I am midway through a renovation and before closing up the structure and I want to put pipe-work in place for a solar thermal array on the roof to run to the thermal store. I am yet to buy the store or the collector so don't know what pipe and size I need to run. Has anyone any suggestions? Also any recommendations for sourcing the tank and array? I'm looking at Newark cylinders and McDonald engineers for the tank (300 litres with coils for solar, and boiler and take offs for underfloor heating (ground floor) and rads (first floor) and a take off for a heat exchanger either by coil or separate exchanger for DHW. McDonalds have quoted me around £1850 for the tank which I thought seemed expensive Am I just out on my estimates?
For the array I was looking at either Eco-nomical or Navitron. ANy advice or guidance very much appreciated.

Incidentally the house is a 1930's 3 bed semi with brick up to around 800 and pebbledash above.. I intend (next year hopefully) to hack off the render and install some EWI hopefully in conjunction with the neighbour, and do a loft conversion, probably without the inclusion of a dormer as the roof space is quite large as it is. My budget is running very thin at the moment due to the fact that the work kind of grew during the strip out due to discovery of woodworm and bowing lintles and purlins which were unsupported and had been cut off just shy of the chimney support at one end it once had! So I now have a ground bearing slab in lieu of the old wormy joists, with 100mm PIR below a concrete screed with underfloor heating in. I have removed a couple of windows and created openings for a couple of others with 'A' rated windows installed. The rest are large double glazed units which will also be swapped out when funds allow.

I seem to have gone a bit off of subject here but its always good to have some back ground! Does anyone think I am going the wrong route with the solar thermal and thermal store? I will also have a largish (7kw) multifuel burner in the lounge to warm the ground floor a bit and its nice to have a real fire.....no back burner unfortunately. I had bought the stove prior to the renovations extending as far as they have.

not plastic, copper only and compression fittings not push fit or solder.

without knowing the system size, flow rates, length of pipe etc I'd have to play safe and say 15mm would definitely be ok. 12mm may well be ok and is more flexible for getting round corners etc, and some would go lower than this, but this may well mean you need a higher power pump, which I think is best avoided.

Metal pipe clips, not nylon. And hi-temp sleeving, not the std grey. It definitely melts!

I paid 2220 Euros for a 2000 litre tank with a 340 litre tank inside it for DHW, with 2 coils and with tappings ALL over the place incl provision for recirculating DHW (which I don't use). There's some sort of diffusers on the inlets but no other stratification provisions as such (works just fine though). Steel, ceramic lined, 100mm jacket, Italy. Makes £1850 for 300 litres look like crazy money to me but I don't have any experience of prices/products other than this one purchase.

What is the depth of concrete slab your UFH pipes are in?

To use a stove in the same room as under floor heating the recommendation is that the UFH pipes are in a thin screed with insulation directly below so that it can react quickly when the stove is lit.

If the pipes are in a thicker slab the slab will continue to give off heat for a long time after the room thermostat has stopped circulation in that loop so with the stove adding heat also you run the risk of over heating. This becomes more critical the better insulated the room is so will depend on what the heat loss from the room is like after you do your EWI.

Getting back to the Thread title. I used flexible Stainless Steel pipe. I had a 23m run with 5 FPs and used 15mm dia. Came already insulated, 19mm wall thickness, return and flow attached and with 2 sensor wires incorporated. I just love my real time insolation reading which I used the spare sensor wire for. I could not have threaded any other type of pipe through the route I had to take. Compression fittings are essential but can be v tricky, especially without the bespoke tool for the specific ss pipe which usually costs a bomb - I wouldn't recommend it for the first time DIYer. OK in theory I could have done it in copper, dozens of soldered joints, all the crud to clean out or filter before commissioning, all the doubt over the integrity of the joints, feeding on the insulation afterwards, a long and bl**dy awkward job.

I could write a long post on solar pipe insulation on its own - strongly recommend 50mm wide electrician's tape wrapped around the whole length or, rather, definitely wherever the pipe bends at all.

Anyway, as wookey says: get thee to the Navitron Forum.

Isn't the stainless pipe just a little more expensive than Cu? Like an arm and leg more? Anyone done a price comparison?

