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How are boilers tested when measuring their efficiency.

Discussion in 'Plumbing and Central Heating' started by bernardgreen, 27 Aug 2018.

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  1. bernardgreen

    bernardgreen

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    Some boilers are claimed to be more than 100% efficient.

    How can a boiler be more than 100% efficient ?. That would defy the laws of science, getting more energy out than the amount of energy supplied is impossible.

    The reality is that tests are carried out on the boilers and data is collected. Then various fiddle factors are applied to this data to calculate a "normalised" value of efficiency.

    Few if any manufacturers will provide information about these fiddle factors.
     
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  3. Dan Robinson

    Dan Robinson

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    Why not ask the institutions that carry out the tests?

    Your pathetic little vendetta is getting rather tiresome.


    Why don't you get your cylinder tested while you're at it?
     
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  4. bernardgreen

    bernardgreen

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    When asked ( not by me ) they decline on the rounds that the manufacturers have commissioned the tests. As you know one testing establishment has returned some very low figures of efficiency when the boilers were tested as if they were being used in a typical domestic situation.

    There is no vendetta. Just a desire to see reality on the claims being made for the efficiency of boilers.


    I would ask what needs testing on a vented cylinder but you wouldn't answer so the question is not beig asked.
     
  5. Dan Robinson

    Dan Robinson

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    This would be the same testing establishment that, from first hand (literally) experience couldn't organise a pizz up in a brewery. I assume they returned similar figures fro all boilers tested rather the one you have a boner for?

    Or rather, I couldn't really give a schit. :rolleyes:
     
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  6. fixitflav

    fixitflav

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    Didn't we discuss this a few weeks back? It's possible if the input heat is calculated on net gas CV (water produced not condensed) but the output heat is measured, and some (not all) condensation occurs. But the ratio of gross CV to net CV for methane is 1.11, so even if complete condensation is achieved, and there are no losses, the efficiency calculated that way cannot exceed 111%. For pure hydrogen, the figure is 1.18. For higher molecular weight hydrocarbons, which are also present in natural gas, the figure is lower.
    I see the thread about Navien boilers has been closed, but on that there was something about efficiency 127% being claimed. I couln't see any links which might have justified it, but on the basis above it's impossible. Can anybody explain where the 127% comes from?
     
  7. muggles

    muggles

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    It gets discussed regularly - it's Bernie's absolute favourite drum to bang
     
  8. Donald_diy

    Donald_diy

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    Thank you for bringing this information into the public domain,Have passed your claim to https://www.bbc.co.uk/programmes/b006mg74/contact
     
  9. vulcancontinental

    vulcancontinental

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    There was an article in the Telegraph recently I think entitled 'are boilers the next PPI misselling scandal' or something. Tim Pollard the bow tied ex-Wolsey renewables guru was trying to raise the subject. Should have come on the Vokera controls course.

    Manufacturers using figures that are not possible simply indicate the tests that produced them are unrepresentative; all use them and it'll come to bite them.
     
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  11. bernardgreen

    bernardgreen

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    The drum is being "banged" elsewhere by people who decide which heating systems will be installed in housing projects.

    One bite has already happened. The procurement officer asked for an explanation of the impossible, the request was ignored. The tender was rejected.
     
  12. cdbe

    cdbe

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    Surely there are some National statistics on average gas consumption per household where a comparison could be made between today and 30 years ago?
    I personally must have saved so many £hundreds on my £500 gas bill with: a new modern boiler, new controls, loft insulation, cavity insulation, double glazing etc that I'm expecting my gas supplier to start sending me refund cheques soon!
     
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  13. ericmark

    ericmark

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    I would guess every boiler has a sweet point where it is at most efficient. This may be when throttled back, or flat out, or anywhere between, so like driving a car, if we know that sweet point we could set the building management computer to keep the boiler at it's sweet point. Maybe starting to heat a room slightly earlier or latter, or slower or quicker to keep the boiler as long as it can at that sweet point.

    Same as when we drive a car, there is a speed at which on that incline it does best MPG.

    However most of us don't have building management so we can't keep the boiler on that sweet point. So just like the car with the different driving conditions with Urban etc. So the boiler will preform better or worse depending on conditions under which it is used, so using the eBUS or using the return water temperature must affect the boilers efficiency. Also using a boiler which is too big or too small.

    If I was to get the years gas bill for this house, it should show how much power is required, and the more years then the more accurate the result, but simple fact that it has never failed to heat the home must show it is too big. I will guess that is in order to get enough domestic hot water? However the two big hot water uses both use electric to heat the water, dish washer and washing machine.

    But gas has according to Boyle's Law and Charles' Law has both heat and volume so to get 100% power from the gas the expansion of the gas must be used, as with power stations where first turbine is gas, then next two or three are steam, even then they don't capture all the power.

    I am told you can get boilers with Sterling engines that turn the last bits of power into electric and use the feed back tariff. I would hope these are the most efficient or there would be little point doing it. This must mean to get maximum efficiency there must be some sort of engine, I am told mini generators with the waste, well not really waste as it is used, but that heat is used to heat a block of flats.

    I saw in Mount Pleasant on the Falklands, the heat from the generators not only heated to accommodation but also warmed the incoming water to get it warm enough so the chemicals in the water treatment plant would work, I note at home shower from gas works A1 in the winter, but in the summer it can go cold, then hot again, reason is the shower head is not allowing enough flow, as warmer input water means thermostat using more cold and less hot water, so heater closes down, have to open hot tap a little to maintain flow.

    I am sure the kettle boils faster in the summer.

    So if all rooms can be maintained at 22°C all year round the boiler is too big, we should expect to have to allow some rooms to cool in order to have enough energy to maintain rooms used at 22°C. Or supplement heating with a gas or electric fire.

    Like a car with Urban and combined etc with different MPG, a boiler would need to have minimum, half throttled back, and maximum efficiency figures before they really mean anything.
     
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  14. Dan Robinson

    Dan Robinson

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    I assume a certain irony in your text but for those who do think that that's how these savings work should realise that the percentage offered is often to be taken from the remaining inefficiency.


    For example. Weather comp could save you ten percent.

    Some think that with a 90% efficient boiler that equals 100%.

    Wrong.

    It means 10% of the remaining 10%. And so on. All of these other savings.... Glazing, loft insulation should be taken the same way but from a related technology.

    This has nothing to do with Bernie's little project. And I don't know any engineers who actually would use 122% efficiency as part of their sales patter. However the figures are their. As I have said before, I have a copy of the test certificate. Bernie is not the only one though, who gets confidential information. ;)
     
  15. bernardgreen

    bernardgreen

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    Sometime in the early 1970's a group of experimentors converted an engine recovered from a car to run on gas and this provided heat and electricity to a couple of small eco homes. They claimed it was the way forward. I suppose gas turbine power stations are similar but on a much larger scale.
     
  16. hard-work

    hard-work

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    Good question Bernard. Don't SEDBUK give their testing methods? Many years ago I read their method, escapes me now.
     
  17. Some boilers are claimed to be more than 100% efficient.

    FFS
     
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