Coal fired back boiler efficiency?

[Adam Aglionby]

Friend has housing association house with single coal fire in lounge that also feeds back boiler that feeds 3 radiators downstairs, secondary radiator in lounge then bathroom and kitchen, electric circulation pump, electric immersion heater back up on hot water supply. Radiators are from days of british empire and are plumbed in wide bore pipe, well it aint narrow microbore anyway.

Geniuses at HA have decided to ,er , upgrade the heating system. This `upgrade` consists of adding 4 extra radiators upstairs, one in each of 3 bedrooms and one on upstairs landing.

These will all supposedly be heated from the back boiler on the single fireplace.

Not an expert on thermodynamics but currently the fireplace needs banked up the chimney to get any heat at all out of the downstairs radiators, adding another 4 radiators seems pointless and not inexpensive.

Presume there is a limit to the amount of heat can obtain from a single fireplace, must be a reason old properties had a fireplace per room.

Is there an accepted method of calculating heat output and requirements, for those without a degree in mathematics, to demonstrate to the HA that they may not be spending money wisely.

Concerned that the additional load on the fire will put friends coal bills unacceptably high and the property is in dire need of a rewire which would seem a better use of limited resources.

Any advice gratefully received.

Adam

[cj]

Hi Think you need to get the HA inspector round before the work starts.They may think you have a Baxi gas system with a back boiler not a coal fired one. Unless I am so out of touch with modern coal heating the open fire with back boiler was little more than a 2/3 gallon metal container bricked in behind the grate with a flue diverter in the chimney which forced the hot gases to be draw around said tank heating it.(like a kettle) . I saw many in my youth and all were very likely to boil when the fire was raging.Some did have a few rad's piped in with a Grunfoss pump for circulation. Systems are around using dedicated 'Arger' or similar fires but these have heat exchangers built in and were very good. In any event a single open grate fireplace would be very unlikely to be able to supply enough heat to run the system the HA propose,and if it could what of the H&S aspects of the water at 100+ degrees if the system boils?

See if you can get a CH bod to have a look at it.

HTH CJ

[AnthonyL]

We have a Parkray that feeds 2 downstairs radiators, 2 bedroom and the bathroom plus the hot water (backed up by immersion heater). It is a

1980's install and just about copes on a cold winter's day.

I don't think ours would take any more.

Banking up isn't the best way for ours to work. It needs enough air to circulate through for the backboiler to be effective though the sides of ours are also part of the boiler/tank.

They would burn less fuel and get more heat if they used a solid-fuel stove (eg one with closing glass doors). This is a route we are thinking of as one big disadvantage of an open fire is the amount of air it needs to draw in.

Have a look around

you might find what you & your friends need from there.

[Steve]

I'm no expert on this, other than living in a coal heated house for many years.

I cannot see any reason why a single coal fire won't heat a house fine, in my parents house its always boiling ( i wear shorts in the middle of winter when visiting). Its going to depend on the exact type of fire though, the newer(well newer than 20 years ago) were a lot better than the very old ones.

Obvious question, this one has a pump thats needed to provide heat to the downstairs radiators, has the one your talking about? They will not work well at all without it.

Steve

[Andy Dingley]

What do you mean by "fireplace" and "back boiler" ?

If it's an old open hearth, then that back boiler is designed for indirect heating of domestic hot water (coil in the tank upstairs). The "boiler" is also just a simple sheet copper tank with barely any heating surface. It'll heat a bath, but it's just not meant to run heating.

If it's an enclosed Parkray or Rayburn with a halfway decent back boiler in there, it's designed to run heating too and according to the varying size of it (which should be on a data plate somewhere) may be capable of heating the Albert Hall. My parent's one, in their small bungalow, was sized on that basis and so makes it insufferably hot whenever you light it.

Either of these will need a circulator pump installed and running if you expect to get useful flow through radiators. They'll do fat-pipe water heating in a tank upstairs by thermosyphon alone, but expecting to drive the longer, thinner and horizontal pipe runs of radiators is too much to ask without assistance.

Fuel consumption won't increase, as more demand doesn't increase draft beyond the basic capacity, but performance won't increase either. Your radiators are likely to get luke warm at best.

[S Viemeister]

I have a back boiler in the open fireplace in my living room - it can easily run 7 radiators, one of which is a very large double.

I also have a Rayburn in the kitchen (converted to oil).

The pumped central heating can be run from either boiler.

[Adam Aglionby]

That appears to be creature, tank in kitchen on ground level with circulation pump.

there, it's designed to run heating too and according to the

Luke warm describes current radiator heating level , adding more radiators really is going to be pointless.

