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Connection of log boiler to accumulation tank
 Started by  sab
 16 Feb 2009, 2:02 PM

Hello, I am new to this forum and wonder if anyone can help me with a question. We have recently installed an Atmos 32kwh log gasification boiler and accumulator tank. We have had many start up problems. We have it installed with a laddomat 21 and originally the installer had the heat carrier from the boiler going to just below the centre of the tank and the outflow to the house from the top. The tank did not heat up and so on investigation (and with no knowledge of such matters myself) I found that the heat carrier should go to the top of the tank. I persuaded the installer to do this for me and things improved greatly but it is not ideal as we have to wait such a long time for heat to the house. However, I have since found in the atmos service manual that there should be a 't' junction in the heat carrier just before it goes into the tank which carries the water to the house (direct from the boiler). This, to my mind, seems a much better arrangement as it means that heat goes to the house before being stored in the accumulator, and only when the valve to the house is shut off because the heating is turned off, does the boiler charge the tank. My installer insists that this is incorrect and that his contact at atmos says the set up causes too many problems. Now I'm confused. Any views?
PS our accumulator (I have only just discovered) is undersize at only 1000 l. We rarely get any heat in the mornings.
GBP-Keith (Guest)
Hi Sab.
Your accumulator should be the heat deliverer to the system, not the boiler.
Are you using radiators or an underfloor system?
It should be set up like this.
Your boiler will run flat out hopefully just once per day for 3 to five hours with a single charge of logs and because it is running flat out it is burning the logs efficiently. The water temperature generated is likely to be too high even for radiators. Your heat delivery system will then take hot water from the top of the tank and use a mixer to ensure that the correct temperture water is delivered to the system. >60degrees C< for radiators and >35-45degrees C< for underfloor.
This way, your tank is not drained of heat too quickly and it is 'eked' out for the duration between burns which as I said should be once per day. If your tank water is not lasting long enough then your system (house losses) are exceeding your generation (boiler run-time times output) so you may need two firings per day on cold days.
Hope this is useful.
PS, your tank size needs to be related to the amount of burning you plan on doing. One firing per day would suggest about 1200ltrs.
By the way, I would tend to agree with your installers opinion, but who can argue with the manufacturer. if you want heat in the mornings then do your firing later in the day, perhaps 4pm. If you are using radiators then the task is harder because they require such high temperatures. Remember that the system would work best if there were two heat stores, the tank and the house!
sab (Guest)
Hello, thanks Keith, that was very helpful. I will stop nagging my installer to change the pipework again then. We have underfloor heating downstairs and radiators upstairs. I do not think we have a mixer valve though! Trouble is, we did a barn conversion and were going to go with oil as the fuel source. We then thought we would be more green, and install the log boiler instead. Our builders' plumber hadn't a clue about log boilers so we got a new local company in to do it, but they have so far only installed a few pellet boilers and we are the first customers to want a log boiler (we didn't know this when we hired them!) Anyway, the communication between the two sets of people was non existent and we ended up in a terrible mess. We have been 5 months without heat until now in the worst winter for years. Still better than the caravan! I wonder if the mixer valve might be fitted inside the house where the hot water comes in from the boiler? I will have to try to find out. I had no idea the two heating systems required different temperatures. Thanks again for your help.
sab (Guest)
Just thought, with your comment about the two heat stores, would it be a good idea to keep the underfloor heating on at night?
We run our underfloor in 40 minutes on and 40 minutes off mode essentially for 19 hours each day that the heat is needed. It is off entirely from 1am-6am. Our underfloor is in quite a thick slab so it holds the heat for a number of hours (hence the on/off regime). If your underfloor is not in a heavyweight slab then it will be more 'responsive' so just start it running earlier in the morning.
If you have no mixing then this is probably why you are running out of heat but I'm surprised that you don't have overheating problems in the house while the boiler is on!
Are you saying that your underfloor and radiators are being given the same temperature water Sab?

sab (Guest)
Hello, I have been told we have a mixer valve next to the underfloor heating panel so everything ok I think! I fed the boiler last night at 9pm and radiators were warm but not hot this morning. It was the 4th load too. Today things seem better, maybe because the core temperature of the house has become much warmer, and maybe because the weather is milder. The boiler is on it's second load and the temperature of the water coming from the bottom of the tank is 65 degrees. I will feed it again last thing and see if we have heat in the morning. Thanks for all your help. PS we have only just installed this boiler. The first boiler we had was a non gasification 20kwh boiler which we had to feed around 12 times a day and it still couldn't heat the house! We were using more than 3 times the amount of wood for nothing. It's all been very frustrating.
If the bottom of the tank water is 65degrees then there is plenty of heat. be careful not to over burn and have nowhere for the heat to go. Remember, the tank is your buffer. If this gets over-hot then your boiler could get dangerously hot. However you should have automatic safety shutoff systems in the case of this happening.
Unless you can get the boiler dow to one feed per day, it may become too much of a burden. Do you know the heat requirements of your house in kWhs?
if you are doing four burns in a 35kW boiler and each burn lasts three hours, then the boiler could conceivably be putting out a massive 420kWh. My boiler has not been lit for three days now as it is so mild but the bottom temerature of my tank rarely exceeds 35 degrees!
PS. the water goes to the bottom of the tank not from it. The important temp as far as your radiators is concerned is the top of the tank.

