purposes.

[djh]

3 way valve as per TDC3 schematic 7.1.5.

There's a 3-way valve in my conventional heating system. The tank loses noticeably more heat overnight if the boiler last supplied heat to the tank rather than to the central heating. I also suspect (based on what I've read here) that in one or the other or both conditions it will be continuously drawing power (but I haven't checked yet). So I'll be tempted to use 2 separate valves in any future system.

Tappings for central heating radiators and underfloor heating – can they be combined or are they better separate to aid stratification?  Return above the bottom solar coil and flow somewhere between the boiler coil and the DHW and top solar coils.

There's been a lot of discussion about achieving stratification. One point I'm convinced of is that there needs to be some means of returning water to the store at the (variable) right height. If I understand right, your design has four coils but still won't achieve that. I suspect you'd do better investing in one of the designs from suppliers in wookey's list. I suggest searching the archives.

Cheers, Dave

[Antman]

... Second solar coil is to give a small amount of hot water quickly before the whole cylinder is heated up.  3 way valve as per TDC3 schematic 7.1.5.  What are the differences between Resol VA300 and Resol VA32? Are either/both suitable?  Could I use two pumps as pumps are cheaper than three way valves?

John

The VA300 uses a thermo-electric (bi-metallic?) actuator whereas the VA32 is a full motor-driven valve. Electrically and mechanically the VA300 is simpler...

You are effectively proposing to charge the store in layer mode i.e. top first then bottom if top is satisfied. As my downloaded TDC3 manual does not have a specific reference to diagram 7.1.5 I will assume you are refereing to Hydraulic Variant 5   
The pump output will still be controlled by R1 - as far as the controller is concerned (since the controller does not know you have changed a valve for a second pump). Hence Pump 1 will still run simultaneously with Pump 2. You could overcome this by switching the Pump1 off via a relay when R2 output energises Pump 2.

There is another option that might work (I'm not saying it will) - Ivan care to comment?

Use Variant 10 (dual store mode) which does use two pumps but set it up so that S2 is in the upper half of the store with the top solar coil / Pump1 and S3 is at the bottom of the store with the lower solar coil / Pump 2.  To all intents and purposes, the controller will not know that the stores are one and the same. This would allow simple pump wiring, you just need to specifiy S2 in the correct location - probably just above the upper solar coil return exit.

Use a one-way valves after each pump to prevent unwarranted induced circulation through the non-pumping coil-pump circuit.

Regards

Antman

[JohnS]

Thanks everyone for the replies and help.  Lots to consider.

Tim
With shape of my roof and veluxes that I shall be installing, there is not easily room for more than 2 * 20 * 47.  300ltrs matches that at 7.5 ltr per tube which is bang in the middle of the 6.5 to 8.5 range.  Having been on Ivan's training course, I don't think that I am too wrong on my ideas and my gut instinct is that I am oversizing a bit.

Guy
I am aware of the pros and cons of thermal stores.  One of the reasons that I prefer one is that it will allow my boiler to be more efficient in winter with longer and fewer burns and staying in condensing mode more.  Again, I am still learning and open to ideas etc.

Cylinder loss is temperature dependent.  If the cylinder gets up to 80 in the summer, it will be because there is lots of available sun.  Insulation and lagging all pipes is the key.

Dave
I am looking for a motor on motor off solar valve and Resol is the only make that I have found.  But see Antman's comments above.

Stratification - yes, I have researched this forum and others a lot and I know its complex.  My thought is that the u/f return will be cooler than the radiator return and should therefore go lower than the radiator return.

My quote is for a Newark store via Navitron.

Antman
Thanks for the info on the VA300.  I am emailing Seconsolar to see if I can get a more detailed spec/description than on the Resol website. 

It is the hydraulic variant 5. It was 7.1.5 on Ivan's course notes.  I have now downloaded the TDC3 manual and am trying to get my head around the on/off temperatures and deltas needed to get it to work.  I was puzzled why the East/West panels (7& and two  stores (9&10) can have either two pumps or a three way valve but not two coils in one cylinder.

However, having looked at the manual, I think I may need a TDC5 so as to have three relays, pump 1, 3way valve/pump 2 and radiator circuit for heat dump.

Many thanks and any more ideas are welcome.

JohnS

PS  Ivan - can you change the spell checker to allow Navitron? 

[Much]

Note, I prefer a separate high efficiency boiler coil rather than having the boiler directly heating the store.  The boiler circuit can be pressurised and is totally independent and isolated from any possible future radiator sludge etc.  Boiler circuit and radiator circuit will be protected with Magnacleans.  Radiator circuit can act as a heat dump without interfering with boiler pump overrun etc.

