Oil boiler output power

Discussion in 'UK DIY' started by Bodgit, Jan 14, 2007.

  1. Bodgit

    Bodgit Guest

    Currently I have 2 boilers: an oil boiler for CH and a small LPG
    multipoint for DHW. I would like to ditch the multipoint and add a
    heatbank to the oil boiler system to get mains pressure hot water.

    I'm quite happy to do all the pipework & control wiring etc. but I'm a
    bit confused when it comes to figuring out the output power of the oil
    boiler.

    The boiler is a Perrymatic Jetstreme Mk.II. The burner has been
    replaced fairly recently with a Riello G3B (rated at 19-35 KW). Looking
    at the adjustment of the air damper, it seems that it is set to an
    output power of approx. 22KW.

    What factors affect what the output power can be set to? Is it possible
    to increase the output power or will that damage the boiler?

    Cheers,
    Dave.
     
    Bodgit, Jan 14, 2007
    #1
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  2. Bodgit

    cynic Guest

    Bodgit wrote:
    > Currently I have 2 boilers: an oil boiler for CH and a small LPG
    > multipoint for DHW. I would like to ditch the multipoint and add a
    > heatbank to the oil boiler system to get mains pressure hot water.
    >
    > I'm quite happy to do all the pipework & control wiring etc. but I'm a
    > bit confused when it comes to figuring out the output power of the oil
    > boiler.


    Depends on the nozzle size, oil pump pressure, heat transfer surface of
    the boiler and its combustion efficiency.

    >
    > The boiler is a Perrymatic Jetstreme Mk.II. The burner has been
    > replaced fairly recently with a Riello G3B (rated at 19-35 KW). Looking
    > at the adjustment of the air damper, it seems that it is set to an
    > output power of approx. 22KW.


    See above

    >
    > What factors affect what the output power can be set to? Is it possible
    > to increase the output power or will that damage the boiler?


    Possible but the heat transferred to the water is limited so you may
    simply burn more oil and lose efficiency instead
     
    cynic, Jan 14, 2007
    #2
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  3. Bodgit

    Bodgit Guest

    > What is the result of your heat loss calculation for the house? How
    > does this compare to the boiler power?


    I've already done the heatloss calculation - The house is a bit
    complicated and the heatloss programs don't really cater for some of
    the peculiarities, but I reckon I need about 28-30KW.

    > How large a heatbank do you wish to have? How quickly do you want to
    > heat it? How will it be controlled? How will the heating be
    > connected to it? What sort of hot water usage do you have?
    >
    > Having cogitated on that the answer to your questions may be that
    > the current boiler settings will work fine. Provided the boiler is
    > capable of putting heat in faster than the heating and hot water is
    > taking heat out, the bank will remain charged. Even if, for
    > relatively short periods, the boiler is not charging the bank fast
    > enough this may not be a problem as there will then be time for it
    > to "catch up".
    >
    > None of us will do the donkey work of calculations for you (well I
    > assume nobody is that generous), but if it looked in the right
    > ballpark I would be inclined to give it a try and see. One strategy
    > would be to couple up the heating and measure how it behaves as
    > stage 1. If it works move part or all of the hot water across and
    > see how it behaves as stage 2. Fiddle if necessary. The multipoint
    > can be retained in reserve, with suitable valving to change between
    > the two. Stage 3 is to remove the multipoint heater after everything
    > is working as you want.


    I wasn't asking anyone to do the calculations for me. I reckon the
    boiler is slightly underrated for what I want. My question was that if
    I was to adjust the burner to increase the output power (I would get
    someone in with all the gas analysis equipment to do this), is it
    possible to get a bit more out of the boiler without breaking it.
    'cynic' pointed out that I might lose efficiency by doing this -
    thanks.

    So given that my boiler is obsolete - I can't find any documentation -
    does anyone know how I can find out how high the burner can be turned
    up?
     
    Bodgit, Jan 15, 2007
    #3
  4. Bodgit

    cynic Guest

    Julian wrote:
    > "Bodgit" <> wrote in message
    > news:...
    >
    > > I wasn't asking anyone to do the calculations for me. I reckon the
    > > boiler is slightly underrated for what I want. My question was that if
    > > I was to adjust the burner to increase the output power (I would get
    > > someone in with all the gas analysis equipment to do this), is it
    > > possible to get a bit more out of the boiler without breaking it.
    > > 'cynic' pointed out that I might lose efficiency by doing this -
    > > thanks.
    > >
    > > So given that my boiler is obsolete - I can't find any documentation -
    > > does anyone know how I can find out how high the burner can be turned
    > > up?

    >
    > Once I shared a breakfast table in a B&B with a oil boiler engineer. I had a
    > pressure jet boiler at the time so I picked his brains.
    >
    > With a pressure jet boiler you can raise the burner pressure to increase the
    > size of the flame, but he said that once the flame starts to touch the metal
    > jacket on the far side of the heat exchanger cavity then you run into smoke
    > and soot problems - so that effectively sets your limit.


