Oil fired heating systems

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Le Démerdeur
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Re: Oil fired heating systems

Post by Le Démerdeur »

I struggle to believe the claims of 97% eficiency for condensing boilers when you feel the heat given off by the flues.

Some manufacturers make similar outlandish claims for woodburners!

Mike
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Re: Oil fired heating systems

Post by Mike »

These efficiency ratings are based on a flue gas analysis, comparing the C02 content to residue fuel in the gas, this as a straight reading gives the best output figures, which to be fair is all the manufacturers can give, if however upon installation in your home and you are running central heating comparing the water output and return temperature this will tell a different story of your whole system, my 25 year old boiler on straight analysis is 87% efficient, however on the whole system this drops to 59% when taking the flow and return temperature into consideration, insulation is the maximum I can install, but I am happy in that the cost per day is £3.03 at the current rate of use.

Mike
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Re: Oil fired heating systems

Post by Mike »

What is interesting is the difference between the flue gas temperature compared to efficiency:

87% efficient = 203.6 deg C flue gas temperature and C02 @ 11.86

84% efficient = 332.5 deg C flue gas temperature and C02 @ 11.94

The adjustment of air content is extremely small between each of these results, pump pressure is obviously according to manufacturers requirements and the nozzle fitted for the combustion chamber shape and pump supply requirements. What is not obvious is having the casing on the boiler and the boiler house door closed also make a vast difference, difficult with a small boiler house, C02 poisoning is not pleasant, except for the feeling of euphoria. :roll:

Le Démerdeur
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Re: Oil fired heating systems

Post by Le Démerdeur »

So they are quoting the efficiency of combustion and not the efficiency of energy transfer to heating the radiator circuit water.

That was why I was questioning the comparison someone was making with electric heating which is effectively 100% efficient and an oil fuelled boiler at supposedly 97% efficiency.

1kw of electric heating gives you 1kw of heating within the dwelling (1.5% max might be lost if the meter is at the property boundary).

1kw of gas or oil heating will give up to 870 watts of heat energy & I reckon half of that goes out the flu to heat the outside air.

A petrol engined vehicle will convert between zero percent (at idle) to 30% at full load (maximum figures for the best of the best) of the fuel energy into motive power, 20% for most driving at part throttle.

I view oil & gas fuelled CH systems in the same way.

Mike
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Re: Oil fired heating systems

Post by Mike »

All manufacturers of any product will always quote the best figures they can extract from their own particular unit no matter what it is, turn something on its head and quote a negative figure someone will miss-read it as positive. :roll:

landmannnn
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Re: Oil fired heating systems

Post by landmannnn »

Le Démerdeur wrote:
Wed Nov 18, 2020 12:30 pm
So they are quoting the efficiency of combustion and not the efficiency of energy transfer to heating the radiator circuit water.

That was why I was questioning the comparison someone was making with electric heating which is effectively 100% efficient and an oil fuelled boiler at supposedly 97% efficiency.

1kw of electric heating gives you 1kw of heating within the dwelling (1.5% max might be lost if the meter is at the property boundary).

1kw of gas or oil heating will give up to 870 watts of heat energy & I reckon half of that goes out the flu to heat the outside air.

A petrol engined vehicle will convert between zero percent (at idle) to 30% at full load (maximum figures for the best of the best) of the fuel energy into motive power, 20% for most driving at part throttle.

I view oil & gas fuelled CH systems in the same way.
Are you sure?

This is a copy and paste

What is boiler efficiency?
Modern condensing boilers are between 92-94% efficient ErP. Boilers that are more than 25 years old can be as little as 60% efficient. What does that mean? A boiler's 'energy efficiency' is the percentage of the total energy used by the boiler to provide useful heating. For a modern boiler with 94% efficiency, 94% of the energy used by the boiler goes to heating the home, only 6% is 'lost'/used to run itself. For a very old boiler with 60% efficiency, only 60% of the energy used by the boiler goes to heating the home, a whopping 40% is lost.

