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Comment by mikewarot | Hacker News Reader

At some point, it would be great to use a natural gas powered engine to run a heat pump. You could then use the exhaust gas as a heat source for the heat pump, possibly eliminating the need for a pre-heater.

Cooling the output should increase the Carnot efficiency of the motor.

Heating the outside air intake with that heat should be sufficient to avoid the need for an electrical resistance pre-heater.

This combination could also run on propane, ethanol, gasified wood, etc. Anything that gets burned now could be used to create far more heat output than straight up combustion.

There's got to be a flaw in this idea, math/physics wise.

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Why would you create new technology with natural gas these days. It seems such an energy source of the past. Europe is jus suffering from the dependency on it and seeks to get away from it as soon as possible.

Agreed. Just electrify everything in the home, then while we still have natural gas then just use it for electricity generation. Natural gas's only benefit is that it is currently cheap, when that stops being true, then it is just worse than electricity across the board.

The great thing about electricity is that it scales REALLY well with new generation and distribution technologies.

So, you burn natural gas in a powerplant to create electricity somewhere around 55% (hopefully) efficiency; in most of the US, the heat output is wasted. You then lose 6% to transmission, getting to 52% efficiency, to put it into a 2x COP heat pump (which we mandate use gases with GWP in the thousands) to get 104% of natural gas heating.

Or, spend the same amount on air sealing reducing heating needs by about 30%, pay workers instead of factories, and get the same reduction in natural gas use, also without the refrigerant bomb waiting to go off, and not needing more power plants built. Mandate every rental have lower than 6 ACH50, since misaligned incentives mean they're usually worse than homeowner-occupied units.

Efficiency percentages are the wrong way to look at it. If you instead frame it in terms of tons CO2 equivalent, then locking in the emissions every year between now and 2050 is going to be worse, compared to the alternative of burning a bunch of natural gas for electricity now but gradually phasing it out in favor of wind and solar.

Most heat pumps aren't going to last 30 years. Passivhaus only needs 1500W maximum of heating, so they usually don't use heat pumps.

Wind and solar also lock in natural gas usage, because they don't provide inter-seasonal storage or even intra-day storage.

I’d rather cook on a gas hob than an electric one at the moment

Infrared absolutely, but induction cooktops are pretty good and the only thing you can't do with them is stir frying.

Why can’t you stir fry?

You can't remove or move the pan during cooking

You can for a few seconds.

You may change your mind when it becomes orders of magnitude more expensive.

I use single dollars a month in gas cooking.

Europe is resource poor and suffering from a dependency on Russia.

55 billion cubic meters annually were set to be added to this dependency as recently as February 21st of this year before yet another land war erupted on the continent, forcing them to suspend certification.

The pipeline is already built though.

> There's got to be a flaw in this idea

The flaw is that we need to stop using fossil fuels now in order to meet Paris targets.

Natural gas in particular is an issue because demand is increasing globally whilst large suppliers i.e. Russia, Australia for many reasons are not able to meet it. Which is pushing up prices and increasing unreliability over the short, medium and long term.

Now is the best time to bite the bullet and transition to a decarbonised world.

Apparently, all of us in the northern part of the US are supposed to build new houses that are super-insulated and run on renewable electricity. Which is a nice goal, but in the here and now, we've got a grid that couldn't possibly handle everyone going fully electric, and it's not reliable because most of it's above ground, where it'll stop working when we need it the most. (In the winter, when it gets icy, and power goes out)

All I'm suggesting is that we take an existing natural gas furnace out of service, and replace it with something that uses FAR LESS natural gas, with the same heat output to the home. It's not perfect, it it's better than what's there, and fits within the infrastructure in place.

These certainly exist and have some, rare use cases.

Personally I’ve seen them use when there are large air conditioning loads but insufficient electrical power

https://www.yanmar.com/global/energy/ghp/

> There's got to be a flaw in this idea

Environmental impact or geopolitics issues aside, an electricity grid is much more convenient and cheaper than a propane/ethanol/gasified wood grid. Transporting gaz by trucks and storing it in individual houses is not very convenient too.

I think you’re basically describing a steam engine that mechanically powers a heat pump, pumping it’s own waste heat and whatever environmental heat it needs.

It’s pretty complicated. Direct hearing via heat exchanger is usually pretty good and much simpler, albeit less efficient. If burning thermal sources, raw efficiency is rarely all that necessary though. The heat output per unit mass is usually pretty high.

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