    There is a very non linear relationship involved. Raising oil pump
    pressure and air supply will increase throughput but this is not always
    accompanird by a longer flame. I have seen flames actually shorten but
    become unstable.

    >
    > The air needs to be set to the minimum that ensures clean combustion - white
    > cloth held over the flue is a good test.


    A professional was he or simply worked in the game? I'd not consider
    that an acceptable test for much at all.

    To the OP - there should be some kind of label or badge with a model
    number indication "somewhere" on the boiler unit, possibly inside the
    outer casing. Maybe an old nozzle with rating ( us GPH and spray
    pattern/angle stamped on one of the flats.
    Also what flue exit temperature do you have at the point of exit from
    the boiler? (somewhere between 200 and 500 degrees C)
     
    cynic, Jan 15, 2007
    #4
  5. Bodgit

    Bodgit Guest

    > To the OP - there should be some kind of label or badge with a model
    > number indication "somewhere" on the boiler unit, possibly inside the
    > outer casing. Maybe an old nozzle with rating ( us GPH and spray
    > pattern/angle stamped on one of the flats.
    > Also what flue exit temperature do you have at the point of exit from
    > the boiler? (somewhere between 200 and 500 degrees C)


    Looking again at the plate with the serial number etc. on it, the model
    number is Jet 70/90. Now I've looked on the internet at other makes, I
    think I can assume that the 70/90 refers to the number of 1000s of
    BTU/h. So I think it should be possible to get 90,000 BTU/h or 26KW out
    of it. Is this a reasonable assumption? If this is the case then it's
    not too far off the lower end of my estimate - I have been a bit
    generous in places!
     
    Bodgit, Jan 15, 2007
    #5
  6. "Bodgit" <> wrote in message
    news:...
    > > What is the result of your heat loss calculation for the house? How
    > > does this compare to the boiler power?

    >
    > I've already done the heatloss calculation - The house is a bit
    > complicated and the heatloss programs don't really cater for some of
    > the peculiarities, but I reckon I need about 28-30KW.
    >
    > > How large a heatbank do you wish to have? How quickly do you want to
    > > heat it? How will it be controlled? How will the heating be
    > > connected to it? What sort of hot water usage do you have?
    > >
    > > Having cogitated on that the answer to your questions may be that
    > > the current boiler settings will work fine. Provided the boiler is
    > > capable of putting heat in faster than the heating and hot water is
    > > taking heat out, the bank will remain charged. Even if, for
    > > relatively short periods, the boiler is not charging the bank fast
    > > enough this may not be a problem as there will then be time for it
    > > to "catch up".
    > >
    > > None of us will do the donkey work of calculations for you (well I
    > > assume nobody is that generous), but if it looked in the right
    > > ballpark I would be inclined to give it a try and see. One strategy
    > > would be to couple up the heating and measure how it behaves as
    > > stage 1. If it works move part or all of the hot water across and
    > > see how it behaves as stage 2. Fiddle if necessary. The multipoint
    > > can be retained in reserve, with suitable valving to change between
    > > the two. Stage 3 is to remove the multipoint heater after everything
    > > is working as you want.

    >
    > I wasn't asking anyone to do the calculations for me. I reckon the
    > boiler is slightly underrated for what I want. My question was that if
    > I was to adjust the burner to increase the output power (I would get
    > someone in with all the gas analysis equipment to do this), is it
    > possible to get a bit more out of the boiler without breaking it.
    > 'cynic' pointed out that I might lose efficiency by doing this -
    > thanks.


    Varying the jet size and oil pump pressure will alter the power input.

    The boiler manual should tell what range of jets can be used. This has been
    possible on the boilers that I have owned.

    The air supply needs to be adjusted accordingly.

    Increasing the water temperature (if not already at maximum) would help the
    boiler output the heat.

    > So given that my boiler is obsolete - I can't find any documentation -
    > does anyone know how I can find out how high the burner can be turned
    > up?


    Ask the manufacturer. - Assuming you can contact them
    Quite often the heat ouput range of a boiler is implicit in the name. Or there
    may be a plate giving this information on the boiler itself. Knowing the heat
    output you could make a guess at what jet size you should use perhaps by looking
    at the specs of other boilers of similar efficiency


    If the boiler does not run continuously, increasing the heat input may not do
    you much good.

    --

    Michael Chare
     
    Michael Chare, Jan 15, 2007
    #6
  7. Bodgit wrote:
    >> What is the result of your heat loss calculation for the house? How
    >> does this compare to the boiler power?

    >
    > I've already done the heatloss calculation - The house is a bit
    > complicated and the heatloss programs don't really cater for some of
    > the peculiarities, but I reckon I need about 28-30KW.
    >

    That is massive. Insulation will pay off quickly at that sort of
    heatloss. I have a 6 bed house here, and the calcs gave just 10KW.

