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Green Building Bible, Fourth Edition
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    • CommentAuthorecowales
    • CommentTimeSep 22nd 2008
    Hi all,

    I've read loads of posts but this is my first. We are renovating a small stone built terraced house and will be installing a new central heating system. There isn't enough room for a boiler and a water tank (and I can't afford both anyway) so what I would like to do is heat the water using a log burner and solar panels. The water from these two heaters would go to a thermal store which would have an electric immersion heater as a back up. I've looked at various thermal stores/heat banks such as the DPS Pandora and alike, it all seems very complicated, my plumbing knowledge is limited and all the local plumbers don't seem to know much about this kind of thing and all say I should get a gas combi boiler instead.

    There are various discussions on here about the best solar panels (evacuated or flat plate) and thermal stores but I can't figure out which are best for me or if they'll work at all.

    Does anyone have any experience of a similar system or can anyone offer any advice? We're a family of 4 with relatively low hot water requirements (4 showers a day), 5 radiators, 1 underfloor heating room. I'm guessing that when the log burner is on most of the house won't really need the radiators on but I'd like the water to stay nice and hot for the morning showers.
    • CommentAuthorskywalker
    • CommentTimeSep 22nd 2008
    Hello & welcome

    I have a system of "

    1. DPS excel flat top 210l combi store (domestic hot water, central heating).
    2. Veissmann Vit' 100 gas boiler
    3. 30 x 47mm navitron evac tube panel.
    4. Soon to be added solid fuel with back boiler.

    An all singing and dancing DPS combi store (hot water, heating, solar set up, central heating controls, etc) will cost you more than a boiler + water tank. Certainly DPS+fire+solar will. The best place to go to get a better understanding is the navitron forum but the DPS makes all the plumbing in very simple and mine just worked out of the box so to speak. Call DPS as well they are very helpfull. The Navitron brigade do not like DPS units, they sell albion water tanks and heat stores. All I can tell you is my DPS unit is great and works exactly as DPS said it would, my Navitron tubes do not perform as their marketing suggests - make your own mind up.

    Plumbers will say that a combi is better. A combi is cheaper and easier to install - not better.

    There are two comps on solar panels essentially it boils down to:

    1. flat plate generally cheaper & better in sunny conditions but no contribution in winter.
    2. Evac tubes better in cloudy conditions and for a longer season.

    That said it has been a terrible year for solar hot water which has shown up the solar suppliers as guilty of overoptimistic performance statements with regard to cloudy performance. On Balance I still fell that evac tubes are the way to go with a heat store where you are wanting maximum gain over the longest season. On the Navitron website, and elsewhere too, you may see (unless they have changed it) that 1 x 47mm evac tube per 6.5 liters is recommended. If you have a thermal store where essentially the whole volume of water is heated in the the store then I would go with a minimum of one tube to 5 liters. With a family of 4 (and depending on how big your store ends up) you may want to go for more tubes. My 30 tubes left me needing to use the boiler to top up the store most days and to be self sufficient this year during summer I would have needed at least 60 tubes - 2 adults 1 child.

    There are many, many other options/configurations of both thermal store or water tank setup which may meet your needs. You can for instance have the solar coil further up the water column thus heating less water or a system which will switch between two coils.

    I would suggest learning much more before you jump just beware of biased advice from people who wish to flog you a particular solution.

    One final thing for now. DPS/albion etc thermal stores are really not quite big enough to be called thermal stores they are really only buffers (you can't store days worth of hot water for a family in much less than 1500l). But you should easily be able to get your morning showers out of one if not the first fill of your heating system.

    Good Luck

    There is nothing quite like your first solar shower!

    • CommentAuthorMiked2714
    • CommentTimeSep 23rd 2008
    Just to check
    I assume you're on mains gas as plumbers have suggested gas boilers. If so then I'd honestly suggest trying to fit in a gas boiler / thermal store / solar setup, with the option of fitting a stove with back boiler at a later date. Heat only gas boilers are quite small and there are alot of options for thermal stores including short fat ones and cube shapes.
    Do you have a supply of easily accessible free wood?
    If money is tight then I'd suggest leaving off the solar panel for now, you can always connect up to a solar coil in your store at a later date, and solar installation costs, scaffolding etc can be significant.

