good stuff. i'm hopefully going to get the assembly of the controller finished today... unfortunately, apparently i sometimes have to do other stuff than this (!) so nothing's been done in the last few days.
looking at what you've suggested, i don't think a dpdt is necessary, just a double throw. essentially to switch between 2 different voltages.. but anyway.. i've basically done (well, if it works as a circuit) the vanilla controller, so i'll stick with that for now.
but if what you suggest is to use the top coil section temperature when it's hotter.. then why not just use it all the time?
the twin coil cylinder i also have lying around (which does have a leak at one of the seams... need to look at whether or not i could patch that...) has the 2 coils at the same height exactly, just on opposite sides of the cylinder. so even if i do succesfully graduate to that one, my reference point for temperature will probably be the same as with the current cylinder.
my sort of gut feeling is just to pick the top turn of the coil and use that as my point.
no matter yet, that's all adjustable. need to get this board made up and then work out some sort of housing for it. good times.
that twin coil you have, sounds unusual (twin coils at same height). i wonder is it a bespoke one (many are). fro where did you salvage it?
using the top turn for the tank sensor will guarantee you do not pump heat out of your tank ever, but it will also run your panel hotter on average (than it would when run with the tank sensor at the lowest coil), which, particularly as the collector panel is a radiator, will lose energy at a greater rate than if you ran the panel cooler. The energy capture efficiency , i.e., the ability of a panel to grab heat from the the sun and deliver it to your tank, has an inverse relationship with the temperature diff between the panel and ambient air. I.e., panels capture solar heat more efficiently when the panel temp is closer to ambient air. The efficiency drop associated with running a panel hotter than it needs to be is much more pronounced with a commercial flat panel compared with a highly insulated evacuated tubed panels, and the problem is even more pronounced with a poorly insulated home made flat panel. You will also be bringing heat in on average for less of the time as the sensor cannot see the cooler water that lies below the top turn which would otherwise be capable of storing lower temp heat energy. The delta T setting of the controller is set 5-6 degrees above the tank sensor's temp anyway, in part acknowledging that there may well be some hotter water further up the coil.
It's all a compromise I guess.
If you get unsatisfactory results from your setup in summertime the first thing to do will be to get a larger collector area as that is quite a small panel you have. This will have a greater impact than the precise location of your tank sensor.
Few links here showing the common location of the tank sensor being at the base of the coil
(Not sure which temp sensors you are using, thermisters will work as you say, with a single pole switch,not sure about those 3 legged digital temp sensors though, don't really know how they'd behave if just toggled between one wire on each)
in the first pic you can just about see the coil connections on the left and the right. it belongs to a friend, he had it in a barge, then it blew out and he just replaced it and it's been lying around since. need to see if it's patchable at all...
right. blobbed some solder onto the little crack today with blowtorch.. it seems to have worked, surprisingly. so.. thunderbirds are go on the dual coil cylinder. next step (after "debugging" the controller) is getting a second pair of pipes up to the fill / expand tank i suppose.. unless anyone thinks i could tee off them somewhere just above the cylinder or something...
That's a nice diagram Steve. Looks like they could both be gravity coils. If you were using this tank as a preheater tank, with the preheater exclusively heated by solar, you could tee the hot from the panel into both the top coil ports and join both bottom ports to the cold return to the panel, this would make for a 'rapid recovery coil' (high heat recovery efficiency) tank. The preheater tank output would then replace the cold inlet to the existing tank, preheating with solar the tank heated by the boiler. The back boiler would then never interfere with the solar and vice versa. A preheater arrangement is not perfect but is an easy way of providing an additional volume used exclusively by the solar. Or you could just use this twin coil on its own for both boiler and solar, but as the coils are at the same level this will not be ideal either. Either of these options probably better than your current arrangement of sharing the boiler coil between the back boiler and the solar. I'm sure there are other options too!
You may be able to silver solder the damage on that tank. If you are unfamiliar with silver I know Paddy has used it. Standard solder may even work but silver would be stronger. Is the metal too think to braze?