Le Démerdeur
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Re: Oil fired heating systems

Post by Le Démerdeur »

I was sure the second that I burnt my hand on the flue gases of a condensing boiler, doubly sure after reading Mikes temperature readings.

I prefer the evidence of my eyes and others senses and above all common sense to decide whether something that is presented authoratively as fact is true or otherwise.

Any heat not used to heat the circulating fluid is heat energy lost.

The only losses in an electric heating system are thermal losses from undersized cables (should be less than 1%) if they are outside of the dwelling

I am not questioning that condensing boilers are not much more efficient than the older boilers, they achieve this by recovering some of the heat lost in the flue gases albeit at the cost of the electricity used in the fan system but with flue gases in the order of 2-300°C then its plain to see that a lot, maybe even most of the energy converted from the combustion is not heating the radiator fluid.

whyme?
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Re: Oil fired heating systems

Post by whyme? »

Le Démerdeur wrote:
Wed Nov 18, 2020 1:42 pm
I was sure the second that I burnt my hand on the flue gases of a condensing boiler, doubly sure after reading Mikes temperature readings.

I prefer the evidence of my eyes and others senses and above all common sense to decide whether something that is presented authoratively as fact is true or otherwise.

Any heat not used to heat the circulating fluid is heat energy lost.

The only losses in an electric heating system are thermal losses from undersized cables (should be less than 1%) if they are outside of the dwelling

I am not questioning that condensing boilers are not much more efficient than the older boilers, they achieve this by recovering some of the heat lost in the flue gases albeit at the cost of the electricity used in the fan system but with flue gases in the order of 2-300°C then its plain to see that a lot, maybe even most of the energy converted from the combustion is not heating the radiator fluid.
you are over simplifying this to suit your own agenda.
Condensing boilers, especially gas boilers in the domestic market are designed to give high efficiencies under certain circumstances.
The water vapeur dew point temperature is 55 deg C therefor the heating system return water temperature needs to be at or below this temperature to allow the boiler to enter condensing mode. Systems have to be designed to allow this to happen whilst still doing what they should ie. heating the building sufficiently well at the lowest designed outside temperature.
Most older 'non condensing' systems are designed on a 82/70 flow/return so if a new condensing boiler is fitted to an existing older system it will either never be in condensing mode when run at these temps or never provide enough heat through existing radiators when run at condensing temperatures.
I doubt very much that folk are advised to uprate radiators etc when a boiler change is made & a condensing boiler fitted so it would not be surprising to see much higher flue gas temperatures & lower efficiencies in colder times when these same folk run the boiler at temperatures outside those it is designed for.

Napoleon
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Re: Oil fired heating systems

Post by Napoleon »

SW31girl wrote:
Sun Nov 15, 2020 3:21 pm
We renewed our gas contract. Earlier this year we paid over 1800€ per ton when our previous contact expired at around 850€ per ton. We’ve now managed to lock in around 1100€ per ton.
Sorry to interrupt the flow of the thread but the post by SW31girl has raised a topic which is currently in my thoughts. I assume you are talking about bulk gas prices from a major supplier. We have been disappointed with the steady rise in price of propane from Antargas over the last twenty years. If you don't mind revealing the name of your supplier and how you went about negotiating the new, low price, please give me some advice on how to tackle Antargas.
This thread has been so interesting. Thanks everyone.
Alistair

SW31girl
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Re: Oil fired heating systems

Post by SW31girl »

Napoleon we used Antargas but now we use Primagas. Antargas were absolutely rogues. It’s a bit of a faff changing suppliers as you have to change the tank as well. I would not recommend changing in winter as you need to have an almost empty tank to be removed. You then wait for the new tank to arrive and then wait for the tanker to fill it up. We have a fixed price for two years then an open market price for the third year of the contract. There is also a fixed annual cost.
It’s worth asking primagas what offers they have. We originally were approached by a third party intermediary to move to primagas. After the three years were up primagas contacted us direct for the new contract.

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