Calculating Kero usage for oil boiler

jodaw

Trying to get my head around the kerosene usage for current oil boiler to establish if is worth changing to an alternative system.

I will try to calculate my usage here and maybe someone can point out the errors in my calcs.

18kw 93% Efficiency Condensing boiler.

Assumptions are:

1 Litre Kero = 9.821Kw but burned at 93% it reduces to 9.13Kw
Currnent Oil Price = €655 / 1000L or €0.65 / litre

So on twice per day for 3hrs each time:
1st hour the boiler runs constantly and for the second to hours the boiler is running for 1 hours.

First Cycle:
Hour1 = 18Kw/9.13kw = 1.97Litres x €0.65 = €1.28
Hour2 = 18Kw/9.13kw X 0.5 = 0.98Litres x €0.65 = €0.64
Hour3 = 18Kw/9.13kw X 0.5 = 0.98Litres x €0.65 = €0.64

Second Cycle:
Hour1 = 18Kw/9.13kw = 1.97Litres x €0.65 = €1.28
Hour2 = 18Kw/9.13kw X 0.5 = 0.98Litres x €0.65 = €0.64
Hour3 = 18Kw/9.13kw X 0.5 = 0.98Litres x €0.65 = €0.64

So with this pattern of use it would be costing €5.12 per day.

Do this calculations look correct or am i way off base?

Wearb

Those figures are near enough, without splitting hairs.

As you have found out, the subsequent hours of time running reduces. The savings made by switching off between running times is therefore not as great as you might at first expect.

agusta

The 93 percent efficiency is only when the boiler is in condensing mode.the effectiveness of the condensing process varies depending on the difference between flow and return temperatures.i would think when not in condensing mode the efficiency would be around 85 percent

jodaw

agusta wrote: »

The 93 percent efficiency is only when the boiler is in condensing mode.the effectiveness of the condensing process varies depending on the difference between flow and return temperatures.i would think when not in condensing mode the efficiency would be around 85 percent

The house in question is a relatively new pretty well insulated with some room thermostats, zones and trv's on all rads.

All bedrooms would be set to about 18-19c and living areas would be about 20c.

In my calculations above i estimated that the boiler would be running 30mins in the hour. In the real world i would hope it would be running a little less when everything is up to temp. Hopefully that would make up for the differences you quoted.

I am trying to calculated the bottom line costs at the current oil price. I would also be all ears for the best way to run the system.

-On for 8 hours straight better then 2 x 3hours?
-Or leave on the boiler all the time? (surely this would cost a fortune?) - guestimation on this would be about 110 euro per week.

agusta

jodaw wrote: »

The house in question is a relatively new pretty well insulated with some room thermostats, zones and trv's on all rads.

All bedrooms would be set to about 18-19c and living areas would be about 20c.

In my calculations above i estimated that the boiler would be running 30mins in the hour. In the real world i would hope it would be running a little less when everything is up to temp. Hopefully that would make up for the differences you quoted.

I am trying to calculated the bottom line costs at the current oil price. I would also be all ears for the best way to run the system.

-On for 8 hours straight better then 2 x 3hours?
-Or leave on the boiler all the time? (surely this would cost a fortune?) - guestimation on this would be about 110 euro per week.

I think you on the right track with the way your running it now.What sq ft size is your house..

jodaw

House size is approx 1200sq ft. 12 Rad for total heat demand of 14.7kw + 2kw for 120litre cyclinder.

Here is the kicker. I am trying to considering a communal system for two houses attached to each other.

One system i was considering was outdoor solid fuel boiler system to heat an accumulator and then this accumulator to supply the needs of both houses.

For this reason i was trying to work out the oil boiler cost x 2.

From my calcs above it seems about €110 to leave the oil boiler on 24/7 x 2 for two houses. So €220 to tun both boilers separately.

My idea was an external solid fuel boiler system to suppply both homes at a cost of about €60/week to supply both homes. I would also have access to a timber supply for batch burning in the warmer month to heat the accumulator for hot water supply.Solar is not on the radar at the moment for water but maybe will down the line depending on how it would tie in with existing system.

I am really just trying to confirm with myself that i am not barking up the wrong tree and the savings would be worth the effort.