Elec vs oil

Tim_25

When comparing actual cost, the engineer used 95% efficient for electric and 75% for oil. Are these numbers correct? Buderus claims 85% and the MPO says 87% but the engineer says that those aren't real seasonal numbers. Thanks to all on this site and thanks to Dan for having it.

Tim

Perry_5

Practical efficiency is different than theroetical efficiency

I back the engineer (and I am one myself).

The theoretical efficiency only occurs at one point of operation. An old style atmospheric boiler has a well rounded efficiency curve - and I would even question if the 75% for seasonal efficiency is not high...

In power plants (where we have boilers 10, 20, and even 30 stories high)and monitor boiler efficiency the effects of boiler load to efficiency is very easy to see. Power Plant boilers have an advantage a home boiler does not have - the ability to modulate multiple burners from off to 100% while modulating air flow and water/steam flow to maximize efficiency at all power levels. Even then - there is still a quite rounded boiler efficiency curve. Most atmospheric boilers (non-condensing) peak efficiency occurs somewhere arround the 80% load point (although the mfr can easily vary that by up to 10% either way).

A mod/con boiler has a much flatter efficiency curve - which may even drop slightly as boiler demand goes up. This is the reason that mod/cons are often so much more efficient from a practical standpoint than an atmospheric boiler even if the theoretical numbers between the two boilers is only 5 or 10%. As an example; a mod con boiler firing at 50% often still has an efficiency around 90% whereas a simple non-condensing atmospheric boiler firing at 50% may only have an efficiency of about 50%. The lower the load rate - the worse the comparison gets too...

Of course - if you are using steam you cannot use a mod/con.

Perry

Tim_25

Thanks Perry,
this will be a couple of 400k btu's DV oil or two 100Kw elec. It all works out in the numbers so long as you have the correct ones.