Wood pellet boilers

[philpjuk100]

The willow figures were interesting though; 26 hectares for 280 tons of wood pellets per year.(quote)
Yes that
seems optimistic to me as well,the spokesman said they will harvest areas on a three year rotation using "green" equipment!
Those figures for air travel/driving are interesting but is this the real"cost" of flying? the ticket pricing is so complex and there are so many people trying to stop you getting there,cabin crew,pilots,air traffic control,customs officers and the baggage handlers who hide your bags! phil.

 

[Flyfisher]

Those figures for air travel/driving are interesting but is this the real"cost" of flying?

It's the real cost for us! Admittedly, it would cost a lot more if we hadn't booked well ahead, but that's the same for train ticket pricing as well. I travelled from Penzance to London by train last year for £21 after booking ahead. The 'on-the-day' ticket price was about £80.

I only wish I could book ahead to fill my car for similar discounts!

 

[Penners]

I only wish I could book ahead to fill my car for similar discounts!

Ah, but you can. Buy all of your 2015 petrol now. Come 2015, you'll be burning the cheapest fuel in the country*.





* OK, I may have glossed over the minor matter of storing it for five years.... :?

 

[Flyfisher]

Five years is a bit risky though - we might all be driving LEAFs by then and won't be able to give petrol away (some hope :roll: ).

 

[Penners]

Don't worry. I shall still be driving my 2002 Ford Focus in 2015, so I'll buy it from you. Mate's rates, eh? :wink:

 

[philpjuk100]

This unleaded stuff goes stale if you keep it too long!.Ive got a lot of litres of stale petrol in my boat,it will run on it but will only start on fresh stuff.(ere! whats this got to do with wood pellet boilers?) phil.

 

[lou]

Hi AMc
I am so glad I read about your ASHP experience. I am on the point of committing to installing one with UFH. I wondered how large your large house is? Ours has 4 bedrooms and we were going to use it for the UFH downstairs - but still debating about how to heat upstairs. All bedrooms have high vaulted ceilings which will have roof insulation one day soon - bats allowing - but there's an open stair well and I can imagine a lot of heat loss that way. The walls are about 2ft thick but as it's listed we won't be insulating walls. The ASHP installation company told us that the model they have recommended (and I'll have to go back and check this now) would heat not only the UFH but also some DHW, though they have recommended a backup gas boiler, which I am not keen on. We aren't on mains gas so this would have to be delivered in canisters. If you were me, what questions would you ask the installers before we go any further?

 

[Flyfisher]

The ASHP installation company told us that the model they have recommended (and I'll have to go back and check this now) would heat not only the UFH but also some DHW, though they have recommended a backup gas boiler, which I am not keen on.

My understanding is that heat pumps (air or ground source) can only provide low temperature heat, which makes them ideal for UFH systems but not for DHW. I may be mistaken but I would certainly ask what the company means by "some DHW". Also, a gas (or oil) boiler seems rather excessive as a "backup" source of DHW. To my mind, "backup" implies infrequently used, in which case I would consider an electric immersion heater for DHW backup. The fact that this option hasn't been mentioned suggests to me that the boiler is likely to be necessary rather more than infrequently.

 

[JohnB]

My understanding is that heat pumps are only suitable for highly insulated houses, due to their low output. If the walls aren't being insulated, is it really a practical option?

 

[MdB]

We have a GSHP heating the underfloor pipes downstairs and nothing else. We heat our water on cheap rate electric as we were advised that it isn't suitable for use with hot water systems due to the low temperatures produced. Our system is rated at 6kW for a 3 and a half bed detached house which is 50% well insulated and 50% poorly insulated. The poorly insulated side gets cold at the moment but will be insulated later when we add an extension. It uses no electricity when off and is just switched on and off by a normal thermostat.

Self install cost was £5300 and running costs are going to be around £300 to £400 for the year I think with no maintenance costs.

We are very happy with our system. If anybody has any questions then please ask.

