| Archive for Downsizer For an ethical approach to consumption |
| Chez |
Gravity fed rads from a woodburnerDoes anyone run a CH system from a woodburner by gravity?It would be four rads maximum, all upstairs, the woodburner downstairs. I understand that early CH systems were run on gravity on a 'single loop' system with very wide pipes and that one should expect the rads at the end of the loop to be significantly cooler than the ones at the beginning. I know that one should allow about 5,000 BTU per 3' by 4' radiator. Just interested in hearing RL experiences ... |
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| jag_clarke |
you will need to use 28mm pipe it will need to be up hill all the way to first radiator the down hill from there as much as possible. if the system isnt plumbed right it wont work well, it wont give even heat output to each radiator, non pumps systems dont meet building regs now, pumps are cheap and you can use smaller pipe saving money it will work far better. modern radiator valves are tiny too small for a string of rads in a gravity circulation system. for hot water cylinder gravity circulation is fine as its simple low resistence circuit but for others its not worth using. | ||
| vegplot |
It would be expensive in copper as the pipework would need to be large diameter. | ||
| Chez |
How does the building regs thing fit in with an off grid dwelling, though, JC? I am concerned that running a pump for the system will be very power-heavy during the winter, when we would be lacking the solar PV input part of the system we are envisioning.
Also, I know that 12v pumps are a no-no for solar thermal installations - apparently they fritz after a couple of days. So I was assuming that a pump for any hot water system would be the same. Perhaps I need to go and re-research that bit of it - I guess that the temperatures might well be lower. Mucking about with inverters seems like too much faff. Designing a house that works on a 12v off-grid system seems as much about what you can do without as about what you need. |
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| Jonnyboy |
Can I ask why Chez? Are you looking at off grid? | ||
| Chez |
Crossposted, JB  .
Yes. We have a couple of options with our mad self-build plan. The non-curtilage of the existing house option would ideally involve off-grid. We have been getting together enough info about what we'd like to do to get the planners to come out and discuss options and I am just kicking ideas around. |
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| jag_clarke |
my grandfarther had a wood stove and gravity circulation of 5 radiators it never worked properly from day one. they used to use 1" intermal diameter which works out as same as 28mm metric the fittings seem to be same size in my experience. copper isnt cheap it will cost u alot more and make it hard to hide pipes, ideally ud want smooth bends rather than angles to improve flow but 28mm pipe isnt easily bent with affordable tools. 22mm main pipe with rads in parrel on 15mm pipe will work far better and a cheap pump about 45pound will only use maybe 20 watts and circulate them fine. | ||
| Chez |
It's 20 watts an hour for 24 hours for at least the six darkest months of the year, though.
I will go google and see if I can find out about whether 12v pumps will cope - thanks! I understand about the pipework needing to be correct and it being quite fiddly to do to get a smoothly functioning system. |
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| jag_clarke |
an alpha a rated pump can average just 5 watts on its lowest setting. | ||
| jag_clarke |
http://www.screwfix.com/prods/79777/Plumbing/Central-Heating-Pumps/Grundfos-Alpha-2-15-50-Domestic-Circulating-Pump it varies its pumping as the rad thermostats open and close and uses perminant magnet motor to reduce its input power
or save a hundread and go http://www.screwfix.com/prods/33590/Plumbing/Central-Heating-Pumps/Wilo-Smart-Pump-Domestic-Circulating-Pump |
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| Chez |
But I don't think they're 12 volt, are they? I've found these, though:
http://www.elyboatchandlers.com/chandlery/marine-pumps/central-heating-pumps.html It looks like it will be possible - thanks for your help! |
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| jag_clarke |
random iv been in there shop in ely few times. yeah that looks low power at 1-2watts cheak it has sufficent head before you buy it a boat is at one level. ul need at least 3-4m head to pump it through rads upstairs, also make sure it doesnt prevent flow should power/motor fail as this could cause boiler to explode. | ||
| Chez |
I was thinking along the lines of an 'always open valve' ... we had a neutraliser in our old place and wanted some kind of gravity fed system to still toddle along if there was a power cut.
