New retrofit install - some questions

[cornishben]

We've finally moved house and hence onto the new project 
I plan in the longer term (1-2 years) to fit thermal store/heatpump/woodburner and possibly PV, as well as numerous insulation projects. However in the short term, due to time/finance constraints, I'd like to get the solar thermal element up and working. Having come from a cottage with solar thermal, our extra use of the immersion/oil boiler is already depressing me..

Currently the house has a 150l-ish single coil cylinder with top mount immersion. My plan is to fit a Navitron 30-tube panel on the SSW facing roof and plumb in via a retro-fit immersion coil. When the all-singing thermal store system is then fitted in a couple of years all I can reuse it all bar the retrofit coil.

Having DIYed a soalr thermal install before, I'm happy with the basics, but have some questions specific to this install:

1. The roof space under the proposed panel location is very constricted (small gable end full of timbers), I think I can squirm down and bolt on mounting straps, but wouldn't by happy soldering joints/plumbing down there.  Roof is concrete tile, hence I'm considering using the 6x stock bolts instead of straps, plus running the twin 10mm pipes in a single 15mm Armaflex (as Paul has done) above roof for 1-2m, before routing into the roof at a more practical point. Anyone foresee any problems with this? (the roof isn't visible from anywhere, so I could do 2 seperate 10mm armaflex runs also if it will be more efficient). 

2. Retrofit coils. Trying to ascertain the difference between the £120 Navitron coil and the ebay £70 one. Neither give a surface area. Any experiences or reasons I should go for Navitron?

3. Thermosyphon from Retrofit coil, some people talk of this being an issue, should I dip the pipes following exit at the top of the cylinder?

4. Pumpstations. Last time I did a complete DIY 'pump station' with all seperate components plumbed together in 15mm copper. Pump stations now seem to have come along, but price-wise seem to be double the individual components. Am I getting anything other than a pretty polystyrene insulation casing for this?  I'm planning to put the expansion vessel/pump/gubbins in the loft as we have very easy access but not much room in the airing cupboard. I would put the TDC3 downstairs for easy viewing though. Hence I don't really need a 'neat' pump station, but wondering if the decent insulation would be worth paying the extra for as it will be in loft. Otherwise I was thinking of just building an insulated ply box up there or something.

Um, think that's it for now, thanks!

[dhaslam]

The length of the retrofit coil is the important dimension because you will need it to go down near the bottom of the cylinder.   

I don't think the  flowbox  is worth the extra except that it is already part assembled.  There is  big air gap  top and bottom in mine which may be there to keep the pump from overheating.   It is a pity not to have the  controller in a position  where you can see ite.    I stayed in a house in Kerry in July that had   a 24 tube system but for some reason both the cylinder and the  controller were located behind a fixed panel in the bathroom.     You will need to fit a  temperature read out somewhere convenient  unless you leave the backup system  on.      The Chinese controller  that I use to control transfers from the buffer tank has a remote readout  that always displays the upper cylinder sensor.       

[cornishben]

The length of the retrofit coil is the important dimension because you will need it to go down near the bottom of the cylinder.   
It is a pity not to have the  controller in a position  where you can see ite.    

Thanks for the feedback. I may go for the ebay coil then as the chap says he'll custom make them to size, so could get it just the right length to reach the bottom.
Just to be clear re the controller. My plan is to have it somewhere visible (airing cupboard) and just have the rest of the gubbins in the loft.

[Brandon]

why don't you go with the fornax for ease?

Ivan will doubtless oblige if you have further questions.

[cornishben]

why don't you go with the fornax for ease?

Yes good point, I wasn't aware of the formax system. I've priced all the parts for a normal setup and they come to ~£1100, so £1200 for a kit isn't bad I guess if half the work is done.  However, I am planning to change to some kind of thermal store/HP/DHW setup in the next year or two and hence the retro coil is an intermediate measure. I guess a standard pressurized loop would hence be more sensible, as it could be more easily ported to a thermal store setup? 

however must admit I like the idea of no expansion vessel/pressurising/air locks/etc..

[ericw]

If you are looking a doing a cheap direct system then all you need to do is to tee in the connections to the cold feed to the cylinder and the hot output (a la Solartwin) . You could also feed 2 10mm (or 8mm) pipes down through the output connection at the top of the cylinder which would then allow you to choose the level at which you extracted/feed in the solar heated water.
If as usual the panel is higher than the cylinder then you must consider how to get rid of the 'new' air which will tends to come out of solution and collect in the panel.

[Antman]

Ben

A pumpstation has some advantages for 'pro' installs but for DIY I would definitely use individual components. You can place them where convenient for pipe runs/cable access rather than being constrained to a given point. Also, future maintenance is easier if required.

You will need a pipe dip of 150-200mm from the top of the retro coils to prevent heat-soak (conduction) up the pipes. The non-return valve will prevent true thermo-syphoning around the loop pipework but the thermal conduction rise will be significant without a dip. Easy to achieve with 10mm 

Antman

[brackwell]

ericw,
I have air in the primary loop even though i have a automatic bleed thingy at the highest point!  I have a feeder tank system and am plagued by air being "produced" in my feeder tank but i put this down to the water softener adding air to my water supply - perhaps.

Antman,
Do you mean conduction - heat will travel from one end of a copper pipe to the other regardless of the angle.  Whats more the more you lag the pipe the more the heat  just travels along the pipe until it finds the point where it can escape.

Ken

[ericw]

Brackwell
You might consider this idea http://www.navitron.org.uk/forum/index.php/topic,1359.msg9522.html#msg9522 which is what I use in my system to force the released air down into the cylinder and out the normal vent pipe.
You should cut the top of the exit pipe at an angle so you can push it right to the top with no danger of it being blocked.

The downside is that if the panel does stagnate then water is not forced out of the panel and you can get steam all the way down to the cylinder, where it will condense harmlessly.

[cornishben]

Ok finally have the install up and working.  It was so much easier the second time around, firstly due to kind of knowing what I was doing, secondly due to the vast improvement in the tube fixings (hard plastic cups rather than all those jubilee clips) but mainly because I used 10mm pipe throughout which was SO easy to route!

I had fun and games replacing the old immersion heater involving many expletives, blow torches, hacksaws and drills, but now the retro coil is in and all seems water tight..

One quick query.  I have mounted the expansion vessel/pump/filling loop/etc. in the loft, with the controller in the airing cupboard.  This all seems fine and makes bleeding the system much easier as the filling loop is 4ft from the air bleed valve coming down through roof from panel     However I'm wondering about insulation up there and frost protection, obviously all the pipework will be lagged but am wondering about the pump/expansion vessel?  Normally the pump isn't lagged to stop overheating right?   

Was wondering about making a celotex box around all the loft gubbins, although would be a bit of a faff.