 

[AMc]

Hi AMc
I am so glad I read about your ASHP experience. I am on the point of committing to installing one with UFH. I wondered how large your large house is? Ours has 4 bedrooms and we were going to use it for the UFH downstairs - but still debating about how to heat upstairs. All bedrooms have high vaulted ceilings which will have roof insulation one day soon - bats allowing - but there's an open stair well and I can imagine a lot of heat loss that way. The walls are about 2ft thick but as it's listed we won't be insulating walls. The ASHP installation company told us that the model they have recommended (and I'll have to go back and check this now) would heat not only the UFH but also some DHW, though they have recommended a backup gas boiler, which I am not keen on. We aren't on mains gas so this would have to be delivered in canisters. If you were me, what questions would you ask the installers before we go any further?

Mine does DHW bringing a 300ltr tank to 45C ever night in about an hour and bringing it to 60C once a week to destroy bacteria - this isn't an issue. I've read it a lot and it simply isn't a problem, efficiency goes down as temp goes up but it's still way cheaper than running the immersion or running and servicing a combi boiler for hot water. You need to use a bigger tank and mix less cold in, that's all.

The house is 5 bed & 5 receptions (inc an 8x4m conservatory with modern double glazing) The foot print is 160m2 with a total floor area of 282m2. Half of that has been insulated to over 2006 PartL1B building regulations - including the walls. The other half is double glazed with solid walls and 300mm of fibre glass in the roof. The projected heat loss was around 16kW at -2C but I think we're losing closer to 20kW based on last winter.

We're underfloor downstairs throughout and parts of upstairs with the old radiators (too small) upstairs.
Heat rises so that stair case will cause problems and will make zoning the system complex. Not internally insulating your walls is also going to be a problem IMHO.

If you don't have or you're going to lift the upstairs floors then I would strongly consider underfloor throughout with separate zones upstairs so you can control timing. It's pretty straightforward to add a pipe work and a lightweight screed and the comfort factor is good.

My underfloor was originally supposed to run at a flow temp of 30-40C but with the problems we had with under capacity it's been flowing at 50-55C most of the winter. The unit modulates the flow temp based on the external temperature - so when it's warmer outside if heats it less, the temp increasing as we approach 0C air temp. That puts it 'ahead' of the actual temperature of the house and allows the pump to start inputting extra heat before the internal temperature starts to drop, compensating for the weather automatically. The hotter the flow temps. the less efficient the pump becomes so you want a large area of pipe in your underfloor.

I would also strongly recommend you look at a substantial heat store/buffer tank regardless of what your installer says - Economy 7 electricity is half the price of peak, so if you can store cheaper heat overnight and run the pump less on peak then all the better for your bills.
You should also look at Economy 10 - which gives you some cheaper electricity during the day though the rate is higher, it's also switched remotely so you can't call on heat when you need it - making a buffer tank an essential IMHO.

On that point contact your electricity provider and make sure the connection you have will be adequate for the load of an ASHP. We originally specified a single phase unit (to save on changing the supply) but the supply was 'unrated' and had to be upgraded at our cost to run the pump (£3K). At that point it made sense to get a 3 phase supply which in turn opened up other choices about heat sources which we'd previously ruled out (due to supply).

I would try very hard to design out the LPG boiler. It sounds to me like this is being added because ASHP is not going to be adequate - even calling on it's electric heater in the depths of winter. Even if you spend quite a lot more on the ASHP you remove a point of complication in the controls, plumbing, fuel supplies and you cut out an annual maintenance contract. A month of running the backup heaters can cost the same as buying a bigger pump.

Your installer will be looking to fit your house to a system they know. They won't necessarily be designing a system that suits your house. You are BUYING the system so I'm afraid you need to educate yourself about the options and look in detail at the running costs before you commit to the system you're being recommended. My company was very, very good at helping when the initial problems were encountered - I now have a second 16kW unit installer at their expense - but in retrospect if I'd been a better customer and made more informed choices we would all have been better off.

