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Heating and cooling: Gasification boiler and buffer tanks

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  1.  
    I have a 35 kw Attack boiler heating my house with ufh.
    I have 2 buffer tanks each 1000 litres, the system is about 4 years old, it is located in my garage about 10 metres from my hot press.
    I am not sure the system is installed correctly and I would like some help if possible.
    The boiler output pipe goes to the top of one tank but there is a feed off this pipe taking water direct to my hotpress,in other words the boiler is supplying my heating with any spare water going
    to the buffers.
    The problem I have is that my boiler can be producing water at 75 Deg for example but the supply reaching my heating can be as low as 40 Deg think the heating pump Is pulling water both from the boiler and the buffers, and if the tanks are down it's reducing my feed temp to the heating.
    Can I fit some sort of valve that would isolate the buffers if the are below a certain temp but yet would allow them to fill when the heating is not taking any more hot water.
    I am not a plumber, and any advice I can get here would be really appreciated as my plumber is not sure of a solution,by the way I am based In Ireland, co clare on the west coast.
    Thanks for reading this
    • CommentAuthorowlman
    • CommentTimeNov 25th 2017
     
    I think I've understood but If you can you do a quick rough sketch of your system it would help.
  3.  
    I will try,also there is a laddomat included in the system
  4.  
    The classic set up would be that the boiler heats the buffer tank(s) only and the heating is taken from the buffer tanks. That way the boiler can run at max efficiency and you can also maximize the heat in the buffers for your heating. The buffers at 2000lts are about right for your boiler but 2 tanks is not the best, but that is what you have. The function of the laddomat is to maintain the temp. of the boiler at about 70 deg by recirculating the (short circuiting) the boiler output to the input to maintain 70 deg. only allowing the excess to go to the buffers.
  5.  
    Yes I believe that it is normal to plumb the boiler feed directly to the heat store, and then to run the heating from the tank.
    I think the reasoning behind my heating having priority over the headstone was that If my thanks were down I could light the boiler and have heat quickly.
    Am I right in thinking that my heating is drawing both from the boiler and buffer and that this is reducing the overall temp of hot water available for my heating.
    Is there any way of preventing water leaving the buffer below a certain temp, a temp valve of some sort?.
    I expect if I change the pipe run and just have the boiler feeding the TS I would eleminate the problem, before doing this I would like to me sure I can't keep the boiler set to feed the heating directly
  6.  
    Instead of headstone I meant heating and tanks instead of thanks ,I'm afraid a small screen and poor eyesight caught me out
    • CommentAuthorowlman
    • CommentTimeNov 26th 2017
     
    A more conventional two tank set up would be for the side by side tanks to be connected top and bottom, e.g. on corresponding sides roughly 1/4 down from the top and 1/4 up from the bottom. The boiler would feed the nearest tank often on the side roughly opposite the connecting feeds. Water circulation would eventually equalise temperatures between the two tanks. The draw off for CH would usually be from the top of the second tank with some form of temp regulation before entering the heating circuit.
    The CH return needs to thought out too, for best efficiency, possibly even split between both tanks.
    IMO, and as Peter says, two tanks are an inferior set up, but often used because of initial access space. The secret is to make them act as one circulation wise. One way would be to make the connecting pipework for the two tanks as big as possible, something like 2".
    I did know of one guy who ran a CH system direct from a log gas boiler, with no buffer tank,- not recommended BTW.
    I think you are right in your assumption that the CH pump is sucking both hot water direct from the boiler flow and cooler water from the tank with little or no recharging taking place until the pump switches off.
    You say you want to feed the heating direct from the boiler. Does that mean you don't want to utilise the storage capacity of the buffer tanks; which is the whole rationale for having them.
  8.  
    Thank you all for your help.
    I like the idea of being able to use the boiler to feed the heating directly if the tanks are down, however as it currently is set up like this and not performing I expect there is nothing I can do but change to a more conventional set up of heating the buffers and then taking my heating from there.
    My plumber say that by putting the feed to the top Of The buffer Ann also taking output from there that we should overcome the issues I currently have.
    I understand that it is impossible to operate without the buffer tanks, would there be any merit in isolating one Of The tanks or would the 1000litres be inadequate from a safety point of view.
    The idea I had of being able to use a valve of some description to prevent the cold water in the tank mixing with the hot supply from the boiler is I presume a non Runner.
    I am running the boiler on good dry wood and it is performing very well, the problem is all my hot water is disappearing and it is very frustrating, again thanks for reading Thia
    • CommentAuthorowlman
    • CommentTimeNov 26th 2017 edited
     