sab (Guest)
I seem to have got it down to 2 feeds a day now. There was plenty of heat yesterday but by morning the tank was cold again. So something is wrong. The tank was up to 80 last night at 9 pm but radiators were luke warm this morning. The heat must be being lost somewhere. I was thinking, that if the underfloor heating has a mixing valve it must be introducing cold water to the system then returning the water at a much lower heat? I'm afraid I am not very knowledgable at this things and husband is even worse!
Are your radiators running overnight?
It would be interesting to leave the heating system (draw) off overnight to see how much the tank is losing to the room as straightforward heat loss.
No the underfloor is only mixing the return cooler water with the flow to the floor, this will actually save you energy. You really should have a mixer on your radiators too as to circulate the water at 80 degrees will cause massive heat losses. a mixer (should be as near to the tank as possible) can ensure that heat is only delivered to the radiators at about 65-70 degrees. this keeps the heat in the tank for the next morning.
No, the radiators go off at night but the underfloor heating comes on if the house drops below 15 degrees. I burnt only one and a half loads yesterday and the boiler had burnt out by 9pm. The water at the bottom of the tank was reading 80 degrees so I left the boiler to go out. We had 1 1/2 hours of hot radiators after that until the heating went off at 10.30pm but the tank was cold by morning! It is a very well insulated tank but there are small gaps in the insulation of some of the pipes. I wouldn't have thought it would be enough to cool the whole tank though.
I would find it hard to believe that you could put 1000 litres through your radiators in 1 1/2 hours and leave a cold tank. It may pay to have a look at the top and bottom temps at 10.30pm when the radiators shut off.
An accumulation tank must always be used in conjunction
with the wood gasification boiler to allow the boiler
to operate in the most efficient manner.
The officials recommend sizing of accumulation tanks for
solid fuel heating is a minimum of 50 liters of water storage
for every 1 kW of rated boiler output. Hence for a 35kW
boiler a minimum accumulation tank size of 1750 litres is
need. To provide an additional safety level will be
supplying a 2000 liter accumulation tank with the 35kW
When the boiler is gasifying properly there is no smoke at all.You get a clean burn when the gasification process is underway, which is to say any time the boiler is operating under load and producing heat.
Greentech are specialists in a range of Gasification Boilers Services
Hi BobWalsh
I am building an outbuilding to take a 40kW gasification boiler. I have 3 1000litre NAD accumulators and a laddomat and mixing valve. Elsewhere I read that 50:1 is a way of working out the size of accumulator needed which makes 2000 litres. Is there are any advantage in using all three? Could I set lever valves off on one except for during the coldest months?
I have just signed up and need advice please !
In October I had installed a Perge 30kw wood burning boiler together with a 3,000 litre accumulator tank. I am now at my wit's end (and so it seems is my installer after my nagging) as the system seeems to be totally incapable of providing even the minimum amount of central heating I require.
It has been designed to heat radiators of various sizes(17) and a small underfloor system in an extension to the house. A number of clitches have been identified and put right by the installer but the main problem remains - it takes many hours to transfer heat to the accumulator even with super-seasoned wood and then the heat rapidly disappears. For example: Yesterday with constant loading it took seven hours (almost one load an hour) to heat the accumulator to 75c degs at the top, 65c degs no 2 section 59 c degs no 3 section and the bottom of the accumlator barely moved at all from its starting point of 35 c degs. The heating came on at 5 pm but by 10 pm when it switched off the accumulator temperatures was down to 40c degs at the top and the other slots were barely above 30 C. I loaded again at midnight and 1am only to find this morning the central heating was again tepid. I was assured by the suppliers and installers that I should get at least two days from the accumulator. (I should say I began loading when the accumulator was showing around 40 degs or slightly less ). It appears the boiler does its work and burns the wood to a fine powder, but transfer of heat to the accumulator is painfully slow and it takes a lot of wood. An Esbe transfer pump valve (I think that is what it is called) is fitted which now, on the advice of the suppliers, I have changed from a speed three to two with no apparent difference. There is also something called a Thermomatic K that controls, I think, the flow of water in the accumulator and a Laddomat that kicks off the Esbe. At this rate I will need Sherwood Forest if I am to continue using it. Fortunately, the boiler has been linked to my oil boiler but that was supposed to be for back-up heating. I find myself in a nightmare situation of having spent 12,000 or so on a system that would appear not fit for purpose. Does anyone have any suggestions as I am getting more and more disheartened. I am a committed wood burning home owner (I previously had some years ago a Thermorosi wood/oil boiler which worked wonderfully well until it overheated !) and I just want the system to work and not take the legal route to try and get some of my money back if the problem can't be solved. Both the installer and the boiler's supplier have so far done their level best to rectify the situation but they appear at this point unable to sort it. I have suggested to the installer that we go back to square one and change the transfer pump/valve and Laddomat but do you think that is a bit over the top.

John W, fitted the same system back in september and having similar problems. After the installer coming out and tweeking the system under advice from perge I normally end up taking the stat out of t
the laddomat, closing the top valve on the laddomat and running it that way. Perge themselves are planning on coming out to look at it so will post after that. The system problems are caused by air in the laddomat, once that air is eliminated I am confident that the system will work well
Bearing in mind the question at the start of the thread as a supplier we have the following schematic drawing supplied by Akvaterm (excellent company to deal with) which covers every eventuality.
Picking up on JohnW comment we encourage a 50 to 1 ration of thermal store to kW output.
ie 25kW to 1500 litre 40kW to 2000 litre accumulator tank
30kW to 3000 litre is twice the ration we would work to.
What heat efficiency is the Perge rated at?
Ours is 92% and it likes wood ideally at 15-20% humidity.
Laddomat 21-60 would be improvement on Laddomat 21.
What make of accumulator tank is it?

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