    > I wasn't asking anyone to do the calculations for me. I reckon the
    > boiler is slightly underrated for what I want. My question was that if
    > I was to adjust the burner to increase the output power (I would get
    > someone in with all the gas analysis equipment to do this), is it
    > possible to get a bit more out of the boiler without breaking it.
    > 'cynic' pointed out that I might lose efficiency by doing this -
    > thanks.


    The boiler wiill always cycle or modulate back to what is needed. With a
    heatbank to cope wig peak hot water demands you don't need any extra for
    showers etc.

    You biggest problem is a boiler that has to ruin 24x7 to keep the house
    warm. Cos its too small. If teh house has a low thermal mass,, then it
    will heat up quickly..mine doesn't and I DO need to run the boiler for a
    long time if it gets cold.

    Conversely it stays warm when the heating goes off. The house itself is
    a massive heatbank.

    >
    > So given that my boiler is obsolete - I can't find any documentation -
    > does anyone know how I can find out how high the burner can be turned
    > up?
    >


    No..just suck it and see.

    In your case I would think long and hard about better insulation rather
    than a new boiler.
     
    The Natural Philosopher, Jan 16, 2007
    #7
  8. Bodgit

    raden Guest

    In message <y0Rqh.51327$>, Julian
    <> writes
    >
    >I think (memory fades somewhat) that he was commisioning some large
    >industrial boiler equipment. (Vauxhalls at Luton)


    I've never heard of Astras described in that fashion

    >So yes, he worked in the
    >game. What's your position and qualifications?
    >


    Believe me - he's qualified and has a lot of experience


    --
    geoff
     
    raden, Jan 16, 2007
    #8
  9. "Bodgit" <> wrote in message
    news:...
    >> What is the result of your heat loss calculation for the house? How
    >> does this compare to the boiler power?

    >
    > I've already done the heatloss calculation - The house is a bit
    > complicated and the heatloss programs don't really cater for some of
    > the peculiarities, but I reckon I need about 28-30KW.
    >
    >> How large a heatbank do you wish to have? How quickly do you want to
    >> heat it? How will it be controlled? How will the heating be
    >> connected to it? What sort of hot water usage do you have?
    >>
    >> Having cogitated on that the answer to your questions may be that
    >> the current boiler settings will work fine. Provided the boiler is
    >> capable of putting heat in faster than the heating and hot water is
    >> taking heat out, the bank will remain charged. Even if, for
    >> relatively short periods, the boiler is not charging the bank fast
    >> enough this may not be a problem as there will then be time for it
    >> to "catch up".
    >>
    >> None of us will do the donkey work of calculations for you (well I
    >> assume nobody is that generous), but if it looked in the right
    >> ballpark I would be inclined to give it a try and see. One strategy
    >> would be to couple up the heating and measure how it behaves as
    >> stage 1. If it works move part or all of the hot water across and
    >> see how it behaves as stage 2. Fiddle if necessary. The multipoint
    >> can be retained in reserve, with suitable valving to change between
    >> the two. Stage 3 is to remove the multipoint heater after everything
    >> is working as you want.

    >
    > I wasn't asking anyone to do the calculations for me. I reckon the
    > boiler is slightly underrated for what I want.


    Using heat bank you can size the boier for "average" use, not peak use as is
    the norm. So a smaller boiler can be used.
     
    Doctor Drivel, Jan 16, 2007
    #9
  10. "Bodgit" <> wrote in message
    news:...
    > Currently I have 2 boilers: an oil boiler for CH and a small LPG
    > multipoint for DHW. I would like to ditch the multipoint and add a
    > heatbank to the oil boiler system to get mains pressure hot water.
    >
    > I'm quite happy to do all the pipework & control wiring etc. but I'm a
    > bit confused when it comes to figuring out the output power of the oil
    > boiler.
    >
    > The boiler is a Perrymatic Jetstreme Mk.II. The burner has been
    > replaced fairly recently with a Riello G3B (rated at 19-35 KW). Looking
    > at the adjustment of the air damper, it seems that it is set to an
    > output power of approx. 22KW.
    >
    > What factors affect what the output power can be set to? Is it possible
    > to increase the output power or will that damage the boiler?
    >
    > Cheers,
    > Dave.


    The heat bank. Have it vented and the boiler heat it directly (no coiled
    heat exchanger). The CH. Have a coil in the bottom section of the heat
    bank (size to the max heat input to the house), to heat the CH. Have the CH
    pressurised using a pressure vessel, discharge valve etc. They can be bought
    as kits hhttp://www.bes.co.uk. Get your heat loss figurers sorted to size
    the CH coil. On the CH return to the cylinder have a Magnaclean filter. On
    the CH have TRVs on all rads and use a Grundfos Alpha pump. No wall stat
    needed. The CH coil will ensure no sludge will accumulate in the cylinder.
    Put 1% by volume of cylidner and boioer and pipes of inhibitor into the
    cylinder. The same with the CH side - put into the rads or fit a filling
    point.
     
    Doctor Drivel, Jan 17, 2007
    #10
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