You need to get your heat losses down to make this a sensible choice. Oil and gas installations with radiators typically work on a back of the envelope calculation for the boiler, pumps and rads - all with a large over sizing margin of error because the extra capacity is cheap. With ground source or air source the balance between efficient and undersized is much closer and you need to be sure that you are on the right side.

If you need to chuck a lot of heat at a leaky, underinsulated building then you want to look at oil again or possibly wood (as per title) because you can cope with increased demand by increasing the flow temps with little or no loss of efficiency.
On cost, to give you some numbers last time I bought oil it was 50p a litre. 1 litre of oil gives you 10kWh of heat the equivalent of 10 units of electricity or 5p per unit. My peak electricity costs 14.1p per kWh. So to be cheaper than oil I would need the ASHP to be running at 3 units out for 1 unit in to be breaking even.

You really should ask your installer to see a unit in action, ideally with a customer to give their opinion. I'm also happy to answer any questions you have providing you're doing the research too

 

[Flyfisher]

Mine [ASHP] does DHW bringing a 300ltr tank to 45C ever night in about an hour and bringing it to 60C once a week to destroy bacteria - this isn't an issue. I've read it a lot and it simply isn't a problem, efficiency goes down as temp goes up but it's still way cheaper than running the immersion or running and servicing a combi boiler for hot water. You need to use a bigger tank and mix less cold in, that's all.

Thanks for that clarification; very interesting. I didn't realise the output temp could be boosted that high, albeit at a lower efficiency. But, as you say, that doesn't seem much of an issue for a weekly boost, especially if it does away with the need for a whole additional boiler system as 'backup'.

Is 60C the maximum temperature possible or just the minimum required to kill any bacteria?

 

[AMc]

Is 60C the maximum temperature possible or just the minimum required to kill any bacteria?

I don't know to be honest. The highest flow temperature I can set for the heating is 55C. I assume it uses the electric backup or is prepared to boost the output temperature above normal for the hour a week taken to pasteurise the tank.
Certainly it's much less efficient to try and sustain the higher flow temperatures so I imagine it's discouraged to prevent installing underpowered pumps and driving them too hard.

 

[Penners]

Is 60C the maximum temperature possible or just the minimum required to kill any bacteria?

I don't know whether this article is any help (it's American so you'll have to do some F/C conversion).

http://housekeeping.about.com/od/cleaning101/f/hotwaterbacteri.htm

 

[Flyfisher]

Thanks for that. As ever, the devil is in the detail.

That article suggests 110F (43C) as a maximum safe temp to avoid scalding.

This article suggests that scalding causes more injuries than legionella and recommends about 50C for DHW at the tap, even though it won't kill legionella.

This article is somewhat more detailed and states:
Legionella bacteria are usually found in low numbers in natural environments such as rivers, lakes and reservoirs. They can survive temperatures as low as 6°C and as high as 50°C. While maximum growth occurs at temperatures between 20° to 45°C, the bacteria seem to become most virulent at around 37°C, but are killed by temperatures above 60°C.

and:
In cold water systems, the ideal is to maintain a temperature below 20°C at all times while in hot water systems, the optimum is storage at 60°C and higher reducing to 50°C or less at the point of use to avoid the risk of scalding.
•70 to 80°C (158 to 176°F): Disinfection range
•At 66°C (151°F): Legionellae die within 2 minutes
•At 60°C (140°F): Legionellae die within 32 minutes
•At 55°C (131°F): Legionellae die within 5 to 6 hours
•Above 50°C (122°F): They can survive but do not multiply
•35 to 46°C (95 to 115°F): Ideal growth range
•20 to 50°C (68 to 122°F): Legionellae growth range
•Below 20°C (68°F): Legionellae can survive but are dormant

 

[lou]

Well - thanks so much AMc - I really appreciate it. I will now go armed with your information to our potential supplier and check out with another for a second opinion. Just for info, I can't put ufh in most rooms upstairs as we have only very ancient wide boards in some and victorian ones in the rest with little or no room between them and the ceiling below. Wish I could put it in all rooms - my daughter has it in her flat. It's so toasty and no ugly radiators!