Thanks Jag, much appreciated. |
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| jag_clarke |
personally id go with tryied and tested alpha 2, u know it can pump enouth u can put it on various settings and even tells u how many watts its using on the screen. it will use less power than the second pump on that site and cost same. u know it can take boiling water without failure. at 5watts it really is very little power to heat your house, i know that 5 watts costs alot with photo voltaics but a 12v dc wont nessarily be using less power the second pump listed on that sight can only take 80 degs uses 21.6 watts and may not have much of a head at just 0.12 bar (about 1psi). also a dc pump will loss fair bit of power in wiring compared to ac. thas alright m8 i plan to do same thing myself eventually going off grid i know every kw hour is worth alot when u have to generate it. they sell bit cheaper on ebay sometimes by the way | ||
| Mr BlueSky |
Our system runs on gravity if the pump isn't switched on. The five rads upstairs all still get hot/warm although as you mentioned the end rad is considerably cooler than the first, which is always scorching. Trouble is withoput the pump on and with the burner going full blast the system overheats which can be scary. | ||
| jag_clarke |
yeah normal central heating systems should be designed so if the pump should fail they naturally circulate using gravity system. they normally only use 22mm pipe down to 15mm and with resistance of pump it doesnt help but it should be enouth hopefully to prevent a boiler explosion which has happened to people with wood stoves and it would be failtal if you were in the room so you must treat it seriously. the thing with gravity circulation is the flow rate is quite slow this means the heat distribution is less even. if u had radiators in series in a modern system (uncommon) then the pump speed could speed up and both radiators would have simular temperatures, for instance with faster flow rate the first rad may cool the water by 10 degrees 80>70 and second from 70>60. on the slow flowing gravity circulation its more likly to be 90>60 then 60>40 so both rads give off quite differnt outputs first being about twice as powerful as second. in pre war times this was fine as it was better than heat in just one room but things have moved on now, its far better to plum the radiators in parrel as it gives low pumping resistance (less power consumption) and even heat dystribution, it would be possible to do this with gravity circulation but very difficult to install with the masses of large pipes.
http://www.diydata.com/planning/central_heating/pipework.php this kind of explains it if u didnt follow me often as a safety feature with a stove or range you can fit a gravity circulation loop firstly to hot water cylinder and secondly to a radiator that has not thermostate. this is usually best in a bathroom or hallway somewhere where should the room be hot it will cause the least discomfort. then should the pump fail water will circulate around that radiator preventing it overheating. its more for say you go out or go to bed and pump fails. genrally ul have it on a slow burn so that radiator will be enouth to disipate the heat preventing it boiling. |
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| Chez |
I am thinking of planning in two appliances - a rayburn to run the DHW and perhaps a rad or towel rail in the bathroom. And then a woodburner with a backboiler to run rads upstairs. With a strawbale build the house should be super-insulated, so hopefully no more than that would be necessary and the woodburner would only be needed when it was very cold. | ||
| eco andrew |
Jag, do you mean the Jabsco Eco Circ 12v when you say the second pump? I am considering buying one (for solar panel use rather than CH). 80 degs should be OK actually if you have the pump on the cooler return-to-boiler side of the circuit (as it should be to minimise strain). Then if the temperature here reached 80 degrees this would mean that the radiators would be even hotter, which would be dangerously hot to touch. 
How did you work out that it uses 21.6 watts? This would be a strong consideration in my purchase. I think by head of 1.2 bar you are referring to the pressure the pump creates itself when operating. It is actually quoted as withstanding system pressure of 10 bar. This pump (as with most CH pumps) works using a spinning impeller so does not impede flow when not in operation. In fact, as I understand, the impeller is spun using magnets rather than a physical connection (a system designed to avoid using seals, so preventing leaks) and so will spin freely offering no resistance to flow should power fail. Chez, Jag is wise to advise that the system should continue to circulate using 'gravity' or 'thermosyphon' if the pump or power should fail. With an uncontrolled heat source like a woodburner (which can't be immediately and automatically switched off by thermostat) there is a serious risk of rapid pressure build-up and explosion otherwise. You would not want your loved ones nearby.  Therefore you need to use 28mm pipes throughout, ensure a continuous rise (no horizontal or downward sections of pipe) up to the first radiator then a continuous fall from there back to the woodburner boiler. If connecting radiators in series this would mean they would need to be at different heights, each subsequent radiator lower than the previous one. You might be able to get round the problem of each radiator becoming progressively cooler by radiator 1 being small and subsequent radiators progressively larger to even out the heat output to each room. The steeper the rise and fall the better for efficient circulation.
You might want to consider separate circuits for each radiator to achieve this, (instead of connecting them in series) maybe siting them on either side of the same wall for instance, as close to a direct line above the woodburner as is possible. Then you may not need a pump at all. You would also need to carefully match the size of radiators to the output heat of the boiler to avoid over-heating, boiling and pressure build-up, perhaps incorporating a heat dump (eg. flow diverting to a water tank or a radiator in the loft) and a pressure relief valve on the circuit for safety. 
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| jag_clarke |
yes that was one i was reffering to. it quotes current drawn as 1.7amps so amps times volts equals watts so 12v x 1.7 amp = 20.4watts. It quotes a head of 0.12bar this from memory is only about 1.2 meters which is of little use unless your system is on the flat. yes you are right about return temperature it should be less than that in normal use. 28mm pipe although is always recomended for gravity circulated central heating systems is not essential for gravity circulation it just helps to avoid systems being plumbed which dont gravity circulate well, also gravity circulated systems still normally use 22 or 3/4" for branch to each radiator. while 28 will work fine in pumped system its difficult and more expensive to work with. if you use 22mm main pipe and try to have steady rise where possible espeshally going to upstairs behind stove then at least some radiators should circulate by gravity enouth to prevent boiling. if you fit a cheak valve (one way valve) in direction of the flow of the central heating pump this will allow the water to circulate by gravity when the pump is static. if you plan to mix gravity and pumped systems you will need an injection tee to allow gravity cirulation when the pump is running. when wiring a pump in use an high limit pipe thermostate that will start the pump when the temperature exceeds what you set it to that way it prevents boiling and overcooling.