    There is a direct relationship between boiler kW output and buffer tank capacity. It used to be approx. 50:1 litres to kW boiler output, so at 2000l you are OK, and the extra bit of safety margin is a good thing. Mine's slightly oversized too.
    I think those figures were originally formulated in case of runaway boilers and having enough capacity to accommodate the extra heat. To some extent that problem has been mitigated with quench coils on the boiler.
    If you consider reducing that margin of safety even further it may not be wise, especially if your boiler doesn't have a quench coil.
    Personally I'd, a; do the plumbing circuit change. b; insulate the buffer tanks as much as possible,. c; get into a routine for charging the buffers on a regular basis and just use the stored heat. That's the usual way, and the way most of us operate. Oh and if you are using so much stored energy what's you home insulation like??
  10.  
    I will have to plumb into the top Of The buffer tank, and is it also from this same tank that I should take the feed for my heating.
    The above is what my plumber is suggesting he says it should mean that I get hot water from the tank almost fast as if it were coming from the boiler
    • CommentAuthorowlman
    • CommentTimeNov 26th 2017
     
    The boiler intake is usually into the side of the buffer tank approx. 1/3 down from the top; it varies from manufacturer to manufacturer; a bit of a black art IMO. The draw off can be literally on the top centre, mine is.
    I feel correct positioning of the boiler intake port into the side of the tank may be crucial. A risk of feeding into and drawing off the same (no1) tank could be to kind of isolate the other. Unless of course you have a good circulatory flow between the two.
    Your plumber appears to know his stuff though and after all he's the guy on the spot.
    As we said initially part of the problem would seem to be the downside of twin buffers, but obviously you have to make the best of it.
  12.  
    Yes the plumber did suggest exactly as you say, feed about one third down and heat outlet from the top Of The tank.
    I understand your concerns about perhaps isolating the second tank but would this create a problem in normal usage, I presume that if we did get the first tank charged fully the second tank would still be able to take Surplus heat.
    • CommentAuthorowlman
    • CommentTimeNov 26th 2017
     
    What size pipework and how many, connects the two tanks?
  14.  
    Owlman,thank for giving this so much time on a Sunday.
    What I currently have is a feed to the top of tank one from the boiler, there is a connection from the bottom of this tank to the top of tank two and the heating return also comes back to the bottom of tank two.
    The heating return pipe is split between the buffer and the boiler .
    Thanks again.
  15.  
    The pipe work is inch diameter
    • CommentAuthorowlman
    • CommentTimeNov 27th 2017
     
    It appears its configured so that tank 1 is being charged first and when that is fully charged then tank 2 follows. I'm guessing therefore, that because your rate of usage tank 2 rarely, if ever gets hot except from the lukewarm return CH water. Is the connection from tank 1 to tank 2 as you describe, the only one?
    I think a diagram would help.
  17.  
    The only connection between the 2 tanks is from the bottom of tank one to the top of tank 2, the heating return also goes back to tank 2.
    I am heating about 2200 square feet of ufh. The tanks struggle to get above mid 40c ,the heating is on constantly , set at 25c on each manifold.
    I am sure it's not perhaps the best sized system but it's what I have and any say I can coax a little more heat from it would be great.
    I started off asking was there any way I could leave it as it is, ie direct feeding and restrict flow from the buffer by a control of some sort, is that a total non Runner as from a safety point of view I can't do without an escape for excess hot water.
    The boiler has a cooling loop that does work well
    • CommentAuthorowlman
    • CommentTimeNov 27th 2017
     
    I think perhaps the two tanks have not been connected in the right way, plus the original misplaced draw off CH tee. Fixing that and altering the boiler feed into tank 1 as your plumber suggests seems OK, and would go some way to partially solve that problem.
    BUT:-
    a. tank 2 doesn't start charging until the hot water in tank 1 charges/stratifies down to the connecting feed at the bottom of that tank.
    b. If you've got constant CH demand that maybe never happens.
    c. tank 2 as configured is therefore mostly redundant from a heating supply point of view.

    Think about it in a circulation perspective:-

    Currently, you've got hot water from the boiler going mainly straight into the CH circuit plus a bit of charging/stratifying. The CH pump is "pulling " that water from the tank 1 top, and at the other ends (tank bottoms 1 and 2 ) it's pushing back in the return water. Because you've only got the one pipe connecting the two tanks you're ending up with two forces fighting one another.
    Thermal expansion, (when the boiler is firing ), in tank one, wants to expand and charge tank 2, especially if the pump is modulating. At the same time hydraulic pressure (from the pump return ) wants to push the other way. Because the thermal expansion is relatively slight, the pump wins, hence partly why your tank/tanks don't charge properly.
    This would be my initial diagnosis from your description and it's where Id be looking for a remedy, I may be wrong.