Quick Google threw up http://www.solarsavings.co.uk/

Take a look on ebay.de it tends to have a lot of decent value on solar stuff although the shipping costs can sometimes take the good out of it.

Take a look on ebay.de it tends to have a lot of decent value on solar stuff although the shipping costs can sometimes take the good out of it.

est tute mi licht.. meine deutch ist einen bischen schleckt!! ich kanst nicht verschtare alus und ich habe veloren meinen Deutch Fertigkeiten!

Sorry, It is a long time since I spoke German and even longer since I tried to spell it.. I THINK I may have found some stainless steel pipe on there with integral insulation but I am not confident it is going to be the right stuff so its probably better I stick to a UK supplier!

When I last looked, stainless pipe (including fittings) was much more expensive, fatter bore (so less efficient) and had thinner insulation (so much less efficient). 10mm copper is very easy to thread and bend - not sure it's really any harder than the stainless stuff. But yes both work - pick whichever you prefer. If you do pick 10mm copper remember to buy inserts for all compression joinst otherwise you'll regret it...

You can get 15mm soft copper on a roll, cant remember where but sourced it for a job a few years ago. I understand that 90'bends give a lot of flow resistance so best to bend pipes (whether flexible of not) rather than use sharp 90'bends. You just have to make sure you use high temp insulation.

10mm soft copper; internal bore 8.6mm, ( too small IMHO) ..........................................£2.00 M.
1/2" imperial, 12.7mm, internal bore 10.9mm ( imperial fittings are expensive)..................£5.47 M.
( these are roll length prices)


DN12 SS uninsulated internal bore 12mm.................................................................£3.15 M.
DN16 SS uninsulated internal bore 16mm.................................................................£2.75 M.
(NB SS prices are for cut lengths for roll lengths discount applies)

I used DN16. All th pump station/manifold fittings are 3/4 BSP, so why use small bore pipe and end up with lots of throttling down of fittings to fit it's all extra expense for a theoretical gain in efficiency. In summer I'll not be worried about that.
Mike.

also went for the SS DN16 as recommended by the solar suppliers. Fitted DIY - no problems with the connections, just followed the directions that came with the pipe.
So far after 2 full summers, the thermal store has been supplied solely by solar from mid march to mid october, so not worrying about minor theoretical efficiency gains.
Cant remember about the price though, but did go back to the suppliers for an offcut from another job to plumb in the stove so couldnt have been excessive. Had a very awkward run through the floor to get to the store which the SS overcame very nicely.

I've just done some a quick and rough calculations for this.

I assumed that each tube needs a fluid flow rate of between 0.1 and 0.25 l/min to take away the heat generated (taken from the Thermomax spec). 30 tubes would need around 6 l/min (at 0.2 l/min per tube), which would give a flow velocity in a 10 mm pipe (8.6 mm bore) of about 1.75 m/S. The Reynolds number of a pipe this diameter at this velocity would be about 27 x 10^3 at 50 deg C. This is well above the critical Reynolds number for water so the flow is fully turbulent giving pressure drop of around 3000 Pa/m, or around 30,000 Pa for a 10 m length. This is equivalent to the pressure for a head of about 3 m. Most small solar pumps are rated to run at a head of around 6m, so such a pump would run the above system OK as long as the physical head was less than about 3 m, which sounds reasonable. If the pipe runs are shorter or fewer tubes are used then the physical head could be a bit higher and still stay within the pump 6 m rating (and I suspect that the pumps may well work OK above 6 m in practice, anyway).

As wookey rightly says, small bore pipe has a lower surface area, so lower heat loss. By the same token, smooth pipe will have a lower surface area than corrugated pipe, so will have lower heat loss. It seems to make sense to use the smallest smooth pipe you can get away with in terms of minimising heat loss from the piping, but if you have a high head system (say, panels on the roof and tank at ground level), a big array or long pipe runs, then you probably need to increase the pipe diameter to stay within the pump working head limits at the needed flow rate. It's worth noting that if the water runs at higher temperatures then the resistance will drop, as the kinematic viscosity of water is strongly temperature dependent (it is around 5.53 x 10^-7 m²/S at 50 deg C, but drops to 3.65 x 10^-7 at 80 deg C, for example), so as temperature increases and the needed flow rate increases the resistance to flow in the piping will drop.