[_aavaa_]

> there’s nothing in that quote that is inherently misleading

The discussion of the issue in terms of primary energy is the very thing that's inherently misleading. To move away from fossil fuels we do not have to replace the primary energy, we have to replace the useful energy that comes out the other side. From the Sankey diagram in the article I linked [0], 67.5 units of energy are not useful energy.

To put it to an extreme, instead of 67.5 units beings wastes, it could be 100 billion units for 32.5 units of useful energy produces. Focusing on the 100 billion is inherently misleading since they are irrelevant when the replacement technology basically creates the useful energy with over 100% efficiency at times.

Heat pumps. Yes their COP is lower during cold winters, but that brings in 2 discussions.

1) any COP value above 1 means that we'll need less primary energy than when buying something, and even in cold weather they manage a COP above that [1].

2) Lower COPs will cost you more, depending on what your natural gas prices are like due to any crazed lunatics invading their neighbours. Which conincidentally is only what pushes electricity prices up in many places that use natural gas for electricity (even just peak demand).

The capital cost difference also depends drastically on situation. Many climates need both heating and cooling, so the price of heat pump versus furnace + AC unit is much smaller than heat pump versus furnace.

> But especially without a strong will today those changes are practically too far off for the 2050 target.

I agree, and even replacing the 1/3rd of the primary energy will be a tough challenge. But Vaclav continual framing in terms of primary energy is actively used to push inaction. His critics have been vocal about this point (and others) for a while, he should know better by now.

[0]: https://spitfireresearch.com/wp-content/uploads/2024/06/LLNL...

[1]: https://www.sciencedirect.com/science/article/pii/S254243512...

[binoct]

Thanks, you have helped at least me think a bit differently about this. I still believe primary energy is a valid way to look at the problem, but see more clearly how easily it can lead an uninformed audience to a bad conclusion.

And on heat pumps - it’s sad to reflect that even if we replaced all heating, it’s still only a couple % of the total rejected heat. There are few easy wins in this game, just many different ways we need to chip away at it.

[_aavaa_]

I'm glad it was helpful.

> it’s sad to reflect that even if we replaced all heating, it’s still only a couple % of the total rejected heat.

It's actually not as bad as it looks.

Even if the home heating is not the biggest contributor from that chart, it is still a worthwhile target. Though EVs are likely a more impactful choice.

One thing not captured by that chart are the 2nd order effects of either heat pump or EV switching. Part of what makes switching economically unattractive (aside from allowing the fossil fuel options to pollute for free) are the economies of scale present for fossil fuels. However, those same economies of scale can easily flip to diseconmics of scale as customers switch away. Every ICE car replaced by an EV makes gasoline and diesel more expensive, the same thing for heat pumps and natural gas andheating oil.

So for natural gas, removing the stream going to residential, significantly impacts the economic calculation for commercial and industrial uses.

For gasoline and diesel, the impact as even more serious. Out of every barrel of crude oil 70% gets turned into gasoline/diesel [0]. The unit economics there are going to be even worse as gasoline demand continues to drop.

[0]: https://www.eia.gov/tools/faqs/faq.php?id=327&t=9

[measurablefunc]

> the replacement technology basically creates the useful energy with over 100% efficiency

I think you're confused. There is no way to avoid the laws of thermodynamics so where are you getting more than 100% efficiency?

[_aavaa_]

Efficiency is not the correct word here.

A gas furnace converts 1 J of chemical potential energy (higher heating value for natural gas) into essentially 1 J of internal energy in the air (raising it’s temperature).

A heat pump can take 1 J of electricity and move (realistically) up to 5 J of internal energy from A to B.

A layman description (if not actually accurate) is that while a gas furnace (or electric resistive heating) can be 100% efficient, a heat pump can be 500% efficient.

[measurablefunc]

Can you point me to the actual literature on the mechanics of heat pumps b/c I don't think you're explaining properly what's going on. If you can get 5J out of 1J then you have a perpetual motion machine & those are physically & logically impossible (assuming physically relevant axioms).

[_aavaa_]

It's likely I am not.

Links below, tldrs here: A heat pump does what the name suggests: it pumps heat. Resistive heating and burning gas is converting energy from one form into another. A heat pumps moves energy from A to B (making A colder and B hotter in the process) in literally the same way AC units

You get 5 J of heat out for every 1 J of electricity in because we're being funny with the units. You put in 1 J of electricity and the rest is put in as heat from your source (A) and then moved into B.

A good YouTube video: https://www.youtube.com/watch?v=7J52mDjZzto

[measurablefunc]

That obviously doesn't make sense if you know basic physics. Converting gas into heat by combusting it heats up the air in the room directly. Burning that gas in a turbine & then transferring that energy through a bunch of transformers to get to the heat pump can't give you more heat than what went into combusting the gas in the first place. This obviously doesn't work in reverse to cool a room but the direction I laid out is obviously correct. You're not using funny units, you're confused about the thermodynamics of the situation. Heat pumps are more efficient air coolers than standard air conditioners but they're not giving you more energy than what you put into it.

[_aavaa_]

> you're confused about the thermodynamics of the situation.

I assure you I am not, it is actually you who still seem confused about where the energy is coming from.

> they're not giving you more energy than what you put into it.

When you burn gas in a furnace, all of the energy that raises the temperature of the house comes from the gas.

When you run a heat pump you have two sources of energy:

1. Electricity running the thing.

2. Heat from the outside that you're moving inside.

#2 is where most of the energy that actually heats up the house comes from. The electricity is used to move it from outside the house to inside.

> Burning that gas in a turbine & then transferring that energy through a bunch of transformers to get to the heat pump can't give you more heat than what went into combusting the gas in the first place.

It actually can. A combined cycle plant can be ~60% efficient (chemical energy -> electricity). Say another 70% for getting it from the plant to your heat pump, then a COP 3 (or "efficiency" of 300%) gives you 0.6x0.7x3 or 1.26. So for every J of natural gas you burn in that plant, you'll heat your house with 1.26 J (compared to at best 1 J, realistically 0.9 J, for a gas furnace).

If you instead look at a ground source heat pump, you can get a COP of ~7 [0]. You're now putting ~3 J of heat into your house of each J of natural gas.

[0]: https://en.wikipedia.org/wiki/Heat_pump#Performance