    I hope that makes sense, whisper me if you want to talk.
  19.  
    OK that does seem to be what's happening, how should I go about remedying it.
    I am happy to try what you suggest as it will only I involve a bit of pipe and a few hours labour and could make a big difference to my heating
    Thanks for your time on this
    •  
      CommentAuthordjh
    • CommentTimeNov 27th 2017
     
    A drawing, even if hand-drawn and scanned in, would help enormously. It provides another way to double-check that one's interpretation of the configuration is correct and helps to visualise possible changes.
  21.  
    Is there a way to add a photo, I'm afraid I don't have access to a scanner
  22.  
    djh I'm sure a picture is worth a thousand words or even more of mine perhaps, but I will try.
    I have a 35 kw boiler with laddomat.
    The outlet from the top Of The laddomat goes to my hotpress,there is a T off this pipe going to the top of buffer tank one.
    At the bottom of tank one there is a pipe going to the top of tank two.
    The return pipe from the heating comes to the laddomat and also is connected to the bottom of tank two.
    I believe that the buffers are letting cool water mix with the feed from the boiler which means my heating supply is quite cool.
    Mr Owlman has given this a lot of his time and he seems to think that this is what's happening as well.
    I now need advice on best to connect to the buffers and eliminate this problem, or even to reduce it.
    I am extremely grateful to All of you for your help, this is a problem that has baffled me for ages.
    •  
      CommentAuthordjh
    • CommentTimeNov 27th 2017
     
    Posted By: harhenmemorials@eircIs there a way to add a photo, I'm afraid I don't have access to a scanner

    Yes, just use the Browse button under the Attachments heading. Make sure it is not too high a resolution, otherwise it won't upload.
  24.  
    At risk of sounding stupid, where is the attachment heading!
    • CommentAuthorowlman
    • CommentTimeNov 28th 2017
     
    I've whispered some comments to you, but you'll need to sign into the forum to see them. If you just click into the forum, each day without signing in, as I often do, you'll miss the full "one to one" picture.
  26.  
    <blockquote><cite>Posted By: harhenmemorials@eirc</cite>The outlet from the top Of The laddomat goes to my hotpress,there is a T off this pipe going to the top of buffer tank one.</blockquote>
    This statement confuses me (some would say easily done !) The top connection on a laddomat is an input, see below.

    <blockquote><cite>Posted By: harhenmemorials@eirc</cite>The outlet from the top Of The laddomat goes to my hotpress,there is a T off this pipe going to the top of buffer tank one.
    At the bottom of tank one there is a pipe going to the top of tank two.
    The return pipe from the heating comes to the laddomat and also is connected to the bottom of tank two.
    I believe that the buffers are letting cool water mix with the feed from the boiler which means my heating supply is quite cool.</blockquote>
    The laddomat has 3 connections and a pump. It is designed to maintain the boiler at around 70 deg. and will divert excess heat after this to the buffer tank. The pump circulates water around the boiler and when the boiler return temp. is sufficient then the laddomat thermostat closes and the pump then pumps the boiler output to the buffer. The laddomat is a mixing valve so the return from the buffer will be mixed with the boiler output to maintain an acceptable boiler return temp. (Last time I looked the laddomat web site had a schematic of the operation)

    The top connection should be connected to the boiler output which is teed to the buffer tank input. The lower left hand connection (when looking at the temp. dials) should be connected to the buffer return and the lower right hand connection should be connected to the boiler return. Laddomats are usually mounted directly at the boiler return, i.e. at the base of the boiler. As said above the boiler should heat the buffer and the buffer runs the heating. so It would be better if the heating return went to the buffer with its own return input rather than share pipework with the laddomat.

    Do you know what your heat load is ? Because if your heat load is at or close to 35kW then you won't be heating the buffer tanks as the demand will match supply with not much left for the tanks. This would be in addition to any plumbing issues with the set up you have.

    With my system (40kW boiler, 2000lt buffer and laddomat) the boiler temp is maintained at 70 deg, the buffer tank heats up to 70 deg starting at the top and working down and when the whole of the buffer tank is at 70 deg then the buffer and the boiler go up in temp together to about 90 deg.. I have to judge the amount of wood to put on the boiler to ensure the burn finishes about the same time as the buffer gets to 90 deg top to bottom. So any over heating of the store is (would be) my fault. The laddomat will allow gravity flow in the event of a power cut and the pipe work between the boiler and the buffer will also allow gravity flow, experience has shown that power cuts are not an issue.
  27.  
    OK, I think I finally worked out How To get some pictures up, I will photo the setup and see what you think

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