Heat pumps with radiators and the spark gap

Calahonda52

Spark gap to oil at the moment is about 3.6

SCOP for most HPs is about 3.5

unless its UFH and night rate it seems to make little sense with rads.

Maybe with a buffer tank

[The Spark Ratio, also known as the ‘Spark Gap’ or ‘Spark Spread’, is a term used to talk about the difference in prices between gas and electricity, measured per kilowatt-hour (kWh). It’s like comparing how much two different things cost, but in this case, it’s the types of energy we use in our homes. ]

graememk

If there's enough radiators, there's no reason not to get higher COP.. - but I do get your point, cant have all the walls filled with K3 radiators!

Buffer tanks usually hurt efficiency though.

Oil for me looking online is coming in at 90-98c/l. I'll take the cheapest, for 1000l 90c.
24hr electric rates are sitting at 25c.
There is 10kWh of heat in a litre of oil

Efficiency of the boiler would depend on if it's condensing or not.

Say 90% for condensing and 70% for non condensing.

Also efficiency is not to be confused with combustion efficiency. To get higher efficiency in condensing mode the return temperature from the radiators needs to be low, mostly done by reducing the flow temperature.

Taking all that into account, to get 10kWh of heat.

Condensing oil : needs 1.11l of oil, €1

Non condensing : 1.42L, €1.57

HP Cop, 10kWh heat

4: €0.65

3.5: €0.71

3 : €0.83

2.5 : €1

1.7 : €1.47

My workings show the spark gap being at about 2.5 for a condensing and possibly as low as 1.7 for non condensing. Where is the 3.6 sourced from?

Am I saying just rip out the oil and replace with HP.

No. Most of the time it will never make it worth your while. Especially at the prices I've seen quoted. - If someone does have a non condensing oil, it may pay to replace the oil boiler and replace the single panel radiators with double panel, to try and run at a lower flow temperature to make the most of the latent heat of condensation.

(If you see steam coming from the flue of a condensing boiler, it's not condensing)

Calahonda52

Thanks, am paying 37 day/23 night at the mo on one account and get heating oil for cash coming in at c 9 cents kWh.

I know thats unusual

Take your point about buffer tanks but I suppose the day night spread would help

KildareP

https://www.boards.ie/discussion/comment/123673689#Comment_123673689

A plume means the boiler IS condensing - if it was a sign of non-condensing then every non-condensing boiler would have plumed as well.

graememk

https://www.boards.ie/discussion/comment/123674010#Comment_123674010

Articles I read tend to disagree

Example: https://www.theheatinghub.co.uk/why-our-condensing-boilers-do-not-condense

If the plume is visible, then it's condensing outside the boiler losing its heat to air rather than in the boiler.

To get the latent heat of condensation it has to happen in the boiler.

It may be condensing a little bit Vs a traditional boiler, but the exhaust gas of a normal boiler doesn't plume because it's much hotter again.

https://www.boards.ie/discussion/comment/123673976#Comment_123673976

9c/ kWh of oil is about 90c/L, and you really should look into a better electric plan, your night rate is nearly as high as 24hr!

KildareP

https://www.boards.ie/discussion/comment/123674257#Comment_123674257

The plume is because so much of the heat has been extracted from the exhaust so when the remaining vapour within it hits the atmosphere it instantly condenses and forms a plume.

Whereas the exhaust from a non-consensing boiler is so hot that the remaining vapour can disperse before it condenses so it does not plume.

If the plume was an indication of not condensing then non-condensing would have always been steaming the place to oblivion for centuries before.

graememk

https://www.boards.ie/discussion/comment/123674857#Comment_123674857

If the vapour is condensing in the air its not condensing in the boiler.

It needs to condense in the boiler to get the latent heat of condensation. And also why it needs a drain for the condensate. That's how the condensing boilers can hit such high efficiencies.

Id admit, if a plume is seen you may be close or a little bit in the condensing mode but a lot of heat could still being potentially lost. - Still better than a traditional boiler. I suppose the volume of plume could be an indicator.

If its wisps, on a cold morning. sure, but if its like a mega vape, on a normal day, it isn't condensing much!

Graph of efficiency of a gas boiler, but the same principles apply for kerosene

Source of the graph : https://www.heatgeek.com/condensing-boilers-efficiency/

unkel

https://www.boards.ie/discussion/comment/123673976#Comment_123673976

Those are absurd rates, why on earth did you pick that plan? Anyway, I would change plan ASAP, it only costs €50 to break contract. Last time I did that, the €50 paid for itself in just a few weeks

KildareP

https://www.boards.ie/discussion/comment/123675184#Comment_123675184

It is not possible to condense 100% of the vapour from the exhaust.

It is most certainly not possible to extract enough that it won't condense immediately upon hitting the outside air on a cold day unless you can get your return temperatures to match that of the outside air.

The only other way you will get no visible plume on a condensing boiler is by having an extremely high exhaust temperature because of a high return temperature to the boiler - which again is why no non-condensing boiler ever has a visible plume despite having all of the vapour sent out the exhaust.