    I'd second Skywalker's comments. We have a very similar system, and whilst we have only struggled for hot water on the rainy days, I'd definitely go for more panel area next time.
    Thermal stores aren't that complicated. In some ways simpler than all the gubbins you get with a combi boiler, especially the more modern fancy ones which have a small hot water store inside.
    It's critical to insulate your solar pipework and use extra insulation around the store.
    • CommentAuthorwookey
    • CommentTimeSep 23rd 2008
    ecowales: a guy called CornishBen on the navitron forum has installed almost exactly the system you are considering. Read some of his threads. In fact he's posted here too:

    DPS make great stores apart from one thing: the insulation. At 40mm it is OK compared to a standard cyclinder from the plumbers merchant, but it is poor compared to a solar buffer store made by almost anyone else (75mm-100mm). As they tend to cost over a grand a bit(lot) more insulation would be in order. I was very tempted by one until I realised this. It's fair to say that no-else offers such good technical advice and custom-specified equipment at quite reasonable prices, so you may decide to just live with the mediocre insulation spec, given all the other good things. It does make a significant difference to overall system performance though - do the sums.

    I have been using my existing 110l bog-standard cylinder with a retro-fit heatexchanger and 40 tubes this year. It was over 80C at the (sunny) weekend, and I haven't turned the boiler on since April, although there have been quite a few days where it was not quite 40C and thus a shower would have been very tepid. If you are not happy to wait a day or two occaisionally then you will need to turn the boiler on from time to time. If my tank had insulation that was any good I reckon it would have provided 100% hot water since summer (in a 2 person low-consumption household). Bear in mind that I only had 20 tubes fitted from April to August and it was still pretty good.

    You can go over to the Navitron forum and contrast my and Skywalker's experiences of solar this year (I think it's great, he's rather disappointed). (My tubes are from eco-nomical, not Navitron - cheaper, but effectively identical, and I can recommend them as great people to deal with - they replaced some duff bits with no quibbling and gave me a spare tube for my trouble).

    Re finding an installer the Navitron fourms have an area for finding installers in your area who know about this stuff, which is worth a try. There are plumbers who understand wood burners, buffer stores and solar but you do have to search them out.
    Couple of points. Most uk manufactures eg DPS/Newark/Albion etc spray on foam (even when cased) whereas most of the continental stores use either a soft foam jacket with a rigid outer shell, or a hard PUR type foam shell all at 100-120mm. Also the above manufacture in copper which limits the length of the protruding spigots (off of which the bits hang) the continental stores are in mild steel with welded on spigots – stronger.

    Cheers, Mike up North
    Any pointers for finding 'continental' stores?
    • CommentAuthorskywalker
    • CommentTimeSep 23rd 2008
    Bear in mind that mine a wookeys systems are, almost literally, different ends of the scale (although at the planning stage they were actually identical). My system heats the whole volume of water his, rather cleverly it has to be said, puts hot water in at the top of his water cylinder.

    As I said there are many, many options.

    My only disappointment was the output of the solar tubes & I have found, with some careful insulation of the store pipe-work, that my DPS loses the same amount of heat as one of the better insulated albion cylinders (compared with Ivans wookey). It is however in a well insulated airing cupboard & by George we needed it this year!

    Navitron also replaced some dud tubes with no fuss for me.

    • CommentAuthorskywalker
    • CommentTimeSep 23rd 2008
    Have a look here too:


    Other options are presented here such as pressurised cylinders.

    Tony Stone (who's company this is) was, until recently, one of the most helpful and genuinely knowledgeable Navitron forum members generous with his advice to a fault. I have no connection to his company and have never bought anything from him but I will be buying my extra tubes from him when I get to that bit!

