Our Wood Pellet Boiler decisions.........

ModelCitizen

R0b279.
Reduction of cycling is the reason heat stores (accumulators) are recommended. The efficiency and longevity of pellet boilers is reduced the more they cycle. Some consultants suggest that boiler size can be reduced if a larger store is used. I know of one example where a property rated as requiring a 24kw boiler instead installed a 15kw boiler with 5000 litre store (obviously they were not pushed for space !). The choice was backed with solid thermal/efficiency calculations.
As I have the space and might consider adding solar latterly (for summer water heating, ala Kittie above) I have pretty much decided that an 850 litre store is the right choice for me.

lostinrates

ModelCitizen wrote: »

I've just had a slightly worrying chat with a 'green' architect. He has stopped recommending pellet boilers for the properties he designs as he say efficiencies quoted by the manufacturers and installation companies are never reached. He blames much of this on the quality of the pellets, stating that the UK produced pellets are inferior and that to get anywhere near the efficiencies quoted you'd have to import top quality pellets from Sweden (not something I want to do).

As a result of his comments I've researched and found that there's an EU standard for pellets called EN Plus (Google it. As a 'new user' I am not allowed to post links).
Does anyone know of this standard or have any comments about efficiency and pellet quality?

We are going through the complaints procedure with ours. It has never worked properly, let alone with the efficiency suggested and I have to admit, I am very put off the technology and the MCS system of complaint handling. Tbh, for me the best result ATM would be to have the company take the wretched thing out. Parts of our house were built specifically to house the thing at the dimensions we were given, and what ever happens its cost us a lot of money, a huge amount of time. We have never managed to have heating and hot water concurrently, let alone the 'on demand' and 'unlimited' hot water we were sold as it having capability to produce.

However, pellets do I believe have to meet a standard. Pellets are shipped not just from Europe/Scandinavia but Australia and n. america too. It's not, as It stands, seemingly a green solution, but it promised to be an efficient one and one that had potential to be progressively sustainable. As the efficiency has failed us I am afraid I feel 'once bitten twice shy' and I am completely at a loss what we should do now for heating and hot water.

lostinrates

R0b279 wrote: »

My rationale may well be flawed, but the discussion I had with the installer was that by allowing the boiler to modulate whilst it is on through the day should be more efficient, as it (in theory) should require less power to get it back up to temperature. However he did say that he had customers who ran their boilers 24/7, or others that stuck rigidly to programmed timings.

The (few) setting combinations I played about with (mainly scaling back the time the water was on) I found that I actually ended up using more pellets, hence why I went back to leaving the boiler on through the day.

Who knows!

We run ours, ATM three times a day, when its working. We would run it for longer but the cylinder loses too much heat when demand is made of it (in either form of hot water or central heating) and the demand needs to be shut off for it to come back up to temperature. It's a bit of a vicious cycle, because the house stays 'cool' and then when the heating comes on the water cools so much in circulation that the temperature of the cylinder plummets.

Though ours was sized for the house on a survey, in practice it seems its simply not large enough. An independent adviser came out and says while surveying accepts our house is ok for 28kw he thinks in practice it should have had two 28kw boilers, (as best practise in case of break down of one to be a self providing source of some heat and hot water) or a 60kw boiler.

We were told we would need nine tonnes of pellets a year, and have already used not far off that in less than half a year.

I read these threads where other people's work brilliantly with envy!

R0b279

Lostinrates

Thanks for that. I'm sorry to hear of your problems. I'm guessing that if you could run your boiler for a longer period you would.

Cold comfort for you, but in comparison to LPG, I'm satisfied with the conversion to pellets. At worst, I've halved my monthly space heating costs.

ModelCitizen

lostinrates wrote: »

We run ours, ATM three times a day, when its working. We would run it for longer but the cylinder loses too much heat when demand is made of it (in either form of hot water or central heating) and the demand needs to be shut off for it to come back up to temperature. It's a bit of a vicious cycle, because the house stays 'cool' and then when the heating comes on the water cools so much in circulation that the temperature of the cylinder plummets.

Though ours was sized for the house on a survey, in practice it seems its simply not large enough. An independent adviser came out and says while surveying accepts our house is ok for 28kw he thinks in practice it should have had two 28kw boilers, (as best practise in case of break down of one to be a self providing source of some heat and hot water) or a 60kw boiler.

We were told we would need nine tonnes of pellets a year, and have already used not far off that in less than half a year.

I red these threads where other people's work brilliantly with envy!

I'm very sorry to hear of your problems.

I'd be very interested to know why yours does not work correctly, what size/type of house you have, what boiler is installed and you what size heat store you have. For a 28kw boiler even nine tons a year seems a lot of pellets. My old detached four bedroom property, standing by itself and windswept, with floor area of 212.57sqm and an abysmal energy efficiency rating of 34 has only been rated at 25kw requirement (by three different companies), with estimated pellet usage of 5-6 tons a year.