Was hoping that there was some numbers in BTU or whatever on output of a single open hearth fire with old style back boiler so could do rough comparison with typical size of gas boiler that would be employed to heat a 3 bedroom house.

As the water tank upstairs just failed drenching a bedroom, concerned about overall condition and safety of existing installation never mind trying to make ill advised extensions.

Being a Housing Assosciation probably considerable politics involved, suspect that the money has been obtained in specific regard to `upgrading ` heating.

Wiring is , er, below acceptable modern standards and distinct lack of enthusiasm for a re-wire from the HA, with the house wrecking that goes into a typical 1 day public housing rewire suspect Bodgit and Scarper (Heating Engineers) will be similar, rather try and get a bit of joined up thinking about basic services in their housing stock.

Numbers are something that might make a more digestible one page executive summary for the bean counters.

Thanks Adam

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Adam Aglionby saying something like:

Better late than never, here's an installation leaflet for a Grant back boiler - pay particular attention to the bottom of page 4 for the info you seek.

[Adam Aglionby]

Much appreciated Dave , thanks.

Suprising numbers your kindly provided data giving 10kW of heat at just over 2Kg burn per hour of coal.

Using whole house boiler guestimator at:

10kW as about right size for 3 bed semi. Darn, dosen`t tally with experience but can see how it was sold to Housing Asosciation as viable plan.

Thanks again. Adam

[Adam Aglionby]

Thought there was something optimistic in the numbers. The Queen Star fire must be approaching 100% efficiency doing much better than a coal fired pwer station with fluidised bed furnaces, according to that bastion of accuracy Wikipedia:

energy density of coal is 6.67 kW=B7h/kg Of the 6.67 kW=B7h of energy per kilogram of coal, about 30% of that can successfully be turned into electricity=97the rest is waste heat. Coal power plants obtain approximately 2.0 kW=B7h per kg of burned coal.

Even as a water boiler/air heater the Queen Star claims 11.9kW/H at

2.12Kg/h of coal , should have a line of Queen Stars at Drax :-)

Hmmm, so can see how the numbers could have been made to seem convincing though like CFL output they never quite measure up. Cheers. Adam

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Adam Aglionby saying something like:

No problem. I knew I had it somewhere...

I'd take those figures with a pinch of salt anyway - probably in ideal conditions in their workshop. The Grant BB is a fairly decent one, as far as I've seen, and if the house is reasonably well insulated the useful output can run a hot cylinder and a few rads to good effect. I'd preferably fit one to a fireplace with an outside air feed though, getting round the draughtiness problem. It still doesn't address the overall efficiency question - it's still pretty crap when most of the heat is going up the chimney.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Adam Aglionby saying something like:

Nay lad, just one giant Queen Star would do it, surely. I wouldn't want to see the hearth, though.

[Tony]

replying to Andy Dingley, Tony wrote: Hi I have a 16" dunsley enterprise open coal fire with a draw rod to either draw the fire to the back boiler or just allow the flame to burn normally.. my fire has a water pump which heats up all the radiators in my home (3 doubles and 5 singles) and believe me when I say that you can't leave your hands on them because they get unbelievable hot..you do have to keep the for backed up at first but when the water is hot I just keep the fire ticking over..cheaper and more health than gas is say.

[Andrew]

Read the bloody date of the post that you are replying to !!.

[harry]

Probably 5% if you're lucky. As a heating system, totally obsolete. You won't get any more heat from the boiler with more radiators. Just distribute what you've got more thinly.

[harry]

The important factor here is the efficiency of the boiler. Very low in this case. And no-one can say what heat output is needed without assessing the heat lo ss of the building.

All forms of solid fuel heating are expensive these days unless you are tal king about a free wood supply. This largely due to the inherent inefficiency of solid fuel boilers.

Plus the fuel has to be stored, boilers have to be refueled and cleaned.

[Brian Gaff]

That is the problem wither that interface its not always as easy to know. Isimply do not understand why its interface cannot actually do a date filter and end the problem for ever. other web based interfaces to Usenet seem to manage it. Brian

[tabbypurr]

loss of the building.

alking about a free wood supply.

The problem with wood is the price of labour. Few people regard the activit y as worthwhile now.

As has been said, an open fireplace is hopelessly inefficient and simply no t fit to heat a house. Aren't there energy efficiency requiremenets nowaday s for CH?

NT

[John Rumm]

appropriate choice of word...

Timely advise from harry as usual. What next, up to the minute style guidance for the best combination of flairs and tank tops?