    • CommentAuthorskywalker
    • CommentTimeSep 23rd 2008
    David -
    The best thing to do is Google for accumulator or buffer etc. The navitron link gives a review of a few such as Akva, TiSun, Capito (Evinox), Consolar. A lot are referenced through solar people. But also any of the sites doing the wood boilers (eg Kotley etc or Atmos boilers) will be selling fairly generic buffer tanks i.e. the very plain ones with or without the solar registers or coils, after that the basic difference is going to be whether there is DHW preparation by coils – copper wrapped up type, large bore stainless coils or internal tank (tank in tank).
    There are a lot on eBay as well. Have a look at Buffer / Accumulators from some of these below, some are manufacturers and some are re-sellers. From the sites that sell wood boilers you’ll probably never find out who actually made it as the PSN/PSR/PSF type names are fairly generic. Most wood boiler suppliers will have their favourites. It may be better to approach from the wood boiler angale than from the solar angle as most will have a solar coil anyway.

    SolarFocus (pellet boilers etc)
    Wagner Solar
    Kloben - solar
    ACV – all sorts of heating
    SolarBayar – Some of these are sold by the renewable energy store web site
    Windhager – CaloWin + all sorts of pellet and wood boilers
    Vario Warm Technic
    Kaukora – wood boilers
    Boiler Nova – Italian fabricator

    Stores are also supplied by UK based commercial suppliers like BOSS/BSS (pricey), McCullum Water Heating, AO Smith.

    Get googling….

    Cheers, Mike up North
    • CommentAuthorskywalker
    • CommentTimeSep 24th 2008

    There will be times, like now probably, when it all seems to just be getting more and more complicated.

    There will be a strong temptation to 'just chuck in a combi' - try to resist.

    All will become clear in time.

    • CommentAuthorecowales
    • CommentTimeSep 27th 2008

    Yes you are correct, it does seem to be getting more and more complicated. When I started looking into it the theory seemed simple, log burner for winter, solar for summer and immersion as a backup, I assumed (rather naively) there would be an 'off the shelf' product made by worcester bosh or something.

    I really want this to work and thanks for all you answers so far. Yes I do have a cheap / free supply of wood and I intend to fit 40 tubes on a south facing roof. I really can't afford a combi as well, the log burner will cost in excess of 2K once the flue has been done.
    • CommentAuthorskywalker
    • CommentTimeSep 28th 2008
    It really could be that simple.

    There will tho Worcester Bosch things but they will be at WB prices - I dread to think.

    I think you should get your store/cylinder with extra bosses for connection to a boiler ( as an insurance policy) and if you have other things get those added before you start (Under floor heating whatever). You may even wish to add two immersions (one near the top and the other lower down). But a 40 tube system with a reasonable sized tank or store + all the gubbins to connect the solar side should cost around £1500 for the bits & pieces (Solar solutions/Navitron, wherever Wookey got his & others) - you just need to fit it (straightforward but requires a few skills and carefull process following).

    If you keep DHW (hot water for washing up showers etc) and CH (central heating) separate it will stay much simpler (I would still keep a facility for adding in a boiler in the future though). Run your CH direct from the back boiler on the wood burner (a number of fires will run a large number of rads and heat your DHW). UFH is a quandry but I'm sure there is a way of doing this in a simple system too (is it fitted yet?) - I confess we chucked out UFH from our plans & I have no real knowledge of how it all works & have not played with it.

    DPS stores are clever and I would not have been able to 'get it all in' to my place without one - but they are only clever if you really need the flexibility that one gives you. If you want a warm house in the evenings & hot water in the morning rocket science is not required.

    Skywalker and Mike (up north).
    Wow, what a response. Many thanks for the expertise, I'll go chasing.
    As people say, DPS Pandora is very neat and they're helpful, but not inexpensive. So I'll check alternatives.
    • CommentAuthorecowales
    • CommentTimeSep 28th 2008
    The DPS tanks seem very versatile as it's basically a bespoke tank to meet each individuals needs but as you say pricey and there seems to be a few complaints about the insualtion on the tank!? Whats the point in heating all this water up only to loose it due to poor insulation, could it be wrapped in a jacket? Also I asked them for a price on a tank over a week ago now and not heard from them since.

