Fan with wood burner

[ericmark]

I have a friend with a wood burner it is standing in centre of floor of a timber frame building and we have been talking about efficiency.

There is an issue which I can do nothing about very little heat storage but the burner was designed for multi-fuel which is complete nonsense as to run efficient the wood needs to burn at a set rate and although all wood gives around the same calories per unit weight they are very different per unit volume so oak burns a lot hotter than pine.

Ideal is to keep the flue at 150°C as then not to much heat is lost through flue and also hot enough to stop tar build up.

Also a combustion air feed very close to the stove reduces drafts so would make the home warmer.

So the problem is how to control air in and also cooling air flow around the stove. Clearly the best way is a new sealed stove with a vent for combustion air to the outside and a hot water store with a variable speed motor which keeps fire at exactly the right temperature. However budget will not stretch that far.

So looking at a simple fan with some switching device which will cut in as the temperature rises which may or may not draw air from outside. The standard system is a sterling motor driving a fan but again very expensive.

He can't be the only guy wanting cheap control and I am sure it has been done many times before. Although I have a spare PLC it has no analogue inputs. I have a MH1210A temperature controller but limit is 120ºC my thoughts are a temporary set-up to prove it works.

So looking for ideas rather than re-inventing the wheel.

 

[Norcon]

Brother has one of these in his front hall....
http://tinyurl.com/ohvvqne

An elegant touch.
The flue section being about 7m long before it enters the roof. So the large space captures a lot off the flue heat that would otherwise be lost.
And no need for a fan.
It's probably a reinvention of the stove as it can rotate 360 degrees.

 

[ericmark]

It is interesting one not "HETAS APPROVED" and two the output range 9kW (Min 5kW Max 10kW) and it is this limited range of output which is the draw back with wood burners.

The stove looks good but in fact it is now rather old technology

this one is state of art wood burning.

One thing to note state of art one has horizontal flue the Rocket stove

also is horizontal but those are the only two I have found.

Efficiency varies from 25% to 99% on wood stoves they have not caught up with gas or oil in the main and in the main its simply you can't control them in the same way. Even the Hughes design can't switch off and on as required.

But that does not mean total loss of control using dampers and fans the standard stove can be made to use far less fuel yet heat the home. Automation in the main means using electric to control it and I am considering what could be added to improve control without ripping it out and fitting another.

I wrote to Hughes and asked what happens in a power cut and no reply. The same problem exists with many of the automated systems there is no fail safe. For a stove in a wood built dwelling in the middle of 25 acres of woodland using a stove which relies on electric to run safely seems rather fool hardy but to just have some optional electrical control makes a lot of sense.

The Sterling motor at £144 is likely the best ready built option but marketed by a company specialising in education toys does little to in still confidence in the system. A fan sited lower down is very likely to do a better job so a small electric fan would seem better.

But the flue should not be cooled below 150°C so not really just a case of just plug in some auto control is required. I am sure I can make a lash up to test it but would be better to get info off others first so I don't repeat any mistakes. Hence the post.

 

[Norcon]

Google wrote....

In line with the BS and European EN standards the efficiency of stoves are now measured in the following way:
A.The manufacturer gets to specify a refuelling period, with a minimum period of 45 mins and no upper limit.
B.The manufacturer gets to specify the heat output to test at.
C.The manufactuer can also specify the size of the fuel (within reason) - but apparently this rarely happens (I spoke to a technician at Gastec at CRE Ltd where they test a lot of stoves in the UK)
D.The efficiency is then calculated as the average efficiency over the period.
E.The flue gas temperature is measured as well as the carbon content of the flue gases. This allows the wasted heat and wasted fuel to be known, because there is a known quantity of fuel being burnt this allows the efficiency of the stove to be calculated

This means that if the manufacturers wants their stove to appear to be very efficient all they have to do is change the refuelling period and the heat output to test at to get the efficiency they want.

So this means that:
A.You cannot compare the efficiency of stoves with each other as they are all tested with different refuelling periods and with the air vents open to varying degrees.
B.The end user is not really left with a way of knowing how efficient the stove is going to be (other than when running under the specific conditions of the test).

 

[ban-all-sheds]

And no doubt if things were changed to benefit the consumer Nigel Farrago would bang on about faceless eurocrats destroying the wood-burning stove industry with red tape.

 

[stillp]

The end user is not really left with a way of knowing how efficient the stove is going to be (other than when running under the specific conditions of the test).

Just the same as cars, refrigerators, washing machines, etc then.