that way you start up fire once the water reaches 70 degrees the pump starts then the boiler cools down to 60 it stops. this will help stop condensation on boiler and tar/creasoate in chimney. it should allow you to leave stove running and it will give off as much heat as it can while maintaining a good combustion temperature. should the pump fail or a power cut then the system will circulate its hot water upstairs by gravity circulation coolling the water enouth to prevent boiling allowing you time to dampen fire. ps although i say large pipes arnt essential, larger pipes used in pumped system will mean the pump can be run at a lower speed so saving a little money in long run. |
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| Tavascarow |
I've not lived in a strawbale but I think you are underestimating their insulating properties & having a rayburn for domestic & cooking I would have thought would have been enough to heat the whole building without central heating if its built on a fairly open plan. My philosophy has always been 'keep it simple stupid' & to plumb two burners for different applications when probably only one will be lit apart from the very coldest nights (& I mean cold) seems a lot of extra expense & energy. Also why aren't you writing solar into the equation. As Arvo gets older he's not going to be so keen to break his back cutting & carrying the amount of wood your idea will need. & to buy it will cost more than oil or gas?
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| jag_clarke |
do a u valve calculation for the construction make sure to include ventilation factors. if you include the walls, roof, doors, windows and floor in your calculations of your likly construction dimentions and specifications you should get a good estimate of the reqired total heating. take the temperature differnce to be 22 degrees (-1 outside 21 inside). if your heating system can do that it should meet building regs. with a wood heating id aim for bit of extra heatout so that you dont have to run it at max output all the time to keep warm in the winter. if you do have open plan one heat source no radiators then you wont get very even heat distribution, the bedrooms may end up at 24 degrees as heat rises and living room 18 degrees. in practice u want the living room 21 and bedrooms about 18. also a thermal store will help you regulate the temperature better taking up excess heat and releasing it when your house cools down, also using solar for moderate weather. | ||
| Mary-Jane |
D'you know - I read the title of this thread as 'Gravity fed rats from a woodburner' 
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| Chez |
Would be possible with large diameter piping I suppose. But I still think you should get the dose of your dried frog pills adjusting
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| Chez |
It's partly just to have a fire to sit in front of during the winter. And it seemed daft to have rads running from an always-on appliance, ie, through the summer as well. But I will investigate more. Solar heating is pants in the UK - assume you mean for DHW? Again, it seems a lot of expense and energy to go for when you have an always-on DHW appliance. Very useful if you are using oil or gas or electric - but with wood that you are growing yourself, it seems like £3K that can be spent elsewhere. I am planning on forcing the children to cut the firewood as we become infirm .
The site we are looking at has a stream, so we are thinking of a low-low turbine for electrickery if we were to get planning. |
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| jag_clarke |
well house will be quite an oven in summer with it being well insulated and having range going so solar is good as it saves alot of work in summer and saves producing unnessary heat in house. if you have a thermal store then why not top it up with solar and have some free central heating in moderate conditions. evacuation tube solar pannels will produce enouth heat until worst mounth of winter you can buy them for about £300 for a reasonable size pannel. a good size kit with sensors manifolding controls pump ect will cost £1200. my friends dad had that kit fitted to his house as he had huge heating bill 4.5K as his house was full of lodgers about 10 of them. now he finds it produces enouth hot water for them right up until november when the boiler boosted the output as days were short. he still found the pannel was heating to near 100 degrees c (goes up to 200+ in summer as it uses glycol coolant). i know solar isnt best in uk for heating house but if pumbed into thermal store when heat is there its free and means you can wait later in the year before having hassle of bringing in wood and lighting fire. if u do it everyday and have to cut up all the wood its not to be underestimated the work involved.
ps it was an aztec solar heating system i was impressed by it, certainly heats alot of water as it soon cuts out as cylinder reaches the set temperature. |
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| Chez |
We had a 40-tube evac solar panel rack and a thermal store in our previous house. It kept the DHW at a steady 30 Celsius during the winter and did pretty much all the DHW between May and September. Also, there are particular issues about a gravity-fed system in a single story flattish-roofed dwelling - and a 12 volt pump in a solar system apparently fries out after about forty eight hours .
We'd have to keep the range on in the summer if were off grid as we wouldn't have the option of an electric cooker ... it's horses for courses. |
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| jag_clarke |
the aztec one uses a grunfos domestic pump and control unit pulses it to reduce power consumtion. good thing is when/if they do go wrong they cost little and can get one at local pumbing supplyier same day. if ur really watching the power the alpha 2 pump uses very little power. |