    I'm a little confused seperating the DHW and CH. Does this mean that the log burner would feed the tank directly rather than through a coil and the rads would also take water directly and then the DHW is taken from a coil/heat exchanger? There will be underfloor heating in one room and I think this will be taken from it's own separate coil in the middle of the tank as the temperature needs to be lower than the rads. I am planning on having 2 immersion heaters, one as a boost half way up and one to heat the entire tank from the bottom (on economy 7) in case of a lack of logs.

    I think I'm getting somewhere with this now. Anyone with experience of a working system or of their tanks from Navitron/DPS or alike. I have looked into this tank from Powertech http://solar.org.uk/productsDetail.php?productID=16 but still waiting for a price on this one.

    Worcester Bosch only seem to supply an unvented cylinder which is not what I want.
    • CommentAuthorecowales
    • CommentTimeSep 28th 2008

    Ok, I've done a little diagram of what I want. Excuse the bad drawing. It all seems to make sense if I've understood everthing correctly. What I have no idea about is pumps thermostats heat dumps etc, I think a plumber should be able to help with that though.

    http://;" >Cheshirehttp://www.tilestop.co.uk/shop/images/schem.jpg" title=" Cheshire " width="668" >

    Any comments

    • CommentAuthorecowales
    • CommentTimeSep 28th 2008
    Hmm that didn't work

    Follow this link to view pic

    • CommentAuthorecowales
    • CommentTimeSep 28th 2008

    I've been reading your posts on the Navitron Forum (I assume it's you). Spending the day sitting in the airing cuboard with my laptop is exactly what I want to avoid! I don't mind doing a bit of research but once it's in I'd like it to run itself ie. the immersion heater kicks in automatically at night time if required and if I want a bath in the evening just hit the boost switch for 20 mins and I get a hot bath.

    I notice you've been a bit disappointed with the performance of the solar panels this summer, your last post being in June, how has the rest of the summer been?

    On the drawing posted, you would not need the heat exchanger coil for the UFH unless you specifically wanted that side of it as a sealed system. You could connected it straight to the accumulator tank and have it vented. It would be vented as the log burner is connected to it. There is a limted amount of heat that can be extracted via an internal loop, if its a lot of heat required an external plate exchanger would be the only way to go, but all of that can be avoided with the direct connection.
    Cheers, Mike up North
    • CommentAuthorMiked2714
    • CommentTimeSep 29th 2008
    You've pretty much drawn a DPS GX system, although as Mike (up North) says, no need for the UFH coil, although I'd have through it will need to be off a blending valve fed from mid and bottom of the tank. The system will need to be open vented with a header tank above the highest radiator, I've a feeling that this is essential for the log boiler part of the system anyway, so its simplest to make the lot open vented. Also the tappings will need to be at the correct heights so that there is always a pool of heating water at the bottom of the tank which is cool enough for the UFH to avoid toasting your feet.

    Re store insulation, it would be nice if DPS used more as standard, but you can always add external insulation (plan for this!) : the foam on the tank doesn't help control heat loss from the heat exchanger circuit itself, all the tappings and pipework etc. Remember that in the winter, any heat loss from the tank into the house is heating, in the summer you just need to ensure you have enough panels so you have enough hot water regardless. In spring and autumn when you don't have the heating on it is an issue.

    Re DPS customer service, just keep calling them!
    • CommentAuthorEd Davies
    • CommentTimeSep 29th 2008
    Posted By: Miked2714Also the tappings will need to be at the correct heights so that there is always a pool of heating water at the bottom of the tank which is cool enough for the UFH to avoid toasting your feet.