Are you getting much heat out of your current setup? (I know the weather has been rubbish the last few weeks but it's picking up again now)
the last few weeks i've got nothing from the solar. but it's been pretty much constantly overcast.
today was constant sunshine on the panel from 10am till 3.30pm. now it's gone overcast a bit... pump on constantly during those 5.5 hours. tank bottom went from 22.4 to 30, tank top from 24.6 to 38. i don't think that's too bad. the sun is noticeably lower in the sky now though.
i'm happy the twin coil cylinder looks like a usable option for now. it's absolutely not ideal, but it's here now, and so am i. this house needs major renovation. the floors need ripping up and screeding, roof nees reslating and all sorts of major stuff i'm not ready to do yet, so for now, it's kind of like a hack-house. all this stuff i'm doing now, is to make the "camping" here better for now, and to learn about what will work, and what things i'd like to get done properly and professionally over the next few years of fixing the place up.
presently looking at a big but still temporary (a year maybe.. hopefully 2 at most...) overhaul of the heating system. i hope to pick up a good multifuel boiler stove stove soon. then rip out the fireplace and back boiler, fit the twin coil cylinder, connect the boiler stove etc. the stove i have my eye on is maybe slightly too big for the setup now, but should fit the needs of the future house. there's a lot of work in this but i'm hoping if i think it through and get all the stuff i need (flexi flues, other flue bits, hearth.. whole lot more pipes etc) it should be doable. next door neighbour is a full time competent builder who's a big fan of stoves, and i know i can get him to ok anything i do, or to do anything he feels i can't. but a lot of the grunt work i can do.
so that's the present situation. the solar is definitely mixing with the back boiler water.. but i've given up on check valves and stuff, and moved on to the idea of the twin coils and 2 separate systems for now.
i like your thoughts on using the 2 coils as a preheater / solar tank though. i'll give that some thought... but for now (or at least for the coming winter and probably next summer) it will be the in dual mode here.
quick pic of the "fix". the crack extended a bit more to the left.. so did a bit more clumsy soldering. filled it up and it didn't leak anymore.. blew into it as hard as we could.. didn't leak a drop under that "pressure". heh. so eh.. hopefully it'll hold for the year or whatever. the current cylinder has a little weepy leak somewhere we've never actually located anyway, so it's nothing new if it drips a little.
That's a nice diagram Steve. Looks like they could both be gravity coils.
how could a coil be non-gravity.?
That tank repair pic is great,fantastic colours too.
good news that you are getting a decent amount of heat from your panel.
The gravity coils tend to be big bore pipe coils that only rise (or fall depending on how you look at them), whereas many 'rapid recovery' (high heat transfer efficiency) coils tend to have a spec which is not suitable for gravity circulation. The spec on tanks with such coils will describe the non-gravity coil as a 'pumped coil', i.e., it needs to be pumped. Solar (lower) coils in many solar tanks will not work on gravity circulation and need to be pumped. E.g., a pumped coil may be comprised of a big bunch of very small bore pipes (to achieve a large surface area for heat transfer) and small bore pipe will offer a larger resistance to flow (basically friction between the water and the pipe walls) necessitating the water to be pumped rather than circulated by gravity/thermosyphon. Other non-gravity coils will have several concentric coils in one, so whilst the outer coil may rise, the top of it will be connected to an inner coil which will fall, and this 'up and down' characteristic within the same coil will not support gravity circulation.
Boiler stoves. Food for thought if you like to build stuff yourself: Non boiler stoves tend to be more efficient than traditional boiler stoves as the boiler cools the fire, lowering the burn temperature and creating a less efficient burn with consequently more tar and smoke. Caveman (member of this forum) refers to boiler stoves as'water cooled fires'. Masonry stoves can be DIY built (including Rocket Mass Heaters which are a very DIYable kind of masonry stove) & can be extremely efficient but tend not be used for heating water. One of the downloadables on www.solarco-op.net describes how to take heat from a flue which can often be more efficient as it does not cool the main burn chamber.
have pulled out the old fireplace and associated brickwork, and fitted a big boiler stove.
swapped out the old cylinder with the previously shown dual coil one. the solder patch has held up. the twin coils are odd. they do heat each other, and when i first plumbed the solar panel to the second coil, the first evening of fire after that heated the solar panel quite a lot, so i put a sort of u-bend into the solar pipe, and used the 2 non return valves i had.. it's working better now.
so yeah.. today has been a good day for solar. got about 10 degrees of heat through the whole cylinder, up to 37 degrees i think.. some dishes and showering done on it.
here are some photos of the fireplace job if anyone's interested.
the last 4 show the initial connection of the solar panel. since then, it's been redone with the U bend i mentioned, so the pump is now down near the floor. and nearly all of it's been lagged. so it's improving all the time.
Great pics thanks and glad to see the progress and that you're getting useful heat from the sun. That U bend idea I take it is to help reduce the heat disappearing to the panel in the evenings? (I removed the non return valve in my own system recently and used a U bend to achieve a similar effect).
Yes, it's been quiet here on this forum. Effort since last summer has mainly been on the free PV project (www.nicommunityenergy.org) and there hasn't been much happening this year yet on the solar thermal - The thermal stuff such as your's is great to see and will hopefully encourage others to do likewise.