Boiler sizing from cubic area, or actual usage

[Kaymo]

Charging for gas based on GCV looks a bit underhand

Its not that charging based on GCV is underhand, its that charging by GCV and then allowing manufacturers to quote NCV is misleading. I suppose what I am saying is that how the unit cost is calculated should be irrelevant to the consumer, because the energy company charges me per kWh. What is important to the consumer is how much of the energy I have paid for is converted into useful heat energy.

BTW what is SAP, is that the German business systems corporation?

I am not sure, I think it is Standard Assessment Procedure. I found a site called the Building Energy Performance Assessment support website https://www.ncm-pcdb.org.uk/sap/searchpod.jsp?id=17 and they seem to list every boiler that ever existed (well going back to the eighties at least) and they have a SAP 2009/2012 annual efficiency (%), SAP 2005 seasonal efficiency (%) figure etc for each boiler. My understanding is that this is a GCV figure, and the benefit for me is that it is a comparable value.

 

[fixitflav]

OK thanks

 

[John D v2.0]

I think people are confused, you're not paying for energy you're paying for gas. The gas quantity just happens to be quoted in energy, but it could equally be measured in litres, or fish, or anything else. In fact it is measured in litres/ft3 on your meter. The cost of the gas to the supplier is more based on the volume anyway.
No one's been done over as the two energy values are not related in any useful way. The energy value is just to standardise the relative cost to the consumer.

 

[D_Hailsham]

I think people are confused, you're not paying for energy you're paying for gas. The gas quantity just happens to be quoted in energy, but it could equally be measured in litres, or fish, or anything else.

Not correct. You are not paying for gas by volume (m³) but by the amount of energy the gas contains. If the CV of the gas increases or decreases the amount you pay for the same volume will go up or down.

 

[fixitflav]

Not correct. You are not paying for gas by volume (m³) but by the amount of energy the gas contains. If the CV of the gas increases or decreases the amount you pay for the same volume will go up or down.

That's right. The meter measures m3. This is multiplied by the CV, usually in MJ/m3 to give MJ, and converted to kWh. Multiplied by price/kWh for the bill.

 

[John D v2.0]

Not correct. You are not paying for gas by volume (m³) but by the amount of energy the gas contains. If the CV of the gas increases or decreases the amount you pay for the same volume will go up or down.

Good point I was explain in a rush so didn't rephrase. But the point is it doesn't matter that we are charged one way and sold boilers another. Even if those ways were unified it wouldn't really change anything, other than a slightly different factor when working out how much it'll cost to run your boiler in lab conditions

 

[Kaymo]

John, I don't see why it wouldn't make any difference. If I am being charged in kWh, and that has been worked out using GCV, and then I am quoted an NCV efficiency value for a boiler, then I am being led to believe that I will get nearly 100% of the cost of that kWh unit back in heat energy, when in reality I am only going to get 90% of the energy.

If I wanted to compare this with electric heating for example, I pay for 1kWh and I get 1kWh of heat energy from this, so its a true 100% efficiency. Of course there are losses in transmission, and losses when the energy is produced, but those are transparent to me because I am paying for 1kWh and that's what I am getting. You could say that I am actually paying for a certain number of electrons, but its what the equates to in kWh that I am charged for.

Not sure if I am explaining myself well here, what I am trying to say is that as a consumer its the cost of the unit of energy, and that is kWh, so I would want to know what percentage of that kWh that I have paid for will be delivered to the heating system.

 

[John D v2.0]

Not sure if I am explaining myself well here, what I am trying to say is that as a consumer its the cost of the unit of energy, and that is kWh, so I would want to know what percentage of that kWh that I have paid for will be delivered to the heating system.

I see what you're saying that it makes predictions a bit more involved, but also see my comment about lab conditions. In reality your electric heating is going to be 100% efficient whatever you do. Your gas boiler will vary a fair bit depending on the temperature of the flue gas and cycling etc. So yes I agree it's a bit of a pain, but I think the only way you'll be able to do the costings is by reading your gas meter every day. You won't be able to buy a boiler today where the quoted efficiency would cost more than electric, but if you never run enough water to get the hot through, you're getting zero efficiency, etc.

 

[Dan Robinson]

It's a bit like moaning about RONs and octane, on one hand, and MPG on the other

 

[Kaymo]

You won't be able to buy a boiler today where the quoted efficiency would cost more than electric

I know that, it was more of a comparison for arguments sake, but I think the original point still stands, that quoting efficiency as net when gas is charged gross is misleading. A lot of the advertising also seems to be quoting the GCV values of old boilers, against the NCV values of new ones as a justification for replacing them.

It's a bit like moaning about RONs and octane, on one hand, and MPG on the other

Eh, its nothing at all like that.

 

[Dan Robinson]

Eh, its nothing at all like that

Yes it is.

 

[bernardgreen]

and MPG on the other

Eh, its nothing at all like that.

Yes it is.

Drive a car at a constant speed on a level road for 100 miles and the MPG figure will be good. Drive the same car for 100 miles stopping and starting in a busy city and the MPG figure will be much lower.

At least car makers do give information about the type of driving that produces the MPG figures they use in advertising. Unlike boiler manufacturer's adverts which completely ignore any mention of stop start operation of their boilers when efficiency can be as low as 30% .

 

[Dan Robinson]

And ultimately its all booloocks.

 

[Dan Robinson]

It's really about how you control the system

 

[bernardgreen]

And ultimately its all booloocks.

Are you referrring to the advertising ? If so I agree, and would add the word un-ethical

It's really about how you control the system

and your lifestyle and how you use the boiler.