    I thought the "done thing" was to use a thermostatic blending valve to mix water from the hot tank with UFH return water to get the right temperature for the UFH feed water. I.e., UFH water is circulated steadily to keep it well mixed and even temperatured with just enough top up from the hot tank to keep at the required temperature.
    Hi, assuming the picture was just a representation, the UFH mixer would be at the UFH manifold so what we see are just feeds off of the store, that said its not unusual to mount it at the store and feed the mixed down water to thr UFH distribution manifold. The mixer could be a simple mixer exactly as per the GX boiler side of the DPS store, or a motorised 3 way mixer.
    Cheers, Mike up North
    • CommentAuthorecowales
    • CommentTimeSep 29th 2008
    The underfloor heating will have it's own blending valve and manifold. The reason I gave it a coil is whenever you look at these tanks they seem to have the option of having an UFH coil so I assumed you needed one?

    Sorry to be a little dense but I don't really understand the plumbing side of things much, valves, vents etc but I would like to know the basic principal of the system I'm buying. Had a quote from DPS for £2800. This is just totally above budget and at that price isn't even an option. I'm looking at the Navitron tanks (not sure who manufactures them) and they seem to be much more reasonable.

    The search continues.
    Hi, The only reason it would have a coil is to keep it as an isolated and sealed circuit. The dPS stores are un-sealed = vented as are built in copper with a max 10m (1 bar) head. Other than that there is no reason, the heat extracted by couil is much less than if it were taken directly.
    The reasons the DPS quote is high is that a) price of copper, b) its a completely pre-fabricated set with all pumps and controls etc etc, that said I have added up the separate parts and there is a bit of a gap (thats their bit). But being fair if you look at the street price of a pre-plumbed un vented stainless DHW (not even twin coil) as a "system fit" ie with cental heating pump and some valves its nearly the same price - hideous.
    The basic buffer tank available is made of mild steel and comes bare, sometimes wihout the insulation and 500lit would be £500ish but its bare, so you would be adding all of the other bits yourself or to a design by a heating engineer with experience of this sort of thing.
    Cheers, Mike up North
    • CommentAuthorskywalker
    • CommentTimeOct 2nd 2008

    Sorry been a bit snowed under.

    Sitting in the airing cupboard was all about trying to work out what the output of the panels was. To cut long story short - not what the vendors claim. I could have completely ignored it, which is what I have done since about mid july, and just let my DPS get on with it but I wanted to check the solar thermal advice I was given against actual performance.

    In short I was advised with a thermal store (heated from the bottom by a coil) that I should get 40 tubes (approx' 1 per 5l) as long as I was prepared to heat dump (my DPS does this - very important if you have a back boiler on a fire as well as for solar) or cover up some tubes in the height of summer. I got 30 tubes as a starter as I wanted to see haw close to heat dumping this got me and make a judgment on wether or not to go for more than 40 tubes. The reason for this is that my partner works from home and we need to heat the house during the day in winter & any small contribution form solar is well worth the few extra £100's. The hottest my 30 tubes managed in mid summer on a sunny day was the late 60's leaving me thinking that I need 60 tubes to get my store near to heat dumping (just over 90 deg C)/trapping & storing the maximum amount of solar that it can in summer and a noticeable contribution in less optimal conditions.

    How well did my tubes do for the rest of the summer? We went on holiday for 2 weeks (to Cornwall, it was warmer in Leeds) when I got back my store was at 45 degrees - a fair reflection of the solar performance over what was a terrible summer. I suspect that the average performance of any solar thermal system has been rubbish this year compared to previous years (it never was, isn't and never will be my suggestion that Navitron tubes are specially rubbish). The weather has contrived to reduce insolation massively ( no ripe peppers in my greenhouse, late tomatoes, late everything actually). The last week or so has seen much better performance linked to some genuinely warm weather.

    If you get a DPS or other make of made up heat store (immersion, solar, wood burner & as I and others would recommend a gas boiler too) when it needs heat it will get it from whichever device it can switch on. Immersions tend to run under their own steam as it were so you either turn them on (for a boost as you suggest) or you turn them off (a backup if all else fails in my case not sure if there is a difference).

