In the early days, our heating oil usage was 1000 gallons per year. Efficiency initiatives reduced that to about 430 gallons per year. 1000 gallons is about 41MWh. 430 gallons is about 17MWh. Going to the heat pump has me using about 7MWh extra electricity per year, while yearly electricity usage had been around 11 MWh per year (with 10 MWh produced by solar). This does not count the car, for which the numbers would be even more skewed by life changes since I drove about 1 to 2 orders of magnitude more when I was in college.
Depending on how you decide to do the accounting, my household’s total energy usage dropped by 65% (if we count the oil usage reductions on top of the heat pump) or by 35% (if we count only the heat pump), without even counting the solar panels. Still, my electricity usage has never been higher.
If you were to try to cook my books so to speak, you could say my household’s total energy usage has decreased by 85% with a electricity usage decrease of 27%, by treating the energy from the solar panels as if it were free. I do not think that is a correct way of doing accounting (although it could be a matter of opinion).
By the way, remarks on climate change could encourage people to claim unrealistic improvements in personal/household energy usage, such as the figures I gave for what I could claim if we “cooked the books”. Of the various figures I gave, I think the 35% reduction in total energy usage is the most honest figure. It had been achieved in the past 2 years, unlike the other factors I mentioned that are many years old.
1,000 gallons of heating oil have ~41 MWh of chemical potential energy (if using the HHV). Those 41 MWh are not directly comparable to 7MWh of electricity. While the units (MWh) are the same, they are measuring two completely different things.
They have as much in common as an American dollar and a Jamaican dollar; yes they're both "dollars", but they refer to different things.
Repent and sin no more.
By the way, I realize my numbers are borderline in showing that, but the past year has been colder than years where I burned oil, and it is hard to account for that when looking at numbers as there is no strict control.
As long as we conflate the two, people will more easily be misinformed and think they need to replace their 41 MWh of heating oil with 41 MWh of electricity. But they don't. They need at most 41 MWh of heating. And as you said, your heat pump is probably getting you and average COP of at least 3. Meaning they will need to pay for fewer "MWh" in order to get the same amount of heat to your house.
It is more efficient, just as it's more efficient to charge and EV of a grid running on natural gas than it is burning the petrol in an ICE. Both are also far better for pollution.
As for needing 41MWh of heat, that is incorrect as my boiler was only 86% efficient and the one it replaced was even less efficient. It is also incorrect as the efficiency gains had reduced oil usage to 18MWh. Heat wise, I only need around 15MWh per year (although I likely needed more this year since it was particularly cold).
I have a suspicion that the ducted method of heat delivery used by my heat pump has more losses than the hot water system previously used to deliver heat. I had been sealing the central AC ducts in the winter to save a few hundred gallons of oil usage. I can no longer do that as heat is delivered via those ducts now.
But my point still stands: You needed 18MWh of oil or 15MWh of heating. Neither of those numbers are how much electricity you will need to run a heat pump.
But in the case of an oil- or gas- fired furnace, their thermal efficiency is at least 80%, and often more, so their potential energy usage is close enough to directly comparable to their heating value.
>Though hath sinned against the 2nd law of thermodynamics!
>...Repent and sin no more.
What is a specific edit to the post that could have been made to avoid your wrath? What text, exactly, should have been written? Thanks.
It actually taught me a lot about innovation - there is no substitute for just trying things; you just can't know by thinking about them ahead of time. A picture is worth 1,000 words, and an experience is worth 100,000 pictures - you can't really convey it in pictures. As a result, I 'just try things' whenever I have the opportunity, and my learning rate has increased dramatically.
There are two questions about efficiency upgrades:
How much power do you use compared to the alternative? It may increase, but more efficiency means it increases less than the alternative.
How much power do you use absolutely? Physics causes climate change, and doesn't care about the hypothetical alternative.