 

[AMc]

You don't need much depth. You fix a 25mm batten to the inside of the joist, then 18mm OSB/Stirling board between them. The pipe is clipped to that and then a 25mm dry mix screed is put on top to the top of the joists. You can replace the screed with aluminium spreader plates but my UFH fitters don't think they're very good. The battens support the pipe and screed, the floorboards are nailed to the joists as before and support the load of the furniture and people. The only downside is you have to notch the joists by 25mm - no worse than if you were running radiator pipes but still destructive.

Downstairs we've got a mix of new engineered Oak boards and the original Georgian wide boards (there are pictures on another thread nearby) with UF throughout. The old boards are not being bothered by the heat - I'm guessing that having lived inside for >150 years and been centrally heated for the last 15 years has lowered their moisture content to the point they're not going to warp or move any more.

Failing that if you're going to fit radiators then oversize them substantially possibly up to 4 times normal size so you can use the same 30C low flow temperature as the underfloor - this will make the pump more efficient and cheaper to run. We're running our old radiators at 50-55C which sounds like it shouldn't be that far off the 65C we used to have from oil but it makes a massive difference to the amount of heat they put into the room.

Ask a lot of questions about how the heating controls and the heat pump will work together. One of my irritations is that mine are both 'too clever' and expect to have full control which means they don't work together as well as they could.

 

[lou]

Ok - thanks AMc. I am both grateful, humbled and not a little challenged by your expertise. Would that this all came to me naturally - but it just doesn't! Anyway, at least I am now a lot better informed about this complex (to me, anyway) subject and can at least sound as if I know what I'm talking about when I next speak to our prospective installers.

I can't help thinking what a great idea it would be if all of you PPUK experts were to offer your services to the more technically challenged amongst us for a reasonable fee or perhaps barter arrangmement. No matter which seller I ask, however ethical and knowledgable they appear - and they really do - I always feel I get just part of the story. Same principle as when you are getting 'free' financial advice. I'd rather pay someone independent. Maybe in another life. In this, I'll just have to trust my instincts.

 

[AMc]

Hi lou,

Honestly I've been to hell and back over the heating system. I'm happy to share my experience because I wish I'd been better armed with information and questions. I fundamentally think that electric heating systems coupled with lots of insulation are the only way we're going to tackle our fossil fuel dependency but at the moment its a rocky road. I don't even think the system I have is bad, just with more careful thought and a little more capital cost at the installation it could have been much, much better.

I had an interesting meeting with my supplier yesterday when we discussed the background power usage - they have a bit of software from the manufacturer that provides an assessment of the output power needed and the cost to run the ASHP. It makes no indication of a continuous 'standby' load which distorts the figures and puts the installer in a very difficult position. I am the first customer to raise the problem and they are now in active discussions with the manufacturer.

I would recommend you browse the Green Building Forum. It costs (£5?) to register and post there, but you are going to get value for money if you're spending £1000s on the heating system. I also recommend the Green Building Bible(s) as a good solid foundation in building with the environment in mind - it counters the "established" building trade views your contractors will give you about lime not being strong enough, insulation not being important, timber comes from the merchant and there's no need to worry about where it came from...

I have detailed more of my experience in these threads but there are others discussing ASHP and the potential pitfalls.
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5130&page=1
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5398
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5383


EDIT because I just remembered...
There is a proposal to pay the owners of ASHP & GSHPs a rebate on their power bills based on the amount of heat their property is assessed to consume. To obtain this rebate you will need to install an MCS accredited system using an accredited installer. As the rebate proposed could be several hundred pounds a year for 18 years you need to be sure your supplier qualifies in case this becomes a reality.

 

[Moo]

A thread that continues for three pages without deviating from the topic.