Could anyone point me to a list of the pros and cons of vented vs. pressered systems for boiler parts of the circuit? And is using the boiler coil overall a better option than directly heating the store fluid? thanks!

[JohnS]

here is a start

http://c-zero.co.uk/e107_plugins/faq/faq.php?0.cat.1.12

Also have a look at the Newark Cylinder site

http://www.newarkcoppercylinder.co.uk/cylinders/thermal_store/

As for the pros and cons of the boiler heating the store directly or via a coil, it is hard to say.  The purer way is probably to do it direct.  If you size everything right, the water is taken out of the bottom of the store, heated to the right temperature and returned to the top.  It only goes through the boiler once and therefore the return temperature is sufficiently low to keep the boiler in condensing mode.

I propose taking the other route as it allows me to keep the boiler independent, keeps any chance of radiator sludge away from the boiler and allows the boiler circuit to be pressurised.  these are my reasons, I think they are valid and i respect others doing it differently.

JohnS

[Much]

Thanks! 
Shortly after posting I also found the thread in 'energy efficiency'; http://www.navitron.org.uk/forum/index.php?topic=3550.0

[markconnor]

Just a note to say I installed a 300 litre twin coil Navitron/Newark solar thermal store about 3 months ago, and it works great for my family (6 of us - 2 adults, one teenager, one 13, one 5 and little fella aged 2).

Have yet to install my solar panels though.  Currently thinking of 1 x 30 tube 58 dia, as have limited roof area - panel will orientate slightly SW.

I have done a bit of a hybrid DHW system with my store as follows;
1)  Kitchen sink is taken directly off the cylinder volume (ie nice hot but standard vented hot water pressures - which is fine as head pressure is OK for kitchen tap.
2)  DHW for showers and WHBs taken off mains pressure DHW coil.

Works great and hopefully will allow me a bit more flexibility on thermal store temperatures when the solar bits are bolted on soon.
Could allow store temperature to fluctuate between about 55 and 70 Deg, and not notice any difference in DHW provision.

Thats what I'm hoping anyway.
Any comments appreciated.



Mark

Mark

[JohnS]

Thanks, sounds similar to what I am going for.

What are the dimensions of your store and how high up are the tappings/coils?  It sounds as though you have a boiler coil in the store like I am intending.

Watch the hot water at the kitchen tap - 70 deg is scolding hot.  Consider a TMV at the kitchen sink.

JohnS

[wookey]

Mark, have you measured the difference in temp between the mains and directly-tapped hot water? I'd expect it to be about 5C, but maybe it's more in practice?

I don't quite understand how you've done this: normally the water in the store is 'system water' and has anti-corrosion stuff in it, so you can't (don't want to!) draw it off through hot taps. Have I got wrong end of stick?

Much. Direct heating of the primary water allows (at least in theory) stratified loading of the cylinder (by feeding back water to get defined top-of-tank temp coming out of boiler). See  http://heatweb.com/products/cylinders/gxv/operation/gxoperation.html for helpful diagrams/explanation. A coil allows the boiler height to be independent of the store (and there are more sealed system boiler than open-vented one to choose from these days).

Open vented boilers may be cheaper (they should be, they are simpler, but lower volume means it doesn't seem to make much difference).
Sealed should be less prone to corrosion (no air in system).
Open vented won't go 'flat' on you slowly, and are much easier to fill.
OV needs anti-corrosion stuff changing more often.

So in general I'd say sealed is 'better' as in more modern, however if stratification matters to you then OV wins because sealed-via-a-coil simply can't do that. Sealed plus a stratifier could acheive the same effect but they are currently pretty-much unobtanium. 

[Midnight Lightning]

Guy, you mention exceptionally long pipe runs, I would be interested to know how far you have between panels and tank - I'm potentially looking at 15m in 10mm but am concerned it might be too far.

Cheers

Mid

[wookey]

Check the pipe-sizing wiki page: http://www.navitron.org.uk/pmwiki/pmwiki.php?n=Main.PipeSizingCalculations
which lets you do the sums to work out what the pressure-drop for that pipe run is and thus what pump you would need. If that pump is beyond the spec of normal pumps then 10mm can be deemed 'too thin'. There is a spreadsheet to do the work for you. 30m at 10mm is long enough thtat doing the sums is a good idea. I think it's fine so long as you haven't got too many panels, but it may well be too much for a low-power pump.