If your consultant recommends that you need boilers rated at a total of 60kw your house must be huge (or made of cardboard!). Having a second for backup is an unusual recommendation (if this is what your consultant was recommending). By this reckoning every house would have a second backup boiler, whatever fuel they used. In reality most people have an immersion for hot water backup (which you can also have with a conventional pellet boiler driven system of course) and individual space heaters in case of heating failure.

As I understand it pellet boilers become more inefficient the more they cycle and so the onus is on the installer to size the boiler exactly to the requirements of the house. Too large a boiler will lead to constant cycling. Unlike oil or gas pellet boilers cannot be governed down.

Would you confirm that when you refer to the 'cylinder', you do not mean hot water cylinder but instead are referring to the heat store, aka as accumulator?

BTW. Has your flue been sized correctly? If you do not own a terribly insulated mansion it sounds like your boiler is just not delivering the power it should be.

R0b279

ModelCitizen

Thanks for that. I guess for me, it's something I'll keep an eye on over time. The boiler should be due a service now (though I'll wait until summer), and will ask the installer then. As I've previously mentioned, I approached 4 possible installers. All in all, I think I had the option of 7 different pellet boilers. Only one option included an accumulator. That installer offered one solution with an accumulator, but their alternative (a Grant Spira 25kw) was quoted with no need of an accumulator.

On an earlier post I mentioned that I had done a wee bit of web research on pellets, and costs. As part of that process I was advised (at that time) that there are three ENPlus-A1 accredited pellet producers in the UK, being; Verdo Renewables, Balcas Brites, and Clifford Jones Timber. I've recently tried Woodlets, produced by Land Energy, and they too have just recently received ENPlus accreditation. I was using Balcas Brites before that, but think the Woodlets burn better.

I'm sorry to hear of problems, as it's a massive outlay/investment. It's only been a year for me, but I'm entirely satisfied, and that's not including any potential benefit of RHI payments.

I considered a number of space heating alternatives, including ground source, and air source, but biomass was the best option for me.

R0b279

ModelCitizen

Meant to add that the accumulator option was actually "sold" to me purely as a back up, should the boiler stop working.

I also remember talking to a plumbing lecturer that I know (after I had installed the system) re biomass solution. I do recall him mentioning an accumulator, but again it was in relation to a boiler failure.

So it's an interesting point you make in relation to boiler longevity & efficiency.

lostinrates

ModelCitizen wrote: »

I'm very sorry to hear of your problems.

I'd be very interested to know why yours does not work correctly, what size/type of house you have, what boiler is installed and you what size heat store you have. For a 28kw boiler even nine tons a year seems a lot of pellets. My old detached four bedroom property, standing by itself and windswept, with floor area of 212.57sqm and an abysmal energy efficiency rating of 34 has only been rated at 25kw requirement (by three different companies), with estimated pellet usage of 5-6 tons a year.

If your consultant recommends that you need boilers rated at a total of 60kw your house must be huge (or made of cardboard!). Having a second for backup is an unusual recommendation (if this is what your consultant was recommending). By this reckoning every house would have a second backup boiler, whatever fuel they used. In reality most people have an immersion for hot water backup (which you can also have with a conventional pellet boiler driven system of course) and individual space heaters in case of heating failure.

As I understand it pellet boilers become more inefficient the more they cycle and so the onus is on the installer to size the boiler exactly to the requirements of the house. Too large a boiler will lead to constant cycling. Unlike oil or gas pellet boilers cannot be governed down.

Would you confirm that when you refer to 'cylinder, you do not mean hot water cylinder but instead are referring to the heat store, aka as accumulator?

BTW. Has your flue been sized correctly? If you do not own a terribly insulated mansion it sounds like your boiler is just not delivering the power it should be.

Rather than derail this thread further,

https://forums.moneysavingexpert.com/discussion/4358107

Is where I have been discussing mine. I want to scream and shout the make and installers so that others do not make the mistake, but I am wary of doing that while things are so contentious and no finding has been made.

Our house is not small, but the boiler was spec'd for our house after extensions are made. In the end this will be two rather large and three more moderate sized reception rooms, a large kitchen, four/five baths and six beds over three floors. It's an old house, so solid wall, and where more modern Victorian walls were is now heavily insulated internally. ATM it's only being asked to serve one bathroom and the kitchen hot tap, and failing, and 'only' has about thirteen rads attached to it.

ModelCitizen

Thanks. Interesting as I am in the same situation, sizing the system for my house as it will be in two years time, after its size has been increased by 38% and I've improved the insulation of the existing Victorian build as much as I ask able. Don't suppose you I've Sussex do you? I'll read your thread now.

diywhynot

Info on ENPlus wood pellet certification and list of producers available here.