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Comment by mmooss | Hacker News Reader

My power usage has dropped by maybe 50% (a bit of a guess, based partly on electricity bills), and quality of life has increased - I simply didn't consider that these options worked better overall until I tried them for power-saving purposes.

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.

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My household energy usage has decreased, but my household electricity usage continues to rise.

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.

Though hath sinned against the 2nd law of thermodynamics!

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.

Energy usage wise, they are the same. That is why the units match after conversions. In any case, I replaced substantial energy usage from heating oil with less substantial use of electricity. Here is a fun fact. It is more energy efficient to run a heat pump off electricity from a commercial generator burning diesel to heat a home than it is to burn the diesel directly. This includes grid losses. The reason for this is that heat pumps exceed 100% efficiency because the environmental energy moved is free as far as accounting is concerned. In my case, the electricity is produced by burning natural gas rather than diesel.

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.

They are not the same though. This leads to issues with prominent people, see Vaclav Smil, making the case that it'll be too difficult to transition from fossil fuels because they conflate these two things. Some do it out of ignorance, others know better and do it since it's in their financial interest.

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.

The two are the same as far as my computation of my household’s reduction in energy usage is concerned. That is why I converted to the same units.

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.

I don’t disagree with you about furnace efficiency.

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.

Dividing 15kWh by the average COP should determine it, although heat demands change from year to year and temperatures vary, causing not only the amount of heat needed to vary, but the average COP to vary too.

Ask yourself what is the difference between a heat pump and an electric resistance heater?

This does not matter for total energy usage calculations unless you consider the environmental heat to be an input, but as far as the industry is concerned, it is free, which is why the COP for heat pumps is greater than 1.

If you were comparing gasoline in a car to an EV I would maybe see what you are talking about- engines are like 30% efficient so the conversion to useful energy requires a large multiple of potential energy.

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.

I don’t know that I disagreed with you. Yes it might be close to their heating value but it’s fundamentally measuring something different.

Energy usage as does not care about whether any of the energy is wasted. If it did, a 100W incandescent light bulbs would only use 1W of power.

Mine was 86% efficient, although for accounting purposes, I considered the waste energy to be part of energy consumption, which seems to be the most sensible way of doing it.

  >Though hath sinned against the 2nd law of thermodynamics!

  >...Repent and sin no more.

Sure.

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.

Ryao is comparing a heat engine to a heat pump. Thermodynamically different objects.

Where did I compare a heat engine to a heat pump? An oil boiler certainly is not a heat engine.

FWIW I'm not cooking books or shifting between energy sources. I changed habits and use much less energy total.

I did not mean to imply you did. I just stated that my own data on my energy usage shows a decrease, but how much depends on how the accounting is done, and I can “cook the books” to produce some truly absurd figures by considering savings from the not so recent past, and treating my solar panels as causing a net decrease.

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