    I'm considering getting some aerogel to play with & use it on my store to boost the casing insulation.

    The Navitron tanks are made by Newark:


    The Newark cylinders are fine but as MIke says you will have to do all the wiring and plumbing/system side yourself. My main reasons for going for the DPS were its pre-plumbed/wired nature and I could get a custom size tank and all the gubbins to run all aspects of my system neatly in a very small space (limited width and headroom).

    Over £2k may sound a lot but when all you have to do is attach the pipes (push fit) and provide the store & immersions with electrickery, switch it on and go and make a cup of tea (as long as your plumbing works) it is not a lot.

    If you are happy to give it a go, with a resource like the Navitron forum (particularly Wookeys DIY heat store thread) you should be able to do it cheaper as long as you don't make any mistakes.

    Good luck either way.

    • CommentAuthorecowales
    • CommentTimeOct 5th 2008
    Thanks for your input Skywalker

    Lots of people have suggested a gas boiler as a back up, unfortunatley I don't have the space or the budget. My parts list would then be, solar panels, thermal store, gas boiler, log burner + rads and UFH.

    There's a similar system about 30 miles from where I live so I'm going to see it before making my descision. Will post the details of hos this one works once I've seen it.
    as wookey said above, I've designed and installed a WBS/solar/thermal store/immersion system similar to what you're planning and am pleased with it, although we only have 2 people in a small cottage so our needs are different. We use the immersion with a timer on Eco7 first thing in the morning to top the tank up to temp to ensure morning showers are always hot. What i haven't got round to fitting yet is a top 'boost' imm heater which would give that 20min boost at the top of tank (however, the low immersion does work, just a bit slower)

    Drop me an email if you have any specific questions (son't have much time currently to browse these forums!) ben @ mendipclimb.org.uk
    Cheers Ben
    • CommentAuthorUndecided
    • CommentTimeOct 11th 2008
    Hi - can I start a new thread folks? I'm another newby, but need to take the plunge. I am looking to put in place a system in a big old Victorian terraced house with high ceilings etc. (16+ rads) and want to use wood to generate to heat rads and hot water; then hopefully solar down maybe in a year or 2; also I have a gas boiler and want to keep its use to minimum / back-up.

    I've already considered option of gas boiler but think there are difficulties with this for me (would be installed about 20m from my house, for a start, which I gather poses technical problems). So thinking now on wood burning stoves. But am a bit concerned that even a big wood burning stove would struggle to heat the house in the winter. Wood I be feeding endless wood etc?

    Question - is a thermal store (accumulator) almost essential in such a system? - I understand that thermal stores/buffers allow multiple systems to be merged, but I'm also interested in storing the heat generated by the wood burning stove, so that have some heat/hot water in the winter mornings etc. This requires a big thermal store I think? Or would it be simpler to just use the gas boiler in the morning, and not try and store too much heat in thermal store?

    Question - would I need as large a thermal store as poss., maybe 750litres, but can something this size but set up inside a house? - can it be got through the door?

    Another Question: is it worth my while to try and use a wood burning stove to heat a thermal store, to access hot water later as described? I mean factoring in the cost of such a large store /installation ... would the amount of hot water stored not be worth the investment and amount of wood required.

    Sorry for so many questions, i'm really in the dark on alot of this stuff, and would really appreciate some wisdom.
    There is a difference between a wood fueled stove ie for the uk something in the fire place which may or may not hace a hot water boiler within it, and a wood fulelled boiler, or a pellet stove. An accumulator is necessary to allow the wood boiler to function as you basically light it and cant then stop it. You have some control over a pellet boiler as they can switch off, but again as there is still heat coming through they need to be able to work into some sort of load, hence the use of accumulators. For pellet min would be 500ish lit, for a wood gasification boiler about 1000+ lit, for a stove the 500-750 should be ok. yes they do go though doorways - even the big ones.
    Decide if the stored heat is for DHW or space heating or both.
    Mike up North
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