In the continental US you get ~2x the heat from burning natural gas in a combined cycle turbine to run a heat pump than you would from using a high efficiency gas furnace.
The market price of electricity vs gas varies quite a bit through time and various distortions of the market. Currently gas is cheap, but you want to compare historical averages when buying something that lasts 15+ years not simply look at current rates.
I don't think the numbers are accurate in the quantity of gas. Since kWh and BTU are both units of energy, finding the cf of gas is unnecessary (assuming the efficiency numbers are correct).
1 kWh = 3.6 megajoules and 1 BTU = 1055 joules
The 6.6 kWh of the heat pump is 23.76 MJ which is 22,521 BTU of energy. Assuming that the power plant and distribution are 60%, it would take 37,535 BTU of gas to produce (22,521/60%).
Instead, using that 37,535 BTU of gas in an 80% efficient furnace would only produce 30,028 BTU of heat, which is worse than the 50,000 BTU from the heat pump.
I'm pretty sure even a poor heat pump will be more efficient than heating directly with gas. (Of course, they have drawbacks, like they can leak their refrigerant that causes more of a greenhouse effect than CO2.)
> "(Of course, they have drawbacks, like they can leak their refrigerant that causes more of a greenhouse effect than CO2.)"
My heat pump contains 2.1 kg of R32 refrigerant. R32 has a GWP of 675, so that 2.1 kg is the equivalent of 1417 kgs of CO2. (older refrigerants were much worse!)
Heat pumps should never leak their refrigerant during their lifetime, and installers will remove and recycle the refrigerant when servicing or decommissioning systems. But of course, accidents happen, so let's pessimistically assume that 50% of systems installed will eventually leak. In the real world it's hopefully far less than that, but that would mean on average 708 kg CO2e in refrigerant is emitted per system over its lifetime.
On the other hand, heating a typical US home with natural gas emits 2900 kgs of CO2 per year.
I think it's safe to say that the climate impact of refrigerant leaks in modern heat pump systems is minuscule compared to that of the CO2 emitted from natural gas heating.
I dont know where EIA gets those numbers, but that was the basis of my calculation. Maybe I shouldn't have multiplied that by the efficiency of the plant, but rather just taken of distribution losses.
They are averaging the efficiency from the current fleet of gas turbines after subtracting the useful heat output and coming up with 44.4%.
However, it’s a misleading number in multiple ways because the fleet is made up of a mix of low and high efficiency turbines. Grid operators use a mix of turbine types as a cost optimization, a far cheaper and far less efficient turbine that’s only used 1% of the time it worth it. The average number of kWh per cf of gas is therefore heavily in favor of high efficiency turbines.
Dear god how do you keep sane with those kinds of units? You're making it so confusing you fail to realise some of your numbers don't quite line up
In sane units:
- 2 m^3 of gas generates 6.6 kWh of electricity
- which generates 14.7 kWh of heat (at some temperature
differential).
- The same 2 m^3 of gas generates 20.8 kWh of heat
- of which about 16.4 kWh is usable assuming some losses.
Of course your implied electricity generation is only around 31% efficient, so I'm not sure what that 60% you mention in the beginning is about. The COP you're using is around 2.2, which together with a 60% efficiency for generating electricity would be greater than 1, outstripping anything that's physically possible to achieve with a furnace.
What kind of system do you have that is only giving you (if I’ve converted the those very confusing units correctly) a COP of 2.2 at 10° C? That’s really very poor… There are air-to-water units that can achieve COP > 4 at 0° C, and even a good air-to-air should still be over COP 3… I’d expect to see a COP like that at -15° C or below on a modern unit…
Replace your heat pump? People installing new heat pumps are going to see much higher efficiency.
50,000 BTU = 5.27528 * 10 ^ 7 J = 14.6 kWh / 6.6 kWh = COP of 2.2 at 50f which is absolutely terrible. Modern heat pumps should have a COP around 4 at those temperatures and 3 near freezing.
Also, “Subtracting 10%” would mean your grid losses are 17%. “annual electricity transmission and distribution (T&D) losses averaged about 5% of the electricity transmitted and distributed in the United States in 2018 through 2022.” So, (70% * (1 - 5%)) = 66.5%, but resistive losses are reduced in the cold. https://www.eia.gov/tools/faqs/faq.php?id=105&t=3
4 * 0.665 = 2.66x though obviously what matters here is the annual average COP. (3 * 0.665) = 1.995 aka 2.
I was assuming something was broken or had made a very poor choice of device. He clarified he was reading the wrong column, so it’s not quite as bad.
The technology isn’t advancing fast enough to make upgrading every 10 years necessary. You could buy units in 2000 with a significantly higher COP than he was implying.
People have; it's a obvious win. There are sites that do this for your zip code correctly, but an efficient EV gets 4 miles / kWH. An efficient hybrid gets under 60 MPG.
California's insanely high electricity rates are about $0.15 / kWh, so the energy costs $0.0375 per mile.
Gas has hovered around $4 / gallon or higher for a long time, giving a fuel cost of $0.0666 per mile.
Big energy guzzling EVs get about 2 miles / kWh, for $0.075 per mile, and gas guzzlers easily get below 15 MPG, or $0.26 per mile.
You'd have to go back to the days of $1 / gallon gas (mid 1990's?) and ignore inflation / lower electricity costs back then to conclude large ICE cars have competitive fuel costs. You'd "only" need to go back to $2 gas for the energy efficient hybrids to be competitive.
The market price of electricity vs gas varies quite a bit through time and various distortions of the market. Currently gas is cheap, but you want to compare historical averages when buying something that lasts 15+ years not simply look at current rates.